Abstract 4221: HSP90 as a therapeutic target in colorectal cancer

Abstract

Abstract Purpose/Objectives: Activation of PI3K /Akt/ NF-κB and MAPK signaling pathway contributes to colorectal cancer cell growth, survival and resistance to therapy. HSP90 is required for PI3K/Akt and MAPK stability, folding and trafficking. Ganetespib is a potent functional inhibitor of HSP90 currently under evaluation in clinical trials. We tested the hypothesis that HSP90 functional inhibition by ganetespib can inhibit PI3K/Akt/ NF-κB and MAPK signaling pathways in colorectal cell lines. Methods: Two colorectal cancer (CRC) cell lines were used, HCT-116 and HT-29. Cells were either untreated (control) or treated with ganetespib at 50nM for 24 hours. Western blot and RT-PCR analyses were carried out to determine the effect of ganetespib on protein molecules involved in cell survival and proliferation. Electrophoretic mobility shift assay (EMSA) was performed in CRC cells to evaluate the effects of ganetespib on NF-κB activity. A subcutaneous xenograft mouse model was used to evaluate the in vivo effects of ganetespib. Results: Treatment of HCT-116 and HT-29 CRC cell lines with ganetespib inhibited survival signaling (PI3K/Akt) and proliferative signaling (MAPK) at the transcriptional and translational level. As validation, HSP90 knockdown similarly inhibited PI3K/Akt and MAPK protein and mRNA levels in both cell lines. Functional inhibition of HSP90 resulted in inhibition of PI3K/Akt and MAPK transcription. Functional inhibition or down regulation of HSP90 was associated with inhibition of NF-κB trafficking (downregulation of NF-κB in nucleus). Ganetespib sensitized colon cancer cell lines to the effects of oxaliplatin and 5FU. Similar effects were also observed in tumors from animals treated with ganetespib. Conclusion: In this study, we present in vitro and animal data supporting the targeting of HSP90 as a method to inhibit the PI3K/Akt/ NF-κB and MAPK signaling pathways in colorectal cancer. We demonstrate that inhibition of HSP90 downregulates PI3K/Akt/ NF-κB and MAPK leading to a decrease in colon cancer cell survival and proliferation, as well as sensitization to chemotherapy. Combining HSP90 inhibitors with chemotherapy is a rational approach for future drug development in colorectal cancer. Citation Format: Ganji Purnachandra Nagaraju, Field F. Willingham, Kevin E. Woods, Patrick Sullivan, Jerome C. Landry, Roberto Diaz, Bassel F. El-Rayes. HSP90 as a therapeutic target in colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4221. doi:10.1158/1538-7445.AM2014-4221