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ToxSci Advance Access published online on May 2, 2003
Toxicological Sciences, doi:10.1093/toxsci/kfg113
Toxicological Sciences © Society of Toxicology 2003; all rights reserved
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Received December 20, 2002; accepted April 9, 2003
© 2003 Society of Toxicology

Carcinogenicity

Selection of Drugs to Test the Specificity of the Tg.AC Assay by Screening for Induction of the gadd153 Promoter in Vitro

Karol L. Thompson 1* Frank D. Sistare 1

1 Division of Applied Pharmacology Research, Office of Testing & Research, Office of Pharmaceutical Sciences, Center for Drug Evaluation & Research, FDA, Laurel, MD

* To whom correspondence should be addressed. E-mail: Thompsonk{at}cder.fda.gov.


  Abstract

Short-term assays for carcinogenicity testing of chemicals that use transgenic mice designed to have altered expression of genes mechanistically relevant to carcinogenesis are attractive alternatives to two year dosing studies in rodents. The models that have been the received the greatest level of performance evaluation include p53(+/-), rasH2, Xpa/p53(+/-), and Tg.AC mice. For use of these models in a regulatory setting to evaluate the carcinogenic potential of pharmaceuticals, it is important to establish an assurance of assay specificity and positive predictivity based on studies using drugs with a wide spectrum of pharmacologic activity. For this purpose, 99 noncarcinogenic drugs were prioritized based on their activity in an in vitro induction assay correlative with a positive response in the Tg.AC assay (induction of the gadd153 promoter in HepG2 cells). Activities in two assays less predictive of Tg.AC activity (induction of c-fos and {zeta}-globin gene promoters) were also measured. Nine percent of the screened drugs induced the gadd153 promoter by at least four-fold. Several criteria were used to select candidates for subsequent in vivo testing in the Tg.AC assay: (1) sufficient drug solubility in appropriate skin paint vehicles to elicit systemic toxicity, (2) the level of induction of the gadd153 promoter by the drug, (3) the in vitro potency of the drug, and (4) the cost of the drug required for a 6-month study. Based on these criteria, amiloride, dipyridamole, and pyrimethamine were selected from 99 rodent noncarcinogens in a drug database for testing the specificity of the Tg.AC assay.

Key Words: Tg.AC, gadd153, c-fos, zeta-globin, HepG2, K562 .


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