PCNA-I1 is a selective inhibitor of proliferating cell nuclear antigen (PCNA, a potential anticancer target). PCNA-I1 selectively binds to PCNA trimers with Kd of ~0.2 to 0.4 μM. PCNA-I1 inhibits the growth of tumor cells of various tissue types with IC50 of ~0.2 μM. PCNA-I1 induces DNA damage and apoptosis in both LNCaP and PC-3 cells. PCNA-I1 also induces autophagy in PC-3 cells.