Amiloride, An Old Diuretic Drug, Is a Potential Therapeutic Agent for Multiple Myeloma

Purpose: The search for new drugs that control the continuous relapses of multiple myeloma is still required. Here, we report for the first time the potent antimyeloma activity of amiloride, an old potassium-sparing diuretic approved for the treatment of hypertension and edema due to heart failure.Experimental Design: Myeloma cell lines and primary samples were used to evaluate cytotoxicity of amiloride. In vivo studies were carried out in a xenograft mouse model. The mechanisms of action were investigated using RNA-Seq experiments, qRT-PCR, immunoblotting, and immunofluorescence assays.Results: Amiloride-induced apoptosis was observed in a broad panel of multiple myeloma cell lines and in a xenograft mouse model. Moreover, amiloride also had a synergistic effect when combined with dexamethasone, melphalan, lenalidomide, and pomalidomide. RNA-Seq experiments showed that amiloride not only significantly altered the level of transcript isoforms and alternative splicing events, but also deregulated the spliceosomal machinery. In addition, disruption of the splicing machinery in immunofluorescence studies was associated with the inhibition of myeloma cell viability after amiloride exposure. Although amiloride was able to induce apoptosis in myeloma cells lacking p53 expression, activation of p53 signaling was observed in wild-type and mutated TP53 cells after amiloride exposure. On the other hand, we did not find a significant systemic toxicity in mice treated with amiloride.Conclusions: Overall, our results demonstrate the antimyeloma activity of amiloride and provide a mechanistic rationale for its use as an alternative treatment option for relapsed multiple myeloma patients, especially those with 17p deletion or TP53 mutations that are resistant to current therapies. Clin Cancer Res; 23(21); 6602-15. ©2017 AACR.