Chemo-sEVs release in cisplatin-resistance ovarian cancer cells are regulated by the lysosomal function

Ovarian cancer (OvCa) is an aggressive disease usually treated with cisplatin (CDDP)-based therapy. However, among the different types of cancers treated with CDDP, OvCa commonly develops chemoresistance to this treatment. The small extracellular vesicles (sEVs) play a central role in chemoresistance. In response to chemotherapy, resistant cells secrete sEVs named chemo-sEVs characterized by specific cargo landscape content involved in the transfer of chemoresistance to recipient cells. sEVs encompass a variety of vesicle types, including exosomes, and are formed as intraluminal vesicles (ILVs) within multivesicular endosomes (MVEs). MVEs follow at least two trafficking pathways regulated by RAB GTPase family members; 1) a secretory pathway where MVEs fuse with the plasma membrane (PM) for sEVs secretion, where RAB27A is the most studied; 2) a degradative pathway where MVEs fuse with lysosomes, an event controlled by RAB7. There is growing evidence suggesting that a loss of lysosomal function can increase sEVs secretion; however, whether sEVs secretion and the transfer of CDDP chemoresistance in OvCa is the result of a fine regulation between these two MVEs trafficking pathways is unknown. In this work, we study the status of these two pathways, between CDDP-sensitive (A2780) and CDDP-resistant (A2780cis) OvCa cells. We found A2780cis cells have an increased number of MVEs and ILVs structures, together with higher levels of ESCRTs machinery components and RAB27A, compared to A2780 cells. Moreover, CDDP promotes the secretion of chemo-sEVs in A2780cis cells. Interestingly, chemo-sEVs contain a high number of proteins related to DNA damage response. In addition, we determine A2780cis cells have a poor lysosomal function with reduced levels of RAB7. Surprisingly, silencing of RAB27A in A2780cis cells was found to be sufficient to restore lysosomal function and levels of RAB7 in A2780cis cells, switching into an A2780-like cellular phenotype. Next, we found rapamycin, a potent enhancer of lysosomal function, reduced the secretion of chemo-sEVs. Taken together, these results indicate that the secretion of chemo-sEVs in OvCa cells is determined by the balance between secretory MVEs and MVEs that are destined for lysosomal degradation. Thus, our results suggest that adjusting this balance between these two MVEs trafficking pathways could be a promising strategy for overcoming CDDP chemoresistance in OvCa. ### Competing Interest Statement The authors have declared no competing interest.