Ambroxol induces myeloma cell death by inhibiting autophagy

1. By drug repositioning, we found that ambroxol hydrochloride induces myeloma cell death by inhibiting late-stage autophagy.

2. Ambroxol synergistically potentiates the anti-myeloma activity of panobinostat. Autophagy is a promising therapeutic target of myeloma.

Over the last decade, newly developed drugs have significantly improved the prognosis of patients with multiple myeloma (MM). However, most patients relapse sooner or later, and thus MM remains an incurable hematological malignancy. In addition, serious adverse events occasionally hamper the continuation of treatment. Exploitation of new drugs that potentiate anti-tumor activities and alleviate the adverse effects of existing drugs is needed. Here, we found through drug repositioning that ambroxol hydrochloride (ambroxol) induces apoptosis of MM cells. Interestingly, turnover assays and reporter assays showed that ambroxol inhibits the late stage of autophagy. Transmission electron microscopy (TEM) observation also showed that MM cells treated with ambroxol accumulated autophagic vacuoles in the cytoplasm, further supporting the inhibition of late-stage autophagy. Existing anti-MM drugs demonstrate various effects on autophagy; panobinostat, a histone deacetylase inhibitor, induces autophagy, whereas bortezomib and lenalidomide do not. When administered together, ambroxol and panobinostat exhibited a synergistic anti-myeloma effect, likely due to ambroxol inhibiting the activation of panobinostat-induced autophagy while also downregulating MCL1 expression. . In the KMS 11-xenograft model, ambroxol significantly delayed tumor growth when administered alone; when coadministered with panobinostat, ambroxol synergistically enhanced the panobinostat-induced inhibition of tumor growth. Interestingly, concomitant use of ambroxol and panobinostat alleviated panobinostat-induced diarrhea. Gene set enrichment analyses (GSEAs) and pathway analysis also showed that ambroxol increased the expression of genes related to autophagy inhibition and unfolded protein response. These results suggested that autophagy is a promising therapeutic target for multiple myeloma.