ABCG2 and cancer: The fact that methoxy groups are favorable for the action of chalcones on ABCG2 was also performed for four naphthochalcones (Tables S1–S3, Compounds 58–61, Figure 4), which were synthesized to evaluate their effect on cancer cell growth on five different entities, using MTT analysis (2,5-diphenyl-2H-tetrazolium bromide).