Exercise-induced extracellular vesicles mediate apoptosis in human colon cancer cells in an exercise intensity-dependent manner

Regular exercise is known to reduce incidence rates and improve the prognosis of all cancers, but the underlying mechanisms remain elusive. Ample evidence suggests that exercise exerts therapeutic effects through extracellular vesicles (EVs), essential for cellular communication. Here, we hypothesized that exercise-induced EVs from serum of healthy young male participants will exert anti-tumorigenic effects on human colon cancer HT-29 cells, in an exercise intensity-dependent manner. 10 healthy young active males (25.4±6.2yrs, with maximal oxygen consumption (VO2max) = 45±3.7 ml.min-1.kg-1 participated in a randomized crossover trial. Participants underwent two different workload-matched, acute bouts of exercise: (1) moderate-intensity continuous exercise (MICE) at 50-55% V02max, and (2) high-intensity interval exercise (HIIE) at 90% V02max on a cycle ergometer. A control session of rest (PRE) was included. EVs were isolated from serum samples collected during PRE and immediately after each exercise session. EVs were co-incubated with colon cancer HT-29 cells (100 µg EVs/ml, 48-72h), and effect on cell viability, migration, and apoptosis measured. EV treatment reduced cell viability in all groups (PRE, MICE, HIIE) by 35%, 43% and 47% respectively, vs. PBS. EVs from HIIE group showed a significantly greater reduction in cell viability vs. PRE, therefore further analysis used these groups only. PRE-EVs reduced migration by 27%, and HIIE-EVs by 39%. EV from HIIE group increased expression of pro-apoptotic markers: Bax/Bcl-2 ratio by 56% and Caspase-3 by 30% vs. PBS, with no change observed in the PRE group. Further, 16% of cells in PRE, and 28% of cells in HIIE were TUNEL-positive, indicating DNA fragmentation, a hallmark feature of apoptosis. Our data show that exercise-induced EVs reduced cell viability, in an exercise intensity-dependent manner. HIIE-derived EVs exerted the most anti-tumorigenic effects: decreased cell viability, reduced cell migration, increase in pro-apoptotic protein expression, and elevated DNA fragmentation. It is likely these changes were mediated by altered EV Cargo induced by exercise, as the amount of EVs was the same in each treatment group. To our knowledge, this is the first human study that illustrates the therapeutic potential of exercise-induced EVs in cancer treatment.