Sister chromatid exchange induction resulting from systemic, topical, and systemic-topical presentations of carcinogens.

Chinese hamster cheek pouch mucosal cells were examined for in vivo sister chromatid exchange formation resulting from the exposure of animals to carcinogens presented in three manners: systemic, topical, and systemic-topical combination. The systemic presentation of cyclophosphamide (5 or 10 mg/kg) through i.p. injection resulted in an increase in sister chromatid exchanges from 4.8 to 9.9 per cell. Topical application of 7,12-dimethylbenz(a)anthracene (0.5% in mineral oil, 0.1 ml) resulted in an increase in the sister chromatid exchange frequency to 11.5/cell, as compared with a value of 5.0/cell in animals treated only with mineral oil. Systemic administration of 8-methoxypsoralen (0.5, 1, 2.5, or 5 mg/kg) through i.p. injection, followed by activation with topical near-ultraviolet light (3.75 x 10(4) ergs/sq mm at 365 nm) resulted in an increase in sister chromatid exchange, reaching 15.4/cell at 5 mg 8-methoxypsoralen per kg. Exposure of animals to 8-methoxypsoralen or near-ultraviolet light alone, but not in combination, did not produce an increase in sister chromatid exchange. Sister chromatid exchange frequencies in cheek pouch cells were also compared with sister chromatid exchange frequencies in marrow cells of identically treated animals to assess the importance of exposure mode and tissue specificity in sister chromatid exchange formation.