Abstract
Although the judicious use of anticancer drugs that target one or more receptor tyrosine kinases constitutes an effective strategy to attenuate tumor growth, drug resistance is commonly encountered in cancer patients. The ATP-binding cassette transporters are one of the major contributors to the development of multidrug resistance as their overexpression significantly decreases the intracellular concentration and thus, the efficacy of certain anticancer drugs. Therefore, the development of treatment strategies that would not be susceptible to efflux or excretion by specific ABC transporters could overcome resistance to treatment. Here, we investigated the anticancer efficacy of saporin, a ribosome-inactivating protein. Since saporin has poor permeability across the cell membrane, it was encapsulated in a lipid-based nanoparticle system (EC16-1) that effectively delivered the formulation (EC16-1/saporin) intracellularly and produced anti-cancer efficacy. EC16-1/saporin, at nanomolar concentrations, significantly inhibited the cellular proliferation of parental and ABCB1- and ABCG2-overexpressing cancer cells. EC16-1/saporin did not significantly alter the subcellular localization of ABCB1 and ABCG2. In addition, EC16-1/saporin induced apoptosis in parental and ABCB1- and ABCG2-overexpressing cancer cells. In a murine model system, EC16-1/saporin significantly inhibited the tumor growth in mice xenografted with parental and ABCB1- and ABCG2-overexpressing cancer cells. Our findings suggest that the EC16-1/saporin combination could potentially be a novel therapeutic treatment in patients with parental or ABCB1- and ABCG2-positive drug-resistant cancers.