Inhibiting heat shock protein 90 and the ubiquitin-proteasome pathway impairs metabolic homeostasis and leads to cell death in human pancreatic cancer cells

BACKGROUNDHeat shock protein 90 (HSP90) and the ubiquitin-proteasome pathway play crucial roles in the homeostasis of pancreatic cancer cells. This study combined for the first time the HSP90 inhibitor ganetespib (Gan) and the proteasome inhibitor carfilzomib (Carf) to target key mechanisms of homeostasis in pancreatic cancer. It was hypothesized that Gan plus Carf would elicit potent antitumor activity by modulating complementary homeostatic processes. METHODSIn vitro and in vivo effects of this combination on mechanisms of cell growth and viability were evaluated with human pancreatic cancer cell lines (MIA PaCa-2 and HPAC). RESULTSCombined treatment with Gan and Carf significantly decreased cell viability. The mechanism varied by cell line and involved G(2)-M cell-cycle arrest accompanied by a consistent reduction in key cell-cycle regulatory proteins and concomitant upregulation of p27. Further studies revealed increased autophagy markers, including the upregulation of autophagy related 7 and light chain 3 cleavage, and evidence of apoptosis (increased Bax expression and processing of caspase 3). Immunoblot analyses confirmed the modulation of other pathways that influence cell viability, including phosphoinositide 3-kinase/Akt and nuclear factor B. Finally, the treatment of athymic mice bearing HPAC tumors with Gan and Carf significantly reduced tumor growth in vivo. An immunoblot analysis of freshly isolated tumors from animals at the end of the study confirmed in vivo modulation of key signaling pathways. CONCLUSIONSThe results reveal Gan plus Carf to be a promising combination with synergistic antiproliferative, apoptotic, and pro-autophagy effects in preclinical studies of pancreatic cancer and will further the exploration of the utility of this treatment combination in clinical trials. Cancer 2017;123:4924-33. (c) 2017 American Cancer Society. Ganetespib and carfilzomib significantly decrease pancreatic cancer cell line viability and tumor growth through the stimulation of G(2)/M cell-cycle arrest, endoplasmic reticulum stress, autophagy, and apoptosis. This reveals that ganetespib and carfilzomib are a promising combination for pancreatic cancer treatment.