Codominance of cisplatin resistance in somatic cell hybrids

SIRT1 contributes in part to cisplatin resistance in cancer cells by altering mitochondrial metabolism

Tumors frequently develop resistance to cisplatin, a platinum drug used as a cornerstone of present-day chemotherapy regimens, significantly decreasing its usefulness in the clinic. Although it is known that cisplatin-resistant (CP-r) cancer cells commonly grow more slowly and exhibit reduced uptake of various compounds, including nutrients, the effect of tumor metabolism on cisplatin resistance is unclear. It was found that in CP-r cells, uptake of 2-deoxyglucose was reduced due to dysfunction and altered morphology of mitochondria compared with cisplatin-sensitive parental cancer cells. The CP-r cells overexpressed SIRT1, a histone deacetylase that plays a central role in DNA damage response and transcriptional silencing. Incubation of drug-sensitive cells in low glucose medium induced the expression of SIRT1 and increased cellular resistance to cisplatin. Reduced SIRT1 expression by a SIRT1 SMART small interfering RNA duplex sensitized the >20-fold resistant CP-r cells to cisplatin treatment 1.5- to 2-fold, and SIRT1 overexpression by SIRT1 cDNA transfection increased cisplatin resistance in cisplatin-sensitive cells by 2- to 3-fold. Our findings therefore suggest that reduced glucose use and altered mitochondrial metabolism mediated by SIRT1 is one of several alterations that contribute to cellular resistance to cisplatin.

Copper transporters regulate the cellular pharmacology and sensitivity to Pt drugs

Recent studies have demonstrated that the major Cu influx transporter CTR1 regulates tumor cell uptake of cisplatin (DDP), carboplatin (CBDCA) and oxaliplatin (L-OHP), and that the two Cu efflux transporters ATP7A and ATP7B regulate the efflux of these drugs. Evidence for the concept that these platinum (Pt) drugs enter cells and are distributed to various subcellular compartments via transporters that have evolved to manage Cu homeostasis includes the demonstration of: (1) bidirectional cross-resistance between cells selected for resistance to either the Pt drugs or Cu; (2) parallel changes in the transport of Pt and Cu drugs in resistant cells; (3) altered cytotoxic sensitivity and Pt drug accumulation in cells transfected with Cu transporters; and (4) altered expression of Cu transporters in Pt drug-resistant tumors. Appreciation of the role of the Cu transporters in the development of resistance to DDP, CBDCA, and L-OHP offers novel insights into strategies for preventing or reversing resistance to this very important family of anticancer drugs.

A pleiotropic defect reducing drug accumulation in cisplatin-resistant cells

The resistance of tumors to cisplatin remains a major cause of treatment failure in cancer patients. Multiple, simultaneous alterations are frequently encountered in cancer cells selected for cisplatin resistance. To determine whether the complex phenotype results from many different cellular alterations, single-step variants were isolated based on one-step selection in cisplatin. Reduced drug accumulation is a common feature of cisplatin-resistant (CP-r) cancer cells, which is probably caused by one or more dominant genes. Pulse-chase labeling and pulse-chase biotinylation of cell surface proteins suggest that membrane protein mislocalization occurs in CP-r cells, caused mainly by a defect in plasma membrane protein recycling, manifested also as a defect in acidification of lysosomes. This membrane protein mislocalization is presumed to reduce cell surface expression of a putative cisplatin carrier or carriers. In cells selected in several steps, decreased expression of folate-binding protein and arsenic-binding proteins, and reduced endocytosis were detected in CP-r cells, contributing to the reduced uptake of cisplatin, methotrexate and other related compounds. Multiple mechanisms in CP-r cells keep cytotoxic platinum compounds out of cells through defective expression of cell surface proteins such as transporters and carriers, and decreased expression of proteins involved in endocytosis.