A Novel Small Molecule RETRA Induces Apoptosis in Multiple Myeloma Cells Irrespective of p53 Status
Yan Chen, Manujendra N Saha, Yijun Yang, Hong Chang. University Health Network, Toronto, Canada; University of Toronto, Toronto, ON, Canada; First Affiliated Hospital of Nanchang University, Nanchang, China
Background: Although p53 mutations/deletions are less frequent in multiple myeloma (MM), these are associated with poor prognosis and resistance to chemotherapy. Restoration of wild type function of mutant p53 is suggested as a widely applicable therapeutic intervention. Small molecule, RETRA has previously been described to specifically suppress a panel of mutant p53 bearing solid tumor cells in vitro and in vivo. However, anti-tumor activity of RETRA in hematological malignancies is not known. In this study, we examined the effects of RETRA in MM cells.
Design: A number of human MM cell lines: H929 (carrying wild type-p53); 8226, LP1 (harboring mutant p53); OCI-MY5 (harboring both wild type and mutant p53); and 8226R5 (p53 null) were treated with different concentrations of RETRA for different time periods. In addition, peripheral blood mononuclear cells (PBMCs) obtained from three healthy donors were similarly treated with RETRA. Cells treated with DMSO were used as control. Cytotoxic effect of RETRA in MM cells and in normal cells was assessed by MTT cell viability assay. The percentage of apoptotic cells was evaluated by Annexin V/PI staining by Flow cytometry.
Results: Treatment of MM cells of different p53 status with 25-100 µM RETRA for a period of 48-96 h resulted in a dose- and time-dependent inhibition of viability of the cells. IC50 of RETRA varies between 20 and 100 µM among the cell lines. In general, 50-100 µM RETRA was required for maximal killing of the MM cells. In contrast, RETRA showed little or no cytotoxic responses (<20% inhibition in the viability) in three normal PBMCs at 100 µM suggesting a differential killing of tumor cells by this agent. In addition, MM cells exposed to RETRA showed a dose- and time-dependent increase in the binding of Annexin V/PI positive cells indicating that inhibition of the viability of MM cells was due to apoptosis induction by RETRA. Apoptosis observed in 8226, 8226R5, LP1, MY5, and H929 cells treated with 100 µM RETRA for 72 h was 31%, 47%, 65%, 79%, and 90%, respectively. The mechanism of RETRA-induced apoptosis in MM cells is currently under investigation.
Conclusions: Our data demonstrates that RETRA induces cytotoxic and apoptotic response in MM cells regardless of p53 status with minimum cytotoxic effect on normal hematopoietic cells. Our study warrants further investigation to evaluate RETRA as a novel therapeutic approach in the treatment of MM.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 231, Wednesday Afternoon