Microvesicles shed from bortezomib-treated or lenalidomide-treated human myeloma cells inhibit angiogenesis in vitro

Angiogenesis plays a significant role in the pathogenesis of multiple myeloma (MM). Microvesicles (MVs), a type of extracellular vesicles, are known as important players in cell-to-cell communication. MM-derived MVs have exhibited the activity of promoting angiogenesis. Bortezomib and lenalidomide are important drugs for treating myeloma. Therefore, the aim of the present study was to investigate whether and how MVs secreted from human myeloma cells exposed to bortezomib and lenalidomide affect angiogenesis. RPMI-8226 human myeloma cells and human umbilical vein endothelial cells (HUVECs) were used. MVs were isolated from the drug-treated RPMI-8226 cells. The number of the MVs were analyzed with flow cytometry. The expression of pro-angiogenic factors was analyzed with PCR and ELISA. The angiogenic potential of HUVECs was examined. NF-κB activation was analyzed using PCR, immunofluorescent staining and western blotting assays. We showed that bortezomib treatment induced an increase in the number of MVs shed from myeloma cells, but the number of MVs was not significantly altered by lenalidomide. The expression levels of vascular endothelial growth factor (VEGF), interleukin 6 (IL-6) and basic Fibroblast Growth Factor (bFGF) were reduced in the MVs from the RPMI-8226 cells exposed to bortezomib and lenalidomide. Consequently, these MVs exhibited reduced angiogenic potential, as evaluated by wound healing tests, Boyden chamber assays and tube formation assays. Co-culturing HUVECs with drug-treated MVs inhibited NF-κB activation in the HUVECs and reduced the secretion of pro-angiogenic factors. In conclusion, bortezomib and lenalidomide treatment of cultured myeloma cells can block MV-induced angiogenesis and hence provides another mechanism for anti-angiogenic therapy.