Identification of OAT1/OAT3 as Contributors to Cisplatin Toxicity.

Cisplatin is among the most widely used anticancer drugs and known to cause a dose-limiting nephrotoxicity, which is partially dependent on the renal uptake carrier OCT2. We here report a previously unrecognized, OCT2-independent pathway of cisplatin-induced renal injury that is mediated by the organic anion transporters OAT1 and OAT3. Using transporter-deficient mouse models, we found that this mechanism regulates renal uptake of a mercapturic acid metabolite of cisplatin that acts as a precursor of a potent nephrotoxin. The function of these two transport systems can be simultaneously inhibited by the tyrosine kinase inhibitor nilotinib through noncompetitive mechanisms, without compromising the anticancer properties of cisplatin. Collectively, our findings reveal a novel pathway that explains the fundamental basis of cisplatin-induced nephrotoxicity, with potential implications for its therapeutic management.

Conjunctive therapy of cisplatin with the OCT2 inhibitor cimetidine: influence on antitumor efficacy and systemic clearance.

The organic cation transporter 2 (OCT2) regulates uptake of cisplatin in proximal tubules, and inhibition of OCT2 protects against severe cisplatin-induced nephrotoxicity. However, it remains uncertain whether potent OCT2 inhibitors, such as cimetidine, can influence the antitumor properties and/or disposition of cisplatin. Using an array of preclinical assays, we found that cimetidine had no effect on the uptake and cytotoxicity of cisplatin in ovarian cancer cells with high OCT2 mRNA levels (IGROV-1 cells). Moreover, the antitumor efficacy of cisplatin in mice bearing luciferase-tagged IGROV-1 xenografts was unaffected by cimetidine (P = 0.39). Data obtained in 18 patients receiving cisplatin (100 mg/m(2)) in a randomized crossover fashion with or without cimetidine (800 mg × 2) revealed that cimetidine did not alter exposure to unbound cisplatin, a marker of antitumor efficacy (4.37 vs. 4.38 µg·h/ml; P = 0.86). These results support the future clinical exploration of OCT2 inhibitors as specific modifiers of cisplatin-induced nephrotoxicity.

Drug trafficking: recent advances in therapeutics and disease.

Drug transporter proteins are of ever-increasing interest because of their role both in processes regulating pharmacokinetic properties of drugs (absorption, distribution, and elimination) and in the development of cellular drug resistance through decreased uptake or increased efflux of drugs in the target organ or tumor. Further understanding of the role of transporters in drug-drug interactions and identification of these proteins as possible therapeutic targets could contribute to improved treatment of a wide variety of diseases.

Associations between ABCC2 polymorphisms and cisplatin disposition and efficacy.

ABCC2 (MRP2, cMOAT) expression has been implicated in cisplatin resistance in vitro. In mice, cisplatin disposition and toxicity were unaffected by Abcc2 knockout (Abcc2−/−). Moreover, in cancer patients (n = 237), cisplatin pharmacokinetics (P > 0.12) and efficacy (P > 0.41) were not associated with seven of the single-nucleotide polymorphisms (SNPs) in ABCC2. These SNPs were also not correlated with ABCC2 expression in the NCI60 panel (P > 0.26) or with cisplatin-induced cytotoxicity (P = 0.21). These findings highlight the importance of verifying drug-transporter interactions with in vitro tests in humans.

The temporal relationship between ABCB1 promoter hypomethylation, ABCB1 expression and acquisition of drug resistance.

Induced expression of the Abcb1 drug transporter often occurs in tumors in response to chemotherapy. The role that epigenetic modifications within the ABCB1 promoter play in Abcb1 expression remains unclear. We selected MCF-7 cells for survival in increasing doses of chemotherapy drugs, and assessed the methylation status of 66 CpG sites within the ABCB1 promoter preceding, accompanying and following the onset of drug resistance. Increased ABCB1 transcript expression coincident with acquisition of resistance to epirubicin or paclitaxel was temporally associated with hypomethylation of the ABCB1 downstream promoter in the absence of gene amplifications or changes in mRNA stability. Treatment of control MCF-7 cells with demethylating and/or acetylating agents increased ABCB1 transcript expression. In addition to broad promoter hypomethylation, dramatic reductions in the methylation of specific CpG sites within the promoter were observed, suggesting that these sites may play a predominant role in transcriptional activation through promoter hypomethylation. Furthermore, our data suggest that allele-specific reductions in ABCB1 promoter methylation regulate promoter usage within paclitaxel-resistant cells. This study provides strong evidence that changes in ABCB1 promoter methylation, ABCB1 promoter usage and ABCB1 transcript expression can be temporally and causally correlated with the acquisition of drug resistance in breast tumor cells.