ATP binding cassette transporter (ABC) is an ancient and huge family, and it is an ATP-driven pump. There are many similarities among ABC members, such as similar substance transport functions and structures. However, with the continuous evolution of genes, there are many differences among members, which are manifested in various aspects of family characteristics, such as structure, function, organ distribution, subcellular localization and so on. Widely distributed in all kinds of organisms from bacteria to humans. Each ABC protein is specific to the gene of a single substrate or related substrate. These substrates can be ions, monosaccharides, amino acids, phospholipids, peptides, polysaccharides and even protein.

Under normal physiological conditions, ABC protein is a transporter of sugar, amino acids, phospholipids and peptides on bacterial plasma membrane, and also a transporter of phospholipids, lipophilic drugs, cholesterol and other small molecules on mammalian plasma membrane. Widely distributed in the plasma membrane of liver, small intestine, kidney and other organs, it can eliminate natural poisons and metabolic wastes in the body.

Multidrug resistance transporter MDR is one of them, which can transport various drugs from cytoplasm to extracellular by using the energy of ATP hydrolysis. Therefore, it is difficult to treat tumors from cells expressing MDR.