Low-Dose Eribulin Promotes NK Cell-Mediated Therapeutic Efficacy in Bladder Cancer

Despite its immunogenic nature, bladder cancer (BCa) responds sub-optimally to FDA-approved immunotherapy.

We have previously shown that natural killer (NK) cells are major contributors to overall patient survival in BCa. In our efforts to identify clinically approved agents that enhance NK cell activation, we identified eribulin, a microtubule destabilizer primarily used in breast cancer. Ongoing clinical trials are investigating the potential integration of eribulin into the standard of care in BCa; however, the mechanistic rationale for these trials remains unclear.

Here, we explore the effects of low-dose eribulin on direct NK cell activation in vitro, including on primary patient samples, and in vivo utilizing multiple murine models. Flow cytometry and RNA sequencing were employed to identify the mechanism of NK cell activation by eribulin, which was associated with increased migration and cytotoxicity of NK cells against BCa cells.

We found that localized eribulin instillation significantly reduces bladder tumor burden and improves survival in primary BCa in an NK cell-dependent manner. Importantly, eribulin promoted the shift of patient-derived intratumoral NK cells towards an anti-tumor CD49a⁺ CD103⁺ NK subset (ieILC1-like) while diminishing the dysfunctional NR4A2-expressing CD49a^- NK subset. Moreover, it decreased the overall expression of exhaustion markers on NK cells, a pattern replicated in our murine models.

These findings are paradigm-shifting given that chemotherapy is traditionally considered immunosuppressive. Our study reveals the novel effect of low-dose eribulin chemotherapy in inhibiting bladder tumor growth by enhancing anti-tumor NK cell immunity, challenging previous assumptions and opening new therapeutic approaches to improve antitumor immunity.