Acriflavine (Acriflavinium chloride) is a fluorescent acridine dye that can be used to label nucleic acid. Acriflavine is an antiseptic agent. Acriflavine is a potent HIF-1 inhibitor that prevents the dimerization of HIF-1alpha and HIF-1beta subunits. Acriflavine inhibits the interaction between monocarboxylate transporter 4 (MCT4) and Basigin. Acriflavine is used in cancer research, such as breast cancer, brain tumor and chronic myeloid leukemia. Acriflavine is a potent papain-like protease (PLpro) inhibitor, which inhibits SARS-CoV-2[1][2][3][4][5][6].