Abstract 3328: Caspase activation as an approach to treat multiple myeloma.
Authors: Zaman Shadia , Wang Rui , Gandhi Varsha 
Published: August 2014

Apoptosis is a cell death program that is essential for normal organ development. Defects in apoptosis lead to uncontrolled cell accumulation resulting in cancer such as multiple myeloma (MM), an incurable plasma cell disorder. MM patients have defective apoptosis machinery largely due to the overexpression of anti-apoptotic proteins such as BCL-2, MCL-1, cIAP1, cIAP2 and XIAP. We are investigating a novel class of procaspase-3 activators as a strategy to activate apoptosis in myeloma cells. The Procaspase Activating Compounds (PAC), PAC-1 and its analog L14R8, were synthesized by Dr. Hergenrother's lab (U. of Illinois, Urbana, IL) and are being developed for clinical application by Vanquish Oncology. PACs convert the inactive zymogen procaspase-3 to caspase-3 which activates apoptosis. Mechanistically, PACs activate procaspase-3 by chelating inhibitory zinc ions thus allowing procaspase-3 to auto-activate to caspase-3. Our hypothesis is that targeting procaspase-3 with PAC agents will bypass inhibitory activity of the anti-apoptotic proteins and induce cell death in myeloma cells. In initial experiments, we examined procaspase-3 expression in a panel of 9 myeloma cell lines and observed that it was expressed in all the cell lines suggesting that PAC agents will be active in myeloma cells. Our investigations with PAC-1 and L14R8 demonstrated that L14R8, but not PAC-1, induced cell death in myeloma cells in a dose- and time-dependent manner. Treatment with 10 μM L14R8 for 24 hours induced &gt;80% apoptosis in U266 and MM.1S cells. Furthermore, L14R8 activity was inhibited by exogenous addition of zinc confirming that the mechanism of L14R8 action is through zinc chelation. The activation of procaspase-3 resulted in the cleavage of its target PARP and decreased the levels of the anti-apoptotic proteins MCL-1 and XIAP. 10 μM L14R8 was also effective in inducing &gt;80% cell death in myeloma cells grown in the presence of protective microenvironment as demonstrated by co-culture experiments with NKtert stromal cells. In addition, when myeloma cells were grown in the presence of exogenous growth factors such as hepatocyte growth factor (50 ng/ml) or interleukin-6 (10 or 50 ng/ml), L14R8 was still able to induce apoptosis (&gt; 60% with 10 μM L14R8 treatment in the presence of either growth factor). Finally, L14R8 was effective in inducing apoptosis in cells resistant to lenalidomide, a standard treatment for myeloma patients. Our future plan is to examine the effectiveness of this drug in primary CD138+ plasma cells (representing malignant myeloma cells). These studies demonstrate that targeting procaspase-3 with L14R8 is an effective strategy to induce myeloma cell death.

Citation Format: Shadia Zaman, Rui Wang, Varsha Gandhi. Caspase activation as an approach to treat multiple myeloma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3328. doi:10.1158/1538-7445.AM2013-3328