Bortezomib treatment modulates autophagy in multiple myeloma

Although the introduction of bortezomib as a therapeutic strategy has improved the overall survival of multiple myeloma (MM) patients, 15-20% of high-risk patients do not respond to bortezomib over time or become resistant to treatment. Therefore, the development of new therapeutic strategies, such as combination therapies, is urgently needed. Methods: Given that bortezomib resistance may be mediated by activation of the autophagy pathway as an alternative mechanism of protein degradation, and that an enormous amounts of misfolded protein is generated in myeloma plasma cells (PCs), we investigated the effect of the simultaneous inhibition of proteasome by bortezomib and autophagy by hydroxychloroquine (HCQ) treatment on PCs and endothelial cells (ECs) isolated from patients with monoclonal gammopathy of undetermined significance (MGUS) and MM. Results: We found that bortezomib combined with HCQ induces synergistic cytotoxicity in myeloma PCs whereas this effect is lost on ECs. Levels of microtubule-associated protein light chain beta (LC3B) and p62 are differentially modulated in PCs and ECs, with effects on cell viability and proliferation. Conclusions: Our results suggest that treatment with bortezomib and HCQ should be associated with an anti-angiogenic drug to prevent the pro-angiogenic effect of bortezomib, the proliferation of a small residual tumor PC clone, and thus the relapse.