Probiotic Supplementation Suppresses Tumor Growth in an Experimental Colorectal Cancer Liver Metastasis Model

Colorectal cancer (CRC) ranks third in incidence and second in mortality of all cancers worldwide. At the time of primary diagnosis, around 20% of patients already have metastatic CRC and only around 20% are candidates for radical resection. Thus, most of the patients have to undergo chemotherapy (CTx). Due to chemoresistance and side effects, novel treatment additives are crucial for controlling the disease and prolonging patient survival. The aim of this study was to evaluate probiotic supplementation and its antitumorigenic effects in an experimental CRC liver metastasis model. Six-week-old male Wistar rats received either a multispecies probiotic (1.2 x 10(9) CFU/daily) or placebo mixture. On day 14 of the experiment, rat CRC cells (CC531) were implanted under the liver capsule later treated by FOLFOX CTx. Change in tumor volume was measured by performing micro computed tomography (micro-CT) scanning on experimental days 28 and 34. Additionally, immunohistochemical staining with anti-MPO, anti-Ki67, and anti-CD31 were performed. Tumor apoptosis was evaluated using TUNEL staining. Micro-CT image analysis indicates that probiotic supplementation significantly inhibits tumor growth. No synergistic effects between probiotic supplementation and FOLFOX CTx was observed. Reduced tumor volume was achieved by inhibiting angiogenesis, as tumor microvascular density was significantly lower in rats receiving probiotic supplementation. This study shows that a multispecies probiotic mixture significantly reduces angiogenesis and inhibits CRC liver metastasis growth in an experimental rat model.