MCA Treatment Research Articles

Correlation of inducibility of aryl hydrocarbon hydroxylase with susceptibility to 3-methylcholanthrene-induced lung cancers

C57BL 6Cum , DBA 2Cum , first filia (F 1), and backcross progeny from these 2 parental strains of mice were evaluated for their susceptibility to 3-methylcholanthrene-induced lung cancers. In the crosses among these mice, aryl hydrocarbon hydroxylase (AHH) responsiveness segregated as a single autosomal dominant gene (the Ah locus). AHH responsive mice ( Ah b allele) expressed 40–60 units AHH activity/g wet wt liver following intraperitoneal treatment with 3-methylcholanthrene (MCA) compared to AHH non-responsive mice ( Ah d allele) which expressed 7–11 units AHH activity/g wet wt liver after MCA treatment. Intratracheal administration of 500 μg MCA for a total of 4 times at weekly intervals yielded a variety of pulmonary cancers, including squamous cell carcinomas, alveolar adenocarcinomas, and adeno-squamous cell carcinomas among mice that survived 1 year after the carcinogen treatment. The AHH responsive C57BL 6Cum , F 1, and C57BL 6Cum × F 1 animals were much more susceptible to MCA-induced lung cancers than the AHH non-responsive DBA 2Cum × F 1 backcross progeny since significantly more lung cancers were found in AHH-responsive progeny than in AHH non-responsive mice. Data support genetic linkage between susceptibility to MCA-induced lung carcinomas and the Ah b allele.

Effects of Subcutaneous Administration of Chemical Carcinogens on Leukemia in C58 Mice2

The effects of sc administration of 3-methylcholanthrene (MCA), 7,12-dimethylbenz[a]anthracene (DMBA), and benzo[a]pyrene (BP) on spontaneous viral leukemia and subcutaneous sarcoma induction have been studied in weanling C58/J mice. MCA produced significantly more sarcomas at the inoculation site than did DMBA or BP; moreover, it interfered with leukemia development. DMBA produced fewer sarcomas, and the incidence of leukemia was comparable to that found in the controls. BP accelerated the incidence of leukemia, although no sarcomas were produced. When the effect of the age of the mice at the time of MCA treatment on the incidence of leukemia and sarcomas was studied, newborn and weanling mice were found to develop primarily sarcomas, whereas no sarcomas were produced in the 16-week-old mice, and 52-64% of the 16-week-old mice developed leukemia. The reason no sarcomas were found in the C58 mice was apparently different from the reason no sarcomas were found in AKR mice, inasmuch as the AKR mice did not live long enough for sarcomas to develop. Immunologic surveillance may have played a part in the sarcoma suppression in the C58 mouse.

Biologic analysis of fetal MRC rat lung epithelial cells treated with 3-methylcholanthrene in culture: premalignant and malignant stages.

Fetal MRC rat lung primary cell sheets, in which reconstruction of bronchial tissue occurred, were treated with 3-methylcholanthrene (MCA) to examine the carcinogen's biologic effect on lung epithelial elements. Cloned lines were established by subculturing of epithelial outgrowths from primary cell sheets induced by MCA treatment. Newborn MRC rats received an sc injection of these cells to assess their tumorigenicity. These MCA-treated cells at the initial stages of culture temporarily formed benign epithelial structures in scar tissue that developed from an sc injection and then regressed. The epithelial structures were roughly classified as tubular and squamous epithelium. The differentiation of cells in vitro was observed as either a type of lamellar keratinization of the premalignant squamous cell form or a type of cyst formation by premalignant secreting epithelium. With further cultivation, six of 24 cell lines became malignant and, when injected into the animal, induced carcinomas. Qualitative changes in the in vitro differentiation of cells were observed in cell lines that formed squamous cell carcinomas. These changes included spherical keratinization (pearl formation) and single-cell keratinization. MCA treatment induced various premalignant alterations in lung epithelial cells, and the subsequent malignancy seemed to stem from these initial premalignant changes.

PH-dependence of epidermal respiration under normal conditions and in chemically induced hyperplasia. Comparison with the mitochondrial tetrazolium reduction.

In normal hairless mouse epidermis the cellular respiration (QO2) on endogenous substrate in vitro is more sensitive to pH variations than the respiration with glucose in the medium. During the first week after painting with the strong carcinogen 20-methylcholanthrene (MCA) the QO2 of hairless mouse epidermis is not more susceptible to pH variations than that of untreated epidermis. A transient broader pH optimum of the respiration to the acidic side after application of the solvent benzene or the irritant cantharidin in benzene is probably due to intracellular accumulation of lactic acid. While the tetrazolium method shows a specific reaction pattern after MCA painting, the oxygen consumption mostly shows an unspecific pattern, reflecting altered cell population kinetics in the epidermis. After MCA treatment there is a discrepancy between oxygen consumption and formazan deposition until the 7th day. The oxygen consumption is decreased while the tetrazolium method gives increased or normal values. A possible explanation is that the mitochondrial membrane has an increased permeability for tetrazolium.

Respiration and glycolysis in relation to cell population kinetics in mouse epidermis treated with carcinogenic or irritant substances: With special reference to the Crabtree and Pasteur effects

The changes in epidermal respiration and glycolysis have been investigated in hairless mice after a single application of the strong carcinogen 20-methylcholanthrene. The results have been compared to similar changes after a single application of cantharidin, a strong irritant, which gives a comparable degree of cellular damage with subsequent proliferation and hyperplasia. Measurements have also been performed with the solvent, benzene, which acts as a weak irritant to the skin. The alterations could be classified into 4 different phases: 1. (1) A toxic phase during the first 4 hr after application where both compounds caused profound cellular damage with depression of both respiration of glycolysis. 2. (2) An intermediary phase from 4 to 24 hr after the treatment where most of the resulting cell loss occurs. A temporary increase of respiration and glycolysis at this stage was found to be solely due to the solvent. Later the solvent did not interfere with the results. 3. (3) A growth phase from 34 to 48 hr, characterized by an explosive proliferation in the epidermal basal cell layer. Isolated basal cells from MCA treated skin exerted a low respiration, while a normal respiration was seen after cantharidin treatment. In both cases the glycolysis of the skin was very high. 4. (4) A hyperplastic phase from 2 to 21 days after painting, where the epidermal cells had very low respiration and glycolysis. The main conclusions of these studies are: 1. (1) The quantitative metabolic alterations after treatment with carcinogenic as well as non-carcinogenic irritants are due to changes both within each single cell and changes in the composition of the tissue due to altered cell population kinetics. The interpretation of metabolic studies is therefore impossible without correlating the data to simultaneous cell population studies. 2. (2) The Crabtree effect, which normally is of a magnitude of 10% in hairless mouse epidermis, is rapidly changing in the different phases after treatment. It is temporarily increased by the solvent. During high proliferative activity the Crabtree effect is very low, indicating that it is not related to the proliferative process. During hyperplasia, the newly formed, young cells, despite their low respiration, exert a very high Crabtree effect, which after MCA treatment is nearly 60%. 3. (3) The Pasteur effect is only slightly altered in the different phases after treatment. It is moderately reduced after MCA treatment. 4. (4) It is suggested that the low respiration and high glycolysis during high proliferative activity after MCA treatment may have some relation to carcinogenesis.