New insight into p-glycoprotein as a drug target

• Published in: Anti-cancer agents in medicinal chemistry Vol. 13; no. 1; p. 159
• Main Authors: Breier, Albert, Gibalova, Lenka, Seres, Mario, Barancik, Miroslav, Sulova, Zdenka
• Format: Journal Article
• Language: English
• Published: Netherlands 01.01.2013
• Subjects: Apoptosis; ATP-Binding Cassette, Sub-Family B, Member 1 - drug effects; ATP-Binding Cassette, Sub-Family B, Member 1 - metabolism; Drug Resistance, Neoplasm; Glycosylation; Humans; Neoplasms - metabolism; Neoplasms - pathology; Protein Kinases - metabolism
• ISSN: 1875-5992
• DOI: 10.2174/187152013804487380

Multidrug resistance (MDR) of cancer tissue is a phenomenon in which cancer cells exhibit reduced sensitivity to a large group of unrelated drugs with different mechanisms of pharmacological activity. Mechanisms that reduce cell sensitivity to damage induced by a variety of chemicals were found to be caused by diverse, albeit well-defined, phenotypic alterations. The molecular basis of MDR commonly involves overexpression of the plasma membrane drug efflux pump - P-glycoprotein (P-gp). This glycoprotein is an ABCB1 member of the ABC transporter family. Cells that develop MDR of this type express massive amounts of P-gp that can induce a drug resistance of more than 100 times higher than normal cells to several drugs, which are substrates of P-gp. Expression of P-gp could be inherent to cancer cells with regard to the specialized tissues from which the cells originated. This is often designated as intrinsic Pgp- mediated MDR. However, overexpression of P-gp may be induced by selection and/or adaptation of cells during exposure to anticancer drugs; this particular example is known as acquired P-gp-mediated MDR. Drugs that are potential inducers of P-gp are often substrates of this transporter. However, several substances that have been proven to not be transportable by P-gp (such as cisplatin or alltrans retinoic acid) could induce minor improvements in P-gp overexpression. It is generally accepted that the drug efflux activity of Pgp is a major cause of reduced cell sensitivity to several compounds. However, P-gp may have side effects that are independent of its drug efflux activity. Several authors have described a direct influence of P-gp on the function of proteins involved in regulatory pathways, including apoptotic progression (such as p53, caspase-3 and Pokemon). Moreover, alterations of cell regulatory pathways, including protein expression, glycosylation and phosphorylation, have been demonstrated in cells overexpressing P-gp, which may consequently induce changes in cell sensitivity to substances that are not P-gp substrates or modulators. We recently reported that P-gppositive L1210 cells exhibit reduced sensitivity to cisplatin, concanavalin A, thapsigargin and tunicamycin. Thus, P-gp-mediated MDR represents a more complex process than was expected, and the unintended effects of P-gp overexpression should be considered when describing this phenotype. The present review aims to provide the most current informations about P-gp-mediated MDR while paying particular attention to the possible dual function of this protein as a drug efflux pump and a regulatory protein that influences diverse cell processes. From a clinical standpoint, overexpression of P-gp in cancer cells represents a real obstacle to effective chemotherapy for malignant diseases. Therefore, this protein should be considered as a viable target for pharmaceutical design.