NVP-AUY922, a novel diarylisoxazole resorcinol HSP90 inhibitor, potently inhibits growth and metastasis of human tumor xenografts

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NVP-AUY922 is a new diarylisoxazole resorcinol heat shock protein 90 (HSP90) inhibitor that was developed from a structure-based design programme based on an original high-throughput screening hit (CCT018159). NVP-AUY922 was selected based on its high potency for the HSP90 target (K_d=1.7 ± 0.5 nM) and its excellent uptake and retention in human tumor cells and xenografts. The purpose of the present studies was to explore the antitumor efficacy of this compound in vitro and in vivo. NVP-AUY922 potently inhibited the proliferation of a wide range of human tumor cell lines with GI50 values of ~ 2-25nM, inducing G1/G2 arrest and apoptosis. This activity was independent of NQO1/DT diaphorase and P-glycoprotein, and was maintained in drug resistant variants and under hypoxic conditions. The molecular signature of HSP90 inhibition, comprising upregulation of HSP72 and downregulation of CRAF, CDK4 and ERBB2 was demonstrated by western blotting in cells treated with NVP-AUY922 in vitro. NVP-AUY922 also inhibited chemomigration (Transwell assay), haptotaxis (scratch wound assay) and matrix invasion of a variety of tumor cells. Daily dosing (50mg/kg i.p. or i.v.) to athymic mice bearing established human tumor xenografts gave statistically significant growth inhibition and a proportion of regressions in many different tumor types with distinct molecular abnormalities, eg BT474 breast carcinoma tumor/control (T/C) 21%, A2780 ovarian carcinoma (T/C 10.5%), U87MG glioblastoma (T/C 7%), PC3LN3 prostate carcinoma (T/C 37%) and WM266.4 BRAF mutant melanoma (T/C 31%). Therapeutic effects were concordant with changes in pharmacodynamic markers including depletion of ERBB2, CRAF, CDK4, P-AKT, HIF-1α and increased HSP72 as determined by western blot, MSD electrochemiluminescence immunoassay or immunohistochemical analysis of xenografts. NVP-AUY922 significantly inhibited established lung metastases from WM266.4 melanoma (reducing the number and size by 72% and 81% respectively) and lymphatic metastasis from orthotopically implanted PC3LN3 prostate carcinoma (mean tumor burden of regional nodes reduced by 52% and distant metastases undetectable). Finally we showed that NVP-AUY922 inhibited human endothelial cell proliferation (GI50 of 3.9 and 2.5nM in HUVEC and HDMEC respectively), chemomigration and tubular differentiation (>50% inhibition at 10nM). This potential antiangiogenic activity was reflected in reduced microvessel density in human tumor xenografts. Collectively the data show that NVP-AUY922 is a potent, novel inhibitor of HSP90, acting via several complementary mechanisms (e.g. cell proliferation, apoptosis, invasion and angiogenesis) to inhibit tumor growth and metastasis. NVP-AUY922 has recently entered Phase I clinical trials.