For slides – [email protected] Progressing fragments for challenging targets Roderick E Hubbard Vernalis (R&D) Ltd, Cambridge YSBL & HYMS, Univ of York, UK Fragments 2013 1 Trends for new technologies • In the beginning – lots of excitement • Which can lead to hype and over‐selling Expectation Technology Trigger 2 Time Analysis / terms initially proposed by Gartner group (Murcko) Trends for new technologies • In the beginning – lots of excitement • Which can lead to hype and over‐selling Expectation Inflated expectations Technology Trigger 3 Time Analysis / terms initially proposed by Gartner group Trends for new technologies • Too rapid (often inexpert) deployment • It doesn’t work ‐ disillusionment Expectation Technology Trigger 4 Inflated expectations Trough of Disillusionment Analysis / terms initially proposed by Gartner group Time Trends for new technologies • Too rapid (often inexpert) deployment • It doesn’t work ‐ disillusionment Expectation Technology Trigger 5 Inflated expectations Trough of Disillusionment Analysis / terms initially proposed by Gartner group Time Trends for new technologies • Eventually, expertise grows • Begin to understand how and where to apply methods Expectation Inflated expectations Slope of Enlightenment Technology Trigger 6 Trough of Disillusionment Analysis / terms initially proposed by Gartner group Time Trends for new technologies • Learn how to integrate the methods into the process • Add to productivity Expectation Inflated expectations Slope of Enlightenment Technology Trigger 7 Plateau of productivity Trough of Disillusionment Analysis / terms initially proposed by Gartner group Time Fragments • The ideas established in the molecular modelling / structural biology community during the 1980s and early 1990s • First reduced to practice by Abbott in SAR by NMR approach in mid 1990s • Other pharmaceutical companies unable to replicate success • Approaches developed in small pharma companies in late 1990s / early 2000s • Astex, Vernalis, Plexxikon, SGX ….. and underground in large pharma … • Underpinning concepts developed in the 2000s – complexity, ligand efficiency • Success has led to increased use • Different aspects of FBLD are on different parts of this curve • And in different organisatiions Expectation 8 Technology Trigger Inflated expectations Trough of Disillusionment Slope of Enlightenment Plateau of productivity Time Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 9 Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 10 Fragments 2009 talk SeeDs process ‐ 2008 Structural Exploitation of Experimental Drug Startpoints* Target abc Biacore Validation X-ray Structures HSQC NMR Competitive Binding Experiment O H2N O H N NH O NH N N N NH NH HN Wet assay / Biacore O H N N H HO N NH O N NH N N N NH NH H N O HN O OH N Fragment Library O N NH O O 11 *Hubbard et al (2007), Curr Topics Med Chem, 7, 1568 Evolution Chen & Hubbard (2009), JCAMD, 23, 603 Fragments 2009 talk Finding fragments • Finding fragments that bind is not difficult • A good way of assessing target “ligandability” 8% Low hit rates (< 2%) High hit rates (> 2%) Class 1 hits rates Validated hit rate 7% 6% 5% protein-protein interaction (0.4-3% hit rate) 4% 3% 2% Kinases (3-5% hit rate) Poor targets 1% 0% 0.0 12 0.2 0.4 0.6 0.8 1.0 Ddruggability sco re 1 Ligandability Calculate calculated from structure (DScore) 1.2 1.4 Chen & Hubbard (2009), JCAMD, 23, 603 Fragments 2009 talk Finding fragments • Finding fragments that bind is not difficult • A good way of assessing target “ligandability” • Low hit rate can indicate difficult to progress • See also Hajduk (2005) J Med Chem, 48, 2518 8% Low hit rates (< 2%) High hit rates (> 2%) Class 1 hits rates Validated hit rate 7% 6% 5% protein-protein interaction (0.4-3% hit rate) 4% 3% 2% Kinases (3-5% hit rate) Poor targets 1% 0% 0.0 13 0.2 0.4 0.6 0.8 1.0 Ddruggability sco re 1 Ligandability Calculate calculated from structure (DScore) 1.2 1.4 Fragments 2009 talk Using fragments • Growing fragments 14 Fragments 2009 talk Using fragments • Growing fragments – CHK1 example Chk-1 IC50 >100µM LE ~ 0.39 15 Fragments 2009 talk Using fragments • Growing fragments – CHK1 example Chk-1 IC50 = 5µM LE = 0.39 GI50 HCT116 >80µM pH2AX (MEC) – inactive 16 Fragments 2009 talk Using fragments • Growing fragments – CHK1 example Chk-1 IC50 = 0.2µM LE = 0.33 GI50 HCT116 = 4µM pH2AX (MEC) = 7µM 17 Fragments 2009 talk Using fragments • Growing fragments – CHK1 example Chk-1 IC50 = 0.013µM LE = 0.39 GI50 HCT116 = 1.8µM pH2AX (MEC) =0.2µM 18 Series members further optimised to identify Candidate V158411 Fragments 2009 talk Using fragments • Merging – HSP90 example Screen Known Ligands Virtual Screening hits Detailed Design 19 Fragments 2009 talk HSP90 – BEP800 story Fragment Evolved fragment NH2 NH2 N N N OMe O N H N S O VER-26734 FP IC50>5mM VER-52959 FP IC50=535M Brough et al (2009) J Med Chem 52,4794‐4809 Roughley et al (2012) Top Curr Chem 317, 61 VER-82576 G97 D93 NVP-BEP800 FP IC50=0.058M KD = 0.9nM (SPR) HCT116 GI50=0.161M BT474 GI50=0.057M H N F138 N S H2N N K58 L107 O Virtual Screening Hit Cl H2N N O Cl N S O N NH2 NH2 N N Cl OEt O N N O Cl VER-41113 FP IC50=1.56M 20Virtual Screening Hit HO HO VER-45616 FP IC50=0.9M N N H N O NVP-AUY922 Vernalis Phase II candidate (FBLD / SBDD derived) NH2 Fragments 2009 talk Pin1 Story • Proline isomerase – persuasive biological rationale that key oncology target • Structure available + D‐peptide tool compound 21 Fragments 2009 talk O Pin1 Story OH NH H3 C • Proline isomerase – persuasive biological rationale that key oncology target • Fragments identified: fragment to hit evolution • No correlation between biophysical and enzyme assays 22 Fragments 2009 talk O Pin1 Story OH NH H3 C • Proline isomerase – persuasive biological rationale that key oncology target • Fragments identified: fragment to hit evolution • Issue with over‐binding – multiple copies of fragment binding to the protein – SPR and Xray 23 Fragments 2009 talk HO O O Pin1 Story OH O HN N NH CH3 NH Potter AJ et al, Bioorg Med Chem Lett. 2010; 20:586‐590 O H3 C • Proline isomerase – persuasive biological rationale that key oncology target • Fragments identified: fragment to hit evolution • Issue with over‐binding – multiple copies of fragment binding to the protein – SPR and Xray • Designed 3D fragment – progressed multiple series < 100nM on target showing cellular activity 24 Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 25 Hubbard et al (2007), Curr Topics Med Chem, 7, 1568 Hubbard and Murray (2011), Methods Enzym, 493, 509 The Vernalis process Target Virtual screen; literature; library screen Screen by SPR, DSF, WAC, biochem or binding assay, Xray Hits Competitive NMR screen Fragment Library N NH2 S NH2 O N N NH2 OMe O OEt H2N NH2 N N H N S N H N S N N Cl Cl O HO N N N O NH2 N Fragment to hit : SAR by catalog off‐rate screening O Cl O Drug? Optimise fragment O N N H Cl HO RU RU N O 8 30 6 25 20 4 R esp o n se N R esp o n se ~ 1200 compounds Ave MW 190 H2N Characterisation 2 0 -2 26 Design, Build & Test 10 5 0 -4 -100 15 -5 -50 0 50 100 Tim e 150 200 250 300 s -50 0 50 100 Time 150 200 250 300 s X‐ray or NMR guided model Some comments on fragment screening Hubbard & Murray (2011), Meth Enzymology, 493, 509 • For “good” target sites (many enzymes): • If assays configured correctly • Same hits identified by ligand observed NMR and SPR • validated hits tend to give crystal structures • Careful QC of fragment library – attention to assay conditions • There can be lots of false negatives from screening by X‐ray • Requires suitable crystal system • “Wet” assays can work sometimes • But high concentrations can confound the assay • Thermal melt methods unreliable • For non‐conventional targets (such as protein‐protein): • Many issues • Overbinding, problems due to properties of compounds and target • Cross‐validate binding by different techniques 27 Leads generated for many Targets • Disclosed targets include: • • • • Kinases: CDK2, Chk1, PDPK1, PDHK1, Pim1, STK33, Pak4 ATPases: DNA gyrase, Grp78, HSP70 and HSP90 protein‐protein interaction targets: Pin1 and Bcl‐2 FAAH and tankyrase • Undisclosed targets include: • kinases with unusual binding sites • protein‐protein interaction targets • novel classes of enzymes in large multi‐domain complexes 28 Summary – fragments and conventional targets • Fragment screen to assess targets • Fragments alongside HTS and knowledge‐based • You always find something new • Fragments to hits for conventional targets is relatively straightforward • (when crystal structures / good models available) • The main issues are organisational and cultural • Discuss !! Expectation 29 Technology Trigger Inflated expectations Trough of Disillusionment Slope of Enlightenment Plateau of productivity Time Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 30 James Murray, Steve Roughley, Natalia Matassova Exploiting the dissociation rate constant k KD = off kon koff (s-1) (M-1s-1) PL P + L kon 31 James Murray, Steve Roughley, Natalia Matassova Exploiting the dissociation rate constant k KD = off kon (s-1) (M-1s-1) • Cannot improve association rate constant above ~10‐8 M‐1s‐1 • No point in drug discovery, too many membranes in the way! • Dissociation rate constant can be infinite (ie covalent!) • We have seen that it is the key driver of potency • As have others (review Copeland, Future Med. Chem. 3(12), 2011) 32 James Murray, Steve Roughley, Natalia Matassova Exploiting the dissociation rate constant k KD = off kon (s-1) (M-1s-1) • Cannot improve association rate constant above ~10‐8 M‐1s‐1 • No point in drug discovery, too many membranes in the way! • Dissociation rate constant can be infinite (ie covalent!) • We have seen that it is the key driver of potency • As have others (review Copeland, Future Med. Chem. 3(12), 2011) Ass ocia Resonance Signal (RU) tion -k on Dissociation - koff Kinetics Concentration Time (s) • Surface plasmon resonance – a way to measure kinetics 33 • FOCUS ON THE Off‐RATE ‐ koff James Murray, Steve Roughley, Natalia Matassova Exploiting the dissociation rate constant k KD = off kon (s-1) (M-1s-1) • Cannot improve association rate constant above ~10‐8 M‐1s‐1 • No point in drug discovery, too many membranes in the way • Dissociation rate constant can be infinite (ie covalent) • We have seen that it is the key driver of potency • As have others (review Copeland, Future Med. Chem. 3(12), 2011) • Independent of concentration • Exploit this to assess unpurified reactions, off‐rate screening (ORS) 34 James Murray, Steve Roughley, Natalia Matassova Off rate screening (ORS): Example • Historical Hsp90: thienopyrimidines • 200 nM – 5 M IC50 by FP assay • Re‐prepared compounds by Suzuki reaction R O N H2N DMF / H2O O N N S O NaHCO3 Pd(Ph3P)2Cl2 100 ºC Microwave 10 min • Minimal work‐up • Evaporate, partition • Purity 50 – 80 % (LCMS) • Screened by ORS 35 R B(OH)2 Cl H2N N S O James Murray, Steve Roughley, Natalia Matassova Off rate screening (ORS): Example • Historical Hsp90: thienopyrimidines • 200 nM – 5 M IC50 by FP assay • Re‐prepared compounds by Suzuki reaction R O N H2N DMF / H2O O N N S O NaHCO3 Pd(Ph3P)2Cl2 100 ºC Microwave 10 min • Minimal work‐up • Evaporate, partition • Purity 50 – 80 % (LCMS) • Screened by ORS 36 R B(OH)2 Cl H2N N S O A: Pure starting material B: Faux reaction James Murray, Steve Roughley, Natalia Matassova Off rate screening (ORS): Example • Historical Hsp90: thienopyrimidines • 200 nM – 5 M IC50 by FP assay • Re‐prepared compounds by Suzuki reaction R O N H2N DMF / H2O O N N S O NaHCO3 Pd(Ph3P)2Cl2 100 ºC Microwave 10 min • Minimal work‐up • Evaporate, partition • Purity 50 – 80 % (LCMS) • Screened by ORS 37 R B(OH)2 Cl H2N N S O A: Pure starting material B: Faux reaction C: Purified product D: Crude reaction Tankyrase ‐ Introduction 38 • Axin is targeted for turnover through poly‐D‐ribose labelling by Tankyrase. This removes axin, which has a role in stabilising ‐catenin • Inhibition of Tankyrase has been proposed to enhance the degradation of ‐catenin, an indirect way of affecting the WNT‐pathway • Crystal structure of tankyrase available in 2007 2RF5 3UH4 Structural Genomics Consortium (2007) Novartis (2012) Alba Macias, Chris Graham and team Tankyrase ‐ Introduction • Axin is targeted for turnover through poly‐D‐ribose labelling by Tankyrase. This removes axin, which has a role in stabilising ‐catenin • Inhibition of Tankyrase is therefore proposed to enhance the degradation of ‐catenin, an indirect way of affecting the WNT‐pathway • Crystal structure of tankyrase available in 2007 • At Vernalis: • Initially – low levels of protein production – insufficient • 39 material for fragment screen by NMR Able to produce large numbers of apo‐crystals that preliminary trials showed were suitable for ligand soaking Alba Macias, Chris Graham and team Tankyrase ‐ Hit identification Crystals Soaked fragments in pools of 8 Data collection (up to 1.6Å resolution) Streamlined structure solution 62 hits from 1563 fragments Characterised by SPR and TSA 40 Alba Macias, Chris Graham and team Tankyrase ‐ Fragment to hit evolution • The most attractive fragments were not suitable for rapid chemistry • Designed a modified fragment • Off‐rate screening libraries identified vectors and substituents • Crystals soaked directly with reaction mixtures • Lead Series driven using combinations of tools • • • • Computational chemistry X‐ray crystallography SPR (ORS), DSF Medicinal Chemistry • Properties • 5 nM vs TNKS2, high ligand efficiency (0.60) • Affects PD markers in cells (stabilises Axin2, inhibits WNT pathway) • Tools to probe the biology 41 PDHK – an unusal kinase • GHKL family protein (like HSP90) • Other companies have targetted for diabetes • AZ and Novartis in the 1990s – various allosteric sites • Vernalis investigated as a cancer metabolism target • Off‐rate screening to selectively evolve a fragment DCA – 2q8h Pfizer – 2bu7 E2 / L2 site AZD‐7545 – 2q8g Novartis – 2bu5 42 ATP site – 2q8i PDHK project • Initial fragment hit for ATP site – also binds to HSP90 • Structure shows which vector(s) to explore • Parallel libraries synthesised and screened by SPR • Using the off‐rate screening method – changes in koff • One SPR channel with HSP90, one with PDHK Fragment bound to PDHK1 VER‐00236029 • Can identify PDHK selective compounds PDHK1 • And HSP90 selective compounds HSP90 VER‐00236030 PDHK1 HSP90 43 Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 44 Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 45 Non‐conventional targets 46 Non‐conventional targets • Can find fragments that bind • Orthogonal biophysical methods can validate and characterise fragment binding 47 Non‐conventional targets • Can find fragments that bind • Evolution requires robust model of fragment binding • Best model is from X‐ray structure • But sometimes high affinity ligand required for structure 48 Non‐conventional targets • Can find fragments that bind • Evolution requires robust model of fragment binding • Best model is from X‐ray structure • NMR methods can provide sufficient quality of model • Experiments can be filtered to reveal just the interactions between protein and ligand Unfiltered NOESY - All NOEs 49 Non‐conventional targets • Can find fragments that bind • Evolution requires robust model of fragment binding • Best model is from X‐ray structure • NMR methods can provide sufficient quality of model • Experiments can be filtered to reveal just the interactions between protein and ligand Protein/ligand Filtered NOESY - Intermolecular NOEs 50 Unfiltered NOESY - All NOEs Non‐conventional targets • Can find fragments that bind • Evolution requires robust model of fragment binding • Best model is from X‐ray structure • NMR methods can provide sufficient quality of model • Experiments can be filtered to reveal just the interactions between protein and ligand • Have developed leads from fragments using NMR models • High affinity ligands give X‐ray structures that confirm model 51 Video of Bcl‐2 plasticity 52 Bcl‐2 ‐ ligandability 8% Low hit rates (< 2%) High hit rates (> 2%) Class 1 hits rates Validated hit rate 7% 6% 5% protein-protein interaction (0.4-3% hit rate) 4% 3% 2% 1% 0% 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Ligandability calculated from structure (DScore) druggability 1 Calculate Dscore • changes dramatically as ligands explore available pockets / flexibility 53 Geneste, Murray, Davidson, leDiguarher et al Selective Bcl‐2 inhibitor program • Structure‐guided optimisation has generated selective Bcl‐2 inhibitors • MW < 780; > 100‐fold selective over other BH3 domains • Sub‐10 nM efficacy in cell models of AML • In vivo, rapid and strong apoptotic response in RS4;11 xenograft models, both iv and oral • Platelet sparing (cf ABT‐263) • Key was biophysical assays to assess cell penetration and compound aggregation 1400 Tumour volumes (mm3) Median +/- InterQuartile Range 1200 1000 800 Compound 3 50 mg/kg 600 Compound 3 100 mg/kg Compound 4 50 mg/kg Compound 4 100 mg/kg 400 ABT-263 50 mg/kg ABT-263 100 mg/kg Control (untreated) 200 54 0 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Time after tumour inoculation (days) Treatment schedule (per os) (Twice a week) Summary ‐ non‐conventional targets • For non‐conventional targets • And where structures are hard to obtain • It takes time – and not yet clear how often fragments can be successful • Integration with biophysical methods can be key • Also – a commitment to the long haul Expectation 55 Technology Trigger Inflated expectations Trough of Disillusionment Slope of Enlightenment Plateau of productivity Time Fragments 2013 talk • Summary from 2009 • Where we were 4 years ago • New approaches / ideas for conventional targets • Screening methods • Off‐rate screening for fragment to hit optimisation • How to approach non‐conventional targets • What is a non‐conventional target? • Methods for determining binding mode • Issues – assays, plasticity, compound properties, 3D • Final remarks 56 Updated from Chen & Hubbard (2009), JCAMD, 23, 603 Finding fragments ‐ issues • For some targets, it can take time to configure a robust assay • For fragment screening but also hit progression • Protein construct, assay conditions, etc, etc 8% Low hit rates (< 2%) High hit rates (> 2%) Class 1 hits rates Validated hit rate 7% 6% 5% protein-protein interaction targets – varying hit rates 4% 3% 2% Kinases high hit rate Poor targets 1% 0% 0.0 57 0.2 0.4 0.6 0.8 1.0 Ddruggability sco re 1 Ligandability Calculate calculated from structure (DScore) 1.2 1.4 3D fragments • Most of the compounds in fragment libraries are commercially available small molecules • Medicinal chemist emphasis on chemical tractability • Some use privileged fragments from existing drugs • Most of the fragments are flat heterocycles • This is fine for some targets (kinases, ATPases) • Perhaps limiting for other (new) target classes • Some initiatives underway to introduce more 3D fragments • The challenge will be synthetic tractability • A York initiative 58 York 3D fragments • Peter O’Brien has developed chemistry for adding lithiated N‐Boc heterocycles 2 (formed from 1) to heterocyclic, symmetrical ketones • The resulting fragments have distinctive 3D shapes, presenting useful looking pharmacophores • Shape measured by principle moments rod 1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0 59 0.1 sphere Vernalis 0.2 0.3 0.4 0.5 disc 0.6 0.7 0.8 0.9 1 rod 1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0 sphere York fragments 0.1 0.2 0.3 0.4 0.5 disc 0.6 0.7 0.8 0.9 1 York 3D fragments • Peter O’Brien has developed chemistry for adding lithiated N‐Boc heterocycles 2 (formed from 1) to heterocyclic, symmetrical ketones • The resulting fragments and lead‐like compounds have distinctive 3D shapes, presenting useful looking pharmacophores • Project underway to explore the chemistry • Generate 500 member library • See how it performs against various targets 60 Concluding remarks • Straight forward to find fragments for most sites on most proteins • Opportunities for new “3D” fragments? • The challenge is knowing what to do with the fragments • Off‐rate screening allows exploration of vectors • Evolving fragments in absence of structure? • For conventional targets • Lots of starting points; opportunity for “good” medicinal chemistry • Issue in some organisations is integration with medicinal chemistry • For non‐conventional targets • Provides starting points when other techniques fail • Close integration with biophysics is crucial; takes time and commitment • Not necessarily faster – patience required 61 • But hopefully better End • References in the slides acknowledge who did the work • FBLD conference • • • • • • 62 2008 – San Diego 2009 – York 2010 – Philadelphia 2012 – San Francisco 2014 – Basle http://www.fbldconference.org Vernalis Research Overview • Approximately 60 staff in research • Based in Cambridge, UK (Granta Park) • Recognised for innovation and delivery in structure and fragment‐based drug discovery • Structure‐based drug discovery since 1997 • Distinctive expertise combining X‐ray, NMR, ITC and SPR to enable drug discovery against established and novel, challenging targets • Portfolio of discovery projects • Six development candidates generated in the past six years • Protein structure, fragments and modelling integrated with medicinal chemistry • Internal Vernalis projects in oncology • Collaborations across all therapeutic areas • e.g. oncology, neurodegeneration, anti‐infectives 63 • Aim to establish additional collaborations during 2013 / 14
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