title: Modulation of the co-promoting activity of gamma interferon in SENCAR and C57BL/6 mouse skin by difluoromethylornithine and the scheduling and duration of interferon treatment.
abstract: The murine skin multistage carcinogenesis model was used to characterize the co-promoting and tumor progressing activities of i.p. administered recombinant DNA-derived murine gamma interferon (rMuIFN-gamma). The dorsal skins of female SENCAR mice were topically initiated with 7,12-dimethylbenz[a]anthracene (DMBA) and promoted twice a week for 20 weeks with 1 microgram of 12-O-tetradecanoylphorbol-13-acetate (TPA). Doses of rMuIFN-gamma that had no effect on papilloma multiplicities when administered 1 day prior to TPA treatment increased the numbers of papillomas per mouse by 33-38% when administered immediately prior (zero time) to TPA application. A minimum of 6 weeks of co-treatment with TPA and rMuIFN-gamma (zero time) were necessary for demonstration of rMuIFN-gamma-dependent co-promotion. The ad libitum administration of either 0.25 or 1% (w/v) solutions of alpha-difluoromethylornithine (DFMO) in the drinking water inhibited by 90% the TPA-dependent elevation of epidermal ornithine decarboxylase activity but had minimal effect on papilloma multiplicities in TPA-promoted mice. However, both doses of DFMO completely suppressed rMuIFN-gamma-dependent co-promotion. Carcinoma incidence and multiplicities by weeks 46-48 of the promotion-progression period were statistically indistinguishable for initiated mice treated with TPA, TPA + DFMO, TPA + IFN-gamma or TPA + DFMO + IFN-gamma. Similarly, i.p. administration of rMuIFN-gamma to papilloma-bearing mice in a tumor progression study, with and without simultaneous topical TPA treatment, did not affect carcinoma latency or carcinoma multiplicities. C57BL/6 mice initiated with DMBA developed few papillomas (0.2 paps/mouse) after 19 weeks of TPA promotion. The i.p. administration of rMuIFN-gamma to C57BL/6 mice at the time of TPA treatment, at doses that were co-promoting in SENCAR mice, did not increase papilloma multiplicities. Collectively, our studies suggest that the co-promoting activity of rMuIFN-gamma is exceptionally sensitive to inhibition by DFMO and dependent upon the scheduling and duration of rMuIFN-gamma treatment, and the mouse strain/stock employed for the studies.
authors.affiliation: Department of Carcinogenesis, University of Texas System Cancer Center, Smithville 78957.
authors.forename: J J
authors.initials: JJ
authors.lastname: Reiners
authors.forename: A
authors.initials: A
authors.lastname: Pavone
authors.forename: T
authors.initials: T
authors.lastname: Rupp
authors.forename: A R
authors.initials: AR
authors.lastname: Cantu
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity*; D000818:Animals; D003043:Cocarcinogenesis; D000518:Eflornithine / Q000627:therapeutic use*; D005260:Female; D007371:Interferon-gamma / Q000627:therapeutic use*; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D011994:Recombinant Proteins; D012878:Skin Neoplasms / Q000139:chemically induced / Q000473:pathology / Q000517:prevention & control*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity*
chemical_list: D011994:Recombinant Proteins; D015127:9,10-Dimethyl-1,2-benzanthracene; D007371:Interferon-gamma; D013755:Tetradecanoylphorbol Acetate; D000518:Eflornithine