do we need to optimize protein binding in drug discovery?€¦ · considerations of protein binding...

Do We Need to Optimize Protein Binding in Drug Discovery?

NEDMDG Summary Meeting June 4, 2013

Xingrong Liu, Ph.D.

Genentech

Free drug interacts with drug targets: Plasma

Total IC50 = 0.3- 300x Ki Free IC50 = 0.1-10x Ki

Liu et al., Drug Metab Dispos 37:1548–1556, 2009

Brain binding does not contribute to the activity: free drug interacts with drug targets

-20

0

20

40

60

80

100

0.01 0.1 1 10 100 1000 10000

Unbound Brain Concentration/KI

SE

RT

Occ

(%)

-20

0

20

40

60

80

100

0.01 0.1 1 10 100 1000 10000

Total Brain Concentration/KI

SE

RT

Occ

(%)

Total IC50 = 1-1000x Ki Free IC50 = 0.3-3x Ki

Liu et al., Drug Metab Dispos 37:1548–1556, 2009

Different effects of protein binding on in vitro and in vivo free concentrations

Cu ↑

Cbound

Cu

fu=0.1 Cbound

fu=0.5 fu=0.1 fu=0.5

Cu ↑

fu=0.5

Cu

fu ↑ Clin↓

fu ↑ Clin↔

Cbound

Cu↔ Cbound

Scenario 1

Scenario 2

In vitro In vivo

fu ↑

0.001

0.01

0.1

1

10

0 6 12 18 24Time (h)

Tota

l Con

c. (u

g/m

L)

G-378895 IV 3 mg/kg

G-378242 IV 3 mg/kg

0.0001

0.001

0.01

0.1

1

0 6 12 18 24Time (h)

Unb

ound

Con

c. (u

g/m

L)

G-378895 IV 3 mg/kg

G-378242 IV 3 mg/kg

Increase of free fraction by 15X increases IV free AUC by 3X

•  3X increase was due to reduced clearance

fup=0.15

fup=0.01 R1

R2

Cl

NR1

R2

0.01

0.1

1

10

0 6 12 18 24Time (h)

Tota

l Con

c. (u

g/m

L)

G-378895 PO 10 mg/kg

G-378242 PO 10 mg/kg

0.001

0.01

0.1

1

0 6 12 18 24Time (h)

Unb

ound

Con

c. (u

g/m

L)

G-378895 PO 10 mg/kg

G-378242 PO 10 mg/kg

Increase of free fraction by 15X increases oral free AUC 2X

•  2X increase was due to reduced clearance

fup=0.01

fup=0.15

R1

R2

Cl

NR1

R2

Protein binding vs. intrinsic clearance

Data form Blakey et al., J Pharmacokinet Biopharm 25:277–312, 1997

HN

HN

OO

R

C2H5

O

R = -(CH2)nCH3 n = 0-8

Protein binding vs. Vdss


HN

HN

OO

R

C2H5

O

R = -(CH2)nCH3 n = 0-8

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

tissue

plasma

fufu

VtVcVd

Protein binding vs. t1/2


HN

HN

OO

R

C2H5

O

R = -(CH2)nCH3 n = 0-8

Protein binding vs. intrinsic clearance

Data form Obach et al., Drug Metab Dispos 36:1385–1405, 2008

0.1

1

10

100

1000

10000

100000

0.0001 0.001 0.01 0.1 1fu

Clin

(ml/m

in/k

g)

Acids

0.1

1

10

100

1000

10000

100000

0.0001 0.001 0.01 0.1 1fu

Clin

(ml/m

in/k

g)

Bases

0.1

1

10

100

1000

10000

100000

0.001 0.01 0.1 1fu

Clin

(ml/m

in/k

g)

Neutrals

1

10

100

1000

0.01 0.1 1fu

Clin

(ml/m

in/k

g)

Zwitterions

Protein binding vs. Vdss


⎟⎟⎠

⎞⎜⎜⎝

⎛+=

tissue

plasma

fufu

VtVcVd

Protein binding not associate with t1/2

0.1

1

10

100

1000

10000

0.0001 0.001 0.01 0.1 1fu

t1/2

(hr)

Acids

0.01

0.1

1

10

100

1000

0.0001 0.001 0.01 0.1 1fu

t1/2

(hr)

Bases

0.1

1

10

100

1000

0.001 0.01 0.1 1fu

t1/2

(hr)

Neutrals

0.1

1

10

100

0.01 0.1 1fu

t1/2

(hr)

Zwitterions


Brain unbound conc. is governed by the BBB and plasma unbound conc.

plasmauefflux

brainu C

PSClC ,,

1

1•

+=

Clefflux: efflux transport activity at the BBB PS: diffusion permeability at the BBB

Protein binding does not associate with brain penetration

Modified from Maurer et al, Drug Metab Dispos 33: 165, 2005

R2=0.077 R2=0.087

Significant effects of P-gp on brain concentration

Chen et al, Curr Drug Metab, 4: 272, 2003

8

14

14-27

16-28

18 CsA

Digoxin

Ivermectin Verapamil

Desloratadine

Compound Efflux Compound Efflux

Considerations of protein binding in drug discovery

•  No need to specifically optimize plasma binding –  Reduction of plasma protein binding alone does not increase free drug

concentration –  Reduction of clearance increases free drug concentration –  Reduction of plasma protein binding tends to associated with reduction

of clearance, as both of the parameters are governed by lipophilicity

•  No need to specifically optimize brain binding •  Reduction of brain tissue binding alone does not increase free brain drug

concentration •  Reduction of efflux activity enhance free brain drug concentration

•  Need to consider protein binding in … –  PK/PD, human PK/dose/DDI prediction, drug transporter/tissue

penetration, safety margin calculation, regulatory filing, etc.

Acknowledgements

•  Marcel Hop

•  Bruce Roth •  Joe Lyssikatos •  R. Scott Obach •  Franco Lombardo •  Nigel J. Waters

•  Dennis A. Smith

0%

5%

10%

15%

20%

25%

30%

<0.001 0.001-0.01 0.01-0.05 0.05-0.1 0.1-0.3 0.3-0.6 0.6-1

Unbound Fraction

Dru

gs (%

)

Protein binding of marketed drugs

Data from Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 11th

n = 267

n=14, fu<0.1

Many successful CNS drugs show high brain binding

0.0001

0.001

0.01

0.1

1

Sertr

alin

e

Chl

orpr

omaz

ine

Fluo

xetin

e

Paro

xetin

e

Nor

tript

ylin

ea

Hal

oper

idol

Cyc

lobe

nzap

rine

Fluv

oxam

ine

Clo

zapi

ne

Hyd

roxy

zine

Mid

azol

am

Cita

lopr

am

Prop

oxyp

hene

Traz

odon

e

Dia

zepa

m

Sele

gilin

e

Ris

perid

one

Phen

ytoi

n

9-O

H-R

ispe

ridon

e

Car

bam

azep

ine

Thio

pent

alc

Zolp

idem

a

Car

isop

rodo

l

Venl

afax

inec

Busp

irone

Lam

otrig

ine

Met

hylp

heni

date

Met

oclo

pera

mid

e

Mor

phin

e

Caf

fein

e

Hyd

roco

done

Sulp

iride

Mep

roba

mat

e

Bra

in fu


0

5

10

15

20

25

thiop

ental

phen

ytoin

sulpi

ride

zolpi

dem

morphin

e

trazo

done

rispe

ridon

e

lamotrigi

ne

metoclo

peram

ide

busp

irone

hydro

codo

ne

propo

xyph

ene

parox

etine

seleg

iline

cloza

pine

venla

faxine

citalo

pram

fluvo

xamine

hydro

xyzin

e

nortr

iptyli

ne

cyclo

benz

aprin

e

fluox

etine

methylp

henid

ate

halop

erido

l

chlor

promaz

ine

sertra

line

midazo

lam

caris

oprod

ol

carba

mazepin

e

caffe

ine

ethos

uxim

ide

diaze

pam

AU

Cbr

ain/

AU

Cpl

asm

a (0

-5h)

0

5

10

15

20

25

thiop

ental

phen

ytoin

sulpi

ride

zolpi

dem

morphin

e

trazo

done

rispe

ridon

e

lamotrigi

ne

metoclo

peram

ide

busp

irone

hydro

codo

ne

propo

xyph

ene

parox

etine

seleg

iline

cloza

pine

venla

faxine

citalo

pram

fluvo

xamine

hydro

xyzin

e

nortr

iptyli

ne

cyclo

benz

aprin

e

fluox

etine

methylp

henid

ate

halop

erido

l

chlor

promaz

ine

sertra

line

midazo

lam

caris

oprod

ol

carba

mazepin

e

caffe

ine

diaze

pam

AU

Cu,

brai

n/A

UC

u,pl

asm

a (0-

5h)

Plasma and brain binding has a significant impact on the B/P ratio

Total Brain/Plasma Ratio

Unbound Brain/Plasma Ratio

Acid: 0.5 (0.4-0.6) Base: 6 ± 7 (0.1-24) Neutral: 0.9 ± 0.7 (0.2-0.8)

Acid: 0.2 (0.2-0.3) Base: 1 ± 0.7 (0.1-3.4) Neutral: 0.5 ± 0.3 (0.1-1)


240x

34x

Protein binding vs. clearance


Protein binding vs. free Vdss


Questions for protein binding •  PPB non-linearity – saturation of PPB as a strategy to increase

unbound concentration – is this a viable strategy? •  Covalent modifiers – does PPB even matter? Is it always total

plasma concentration? •  What about "exceptions to the rule"? - e.g. Active transport? Non-

well stirred assumption? •  Impact on Cmax and Cmin – this could be sensitive to fu – see

Derendorf paper I circulated •  Determination of unbound PK parameters (Clunbound –

Vd,ssunbound) – does this simplify or complicate things? •  Species differences? •  What should we use PPB data for in drug discovery?

do we need to optimize protein binding in drug discovery?€¦ · considerations of protein binding...

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