Previous works indicate that GCS and MDR1 are co-overexpressed in drug-resistant leukemia [33] and in drug-resistant cancer cells including human ovarian cancer (NCI/ADR-RES), cervical cancer (KB-V1), leukemia (HL-60/VCR), melanoma (MeWo Eto) and colon cancer (SW620/AD) [13,28]. Here, ABCB1 is linked to melanoma.