Elucidation of -methyladenosine as a Potential Surrogate Biomarker for Drug Interaction Studies Involving Renal Organic Cation Transporters.

Endogenous substrates are emerging biomarkers for drug transporters, which serve as surrogate probes in drug-drug interaction (DDI) studies. In this study, the results of metabolome analysis using wild-type and Oct1/2 double knockout mice suggested that -methyladenosine (mA) was a novel organic cation transporter (OCT) 2 substrate. An in vitro transport study revealed that mA is a substrate of mouse Oct1, Oct2, Mate1, human OCT1, OCT2, and multidrug and toxin exclusion protein (MATE) 2-K, but not human MATE1. Urinary excretion accounted for 77% of the systemic elimination of mA in mice. The renal clearance (46.9 ± 4.9 ml/min per kilogram) of exogenously given mA was decreased to near the glomerular filtration rates by Oct1/2 double knockout or Mate1 inhibition by pyrimethamine (16.6 ± 2.6 and 24.3 ± 0.6 ml/min per kilogram, respectively), accompanied by significantly higher plasma concentrations. In vivo inhibition of OCT2/MATE2-K by a single dose of 7-[(3)-3-(1-aminocyclopropyl)pyrrolidin-1-yl]-1-[(1,2)-2-fluorocyclopropyl]-8-methoxy-4-oxoquinoline-3-carboxylic acid in cynomolgus monkeys resulted in the elevation of the area under the curve of mA (1.72-fold) as well as metformin (2.18-fold). The plasma mA concentration profile showed low diurnal and interindividual variation in healthy volunteers. The renal clearance of mA in younger (21-45 year old) and older (65-79 year old) volunteers (244 ± 58 and 169 ± 22 ml/min per kilogram, respectively) was about 2-fold higher than the creatinine clearance. The renal clearances of mA and creatinine were 31% and 17% smaller in older than in younger volunteers. Thus, mA could be a surrogate probe for the evaluation of DDIs involving OCT2/MATE2-K. SIGNIFICANCE STATEMENT: Endogenous substrates can serve as surrogate probes for clinical drug-drug interaction studies involving drug transporters or enzymes. In this study, mA was found to be a novel substrate of renal cationic drug transporters OCT2 and MATE2-K. -methyladenosine was revealed to have some advantages compared to other OCT2/MATE substrates (creatinine and -methylnicotinamide). The genetic or chemical impairment of OCT2 or MATE2-K caused a significant increase in the plasma mA concentration in mice and cynomolgus monkeys due to the high contribution of tubular secretion to the net elimination of mA. The plasma mA concentration profile showed low diurnal and interindividual variation in healthy volunteers. Thus, mA could be a better biomarker of variations in OCT2/MATE2-K activity caused by inhibitory drugs.