Plant-Derived Molecules Modulate Multidrug Resistance in Gastrointestinal Cancers: A Comprehensive Review

Multidrug resistance (MDR) development against cytotoxic drugs by tumor cells is one of the main causes of treatment failure in gastrointestinal cancers, a group of cancers of great relevance due to their prevalence and/or mortality. This phenomenon is mediated by diverse mechanisms, including the overexpression of members of the superfamily of membrane transporters of the ATP-binding cassette (ABC). Most of these molecules, including P-glycoprotein (P-gp or MDR1/ABCB), MDR-associated protein 1 (MRP1/ABCC1), MRP2, and breast cancer resistance protein (BCRP/ABCG2), are integrated in the cell membrane, acting as drug efflux pumps. Despite the use of various MDR modulators as adjuvants to improve the chemotherapy response, the results have not been satisfactory. Natural products from plants, such as flavonoids, alkaloids, terpenoids, and coumarins, are capable of modifying drug resistance, suggesting an improvement in the antitumoral effect of the current treatments without generating side effects. This review aims to provide an overview of the most recent studies in relation to plant-derived molecules and extracts that modulate resistance to antitumor drugs and that could be applied in the future in clinical practice to improve the treatment of patients with gastrointestinal cancer.