Abstract LB-289: Synthetic Hsp90 inhibitor, PF-04928473 and prodrug PF-04929113, demonstrates potent antitumor activity in head and neck cancer by inhibiting multiple proliferative and prosurvival signaling pathways

Purpose: Heat shock protein 90 (Hsp90) is a molecular chaperone that stabilizes client substrates involved in cell proliferation, survival, and apoptosis. Cancer cells display increased dependency on Hsp90 and client oncoproteins, and Hsp90 has been identified as a druggable target. This study investigated the biological activity of a synthetic small molecule inhibitor of Hsp90, PF-04928473 and the orally available pro-drug PF-04929113 in head and neck squamous cell carcinoma (HNSCC). Experimental Design: Hsp90 expression was examined in nine human HNSCC cell lines (UMSCC). In vitro, the effect of PF-04928473 on cell proliferation, death and cell cycle were examined by MTT assay and flow cytometry. The effects on signaling molecules and cytokine production were determined using Western blot, reporter gene, and Luminex assays. In vitro combination with radiation was examined using the clonogenic survival assay. The effect of pro-drug PF-04929113 on UMSCC-11A tumor growth and Hsp90 client proteins were examined in the murine xenograft model and by immunohistochemistry (IHC). Results: UMSCC cell lines over-expressed Hsp90 mRNA and protein when compared with normal keratinocytes. In vitro, PF-04928473 potently inhibited UMSCC cell growth, induced cell death and modulated cell cycle, with an IC50 range of 32-73nmol/L. Combining radiation and PF-04928473 increased radiation sensitivity by a dose modifying effect of 1.4. PF-04928473 significantly modulated signaling molecules, including down-regulation of c-Met receptor, IKK, IKK, and BCLXL, as well as up-regulation of cleaved PARP, pro-apoptotic p53, PUMA, and p21 protein expression. The drug inhibited AKT, ERK, and STAT3 phosphorylation, suppressed NF- B, AP-1, BCLXL, and IL8 reporter activities, and blocked IL8, IL6, and VEGF production. In vivo, pro-drug PF-04929113 20mg/kg daily for 3-7 weeks significantly inhibited tumor growth. After treatment, tumor specimens showed increased IHC staining for p53, PUMA, and TUNEL, and decreased staining for c-Met, SRC, p-STAT3, p-AKT, p-ERK, IKK, RELB, Ki67 and CD31. Conclusion: Synthetic Hsp90 inhibitor PF-04928473 effectively modulated proliferation, cell survival, and inflammatory and angiogeneic cytokine production in HNSCC in vitro. Pro-drug PF-04929113 inhibits tumor growth in vivo by promoting apoptosis through inhibition of several key signaling pathways. [Supported by NIDCD project ZIA-DC-000073] Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-289.