Abstract 1521: Influence of Oct1/Oct2-deficiency on cisplatin-induced changes in urinary N-acetyl-β-D-glucosaminidase

Abstract

Abstract Cisplatin is among the most widely used anticancer drugs and known to cause dose-limiting nephrotoxicity. We recently reported that renal organic cation transporters (OCT2 in humans, Oct1 and Oct2 in mice) are involved in the urinary excretion and nephrotoxicity of cisplatin (Filipski et al, Clin Pharmacol Ther 2009). Tubular secretion of cisplatin is abolished in mice lacking both Oct1 and Oct2 [Oct1/2(-/-) mice], and these mice are protected from experiencing severe (grade 4) cisplatin-induced renal tubular damage. We hypothesized that inhibition of Oct1/Oct2 function would affect biomarkers of cisplatin nephrotoxicity. In wildtype mice, we found that clinically used nephrotoxicity biomarkers such as blood urea nitrogen (BUN) and serum creatinine were not elevated until 72 hours after cisplatin administration, and these changes only occurred after substantial kidney damage. In addition, the ratio of the renal clearance of creatinine and the glomerular filtration rate (GFR) at baseline was 1.67 ± 0.245 in wildtype mice and 0.986 ± 0.0784 in Oct1/2(-/-) mice (P=0.026), indicating that creatinine undergoes tubular secretion in wildtype mice but not in Oct1/2(-/-) mice. As an alternative to BUN and creatinine, we explored the utility of measuring urinary activity of N-acetyl-β-D-glucosaminidase (NAG), a marker for tubular damage. No differences were seen in cisplatin-induced changes in urinary NAG activity between wildtype, Oct1(-/-), and Oct2(-/-) mice, where activity peaked within 24 hours. However, Oct1/2(-/-) mice experienced significantly decreased changes in NAG (∼4-fold, P=0.0016), further suggesting that in mice Oct1 and Oct2 may together fulfill a role equivalent to that of OCT2 in humans. A cutoff for cumulative urinary NAG activity of >0.4 AU was associated with a 21-fold increased odds for severe nephrotoxicity (P=0.0017), which in turn is linked with overall survival [hazard ratio (95%CI), 8.1 (2.1-31), P=0.0078]. Next, we screened 16 agents at varying concentrations for OCT2 inhibitory potential using transfected 293 Flp-In cells, as measured by uptake of [14C]tetraethylammonium or cisplatin as test substrates. We focused further on the possible utility of cimetidine as an OCT2 inhibitor because of its strong inhibitory potency (>95% inhibition at a substrate-to-inhibitor concentration ratio of 1:2), and because this agent is not routinely co-administered with cisplatin. In wildtype mice, cimetidine (30 mg/kg, i.v.) inhibited cisplatin-induced urinary NAG activity changes to a degree significantly different from vehicle-control treated (P=0.016), but similar to that seen in Oct1/2(-/-) mice (P=0.91). Collectively, this study suggests that OCT2 inhibitors such as cimetidine are able to completely inhibit organic cation transporter-mediated uptake of cisplatin in renal proximal tubular cells, and subsequently ameliorate cisplatin-induced nephrotoxicity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1521.