KCP-4 is a cisplatin-resistant cell line established from human epidermoid carcinoma KB-3-1 cells. Although our previous study revealed that one of the mechanisms for cisplatin resistance in KCP-4 cells is the activation of NF-κB, its high resistance is considered to be induced by multiple mechanisms. In the present study, we explored other factors involved in the development of cisplatin resistance in KCP-4 cells. Since it has been reported that an unknown efflux pump exports cisplatin from

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... -4 cells in an ATP-dependent manner, we examined 48 types of ATP-binding cassette proteins as candidate cisplatin efflux transporters. The mRNA expression levels of ABCA1, ABCA3, ABCA7 and ABCB10 in KCP-4 cells were higher when compared to those in KB-3-1 cells. These expression levels in cisplatin-sensitive revertant KCP-4 cells (KCP-4R cells), were reduced in parallel with the sensitivity of these cells to cisplatin and their intracellular accumulation of cisplatin. Next, we investigated the occurrence of mutations in p53 in KCP-4 cells. We found a heterozygous missense mutation at codon 72 (p.Pro72Arg) in p53 of both KCP-4 and KB-3-1 cells, but the protein expression level of p53 in KCP-4 cells was higher when compared to that in KB-3-1. These results suggest that ABCA1, ABCA3, ABCA7 and ABCB10 are candidate genes for the cisplatin efflux transporter that is involved in the cisplatin resistance of KCP-4 cells, and that the mutation at codon 72 of p53 may contribute to the development of cisplatin resistance.