New Directions in GIST

1
New Directions in GIST

• George D. Demetri, MD
• Dana-Farber Cancer Institute and Harvard Medical
  School
• Ludwig Institute for Cancer Research
• Boston, Massachusetts

ESMO Symposium Sarcoma and GIST Milan 05/2008
2
What Are The Questions in GIST?

• How best to manage primary GIST?
• Best drug?
• Personalizing choice based on genotype and
  clinical characteristics
• How best to maintain the benefits of TKI
  therapy?
• How best to manage GIST progression after
  initial benefit of TKI therapy?

3
Primary GIST Management

• Multimodality management
• Is there a value to resecting residual disease
  after benefit with TKI therapy?
• What is the best TKI to use first, and how
  should it be dosed?
• Imatinib vs. some other -ib?
• Empiric dosing vs. drug level-based dosing

4
Imatinib Cmin (Trough) Distribution 400 mg and
600 mg Data Combined
Q4
Q2-Q3
Q1
5
Time to Progression in GIST PatientsImatinib PK
Profiles by Cmin Quartiles
Q2/3 Q4

• Patients in lowest imatinib exposure quartile
  (Q1) had shorter TTP (median 11.3 m) than
  patients in thethree higher quartiles (30.6 m P
  0.0029)

6
Variations on a Theme of Resistance in GIST

• Inability to induce complete tumor cell kill
• Inability to cure with TKI therapy
• Lack of tumor cell kill
• What other signals keep GIST cells alive but
  stable with TKI therapy?
• Progression after initial TKI benefit
• Clonal expansion and genomic instability

7
Secondary Mutations in KIT CanConfer Resistance
to Imatinib in GIST
KIT
Primary Mutations
Secondary Mutations
Membrane
Cytoplasm
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How to Manage Resistance withStructural Variants
of an Oncogenic Kinase?

• Develop a different structural inhibitor of the
  oncogenic kinase
• Target more than one pathway
• (ideally, determine which of the above is
  more important!)

9
Modifying the Structural Interaction of Kinase
Inhibitor with Target
Courtesy Paul Manley, Novartis Oncology
10
Other TKIs for GIST Sorafenib Dasatinib
AB1010 (masatinib) OSI 930 XL 820
Pazopanib Other multi-targeted agents
(Sunitinib-oid)
11
Developing Rational Combination Therapies
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Targeting Multiple Pathways in GIST
KIT
P
P
P
P
13
New Structural Biology Insights Mechanisms of
KIT Resistanceto Kinase Inhibitors
14
Structural Basis for KIT Activation
Inactive
Active
Yuzawa, Schlessinger, Cell, 2007
Receptor domain
Intra-cellular Kinase domain
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Secondary KIT Mutations Evolve in GIST
withDifferent Patterns of Resistance to Imatinib
vs. Sunitinib
What is the mechanism of resistance?
16
Sites of Secondary Acquired KIT Mutations in
GIST Heinrich, Corless, Demetri, Fletcher JCO
2006
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Collaborative Exploration with Pfizer
ScientistsKIT Structural Biology
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Exploration of Clinically Relevant Mutations in
KIT and Sunitinib Interactions
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WT and Mutant KIT Follow the SamePhosphorylation
Patterns
WT cKit
time (min) 60 90 120 150 180 210 240
pY547

• 1st Phase (t60-120 min) Sequential
  phosphorylation events take place on the JM
  domain (Y547,Y553,Y568,Y570).
• 2nd Phase (t150-240 min) Phosphorylation of
  A-loop tyrosine (Y823).

pY553
pY570
pY823
pY568
D816H KIT Mutant Full activation observed in 10
minutes Same phosphorylation sites pattern
20
Molecular recognition of TKI Binding Site
21
Sunitinibdoes not access the space around T670
or V654,unlikeImatinib
Imatinib
Sunitinib
22
HYPOTHESIS

• Continued appearance and expansion of genomically
  and structurally diverseKIT mutants will limit
  the efficacy ofany small-molecule kinase
  inhibitor orsmall-molecule combination

23
Heterogeneous imatinib-resistance mutations in
different GIST metastases from patient
progressing on imatinib
Exon 9 Exon 17 D820E
Exon 9 Exon 17 N822K
PRIMARY Exon 9 mutant (1530 ins 6) (dupl Ala502
and Tyr503)
Exon 9 Exon 17 D820G
Exon 9 Exon 17 N822Y
Exon 9 Exon 17 N822H
Exon 9 Exon 13 V654A
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GIST is not genomically stable

• Pre-existing resistance mutants
• Evolution of new genetic and epi-genetic
  mutations to evade TKI effects
• Patients will need therapy with adifferent
  mechanism for activity against a wide spectrum of
  evolving mutations

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Hsp90 Inhibition Mechanism of Action
Hsp90 is a chaperone protein responsible for
proper folding and function of some oncogenic
proteins
IPI-504 binds at ATP site of Hsp90 and inhibits
proper folding of the oncogenic protein
Unstable misfolded oncogenic protein degraded
tumor growth inhibited
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Both Sunitinib and Imatinib fail to inhibit KIT
activity in GIST cell lines with Exon 17
activation loop mutations
GIST 430KIT Exon 11 ATP BP Mutation
GIST 48KIT Exon 11 Act Loop Mutation
0 100 250 500 1,000 100 250 1,000
0 100 250 500 1,000 100 250 1,000
pKIT
KIT
Wen-bin Ou Fletcher Lab,
Dana-Farber/Harvard
27
Primary GIST cell lines with secondary KIT
mutations resistant toimatinib and sunitinib
retain sensitivity to IPI-504
28
Primary mutant PDGFRa (D842V) GIST cell line
isresistant to imatinib1 and sunitinib2 but
sensitive to IPI-504
1. Dewaele et al, submitted to Clin Canc Res 2.
Prenen et al, Clin Canc Res 2006
Courtesy of M. Debiec-Rychter
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Serial 18FDG-PET Imaging of Patient following
failure of Imatinib, Sunitinib, AMG 706 etc.
(IPI-504 400 mg/m2)
Baseline
Cycle 1, Day 12 24 hours post 4th IPI-504 dose
Cycle 1, Day 22 After 11 daysoff IPI-504
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CT for patient on IPI-504 400 mg/m2following
failure of Imatinib and Sunitinib
End of Cycle 3(Schedule A)
Screening
End of Cycle 3
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OBSERVATION

• GIST cells remain dependent uponKIT expression
  and signaling even after the development of
  multiple mutations

32
POSTULATE

• By targeting the extracellular domain of KIT with
  the aim of preventing dimerization, signaling
  could be silenced with pro-apoptotic impact on
  GIST cells even after the development of multiple
  mutations

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D5D5 interface formed by indirect interactions
34
Loss-of-function and Gain-of-function Kit
mutations in human diseases
Human Piebaldism (loss)
GIST (gain)
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Structural Biology of the EXTRACELLULAR DOMAINof
the KIT Receptor Tyrosine Kinase
1
2
3
4
5
Yuzawa, Schlessinger, et al. Cell 2007
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The Next Steps

• Continue new drug development
• Focus on new mechanisms beyond 3rd-generation
  KIT inhibitors
• Develop novel rational combinations
• Rigorously prove benefit so that GISTwill remain
  an effective proof of concept for innovative drug
  development
• Use these lessons to understand other sarcomas
  and new drugs such as IGF1-R-ibs

37
Thanks to All Our Collaborators and Patients

• Clinical Teams at Dana-Farber/Harvard Cancer
  Center
• Andy Wagner, Jeff Morgan, Suzanne George, James
  Butrynski, Karen Albritton, A Potter, K Polson,
  B Dirr
• Molecular Biology and Molecular Pathology
• Michael Heinrich, Jonathan Fletcher
• Immunohistochemistry and Anatomic Pathology
• Christopher Fletcher, Chris Corless
• Radiology and Imaging
• Annick van den Abbeele, David Israel, Ritu Gill
• Surgical Oncology
• Chan Raut, Monica Bertagnolli, Burt Eisenberg,
  Sam Singer, Peter Roberts
• Statistics
• Judith Manola
• Clinical Teams (US-Finnish C. Blanke, M. von
  Mehren, H. Joensuu)
• EORTC P. Casali, J. Verweij, JY. Blay, A.
  LeCesne, I. Judson, A. van Oosterom
• Australia J. Zalcberg, G. McArthur, J. Desai
• Industry Collaborators
• Novartis
• Pfizer
• Infinity and Astra-Zeneca

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Effect of sunitinib and imatinib on cellular
proliferation of KIT Exon 11 mutant
Exon 11 V560G Parental Cell Line
100 80 60 40 20 0
Sunitinib
Imatinib
Inhibition ()
0 200 400 600 800 1,000
Concentration (nM)
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Sunitinib is superior to imatinib in inhibiting
proliferation of KIT double mutants (Exon 11
ATP-binding pocket mutation)
Exon 11 Exon 13V560G V654A
Exon 11 Exon 14V560G T670I
100 80 60 40 20 0
100 80 60 40 20 0
Inhibition ()
Inhibition ()
0 200 400 600 800 1,000
0 200 400 600 800 1,000
Concentration (nM)
Concentration (nM)
40
Both sunitinib and imatinib fail to inhibit
proliferation of double mutant KIT Exon 11 with
activation loop mutation
Exon 11 Exon 17V560G D816V
100 90 80 70 60 50 40 30 20 10 0
Sunitinib
Imatinib
Inhibition ()
0 200 400 600 800 1,000
Concentration (nM)
41
IPI-504 Inhibits Oncogenic KIT Signaling in Human
GIST cell lines
See alsoS. Bauer, J. Fletcher, et al Cancer
Res. 200666(18)9153-61 (17-AAG)