As none of the melanoma cell lines expressed a detectable level of P-gp protein in vitro, DLKP-A (P-gp over-expressing lung cancer cell line) were used as a model of P-gp over-expression [28] and DLKP-MITOX cells were used as a positive control for BCRP protein expression [29]. The gene discussed is ABCG2; the disease is lung carcinoma.