Malignant transformation of human bronchial epithelial cells with the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Sufficient evidence has demonstrated that cigarette smoking is causally associated with various types of human cancers. In the United States, about 90% of deaths from lung cancer among men and 79% of those among women are associated with smoking. Tobacco-specific nitrosamines are formed from nicotine and related tobacco alkaloids and are the most carcinogenic compounds of tobacco smoke. The most potent N-nitrosamine contained in tobacco smoke is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK. In the our study, the oncogenic transforming effects of graded doses of NNK were examined using papillomavirus-immortalized human bronchial epithelial cells. Growth kinetics, saturation density, resistance to serum-induced terminal differentiation, anchorage independent growth and tumorigenicity in nude mice were used to investigate the various stages of transformation in bronchial epithelial cells. We show here that immortalized human bronchial epithelial cells in culture can be malignantly transformed by treatment with NNK (100 microg/ml or 400 microg/ml) for 7 days. Transformed cells produced progressively growing subcutaneous tumors upon inoculation into nude mice. Immunofluorescence staining for keratin expression confirmed the epithelial nature of the tumor cells. Increased expression of p16, beta-catenin and PCNA in the established cell lines were detected by immunofluorescence staining and quantified by confocal microscopy. These data suggested that NNK can induce malignant transformation of human bronchial epithelial cells, and the tumor cell lines established are useful models in investigating the carcinogenic mechanism(s) of NNK.

Organophosphorous pesticides in breast cancer progression

Environmental substances may be involved in the etiology of breast cancers. Many studies have found an association between cancer in humans and exposure to agricultural pesticides. Organophosphorous pesticides have been used to control mosquito plagues. Parathion and malathion, organophosphorous pesticides are cholinesterase inhibitors responsible for the hydrolysis of body choline esters, including acetylcholine at cholinergic synapses. Their primary target of action in insects is the nervous system whereby they inhibit the enzyme acetylcholinesterase at synaptic junction. Atropine is a parasympatholytic alkaloid used as an antidote to acetylcholinesterase inhibitors. We have established an experimental breast cancer model, where epithelial cells in the rat mammary gland underwent a stepwise transformation into malignant cells by exposure to pesticides (Cabello et al, 2001). The aim of this work was to examine whether pesticides were able to induce progression of malignant transformation of a human breast epithelial cell line, MCF7. These results showed that parathion and malathion increased PCNA and induced mutant p53 protein expression of MCF7 cells in comparison to controls and atropine inhibited such action. These results indicated that organophosphorous pesticides can induce more changes in this malignant breast cell line, inducing another step in the progression of the transformation process and atropine on the other hand inhibited the effect of such substances.

Short-chain fatty acids inhibit invasive human colon cancer by modulating uPA, TIMP-1, TIMP-2, mutant p53, Bcl-2, Bax, p21 and PCNA protein expression in an in vitro cell culture model

High intakes of dietary fiber or resistant starches have been associated with a lower incidence of colon cancers. Because short-chain fatty acids (SCFA) such as butyrate are produced in the colonic lumen by the bacterial fermentation of dietary fibers and resistant starches, we hypothesized that SCFA may inhibit the development of invasive human colon cancers. To test this hypothesis, primary human invasive colonocytes were isolated from fresh surgical specimens and treated with 0.01 mol/L acetate, propionate or butyrate; cell invasion, cell adhesion, F-actin polymerization, urokinase plasminogen activator (uPA), tissue inhibitor matrix metalloproteinase (TIMP)-1, TIMP-2 and mutant p53, Bcl-2, Bax, p21 and proliferating cell nuclear antigen (PCNA) protein expression levels were examined. Although each of the SCFA tested significantly reduced primary cell invasion, butyrate was the most potent, inhibiting primary invasive human colon cancer invasion by 54% (P < 0.0001). The effects of SCFA on primary cell invasion appeared to be independent of cell adhesion and F-actin polymerization but dependent on the inhibition of uPA (P < 0.05) and the stimulation of TIMP-1 and TIMP-2 activities (P < 0.05). Protein expression levels of mutant p53, p21, Bax, Bcl-2 and PCNA were significantly altered by each of the SCFA tested (P < 0.05). These data indicate that SCFA inhibit invasive human colon cancer by modulating proteolytic uPA and antiproteolytic TIMP-1 and TIMP-2 activities, but their mechanisms of action on tumor suppression, apoptosis and growth arrest may differ.

Establishment of a radiation- and estrogen-induced breast cancer model

It is well accepted that cancer arises in a multistep fashion in which exposure to environmental carcinogens is a major etiological factor. The aim of this work was to establish an experimental breast cancer model in order to understand the mechanism of neoplastic transformation induced by high LET radiation in the presence of 17beta-estradiol (E). Immortalized human breast cells (MCF-10F) were exposed to low doses of high LET alpha particles (150 keV/microm) and subsequently cultured in the presence or absence of E for periods of up to 10 months post-irradiation. MCF-10F cells irradiated with either a single 60 cGy dose or 60/60 cGy doses of alpha particles showed gradual phenotypic changes including altered morphology, increase in cell proliferation relative to the control, anchorage-independent growth and invasive capability before becoming tumorigenic in nude mice. In alpha particle-irradiated cells and in those cells subsequently cultured in the presence of E, increased BRCA1, BRCA2 and RAD51 expression were detected by immunofluorescence staining and quantified by confocal microscopy. These studies showed that high LET radiation such as that emitted by radon progeny, in the presence of estrogen, induced a cascade of events indicative of cell transformation and tumorigenicity in human breast epithelial cells.