CDK4 and neoplasm: Overall, our results suggest that Juglone and KPT6566 suppress proliferation of Caco-2 cells by downregulating expression cyclin D1, cyclin D2, cyclin D3, CDK4, and CDK6, and that this may contribute to the anti-tumorigenic effects of Juglone or KPT6566 against CD44+CD133+ tumor-initiating Caco-2 cells.