Multiple myeloma (MM) is an incurable plasma cell malignancy with frequent patient relapse due to innate or acquired drug resistance. Cholesterol metabolism is reported to be altered in MM; therefore, we investigated the potential anti-myeloma activity of two cholesterol derivatives: the 5,6 α- and 5,6 β-epoxycholesterol (EC) isomers. To this end, viability assays were used, and isomers were shown to exhibit important anti-tumor activity in vitro in JJN3 and U266 human myeloma cell lines (HMCLs) and ex vivo in myeloma patients’ sorted CD138+ malignant cells. Moreover, we confirmed that 5,6 α-EC and 5,6 β-EC induced oxiapoptophagy through concomitant oxidative stress and caspase-3-mediated apoptosis and autophagy. Interestingly, in combination treatment a synergistic interaction was observed between 5,6 α-EC and 5,6 β-EC on myeloma cells. These data highlight a striking anti-tumor activity of 5,6 α-EC and 5,6 β-EC bioactive molecules against human myeloma cells, paving the way for their potential role in future therapeutic strategies in MM.

Background/Objectives: Multiple myeloma (MM) is a hematologic malignancy characterized by the clonal proliferation of abnormal plasma cells in bone marrow, predominantly affecting individuals over 65 years of age. Despite recent therapeutic advances, MM remains largely incurable due to frequent relapses and the emergence of drug resistance. MicroRNAs have emerged as key post-transcriptional regulators implicated in cancer progression, with miR-429 exhibiting context-dependent oncogenic or tumor-suppressive roles in various cancers. However, its function in MM has not been thoroughly investigated. Methods: miR-429 expression was evaluated in MM cells and patient samples by qRT-PCR. Functional effects were assessed through inhibition studies, proliferation/apoptosis assays, and co-culture with stromal cells. Results: In this study, we found that miR-429 expression is significantly downregulated in MM cell lines and primary malignant plasma cells compared to normal plasma cells. The functional inhibition of miR-429 in U266 cells led to a significant increase in cell proliferation without affecting spontaneous apoptosis, as confirmed in both MM cell lines and patient-derived plasma cells. Additionally, the inhibition of miR-429 in HS-5 stromal cells enhanced the proliferation of co-cultured MM cells, highlighting the role of the bone marrow microenvironment in disease progression. Conclusions: These findings suggest that miR-429 may act as a tumor suppressor by modulating MM cell proliferation. Although preliminary, our results support the need for further investigation into miR-429 as a potential biomarker or therapeutic target.