DPP4 and breast cancer: Western blotting showed that DPP-4 inhibition decreased the levels of cleaved caspase-3, an apoptosis-associated protein, in the human MCF7 and MDA-MB-231 breast cancer cell lines; however, the autophagy inhibitor 3-methyladenine (3-MA) remarkably restored the levels of cleaved caspase-3 (Figure 4A).