A Novel Small Molecule MIRA-1 Induces Cytotoxicity in Multiple Myeloma Cells Harbouring Wild-Type or Mutant p53
Manujendra N Saha, Jerry Jiang, Hong Chang. University Health Network, Toronto, Canada
Background: Multiple myeloma patients with mutations or deletions of p53 tumor supressor gene (10-15%) are considered as very high-risk group due to their resistant to conventional or novel therapies. Therefore, reactivation of mutant p53 may provide important benefits for the treatment of therapy-resistant MM cells. MIRA-1(mutant p53-dependent induction of rapid apoptosis), a novel class of small molecules, has the ability to restore wild type conformation and function to mutant p53. MIRA-1 has shown to induce apoptosis in certain types of solid tumors harboring mutant p53 but sofar has not been evaluated in hematological malignancies. In this study, we examined anti-myeloma activity of MIRA-1.
Design: Human MM cell lines harbouring wild type (MM.1S and H929) or mutant (8226 and LP1) and primary MM samples collected from newly diagnosed patients were treated with MIRA-1 alone or in combination with conventional chemotherapeutic drugs, doxorubicin or dexamethasone. Cells treated with these agents were assessed for cell viability by MTT assay and apoptosis induction by Annexin V-binding measured by Flow cytometry. In addition, we have also examined the modulation apoptotic targets in MM cells upon stimulation with MIRA-1.
Results: Treatment of 4 MM cell lines and 3 primary MM samples with MIRA-1 resulted in significant inhibition of proliferation of MM cells harboring either wild type or mutant p53. The IC50 of MIRA-1 observed in these cells was ranged between 10 and 20 µM. However, MIRA-1 displayed no significant cytotoxicity in normal bone marrow mononuclear cells or peripheral blood mononuclear cells obtained from healthy donors. Consistent with the results obtained by MTT assay, 48 hrs after treatment with 40 µM MIRA-1 more than 90% of 8226 and LP1 cells were positive for Annexin V-binding. Apoptosis induced by MIRA-1 in H929 or LP1 cells was associated with time- and dose-dependent activation of caspas-8, caspase-3 and PARP and down-regulation of an anti-apoptotic protein, Mcl-1. Importantly, MIRA-1 in combination with doxorubicin or dexamethasone produced a synergistic cytotoxic response in both 8226 and LP1 cell lines.
Conclusions: Our results demonstrate potent anti-myeloma activity of MIRA-1 and thus provide a framework for clinical evaluation of MIRA-1 either alone or in combination with current chemotherapeutic agents. Reactivation of mutant p53 by MIRA-1 may represent a novel and more efficient therapeutic strategy for treatment of this high-risk group of MM patients with alterations of TP53.
Wednesday, March 21, 2012 1:00 PM
Poster Session VI # 216, Wednesday Afternoon