From the cytotoxicity studies, 1 and 3 μM of GS-9973 were used for the reversal experiments in the ABCG2 overexpressing cell line as the cell survival fraction was around 85% after 72 h incubation in both the NCI-H460 parental and resistant NCI-H460/MX20 cancer cells. This evidence concerns the gene ABCG2 and cancer.