Effects of novel 3,4-bisphenylhex(3)enes on cell proliferation in malignant and normal cells.

The growth-inhibitory effect of several newly synthesized alkyl derivatives of 3,4-bisphenylhex(3)ene was studied in four tumor cell lines and three healthy primary cell systems. A marked inhibition of cell proliferation was noted in the neoplastic cells but not in the primary systems. No effect on the cytoplasmic or mitotic microtubule system but an increase in the gross level of 5-methylcytosine in nuclear DNA was observed. It is speculated that the selective growth inhibition of tumor cells is due to DNA-hypermethylation.

5-azacytidine induces micronuclei in and morphological transformation of Syrian hamster embryo fibroblasts in the absence of unscheduled DNA synthesis.

It is known that 5-azacytidine (5-AC) induces tumors in several organs of rats and mice. The mechanisms of these effects are still poorly understood although it is known that 5-AC can be incorporated into DNA. Furthermore, it can inhibit DNA methylation. The known data on its clastogenic and/or gene mutation-inducing potential are still controversial. Therefore, we have investigated the kinds of genotoxic effects caused by 5-AC in Syrian hamster embryo (SHE) fibroblasts. Three different endpoints (micronucleus formation, unscheduled DNA synthesis (UDS) and cell transformation) were assayed under similar conditions of metabolism and dose at target in this cell system. 5-AC induces morphological transformation of SHE cells, but not UDS. Therefore, 5-AC does not seem to cause repairable DNA lesions. Furthermore, our studies revealed that 5-AC is a potent inducer of micronuclei in the SHE system. Immunocytochemical analysis revealed that a certain percentage of these contain kinetochores indicating that 5-AC may induce both clastogenic events and numerical chromosome changes.

Activation of cellular oncogenes by chemical carcinogens in Syrian hamster embryo fibroblasts.

Carcinogen-induced point mutations resulting in activation of ras oncogenes have been demonstrated in various experimental systems such as skin carcinogenesis, mammary, and liver carcinogenesis. In many cases, the data support the conclusion that these point mutations are critical changes in the initiation of these tumors. The Syrian hamster embryo (SHE) cell transformation model system has been widely used to study the multistep process of chemically induced neoplastic transformation. Recent data suggest that activation of the Ha-ras gene via point mutation is one of the crucial events in the transformation of these cells. We have now cloned the c-Ha-ras proto-oncogene from SHE cDNA-libraries, and we have performed polymerase chain reaction and direct sequencing to analyze tumor cell lines induced by different chemical carcinogens for the presence of point mutations. No changes were detectable at codons 12, 13, 59, 61, and 117 or adjacent regions in tumor cell lines induced by diethylstilbestrol, asbestos, benzo(a)pyrene, trenbolone, or aflatoxin B1. Thus, it is not known whether point mutations in the Ha-ras proto-oncogene are essential for the acquisition of the neoplastic phenotype of SHE cells. Activation of other oncogenes or inactivation of tumor suppressor genes may be responsible for the neoplastic progression of these cells. However, in SHE cells neoplastically transformed by diethylstilbestrol or trenbolone, a significant elevation of the c-Ha-ras expression was observed. Enhanced expression of c-myc was detected in SHE cells transformed by benzo(a)pyrene or trenbolone.

Trenbolone induces micronucleus formation and neoplastic transformation in Syrian hamster embryo fibroblasts but not in mouse C3H10T1/2 cells.

The synthetic androgen 17 beta-trenbolone (beta-TBOH), used as a growth promotant in cattle, and its metabolite 17 alpha-trenbolone (alpha-TBOH) were tested for genetic toxicity in Syrian hamster embryo (SHE) cells and in mouse C3H10T1/2 embryo fibroblasts by measuring the induction of micronucleus formation and neoplastic cell transformation. Both beta-TBOH and alpha-TBOH, but not testosterone nor its hormonally active metabolite, 5 alpha-dihydrotestosterone, caused a dose-related induction of micronuclei in SHE cells. In C3H10T1/2 cells, neither beta-TBOH nor alpha-TBOH gave rise to micronucleus induction. Furthermore, both beta-TBOH and alpha-TBOH, but not testosterone, were found to transform SHE cells but not C3H10T1/2 cells morphologically. The beta-TBOH-transformed SHE cells proved to be neoplastic in thymus-aplastic nude mice. These data show that beta-TBOH is able to cause changes at the chromosomal level and neoplastic transformation independent of its hormonal activity in one mammalian cell system but not in another one. The implications of these data for the risk evaluation of beta-TBOH are discussed.

Are small RNAs associated with Crohn's disease?

Two-dimensional and bidirectional electrophoretic techniques previously developed for the specific detection of circular viroids and virusoids in plants material were used to analyze preparations of low molecular weight RNA from the granulomatous bowel tissue of patients with Crohn's disease and from corresponding tissue of healthy controls. A major and two minor RNA species of about 300 nucleotides length were detected in RNA samples from eight Crohn's disease patients and not in those from three healthy controls. It remains to be established whether these disease-associated RNAs with viroid-like electrophoretic properties play a causative role in Crohn's disease.