Genetic polymorphisms in fatty acid metabolism genes and colorectal cancer.

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. Epidemiological risk factors for CRC included dietary fat intake; consequently, the role of genes in the fatty acid biosynthesis and metabolism pathways is of particular interest. Moreover, hyperlipidaemia has been associated with different type of cancer and serum lipid levels could be affected by genetic factors, including polymorphisms in the lipid metabolism pathway. The aim of this study is to assess the association between single-nucleotide polymorphisms (SNPs) in fatty acid metabolism genes, serum lipid levels, body mass index (BMI) and dietary fat intake and CRC risk; 30 SNPs from 8 candidate genes included in fatty acid biosynthesis and metabolism pathways were genotyped in 1780 CRC cases and 1864 matched controls from the Molecular Epidemiology of Colorectal Cancer study. Information on clinicopathological characteristics, lifestyle and dietary habits were also obtained. Logistic regression and association analysis were conducted. Several LIPC (lipase, hepatic) polymorphisms were found to be associated with CRC risk, although no particular haplotype was related to CRC. The SNP rs12299484 showed an association with CRC risk after Bonferroni correction. We replicate the association between the T allele of the LIPC SNP rs1800588 and higher serum high-density lipoprotein levels. Weak associations between selected polymorphism in the LIPC and PPARG genes and BMI were observed. A path analysis based on structural equation modelling showed a direct effect of LIPC gene polymorphisms on colorectal carcinogenesis as well as an indirect effect mediated through serum lipid levels. Genetic polymorphisms in the hepatic lipase gene have a potential role in colorectal carcinogenesis, perhaps though the regulation of serum lipid levels.

The metabolism and pharmacokinetics of phospho-sulindac (OXT-328) and the effect of difluoromethylornithine.

BACKGROUND AND PURPOSE: Phospho-sulindac (PS; OXT-328) prevents colon cancer in mice, especially when combined with difluoromethylornithine (DFMO). Here, we explored its metabolism and pharmacokinetics. EXPERIMENTAL APPROACH: PS metabolism was studied in cultured cells, liver microsomes and cytosol, intestinal microsomes and in mice. Pharmacokinetics and biodistribution of PS were studied in mice. KEY RESULTS: PS undergoes reduction and oxidation yielding PS sulphide and PS sulphone; is hydrolysed releasing sulindac, which generates sulindac sulphide (SSide) and sulindac sulphone (SSone), all of which are glucuronidated. Liver and intestinal microsomes metabolized PS extensively but cultured cells converted only 10% of it to PS sulphide and PS sulphone. In mice, oral PS is rapidly absorbed, metabolized and distributed to the blood and other tissues. PS survives only partially intact in blood; of its three major metabolites (sulindac, SSide and SSone), sulindac has the highest C(max) and SSone the highest t(1/2) ; their AUC(0-24h) are similar. Compared with conventional sulindac, PS generated more SSone but less SSide, which may contribute to the safety of PS. In the gastroduodenal wall of mice, 71% of PS was intact; sulindac, SSide and SSone together accounted for <30% of the total. This finding may explain the lack of gastrointestinal toxicity by PS. DFMO had no effect on PS metabolism but significantly reduced drug level in mouse plasma and other tissues. CONCLUSIONS AND IMPLICATIONS: Our findings establish the metabolism of PS define its pharmacokinetics and biodistribution, describe its interactions with DFMO and largely explain its gastrointestinal safety.

Immortalization of epithelial progenitor cells mediated by resveratrol.

Within the hierarchy of epithelial stem cells, normal progenitor cells may express regulated telomerase during renewal cycles of proliferation and differentiation. Discontinuous telomerase activity may promote increased renewal capacity of progenitor cells, while deregulated/continuous telomerase activity may promote immortalization when differentiation and/or senescent pathways are compromised. In the present work, we show that resveratrol activates, while progesterone inactivates, continuous telomerase activity within 24 h in subpopulations of human Li-Fraumeni syndrome-derived breast epithelial cells. Resveratrol results in immortalization of mixed progenitor cells with mutant p53, but not human epithelial cells with wild type p53. Our results demonstrate the potential for renewing progenitor cells with mutant p53 to immortalize after continuous telomerase expression when exposed to certain environmental compounds. Understanding the effects of telomerase modulators on endogenous telomerase activity in progenitor cells is relevant to the role of immortalization in the initiation and progression of cancer subtypes.

Negative regulation of chemokine receptor CXCR4 by tumor suppressor p53 in breast cancer cells: implications of p53 mutation or isoform expression on breast cancer cell invasion.

Chemokine receptor CXCR4 and its ligand CXCL12 are suggested to be involved in migration, invasion and metastasis of breast cancer cells. Mutation of the tumor suppressor gene p53 in breast cancer is associated with metastasis and aggressive clinical phenotype. In this report, we demonstrate that wild type but not the dominant-negative mutant (V143A) or cancer-specific mutants (R175H or R280K) of p53 repress CXCR4 expression. Recently described cancer-specific p53 isoform, Delta133p53, also failed to repress CXCR4 promoter activity. Short-interfering RNA-mediated depletion of p53 increased endogenous CXCR4 expression in MCF-7 breast cancer cells that contain wild-type p53. Basal CXCR4 promoter activity in HCT116 colon carcinoma cells deleted of p53 [HCT116(p53KO)] was 10-fold higher compared to that in parental HCT116 cells with functional wild-type p53. Deletion analysis of CXCR4 promoter identified a seven-base pair p53-repressor element homologous to cyclic AMP/AP-1 response (CRE/AP-1) element. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed binding of ATF-1 and cJun to the CRE/AP-1 element. The p53 rescue drug PRIMA-1 reduced CXCR4 mRNA and cell surface expression in MDA-MB-231 cells, which express R280K mutant p53. CP-31398, another p53 rescue drug, similarly reduced cell surface levels of CXCR4. PRIMA-1-mediated decrease in CXCR4 expression correlated with reduced invasion of MDA-MB-231 cells through matrigel. These results suggest a mechanism for elevated CXCR4 expression and metastasis of breast cancers with p53 mutations or isoform expression. We propose that p53 rescue drugs either alone or in combination with chemotherapeutic drugs may be effective in reducing CXCR4-mediated metastasis.

A Western-style diet induces benign and malignant neoplasms in the colon of normal C57Bl/6 mice.

Decreased dietary intakes of calcium, vitamin D and folic acid have been suggested as risk factors for human colon cancer. We previously fed a Western-style diet (WD) containing reduced calcium, vitamin D and increased fat content to normal C57/Bl6 mice: hyperproliferation, hyperplasia and whole crypt dysplasias developed in the colon following WD administration. Utilizing the same diet, we now also decreased the levels of several nutrients that are required for biochemical reactions involving methyl group inadequacy, i.e. folic acid, methionine, choline and vitamin B(12). Dietary levels of these nutrients were reduced to nutrient-density levels approximating those consumed by large segments of human Western populations. This further modification of the WD resulted in adenoma and carcinoma development in normal mouse colon (P < 0.04 compared with AIN-76A diet). The results indicate, for the first time, that a semi-purified rodent diet designed to mimic the human Western diet can induce colonic tumors in normal mice without carcinogen exposure.

Chemoprevention of basal cell carcinomas in the ptc1+/- mouse--green and black tea.

Skin cancers are a rising menace as their incidence increases, attributed in part to increasing ultraviolet radiation exposure. This increasing problem has stimulated efforts to devise useful preventive approaches. The uncertain efficacy of exhortations to avoid sun exposure and to use protective clothing and sunscreens to reduce damage when exposed argue for the development of an oral chemopreventive agent. Bickers and others have studied the effects and mechanisms of tea and of its putative active components on inhibition of skin cancer in experimental models. To continue this work, we have studied the effects of oral green tea and black tea on a new model of ultraviolet-induced skin carcinogenesis - the development of basal cell carcinomas in ptc1+/- mice. To our surprise, we have found that tea preparations which others have used to prevent squamous cell carcinoma formation in mice fail to inhibit basal cell carcinogenesis in our model, suggesting that prevention of this cancer may require special, tumor-specific approaches.

Agents, biomarkers, and cohorts for chemopreventive agent development in prostate cancer.

Chemoprevention is the use of agents to slow progression of, reverse, or inhibit carcinogenesis thereby lowering the risk of developing invasive or clinically significant disease. With its long latency, high incidence and significant morbidity and mortality, prostate cancer is a relevant target for chemoprevention. Developing rational chemopreventive strategies for prostate cancer requires well-characterized agents, suitable cohorts, and reliable intermediate biomarkers of cancer. Chemopreventive agent requirements are experimental or epidemiologic data showing efficacy, safety on chronic administration, and a mechanistic rationale for activity. Current promising agents include antiandrogens and antiestrogens; steroid aromatase inhibitors; retinoids and their modulators; 5alpha-reductase inhibitors; vitamins D, E, and analogs; selenium compounds; carotenoids; soy isoflavones; dehydroepiandrostenedione and analogs; 2-difluoromethylornithine; lipoxygenase inhibitors; apoptosis inducers; and nonsteroidal anti-inflammatory drugs. Identifying biomarkers and validating them as surrogate endpoints for cancer incidence are critical for prostate chemoprevention trials. Potentially useful biomarkers for prostate chemoprevention are associated with histologic, proliferative, differentiation-related, biochemical, and genetic/regulatory features of prostatic disease. In that the prostate is not easily visualized, critical issues also include adequacy and consistency of tissue sampling. Various drugs for the chemoprevention of prostate cancer are now under evaluation in phase 1, 2, and 3 clinical trials. Cohort selection should be based on various patient characteristics (stage of the disease, previous cancers or premalignant lesions, or high risk factors) and should be conducted within the context of standard treatment.

Effects of chemopreventive and antitelomerase agents on the spontaneous immortalization of breast epithelial cells.

BACKGROUND: Activation of telomerase is an early event in the development of breast and other cancers that may lead to cell immortalization, a critical and rate-limiting step in cancer progression. Breast epithelial cells from women with Li-Fraumeni syndrome (LFS) immortalize spontaneously and reproducibly in culture. We, therefore, tested whether immortalization of these cells could be prevented by treating them with chemopreventive agents and by inhibiting telomerase activity. METHODS: Noncancerous, preimmortal breast epithelial cells derived from a patient with LFS were treated for 3 months with nontoxic concentrations of the chemopreventive agents oltipraz, difluoromethylornithine, tamoxifen, and retinoic acid or with two different telomerase inhibitors. The frequency of spontaneous immortalization of LFS-derived cells was estimated by an approach based on fluctuation analyses. Statistical analyses were two-sided. RESULTS: The frequency of spontaneous immortalization events of LFS-derived breast epithelial cells was reduced by long-term treatment with retinoic acid (P<0.001) or tamoxifen (P<0.05) compared with solvent-treated cells. The frequency of immortalization was also reduced by treating LFS-derived cells with an antitelomerase antisense oligonucleotide (P<0.001) or by inducing the cells to express a dominant negative mutant of telomerase (P<0.025) compared with cells treated with a control oligonucleotide or with empty vector, respectively. CONCLUSIONS: Treatment of preimmortal LFS breast epithelial cells with chemopreventive and antitelomerase agents decreased the frequency of spontaneous immortalization in vitro. These studies validate the application of a new cell culture model system to screen the effects of novel chemopreventive agents by use of cell immortalization as an end point. The results also suggest that the telomerase ribonucleoprotein complex may be an important molecular target for breast cancer prevention.

Chemopreventive agents inhibit aberrant proliferation of the aneuploid phenotype in a colon epithelial cell line established from Apc 1638N [+/-] mouse.

Loss of function of the adenomatous polyposis coli (APC) tumor suppressor gene predisposes for familial adenomatous polyposis (FAP) syndrome. The Apc gene knockout mice exhibit accelerated intestinal carcinogensis modifiable by diverse pharmacological agents. Present experiments utilized the Apc[+/-] 1638N COL colon epithelial cell line (origin: histologically normal colon) as the model. Retinoid receptor modulator 9-cis-retinoic acid (9-cis-RA), ornithine decarboxylase inhibitor difluoromethyl ornithine (DFMO), and nonselective cyclooxygenase inhibitor sulindac (SUL) represented the chemopreventive test compounds. Population doubling, cell cycle progression, and anchorage-independent growth provided mechanistic end points for chemopreventive efficacy. Treatment of 1638N COL cells with 9-cis-RA, DFMO and SUL produced a dose-dependent cytostatic growth arrest by decreasing the number of population doublings and altering aneuploid G0/G1:S+G2/M ratio. The clonally expanded 1638N-Cl1 cells selected for anchorage-independent growth exhibited decreased anchorage-independent colony formation in response to treatment with the three test compounds. Susceptibility of preneoplastic 1638N COL cells to mechanistically distinct chemopreventive agents validates a unique epithelial cell culture model for FAP syndrome, and facilitates investigations on Apc regulated colon carcinogenesis and cancer prevention.

A quantitative angiogenesis model for efficacy testing of chemopreventive agents.

One of the approaches in chemoprevention to prevent or delay the progression of precancerous lesions, is to apply chemopreventive agents that can potentially block angiogenesis. A quantitative in vivo angiogenesis inhibition assay was developed to test the efficacy of twelve chemopreventive agents that represent different chemical classes and multiple biological activities, using the chick chorioallantoic membrane (CAM) model and an oncogene-transfected angiogenic cell line (6 Ti ras/SV myc # 4). These tumorigenic cells held by a primary agarose pellet, were placed alone or with a secondary pellet incorporating five concentrations of the test agent, on an exposed CAM of 7-day-old chick embryo for 72 hours in a humidified chamber at 35 degrees C. The cell-induced angiogenic blood vessels, including the microvessels radiating from the cell pellet focal area, were scored using a computerized custom image analysis system. The results show that nonsteroidal antiinflammatory drugs (NSAIDS); aspirin, sulindac, sulindac sulfide and sulindac sulfone, were effective inhibitors of cell-induced angiogenesis (23-66%). Aspirin displayed a dose-dependent response with the highest inhibition at 300 microM and an EC50 (the effective molar concentration that inhibits angiogenesis by 50%) of 26 microM. Sulindac sulfone was more effective than sulindac with an EC50 of 5 microM versus 85 microM. However, sulindac sulfide showed an intermediate response with an EC50 of 41 microM. The retinoids; all-trans-retinoic acid (ATRA), 9-cis-retinoic acid (9-cis-RA), and 13-cis-retinoic acid (13-cis-RA) were also highly effective inhibitors of cell-mediated CAM-angiogenesis. 13-cis-RA with an EC50 of 3.6 nM, has been the most efficacious test agent. > 400-fold more effective than 9-cis-RA (1.5 microM). ATRA exhibited an intermediate response between 9-cis-RA and 13-cis-RA with an EC50 of 0.3 microM, and was 100-fold more efficacious than 9-cis-RA. However, the synthetic retinoid, N-(4-hydroxyphenyl) retinamide (4-HPR), was not an effective inhibitor of CAM angiogenesis. Thalidomide, a compound with multiple biological activities, exhibited dose-dependent inhibition ranging from 10-1000 microM with an EC50 of 19 microM. Other agents that exhibited dose-dependent inhibition included Bowman-Birk inhibitor (BBI), EC50: 10 microg/ml, tamoxifen, EC50, 0.05 microM and difluoromethyl omithine (DFMO), with an EC50 of 13 microM. These results suggest that tumor-associated angiogenesis can be modulated by non-toxic concentrations of chemopreventive agents representing multiple biological activities and multiple targets.

Potential use of lipoxygenase inhibitors for cancer chemoprevention.

Increasing evidence suggests that lipoxygenase (LO)-catalysed metabolites have a profound influence on the development and progression of human cancers. Compared with normal tissues, significantly elevated levels of LO products have been found in breast tumours, colon cancers, lung, skin and prostate cancers, as well as in cells from patients with both acute and chronic leukaemias. LO-mediated products elicit diverse biological activities needed for neoplastic cell growth, influencing growth factor and transcription factor activation, oncogene induction, stimulation of tumour cell adhesion and regulation of apoptotic cell death. Agents that block LO catalytic activity may be effective in preventing cancer by interfering with signalling events needed for tumour growth. In the past ten years, pharmaceuticals agents that specifically inhibit the 5-LO metabolic pathway have been developed to treat inflammatory diseases such as asthma, arthritis and psoriasis. Some of these compounds possess anti-oxidant properties and may be effective in preventing cancer by blocking free radical-induced genetic damage or by preventing the metabolic activation of carcinogens. Other compounds may work by negatively modulating DNA synthesis. Pharmacological profiles of potential chemopreventive agents are compiled from enzyme assays, in vitro testing (e.g., cell proliferation inhibition in human cancer cells) and in vivo animal carcinogenesis models (e.g., N-methyl-N-nitrosourea-induced rat mammary cancer, benzo(a)pyrene-induced lung tumours in strain A/J mice and hormone-induced prostate tumours in rats). In this way, compounds are identified for chemoprevention trials in human subjects. Based on currently available data, it is expected that the prevention of lung and prostate cancer will be initially studied in human trials of LO inhibitors.

Progress in cancer chemoprevention: development of diet-derived chemopreventive agents.

Because of their safety and the fact that they are not perceived as "medicine," food-derived products are highly interesting for development as chemopreventive agents that may find widespread, long-term use in populations at normal risk. Numerous diet-derived agents are included among the >40 promising agents and agent combinations that are being evaluated clinically as chemopreventive agents for major cancer targets including breast, prostate, colon and lung. Examples include green and black tea polyphenols, soy isoflavones, Bowman-Birk soy protease inhibitor, curcumin, phenethyl isothiocyanate, sulforaphane, lycopene, indole-3-carbinol, perillyl alcohol, vitamin D, vitamin E, selenium and calcium. Many food-derived agents are extracts, containing multiple compounds or classes of compounds. For developing such agents, the National Cancer Institute (NCI) has advocated codevelopment of a single or a few putative active compounds that are contained in the food-derived agent. The active compounds provide mechanistic and pharmacologic data that may be used to characterize the chemopreventive potential of the extract, and these compounds may find use as chemopreventives in higher risk subjects (patients with precancers or previous cancers). Other critical aspects to developing the food-derived products are careful analysis and definition of the extract to ensure reproducibility (e.g., growth conditions, chromatographic characteristics or composition), and basic science studies to confirm epidemiologic findings associating the food product with cancer prevention.

Lipoxygenase inhibitors as potential cancer chemopreventives.

Mounting evidence suggests that lipoxygenase (LO)-catalyzed products have a profound influence on the development and progression of human cancers. Compared with normal tissues, significantly elevated levels of LO metabolites have been found in lung, prostate, breast, colon, and skin cancer cells, as well as in cells from patients with both acute and chronic leukemias. LO-mediated products elicit diverse biological activities needed for neoplastic cell growth, influencing growth factor and transcription factor activation, oncogene induction, stimulation of tumor cell adhesion, and regulation of apoptotic cell death. Agents that block LO-catalyzed activity may be effective in preventing cancer by interfering with signaling events needed for tumor growth. In fact, in a few studies, LO inhibitors have prevented carcinogen-induced lung adenomas and rat mammary gland cancers. During the past 10 years, pharmacological agents that specifically inhibit the LO-mediated signaling pathways are now commercially available to treat inflammatory diseases such as asthma, arthritis, and psoriasis. These well-characterized agents, representing two general drug effect mechanisms, are considered good candidates for clinical chemoprevention studies. One mechanism is inhibition of LO activity (5-LO and associated enzymes, or 12-LO); the second is leukotriene receptor antagonism. Although the receptor antagonists have high potential in treating asthma and other diseases where drug effects are clearly mediated by the leukotriene receptors, enzyme activity inhibitors may be better candidates for chemopreventive intervention, because inhibition of these enzymes directly reduces fatty acid metabolite production, with concomitant damping of the associated inflammatory, proliferative, and metastatic activities that contribute to carcinogenesis. However, because receptor antagonists have aerosol formulations and possible antiproliferative activity, they may also have potential, particularly in the lung, where topical application of such formulations is feasible.

Progress in cancer chemoprevention.

More than 40 promising agents and agent combinations are being evaluated clinically as chemopreventive drugs for major cancer targets. A few have been in vanguard, large-scale intervention trials--for example, the studies of tamoxifen and fenretinide in breast, 13-cis-retinoic acid in head and neck, vitamin E and selenium in prostate, and calcium in colon. These and other agents are currently in phase II chemoprevention trials to establish the scope of their chemopreventive efficacy and to develop intermediate biomarkers as surrogate end points for cancer incidence in future studies. In this group are fenretinide, 2-difluoromethylornithine, and oltipraz. Nonsteroidal anti-inflammatories (NSAID) are also in this group because of their colon cancer chemopreventive effects in clinical intervention, epidemiological, and animal studies. New agents are continually considered for development as chemopreventive drugs. Preventive strategies with antiandrogens are evolving for prostate cancer. Anti-inflammatories that selectively inhibit inducible cyclooxygenase (COX)-2 are being investigated in colon as alternatives to the NSAID, which inhibit both COX-1 and COX-2 and derive their toxicity from COX-1 inhibition. Newer retinoids with reduced toxicity, increased efficacy, or both (e.g., 9-cis-retinoic acid) are being investigated. Promising chemopreventive drugs are also being developed from dietary substances (e.g., green and black tea polyphenols, soy isoflavones, curcumin, phenethyl isothiocyanate, sulforaphane, lycopene, indole-3-carbinol, perillyl alcohol). Basic and translational research necessary to progress in chemopreventive agent development includes, for example, (1) molecular and genomic biomarkers that can be used for risk assessment and as surrogate end points in clinical studies, (2) animal carcinogenesis models that mimic human disease (including transgenic and gene knockout mice), and (3) novel agent treatment regimens (e.g., local delivery to cancer targets, agent combinations, and pharmacodynamically guided dosing).

Differentiation of human fibroblasts to tissue macrophages by the Snyder-Theilen feline sarcoma virus (ST:FeSV): growth modulation of human tumor cell lines in agar.

BACKGROUND: Snyder-Theilen feline sarcoma virus (ST:FeSV)-transduced human fibroblasts differentiate into tissue macrophages(1-9). The ST:FeSV-induced macrophages demonstrate macrophage-mediated cytotoxicity (MTC) and antibody-dependent cellular cytotoxicity (ADCC), including growth modulation of tumor cells in agar (3,4,6). MATERIALS AND METHODS: Here we tested the effects of ST:FeSV-induced macrophages in agar on the following human tumor cell lines: colon adenocarcinoma, prostate adenocarcinoma, breast adenocarcinoma, malignant melanoma, leiomyosarcoma, fibrosarcoma, and fibrous histiocytoma. The tumor cells were co-incubated in agar with ST:FeSV-induced macrophages in the absence or presence of 10% fetal bovine serum (FBS). RESULTS: Regardless of serum conditions, the growth of all tumor cells tested was inhibited considerably by the ST:FeSV-induced macrophages. Colon adenocarcinoma cells were the least affected, and fibrosarcoma or fibrous histiocytoma cells were the most sensitive to growth inhibition by the ST:FeSV-induced macrophages. A notable exception was the growth stimulation of breast adenocarcinoma (BT-20; MCF-7), and of prostate adenocarcinoma (TSU-prl) tumor cell lines by the ST:FeSV-induced macrophages in the absence of FBS. CONCLUSIONS: The results attest to the potency of secreted proteins that are expressed by ST:FeSVinduced macrophages which can modulate tumor cell growth in agar. The results further indicate that serum is likely to have an impact on the effects of these growth regulatory factors on human tumor cells.

Absence of germline mutations in exons 5-9 of the p53 gene in patients with Li-Fraumeni-like (SBLA) and familial adenomatous polyposis heritable cancer syndromes.

Although acquired mutations in the human p53 gene occur in many tumor types, germline mutations are rare. An exception is the occurrence of germline p53 mutations in a fraction of families afflicted with the Li-Fraumeni syndrome (LFS). Previous studies from our laboratory demonstrated increased levels of wild type p53 protein in skin fibroblasts (SF) of patients from heritable cancer syndrome, including familial adenomatous polyposis (FAP), neurofibromatosis type 1 (NF1), and bilateral retinoblastoma (bRB) (Kopelovich and DeLeo, 1984,1986). Here, we further address the association between germline p53 alterations and genetic predisposition to cancer in the SBLA syndrome and in FAP. DNA sequencing and single-stranded conformational polymorphism analysis (SSCP) were utilized to screen for the presence of mutations within exons 5-9 of the p53 gene in SF and in benign tumors. Thus we observed no germline mutations in exons 5-9 of the p53 gene in SF from SBLA or FAP patients, including the Gardner variant. In addition, we observed no acquired mutations in exons 5-9 of the p53 gene in benign tumors from FAP patients. In conclusion, we found no association between germline p53 mutations and SBLA or FAP. How mechanisms that involve nonmutational activation of the p53 protein might affect genetic predisposition to cancer remains to be established.

Differentiation of human fibroblasts to tissue macrophages by the Snyder-Theilen feline sarcoma virus (ST:FeSV).

We have previously reported the conversion of human fibroblasts (HF) to tissue macrophages (TM) by transduction with the Snyder-Theilen feline sarcoma virus [ST:FeSV(FeLV)]. Here, we have demonstrated macrophage mediated tumor cytotoxicity (MTC) of human teratocarcinoma cells (NTERA-2) by ST:FeSV-induced TM. Inclusion of the NTERA-2 specific antibody (SSEA-4), substantially increased antibody-dependent cellular cytotoxicity (ADCC) of the tumor cells by ST:FeSV-induced TM. Tumor cell lysis by ST:FeSV-induced TM through either MTC or ADCC was especially effective at low serum concentrations (1%). The presence of cytokines during co-incubation, M-CSF in particular, enhanced the lysis of NTERA-2 cells by ST:FeSV-induced TM. Whereas pretreatment of the NTEBA-2 cells with all-trans retinoic acid (AtRA) enhanced MTC-induced lysis, it abrogated ADCC-induced lysis of the tumor cells by ST:FeSV-induced TM. Significantly, the co-incubation of NTERA-2 cells with ST:FeSV-induced TM in agar, resulted in a considerable stimulation of growth of untreated and TPA-pretreated NTERA-2 cells. In contrast, the growth of AtRA-pretreated NTERA-2 cells in agar was completely inhibited by ST:FeSV-induced TM. These results indicate that ST:FeSV-induced TM can produce potent growth-modulating cytokines, and that AtRA can modify their antitumor activity in monolayer cultures and in agar. The effects by AtRA, serum, and growth conditions (whether monolayers or agar) point to several levels of complexity regarding the interaction of tissue macrophages with tumor cells.