Abstract A212: A novel, small molecule inhibitor of Hsc70/Hsp70 potentiates Hsp90 inhibitor-induced apoptosis in HCT116 colon carcinoma cells

Abstract

Abstract The role of the 70 kDa heat shock protein isoforms (Hsc70 and Hsp70) in cancer development and progression through their ability to inhibit apoptosis and via their role as Hsp90 co-chaperones has been well documented. Dual targeting of Hsc70 and Hsp70 with siRNA has previously been demonstrated to induce proteasome-dependent degradation of Hsp90 client proteins and extensive tumor specific apoptosis as well as the potentiation of tumor cell apoptosis following pharmacological Hsp90 inhibition. The design and synthesis of novel adenosine-derived inhibitors of Hsp70, guided by modelling and X-ray crystallographic structures of these compounds in complex with Hsc70/BAG-1, has been described.1 These were the first inhibitors described to target the ATPase binding domain of this family of chaperones. Many of these compounds exhibited submicromolar affinity for Hsp70, were highly selective over Hsp90, and displayed in vitro activity against a variety of human tumor cell lines. We further describe the in vitro mode of action of one of the most potent analogues, VER-155008 in HCT116, HT29, BT474 and MDA-MB-468 carcinoma cell lines. Cell proliferation, cell cycle, cell apoptosis and caspase 3/7 activity was determined for VER-155008 in the absence or presence of small molecule Hsp90 inhibitors. VER-155008 inhibited the proliferation of human breast and colon cancer cell lines with GI50s in the range 5.3 to 14.4 M, and induced Hsp90 client protein degradation in both HCT116 and BT474 cells. As a single agent, VER-155008 induced caspase-3/7 dependent apoptosis in BT474 cells and non-caspase dependent cell death in HCT116 and HT29 cells. VER-155008 potentiated the apoptotic potential of the small molecule Hsp90 inhibitors VER-821602 and 17-AAG in HCT116 but not HT29 or MDA-MB-468 cells. In vivo, VER-155008 demonstrated rapid metabolism and clearance, along with tumor levels below the predicted pharmacologically active level. These data suggest that as a single agent, small molecule inhibitors of Hsc70/Hsp70 phenotypically mimic the cellular mode of action of a small molecule Hsp90 inhibitor and can potentiate the apoptotic potential of a small molecule Hsp90 inhibitor in certain cell lines. The factors determining whether or not cells apoptose in response to Hsp90 inhibition or the combination of Hsp90 plus Hsc70/Hsp70 inhibition remain to be determined. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A212.