WHOTDR Drug discovery

1
WHO/TDR Drug discovery

• Urgent requirement for novel drugs for target
  diseases malaria, Afr. and S. Amer.
  trypanosomiasis, leishmaniasis, lymph.
  filariasis, onchocerciasis, schistosomiasis
• Dual strategy being pursued
• de novo discovery of new chemical entities
• extending the indications of existing drugs to
  WHO target diseases

2
TDR Screening Network

• Protozoa
• STI (Brun) Primary centre for malaria, Afr. S.
  American trypanosomiasis, leishmaniasis
• LSHTM (Bickle) Secondary evaluation centre
• Kitasato Institute malaria screens for Japanese
  compounds
• Antwerp DDC (Maes)Primary centre,protozoa.
  Tibotec off shoot initial focus natural products
• Helminths
• NPIMR (Townson)Prim./sec. centre v filariasis
• LSHTM (Bickle) schistosomiasis
• TBRI (Yousif) schistosomiasis

3
Output from Compound Assessment Centres
4
Drug Discovery Process
LeadOptimisation
Leads
Secondaryin vivo assay
Biopharmacy(Developability)

Hits
2 - 6 years
Tertiary assays
Primaryin vitroassay
Development Candidate
Chemistry
Samples
5
The NetworkTDR-Funded Compound Assessment Centres
LSHTM (Q. Bickle) and TBRI (F. Yousif) schistosomi
asis
STI R. Brun protozoa cytotox
NPIMR S. Townson filariasis
Antwerp L. Maes protozoa cytotox
Primary in vitro assays hit id
LSHTM Q. Bickle malaria, leish, Chagas
Secondary repeat in vitro assays in vivo
assays lead id
STI Afr tryps, malaria
LSHTM / TBRI schistosomiasis
NPIMR filariasis
VCP W. Charman metabolism, PK studies
WRAIR W. Milhous malaria in vitro profile on
multiple strains
Follow-on studies lead op.
6
Lead identification process

• Compounds screened in vitro v biochemical targets
  or whole parasites
• Activity criteria for progression of hits
• Protozoa and proteins IC50 lt 1ug/ml
• O. gutturosa 100 I motility _at_ 1.25 x 10-5M
• S. mansoni 100 I motility _at_ 10ug/ml
• Activity of hits confirmed analogues sourced
  tested (hit expansion)
• Test most active hits in vivo ip then po to id
  leads i.e.- cmpds with activity at ?100mg/kg
  without overt toxicity

7
Lead Optimisation

• The identification of efficacious, safe,
  metabolically robust and orally bioavailable
  compounds for development
• Most difficult and expensive part of pre-clinical
  research with high rate of attrition
• Increase in availability of 3rd party funding
  agencies has made possible advancement of TDR
  compounds into lead optimisation programmes

8
Relay strategy

• Identify lead compounds
• Conduct limited exploration of SAR by acquiring
  analogues from chemical suppliers or original
  supplier
• Commission limited synthesis of additional
  amounts of leads, plus close analogues
• Acquire additional biological data if possible
  preliminary PK information
• Build data package allowing TDR or original
  supplier to seek 3rd party funding for LO studies
  to id development candidate

9
Successes

• Malaria (MMV)
• DB289, bisamidine Phase 2
• OZ277, synthetic peroxide Phase 2
• artemifone, semi-synthetic artemisinin Phase 2
• Protein farnesyl transferase inhibitors lead
  optimisation
• Manzamines lead optimisation
• Novel bisamidines lead optimisation
• DHFR inhibitors lead optimisation

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Successes

• African trypanosomiasis
• DB289, bisamidine Phase 2 (Gates)
• Protein farnesyl transferase inhibitors lead
  optimisation (DNDi)
• Onchocerciasis
• Moxydectin Phase 1 (Fort Dodge)

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Lead Series

• Protozoa
• Malaria
• 15087 series
• 32750 series
• 17516/42098 series
• borrelidins
• African trypanosomiasis
• 20364 series
• Helminths - onchocerciasis/lym. filariasis
• depsipeptides
• tetracyclines

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32750 series

• 32750 (ChemDiv) IC50 0.0029ug/ml v P. fal. K1 (CQ
  0.03ug/ml) 97.7I _at_ 4 x 100mg/kg ip v P.
  berghei, -ve by po route
• 338 analogues sourced from ChemDiv - 5 with
  IC50s lt0.1ug/ml 17 analogues from PrincetonBio
  - 2 with IC50s lt0.1ug/ml

13
Depsipeptides

• Sourced from Pharmacia (41443), Bayer (46620 -
  emodepside), Pfizer (11 cmpds), Meiji (27 cmpds).
• Emodepside being developed as vet. anthelmintic
  Bayer have provided tox. details

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Depsipeptides

• Extremely potent in vitro/in vivo e.g. 46620In
  vitro v O. gutturosa adultsEC50Mot 9 x 10-10 M
  In vivo v O. lienalis in mice 5 x 1.56 mg/kg sc
  - 100 mf redn 5 x 6.25 mg/kg po - 99 mf redn
  no overt toxicity noted. (cf DEC 5 x 100mg/kg sc
  66 mf redn ivermectin 1 x 2ug/kg sc 90 mf
  redn)
• Test remaining analogues - Meiji samples
• Progress emodepside
• Review tox package
• Test v adult O. volvulus and B. malayi in vitro

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Hit/Lead generation

• Whole cell screening
• compounds with biochemical or biological
  rationale
• natural products, especially with claimed
  medicinal properties
• diverse compounds
• HTS v molecular targets

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Major Compound Suppliers

• ChemDiv, PrincetonBio, SPECS
• Dow, Syngenta, Pfizer/Pharmacia, Meiji Bayer,
  Paratek, GSK
• Amura, TopoTarget, Kemin, LICA, Faulk Pharma
• Academia - e.g. U.s of Chicago, Sheffield, Buea,
  Murdock U., WEHI

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Target-based approach

• Target-based approach relevant to whole cell and
  protein assays
• Deconvolution of parasite genomes identifies
  molecular targets
• drives rational procurement of putative
  inhibitors
• aids validation and selection of in vitro and in
  vivo test systems
• assists in understanding molecular basis of drug
  resistance

18
Lead generation - HDAC inhibitors

• HDAC sequences found in P. fal. genome,
  TopoTarget provided 25 cmpds
• Actives found v P. fal.K1 - confirmed v other
  strains at WRAIR, IC50s 0.002ug/ml-0.006ug/ml
  (CQ 0.003ug/ml-0.127ug/ml)
• 42014, 42016 and 42017 provided (plus ADMET
  data) for test _at_ 4 x 50mg/kg ip v P. berghei -
  data awaited

19
HTS v Molecular targets

• Dominant pharma drug discovery paradigm
• Harvests output of genomics/proteomics programmes
• Sub mg sample requirement allows access to
  greater compound numbers/structural diversity
• HTS v protein assays supplements, not replaces,
  whole parasite testing - ensures a flow of
  compounds with good rationale for whole cell
  testing activity provides chemical validation of
  target

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What molecular targets

• Factors governing choice include
• uniqueness, validation, potential for selective
  inhibition
• structure, biochemical characterisation
• potential for resistance development
• assay suitability
• druggability
• WHO HTS campaigns on-going at Walter and Eliza
  Hall Institute (WEHI) and Serono other
  possibilities include Pfizer, Lundbeck, Harvard,
  SouthWestern, MRCT

21
WEHI Project

• Funded in Dec. 2003 (500, 000), no cost ext. to
  Dec. 2005. Provides limited PK and chemistry for
  early stage lead optimisation
• Three targets being pursued using non-prop.
  library of 100, 000 cmpds
• TR (Afr. tryps) initial screen completed - 40
  hits idd for whole cell assay
• PPPK (malaria) initial screen completed - hits
  being confirmed/triaged
• FPPS (Afr. tryps.) assay developed - HTS about
  to commence

22
Serono Project

• Commenced Sept. 2004 costs mainly borne by
  Serono, includes supporting 2 scientists from
  developing countries for training
• 6 targets proposed v proprietary libraries
• Malaria Pf Sub-1 serine protease, Blackman, MRC
  Pf CDK1 Ca-dependent protein kinase, Kappes,
  Heidelberg Pf GSK-3 glycogen synthase kinase-3
  and Pf nek-1 protein kinase, Doerig, Glasgow
• Leishmaniasis CK1 caesin kinase, Grant, Glasgow
  CPB cysteine peptidase B, Mottram, Glasgow

23
Further Molecular targets

• Need to conduct bioinformatic analysis on all
  target parasite genomes
• Set up expert review panel using pharma-type
  criteria to select putative targets
• Be pro-active in accessing targets
• Fund protein expression and assay development
• Select HTS centre according to target -experience
  with related proteins, availability of libraries
  - focussed or diverse

24
Recommendations

• Increase emphasis on HTS v molecular targets in
  helminths to overcome limitations in parasite
  assay throughput
• Make funds available to conduct early-stage lead
  optimisation - esp. need medicinal chemistry and
  PK
• Maximise collaboration with other organisations
  pursuing parasite chemotherapy - MMV, DNDi, WRAIR