targeting hsp90 in im-resistant gist: kit degradation as a broadly relevant salvage strategy
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TARGETING HSP90 IN IM-RESISTANT GIST:
KIT DEGRADATION AS A BROADLY RELEVANT SALVAGE STRATEGY
Sebastian Bauer1,2, Lynn Yu1, George Demetri3, Jonathan Fletcher1
1Brigham & Women's Hospital, Harvard Medical School, Boston, MA, USA 2Westgerman Cancer Center, University of Essen, Germany
3Dana Farber Cancer Institute,
CTOS – Boca Raton, November 21st, 2005
• Biochemical inhibition of oncogenic KIT induces
clinical responses in most GIST patients
• BUT...many patients eventually progress
• Heterogeneous imatinib resistance mechanisms:
secondary KIT/PDGFRA kinase domain mutations genomic amplification activation of alternate oncogenes +/- loss of KIT
• Salvage therapies with alternative KIT/PDGFRA inhibitors = moderate benefit
Introduction (1) Imatinib in GIST
Ex 11
Ex 13
Ex 9
Ex 17
Ex 11
Ex 13
Ex 9
Ex 17
p85
p110
Ex 11
Ex 13
Ex 9
Ex 17
Survival Transcription
RasRaf
MEK
MAPK
GR
B2
Proliferation
AKT
MTOR
p70S6K
S6
4EBP1
eIF4E
PP
P P
PDK1
JAKSTAT
PTEN
?
Ex 11
Ex 13
Ex 9
Ex 17
Ex 11
Ex 13
Ex 9
Ex 17
Adhesion/ Motility
FAK
PAK
NUCLEUS
SOS SHCDOK
Introduction (2) KIT signaling in GIST
PI3K
Workman, TMM 2004
Introduction (4) HSP90 background
Chaperone family:
• protein folding
• translocation
• stabilization
• prevent aggregation
• elimination
, activated!
• 17-AAG inhibition of HSP90 downregulates
crucial tyrosine kinases in various cancers:
• BCR-ABL CML
• ZAP70 CLL
• FLT3 AML
• EGFR lung cancer
• KIT mast cell disease
Introduction (5) Rationale for HSP90 inhibition
• Mast cell line harboring IM-resistant D816 KIT mutation
sensitive to HSP90 inhibition by 17-AAG
Introduction (6) Rationale for HSP90 inhibition
µM
pKIT
KIT
HMC-1.1 HMC-1.2 HMC-1.2 HMC-1.20 .1 .5 1.0 0 2 4 8 24h0 .1 1.0 0 1 10 µM
IMATINIB 17-AAGMa, Blood 2002 Fumo, Blood 2004
pKIT
KIT
• KIT/PDGFRA activation is crucial to transformed
state at PROGRESSION
• Heterogeneous KIT/PDGFRA mutations at
progression
• KIT/PDGFRA small molecule inhibitors
• efficacy depends on mutation type & kinase structure
• HSP90 inhibitors
• efficacy depends on kinase activation
Introduction (7) HSP90 inhibition ideal in GIST?
• Evaluation of 17-AAG mediated HSP90 inhibition in IM-
sensitive and IM-resistant in GIST cell lines
• Biological consequences of HSP90 inhibition were
determined by - immunoblotting
- cell proliferation assays (Cell titer Glo®)
- apoptosis assays (Caspase Glo®)
Methods (1) Assays
Methods (2) Cell line KIT mutations
• GIST882: IM-sensitive / hom K642E
• GIST48: IM-sensitive / hom V560D
IM-resistant / het D820A
• GIST430: IM-sensitive / het JM deletion
IM-resistant / het V654A
• GIST62: IM-resistant / KIT negative
Results (1) Effect of 17-AAG on KIT in GIST
Results (2) 17-AAG in IM resistant GIST
Results (4) Effect of 17-AAG on KIT signaling
Results (5) 17-AAG in IM resistant GIST
Results (6) 17-AAG time course in GIST882
Results (7) Effect of 17-AAG on wt-KIT
Results (8a) Effect of 17-AAG on proliferation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1 10 100 1000 10000
17-AAG17-AAG + 100nM IM17-AAG + 1000nM IM
GIST882Ex 13
IC50:320nM
Results (8b) Effect of 17-AAG on proliferation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1 10 100 1000 10000
17-AAG17-AAG + 100nM IM17-AAG + 1000nM IM
GIST430Ex 11Ex 13
IC50:220nM
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1 10 100 1000 10000
17-AAG17-AAG + 100nM IM17-AAG + 1000nM IM
Results (8c) Effect of 17-AAG on proliferation
GIST48Ex 11Ex 17
IC50:130nM
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1 10 100 1000 10000
17-AAG17-AAG + 100nM IM17-AAG + 1000nM IM
Results (8d) Effect of 17-AAG on proliferation
GIST62Ex 11KIT neg
IC50:>5000nM
Results (9) Effect of 17-AAG on apoptosis
Conclusions (1)
• HSP90-mediated stabilization crucial for KIT
expression and activation in GIST
• 17-AAG has strong antiproliferative and
proapoptotic effects in IM-resistant GISTs at
clinically achievable doses
• HSP90 targeting inhibits KIT oncoproteins with
IM resistance mutations
Conclusions (2)
• Degradation of KIT by 17-AAG depends on KIT
activation irrespective of resistance mutations
• No substantial additive or antagonistic effects
with IM
• Compelling rationale for clinical evaluation of
HSP90 inhibitors in (KIT-positive) GIST
Acknowledgements
Brigham and Women‘s HospitalJonathan FletcherLynn YuMeijun ZhuWenbin OuCJ ChenKatherine JanewayChris HubertLeigh Johnson-Abt
Dana-Farber Cancer InstituteGeorge DemetriSuzanne GeorgeJeffrey MorganPalma Dileo
Results (3) 17-AAG in IM resistant GIST
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