Knockdown of TOPK, PRPK or both inhibits metastasis of human colon cancer HCT116 cells in a xenograft mouse model. (a, insert) Knockdown efficiency of TOPK (shTOPK), PRPK (shPRPK) or both (shPRPK/shTOPK) in HCT116 colon cancer cells before intrasplenic inoculation. (a) Quantification and standardization of the area of liver metastasis was analyzed using the ImagePro Plus 6.2 software program. The area of liver metastasis in mice (5 mice/group) injected with shTOPK, shPRPK, or shPRPK/shTOPK HCT116 cells is significantly decreased compared to mice injected with cells expressing vector (shMock). Tumors in the spleen (circles) and liver metastasis (arrows or circles) are shown (one representative mouse per group) at 10 days after injection of cells. Asterisks (***) indicate a significant (p < 0.002) decreased area of liver metastasis in mice injected with shTOPK or shPRPK cells compared with shMock. The asterisks (****) indicate a significant (p < 0.0005) decreased area of liver metastasis in mice injected with shPRPK/shTOPK cells compared with shMock cells. (b) H&E staining and (c) Ki67 staining as a proliferation maker of non-metastatic and metastatic liver tissue (4 μm section; 100 × magnification).