Exosome-mediated modulation of bortezomib cytotoxicity in multiple myeloma cells: involvement of redox balance and cell cycle arrest through ketotifen treatment.

Multiple myeloma (MM), characterized by uncontrolled proliferation of malignant plasma cells, remains a hard-to-treat malignancy due to the development of drug resistance, even to proteasome inhibitors such as Bortezomib. Recent studies highlight the role of tumor-derived exosomes in mediating drug resistance, immune escape, and stress adaptation in MM. Pharmacologic inhibition of exosome secretion may potentiate the cytotoxic effects of Bortezomib by impairing cellular stress responses. RPMI 8226 cells were treated with Bortezomib, Ketotifen, or their combination. Cell viability was assessed using the MTT assay. Intracellular reactive oxygen species and cell cycle progression were analyzed via flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate and propidium iodide staining. Exosomes were isolated and characterized by dynamic light scattering and flow cytometry. Total exosomal protein content was quantified via BCA assay. Gene expression levels of ALIX and MUNC13-4 were measured using quantitative reverse transcriptase PCR. Ketotifen showed the least toxicity at 1 µM, and co-treatment with Bortezomib increased cell viability compared to Bortezomib alone. Ketotifen significantly reduced ALIX expression and total exosomal protein content without altering MUNC13-4 expression. It attenuated Bortezomib-induced ROS accumulation and altered cell cycle dynamics. Exosomes from Bortezomib-treated cells were more cytotoxic than those from the co-treatment group, while the supernatant of the combination induced greater cell death. Ketotifen suppresses exosome biogenesis and modulates oxidative and cell cycle responses in MM cells, potentially enhancing Bortezomib efficacy. These findings support further investigation of Ketotifen as an adjunct strategy to modulate exosome-mediated drug resistance in MM.