Abstract: An ABC transporter protein expression inhibitor comprising, as the active ingredient(s), 0.001 to 100 nM of one or more members selected from among steroid hormones, compounds having a female hormone function, analogous compounds thereof and antagonistic inhibitors therefor; an anticancer composition containing this ABC transporter protein expression inhibitor and an anticancer drug; and cells useful in the development of an anticancer drug. The present invention provides a drug which inhibits the expression of an ABC transporter to thereby overcome resistance to anticancer drugs; cancer cells useful in screening such drugs; and an anticancer drug efficacious even against such a cancer as having acquired resistance to anticancer drugs.

Abstract: An ABC transporter protein expression inhibitor comprising, as the active ingredient(s), 0.001 to 100 nM of one or more members selected from among steroid hormones, compounds having a female hormone function, analogous compounds thereof and antagonistic inhibitors therefor; an anticancer composition containing this ABC transporter protein expression inhibitor and an anticancer drug; and cells useful in the development of an anticancer drug. The present invention provides a drug which inhibits the expression of an ABC transporter to thereby overcome resistance to anticancer drugs; cancer cells useful in screening such drugs; and an anticancer drug efficacious even against such a cancer as having acquired resistance to anticancer drugs.