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Ganetespib
STA-9090
HSP90 inhibitor (non-ansamycin resorcinol-based)
Evidence Score
28
Ganetespib (STA-9090; Synta Pharmaceuticals) is a second-generation, non-ansamycin, resorcinol-based HSP90 inhibitor that binds the N-terminal ATP-binding pocket of HSP90 with high affinity (Kd ~1 nM). It is not FDA-approved but has completed multiple Phase 2 trials including in GIST (NCT01039519). In SDH-deficient tumors, the mechanistic rationale exploits constitutive pseudohypoxia. SDH loss → succinate accumulation → PHD2/PHD3 inhibition → permanent HIF-1α/2α stabilization (VHL remains functional but cannot target PHD-unhydroxylated HIF-α for degradation). This locks HIF-1α/2α in their active conformations and creates an absolute cellular dependence on HSP90 chaperone activity to maintain the hyperactive pseudohypoxic transcriptome. HIF-1α is an obligate HSP90 client protein. Katschinski et al. (Cell Physiol Biochem 2004, PMID 15989551) established that HSP90α (encoded by HSP90AA1) is the dominant cytoplasmic chaperone maintaining HIF-1α in a VHL-binding-competent and transcription-competent conformation. Isaacs et al. (Cancer Res 2002) demonstrated that HSP90 inhibition routes HIF-1α to proteasomal degradation via a VHL-independent ubiquitin ligase pathway, and that this occurs at pharmacologically achievable HSP90 inhibitor concentrations. Minet et al. (Biochem Biophys Res Commun 2000, PMID 10930466) established the direct HSP90-HIF-1α physical interaction underlying this chaperone dependency. Critical dose-response nuance (Ibrahim et al. Cancer Res 2005, PMID 16322259): low concentrations of HSP90 inhibitors can paradoxically increase HIF-1α protein levels by impairing VHL-competent conformation without achieving proteasomal routing threshold; anti-tumor activity requires doses that drive net HIF-1α reduction. Ganetespib's high HSP90 affinity (Kd ~1 nM) relative to first-generation agents (17-AAG Kd ~26 nM) makes it more likely to achieve the threshold for HIF-α client degradation at tolerable plasma concentrations. In SDH-deficient GIST specifically: NCT01039519 (Phase 2, Synta/DFCI, n=27 imatinib-refractory GIST, completed) provides the direct clinical anchor. GIST is mechanistically selected because SDH-deficient GIST is imatinib-resistant (no KIT/PDGFRA driver) and constitutively pseudohypoxic — precisely the context where HIF-α client degradation via HSP90 inhibition has the highest theoretical selectivity over SDH-intact KIT-driven GIST. Additional HSP90 client proteins degraded by ganetespib (VEGFR2, CDK4, AKT) provide combinatorial benefit across pathways already implicated in SDH-deficient tumors (VEGF signaling [Mechanism 3], CDK4/6 [Mechanism 22], mTOR/AKT [Mechanism 4]), making ganetespib a pleiotropic inhibitor aligned across multiple SDH-loss-driven oncogenic axes. Key limitation: No published data directly test ganetespib or any HSP90 inhibitor in isogenic SDH-null GIST cell lines. The NCT01039519 GIST trial enrolled mixed GIST subtypes; SDH-deficient subgroup data have not been separately reported. Direct in vitro validation (dose-response curves in SDHA/B-null vs SDH-intact GIST lines; HIF-1α protein levels and VEGF/GLUT1 transcription as pharmacodynamic readouts; rescue by HIF-1α overexpression) is the required next experimental step. Evidence_score 28 (theoretical) reflects a rigorous mechanistic chain from SDH loss → constitutive HIF-α → HSP90 client dependency, the well-established HSP90-HIF-1α client biology (PMID 15989551, PMID 10930466, PMID 16322259), the Phase 2 clinical trial data in GIST (NCT01039519), and the absence of SDH-specific experimental validation.
Succinate accumulation inhibits PHD enzymes, stabilizing HIF-1α and HIF-2α regardless of oxygen levels. This drives angiogenesis (VEGF), metabolic reprogramming (glycolysis shift), and growth factor signaling.
Upstream event:
Succinate inhibits PHD1/2/3 (α-KG-dependent dioxygenases)
Downstream effects:
HIF-1α and HIF-2α are obligate HSP90 client proteins: HSP90 maintains HIF-α subunits in a stable, VHL-competent conformation under normoxia and in an active, transcription-competent conformation under hypoxia. In SDH-deficient tumors, constitutive PHD inhibition by accumulated succinate drives permanent HIF-α stabilization, creating an absolute cellular dependence on HSP90 chaperone activity to maintain the hyperactive pseudohypoxic transcriptome. HSP90 inhibition at sufficient doses disrupts HIF-1α/2α conformation, directing these client proteins to proteasomal degradation independently of VHL, collapsing the SDH-loss-driven pseudohypoxic gene expression program.
Upstream event:
SDH loss → succinate accumulation → PHD2/PHD3 inhibition → VHL-independent HIF-1α/2α stabilization → constitutive pseudohypoxic transcription → HSP90 required to maintain HIF-α client proteins in active conformation → tumor HSP90 chaperone dependency for pseudohypoxic proteome maintenance
Downstream effects:
HSP90AA1
Heat shock protein HSP 90-alpha (HSP90α)
Constitutively expressed cytoplasmic ATP-dependent molecular chaperone that maintains client proteins in stable, functionally competent conformations. HSP90α (encoded by HSP90AA1) is required for folding, stabilization, and activation of ~200 client proteins including kinases (HER2, BCR-ABL, CDK4), transcription factors, and critically HIF-1α and HIF-2α. HIF-1α is an obligate HSP90 client protein: HSP90 maintains the HIF-1α PAS-B domain in a conformation competent for VHL interaction under normoxia, and in an active transcription-competent conformation under hypoxia. Isaacs et al. demonstrated that HSP90 inhibition disrupts HIF-1α stability via a VHL-independent, proteasome-dependent pathway — distinct from the canonical PHD/VHL oxygen-sensing route. Minet et al. (Biochem Biophys Res Commun 2000, PMID 10930466) established the HSP90-HIF-1α physical interaction, and Katschinski et al. (Cell Physiol Biochem 2004, PMID 15989551) confirmed HSP90α as the dominant chaperone isoform maintaining HIF-1α client stability. Critical dose-response nuance (Ibrahim et al. Cancer Res 2005, PMID 16322259): low-dose HSP90 inhibition can paradoxically increase HIF-1α protein levels by impairing the VHL binding interface while not achieving the threshold required for proteasomal client routing; high-dose inhibition drives net HIF-1α reduction through a post-translational, proteasome-dependent mechanism. Ganetespib (STA-9090), a second-generation resorcinol-based HSP90 inhibitor, achieves high-affinity HSP90 occupancy (Kd ~1 nM) and demonstrated HIF-1α client degradation at pharmacologically achievable concentrations in preclinical models, without the hepatotoxicity of first-generation benzoquinone ansamycin agents (geldanamycin, 17-AAG). In SDH-deficient tumors, constitutive PHD inhibition by accumulated succinate locks HIF-1α/2α in a permanently stabilized, transcriptionally active state — making the HSP90 chaperone machinery that maintains this active pseudohypoxic proteome an obligate survival dependency. NCT01039519 (Phase 2 ganetespib in imatinib-refractory GIST, n=27, completed) is the most direct clinical anchor for HSP90 inhibition in GIST.
UniProt: P07900
Tumor Type Applicability
Evidence from PubMed, OpenTargets, and ChEMBL will appear here once external data integration is enabled.
Coming in Phase 3
For research exploration only — not medical advice. Consult your doctor before acting on any information.
Have Claude analyze this drug's repurposing potential for SDH-deficient diseases.