RITA Induces Apoptosis in Multiple Myeloma Cells Independent of p53 Mutation Status
A Azuma-Mukai, MN Saha, H Chang. University of Toronto, Toronto, Canada
Background: RITA is a recently discovered low molecular weight compound that can restore the tumor suppressor function of p53 in cancer cells. It binds to p53 and induces its accumulation in tumor cells, increasing its half-life by preventing p53-MDM2 interaction. RITA has been shown to induce apoptosis in tumor cells from hematological malignancies such as acute myeloid leukemia and chronic lymphocytic leukemia, however, the antitumor effect of RITA in multiple myeloma (MM) has not been established.
Design: To evaluate the effect of RITA in MM, two human myeloma cell lines MM1.S (carrying wild type-p53) and 8226 (harboring mutant p53) were used in this study. After MM cells were exposed to RITA, its cytotoxic effect was assessed by MTT assay, the percentage of apoptotic cells was monitored by fluorescence-activated cell sorting (FACS), and the induction of p53 and its immediate downstream transcriptional target MDM2 were measured by Western blotting.
Results: Treatment of MM1.S cells with RITA exerted a dose dependent decline in survival with an IC50 of 0.37 uM whereas RITA reduced cell viability in 8226 cells with an IC50 of 3.5 uM. RITA also exerted a dose dependent cytotoxicity in primary bone marrow samples from 2 MM patients. The percentage of specific apoptosis of myeloma cells was estimated after 72 hrs exposure to 2 uM RITA for MM1.S or 10 uM RITA for 8226. MM1.S cells underwent significant apoptosis of approx.50%, and 8226 showed apoptosis of approx. 61%. Moreover, activation of p53 pathway by RITA was demonstrated by a dose dependent up-regulation of p53 and MDM2 in MM1.S cells but not in 8226 cells.
Conclusions: Our results indicate that RITA can activate p53 pathway in MM cells carrying wt-p53, and is capable of inducing apoptosis in MM cells with either wild-type or mutant p53. Although the mechanism of RITA-induced apoptosis in MM cells with mutant p53 remains to be determined, RITA appears a promising small molecule for further evaluation as a novel approach in the treatment of MM.
Tuesday, March 23, 2010 9:30 AM
Poster Session III # 211, Tuesday Morning