Heat shock protein 90 (Hsp90), a molecular chaperone that regulates proper folding, stabilization and degradation of key regulatory client proteins, has also been implicated in maintenance of high levels of aberrantly expressed proteins such as kinases and transcription factors in several malignancies. Hence Hsp90 inhibition has emerged as a novel strategy for therapeutic targeting of cancers. Several Hsp90 inhibitors (Hsp90i) have demonstrated efficacy as anti-neoplastic agents in pre-clinical studies by inducing downregulation of key oncogenic proteins such as Akt, EGFR, ErKs, STAT3 and VEGFR resulting in differentiation or death of malignant cells. DEBIO0932 is an orally bioavailable second generation HSP90i which can cross the blood brain barrier (BBB) and has shown preclinical efficacy both as a single agent and in combination therapy against several malignancies. However, its possible efficacy in gliomas has not been fully characterized. We examined the effects of DEBIO0932 as a single agent and in combination with temozolomide (TMZ) using glioma cell lines (U373, LN229, U251HF) and glioma stem-like cells (GSC11, GSC23). DEBIO0932-treated glioma cells and GSC showed decreased proliferation in a WST-1 assay and induction of apoptosis by flow cytometry. Western blot analysis of DEBIO0932 treated cells showed activation of apoptotic pathways and downregulation of EGFR, Akt and MAPK which are key regulators of survival pathways and drivers of malignancy in glioblastoma. Wound healing and migration assay showed reduced Glioma cell motility, decreased migration and invasion after DEBIO0932 treatment. Analysis of effects of DEBIO0932 on key signaling molecules using a kinase array showed downregulation of several key kinases relevant to glioma biology; of particular interest, treatment with DEBIO0932 caused downregulation of β-catenin which has been implicated in maintenance of tumor stem cell state. Corresponding to this, we also observed downregulation of CD133, a marker enriched in glioma stem cells. Additionally, given the downregulation of several proteins implicated in cell survival and treatment resistance, we tested the ability of DEBIO0932 to increase the cytotoxic effect of temozolomide (TMZ) in glioma cells. Combination studies showed a synergistic effect of DEBIO0932 and TMZ against gliomas cells and GSC indicating the potential for Hsp90i in overcoming tumor cell resistance to cytotoxic signals. Our results strongly support the potential for Hsp90 inhibition as a therapeutic strategy against gliomas particularly in combination with cytotoxic agents such as TMZ. The oral bioavailability and ability to cross the BBB make DEBIO0932 a promising agent for therapeutic targeting of glioblastoma.

Citation Format: Alessandro Canella, Jihong Xu, W. Hans Meisen, Balveen Kaur, Lara Rizzotto, Divya Kesanakurti, Prabakaran Nagarajan, Vinay K. Puduvalli. DEBIO0932, an Hsp90 inhibitor downregulates key signaling pathways and sensitizes glioma cells to temozolomide. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 683. doi:10.1158/1538-7445.AM2015-683

©2015 American Association for Cancer Research.
2015