Abstract 5451: Role of novel peptides targeting Hsp90-EGFR interaction to promote EGFR degradation and cisplatin cytotoxicity in head and neck cancer

Abstract

Abstract Background: The eukaryotic heat shock protein 90 (Hsp90) is a ubiquitous chaperone protein that regulates many client proteins involved in signal transduction, cell cycle control and transcriptional regulation. These include the kinases implicated in tumorigenesis such as EGFR, Raf-1, ErbB-2, v-Src family kinases and Cdk4. Our previous data indicated that the interaction of Hsp90 with EGFR is critical for head and neck cancer cell survival upon treatment with cisplatin. We have also identified a potential region in EGFR that is involved in its interaction with Hsp90. We hypothesized that a small peptide analogous to this binding region of EGFR will competitively inhibit Hsp90 binding to EGFR, and therefore EGFR will not be protected from cisplatin induced degradation leading to cell death. Methods and Results: Using Immunoblotting and clonogenic survival assays in eight head and neck squamous cancer cell lines we found that cisplatin-induced EGFR degradation significantly correlates with cytotoxicity. Immunoprecipitation of Hsp90 and/or EGFR showed that cisplatin induced EGFR degradation followed with its dissociation from Hsp90 in cisplatin sensitive cells. In contrary, cisplatin resistant cells showed a stabilized Hsp90-EGFR interaction and therefore EGFR was protected from cisplatin induced degradation. We also found that the Hsp90-EGFR interaction is reduced between EGFR mutants for the binding region of Hsp90 when compared to wild-type EGFR in Chinese hamster ovary cells (EGFR negative). Therefore, we design peptides targeting Hsp90-EGFR binding region. Importantly, we found that transfection of a novel peptide (8 amino acids) abolished the Hsp90-EGFR interaction in cisplatin resistant UMSCC-1 cells, promoted EGFR degradation and sensitized these cells to cisplatin in both culture and xenograft models. We further confirmed by using HIV-TAT-biotin derivative of this peptide that the peptide is getting internalized in cells and tumors. We also found the interaction of specific peptide with Hsp90. Conclusions: Our results indicated that enhanced Hsp90-EGFR interaction is an adaptive response that can protect EGFR degradation induced by cisplatin treatment. We have identified a region in EGFR which is required for its interaction with Hsp90. Our data also indicated that using a novel peptide this interaction can be disrupted which promotes EGFR degradation and increases cytotoxicity in both culture and xenograft models. We are now investigating the role of this peptide in radiosensitization in head and neck carcinoma cell lines. 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 5451.