Abstract 2617: MPC-3100, a synthetic Hsp90 inhibitor, induces biomarker changes in vitro and in vivo

Introduction: MPC-3100 is a fully synthetic, orally bioavailable, Hsp90 inhibitor in clinical development. It is broadly active in xenograft models with anti-tumor activity ranging from tumor regression to tumor growth inhibition in many cancer types including colon, gastric, ovarian, prostate, breast, lung and myeloid leukemia. Here we evaluate the effect of MPC-3100 on stability of client proteins in cells and xenograft tumors. We also determine the effect on Hsp70 protein levels, a biomarker of Hsp90 inhibition, in peripheral blood mononuclear cells (PBMCs) from cancer patients receiving MPC-3100. Methods: Her2, Akt, Cdk4, c-Raf and Hsp70 client protein levels were monitored in cell culture with protein immunoblots. Formalin-fixed, paraffin-embedded sections of xenograft tumors from mice dosed orally with MPC-3100 were analyzed by immunohistochemistry (IHC) to monitor changes in Her2, Akt and Hsp70 protein levels. To monitor changes in Hsp70 in cancer patients treated with MPC-3100, PBMCs were collected prior to drug administration, 8 and 24 hours post-dose on Day 1 and 24 hours post-dose on Days 7 and 21 of the first treatment cycle. Hsp70 protein levels were determined by ELISA. Results: Exposure of HCT-116, NCI-N87 and DU-145 cells to MPC-3100 in vitro resulted in a time-dependent reduction in client protein levels with maximal reduction by 24 hours. The IC 50 values for client protein reduction ranged from 0.1 μM to 0.5 μM, comparable to the cellular cytotoxicity values of MPC-3100 at 72 hours for the various cell lines. IHC revealed reduction in Her2 and Akt protein in N87 xenografts in mice given a single oral dose of 200 mg/kg MPC-3100 relative to tumors from animals dosed with vehicle. Healthy volunteer PBMCs exposed to 1 μM MPC-3100 for 24 hours ex vivo revealed a reduction in Akt, c-Raf and Cdk4 protein levels ranging from 50% to 90%. PBMCs from cancer patients receiving MPC-3100 showed an increase of 28 to 589 ng of Hsp70 protein per mg total protein over baseline by Day 8. The increase in Hsp70 expression was seen as early as 8 hours after the first dose and sustained through at least Day 22. Conclusions: The changes in client proteins and biomarkers observed in cells and tumor xenografts exposed to MPC-3100 confirm that the cellular cytotoxic activity and anti-tumor activity in xenografts are a result of Hsp90 inhibition. The consistent increase in Hsp70 expression in PBMCs from cancer patients receiving MPC-3100 indicates that Hsp90 function is inhibited in patients at doses that have been well tolerated in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2617. doi:10.1158/1538-7445.AM2011-2617