A strong correlation exists between the presence of specific types of human papillomavirus (HPV) and the development of anogenital cancer, as well as significant epidemiologic evidence suggesting smokers are at increased risk of developing cervical, vulvar and/or anal carcinomas. Primary and human papillomavirus type 18 (HPV-8)-immortalized human keratinocytes were used to address the co-carcinogenic potential of HPV and nitrosomethylurea (NMU) in tumorigenesis. Only cells containing HPV-18 and treated with NMU and the tumor-promoting phorbol ester, TPA, were transformed to a malignant phenotype. An in vitro system is described which initiates studies involving the mechanisms of HPV and chemical carcinogen co-operation in the etiology of squamous cell carcinomas.

To determine whether B or T lymphoid malignancies could be induced following the exposure of lymphoid cells within different lymphoid organs to a potential chemical carcinogen, 3-methylcholanthrene (3-MC) was directly injected into surgically exposed Peyer's patches (PP), mesenteric lymph nodes (MLN), axillary lymph nodes (ALN) or spleens (SP) of Copenhagen rats. A high incidence of lymphoproliferative disorders was observed within rats which received 3-MC injections into the PP, but not in MLN, ALN or SP injected groups of rats. In addition to the PP environment, the dose of 3-MC and exposure to pristane were important factors in the induction of T versus B cell disorders. Whereas the B cell diseases were observed in pristane-treated rats which also received PP injections of low doses (5 or 50 micrograms) of 3-MC, in animals receiving a higher dose (500 micrograms) a much higher incidence of T cell disorders was detected. The observed lymphoproliferative diseases were categorized as B lymphocytic leukemias, B lymphomas or thymic lymphomas on the basis of histological examination of the tissues, white blood cell numbers and differentials, and the morphological and phenotypic characteristics of cell isolates. Abnormal DNA staining characteristics, increased soft agar cloning frequencies and metastasis of the leukemia or tumor cells indicated that malignant cells were associated with the proliferative diseases. Collectively the data indicate that primary lymphoid malignancies of either B or T cell origins may be preferentially and reproducibly induced by localizing low or high doses respectively, of 3-MC within the PP of rats exposed to pristane. These results suggest that PP may have a possible role in the carcinogenesis of lymphocytes following the exposure to chemical carcinogens via the gastrointestinal tract.

The effects of pristane (2,6,10,14-tetramethylpentadecane) on the cellular DNA of lymphoid cells from Copenhagen rats were examined by flow cytometry. Significant reductions in the mean relative fluorescent intensities of propidium iodide (PI) stained lymphocytes from peripheral blood, spleen, thymus and lymph nodes were observed after a single intraperitoneal injection of pristane. The altered PI staining characteristics were observed as early as 4 days and reached a maximum decrease between 1-4 weeks (depending upon the lymphoid cells examined) post pristane treatment. The pristane-induced effects on peripheral blood lymphocytes were observed to be dose dependent, transient and reinducible by a subsequent exposure to pristane. Further analyses, using gas-liquid chromatography to detect pristane in the blood and lymphoid tissues of treated rats, indicated significant increases over normal amounts of pristane. Furthermore, correlations existed between the times of maximum decrease in the fluorescence of PI stained cells and the amounts of pristane detected within the respective lymphoid tissues. By contrast no changes in the PI staining characteristics of kidney cells were observed, even though appreciable amounts of pristane were detected in this organ. Diphenylamine analyses indicated no differences in the amounts of DNA in lymphoid cells from pristane treated and untreated rats. Furthermore, lymphocytes from pristane-treated rats did not exhibit decreased fluorescence when fixed at pH 10 rather than pH 7.4 prior to PI staining. Collectively these results suggest that pristane may preferentially induce qualitative rather than quantitative changes in the DNA of lymphocytes.

No abstract