Initiation-promotion

VEs such as MVE polymerize slowly in the presence of free-radical initiators to form low mol wt products of no commercial importance (9). Examples of anionic polymerization are unknown, whereas cationic initiation promotes rapid polymerization to high mol wt polymers in excellent yield and has been extensively studied (10). 

Antitumour activity has been reported for alkyltins, particularly dibutyltin. The effect in mouse skin initiation/promotion protocols showed dibutyltin inhibiting the promotion stage (Arakawa Wada,... 

Experiments were conducted in which purified trichloroethylene (1 mg in acetone) was applied to the shaved backs of female ICR/Ha Swiss mice (Van Duuren et al. 1979). In an initiation-promotion study, a single application of trichloroethylene was followed by repeated application of phorbol myristate acetate (PMA) promoter. In a second study, mice were treated with trichloroethylene three times per week without a promoter. No significant tumor incidences were observed in these studies. Doses used in these studies were well below the maximum tolerated dose, which is often not reached in dermal studies. 

Cancer is a major cause of premature death in modern society. In vitro and animal research indicates that tea, mainly green tea, may be effective against a wide variety of cancers. Activity has been observed in vitro at all three levels of cancer progression, namely initiation, promotion and transformation (Mitscher et al, 1997). 

Solgaard, A. de Leeuw, B. (2002) UNEP/SETAC Life Cycle Initiative Promoting the Life-Cycle Approach. International ]ournal of Life Cycle Assessment, 7, 1999-2002. 

Carcinogenesis develops in three stages initiation, promotion, and progression. Chem-ical substances can act at the initiation stage or at the promotion stage. Moreover, some chemicals have both initiating and promoting activities. 

Figure 9.5 Karyotypic changes during initiation, promotion, and progression stages of carcinogenesis.

More detailed reviews of the complex initiation-promotion literature should be consulted for a full appreciation of this topic (30,31). 

In the newborn mouse system (Table II), the (+) anti dihydrodiol epoxide is clearly more effective than benzo[ajpyrene but this is not the case in initiation-promotion studies or in complete carcinogenesis studies on mouse skin. Nevertheless, there is always... 

Figure 7.13f). Although addition of Cu initially promotes isomerization of 1-alk-ene (initially higher l-alkene/2-alkene ratio for 100Fe/4.6Si/5.0K/2.0Cu in comparison with 100Fe/5.1Si/5.0K catalyst Figure 7.13e), at steady conditions the effect is marginal.

As indicated above in the section on "Genotoxic Effects", it is likely that mirex and chlordecone are tumor promoters and not tumor initiators. Initiators irreversibly alter DNA by a mutation, chromosomal aberration, or other alteration. Promoters act by facilitating the proliferation of previously initiated preneoplastic cells. One of the mechanisms for promotion is believed to involve suppression of inhibitory proliferative control through inhibition of gap-junctional-mediated intercellular communication as well as enzyme induction (Trosko et al. 1983). The results of studies to evaluate the promotional activity potential of mirex in mice indicate that mirex is a mouse skin cancer promoter but exerts this toxicity through a hitherto unknown mechanism that is different from that of phorbol esters, such as TPA (Meyer et al. 1993, 1994 Moser et al. 1992, 1993). Unlike initiation, promotion is a reversible process to a point. This implies, at least in theory, that there may be justification for setting NOAELs for promoters. 

Lindane, a widespread insecticide constituted of technical mixtures of hexa-chlorocyclohexane (HCH), was dechlorinated using Pd/C, Pt/C, or Raney-Ni. The product using the multiphasic system was benzene, obtained within 1 hour. The base initially promoted HCl ehmination from HCH to yield trichlorobenzene, which then underwent the usual hydrodechlorination reaction. 

Gelderblom, W.C. et al.. Cancer promoting potential of different strains of Fusarium moniliforme in a short-term cancer initiation/promotion assay. Carcinogenesis, 9, 1405, 1988. 

Mechanism of ozone decomposition in water depends on the presence of chemical species that can initiate, promote and/or inhibit its decomposition. The most accepted ozone decomposition mechanism is given in Figrtre 3. 

Furnace oil (CAS no. 68474-30-2) was evaluated for skin carcinogenicity with both lifetime skin-painting and an initiation/promotion bioassay (Gerhart et al. 1988). Briefly, in the lifetime skin-painting study, 50 microliters of undiluted furnace oil was applied to 50 male C3H/HeN mice twice weekly for the lifetime of the animals. A sham negative control group of equal size was ran concomitantly. In the initiation portion of the initiation/promotion bioassay, 30 CD-I mice received five treatments of 25 microliters or five treatments of 50 microliters of furnace oil, and both groups were subsequently treated with 50 microliters of 0.1 mg/mL phorbol-12-myristate-13-acetate (PMA) twice weekly for 25 weeks. Thirty mice received... 

National Toxicology Program Toxicology and Carcinogenesis Studies of Diethyl-Phthalate in F344/N Rats and B6C3F11 Mice (Dermal Studies) with Dermal Initiation/Promotion Study of Diethylphthalate and Dimethylphthalate in Male Swiss (CD-I) Mice. NTP Technical Report Series 429 1-278, 1995... 

HCBD did not produce skin tumors after repeated application or show initiating activity in a two-stage initiation-promotion study in mice. ... 

Harris L, Morris LE, Farber E. 1989. Protective value of a liver initiation- promotion regimen against the lethal effect of carbon tetrachloride in rats. Lab Invest 61 467-470. 

A variety of other anionic initiators promote the polymerization of thio-carbonyl fluoride. Among them are aluminum isopropoxide, di(hydrogenated tal-low)dimethylammonium methoxide and chloride, N-nitrosodimethylamine, diisopropylamine, and triethylamine (59). Combinations of either [(C6H 5)3 P] 3RhCl or... 

Liver cancer can be induced in rats by localized irradiation (UNSCEAR, 1977) or by a number of different chemicals and dosage schedules (Farber, 1984). Initiation-promotion protocols are also effective inducers of liver tumors. The predominant lesions are preneoplastic nodules, but as in the skin, carcinomas arise late in the process. Altered hepatic cell fod can be identified within a few weeks after the start of carcinogen treatment by specific changes in enzyme activity, inability... 

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