Solamargine induces autophagy-mediated apoptosis and enhances bortezomib activity in multiple myeloma

Multiple myeloma (MM) is an incurable plasma cell malignancy with a poor survival rate. Conventional chemotherapeutic agent-induced adverse events, including toxicity, neuropathy or drug resistance, significantly decrease the patients' quality of life and can even lead to interruption of treatment. Therefore, novel therapeutic drugs and strategies are urgently needed to improve MM therapy and patient outcomes. Here, we show that solamargine (SM), a steroidal alkaloid glycoside isolated from a Chinese herb Solanum nigrum L., exhibits promising anti-MM activity. In particular, SM suppressed the viability of MM cell lines (ARP-1 and NCI-H929) in a concentration- and time-dependent manner, inducing apoptosis in these cells. RNA-seq analysis showed that treatment with SM led to the upregulation of genes associated with cell death and autophagy in H929 cells. Further, we found that treatment with SM activated autophagy in the MM cells, as incubation with 3-Methyladenine, an inhibitor of autophagy, significantly alleviated SM-triggered apoptosis and inhibition of viability in MM cells. Interestingly, we also observed a synergistic effect between SM and bortezomib (BTZ), a common chemotherapeutic agent for MM, in both MM cells and human bone marrow CD138+ primary myeloma cells. We also confirmed the single-agent efficacy of SM and the synergistic effects between SM and BTZ in an MM xenograft mouse model. Collectively, these findings indicate that SM exerts an anti-MM effect, at least in part, by activating cell autophagy and reveal that SM alone or in combination with BTZ is a potential therapeutic strategy for treating MM.