Cyclosporin A, tacrolimus and sirolimus are potent inhibitors of the human breast cancer resistance protein (ABCG2) and reverse resistance to mitoxantrone and topotecan. - Gupta A; Dai Y; Vethanayagam RR; Hebert MF; Thummel KE; Unadkat JD; Ross DD; Mao Q (Cancer chemotherapy and pharmacology, 2006)