Effects of epidermal chalone and epidermal growth factor on a transplantable epidermal carcinoma (Hewitt) of the mouse in vivo.

Abstract

Abstract The effects of chalone-containing skin preparations and of epidermal growth factor on the proliferative activity of a transplantable nonkeratinizing epidermal carcinoma (Hewitt) of the mouse have been studied in vivo . Whereas crude skin extracts suppressed DNA labeling (probably due to cytotoxic effects), highly enriched epidermal G 1 chalone was found to inhibit neither DNA synthesis nor tumor growth. Consequently, repeated injections of the factor did not prolong the survival rate of tumor-bearing animals. Extracts made from tumor tissue did not show any G 1 chalone activity when injected into normal mice, whereas extracts from normal mouse epidermis exhibited a strong inhibitory effect on epidermal DNA labeling. Despite being resistant to epidermal G 1 chalone, the carcinoma was found to be susceptible to the antimitotic effects of skin extracts which are most probably due to the epidermal G 2 chalone. A single i.p. injection of epidermal growth factor caused a doubling of DNA labeling in the transplanted tumor. These observations are consistent with the hypothesis that epidermal G 1 chalone controls only the proliferation of epidermal “stem cells” in a rather advanced stage of differentiation, whereas epidermal G 2 chalone as well as epidermal growth factor appear to affect more primitive cell types.