Abstract 1534: Hes1 regulates hypoxia induced chemoresistance of myeloma cells

Abstract Bone marrow (BM) microenvironment plays a critical role in response of tumor cells to chemotherapeutic drugs. Hypoxia has been shown to contribute to pathogenesis not only solid but also hematological tumors. While normal BM environment is hypoxic, tumor growth is associated with increased hypoxia in BM niche. We have previously demonstrated that activation of Notch signaling could be one of the mechanisms responsible for survival of multiple myeloma (MM) cells from chemotherapeutic drugs. Here we investigated whether hypoxia could modulate Notch signaling and induce chemoresistance of MM cells. Three MM cell lines were treated with doxorubicin or melphalan in hypoxic (1% O2) or normoxic conditions. Using Annexin V binding assay we demonstrated that hypoxia induced chemoresistance in only one (H929) cell line studied. This effect was associated with significant up-regulation of expression of Notch target gene Hes1 and its protein level while Hes1 level was unchanged in other two MM cell lines. Inhibition of Hes1 with siRNA canceled the protective effect of hypoxia on MM cells. To further confirm the involvement of Notch pathway in regulation of drug sensitivity, Hes-1 was overexpressed in MM cells in normoxic condition using vector pIRES-AcGFP-Hes-1. MM cells with increased Hes1 level became less sensitive to chemotherapeutics as compared to cells transfected with control vector. Hes-1 is considered to be a Notch target gene. However, hypoxia did not affect Notch receptors expression level in MM cells. The effect of hypoxia on Hes1 was Notch-independent as was evident from Notch/CBF1 reporter assay. In addition, inhibition of Notch receptor cleavage with gamma-secretase inhibitor GSI-XII (Calbiochem) did not affect hypoxia induced MM cell chemoresistance. Up-regulation of Hes-1 was induced by HIF-1a as treatment of MM cells with hypoxia mimetic deferoxamine resulted in up-regulation of Hes1 and inhibition of HIF-1a with siRNA abrogated hypoxia-induced protection of MM cells. Thus, our study, for the first time, demonstrates that hypoxia could induce chemoresistance of MM cells through Notch-independent up-regulation of Hes-1. These results could be important not only for understanding the cancer biology but for designing therapeutic intervention in MM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1534. doi:1538-7445.AM2012-1534