DMBA Group Research Articles

Interactions between 7,12-Dimethylbenz(a)anthracene (DMBA) and Repeated Low-Level X Radiation in Hamster Cheek Pouch Carcinogenesis: Dependence on the Relative Timing of DMBA and Radiation Treatments

peated Low-Level X Radiation in Hamster Cheek Pouch Carcinogenesis: Dependence on the Relative Timing of DMBA and Radiation Treatments. Radiat. Res. 90, 155-164 (1982). Low-level X radiation was shown to enhance Syrian hamster cheek pouch carcinogenesis by 7,12-dimethylbenz(a)anthracene (DMBA) when radiation was administered concurrently with and following DMBA applications. We studied the effects of altering the timing of radiation and DMBA applications on this enhancement. DMBA in mineral oil was applied twice weekly for 10 weeks and 20 R head and neck X radiation once weekly for 17 weeks. In duplicate studies, animals received radiation, DMBA, or DMBA plus X radiation. In the DMBA plus X-ray group, there were 9 weeks of preirradiation and 7 weeks of concurrent treatments. Radiation alone did not result in any histologically detectable changes. In one study, preirradiation may have reduced the carcinogenic activity of DMBA, while in the second study there were no significant differences in tumor incidences between X radiation plus DMBA and DMBA only groups. Thus, while repeated 20-R X-ray exposures during and following DMBA applications enhance DMBA carcinogenesis, identical X-ray exposures prior to and during DMBA applications appear either to slightly inhibit or to have no appreciable effect on DMBA carcinogenesis.

Enhancement of DMBA Tumorigenesis in Hamster Cheek Pouch Epithelium by Repeated Exposures to Low-Level X Radiation

Duplicate studies were conducted to determine the effects of repeated exposures to low-level X radiation on the incidence, volume, and latent period of DMBA-induced neoplasms in Syrian hamster cheek pouch epithelium. Doses employed were 0.05 ml of 0.1% 7,12-dimethylbenz[a]anthracene (DMBA) in mineral oil twice weekly for 10 weeks and 20-R head and neck X radiation once weekly for 17 weeks. Animals received either radiation alone, DMBA alone, or simultaneous radiation + DMBA beginning together. Appropriate controls were performed. Radiation alone did not result in any detectable pathology. In one study, the incidence (68 vs 40%) and volumes of tumors were significantly greater in animals receiving radiation + DMBA than in animals receiving DMBA alone. The latent period for earliest tumor appearance was shorter in animals receiving radiation + DMBA than in animals receiving DMBA alone (9 weeks vs 24 weeks). In the repeat study, increased tumor incidence in the radiation + DMBA group was again observed, but ...

The effect of methotrexate on experimental salivary gland neoplasia in rats

Sixty young adult male Sprague-Dawley rats approximately 90 days old and weighing 250 g were studied for the effect of systemically administered methotrexate upon chemically induced neoplasms of submandibular gland. The animals were divided into four equal experimental groups. Group I and group II animals had pellets of 9,10-dimethyl-1,2-benzanthracene (DMBA) implanted in the right submandibular gland. Group II animals received subcutaneous injections of 1.0 mg sodium methotrexate twice weekly in addition to the carcinogen implants. Groups III and IV animals served as methotrexate and uninjected controls. Methotrexate was found to accelerate the process of chemical carcinogenesis of the rat submandibular gland. The epidermoid carcinomas in the DMBA-plus-methotrexate animals developed within the walls of epidermoid cysts, as in the DMBA animals, but were well established at 10 weeks, while the carcinomas were beginning to develop in the DMBA animals. At 12 weeks the carcinomas in the DMBA-plus-methotrexate animals were considerably larger than in the DMBA group and there was greater invasiveness into the glandular tissue. Systemically administered methotrexate augmented the carcinogenic activity of DMBA implanted in rat salivary gland tissue.

The effect of antilymphocyte serum on experimental hamster buccal pouch carcinogenesis.

The effect of systemically injected anti-hamster lymphocyte serum (ALS) on chemical carcinogenesis of the buccal pouch has been studied in thirty Syrian hamsters. In ten animals the right buccal pouch was painted with a 0.5 per cent solution of 9,10-dimethyl-1,2-benzanthracene (DMBA) in heavy mineral oil. Ten animals were painted with DMBA and also injected intraperitoneally with 0.45 ml. of ALS. The remaining ten animals served as untreated controls. There was a higher incidence of carcinoma in the ALS DMBA group and a suggestion of earlier tumor development. Histologically, the ALS DMBA group presented a consistent tumor pattern with more deep invasion and more anaplasticity than the control group. The pouches of the ALS DMBA group were more extensively involved in the development of neoplastic changes.

Experimental Rhabdomyosarcomas in Rats and Guinea Pigs

The present investigation deals with the morphological study of the subcutaneous sarcomas which developed in rats and guinea-pigs, following a single injection of polyciclic hydrocarbons. Sixty-one rats of both sexes and different ages were injected with 5 mg or 3 mg of 9,10-dimethyl-l,2-benzanthracene (DBMA) (groups I - VI), and 3 groups, each of 8 male rats, 21 weeks old, with 5 mg of 20-methylcholanthrene (MC) (group VII), 5 mg of 3,4-benzopyrene (BP) (group VIII), and 5 mg of 1,2,5,6-dibenzanthracene (DB) (group IX). Four groups of 8-10 guinea-pigs, 26 weeks old, received an injection of 5 mg of DMBA (group X), 5 mg of MC (group XI), 5 mg of BP (group XII), 5 mg of DB (group XIII). Olive oil was used as vehicle. Fourthy-three rats treated with DMBA, 1 rat with BP, and 1 rat with DB, developed subcutaneous tumors. No tumors were obtained in the rats treated with MC. Subcutaneous tumors arose in 6 and 4 guinea-pigs treated with DMBA and with MC respectively, but not in guinea-pigs treated with BP or DB. The reason of the negative results in rats injected with MC and of the low incidence of tumors in rats injected with BP and DB, is to be related to the high early mortality of the animals of these groups, due to the toxicity of the treatment. All the subcutaneous tumors resulted to be rhabdomyosarcomas. The diagnosis was made on the basis of the presence of typical cells, such as round or oval giant cells, strap-shaped and racquet-shaped cells, of the nuclear and cytoplasmic characters, and of the arrangement of the reticular fibers. Cross striations were observed only rarely, but their presence has not been considered necessary for the diagnosis of rhabdomyosarcoma. Development of rhabdomyosarcomas in rats treated with various oncogenic agents has been reported by other authors: it is the first time, however, that these tumors are seen to arise in such a high incidence. As far as we know, these tumors have never been reported to occur in guinea-pigs.