Nanocarriers in Improving Chemotherapy of Multidrug Resistant Tumors: Key Developments and Perspectives.

The multidrug resistance (MDR) of tumor cells significantly reduces the efficiency of traditional anticancer therapy. Tumor MDR is complex and involves several mechanisms such as decreased drug uptake, increased drug efflux, enhanced drug exocytosis, increased drug detoxification and inactivation by drugmetabolizing enzymes, altered drug targets due to genetic and epigenetic modifications, altered DNA repair, and impaired apoptotic pathways. Implementation of nanoparticles can markedly improve drug delivery through increased stability in the plasma, prolonged half-life, enhanced specificity of transfer, and advanced drug accumulation and retention in the tumor cells. So far, many various types of nanocarriers have been used for the delivery of anticancer agents. These carriers greatly increase anti-tumor effects of cytotoxic agents since drug-carrying nanoparticles are able to reverse MDR. The promising integrative approach in cancer nanotherapy assumes the development of multifunctional delivery systems simultaneously transmitting various agents such as drugs, genes, imaging agents, and targeting ligands in order to enhance anti-tumor toxicity and nanoparticle tracking.