The role of the human ABCG2 multidrug transporter and its variants in cancer therapy and toxicology

• Published in: Cancer letters 2006-03, Vol.234 (1), p.62-72
• Main Authors: Cervenak, Judit, Andrikovics, Hajnalka, Özvegy-Laczka, Csilla, Tordai, Attila, Német, Katalin, Váradi, András, Sarkadi, Balázs
• Format: Article
• Language: English
• Subjects: ABC transporter proteins; ABCG2; African Americans; ATP Binding Cassette Transporter, Sub-Family G, Member 2; ATP-Binding Cassette Transporters - physiology; Biological Transport; Cancer; Cancer drug resistance; Cancer therapies; Chemotherapy; Confidence intervals; Cyclin-dependent kinases; Drug resistance; Drug Resistance - physiology; Drug-Related Side Effects and Adverse Reactions; Humans; Kinases; Metabolites; Multidrug transporter; Neoplasm Proteins - physiology; Neoplasms - drug therapy; Pharmaceutical Preparations - metabolism; Plymorphic variants; Proteins; Rodents; Toxicology; Xenobiotics resistance
• ISSN: 0304-3835; 1872-7980
• DOI: 10.1016/j.canlet.2005.01.061

The human multidrug resistance ABC transporters provide a protective function in our body against a large number of toxic compounds. These proteins, residing in the plasma membrane, perform an active, ATP-dependent extrusion of such xenobiotics. However, the same proteins are also used by the tumor cells to fight various anticancer agents. ABCG2 is an important member of the multidrug resistance proteins, an ‘ABC half transporter’, which functions as a homodimer in the cell membrane. In this review, we provide a basic overview of ABCG2 function in physiology and drug metabolism, but concentrate on the discussion of mutations and polymorphisms discovered in this protein. Interestingly, a single nucleotide mutation, changing amino acid 482 from arginine to threonine or glycine in ABCG2, results in a major increase in the catalytic activity and a wider drug recognition by this protein. Still, this mutation proved to be an in vitro artifact, produced only in heavily drug-selected cell lines. In contrast, at least two, but possibly more polymorphic variants of ABCG2 were found to be present in large human populations with different ethnic background. However, currently available experimental data regarding the cellular expression, localization and function of these ABCG2 variants are strongly contradictory. Since, the proteins produced by these variant alleles may differently modulate cancer treatment, general drug absorption and toxicity, may represent risk factors in fetal toxicity, or alter the differentiation of stem cells, their exact characterization is a major challenge in this field.