Liposome-based approaches to overcome anticancer drug resistance.

Drug resistance remains an important obstacle towards better outcomes in the treatment of cancer. One general approach to overcome this problem has been to inhibit specific resistance mechanisms, such as P-glycoprotein (PGP)-mediated drug efflux, using small molecule agents or other therapeutic strategies. Alternatively, drug delivery approaches using liposomes or other carriers can in principle target drugs to tumor tissue, tumor cells, or even compartments within tumor cells. By increasing bioavailability of drugs at sites of action, these approaches may provide therapeutic advantages, including enhanced efficacy against resistant tumors. Current liposomal anthracyclines have achieved clinical use in cancer treatment by providing efficient encapsulation of drug in stable and non-reactive carriers, and there is evidence indicating potential benefit in some clinical settings involving resistant tumors. Other liposome-based strategies include constructs designed to be taken up by tumor cells, as well as further modifications to allow triggered drug release. These approaches seek to overcome drug resistance by more efficient delivery to tumor cells, and in some cases by concomitant avoidance or inhibition of drug efflux mechanisms. Newer agents employ molecular targeting, such as immunoliposomes using antibody-directed binding and internalization. These agents selectively deliver drug to tumor cells, can efficiently internalize for intracellular drug release, and can potentially enhance both efficacy and safety.