Mechanistic studies showed that Co-Sp reduced the expression of cyclin D1, cyclin E, CDK4, CDK2, MMP-9, MMP-1, and Bcl-2, and increased the expression of p21, cleaved caspase-9, cleaved caspase-3, cleaved PARP, and Bax in prostate cancer cells. This evidence concerns the gene CASP9 and prostate cancer.