Abstract Background: Selinexor, a selective nuclear export inhibitor that blocks XPO1 and reduces the translation of oncoprotein mRNA, has been approved for the treatment of multiple myeloma (MM) patients refractory to proteasome inhibitors, immunomodulators, or anti-CD38 antibodies. However, selinexor exhibits limited efficacy (with an overall response rate [ORR] of 29%) and fails to fully overcome drug resistance. To enhance treatment efficacy, we attempted to combine selinexor with a CD73 inhibitor in a murine myeloma model.

Methods: We leveraged gene-expression profiling of multiple myeloma (MM) cell lines to confirm that selinexor up-regulates CD73. J558 tumor-bearing BALB/c mice were randomized to receive vehicle, the CD73 inhibitor ATG-037, selinexor (ATG-010), or the combination. Single-cell RNA sequencing defined immune-cell subsets and tumor–immune crosstalk, findings that were corroborated by immunofluorescence on histological sections. Co-culture assays of CD8⁺ T cells with MM cells further quantified the gain in tumor-cell killing and elucidated the underlying mechanism.

Results: Selinexor up-regulated CD73 in the majority of MM cell lines. Combination therapy reduced tumor burden by 62%, outperforming either ATG-037 (31%) or selinexor (43%) alone. Single-cell RNA-seq showed that the combination synergistically amplified CD8⁺ T-cell activation, primarily by augmenting CD80-CD28 signaling and enhancing CD8⁺ T-cell–Enpp1 cross-talk. These transcriptional findings were mirrored by a marked increase in intratumoral CD8⁺ T cells on immunofluorescence. In co-culture assays, CD73 blockade heightened selinexor-induced cytotoxicity, as evidenced by elevated Granzyme B (P = 0.0252) and IFN-γ (P = 0.0067) secretion from CD8⁺ T cells.

Conclusion: CD73 inhibition potentiates selinexor efficacy by selectively activating CD8⁺ T cells, thereby accelerating myeloma cell death.

Keywords: multiple myeloma; selinexor; CD73 inhibitor; CD8+ T cell; CD80-CD28 interaction; apoptosis.

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2025
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