Abstract 4049: The synergistic effect of melphalan and XPO1 inhibition in preclinical models of multiple myeloma
Authors: Turner Joel G. 
Published: July 2017

Introduction: Significant increases in response/survival have been seen over the past several years; however, multiple myeloma (MM) remains incurable. In this study we have demonstrated that the XPO1 inhibitors (XPO1i), selinexor (SEL) and KPT-8602, sensitize both wild-type and drug-resistant MM cells to melphalan (MEL) in preclinical models.

Materials and Methods: We used the XPO1i SEL (300nM), KPT-8602 (300nM), and KOS-2464 (10nM) +/- MEL (5-20 μM) to treat human 8226, H929 and U266 MM cells, and MEL resistant 8226LR5 and U266LR6 cell lines and assayed for apoptosis. DNA damage was assayed by comet assay and γ-H2AX in H929 human MM cells. XPO1i/MEL-treated MM cells were assayed for P53, NFkB, IKKα, and Fanconi Anemia (FANC)/BRCA DNA repair proteins by Western blot and electrochemiluminescent immunoassay(ECL-I). We also treated cells from patients with newly diagnosed or relapsed/refractory MM with the XPO1i +/- MEL and assayed for apoptosis. NOD/SCID-γ (NSG) mice challenged with U226 or U266LR6 MM tumors were treated with XPO1i/MEL and assayed for tumor growth, survival, and toxicity.

Results: The addition of the XPO1i’s SEL, KPT-8602 or KOS-2464 (P &lt; 0.03) sensitized drug-resistant 8226LR5 and U266LR6 cells to MEL when compared to single-agent MEL. The XPO1i/MEL drug combination increased DNA damage (Comet assay/γ-H2AX) more than single agent MEL or XPO1i alone (P &lt; 0.005). Western blot and ECL-I showed that XPO1i treatment can increase P53 and decrease NFkB, IKKα, FANC/BRAC pathway proteins including FANCD2 in MM cells. CD138+/light chain+ MM cells from newly diagnosed and relapsed/refractory MM patients were sensitized (20-fold and 5-10 fold respectively) by XPO1i to MEL. XPO1i/MEL combination treatment demonstrated a strong synergistic antitumor effect when compared to single-agent MEL (SEL/MEL, P = 0.0024 and KPT-8602/MEL, P = 0.0030) in NSG mice challenged with U266, with little toxicity as assessed by weight loss. Similar results were found with MEL resistant U266LR6 tumors in NSG mice.

Conclusions: XPO1i's sensitized human MM cell lines, both parental and MEL resistant, and patient MM cells to MEL both in vitro and ex vivo, and in in vivo NSG mouse models. Our data show that the synergistic cell kill may be due to increased XPO1i/MEL-induced DNA damage. The mechanism of this synergy may be due to increased nuclear P53, in combination with decreased NFkB and IKKα, and decreased DNA repair activity of the FANC/BRCA pathway. Thus, combination therapies of XPO1i, especially the clinical compounds SEL and KPT-8602 +/- MEL, may have potential to improve the treatment outcomes of MM. The combination of XPO1i and melphalan are being investigated in the context of high-dose chemotherapy and autologous transplant (NCT 02780609).

Citation Format: Joel G. Turner. The synergistic effect of melphalan and XPO1 inhibition in preclinical models of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4049. doi:10.1158/1538-7445.AM2017-4049