Melphalan And Xpo1 Inhibition Are Synergistic In Pre-Clinical Models Of Multiple Myeloma

Introduction: Multiple myeloma (MM) accounts for about 10% of all hematologic malignancies, with estimated numbers of new cases and deaths for 2015 in the US at 26,850 and 11,240, respectively. Significant increases in response/survival have been seen over the past several years; however, MM remains incurable and patients ultimately die from progressive disease refractory to anti-myeloma therapy. There is clearly a need for additional effective therapies. Materials and Methods: Human MM parental and melphalan (MEL) resistant cell lines were treated with XPO1 inhibitors (XPO1i) KPT330 or KPT8602 +/- MEL and assayed for apoptosis and viability by flow cytometry. Treated cells were assayed for DNA damage by comet assay and phospho-H2AX protein expression. XPO1/MEL treated cells were assayed for p53, NFkB, IKKα, FANCF, and FANCL by Western blot. Cells from patients with newly diagnosed or relapsed/refractory MM treated with XPO1i/MEL were assayed for apoptosis. NOD/SCID-gamma mice with MM tumors were treated with XPO1i/MEL and assayed for tumor growth, survival, and toxicity. Results: MM cell viability was decreased synergistically and apoptosis increased by XPO1I/MEL treatment in all MM cell lines tested. XPO1/MEL drug combination significantly increased DNA damage when compared to either MEL or XPO1 alone, as shown by comet assay and increased phospho-H2AX expression. Western blot showed that XPO1i treatment of MM cells increased p53 and decreased NFkB, IKKα, FANCF, and FANCL. MEL-resistant MM cell lines were found to be sensitized by XPO1i to MEL as shown by apoptosis assay (20-fold). CD138+/light chain+ MM cells from newly diagnosed and relapsed/refractory MM patients were also sensitized (5-10 fold) by XPO1i to MEL (apoptosis assay). NOD/SCID-gamma mice challenged with MM tumors demonstrated a strong synergistic antitumor effect in XPO1i/MEL-treated mice, with increased survival and no significant toxicity. Conclusions: XPO1i9s improved the response of human MM cell lines and patient MM cells to MEL in vitro and ex vivo. It is possible that this synergy may be due to increased nuclear p53 in combination with decreased NFkB and IKKα and decreased DNA repair proteins FANCL and FANCF reversing MEL resistance by the Fanconi Anemia/BRCA pathway. These preliminary data suggest that XPO1i9s augment MEL-induced DNA damage and may also block the repair of the DNA damage—both of which could result in synergistic cell kill. Combination therapies using XPO1i, especially the clinical compounds KPT330 (selinexor) and KPT8602 +/- MEL, may significantly improve the treatment outcomes of MM. Citation Format: Joel G. Turner, Jana L. Dawson, Daniel M. Sullivan. Melphalan and XPO1 inhibition are synergistic in pre-clinical models of multiple myeloma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 289.