Mechanisms of SEPA 0009-Induced Tumorigenesis in v-rasHa Transgenic Tg.AC Mice

Abstract

Genetically engineered mouse models with altered oncogene or tumor suppressor gene activity have been utilized recently for carcinogen identification. The v -rasHa transgenic Tg.AC mouse, with its enhanced susceptibility to skin tumorigenesis, is thought to be well suited for examining the carcinogenicity of topically applied agents. Tg.AC mice were used to examine the carcinogenicity of SEPA 0009, a rationally designed organic molecule designed to enhance drug penetration through the skin. Fifty mg SEPA 0009/kg body weight, 1500 mg SEPA 0009/kg body weight, or the vehicle alone was applied daily to the skin of Tg.AC mice. Nontransgenic FVB/N mice were also treated with the vehicle alone or 1500 mg SEPA 0009. Daily application of a high-dose of SEPA 0009 caused severe and chronic irritation by 1 week that was maintained throughout the experiment. The irritation was accompanied by increased proliferation, increased apoptosis, and expression of the wound-associated keratin 6. High-dose SEPA 0009 induced squamous papillomas in Tg.AC, but not in nontransgenic mice, by 6 weeks. In mice treated with the high dose SEPA 0009, transgene expression was detected in papillomas at week 9, well after the onset of skin irritation and hyperplasia. In contrast, low-dose SEPA 0009 was not irritating to the skin and did not induce papillomas. Thus, SEPA 0009-induced tumorigenesis was associated with chronic and severe irritation. We propose that SEPA 0009-induced tumorigenesis in Tg.AC mice proceeds through an indirect mechanism that is secondary to cutaneous irritation.