ABSTRACT
Cisplatin, cis-diamminedichloro-platinum (CDDP), is a widely used anticancer agent, the clinical applications of which have been limited by severe nephrotoxicity. Although dosing time-dependent differences in CDDP-induced nephrotoxicity have been reported in both humans and laboratory animals, the underlying mechanism remains unknown. In the present study, we investigated the molecular mechanism for the dosing-time dependency of the nephrotoxic effect of CDDP in mice. CDDP-induced nephrotoxicity was significantly attenuated by injecting CDDP at times of the day when its renal clearance was enhanced. The dosing-time dependency of the nephrotoxic effect was parallel to that of CDDP incorporation into renal DNA. Two types of transporters, organic cation transporter 2 (OCT2, encoded by Slc22a2) and multidrug and toxin extrusion 1 (MATE1, encoded by Slc47a1), are responsible for the renal excretion of CDDP. The expression of OCT2, but not MATE1, exhibited a significant time-dependent oscillation in the kidneys of mice. The circadian expression of OCT2 was closely related to the dosing-time dependency of CDDP incorporation into renal DNA. Molecular components of the circadian clock regulated the renal expression of Slc22a2 mRNA by mediating peroxisome proliferator-activated receptor-α, which resulted in rhythmic oscillations in OCT2 protein levels. These findings indicate a clock-regulated mechanism of dosing time-dependent changes in CDDP-induced nephrotoxicity and also suggest a molecular link between the circadian clock and renal xenobiotic excretion.
Subject(s)
Antineoplastic Agents/toxicity , Circadian Clocks/physiology , Cisplatin/toxicity , Kidney/metabolism , Organic Cation Transport Proteins/biosynthesis , Animals , Circadian Clocks/drug effects , Dose-Response Relationship, Drug , Kidney/drug effects , Kidney/pathology , Male , Mice , Mice, Inbred C57BL , Mice, Inbred ICR , Mice, Knockout , NIH 3T3 Cells , Organic Cation Transporter 2 , Time FactorsABSTRACT
Circadian clock systems regulate many biologic functions, including cell division and hormone secretion in mammals. In this study, we explored the effects of circadian control on the pivot cell growth regulatory mTOR, the activity of which is deregulated in tumor cells compared with normal cells. Specifically, we investigated whether the antitumor effect of an mTOR inhibitor could be improved by changing its dosing schedule in RenCa tumor-bearing mice. Active, phosphorylated mTOR displayed a 24-hour rhythm, and levels of total mTOR protein (but not mRNA) also showed a circadian rhythm in RenCa tumor masses. Through investigations of the oscillation mechanism for mTOR expression, we identified the ubiquitination factor Fbxw7 as an mTOR regulator that oscillated in its expression in a manner opposite from mTOR. Fbxw7 transcription was regulated by the circadian regulator D-site-binding protein. Notably, administration of the mTOR inhibitor everolimus during periods of elevated mTOR improved survival in tumor-bearing mice. Our findings demonstrate that the circadian oscillation of mTOR activity is regulated by circadian clock systems, which influence the antitumor effect of mTOR inhibitors.
