Carrie E. Whitmire

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

C57BL/6Cum, DBA/2Cum, first filia (F1), 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 (Ahb allele) expressed 40-60 units AHH activity/g wet wt liver following intraperitoneal treatment with 3-methylcholanthrene (MCA) compared to AHH non-responsive mice (Ahd allele) which expressed 7-11 units AHH activity/g wet wt liver after MCA treatment. Intratracheal administration of 500 microgram 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, F1, and C57BL/6Cum X F1 animals were much more susceptible to MCA-induced lung cancers than the AHH non-responsive DBA/2Cum mice. The lung cancers were also not randomly distributed in DBA/2Cum X F1 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 Ahb allele.

Studies on pulmonary aryl hydrocarbon hydroxylase activity in inbred strains of mice.

Pulmonary and hepatic levels of aryl hydrocarbon hydroxylase (AHH) were studied in inbred strains of mice following intratracheal (i.t.) instillation of 3-methylcholanthrene (MCA). I.t. instillation of 188 mug MCA in sterile 0.2% gelatin in saline resulted in preferential induction of pulmonary AHH. After treatment with this dose of MCA, the pulmonary AHH levels of strains C57BL/6Cum, C57BL/6J, BALB/cMai, C3H/fMai, and C57L/J were observed to be induced within 24 h after treatment. Strains DBA/2Cum, AKR/J, SJL/J, DBA/2J and RF/J expressed no such increase. At a dose of 500 mug MCA, the pulmonary tissue of DBA/2 mice did express a 4-fold increase. This increase in AHH was determined to be quite different from the increase observed in C57BL/6 mice by: (1) specific activity of the enzymes, (2) genetic regulation, (3) susceptibility to inhibition by 7,8-benzoflavone, and (4) spectral properties of the associated cytochromes. It was of major importance that induction of pulmonary AHH was observed to be regulated by a single dominant gene in crosses involving the C57BL/6Cum and DBA/2Cum strains of mice. Results were discussed with the view in mind that these genetically regulated levels of AHH may play a role in susceptibility to cancers induced by polycyclic aromatic hydrocarbon carcinogens.

The Significance of Aryl Hydrocarbon Hydroxylase Enzyme Systems in the Selection of Model Systems for Respiratory Carcinogenesis

Aryl hydrocarbon hydroxylase (AHH) is a multicomponent, microsomal-bound enzyme system which converts a variety of lipid-soluble compounds to water-soluble forms for subsequent elimination from the body. The enzyme system is inducible by a variety of endogenous and exogenous compounds including steroid hormones, barbiturates, insecticides, polycyclic aromatic hydrocarbons (PAH), and whole cigarette smoke. Recent results have demonstrated that inducibility is host-gene regulated, the inducibility of this enzyme correlates with carcinogenic susceptibility to PAH in animal, and bronchogenic squamous cell carcinoma in humans (probably cigarette smoke induced).

Influence of Preinfection of C57BL/6 Mice with Graffi Leukemia Virus on 3-Methylcholanthrene-Induced Subcutaneous Sarcoma

Summary When C57BL/6 mice were given both Graffi leukemia virus and 3-methyl-cholanthrene the development of either leukemia and/or sarcoma was dependent on the dose of each carcinogen given. A high dose of virus reduced sarcoma induction because the survival time of the mice was less than the average latency period required for sarcoma induction due to the high incidence of leukemia. A high dose of 3-methylcholanthrene (300 μg) increased the incidence of leukemia induction by a low dose of virus without affecting the incidence of sarcoma. This occurred since the latency period for sarcoma and leukemia coincided and 25% of the mice developed both leukemia and sarcoma. The combination of a low dose of virus and a low dose of 3-methylcholanthrene did not alter the incidence of leukemia or sarcoma; however, with this combination of virus and chemical carcinogens, the average latency period for the development of leukemia was delayed and the average latency period for sarcoma induction was accelerated. Graffi virus failed to increase the incidence of MCA induced sarcoma under the conditions studied. The authors thank Drs. R. J. Huebner, R. E. Kouri and M. L. Vernon for reviewing the manuscript, Dr. L. S. Rabstein for histopathological diagnosis, Mr. S. Zelnio, Mr. H. Ratrie, and Mr. T. Black for their technical assistance.

Effects of Thymectomy, Splenectomy and 3-Methylcholanthrene on Neoplasia Expression, Incidence and Latency in AKR Mice

Summary The effects of thymectomy, splenectomy and 3MC treatment on neoplastic expressions were studied in AKR mice. In the intact and splenectomized mice, 3MC increased the total incidence of neoplastic expression due to the development of sc tumors at the site of 3MC treatment and not to an increase in incidence of leukemia. Thymectomy eliminates leukemia during the nine-month observation period in the trioctanoin vehicle control mice and reduced the incidence of leukemia to 1/18 in the 3MC treated mice. The incidence of 3MC induced sarcomas was not increased by thymectomy even in the absence of leukemia, therefore the total incidence of neoplasia was reduced from 100% to 56%. Both thymectomy and splenectomy reduced the latency period for 3MC sarcoma induction.

Cell-Mediated Immunity after Intratracheal Exposure to 3-Methylcholanthrene, and its Relationship to Tumor Transplant Growth in C3H/f Mai Mice

Immunological deficiencies have often been observed to occur in association with cancer although the exact nature of this relationship has not been fully characterized. The relative immunocompetence of an individual definitely plays a major role in the ultimate susceptibility or resistance to cancer. Numerous studies support the concept that cell-mediated immunity (CMI) is largely responsible for the body’s defense against cancer. Our laboratory is currently interested in the levels of chemicals at which tumorigenesis occurs in various strains of mice and whether immunocompetence of the animals is affected.

The Role of the Host in the Development of in vivo Models for Carcinogenesis Studies

The development of cancer depends upon the se of the host to the carcinogen and to the initial transformation event. Genetic factors determine the host’s potential to respond to chemical and viral carcinogens, while endogenous and exogenous environmental factors influence the realization of the genetic potential. In chemical carcinogenesis

Problems in the detection of rubella virus in African green monkey kidney tissue culture.

Summary The sensitivity to rubella virus of 96 lots of AGMK tissue culture was evaluated using the enterovirus interference technique. Wide variation in sensitivity was found leading to the classification of 32 of the lots tested as resistant to rubella virus. The use of these resistant lots of tissue culture for the isolation or titration of rubella virus would lead to invalid test results. Appropriate controls are needed to assure the validity of studies in which rubella virus is detected with African green monkey kidney tissue culture.