The treatment of chemoresistant tumors represents an important challenge in the field of oncology. Primary or acquired overexpression of ATP-dependent transporters, in particular P-glycoprotein (Pgp, MDR1 protein), is a major cause of multidrug resistance and reduced patient survival. Sustained efforts have thereby been undertaken to find agents overcoming this resistance. This review provides a chemical and biological overview on bioactive metabolites from the marine field (natural molecules and analogues) that can overcome or circumvent resistance to ATP-dependent efflux pumps, their mechanisms of action and their structure-activity relationships. Their clinical relevance and status are presented. Active compounds (often microtubule-interacting agents) have been isolated from sponges and ascidians and, in lesser extent from cnidarians, and molluscs. The toxicity and the reversal activity can be uncoupled but, marine metabolites usually maintain high toxicity in multiresistant cancer cells. Certain display synergistic effects with clinically important anticancer drugs. The marine drug recently approved for cancer therapy [Trabectedin (Yondelis®)] and those entered into clinical trials act on multiple targets and, circumvent or overcome chemoresistance through very unusual mechanisms of action. Pharmacological and clinical data suggest that metabolites from the marine field could provide new therapeutic options for patients with tumors resistant to conventional therapy.
Keywords: Marine metabolites, cancer, ABC-dependent transporters, P-glycoprotein, multidrug resistance (MDR), reversal activity, synergism with conventional therapy
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