novel approaches to antibiotic resistance gili regev-yochay harvard school of public health...
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Novel approaches to antibiotic resistance
Gili Regev-Yochay
Harvard School of Public Health
Children’s Hospital
We are reaching/have reached the post-antibiotic era
• Past 20 years number of new drugs that reached the marked has fallen to less than 50% the previous level.
• Past 40 years only 2 novel Ab classes (lipopeptide- Daptomycin, Oxazolidinone- linezolid)
• Rate of loss of efficacy of old Ab is outstripping their replacement with new ones
• Particularly worrisome for Gram-negative Ab.
Who is to blame?
• Ab industry?• Grant funding agencies? Less funding for Ab
development?• Financial reward to develop new Ab is
unfavorable (restricting Ab to control resistance will paradoxically reduce rate of development).
• 10/15 major pharma reduced or eliminated Ab R&D – Reason: Ab less valuable: short course therapies,
curable disease.
Novel approaches• Ab in non-culturable bacteria
• Bacteriophage
• Bacterial interference
• Don’t kill the pathogen – kill the virulence factors
• Immunomodulation
• Drug interactions (Kishony group)
Novel methods using natural sources
• The original source of antibiotics: bacteria (aimed to killl or inhibit the replication of competitors).
• Most marketed Ab -derivatives from bacterial Ab.– All from culturable bacteria.– What about non culturable bacteria (clone large
fragments of non-culturable bacterial genome)
Natural compounds: non-culturable bacteria/ Lee et al. Biotechnol. Lett 2007, Garcia et al. nat. Biotechnol.
2006
Bacteriophages• Bacteriophages = bacterial viruses
• Estimated: every 2 days 50% of the world’s population is destroyed by bacteriophages.
• Initially discovered in 1915 by Twort and independetly in 1917 by d’Herelle
• Used before introduction of penicillin even in US. Was abandoned since Ab use.
• During Ab era considered “non-conventional” medicine.• Continued use in former USSR: Eliave Institute in Tbilisi
(http://www.evergreen.edu/phage/home.htm).
• FDA approved use of bacteriophages in poultry and cattle for Listeria monocytogenes contamination of meat.
• Recent year: 90 papers on Bacteriophage treatment!
Phage Therapy• Appealing:
– Specific, does not disrupt flora– Either use cocktail of phages or have initial
identification of bacteria to treat
• Marketed phage: ListexTM P100 for controlling Listeria in cheese & meat
• Option: use of lysis-deficient phages that still kill bacteria.
• Can be used as such to induce immunity (WCV).
Bacteriophage – other optional uses
• Therapy delivery systems
• Lytic enzymes (Fischetti et al. 2005. Trends Microbiol)– Phage use lysins which are host specific– Active also on non-replicating bacteria or biofilms.– Resistance is rare
• Combined.– Phage or phage lysins + Ab: available comercially in Georgia
“PhagoBioDerm” biogradable polymer impregnated with lytic phage cocktail + Cipro (Markoishvili et al. 2002. Int. J. Dermatology).
Phage treatment – potential problems
• Quality control and standardization.
• Highly immunogenic and induce neutralizing ab -> single use per patient? Or only external use?
• Safety:– Massive bacterial lysis may lead to toxic shock.– lysogeny, transduction of virulent/Ab resistance genes…
• Another reason for reluctance in the West:– Difficult to obtain IP rights (public for many years)
Bacterial interference• Exchange of “bad” bugs with “good” bugs
• 1909 Danish physician Schiotz: sprayed S. aureus in throats of diphteria carriers and eliminated carriage of diphteria.
• Initially Shinefield et al. 1960-1970s
• 1965 Bacterial interference; protection of adults against nasal S. aureus infection after colonization with a heterologous S. aureus strain. Boris et al.
• 1974 Bacterial interference between strains of S. aureus Shinefield et al. Ann NY Acad Sci.
Bacterial interference – Shinefield et al.
• Direct inoculation of infants, medical students and prisoners with a low virulence S. aureus (502A)
• Controlling S. aureus outbreaks in neonatal units. Neonates colonized with 502A (at birth) completely protected from epidemic S. aureus.
• 4,000 neonates artificially colonized with 502A (nose & umbilical stump).
• Adverse events: 5-15% local infection in the umbilical area (vesicles). One nursery 34% vesicles.
• One case of conjuctivitis
• Sepsis and death at 84h. (colonized at 3h), cathetrized into ubmilical vein (area of colonization).
Bacterial interference - Probiotics• Bacterial vaginosis• Med. J. Aust. 2007 Treatment of VRE carriage with lactobacillus
Don’t aim at the bacteria - aim at its virulence factors
• S. aureus golden pigment impairs neutrophil killing and promotes virulence through its antioxidant activity/ Liu GY et al. JEM 2005
– “white” S. aureus, are not as pathogenic.– Can we target this virulence factor?
• Biosynthesis of the staphyloxanthin is similar to biosynthesis of cholesterol
• SKF-525A drug in the pipeline of cholesterol Rx. But not as good as statins.
• Indeed if added to growing culture of SA-> “white” SA
S. aureus golden pigment impairs neutrophil killing and promotes virulence through its antioxidant activity/ Liu GY et al.
JEM 2005
Immunomodulation
• Induce the immune system to eliminate infections:– Vaccines
– Antimicrobial peptides
– Other:• Hypoxia-induced factor (HIF) -1
Vaccines
• Vaccination can reduce Ab resistance in several ways:
• As in the case of PCV7 – reduction in the most popular strains which were also the main burden of resistance.
Vaccine types associated with drug resistance
US, invasive disease, pre-PCV
0
5
10
1520
25
30
35
4014
19F
6B 18C 4
23F
9V 6A 19A
9A 7F 22F 3
12F
Oth
ers
Serotype
Per
cen
t o
f al
l cas
es
Nonsusceptible Susceptible
Conjugatevaccine
Not in vaccine
General decline in VT + VT association with drug resistance = modest decline in
proportion resistant
39.0%37.4%
Kyaw et al. 2006, NEJM
Resistance is now creeping upwards within NVT
Kyaw et al. 2006, NEJM
Penicillin Nonsusceptibility Among NVT, ABCs USA
0%
2%
4%
6%
8%
10%
12%
14%
<2 65+ All
Pro
po
rtio
n P
en
-NS
1999
2004
Based on Kyaw et al. 2006, NEJM
Serotype replacement in Massachusetts USA:broad range of clones carried; these maintained
their resistance profiles
NVT or 19F/A
Hanage et al. JID 2007
Vaccination -> reduced resistance
• VT association with drug resistance => vaccine disproportionately reduced resistant strains
• After 2-3 years, resistance began creeping up again
• Mainly outgrowth of previously existing, resistant clones
• Some serotype switching• Stay tuned: likely evolution of resistance in
previously susceptible clones
Other ways by which vaccines can reduce ab resistance:
• Indirect – by reduction of Ab use– Less pneumococcal infections– Less fear of physicians to “miss”
pneumococcal infections.
• Both directed at the disease• Empiric treatment.
Antimicrobial peptides • Cationic host defense peptides (innate
immunity)
• Small , highly basic cystein-rich peptides.
• Initial antimicrobial barrier for mucosal surfaces.
• Broad spectrum, non specific.
Antimicrobial peptides - mechanism
• Mechanism of antimicrobial action is unclear.
• Involves targeting membranes whose composition includes negatively charged phospholipids (in contrast to mammalian – mostly neutral).
• In addition modulate components of the innate immune system by activating MO (mechanism unknown, but not through TLR). But activation of TLR4 can lead to up-regulation of β-defensins by epithelial cells.
• Recent studies have also suggested that they have a role in modulating the adaptive immune system through activation of immature dendritic cells.
Studies of potential uses:
• Display antibacterial, antifungal and antiviral activity, non-cytotoxic
• From plant and insect – antifungal defensins.
• TB – α + β defensins possess anti-TB activity• Anthrax – inactivate the enzymatic activity of anthrax
lethal factor.
• Can serve as a valuable resource as a template for designing small synthetic peptides
• Problems: unknown PD and toxicology• Phase IIIa trials as topical direct antimicrobial
treatment
Hypoxia-induced factor (HIF) -1 / Nizet et al. JID 2008
• A transcriptional regulator (HIF-1a) plays a role in supporting the inflammatory and bactericidal activity of neutrophils & MO (murine model).
• Use of HIF-1a agonist (Developed for angiogenesis and cancer).
• Check this in vitro for S. aureus and human neutrophil cells.
• HIF-1a boosts capacity of phagocyts to kill SA