Exosomes derived from bone marrow stromal cells decrease the sensitivity of leukemic cells to etoposide.

The aim of the study was to investigate the effect of exosomes derived from bone marrow stromal cells (BM-SCs) on the chemoresistant characteristics of nalm-6 cells treated with etoposide (VP16). The present study isolated exosomes from BM-SC-conditioned medium by using standard differential centrifugation steps and detected the expression of 70 kilodalton heat shock proteins (HSP70) and lysosomal-associated membrane protein 3 (CD63) in exosomes by western blot analysis. Nalm-6 cells were co-cultured with exosomes in the presence of VP16. Cell viability and apoptosis were then detected using the Cell Counting Kit-8 method and Annexin-V/propidium iodide, respectively. Finally, protein levels of B-cell lymphoma 2 (BCL-2), BCL-2-like protein 4 (BAX), caspase-3, and poly ADP-ribose polymerase (PARP) were examined by western blot analysis. Exosomes were successfully isolated from the conditioned medium and confirmed by the expression of HSP70 and CD63. BM-SC-derived exosomes increased the viability of nalm-6 cells in the presence of VP16 and inhibited the apoptosis induced by VP16. Western blot analysis results showed that exosomes can block the significant reduction of BCL-2, full-length caspase-3 and full-length PARP, while preventing the increase of BAX, cleaved caspase-3 and cleaved PARP induced by VP16. Exosomes derived from BM-SCs can protect nalm-6 cells from VP16-induced apoptosis to maintain their survival and induce resistance to VP16. In addition, BCL-2/BAX, caspase-3, and PARP may be involved in the mechanism of exosome-induced drug resistance.