ABCG2 and cancer: Knowing that ABCB1 and ABCG2 could reduce the cytotoxicity of HS-173 in cancer cell lines, we next examined the impact of ABCB1 and ABCG2 on G2/M cell cycle arrest and apoptosis induced by HS-173, which are characteristic effects of HS-173 treatment [8,9] in human cancer cell lines.