Evaluation of the Carcinogenic Potential of Clofibrate in the rasH2 Mouse

Abstract

The purpose of the study was to support of the International Life Sciences Institute (ILSI) alternative carcinogenicity models initiative to evaluate the carcinogenic potential of the nongenotoxic carcinogen, clofibrate, a peroxisome proliferator-activated receptor (PPAR) alpha agonist, following oral administration to rasH2 mice. Peroxisome proliferators are one of the most widely studied of the nongenotoxic carcinogens and have diverse industrial and therapeutic uses (Gonzalez et al. J. Nat. Cancer Inst. 90: 1702-1709, 1998); however, the nongenotoxic mechanism of carcinogenicity is currently unknown. Male mice were administered doses of clofibrate at 50, 100, or 200 mg/kg/day and female mice were administered doses of 50, 150, or 250 mg/kg/day by oral gavage at 10 ml/kg for 27 weeks. In addition, rasH2 male and female mice were treated with N-nitroso-N-methylurea (NMU). Nontransgenic male and female mice were treated with 200 and 250 mg/kg/day, respectively, of clofibrate. The NMU-treated mice were given a single intraperitoneal dose of 75 mg/kg, which was followed by a 90-day observation period; all others were sacrificed after 6 months of daily dosing. Hepatocellular neoplasms were observed in clofibrate-treated rasH2 male mice after 6 months of treatment but not in nontransgenic males or females. Clofibrate treatment (250 mg/kg/day) of female rasH2 mice was associated with a slight increase in the incidence of various neoplasms (harderian gland, lungs, skin, spleen, tail, thymus, and uterus) compared with untreated transgenic mice and with similarly treated nontransgenic mice. Non-neoplastic changes were found in the liver of transgenic and nontransgenic mice of both sexes and in the kidneys of male mice. NMU produced findings are consistent with previous studies. The data suggest that the rasH2 mice are a good model for testing epigenetic carcinogens in a shorter timeframe than conventional mouse carcinogenicity bioassays.

Evaluation of the Carcinogenic Potential of Clofibrate in the p53+/− Mouse

“…No neoplastic response was observed with the nongenotoxic carcinogen, clofibrate, at doses up to 100 (males) or 125 (females) mg/kg/day, whereas p-cresidine at 400 mg/kg/day produced urinary bladder carcinogenesis. In contrast, clofibrate treatment (250 mg/kg/day) of female rasH2 mice was also associated with a slight increase in the incidence of various nonhepatic neoplasms compared with untreated transgenic mice and with similarly treated nontransgenic mice (Nesfield et al 2005a). The reason for this difference is unknown, but may be related to unexpected toxicity in the p53 +/− study, strain-specific differences in the mechanism of PPARα-induced carcinogenesis, or degree of peroxisomal proliferation as indicated by hepatic centrilobular granular eosinophilia in the rasH2 mice study.…”

Peroxisome Proliferator-Activated Receptor α Regulates a MicroRNA-Mediated Signaling Cascade Responsible for Hepatocellular Proliferation

“…Interestingly, several PPAR␣ agonists have been shown to induce ras (12,20). In addition, transgenic mice overexpressing ras or carrying a mutant ras demonstrate a decrease in tumor latency following chronic PPAR␣ agonist treatment (40,51,52). Currently, the relative contributions of ras and c-myc in Wy-14,643-induced cellular proliferation are not known; however, it is likely that both play an integral role in hepatocyte proliferation.…”

Hepatocarcinogenic Susceptibility of Fenofibrate and Its Possible Mechanism of Carcinogenicity in a Two-Stage Hepatocarcinogenesis Model of rasH2 Mice

“…These results suggest that oxidative stress is involved in the development of FF-induced hepatocellular preneoplastic foci in rats . Hepatocellular neoplasms were induced in male rasH2 mice given clofibrate for six months (Nesfield et al 2005), but there is no report dealing with the molecular mechanism of hepatocarcinogenesis of PPARα agonists in rasH2 mice.…”

“…Based on this information, the new guidelines provided by the FDA for compounds in this class indicate that the carcinogenic potential of these PPAR agonists cannot be evaluated in TG or KO mice, and clinical studies longer than six months in duration cannot be initiated until two-year rodent carcinogenicity studies are completed and submitted for the agency to review (El-Hage 2004). On the other hand, it is well recognized that rasH2 mice, hemizygous transgenic mice carrying the human prototype c-Ha-ras gene with its own promoter and enhancer, are susceptible not only to genotoxic carcinogens but also to some non-genotoxic carcinogens classified as PPARα agonists, such as clofibrate, diethyl hexylphalate (DEHP), and Wy-14643 (Nesfield et al 2005;Toyosawa et al 2001;Yamamoto et al 1996). This means that in the absence of a database on rasH2 mice, the FDA recognizes the insusceptibility of these TG and KO mice to PPAR agonists.…”