Heat shock protein 90 (HSP90) inhibition in squamous cell carcinoma of the head and neck (SCCHN): An in vitro analysis with a focus on p16 status.

Abstract

2552 Background: Despite advances in therapy, the overall 5 year survival for SCCHN is close to 50%. Cisplatin and radiation therapy remain the current standard for treating locally advanced SCCHN. Novel treatment approaches are urgently needed, especially in HPV negative disease. We examined the expression of HSP90 in HPV positive and negative SCCHN and investigated if the HSP90 inhibitor ganetespib can sensitize mutant p53 SCCHN to cisplatin and radiation therapy in vitro. Methods: Phase 1 trials of ganetespib at 150 mg/m2 have shown the maximum clinically achievable concentration (CAC) in patients to be ~166 nM. We treated p53 deficient or mutant p53 SCCHN cells (SCC25 and Detroit 568, CAL27and FADU, respectively) with ganetespib at 10-50 nM alone and in combination with cisplatin or radiation therapy and assessed survival. We measured HSP90, HSP70 and p53 protein expression levels in SCCHN cell lines by immunoblotting and analyzed HSP90 protein levels in p16 positive and p16 negative SCCHN tumor samples by immunohistochemistry. Results: Ganetespib at CAC was significantly more cytotoxic in mutant p53 compared to p53 deficient SCCHN cells (p < 0.05). When combined with CAC doses of cisplatin or radiation therapy, ganetespib displayed strong sensitizing activity (p < 0.05 and p < 0.01 respectively). Ganetespib treatment upregulated HSP70 and HSP90 expression while decreasing p53 expression in the mutant cell lines. HSP90 expression was significantly higher in p16 negative than p16 positive SCCHN tumor samples (79.5% vs. 51%, ANOVA p = 0.016). Conclusions: Our results demonstrate a potential efficacy of ganetespib as a single agent and in combination with cisplatin and radiation therapy in SCCHN. HSP90 expression is upregulated in p16 negative SCCHN. Further exploration of the role of HSP90 in SCCHN, and utility of HSP90 inhibitors, is warranted.