CD73 inhibitor enhances the antitumor activity of selinexor in multiple myeloma by restoring the activation of CD8+ T cells.

Selinexor, a selective nuclear export inhibitor, blocks exportin-1 and reduces oncoprotein messenger RNA translation, and is approved for the treatment of relapsed/refractory multiple myeloma in combination with proteasome inhibitors, immunomodulators, anti-CD38 antibodies, etc. Nevertheless, selinexor presents limited monotherapy efficacy with an objective response rate of 29% and fails to completely overcome drug resistance. To improve the therapeutic outcome, this study investigated the combined treatment of selinexor and a CD73 inhibitor in a murine tumor model. The expression of CD73 in multiple tumor cell lines following selinexor treatment was first analyzed. In vivo experiments were performed on J558-inoculated BALB/c mice, which were divided into vehicle group, ATG-037 (CD73 inhibitor) monotherapy group, ATG-010 (selinexor) monotherapy group, and combination therapy group. Single-cell RNA sequencing (scRNA-seq) was utilized to characterize immune cell subtypes and tumor-immune crosstalk, and immunofluorescence staining was conducted on histological tumor samples. In addition, a co-culture model of CD8+ T cells and multiple myeloma cell lines was established to verify the synergistic anti-tumor effect and underlying mechanism of the combined regimen. The results demonstrated that selinexor treatment upregulated CD73 expression in the majority of tumors. The combination therapy remarkably suppressed tumor growth with an inhibition rate of 62%, which was superior to the monotherapy of ATG-037 (31%) and selinexor (43%). scRNA-seq analysis revealed that the combination treatment synergistically potentiates CD8+ T cell activation by enhancing the interaction between CD8+ T cells and Enpp1 cells via the CD80-CD28 signaling pathway, and the increased infiltration of CD8+ T cells in tumor tissues of the combination group was further validated by immunofluorescence staining. Co-culture experiments further confirmed that CD73 inhibition strengthens selinexor-mediated tumor cell killing by activating CD8+ T cells, as evidenced by significantly elevated levels of Granzyme B (P = 0.0252) and IFN-γ (P = 0.0067). In conclusion, CD73 inhibition enhances the anti-myeloma efficacy of selinexor by specifically activating CD8+ T cells and ultimately promoting the apoptosis of multiple myeloma cells.