The tumor-promoting activity of tobacco leaf extract and whole cigarette tar.

Abstract

IN recent work in this laboratory it was shown that an extract of flue-cured cigarette tobacco leaf (WTE) as well as cigarette smoke condensate (WCT) exhibit tumor-promoting activity (Van Duuren et al., 1966). In these experiments a single dose of 7,12-dimethylbenz[a]anthracene (DMBA) was applied on mouse skin as initiator followed by repeated skin application of the promoting agents. While this procedure proved satisfactory for bioassay of a number of fractions and subfractions derived from tobacco leaf and tars, it was desirable also to explore systemic treatment with several initiating agents followed by skin application of the promoting agents. The present report describes the bioassay of several promoting agents with DMBA, benzo[a]pyrene (BP) and urethane as initiators. The initiators were given by subcutaneous and intraperitoneal injection in mice; the promoting agents were applied on skin. The results of these experiments are compared with our earlier results, in which both the initiator and promoter were applied on mouse skin (Van Duuren and Orris, 1965;Van Duuren et al., 1966). MATERIAL.S AND METHODSThe test animals were female HA/ICR Swiss mice and 20 animals were used per group. The initiators used in these experiments were DMBA at several dosages (0.5-500 jug.), BP and urethane, each at 1 dosage level; 0-5 mg., and 20 mg. respectively. The initiators were injected in tricaprylin or saline with a 26 gauge, 3 in. needle, in a single dose, either subcutaneously on the left flank or intraperitoneally on the left side of the abdomen. The promoters used were croton resin (CR), whole tobacco extract (WTE), and whole cigarette tar (WCT). The methods of preparation of these materials were described in our earlier reports (Van Duuren and Orris, 1965;Van Duuren et al., 1966). The dosages and solvents used were as follows: CR: 25 ,ug./0 1 ml. acetone; WTE: 25 mg. /0.1 ml. acetone-water (1 : 1); WCT: 25 mg./0 1 ml. acetone. Promoters were applied to the clipped dorsal skin 3 times weekly with a No. 5 squirrel hair brush delivering close to 100 mg. of solution per application. Promotion treatments were started 2 weeks after initiation. In a few experiments a longer interval was allowed to elapse between initiation and promotion, and these are indicated under results.Included in the test series were the following control groups: animals that received initiator only, promoter only, solvent controls, and groups which received no treatment.

Selective clonal expansion and microenvironmental permissiveness in tobacco carcinogenesis

“…The combination of condensate and croton oil produced no more tumors than the sum of tumors produced by each alone (not shown), indicating that the condensate had minimal tumor-initiating activity. Confirmation of the promoting activity of the condensate using DMBA as initiator was obtained later, leading the authors to assert the 'condensate showed remarkable promoting activity' (Van Duuren et al, 1971, 1966and Table 3). …”

“…The role of smoke-induced mutations in tobacco carcinogenesis is to be considered by others in this Review issue, e.g., Chemical Carcinogenesis by Pfeifer and Hecht and Molecular Epidemiology by Hussain and Harris. The combination of mutagens and clonal selection cannot be resolved without considering the historical experimental work described here which concluded that the concentration of PAHs in cigarette smoke is far too low to account by itself for the carcinogenic activity of the condensate (Wynder andHoffmann, 1959, 1961) and the activity of promoters and co-carcinogens is high enough to contribute significantly to tumor development (Gellhorn, 1958;Hecht et al, 1981;Roe et al, 1959;Van Duuren and Goldschmidt, 1976;Van Duuren et al, 1966).…”

“…In contrast, the content of promoters and co-carcinogens was sufficient to produce tumors in mouse skin that had either been initiated by a single dose of PAH (Gellhorn, 1958;Roe et al, 1959;Van Duuren et al, 1966) or by repeated simultaneous applications of weak doses of PAH with various constituents of the condensate (Van Duuren and Goldschmidt, 1976;Van Duuren et al, 1973). It was also noted that some PAHs that were themselves borderline or non-carcinogens could act as initiators when followed by promoters (Van Duuren et al, 1970).…”

Cigarette smoke components inhibited intercellular communication and differentiation in human pancreatic ductal epithelial cells

“…DH, the heat-inactivated control. (BaP), 46 and that cigarette smoke is a strong promoter and weak complete carcinogen 11,[47][48][49] suggest that this fraction could significantly contribute to cancer. Ten to 15 years after giving up smoking, the exsmoker faces the same low risk of developing cancer of the upper digestive tract, the lung, the pancreas, and the urinary tract as the nonsmoker.…”

Possible Mechanisms of Combination Effects in Chemical Carcinogenesis

“…where tobacco is used in the recipe [Eisen 1946). Ex tracts of unsmoked tobacco were found to contain promo ters [Van Duuren et al 1967, Bock 1968], but these pro moters have not been identified. Liver damage due to carbon tetrachloride has been correla ted with changes in the rate of metabolism and the formation of certain metabolites of benzo(a)pyrene.…”