8601 Background: The mutations of P53 tumor suppressor protein are associated with progressive in Multiple Myeloma (MM), conversely, stabilization of P53 leads to cell cycle arrest and apoptosis. In this study, we examined p53 protein expression and demonstrated the effect of P53 stabilization using a novel specific P53 stabilizer CBS9106 in MM. Method: We examined P53 protein expression using Immunoblot analysis, as well as the growth inhibitory effect of CBS9106 in MM cell lines and primary tumor cells from MM patients. We also defined whether CBS9106 can overcome the growth promoting effect of exogenous cytokines and bone marrow stroma cells (BMSCs) using [3H]-thymidine uptake assay. Results: Expression of P53 protein was observed in 3/3 primary tumor cells from MM patients and 6/6 MM cell lines. CBS9106 at low nM levels triggered cytotoxicity against p53 wild type MM cell lines and primary tumor cells from MM patients, associated with phosphorylation of P53 (serine15 and 20). In contrast, CBS9106 did not affect the survival of normal peripheral blood mononuclear cells from healthy volunteers at concentrations as high as 10 μM. This agent also induced G1 cell cycle arrest, followed by apoptosis associated with cleavage of caspase-3, -8, -9 and PARP. Neither growth stimulating cytokines (IL-6 and IGF-1) nor BMSCs protected against apoptotic effect of CBS9106. Moreover, we demonstrate that combination of CBS9106 with MDM2 inhibitor Nutrin3 or proteasome inhibitor bortezomib induces synergistic anti-MM activity in both P53 wild type MM cell lines and primary tumor cells from MM patients. Conclusions: Stabilizing P53 by CBS9106 represents a novel promising p53-based therapy in MM. These results provide the preclinical framework supporting evaluation of CBS9106 in clinical trials to improve patient outcome in MM. No significant financial relationships to disclose.
p53 protein expression in non-Hodgkin's lymphoma. Comparative study with the wild type p53 induced proteins mdm2 and p21/waf1