CSNK1A1 and breast cancer: Since pyrvinium inhibits proliferation of HCT-116 through activating CK1α [15], we next determined whether the target of pyrvinium is cell-type specific Consistent with the findings of Throne et al., pyrvinium-induced growth inhibition of HCT-116 colon cancer and SUM159 breast cancer cells was abolished by depletion of CK1α (Figures 3e–3f and Supplemental Figure S3c), suggesting that CK1α is required for the mechanism of action of pyrvinium in breast and colon cancer.