Voluntary exercise influences metastatic organotropism in a murine colorectal cancer model

Abstract Background Physical activity is associated with a lower risk of colorectal cancer (CRC) and CRC‐specific mortality. However, evidence for a causal relationship between physical activity and disease progression is lacking. Here, we have used CRC organoids to create a novel mouse model for spontaneous metastasis formation to multiple organs. We have used this model to assess the influence of voluntary exercise on disease progression. Methods Collagen‐embedded murine colorectal tumour organoids were transplanted into the livers of immunocompetent C57Bl/6 mice using microsurgery. Voluntary exercise in tumour‐bearing mice was modelled by offering running wheels continuously (n = 12) or 3 h/day (n = 12) versus no wheel access (n = 12). Running wheel revolutions were cumulatively measured every 30 min and physical activity was continuously monitored by infrared cameras. Food intake was monitored throughout the experiment and body composition was assessed with echoMRI. Animals were sacrificed 14 weeks after tumour initiation. Tumour load was quantified by EpCAM immunohistochemistry staining. Systemic inflammation parameters were assessed in blood plasma by a multiplex immunoassay. Results Tumour growth was initiated by implantation of CRC organoids into the livers of immunocompetent mice. The resulting tumours spontaneously formed distant metastases to non‐implanted liver lobes and to the lungs. Mice with access to the running wheels for 3 h/day ran relatively short distances (2.3 ± 0.3 km/night; 221 ± 29 km total distance) with relatively high intensity (wheel revolutions/h). Mice with continuous access to the running wheels ran significantly longer distances (6.6 ± 3.0 km/night; 600 ± 290 km total distance) with a significantly lower intensity. Both exercise groups showed increased lean body mass, and decreased fat mass and body weight compared with tumour‐bearing control mice. Food intake was unaffected by exercise or tumour growth. Primary tumour growth was not significantly affected by exercise. However, mice with continuous wheel access (long distance‐lower intensity group) displayed increased lung metastasis and decreased liver metastasis formation, when compared with the sedentary control group. Short distance‐higher intensity exercise did not affect metastasis formation. Analysis of blood cytokine levels revealed that mice with continuous wheel access displayed signs of systemic inflammation. Conclusions These results suggest that exercise has the potential to influence the patterns and extent of metastasis in CRC, and that the degree and intensity of exercise are likely to be important variables. Confirmation of these results in additional preclinical models with or without systemic treatment is warranted.