introduction and neoplasia - pharmacology

8/14/2019 introduction and neoplasia - pharmacology

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Pharmacology : Introduction & Neoplasia

Table of Contents:

Overview of pharmacology ........................................................................................................................................2

Drugs and enzymes.....................................................................................................................................................3Receptors: Targets for Drug Action ............................................................................................................................4

Drug Metabolism ........................................................................................................................................................6

Principles of drug development .................................................................................................................................8

Complementary & alternative medicines ............................................................................................................... 10

Molecular Imaging ................................................................................................................................................... 11

Pharmacokinetics .................................................................................................................................................... 12

Autonomic Pharmacology I - Parasympathetic ....................................................................................................... 16

Autonomic Pharmacology II - Sympathetic ............................................................................................................. 19

An Overview of Cancer Chemotherapy ................................................................................................................... 23

Principles of antibody therapy for cancer ............................................................................................................... 26

Mechanisms and uses of antimetabolite drugs, signal transduction inhibitors, and anti-angiogenesis drugs in

antineoplastic therapy ............................................................................................................................................. 28

Cancer Chemoprevention ........................................................................................................................................ 32

Antineoplastic alkylating agents and platinum compounds ................................................................................... 34

DNA Topoisomerase-targeted drugs and mitotic spindle poisons .......................................................................... 39


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Overview of pharmacology

Egyptians had all kinds of prescriptions: active constituents, carriers, formulations, deliveries.

Greeks & Romans used drugs like juniper oil (diuretic & abortifacient). Homer described opiates, Socrates took

hemlock (glycine receptor agonist), Hippocraties didnt like drugs, and Pedanius discordies (physician for Nero)

wrote about 900+ drugs. Claudius Galenius made one of the best discoveries: dont use urine & feces as drugs,but also advocated polypharmacy (which didnt work, so people stopped studying drugs)

16th-18th c.: Ascorbate (vit. C) for scurvy , Quinine for malaria, Digitalis for dropsy (=CHF edema) from foxglove.

Modern approaches:

1. Natural productsthrough 1960, usually studying extracts effects on animals or disease models, andthen purifying compounds to study (in vivo / cellular, etc.). Analogs then synthesized & optimized

2. Drug target screens with synthetic compoundsmagic bullets(Ehrlichs approach, 1900-present).Screen compounds against organisms / receptors / enzymes & use hits as basis for more specific /

potent analogs. E.g. salvarsan for syphilis. Precursor of combinatorial chemistry

3. Rational drug design (1970-present). Examine molecular target (protein target, ligand, substrate) &design high affinity molecules (e.g. ACE inhibitors, protease inhibitors). Manipulate synthetically as

needed.

4. Biotechnology (1980-present). Genetically engineer proteins (e.g. recombinant insulin), monoclonal Ab(e.g. rituximab), maybe gene therapy in the future.

Challenges:

Few well-validated human gene targets identified Need blockbusters for big pharma to invest Need to expand chemical space (more new classes of drugs) Need rational approaches to ADME (absorption, distribution, metabolism, excretion)


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Drugs and enzymes

Constant Percent Effect

Many systems: function on a % effect basis (that is, constant % of cellular units affected per unit timeregardless of # of units in the system.

E.g. same % of enzyme inhibited if you keep inhibitor concentration the same, same % of max velocityobtained if you keep substrate the same, same % of cancer cells killed if you keep chemo or radiation

the same.

If X>>A (drug >> target, etc.), then it doesnt matter how many targets there are the same % will beaffected (field effect). Absolute numbers will differ, however

Graphing:

You can plot [AX] vs [X] (e.g. velocity vs.substrate, response vs. drug, binding vs.

receptor) and get a saturated curve

(rectangular hyperbola). If you use

log([X]), you get a sigmoid curve (semilogplot).

The point where youre at half max (inflection in semi-log plot) goes by different names: Km for enzyme,Ki for inhibitor, ED50 for drug, Kd for receptor binding. But its all the same a measure of how the

thing youre analyzing works & at what concentration its effective.

If you vary the enzyme or target, when youve got a high amount of substrate, you see zero orderkinetics (e.g. the amount doesnt matter because youre usually saturated).

In a rectangular hyperbola example, youre usually in zero order situations at the point of saturationyoure processing a constant amount of something per unit time.

When youre in the linear early part of thecurve, youre in first order kinetics: processing a constantpercentage per unit time.

Inhibitors:

Competitive inhibitors change Km, not Vmax (changing how well it binds, but can be overwhelmed bymore drug). Efficacyis the same (maximum effect)

Noncompetitive inhibitors change Vmax, not Km (same binding, just taking some enzyme out ofpicture). Efficacyis lowered.

So look at the graph: is Vmax changing? Then its noncompetitive. Is Km changing? Competitive. Potencymeans you can get the same effect if you just use more of a dose (effect per dose)

Scatchard plot has drug bound/ drug free on Y axis, drug bound on X-axis.

The x-intercept is Bmax, the highest amount of bound drug possible. The slope is -1/Kd Scatchard plot and Eadie-hofstee plots are reciprocals of the same graph.

Therapeutic index: LD50/ED50.You want a big therapeutic index

Kinetics: first order rate means that a constant % is removed per unit time. = 0 Example: ethanol. One of very few substances that gets into zero order metabolism (constant amount) because

you ingest in grams scale.


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Receptors: Targets for Drug Action

Receptor attributes: discrimination (selective subtypes), sensitivity

(respond to range of concentrations; range varies based on receptor),

amplification (big downstream effects).

Have different targets: membrane receptors, nuclear receptors

Different signals: hormones, neurotransmitters, drugs, toxins

Model for receptor action:

R + L RL RL E (receptor binds ligand, undergoes conformational change, downstream effect results)

Occupancy theory: biologicaleffect (E) proportional to theconcentrationofthe receptor-ligand complex ([RL])

Bioassay and ligand binding

Effect of a drug/hormone/ligand is based on:

1. Ligand concentration around receptor2. Receptor concentration3. Affinity between ligand & receptor4. Nature of post-binding cellular response

Bioassay: quantitative analysis ofAgonist action

Vary total ligand concentration(Lt) and measurebiological effect(E)

Assume: occupancy theory holds, only one class ofreceptor, each receptor is independent

=

=

max=

+

Plot results as log dose response curve (LDR)o X-axis: log ([ligand])o Y-axis: effecto Estimate KD from ED50: SMALLER KD = MORE POTENT DRUGo Can use to compare drugs (multiple curves) or analyze

antagonists vs agonists

Agonist vs. Antagonist vs. Partial agonisto This only applies to competitive inhibitors.

(noncompetitive inhibitors would lower the maximum

effect lower maximum on y-axis)

o Competitive ligands compete for binding at the samereceptor

o Biological effect depends on Concentration of each ligand Their respective binding constants

Random interesting fact:

KD is an intrinsic / fundamentalrelationship (KI too)

ED50 is an experimentallyobserved relationship (IC50 too)

= occupancyKD = equilibrium dissociation constant

Emax = maximum biological effect

Rt= total receptor concentration

At 1/10th KD, you get 10% of the max response

At 10 times KD, you get 90% of the max response


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Apply to receptor with no ligand Apply to receptor along with ligand

Agonist Full effect (stimulation) No effect

Antagonist No effect Full effect (inhibition)

Partial agonist Partial effect (some stimulation) Partial effect (some inhibition)

(Note that to detect an antagonist, you need to start

the system with some activity. Otherwise it might just

be inert)

Bioassay for antagonist action

Add ligand at constant concentration and thenvary inhibitor concentration [I]

Plot as a log dose inhibition curve (like LDRcurve but with inhibitor concentration on X-axis on a log scale). IC50 is approximation for KI

Can use to compare various inhibitors as well SMALLER KI = MORE POTENT INHIBITOR

Ligand Binding

Use labeled (radiolabeled) ligand Vary ligand concentration[Lt] Measure receptor-bound ligand concentration

([RL]) and free ligand concentration ([L])

Plot as either rectangular hyperbola orscatchard plot (RL/L vs RL on linear scale)

where slope = -1/KD, intercept = Bmax (Rt)

o Steeper line = higher affinity Can also use the same method to see

binding ofinhibitor, but it wont actually

tell you what its doing: need to do a

bioassay.

o This method has no info aboutbiological effect could be

agonist, antagonist, or partialagonist.

Receptors: can belong to different families; ligand binding & effector domains usually linked. Subtypes exist for

most ligands (hormones, neurotransmitters, drugs). Subtypes can have different downstream effects & patterns

of expression (in different tissues or at different times in development.


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Drug MetabolismDrug metabolism: generally producing more polar / water soluble conjugates (better excretion). Can sometimes

make more active/toxic compound

Liver is key for majority of drug metabolism.

Important for:

Toxicity: sometimes you can generate toxic/teratogenic metabolites (e.g. thalidomide) Activity: metabolites can be active (e.g. terfenadine) Drug interactions (inhibition of metabolism): another drug can increase to toxic levels (e.g.

ketoconazole and terfenadine)

Drug interactions (induction of metabolism): another drug can decrease to sub-therapeutic levels (e.g.rifampin and oral contraceptives)

Almost no oral drugs are absorbed in stomach. Most absorbed in small intestine like food & have to pass

through portal circulation to the liver (makes sense want to detoxify them first.)

First-pass metabolism: metabolism that drug goes through in that first pass through the liver (before reaching

systemic circulation / central compartment)

high extraction: drugs that are taken up & heavily metabolized by hepatocytes during first pass; theirhepatic clearance is dependent on liver blood flow

low extraction: negligible first-pass effect How to circumvent:

o Change the routeofdelivery (IV, sublingual, transdermal, rectal distal colon to IVC)o Change the rate ofmetabolism (co-administer inhibitor of metabolism)

Hepatic drug metabolism

Phase I: oxidation, reduction, hydrolysis. Cytochrome P450 enzymes or mixed-function oxidases.o CP450s: oxidation rxns, distinct classes, metabolize different groups of drugs

Similar to e- transport chain Vast majority of drugs metabolized by CYP3A4 (and CYP2D6) Example: thalidomide (metabolized to teratogenic metabolite by phase I rxn)

Phase II: glucuronidation (glucuronyl transferases), acetylation (N-acetyltransferases),methylation(methionine transferases), sulfation (sulfotransferases)

o E.g. sulfanilamide Both phases enzymes present in microsomal fraction of liver homogenate (located in SER, membrane-

associated)

Non-microsomal & extra-hepatic metabolism

Cytosolic / mitochondrial fractions: alcohol/aldehyde dehydrogenase, monoamine oxidase, proteases Intestinal CYP450s: intestinal enzymes (including 3A4) may contribute to apparently poororal

bioavailability or high first pass metabolism (up to 50%).

o Good for hepatotoxic toxins (teleologically) Also glucuronyl transferases (e.g. kidney) but liver does most work N-acetyltransferase in musclemay play a role for slow acetylators

CYP450s & drugs

Drugs can be: substrates, inhibitors, & inducers of CYP450s (one drug can actually do all 3)

P450 inhibitor: any drug that inhibits the metabolism or biotransformation of another drug by enzymesin the cytochrome P450 family (competitive & reversible) usually substrates too


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o Can inhibit one or several classes of P450so Major offenders: cimetidine (anti-ulcer), macrolide antibiotics (erythromycin), antifungal azoles

(ketoconazole)

o Example: terfenadine levels increase if administered with ketoconazole; original form of drugcauses arrhythmias (before metabolized)

P450 Inducer: Any drug that causes increased production of enzymes responsible for the metabolism orbiotransformation of another drug (drug acts as promoter, increases transcription)

o Increased mRNA levels (drug binds to enhancer elements upstream from enzyme coding region)o Major offenders: phenobarbitol (anticonvulsant); rifampin (antibiotic) e.g. with contraceptives

Effects of aging, disease, genetics

Neonates: low levels of functional glucuronosyl transferases (until ~1 mo) can be particularly susceptible to

toxicity from toxins & drugs that are inactivated / cleared through glucuronidation

Elderly: can have reduced liver blood flow / reduced Phase I capacity (underlying disease, aging)

Cirrhosis can affect drug clearance via 2 mechanismso Liver fibrosis (reduced blood flow through portal circulation: less 1st pass effect, higher systemic

concentrations of parent drugs

o Decrease in functional hepatocytes = less phase I capacity (mostly late in liver dz) Phase I reactions:impaired in acute & chronic liver disease; Phase II (conjugations) usually only in end-stage liver disease

Pharmacogenetics: polymorphisms in drug metabolism (altered amounts of enzymes or mutations in enzymes),

mostly affecting promoter region (altered amount more common)

Classic example: Isoniazid (some are rapid metabolizers, some are slow metabolizers).


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Principles of drug developmentFive major players: pharma, regulatory agencies (FDA), consumers, academia, legislature)

History of drug development: chance observation trial and errortargeted screening (Ehrlichs magic

bullet, pasteurs anti-bodies & lock & key model)

Discovery vs Development

Discovery:identify the lock, develop a pattern of chemical keys, rapid-throughput screening, in vitroor in vivo model systems or can exploit a chance observation (still possible)

Development: getting the drug discovered, through the system & to the patient.o 15-20% of overall health care expenditures, but changes from year to year (can regulate and

theres a trade-off with savings from reduced hospital days / morbidity / mortality)

o $420B in 2005; increasing market for generics (2/3 Rx in 2009) and worldwide 1:30,000 chemicals licensed drug 1:10 drugs in clinical testing licensed drug 1:5 licensed drugs covers R&D expenditure

o Costs ~ $1B and patent life is 8-10 years so need $50-100M/yearo So pharma focuses on blockbusters (high use & profitability prevalent chronic conditions)

Phases of drugs

Pre-clinical drug developmento Efficacy, mechanism of action, toxicologyo Pharmacokinetics (ADME) Absorption, Distribution, Metabolism, Excretiono Pharmaceutics (formulation development)

Phase I: short-term safety & tolerability; pharmacokineticso 10s ofhealthy volunteers; days to weeks

Phase II: medium-term safety and tolerability; initial evidence of beneficial activityo 100s ofpatients; weeks to monthso proof of concept

Phase III: long-term safety and tolerability; clinical efficacyo 1000s of patients; yearso proof of effectiveness convince FDA that drugs ready for marketo Very expensive phase imaging, testing monitoring

Phase IV: post-marketing surveillance; develop new indicationso study special pt populations, real-world effectivenesso 1000s of patients; often retrospective

DEFINITIONS KNOW THIS STUFF

Drug: any chemical administered with therapeutic intent. Different from foods, health foods (legistlative artifact), GRAS substances

Orphan drugs: intended for conditions affecting


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New route of administration, formulation, dose, pt. population with increase in risk IRB asks for it

New Drug Application: data submitted to support marketingapproval of investigational new drug

Reviewed by advisory committee who make recommendation (approve / disapprove)

FDA not obliged to follow advisory committee recommendations


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Complementary & alternative medicinesCAMs are important. 11.2% of all out-of-pocket spending in US, 38% of pts use CAMs

Extracts are combinations, supplements, not isolated

Drugs are isolated, pure chemical entities

Herbals are a subset of CAMs (also chiropractics, meditation, acupuncture)

Echinacea is the most common herbal product (cold remedy)

No evidence that any of these are safe or effective.

Healing is belief based and science based. Whereas scientific medicine is evidence based & changing,

traditional medicine is belief-based, anecdotal, static, and authoritarian. Science = good, other stuff = bad.

THIS IS WHAT YOU NEED TO MEMORIZEALL MEDICINE (TRADITIONAL, SCIENTIFIC, HOLISTIC) NEEDS TO FOLLOW THESE 3 PRINCIPLES:

1. Product must be standardized & rigorouslyregulated2. Product must be proven to be effective for something that is of value to the patient3. Product must be proven to be acceptably safe1994: Dietary supplement health and education act (DSHEA) effectively neutered FDA (health food lobby won

out; FDA has very little control)

CAM development circumvents the 8-10 year, $1B drug development process: but at the cost of safety/toxicity

studies, effectiveness proven, standardization of the product

Example: PC-SPES (for prostate cancer even in NEJM) but turned out to have synthetic drugs (hoax)

Herbal medicines generally not standardized (so you cant study them well or refute claims). Many areadulterated or inconsistent with their labeling.

Ethically need to be able to know what youre giving patients. Scientifically need to be able to replicate a study.

NEEDS TO BE EFFECTIVE & ACCEPTABLY SAFE

Only one herbal medicine has been approved (veregen for topical tx of genital & perianal warts in

immunosuppressed patients)and even that doesnt have great results

Several others (witch hazel = cuts & scrapes, senna & psyillum = laxatives) have been approved for modest value

in some illnesses.

CAMS can cause drug interactions.

E.g. St. Johns Wort increases metabolism of cyclosporin (an immunosuppressant) by P450 3A4, which caused

transplant patients to lose their new hearts (immune response & rejection)


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Molecular ImagingMolecular imaging: the remote sensing of cellular processes at the molecular level in vivo

(people or lab animals) Allows early detection of changes in tissue; manage changes in real time for patient (personalized

medicine), facilitates drug development (where is drug going?)

Modalities:

Keys: spatial resolution of techniques, sensitivity (what quantities can be measured e.g. optical =picomolar, MRI = micromolar), specificity of probe (just hit target, not normal tissue)

Can be combined with anatomic techniques like CT Four modalities: Optical, Nuclear (radiopharmaceutical) , Magnetic Resonance (MR), or Ultrasound

Nuclear imaging:

PET (Positron emission tomography) currently the most clinically translatable modalityo More expensive; requires cyclotron, quantitative, 4mm resolutiono Physiologic tracers (15O, 13N, 11C, 18F, 124I)o Combine with CT: PET-CT to see anatomyo Receptor/enzyme/transporter mapping; assess metabolism; calculate drug receptor occupancy;

monitor biomarkers for therapy & patient selection for treatments

SPECT (Single photo emission computed tomography)o Less expensive ($500k), qualitative, 1.5cm resolutiono Uses chelation chemistryo Example: image for prostate-specific membrane antigen (PSMA) for prostate cancer (if present

outside of prostate, could be recurrance of cancer

Tracer principle: use concentrations of a probe that are so low that they wont alter the physiology of the

system under study (no pharmacological effect). Makes use in humans more easily approved. Especially good

for radiopharmaceuticals.

Receptor pre-blockade: saturate the target sites with a normal nonlabeled ligand, then apply your probe /

imaging agent. If theres any signal detected, that shows non-specific / background signal (should only be

binding to your site of interest). Shows specificity. Could also use knockout animals

Direct imaging: probe binds directly to target (e.g. PSMA)

Indirect imaging: for instance, a reporter gene / reporter probe system (e.g. introduce a certain kinase gene

that will phosphorylate your probe & trap it in the cell, and put it behind a promoter that also controls

your gene of interest. When your gene of interest is turned on, the kinase will also be made, and your

probe will be trapped in those cells to be imaged)

Signal amplification: enzymatic reporters can be useful because they amplify the signal (your probe, forinstance) keep working inside the cell (especially good for less sensitive modalities like MR)

Example: C. novyi (anaerobic, goes to anoxic center of tumor). How to image bacteria as they home in? image

with 125I (FIAU) the toxin produced by a bacterial kinase . Turned out to be toxic (5 deaths) so not a Tx now.

Can also image breast cancer using PET (18F-fluorothymididine = FLT-PET) to detect early cancers.


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PharmacokineticsPharmacodynamics: what the drug does to the body (deciding on the target) effect vs. concentration

Pharmacokinetics: what the body does to the drug (hitting the target) concentration vs. time

What were really interested in: PK/PD interrelationship (effect vs. time)

Movement across membranes depends on various factors (size, dynamic polarity, water:octanol distribution,

protein binding, pKa, membrane transporters). Needs to be uncharged to get across (low dynamic polar

surface area < 140 angstoms, lower for brain/blood barrier)

Absorption determinants:

Passive movement: middle ground for hydrophobicity is best to move between compartments Proteinbinding: generally only unbound drug can move across membranes Efficiency issue: high binding is not failure (if approved, it has effect) Albumin & -acid glycoprotein are major proteins Varies with time ( -a-g with inflammation, albumin with cirrhosis & nephrotic syndrome) so can

change concentrations of highly bound drugs Affinity can also change (uremia in renal failure decreases binding) Displacement theoretically possible but no known drug-drug examples

Henderson-Hasselbach Equation

pH = pKa + log(A-/HA); pH = pKa when HA = A- Acid uncharged when pH < pKa (HA+) Base uncharged when pH > pKa (HA) Disease conditions (alkalosis or acidosis) can change how drug moves across membrane

o Gastric fluid 1.5-7, urine 4.5-7.5, blood etc. 7.4. Some drugs can be trapped depending on pHo pH can change with other drugs (e.g. gastric fluid pH & omeprazole)

Transporters: active movement

Can block transporters to keep drug in or to keep from being pumped out, but usually work to pump outrange of drugs

E.g. organic ion (pumps from cell into lumen); P-glycoprotein (pumps from capillary into cell)Basic definitions

AUC (mg/mL * hours): drug exposure per time

F: Bioavailability (unitless): fraction reaching systemic circulation. Limited by failure to enter solution, short

exposure to absorptive surface, failure to pass across membrane, pre-systemic metabolism so less than 1 in

almost all circumstances.

Bioavailability= (where EV = after extravascular dose, IV = after intravascular dose) EV peaks later, around longer than IV Low bioavailability affects ability to dose po (may need frequent doses or IV) & can be a feasibility issue F


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S: Salt (unitless): some drugs are composed of other stuff by weight too

= Analogous to F E.g. aminophylline is 80% theophyilline by weight

Vd: Volume of distribution (L): Volume into which dose appears to be uniformly distributed

= Affected by drug movement across membrane (less movement = higher conc in central compartment) Use population Vd (adjust for weight given in L/kg) as first estimate. Can be lean weight if not fat

soluble

Generally a theoretical concept: measuring only total, not free drug; only sampling central compartment ke: Elimination rate constant (1/time): fraction of drug eliminated in a unit of time

Not the elimination rate First order (not saturated) constant value (constant fraction eliminated); goes down as saturation

occurs (zero order constant amount eliminated)

= for elimination Plot ln(Concentration) vs. Time and your slope isk Can backwards-extrapolate to get C0, your initial concentration = /

t1/2 : half life (time): how long it takes concentration to drop by half.

Only works for first order. When Ct/C0 = , equation above simplifies

o ./ = Another way to look at it

o = o n = number of half lives elapsed post dose, or number of half lives in dosing interval to find

trough.

Or:o =

Cl: Clearance (L/hr)

Relates concentration to rate of elimination (First order, saturable process). = Varies with drug and patient Cl = Q * E (depends on flow and extraction ratio across organ)

o E.g. hepatic clearance is a function of hepatic blood flow and extraction ratio, which in turndepends on metabolizing enzyme function

o Renal clearance varies with protein binding (filtration + secretion absorption) Total clearance = renal + hepatic + other Apparent clearance = Clearance / bioavailability

o =


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Rac: Rate of accumulation

= , ,1 = 11 = 11 12

If youre dosing a drug with a long half life and dosing, say, every 1/5 half life, you can get a big variationover time. If youre dosing ever 4-5 half-lives, you dont get much buildup

Loading dose: achieve a desired drug concentration.

Assumes instantaneous, uniform distribution throughout body with no account for time = Adjust for F and S as needed

Calculating an individuals Vd and t1/2 Measure drug concentrations at two timepoints during decay Plot ln(concentration) vs time Find slope (-k) and calculate using k = 0.7 / t1/2 Find intercept = C0 and then calculate Vd (Vd = dose * C0, corrected for F)

Continuous infusion: elimination rate matches infusion rate exactly (quasi-steady-state)

= Adjust for F as needed Note that things that change clearance (other drugs, etc) will affect this concentration at SS

If you give a loading dose & follow up with continuous infusion, the curves sum to be almost square (infusion

accumulates as loading dose decays.

Intermittent & continuous dosing

Average dose is the same by either method (elimination rate is slow at first for intermittent dosing butthen evens out)

Fixed daily dose, different interval: peak/trough changes, concentration at steady state doesnt Same dose, different interval: same peak/trough, different Css

Basic half-life equations:

o Rise: = 1 = (1 12)o Fall: = 0 = 0( 12)

Time to 95% (up or down)= 4 to 5 half-lives

Concentration-constrained dosing: how to calculate dose & interval for peak & trough

Shortcut: if you want Cmax / Cmin to be 2, max interval is t(1/2). If you want 4, 2t(1/2) is your interval Interval (Rate = ratio) Cmax/Cmin = 2n

o = ln , , where = 0.7/1

2

Dose=Differenceo Single loading dose (get up to the max SS)o = , o Correct for F, S when needed

Intermittent maintenance dose (given every )


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o = , o Correct for F, S when needed

A few other topics:

Distribution: at first, both drug moving out of central compartment (distribution) and being eliminated, so rate

of drop in concentration is higher. Implications

o Delayed effect if peripheral site of actiono Big distribution phase increases risk for central toxicity (if narrow therapeutic index)o Need to monitor post-distribution levels (otherwise artificially overestimate initial

concentration)

Short infusions are more common than IV bolus infusions: distribution can apply though

Ka (absorption rate constant) if a lower Ka, then slower abosorption. Peak is lower, trough is higher, and AUC

is the same. Peak is also later.

Slower absorption can be good keeps a narrow window in your peaks and troughs (e.g. extravasculardosing)

Things to adjust away from population values if needed

Loading dose: altered Vd (linearly proportional) Maintenance intermittent dosing (if t1/2 changes, not linearly proportional) Maintenance infusion dosing rate: altered Cl (linearly proportional) Time to steady state: linearly proportional to t1/2

Renal clearance: can adjust for creatinine clearance if drug is cleared by the kidney (age, weight, gender taken

into account). If creatinine clearance is lower, you can drop your infusion to get to the same steady state

concentration (but it will take longer! T1/2 is larger)


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Autonomic Pharmacology I - Parasympathetic

Basics:

Nervous system: afferent (sensory information), integration in ganglia in CNS structure, efferent(somatic motor = voluntary skeletal mm, autonomic involuntary smooth mm), mostly antagonistic

Parasympathetc = homeostasis, sympathetic = fight or flightParasympathetic Nervous System

Anatomy: originates from midbrain, medulla, sacral spinal cord, long presynaptics, ganglia near targetsso stimulation gives localized effects

Ganglionic receptors = nicotinic AcH (gated ion channel) Target receptors = muscarinic AcH (GCPR)

PNS Actions:

Homeostasis, opposes sympathetic activity generally Constricts smooth muscle, increases glandular secretions usually Classical actions: pupil constriction, bronchial constriction, decreased heart rate, relax sphincters &contract GI segmental/longitudinal mm, contract bladder (relax sphincter)

Cholinergic synapse:

AcH synthesized by choline acetyltransferase Ca+ dependent release (+ B-bungarotoxin, black widow venom, - botulism toxin by cleaving SNARE) Muscarinic AcH receptor (+pilocarpine, - atropine)

o 7-membrane-spanning GPCRo M1-M5 subtypes with selective tissue expression, specific functions but overlapo M2 is cardiac-selective; subtyping hasnt really been exploited clinically so far

Acetylcholinesterase breaks it down (- neostigmine, soman)o

This is the turnoff (compare to sympathetic)o Neuronal AchE and also serum/liver (butrylcholinesterase) so you cant just inject Ach into gut

Choline uptakeMUSCARINIC AGONISTS

Generally: choline esters & other cholinomimetics

pilocarpine Mechanism of Action: muscarinic AcH receptor agonist

Effects: generalized muscarinic (incl. ocular-pupillary constriction, fall in intraocular pressure after

sudden rise, miosis = constriction of pupil lasts several hours)

Indications: glaucoma (esp. open angle)

Administration: aqueous opthalmic solution (prevent cardiac effects)


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metoclopramide Mechanism of Action: Muscarinic AcH receptor agonist

Effects: increases gastric emptying; anti-emetic (dopamine receptor agonist), also enhances cholinergic

effects

Indications: First-line gastroparesis & anti-emetic agent

Administration: oral

Other: a.k.a. "Reglan"

MUSCARINIC ANTAGONISTS

atropine Mechanism of Action: competitive antagonist of muscarinic Ach receptors

Effects: dry mouth, constipation, urinary retention, dry skin, flush, bronchodilation, mydriasis (=pupil

dilation), delirium. Mad as a hatter, red as a beet, dry as a bone

Indications: Stop asystole (code blue), diarrhea, antidote to AchE toxins, pupil dilation

Administration: po, opthalmic, or by injection

scopolamine Mechanism of Action: muscarinic Ach receptor antagonist

Indications: motion sickness

Administration: oral or transdermal

ipratropium

bromide

Mechanism of Action: muscarinic Ach receptor antagonist

Effects: bronchodilation

Indications: asthma, COPD

Administration: metered dose inhaler

Other: a.k.a. atrovent

ACETYLCHOLINESTERASE INHIBITORS

May be therapeutics (physostigmine for glaucoma), antidotes to poisons (pyridostigmine), or toxinsthemselves (sarin) depending on their affinity for AchE, route of administration, dose, etc.

Many insecticides, nerve gases, etc. fall in this category AchE is a serine protease that cleaves Ach to acetate & choline in synaptic cleft Found in high molecular weight aggregates (stable = low turnover = really bad if you mess it up)

neostigmine Mechanism of Action: reversible covalent inhibitor of AchE

Indications: can be used for prophylactic protection to AchE inhibitor nerve gases (fills up site, then

wears off unlike sarin, etc.)

sarin Mechanism of Action: "irreversible" covalent inhibitor of AchE

Effects: signs of AchE poisoning: bronchial spasm, salivation, lacrimation, defecation, urination,

bradycardia, hypotension, muscle weakness, death in minutes to hours

Administration: nerve gas / chemical warfare agentOther: can be reversed with pralidoxime rescue if "aging" doesn't occur first (irreversible complex

formed with AchE over time, preventing palidoxime's nucleophilic attack). Treatment also includes large

quantities of atropine


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pralidoxime Mechanism of Action: nucleophilic attack on AchE-sarin covalent complex

Effects: Reversal of sarin AchE poisoning

Indications: sarin AchE poisoning

Other: used along with atropine for sarin & other similar AchE poisons


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Autonomic Pharmacology II - SympatheticAnatomy:

From thoracolumbar spinal cord; ganglia are paraverterbral & longer post-synaptic fibers Ganglionic receptors: nicotinic cholinergic Target receptors: adrenergic Primary postganglionic neurotransmitter: norepinephrine Adrenal medulla is like a big postganglionic neuron, releases epinephrine Stimulation results in a widespread reaction

Physiology:

Fight or flightresponse Smooth mm: relax or constrict Classical actions: dilate bronchi, glucose from liver, rate & stroke volume from heart ( cardiac

output), blood flow to skeletal mm, motility & sphincter tone in gut

Activation via enervation of target and adrenaline (=epinephrine) in blood circulation from adrenalsAdrenergic synapses

NE synthesized in neuron (tyrDOPA dopamineNE). Epinephrine synthesized in adrenal gland Tyrosine hydroxylase is the rate-limiting step of synthesis & activated by sympathetic stim.

o -methyltyrosine blocks tyrosine hydroxylase, used in management ofpheochromocytoma(usually benign tumor of adrenal that fires out too much catecholamine)

Release of NE is Ca-dependento Some agents can act as false neurotransmitters, replacing NE in secreted vesicle & NE effecto Tyramine, amphetamine, ephedrine: sympathomimetic (enhance NE secretion)

Adrenergic receptor (many agonists & antagonists) on post-synaptic sideo GPCR

NE transporter brings NE back into pre-synaptic neuron (blocked by tricyclic antidepressants)o Turnoff mechanism is re-uptake (not breakdown like parasympathetic)

Monoamine oxidase breaks down NE & deaminated products extruded (target of antidepressants)Adrenal glands have PNMT which converts NE (noradrenaline) to ephinephrine (adrenaline), major adrenal

medulla hormone. NE and ephinephrine have different pharmacological effects

Subtypes of the adrenergic receptors:

1(with 3 subtypes 1A, 1B, 1C): mixed effects 2(with 3 subtypes 2A, 2B, 2C): adenylate cyclase, Ca channels, K channels (with 3 subtypes 1,2, 3): adenylate cyclase Dopamine receptors (D1-5) in vascular bed (D1) and CNS (all 5) can also bind catecholamine derivatives;

dopamine can bind -receptor

-receptor pharmacology

Non-selective -receptor agonists: epinephrine, NE, phenylephrine, dopamine (see end of section)

Non-selective -receptor antagonists:


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phenoxybenzamine Mechanism of Action:nonselective antagonist of adrenergic receptors

Effects: Reduces NE effect via inhibition

Indications: pheochromocytoma: adrenal tumor producing large amounts of

catecholamines (tumor usually benign; reverse effects)

1-receptor agonists:

phenylephrine Mechanism of Action:selective agonist of the 1 adrenergic receptor

Effects: induces vasoconstriction

Indications: hypotension, nasal congestion

Administration: po or nasal spray as decongestant

1-receptor antagonists:

prazosin Mechanism of Action:selective antagonist of the 1 adrenergic receptor

Effects: blocks smooth muscle constriction (relaxes ureters); vasodilation (can help with

hypertension)Indications: enhances urine flow in benign prostatic hyperplasia, especially with hypertension

2-receptor agonists:

clonidine Mechanism of Action:selective agonist of the 2 adrenergic receptor.

Effects: decreases NE release pre-synaptically (2 is on pre-synaptic side, for feedback inhibition).

Indications: hypertension (reduces blood pressure), used for withdrawal in substance abuse

Administration: orally (both indications) or patch (substance abuse)

2-receptor antagonists: yohimbine but questionable clinical use

-receptor pharmacology

Non-specific receptor agonists:

isoproterenol Mechanism of Action: nonselective agonist of the adrenergic receptors

Effects: stimulates cardiac output, dilates bronchial smooth muscle, dilates vascular smooth

muscle

Indications: bradychardia or heart block; rarely used to treat asthma

Non-specific receptor antagonists:

propranolol Mechanism of Action: nonselective antagonist of adrenergic receptors (general blocker)

Effects: decreased cardiac output, bronchial smooth mm constriction

Indications: used to treat hypertension, angina, anxiety, vasovagal syncope (when heart rate

rises, blood vessels dilate too much, decreased brain perfusion, patient faints), arrythmias

1 receptor agonists:


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dobutamine Mechanism of Action: selective agonist of 1 adrenergic receptor

Effects: increases cardiac rate & force of contraction (increased cardiac output); dilates

coronary arteries to reduce afterload

Indications: cardiomyopathy with CHF, especially in anginal states

Administration: IVOther: doesn't work indefinitely

1 receptor antagonists:

metoprolol Mechanism of Action: selective antagonist of 1 adrenergic receptor (beta-blocker)

Effects: reduces cardiac output, reducing demand on heart

Indications: hypertension & angina

Other: also may promote better filling of coronary arteries by increasing length of diastolic phase

2 receptor agonists:

albuterol Mechanism of Action: selective agonist of 2 adrenergic receptorEffects: dilates bronchial smooth muscle & uterine smooth muscle

Indications: asthma; stopping premature labor

Other: very few cardiac side effects because of 2 selectivity. Also promotes glycogenolysis in liver

(be careful not to precipitate diabetic state)

2 receptor antagonists: not useful clinically

Some interest in3 receptor agonists to reduce adipose tissue in adiposity

Epi, NE, and dopamine

epinephrine Mechanism of Action:predominantly an agonist of adrenergic receptors (over )Effects: increases cardiac output & systolic arterial blood pressure; large metabolic effect

(increases O2 comsumption & blood glucose)

Indications: stopping anaphylactic response, used in code blue settings

norepinephrine Mechanism of Action:Primarily an agonist of adrenergic receptors

Effects: Increases systolic and diastolic blood pressure; less effect on cardiac output &

metabolism

Indications: Hypotensive shock (largely replaced by phenylephrine now)

dopamine Mechanism of Action:Acts on D1 receptor in vasculature; also and in high doses

Effects: Pressor (increases blood pressure), used in cardiac situations.

Indications: Low dose (renal dose) can be used to impact D1 receptor only if patient has low renal

perfusion; higher doses impact D, , and receptors and is first pressor in most instances of

shock (low BP)

Misc: Adenosine receptor pharmacology: treating asthma, for example, by antagonizing adenosine at airways;

Nitric oxide signaling is also autonomic.


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SUMMARY TABLE (autonomic I and II)


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An Overview of Cancer Chemotherapy

Current treatment strategies: prevent, cure, or palliate Cancer can cause morbidity & mortality by disrupting physiology locally (invade/disrupt vital organ function)

or systemically (metastatic spread) so treatment can be directed locally or systemically as well Important rise in # of cancer survivors in US have to re-calibrate their health risks (Tx after-effects, etc.)Local treatments

Surgery (solid organ malignancy; need systemic disease, need staging before surgery to determine extent) Radiation therapy(localized cancers that cant be removed surgery; also as adjuvantwith surgery &

palliation of metastases that can cause morbidity)

Chemotherapy (sometimes given regionally e.g. hepatic artery for colonic cancer liver metasteses) Other (immunotherapies, etc. often experimental)Systemic treatments

Hormone / Growth Factor (remove / antagonize trophichormones, e.g. estrogen for breast cancer, androgens forprostate cancer)

o Tamoxifen (anti-estrogen) adjuvant after resection ofbreast cancer or systemic for metastatic

Chemotherapy: forsystemic cancers, for cure (leukemia, testis,lymphoma) or pallation (solid organ cancers)

o Can be used as adjuvant to improve local treatmentpotential

Other (immunotherapy, gene therapy, etc.)Treatments can target:

Targets unique to cancer cells (mutant gene products,oncogenic virus products)

Qualitative/quantitative differences in cancer cells (cell cycleeffectors, macromolecules, biosynthetic enzymes, signal transduction pathway components) that are also

present in normal cells

o Therapeutic index (LD50/ED50)usually low for anti-cancer drugs (bad) because of thisAntineoplastic drugs: cytotoxicmechanisms of action

(based on the idea that cancer cells divide more rapidly; not actually that

simple)

Damage cancer cell DNA (alkylating agents) Limit supply of precursors for DNA synthesis (antimetabolites) Interfere with DNA replication (topoisomerase poisons) Interfere with mitotic segregationCancer cells in an exponential growth phase are more sensitive to cytotoxic

agents than those in plateau phases

Log-linear kill kinetic behavior of antineoplastic drugs:

Cancers vary in responsiveness to

cytotoxic chemotherapy

Highlyresponsive (Hodgkins, Wilmstumor)

Responsive (acute leukemia inchildren, retinoblastoma, testicular

cancer)

Moderately responsive (acuteleukemia in adults, multiple myeloma,

breast cancer, prostate, ovarian)

Partially responsive (glioblastoma,colorectal, pancreatic islet cell

carcinoma, bladder)

Minimally responsive: (liver,pancreatic cancer; melanoma)


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Fractional cell kill: a specific dose of chemotherapeutic drug kills a specific fraction of tumor cells regardlessof tumor cell population (see logarithmic decline with therapy)

Norton-Simon hypothesis

Based on observation that improvements in response rates fromchemotherapy doesnt lead to improvements in survival

General idea: a more effective treatment will kill lots of cells, getdown to the exponential growth part of the curve; cancer cells

replicate quickly and catch up to a similar less-effective

treatment. Mortality occurs way out in plateau phase.Activation of apoptosis by antineoplastic drugs

Accumulation of neoplastic cells = division, death, or both Cancer cells can escape apoptosis by activating senescence or autophagy p53 or Bcl-2 are common mutations to avoid Antineoplastic agents can stabilize p53 or use other strategies to induce apoptosis

o Many classes create DNA strand breaks to increase p53 activity & apoptosis New pathways for targeting: caspasecascade, other cell-death signal transduction pathwaysAntineoplastic drug resistance

Cancers arise clonally but have heterogeneity in later populations (tumor cell heterogeneity) Subclones can be resistant to drugs

o ABC transporter family: pump out lots of kinds of drugs in ATP-dependent manner. Blocking isdifficult therapeutic target (also pump drugs out in kidney, etc. increased toxicity)

Goldie-Coldman hypothesis

Luria and Delbruck: in bacteria, rate ofgenetic variants appearing related to rate ofcell division &probability of variant arising with each division (genetic instability)

Goldie / Coldman: considered in cancer cells & anti-neoplastic drofgenetic instability in populationo Although rate of appearance is independent of total number, absolute number of subclones is

greater for a greater size of cancer cell population (need to detect early!)

Experiment (L-D Fluctuation Analysis): culture cells and then:o Plate concentration of mixture of cultured cells on a bunch of plates: about the same amount of

resistance occurs in each plate (Poisson distribution = random)

o Pick out individual cells, grow up clonal population, and plate same concentration. Non-Poissondistribution in amount of resistance on each plate (mutation can occur early or late in clonal

growth process)


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So: cancer might respond well but eventually these subclones can emerge and treatmentfails.

Rationale for combination chemotherapy, combined modality treatments, debulking surgery: rapidly reduce

the total # cancer cells and absolute # drug-resistant subclones

Why are some cancers readily curable & others poorly responsive?

1. Cancer cell kinetic properties. Curable cancers may have more rapid growth (antineoplastic drugs killthem better).

2. Cancer cell biochemical properties. Noncurable cancers can detoxify, extrude, or otherwise escapeantineoplastic drugs.

3. Cancer cell phenotypic properties. Related to cells of origin of cancer (not well defined) e.g. testiscancer more responsive than prostate.

Cancer stem cells

Normal renewing cell populations have rare stem cells around (differentiate to transient amplifyingthen fully differentiated, non-proliferative cells)

Cancer may be similar Theory (controversial):

Tx that kill differentiated cancer cells show treatment response but not improved survival or cure Tx that kill stem cells might prolong surviva but notshow initial response

Developing new drugs:

Historically: Phase I (tolerance, dose-limiting toxicities, maximally tolerated dose = MTD), Phase II(efficacy: complete & partial responses), Phase III (comparative efficacy & toxicity vs current regimens),

Phase IV (integrating into standard treatment after FDA marketing). 10 years, $1 Billion.

Now: more common Phase I/II combinatorial trials after molecular biomarker use. Cheaper & quicker Big bottleneck: not discovery but rather clinical trials / approval


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o Directly induces apoptosis (lymphocytes own self-destruct mechanism triggered by CD20binding)

o Antibody dependent cell-mediated cytotoxicity (ADCC)killed by NK cells & otherso Complement fixed & cells lysed.

Reistanceo CD20 not downregulated & escape mutations are rareo Major mechanisms:

1. Failure to generate ADCC (genetic variant in Fc binding receptor)2. Variations in apoptotic pathways (probably most common)

o Overall:Ab still binds to tumor, just doesnt kill it Treatment considerations:

o Everyone eventually relapseso Maintenance therapy?

1. inhibits ability to generate new IgG2. susceptibility to certain infections

o Retreatment generally works if pts have not received rituximab recently (but not if onmaintence)

Antibody conjugates

Radioimmunoconjugateso Murine Ab; target CD20 and conjugated to

radioactive isotopes

o Crossfire increases action (overcomes resistance)because neighboring cells are killed too by

radiation (those which are apoptosis-resistant)

Immunotoxins work by a similar idea If tumor is radiosensitive, conjugate radioactivity; if not,

conjugate a toxin (but toxin may be antigenic, preventing

retreatment

Consequences of Ab therapy

Targetso Looking for muntant proteins, only in cancer, etc.

but now maybe some tissues (e.g. b-cells) are

disposable? Thyroid / prostate?

Half-lives

Fab = hours Mouse = days Chimera = days to weeks Human = months

NomenclatureRi-tu-xi-mab; 1-2-3-4

1. Anything2. tu(m) = tumor is target3. type of antibody

a. o = mouseb. xi = chimericc. zu = humanized

4. mab = monoclonal antibody


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Mechanisms and uses of antimetabolite drugs, signal transduction inhibitors, and anti-

angiogenesis drugs in antineoplastic therapy

General notes:

Antimetabolites: In the end, these pretty much all work by leading to DNA double-strand breaks(nucleotide pool or DNA polymerase speed; causing DNApol to get stuck & cause DBS without

repair)

o All pretty much have bone marrow toxicity In traditional treatment, all roads lead to DNA (now more of a targeted approach

Antimetabolites:

Mimic structure ofnormal metabolic species; inhibit enzymes in both normal and tumor cells Administered as prodrugs that require metabolic activation Inhibit deoxynucleotide and DNA synthesis; kill cells in S phase Targeting tumor cells: take advantage of different transport or enzymatic activation of prodrug, or of

cells that are progressing through cell cycle

Nonneoplastic cells most affected: rapid cell divisiono Hair follicle, bone marrow, intestinal epithelium cellso Therapy induced leukemia is major complication

Limitations: drug delivery (central hypoxic zone of solid tumors), not all tumor cells are cycling, fixedpercentage killed with each treatment, need active immune system, drug resistance common

Folate antagonists:

Inhibit dihydrofolate reductase (DHFR) which reduces folic acid to dihydrofolate (DHF) andtetrahydrofolate (THF)

THF is required to carry methyl & methylene (1-C) groups for thymidine and purine biosynthesis

methotrexate Mechanism of Action: Folic antagonist (antimetabolite). Inhibits dihydrofolate reductase (DHFR).

Effects: Inhibits DHFR which is involved in synthesis of THF from folic acid. THF is the methyl/methelyne

carrier for purine and thymidine synthesis.

Indications: wide variety of cancer breast cancer, colorectal cancer, lymphoma

Administration: often paired with leucovorin shortly after MTX given ("leucovorin rescue") - replentishes

folate stores

Toxicity: mucositis, kidney damage, hepatotoxicityResistance: Reduced uptake; reduction in enzymes that add polyglutamate; DHFR gene amplification

Other: Actively transported into cells. Requires activation by addition of several glutamates (traps in cell;

enhances inhibition). Aka MTX

Deoxynucleotide synthesis antagonists


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hydroxyurea Mechanism of Action: Inhibits ribonucleotide reductase. Antimetabolite antineoplastic agent.

Effects: Ribonucleotide reductase reduces NDPs to dNDPs for DNA synthesis

Indications: Leukemias; head and neck cancers

Toxicity: Standard (bone marrow, etc.)

Resistance: Overexpression of reductase

Note: Nucleoside analogs (5-FU, 6-percaptopurine, 6-thioguanine, etc.) are able to be transported into cell via

nucleoside transporter, and are then p-lated and trapped in cell. They must fit into a kinase in the cell, however

(resistance mechanism)

Pyrimidine biosynthesis antagonists

5-fluorouracil Mechanism of Action: Covalently modifies thymidylate synthase, the enzyme which converts dUMP to

TMP. Triphosphate form can also be incorporated into DNA and cause strand breaks

Effects: Antimetabolite antineoplastic agent.

Indications: Colorectal and breast cancer

Administration: IV and oral. Often co-administered with leucovorin. TS uses folate as a cofactor (also when

5-FU binding), so adding a folate analog like leucovorin pushese the inhibitory equilibrium through

(LeChatlier's). Also often co-administered with 5-ethynyluracil, which inhibits dihydropyrimidine

dehydrogenase in intestine.

Toxicity: Bone marrow suppression

Resistance: Decreased activity of activating enzyme. Intestinal enzyme dihydropyrimidine dehydrogenase

can inactivate by converting it to dihydroform and preventing absorption.

Other: Transported in via nucleoside transporter, then P-lated and trapped in cell (needs to fit in kinase)

Purine biosynthesis antagonists

6-mercaptopurine,

6-thioguanine,

azathioprine

Mechanism of Action: Competitive inhibitor of several enzymes in purine synthesis pathways (looks

like guanine); also gets incorporated into DNA

Effects: Purine biosynthesis antagonist; antimetabolite antineoplastic agent.

Indications: leukemias

Administration: oral

Toxicity: Bone marrow suppression

Resistance: inactivated by xanthine oxidase (XO). Decrease in HGPRTase activity is common resistancemechanism.

Other: Must undergo activation to form mononucleotide (add sugar) via HGPRTase. Also inactivation,

elimination in urine pathways competing.

Inhibitors of DNA polymerase


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gemcitabine (2', 2' difluorodeoxycitidine)

cytosine arabinoside (cytarabine, Ara-C.)

fludarabine (arabinosyl-2-fluoroadenine)

5-azacytidine (5-aza-C)

2-chlorodeoxyadenosine (cladribine, 2-CdA)

Mechanism of Action: Inhibits DNA polymerase by blocking DNA strand

elongation (substrate but can't elongage afterwards)

Effects: Antimetabolite antineoplastic agent

Indications: pancreatic cancer (gemcitabine), chronic lymphocytic leukemia

(CLL fludarabine), acute myelogenous leukemia (AML cytosinearabinoside)

Toxicity: myelosuppression

Resistance: decreased activity of activating enzymes; decreased nucleoside

transport across cell membrane

Other: Must be activated by deoxycytidylate kinase and nucleoside

diphosphate kinase

New strategies: signal transduction inhibitors

Receptor & non-receptor protein kinases

Resistance to all of these is via amplifaction of oncogenic protein kinase gene, resistance mutations in kinase

catalytic domain. Second-generation protein kinase inhibitors have bene developed (active against mutant PKs)

imatinib Mechanism of Action: inhibits tyrosine kinases (BCR-ABL, c-KIT, PGDF receptor kinase)

Effects: Tyrosine kinase inhibitor; antineoplastic agent. BCR-ABL is a hyperactive fusion kinase implicated in

CML (philadelphia chromosome). PGDF RK = platelet-derived growth factor receptor kinase

Indications:CML, gastrointestinal stromal cancer.

Resistance: amplifaction of oncogenic protein kinase gene, resistance mutations in kinase catalytic domain.

Second-generation protein kinase inhibitors have bene developed (active against mutant PKs)

Other: aka Gleevec. BCR-ABL + cells are resistant to apoptosis, proliferate more, and have altered adhesion

properties.

trastuzumab Mechanism of Action: monoclonal antibody that binds to extracellular region of HER2, a

transmembrane receptor tyrosine kinase from epidermal growth factor receptor family

Indications: Antineoplastic agent. Breast cancer (25% invasive primary breast cancers have HER2

overexpression)

Resistance: amplifaction of oncogenic protein kinase gene, resistance mutations in kinase catalytic

domain. Second-generation protein kinase inhibitors have bene developed (active against mutant

PKs)Resistance:

Other: a.k.a. Herceptin


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cetuximab Mechanism of Action: monoclonal antibody against epidermal growth factor receptor (EGFR).

Indications: Antineoplastic agent. Epithelial tumors (colorectal cancer, head and neck tumors)

Resistance: amplifaction of oncogenic protein kinase gene, resistance mutations in kinase catalytic

domain. Second-generation protein kinase inhibitors have bene developed (active against mutant PKs)

gefitinib Mechanism of Action: Tyrosine kinase inhibitor (inhibits epithelial growth factor receptor kinase)

Indications: Non-small-cell lung cancer (NSCLC)

Resistance:amplifaction of oncogenic protein kinase gene, resistance mutations in kinase catalytic domain.

Second-generation protein kinase inhibitors have bene developed (active against mutant PKs)

Other: Higher response if EGFR mutated or overexpressed.

Anti-angiogenesis drugs (investigational)

Basic idea: formation of new blood vessels essential for tumor progression.

Protease inhibitors block ECM breakdown Inhibitors of endothelial cell proliferation (small molecule receptor protein kinase inhibitors like

Gleevec & endogenous peptides)

Proteosome inhibition

Basic idea:

NF-kappa-B controls expression of stress response genes & others that promote cell survival I-kappa-B inhibits NF-kappa-B, degraded in proteosome after ubiquination to activate NF-kappa-B Less proteosome activity = more NF-kappa-B inhibition

Velcade Mechanism of Action: Proteosome inhibitor. Antineoplastic agent

Effects: Inhibits the chymotrypsin-like active site of proteosome.

Indications: myeloma

Other: Boronic acid dipeptide; mimics tetrahedral peptidase reaction site.


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Cancer Chemoprevention

As many as 80% cancers in men, 77% in women can be prevented idea is to detect early for public health

intervention before clinical appearance. For instance, Japanese migrants to US assume US-type cancer risk

profile, and their sons even more so (even without genetic mixing).

Long latency for many cancers helps in potential for chemoprevention.

Tobacco and diet are the big risks (30%, 35% cancer deaths attributable respectively)

Can be synergistic interactions between risk factors (e.g. alcohol & tobacco use in squamous carcinoma of

esophagus 150x higher risk if heavy use of both)

Principles for control of human cancer:

1. Prevention (requires knowledge of carcinogens). Diet, exercise, tobacco, alcohol, etc.2. Protection: inhibit or attenuate carcinogen effect. Doesnt require knowledge of carcinogens3. Treatment of premalignancy (screening).

Cancer chemoprevention: the use of natural or synthetic agents that retard, block, or reverse carcinogenesis

before invasive malignancy develops. (chemotherapy is for those who already have cancer)

To determine preventive measure, need to consider cancer risk, treatment risk, and treatment benefit: low risk

requires low intervention like lifestyle modification, high risk can require high-level intervention like surgery.

Medium-high risk might require chemoprevention.

Breast cancer and Selective Estrogen Receptor Modifiers (SERMs)

Estrogen has good and badeffects (improves cognition, lowers cholesterol, prevents bone loss but also

increases breast / endometrial cancer & thromboembolism risk).

Tamoxifen and raloxifene are two examples of SERMS can act like estrogen in some tissues and antagonize

estrogen in others

Several big randomized trials (MORE, STAR, etc.):

1. Tamoxifen vs. placebo(ER+ breastcancer but endometrial cancer, blood clots, stroke)2. Raloxifene vs placebo(ER+ breastcancer but endometrial cancer, no change in blood clots, stroke)3. Tamoxifen vs raloxifene similar but raloxifene fewer endometrial cancers, blood clots

5- Reductase Inhibitors and Prostate Cancer

Idea: reduce androgen activity. There are a bunch of inihibitors of all steps of androgen synthesis.

In some prostate cancers, oncogene translocated behind androgen-based promoter.

Finasteride and duasteride approved for male pattern baldness, BPH (PC chemoprevention)

Two big trials (PCPT & REDUCE): big prevalence of prostate cancer already; couldnt use PSA becausePSA production related to androgens so had to use biopsy

Outcomes: both saw reduction in prostate cancer, but one showed increase in high grade cancer.


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Random area biopsy maybe shrinking prostate with inhibitors increased chance that high grade cancerwould be found?

Aspirin and Coxibs for Colorectal Cancer Prevention

Basic idea: arachidonic acid, inflammation might be part of adenoma cancer recurrence in colorectal cancer.

Wanted to use COX-2 inihbitors like celecoxib (Celebrex) and rofexocib (Vioxx) to selectively inhibit COX-2

(NSAIDs, originally for arthritis). COX-2 makes prostaglandins around epithelial cells of GI tract.

Multiple randomized trials

Aspirin vs. placebo: decrease in colorectal cancer but increased risk of serious GI bleeding APC: celecoxib vs placebo. Reduction in polyp recurrence but increase in cardiovascular events 2.6x Approve: rofecoxib vs placebo (similar reduction in polyps & increase in CV events 1.8x)

More stuff:

Cruciferous vegetables might help cancer chemoprevention: sulforaphane

Problems that you might run into in chemoprevention

Toxicity in a large population Side effects could be significant & hurt adherence No easily identifiable end-point to study (like cholesterol, for instance) Need big population and long durations Poor definition of the best dose (no dose-response curve easily made)


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Antineoplastic alkylating agents and platinum compounds

Alkylating agents: basic principles

Akylating agents react with certain nucleophilicareas in DNA (e.g. N7 of guanine) with several consequences:

Mispairing of modified base Crosslinking of DNA bases on same strand (intrastrand)or opposite strands (interstrand) Crosslinking DNA to proteins, RNA, other macromolecules DNA strand scission (weaken sugar-phosphate backbone; endonucleases attack during repair attempt)

Monofunctional alkylating agents have one arm to react with DNA

Bifunctional agents have two and therefore are the only ones that can crosslink. CROSSLINKING IS KEY.

If bifunctional agents react with water, they can behave like monofunctional agents. Bifunctional agents are

more selective for replicative-based effects because they can work via crosslinking mechanisms

Types of alkylating agents

1.

Nitrogen mustards:mechlorethamine is basic nitrogen mustard; very active & used up quickly.mechlorethamine Mechanism of Action: Bifunctional alkylating agent; antineoplastic agent.

Effects: Forms interstrand or intrastrand DNA cross-links. Can also cross-link DNA to other

macromolecules, cause DNA strand scission, or mispairing of modified base.

Indications: Hodgkin's disease, mycosis fungoides (cutaneous lymphoma)

Administration: part of MOPP regimen. IV, very short half-life

Toxicity: nausea, vomiting, phlebitis, bone marrow suppression

Other: nitrogen mustard. Very reactive (reacts with everything even in blood, so have to give IV)

2. Substituted nitrogen mustards (melphalan & chlorambucil) which are less reactive & can be given po.melphalan,

chlorambucil

Mechanism of Action: Bifunctional alkylating agent; antineoplastic agent.

Effects: Forms interstrand or intrastrand DNA cross-links. Can also cross-link DNA to other macromolecules,

cause DNA strand scission, or mispairing of modified base

Indications: multiple myeloma (mephlan), chronic lymphocytic leukemia (CLL), indolent lymphomas,

Waldenstrom's macroglobulinemia (chlorambucil)

Administration: can give PO

Toxicity: bone marrow suppression, amenorrhea, sterility

Other: substituted nitrogen mustard; less reactive than mechlorethamine

3. Nitrogen mustards that require metabolic activation (cyclophosphamide & ifosfamide).Cyclophosphamide is most commonly used.


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cyclophosphamide,

ifosfamide

Mechanism of Action: Bifunctional alkylating agent

Effects: Must first undergo metabolic activation (P450). Forms interstrand or intrastrand DNA cross-

links. Can also cross-link DNA to other macromolecules, cause DNA strand scission, or mispairing of

modified base.

Indications: Cyclophosphamide: Many human cancers (non-Hodgkin's lymphoma, breast cancer).Can also be used with bone marrow or peripheral hematopoietic stem cell transplantation therapy

(high-dose). Used to treat auto-immune diseases as well. Ifosfamide: sarcomas & many other cancers

Administration: Administering with 2-mecaptoethane sulfonate and vigorous hydration can help

prevent cystitis

Toxicity: bone marrow suppression, alopecia, gonadal toxicity, and hemorrhagic cystitis (diffuse

inflammation of the bladder leading to dysuria, hematuria, and hemorrhage) resulting from excretion

of a reactive metabolite (acrolein). Ifosfamide has more hemorrhagic cystitis, less bone marrow

suppression than cyclophosphamide

Other: Most commonly used alkylating agent. Stem cells have aldehyde dehydrogenase, which

protects from the active form of cyclophosphamide (which means they won't get killed)

Platinum compounds: basic principles

Early experiments: cis platinum compounds had effect on E. coli, while transdidnt (from electrodes) DNA is target (interstrand & intrastrand crosslinking of DNA, or crosslinking to other macromolecules). Difference is in speed of aquation & elimination. Slower aquation (carboplatin, oxaliplatin) means less

kidney damage than cisplatin.

cisplatin Mechanism of Action: DNA cross-linking agent (antineoplastic platinum compound)

Effects: Intra- and inter-strand crosslinking of DNA; crosslinking of DNA to other molecules.Indications: Wide variety of cancers, esp. epithelial (carcinomas of lung, bladder, stomach, ovary) & testis

cancer.

Toxicity: nephrotoxicity, ototoxicity, peripheral neuropathy

Resistance: chemical detoxification, DNA repair

Other: more side effects (shorter half-life) than carboplatin, oxaliplatin (which have bone marrow toxicity as dose

limiting side effect rather than nephrotoxicity)

carboplatin,

oxaliplatin

Mechanism of Action: DNA cross-linking agent (antineoplastic platinum compound)

Effects: Intra- and inter-strand crosslinking of DNA; crosslinking of DNA to other molecules.

Indications: Wide variety of cancers, esp. epithelial (carcinomas of lung, bladder, stomach, ovary) & testis

cancer.

Toxicity: bone marrow suppression

Resistance: chemical detoxification, DNA repair

Other: shorter half life than cisplatin (less nephrotoxicity)


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Mechanisms of resistance to antineoplastic drugs generally fall under two categories:

1. Chemical detoxification. E.g. glutathione, glutathione-S-transferases, etc. Resistance usually comesfrom this pathway (think phase II enzymes, etc. could be upregulated, for instance)

2. DNA repair. Less common excision repair, mismatch repair, etc.Side effects related to antineoplastic drug treatment

Think: these are very near to their maximum tolerance, so lots of side effects will happen - low therapeutic index

Nausea and vomitingo Profound before; less nowo Complex neurological interactions: chemo triggers pretty much all of these

Chemoreceptor trigger zone (metabolic disorders, drugs like chemo) Peripheral receptors (vagal/splanchnic nerves) e.g. in gut (damage from chemo) Vestibular center (motion sickness) Cerebral cortex (anticipatory emesis from chemotherapy)

o All converge to vomiting center in brainstemo What matters: which drug & how much

Cisplatin is notorious (as is cyclophosphamide in high doses) for causing nausea Less for less dose

o Brainstem receptors use dopamine pathways, so nowselective 5-HT3 receptor agonists work well for

cisplatin nausea and vomiting

Alopeciao Usually a few days into 1st or 2nd cycle (1-2 weeks after

chemo)

o Hair will grow back but big psychological effecto Hair follicle: anagen (growth), categen (involution),

telogen (resting)

Hair damaged during anagen (growth phase) Falls out in order of most growing (most in

anagen) scalp>eyebrows, eyelashes, face, axilla,

body, etc.

Bone marrow toxicity (granulocytopenia, anemia,thrombocytopenia, etc.)

o Usually dose limiting toxicitieso Fall & recover in predictable wayso Chemotherapy-induced neutropenia

Like clockwork (around 10th day) PNMsaffected 10-14 days because of speed ofproduction (stem cells resistant to

cyclophosphamide because of aldehyde

dehydrogenase expression so they dont die)

Dose-response doesnt change timing, just thedepth of the nadir

Hematopoetic cytokines (e.g. G-CSF) can beused to shorten the length of the nadir (same


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depth, just less broad)o Transfusion of RBC or platelets can sometimes be used

Gonadal dysfunctiono Lots of ongoing mitosis/meiosis & proliferation in this areao Testes > ovarian follicles for dysfunction (ongoing spermatogenesis vs arrested ova)o Important factors:

Age/gender (pubertal gonads resistant; women < men for dysfunction) Chemo agent & dose (alkylating agents & platinum compounds especially bad

Make sure to bank sperm / store eggs if possible! Some regimens have huge differences in recovery rates

Secondary cancers (leukemia, etc.)o Really worrisome genome damage could lead to malignant transformationso Limited mostly to alkylating agents: monofunctional agents are carcinogens (modify the base &

cause damage but not necessarily lethal)

If cell doesnt die (e.g. if only one arm able to fire for bifunctional agent) normal tissuescan get mutations

o Very hard cancers to treat; up to 10% in Hodgkins pts with radiation+alkylators can get AML


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Additional drugs (maybe know?) Under other (alkylating agents?)

Nitrosureas

Carmustine: lipophilic; treat brain tumors (drug-implanted wafer: glioblastoma multiforme)o (toxicities: bone marrow suppression, nausea & vomiting)

Streptozotocin: antibiotic that is retained in beta-islet cells of pancreas; treats islet cells tumorso Nephrotoxicity, hepatotoxicity, diabetes

Aziridines

Thiotepa: breast cancer; instill in bladder for superficial bladder cancero Usual toxicities

Mitomycin C: antibiotic limited use in recta / pancreatic cancer; superficial bladder cancer as instillateo Usual toxicitieso Rare but significant: interstitial pneumonitis, nephrotoxicity, hepatic veno-occlusive disease,

hemolytic-uremic syndrome

Alkane sulfonates

Busulfan: high dose chemo for bone marrow or peripheral hematopoetic stem cell transplantso Usual toxicities + pulmonary fibrosis, hepatic veno-occlusive disease, skin pigment changes

Methylating agents

Procarbazine: Hodgkins disease. Normal toxicities + peripheral neuropathy, sterility, secondaryleukemia

Dacarbazine:Hodgkins disease. Normal side effects + flu-like syndrome, Budd-Chiari syndrome,photosensitivity


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DNA Topoisomerase-targeted drugs and mitotic spindle poisons

Many of the other drugs (alkylating agents, etc.) were rationally designed; these are screened natural products

Topoisomerase-targeted drugs

All topoisomerases: reversible nucleophilic substitution; active site tyrosine as nucleophile

Preserves energy of initial phosphodiester bond; prevents loss of end of DNA All form covalent enzyme-DNA intermediates (keep ends of DNA together to minimize recombination /

DSB; reversible after unwinding, DNA can re-attack the tyrosine-DNA linkage & rejoin

Help relieve supercoiling / superhelical strain from normal DNA activities (transcription, replication,segregation, chromosone condensation, etc.)

Type I topoisomerase: monomeric, single tyrosine,

cleave one strand of DNA, noATP requirement

DNA can freely rotate around remainingstrands axis

Removes one supercoil per cleavage

Type II topoisomerase:dimeric, two tyrosines, cleave both

strands of DNA, ATP / Mg required

Enzyme holds in place prevents DSB Forms gatefor duplexed DNA to pass through Removes two supercoils per cleavage

Cell killing mechanism of topo poisons:

Stabilize covalent complexDNA replication fork arrest & breakage (DSB) (also RNA transcription arrested) Topo I: G2 cell cycle arrest Induce apoptosis through these mechanisms

Type I topoisomerase-targeting drugs

Stabilize covalent DNA-enzyme complex by:o DNA intercalation(direct block): wedge in between 5 leaving group and 3 phosphate to

sterically block the reversal of the covalent enzyme-DNA binding. E.g. camptothecins

camptothecin

topotecan

irinotecan

(CPT-11)

Mechanism of Action: Topoisomerase I-targeted drug (antineoplastic agent)

Effects: Intercalates into & stabilizes topo-I / DNA covalent complex (sterically blocks DNA-DNA nucleophilic

attack & reversal of enzyme-DNA complex formation).

Indications: Solid tumors (first line for colorectal cancer in US/europe), also ovarian & other adult

maligancies

Toxicity: myelosuppression, nausea, hair loss, fatigue. Irinotecan: liver toxicity in patients with

gluconconjugation deficiencies. Early and late onset diarrhea.

Resistance: MDR drug efflux pumps (ABC-type)

Other: lactone ring is not stable at neutral or basic pH (converts to inactive form). Irinotecan: Administered

as a prodrug; more bioavailable but gives diarrhea / liver toxicities from cleaved off prodrug part. Must be

activated by carboxyesterase

o DNA bending(indirect block): bend DNA in a way that puts active site in conformation wherereversal of attack isnt favorable. E.g. minor groove binding agents (investigational).

Curved structure and positive charges let them fit in to minor groove well


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Increase amount ofcovalent complex by DNA bending; S-phase specific Can increase/decrease effects of other topo I poisons

o Actinomycin D Induces DNA bending / structural pertubations Precise genomic target not known (maybe RNApol instead of topo I)

actinomycin D Mechanism of Action: "hybrid" minor groove binding antineoplastic agent

Effects: Precise target not known. Probably induces DNA bending / structural pertubations (may target

RNA polymerase instead of topoisomerase I)

Indications: Childhood malignancies (Wilm's tumor, Ewing's sarcoma, embryonal rhabdosarcoma)

Toxicity: Usual (myelosupression, hair loss, oral / GI ulceration)


Type II topoisomerase-targeting drugs

Probably a similar stabilization of covalent complex (not well understood)Epipodophylotoxins (non-intercalative)

etoposide

teniposide

Mechanism of Action: Topoisomerase II-targeted antineoplastic agent.

Effects:Nonintercalative; increases covalent DNA-enzyme complex by unknown structural mechanism

Indications: Many types of cancers

Toxicity: Usual (myelosuppression, mucositis, nausea, anaphylaxis)


Anthracyclines (intercalative)

doxorubicin

daunorubicin

Mechanism of Action: Topoisomerase-II-targeted antineoplastic agent.

Effects:Intercalates into & stabilizes DNA-topo II covalent complex by direct or indirect interaction

Indications: solid tumors (doxorubicin); ALL, AML (acute leukemias) (daunorubicin)

Toxicity: Dose-limiting acute & chronic cardiotoxicity. Liver toxicity (where metabolism occurs -

hydrophobic, so bile excretion).

Resistance: MDR drug efflux pumps (ABC-type). Cardiotoxicity from quinone groups (generates hydroxyl

radicals)

Mitotic spindle poisons

Spindle basics:

Made ofmicrotubules( & subunits; dynamic structure ; bind GTP & hydrolize to GDP) Assemble: heterodimers protofilaments microtubules Important in mitosis (dont get good DNA segregation without it) Lots oftubulin in neurons for axonal transportneurologic toxicity of tubulin-binding agents

Basic idea: spindle poisons slow microtubule polymerization dynamics.

Freezing/slowing down the dynamic equilibrium interferes with spindle action during mitosis


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Vinca alkaloids

Bind to -tubulin (as monomer?), which disturbs polymerization & disrupts protofilament structurevincristine

vinblastine

vinorelbine

Mechanism of Action: Mitotic spindle poison (antineoplastic agent). Vinca alkaloid

Effects: binds to beta-tubulin (distorts protofilament structure / polymerization, slows dynamics, affecting

ability to undergo mitosis)

Indications: ALL, lymphoma, hodgkin's, childhood malignancies (vincristine), germ cell tumors, Hodgkin's

disease (vinblastine), lung, breast cancer (vinorelbine)

Toxicity: liver toxicity, myelosuppression. Vincristine: neurotoxicity (limits dosage)

Resistance:MDR drug efflux pumps (ABC-type)

Taxanes

Bind to -tubulin, stabilizing lateral tubulin contacts (freezing filaments in place)paclitaxel

docetaxel

Mechanism of Action: Mitotic spindle poison. Taxane.

Effects:Binds to beta-tubulin, maybe stabilizing lateral contacts & freezing protofilament in place. Slows down

microtubule dynamics, hurting ability to undergo mitosis.

Indications: ovarian, breast cancers (paclitaxel), metastatic breast cancer (docetaxel)

Toxicity: dose-limiting myelosuppression. Peripheral neuropathy (paclitaxel more effects than docetaxel)


Mechanisms of drug resistance

1. Multidrug resistance: ATP-dependent transporter proteins (ABC family = ATP-binding cassette).a. Cellular drug effluxb. Intracellular redistribution of drug away from target (?)

Drug needs to accumulate in cell before it has an effect.

Also important in antibiotic therapy (bacteria have these too)

These pumps are very non-specific

2. Atypical drug resistanceo Mutation of drug binding site (e.g. HIV drugs)o Downregulation of gene expression of protein target (e.g. topo I/II)o Ubquitination & proteolysis of target protein (topo I/II)o Decreased enzyme activity for activation of prodrug (e.g. carboxylesterase & irinotecan)

3.

Detoxification by metabolism (e.g. phase I, phase II enzymes) overexpress or increase activity

introduction and neoplasia - pharmacology

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