Natural Products as a Tool to Modulate the Activity and Expression of Multidrug Resistance Proteins of Intestinal Barrier

The role of intestinal barrier homeostasis in an individual’s general well-being has been widely addressed by the scientific community. Colorectal cancer is among the illnesses that most affect this biological barrier. While chemotherapy is the first choice to treat this type of cancer, multidrug resistance (MDR) is the major setback against the commonly used drugs, with the ATP-binding cassette transporters (ABC transporters) being the major players. The role of P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), or breast cancer resistance protein (ABCG2) in the efflux of chemotherapeutic drugs is well described in cancer cells, highlighting these proteins as interesting druggable targets to reverse MDR, decrease drug dosage, and consequently undesired toxicity. Natural products, especially phytochemicals, have a wide diversity of chemical structures, and some particular classes, such as phenolic acids, flavonoids, or pentacyclic triterpenoids, have been reported as inhibitors of P-gp, MRP1, and ABCG2, being able to sensitize cancer cells to chemotherapy drugs. Nevertheless, ABC transporters play a vital role in the cell’s defense against xenobiotics, and some phytochemicals have also been shown to induce the transporters’ activity. A balance must be obtained between xenobiotic efflux in non-tumor cells and bioaccumulation of chemotherapy drugs in cancer cells, in which ABC transporters are essential and natural products play a pivotal role that must be further analyzed. This review summarizes the knowledge concerning the nomenclature and function of ABC-transporters, emphasizing their role in the intestinal barrier cells. In addition, it also focuses on the role of natural products commonly found in food products, e.g., phytochemicals, as modulators of ABC-transporter activity and expression, which are promising nutraceutical molecules to formulate new drug combinations to overcome multidrug resistance.