ABCB1 and cancer: Finally, the P-glycoprotein MDR1, expressed by the ABCB1 gene, is involved in the transport of a broad spectrum of structurally variable substances; it not only confers multidrug resistance to cancer cells by actively excreting various chemotherapeutics, but also affects the pharmacokinetic properties of various hydrophobic therapeutic drugs, including alkaloids, flavonoids, and other hydrophobic natural toxic compounds [24].