fenretinide and Cell-Transformation--Neoplastic

N-(4-hydroxyphenyl) retinamide (4HPR, fenretinide) is a synthetic retinoid that has been tested in clinical trials as a cancer therapeutic and chemopreventive agent. Although 4HPR has been shown to be cytotoxic to many kinds of cancer cells, the underlying molecular mechanisms are only partially understood. Until now, no direct cancer-related molecular target has been reported to be involved in the antitumor activities of 4HPR. Herein, we found that 4HPR inhibited mammalian target of rapamycin (mTOR) kinase activity by directly binding with mTOR, which suppressed the activities of both the mTORC1 and the mTORC2 complexes. The predicted binding mode of 4HPR with mTOR was based on a homology computer model, which showed that 4HPR could bind in the ATP-binding pocket of the mTOR protein through hydrogen bonds and hydrophobic interactions. In vitro studies also showed that 4HPR attenuated mTOR downstream signaling in a panel of non-small-cell lung cancer cells, resulting in growth inhibition. Moreover, knockdown of mTOR in cancer cells decreased their sensitivity to 4HPR. Results of an in vivo study demonstrated that i.p. injection of 4HPR in A549 lung tumor-bearing mice effectively suppressed cancer growth. The expression of mTOR downstream signaling molecules in tumor tissues was also decreased after 4HPR treatment. Taken together, our results are the first to identify mTOR as a direct antitumor target of 4HPR both in vitro and in vivo, providing a valuable rationale for guiding the clinical uses of 4HPR.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Cell Transformation, Neoplastic; Epidermal Growth Factor; Fenretinide; Humans; Mechanistic Target of Rapamycin Complex 1; Mice; Multiprotein Complexes; Proteins; Signal Transduction; TOR Serine-Threonine Kinases; Transcription Factors; Xenograft Model Antitumor Assays

In a previous study, we demonstrated that the anticancer synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) redox cycles at the mitochondrial enzyme dihydroorotate dehydrogenase to trigger anomalous reactive oxygen species (ROS) production and attendant apoptosis in transformed human epithelial cells. Furthermore, we speculated that the hydroxyl functional group of 4HPR was required for this pro-oxidant property. In this study, we investigated the role of the hydroxyl functional group in the in vitro cytotoxicity of 4HPR. Using 4HPR, its primary in vivo metabolite N-(4-methoxyphenyl)retinamide (4MPR), and the synthetic derivative N-(4-trifluoromethylphenyl)retinamide (4TPR), we examined the pro-oxidant and apoptotic effects, as well as the cellular uptake, of these three N-(4-substituted-phenyl)retinamides in premalignant and malignant human skin, prostate, and breast epithelial cells. Compared to 4HPR, both 4MPR and 4TPR were ineffective in promoting conspicuous cellular ROS production, mitochondrial disruption, or DNA fragmentation in these transformed cells. Interestingly, both 4MPR and 4TPR were not particularly cell permeative relative to 4HPR in skin or breast epithelial cells, which implied an additional role for the hydroxyl functional group in the cellular uptake of 4HPR. Moreover, the short-term uptake of 4HPR was directly proportional to cell size, but this characteristic, in obvious contrast to cellular bioenergetic status and/or dihydroorotate dehydrogenase expression, was not fundamentally influential in the overall sensitivity to the promotion of cellular ROS production and apoptosis induction by this agent. Together, these results strongly implicate the hydroxyl functional group in the cytotoxic effects of 4HPR.

Topics: Antineoplastic Agents; Apoptosis; Cell Line, Transformed; Cell Line, Tumor; Cell Shape; Cell Transformation, Neoplastic; Dihydroorotate Dehydrogenase; DNA Fragmentation; Electron Transport Complex IV; Epithelial Cells; Fenretinide; Humans; Hydroxides; Mitochondria; Oxidoreductases Acting on CH-CH Group Donors; Permeability; Reactive Oxygen Species; Tretinoin

Cell-cycle deregulation is an early event of hepatocarcinogenesis. We evaluated the role of changes in activity of nuclear factor kappaB (NF-kappaB) and some related pathways in this alteration, and the interference of N-(4-hydroxyphenyl)retinamide (HPR), a retinoid chemopreventive for various cancer types, with these molecular mechanisms and the evolution of preneoplastic liver to cancer. Male F344 rats, initiated according to the 'resistant hepatocyte' model of liver carcinogenesis, received weekly 840 nmol of liposomal HPR (SL-HPR)/100 g body wt or empty liposomes, between 5 and 25 weeks after initiation. Inhibition of DNA synthesis and induction of apoptosis occurred in pre-cancerous lesions, 7-147 days after starting SL-HPR, and a decrease in carcinoma incidence and multiplicity was observed 25 weeks after arresting treatment. An increase in NF-kappaB expression and binding activity, and under-expression of the inhibitor kappaB-alpha (IkappaB-alpha) were found in preneoplastic liver and neoplastic nodules, 5 and 25 weeks after initiation, respectively. These lesions also showed low expression of Mat1A and low activity of methionine adenosyltransferase I/III, whose reaction product, S-adenosyl-l-methionine, enhances IkappaB-alpha expression. SL-HPR prevented these changes and induced a decrease in expression of iNos, c-myc, cyclin D1 and Vegf-A genes, that were over-expressed in preneoplastic liver and nodules, and a decrease in Bcl-2/Bax, Bcl-2/Bad and Bcl-xL/Bax mRNA ratios with respect to the lesions of control rats. Liposomes alone did not influence the parameters tested. These results indicate that signal transduction pathways controlled by NF-kappaB, nitric oxide and S-adenosyl-l-methionine are deregulated in pre-cancerous lesions. Recovery from these alterations by SL-HPR is associated with chemoprevention of hepatocarcinogenesis. Overall, these studies elucidate some molecular changes, in early stages of hepatocarcinogenesis, and underline their pathogenetic role. Moreover, they demonstrate a partially new mechanism of HPR chemopreventive effect and indicate the potential clinical relevance of this compound for prevention of hepatocellular carcinoma.

Topics: Animals; Antineoplastic Agents; Apoptosis; Cell Transformation, Neoplastic; Cyclin D1; Fenretinide; I-kappa B Proteins; Liposomes; Liver; Liver Neoplasms; Male; Methionine Adenosyltransferase; NF-KappaB Inhibitor alpha; NF-kappaB-Inducing Kinase; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-myc; Rats; Rats, Inbred F344; S-Adenosylmethionine; Vascular Endothelial Growth Factor A

Squamous cell carcinoma (SCC) is the most prevalent form of epithelial cancer. SCC results when normal epithelial cells undergo multiple neoplastic changes that culminate in the evolution of an invasive cancer. Retinoids are commonly used as chemopreventive and treatment agents in skin cancer; however, SCC progression is accompanied by a gradual loss of retinoid responsiveness. The synthetic retinoid N-(4-hydroxyphenyl)retinamide (HPR) has shown promising anti-neoplastic activity in a variety of tumor cells, including those that are resistant to all-trans retinoic acid (t-RA). We investigated the effect of HPR on growth and apoptosis of squamous cells at different stages of carcinogenesis. We then determined if retinoic acid receptor (RAR) overexpression affected the outcome of HPR treatment. To model SCC malignant progression, we used a panel of murine keratinocytes representing different stages of squamous cell carcinogenesis. This panel consisted of primary keratinocytes, SP1 and 308 papilloma cell lines, the PAM-212 squamous carcinoma cell line, and the spindle I7 cell line. With the exception of the primary keratinocytes, all cells were unresponsive to t-RA treatment. Pharmacological concentrations of HPR were non-cytotoxic to all keratinocytes tested and HPR sensitivity was stage-dependent, with the papilloma cell lines being the most sensitive, and the spindle cells being the most resistant. Overexpression of RARgamma in SP1 papilloma cells enhanced growth suppression and apoptosis induction by HPR. HPR-induced growth suppression was accompanied by a simultaneous block in the G(1) phase of the cell cycle in RAR-transduced and control SP1 cells and differential regulation of cell cycle and apoptotic mediators.

Topics: Animals; Antineoplastic Agents; Apoptosis; Benzimidazoles; Carcinoma, Squamous Cell; Cell Division; Cell Transformation, Neoplastic; Cells, Cultured; Fenretinide; G1 Phase; Keratinocytes; Mice; Mice, Inbred BALB C; Neoplasm Staging; Nevus, Spindle Cell; Papilloma; Propidium; Receptors, Retinoic Acid; Ribonucleases; Tretinoin

The development of prostate cancer through a multistep process of carcinogenesis may have a long latent period of 20-30 years. It is possible that progression to a malignant state could be blocked or reversed during this time. This study focuses on the ability of the synthetic retinoid, N-(4-hydroxyphenyl)-retinamide (4-HPR), to reverse changes associated with malignant transformation and tumor progression, towards a normal phenotype. To examine the responsiveness of cells at different steps of prostate carcinogenesis, three immortalized, but non-tumorigenic (RWPE-1, WPE1-7 and WPE1-10), and one human prostate carcinoma cell line (DU-145), were used. The effects of 4-HPR on cell proliferation, expression of intermediate filament proteins cytokeratin 18 and vimentin, and tumor suppressor proteins p53 and pRb were examined by immunostaining and compared. Results show that 4-HPR caused inhibition of growth in all cell lines in a dose-dependent manner. 4-HPR induced an increase in staining for cytokeratin 18, a marker of differentiation for prostate epithelial cells. While all cell lines showed strong immunostaining for vimentin, treatment with 4-HPR for 8 days caused a marked decrease in staining for vimentin in all cell lines. In an in vitro assay, 4-HPR also caused inhibition of invasion by DU-145 cells in a dose-dependent manner. Furthermore, 4-HPR treatment was effective in significantly decreasing the abnormal nuclear staining for the tumor suppressor proteins p53 and pRb. Because 4-HPR decreased invasion-associated vimentin expression, inhibited invasion, and normalized p53 and pRb immunostaining, we propose that 4-HPR may be an effective agent for secondary and tertiary prevention, i.e. promotion and progression stages, respectively, of prostate cancer.

Topics: Anticarcinogenic Agents; Cell Count; Cell Division; Cell Line, Transformed; Cell Transformation, Neoplastic; Dose-Response Relationship, Drug; Fenretinide; Humans; Immunoenzyme Techniques; Keratins; Male; Neoplasm Invasiveness; Phenotype; Prostate; Prostatic Neoplasms; Retinoblastoma Protein; Tumor Cells, Cultured; Tumor Suppressor Protein p53; Vimentin

Precancerous lesion is one of most important steps in tumorigenesis. It has been shown that retinoids have reliable effects on controlling many kinds of animal tumor and malignant tumor cell lines in vitro, but there is no laboratory report on the biological effect of retinoids on the precancerous lesion of human lung cancer. In this study the methods including of cell serum-free culture, precancerous model of human bronchial epithelium reconstructed in rat trachea/xenotransplanted in nude mice, flowcytometry, immunohistochemistry, TUNEL and pathological observation have been used to study the biological effects of N-(4-hydroxylphenol) retinamide (4-HPR), one new kind of retinoids, on transformed human bronchial epithelial cells in vitro and premalignant human bronchial epithelium in vivo. The results showed that in the study in vitro, the proliferation of transformed human bronchial epithelial cells, the ratio of cells in S phase, and the percentage of cells that positively react to antibody Ki-67 and mpm-2 were inhibited, but apoptotic cells were induced significantly by 4-HPR exposure. At the experiment in vivo, both growth rates and precancerous grades of the reconstructed human bronchial epithelium were reduced, and apoptotic cells were also observed in epithelium after 4-HPR treatment. The results suggested that 4-HPR is one of hopeful chemopreventive medicines to lung cancer.

Topics: Adult; Animals; Anticarcinogenic Agents; Bronchi; Cell Division; Cell Transformation, Neoplastic; Cells, Cultured; Epithelial Cells; Female; Fenretinide; Humans; Male; Mice; Mice, Inbred BALB C; Precancerous Conditions

A clinical trial of N-[4-hydroxyphenyl]retinamide (4-HPR) has been in progress for the past 4 years to evaluate its role in chemoprevention of breast cancer. However, it is currently not known whether the effect of 4-HPR in breast cells is mediated by 4-HPR directly or through one of its metabolites. In this report, we investigated in vivo and in vitro effects of 4-HPR on three different breast carcinoma cells and two different melanoma cell lines. In vitro, the growth of all three breast carcinoma cell lines was inhibited by 4-HPR. Only one of two melanoma cell lines (UISO-Mel-1) showed growth inhibition to 4-HPR. The cell lines sensitive to 4-HPR in vitro also showed inhibition to 4-HPR in a xenograft model. Dietary 4-HPR (0.5 mmol/kg diet) reduced the growth of UISO-BCA-1 xenografts in female athymic mice, but had no effect on UISO-Mel-6 xenografts. Metabolism investigations of the 4-HPR-sensitive and insensitive cell lines indicated that N-[4-methoxyphenyl]retinamide (4-MPR), the major metabolite of 4-HPR, was detected only in cells sensitive to 4-HPR. Further in vitro studies with 4-MPR suggested that it is not an active metabolite of 4-HPR as it failed to inhibit growth of 4-HPR-resistant UISO-Mel-6 cells, and showed no dose-dependent inhibition of 4-HPR-sensitive breast carcinoma and melanoma cell lines. Our results in the present study indicate that, although 4-MPR is not an active metabolite of 4-HPR, detection of this metabolite in the malignant cells may serve as an indirect biomarker to predict response of cells to 4-HPR.

Topics: Animals; Antineoplastic Agents; Biomarkers, Tumor; Breast Neoplasms; Cell Transformation, Neoplastic; Dietary Supplements; Female; Fenretinide; Humans; Melanoma; Mice; Mice, Nude; Neoplasm Transplantation; Skin Neoplasms; Tumor Cells, Cultured

Several epidemiological studies have implicated low dietary and serum levels of retinol with an increased risk for the development of human prostate cancer. In a recent report, dietary fenretinide [N-[(4-hydroxyphenyl)] retinamide], a synthetic retinoid with low toxicity, decreased the incidence of experimentally induced prostate cancer. Fenretinide is currently being evaluated in phase I and phase II clinical trials as an agent for both the treatment and chemoprevention of human prostate cancer. Because of these findings, we investigated whether dietary fenretinide could alter the incidence of phenotype of oncogene-induced prostate cancer in the mouse prostate reconstitution model system. When compared to control-fed animals, dietary fenretinide reduced the tumor incidence by 49% and the tumor mass by 52% of ras+myc-induced cancers in the mouse prostate reconstitution model system, which was modified to prolong the latency period before cancer development. Retinoids have a wide ranging effect on cellular differentiation, growth factor synthesis, and immune function. While its mechanism of action in this system remains unclear, fenretinide is an effective agent for the chemoprevention and growth modulation of oncogene-induced prostate cancer in the mouse prostate reconstitution model system and may be effective for the chemoprevention of human prostate cancer.

Topics: Animals; Anticarcinogenic Agents; Cell Transformation, Neoplastic; Diet; Fenretinide; Fetus; Genes, myc; Genes, ras; Genetic Vectors; Male; Mice; Mice, Inbred C57BL; Promoter Regions, Genetic; Prostate; Prostatic Neoplasms; Transfection

Twenty-eight compounds were screened for chemopreventive activity by using a rat tracheal epithelial cell transformation inhibition assay. In this new assay, chemicals were tested for their ability to inhibit the formation of transformed rat tracheal epithelial cell colonies which arise following exposure to the carcinogen benzo(a)pyrene. The 15 positive compounds were N-acetylcysteine, bismuththiol, calcium glucarate, (+/-) catechin, diallyl disulfide, glycaric acid, D-glucaro-1,4-lactone, N-(4-hydroxyphenyl)retinamide, D-limonene, mesna, retinoic acid, rutin, quercetin, silymarin, and taurine. In examining the nature of compounds that inhibited rat tracheal epithelial cell transformation, several possible chemopreventive mechanisms appeared to be predominant: compounds that were positive (a) increased glutathione levels or enhanced conjugation; (b) increased cytochrome P-450 activity; (c) displayed nucleophilic activity; or (d) induced differentiation. Thirteen compounds were negative in the rat tracheal epithelial transformation inhibition assay: crocetin, difluoromethylornithine, ellagic acid, esculetin, enoxalone, ibuprofen, levamisole, nordihydroguaiaretic acid, L-2-oxothiazolidine-4-carboxylate, piroxicam, sodium butyrate, D-alpha-tocopherol acetate, and polyethylene glycol 400. It was evident from these results that this assay would not detect compounds that were (a) anti-promoting in nature; (b) glutathione inhibitors; (c) differentiation inhibitors; (d) O6-methylguanine inhibitors; (e) organ specific; or (f) inactive. The rat tracheal epithelial cell transformation inhibition assay appeared to identify chemopreventive compounds that act at early stages of the carcinogenic process.

Topics: Animals; Antineoplastic Agents; Cell Transformation, Neoplastic; DNA Damage; Epithelium; Fenretinide; Glucaric Acid; In Vitro Techniques; Quercetin; Rats; Trachea; Tretinoin; Vitamin E

The purpose of the present studies was to determine the influence of the chemopreventive agents selenium, 4-(hydroxyphenyl)-retinamide (4-HPR) and beta-carotene, on functional differentiation (lactogenesis) of the mouse mammary gland cells. The hormone-induced expression of the milk-protein genes, beta-casein, epsilon-casein and the whey acidic protein (WAP) was used as molecular marker of differentiation of the mammary cells in organ culture medium containing insulin, prolactin, aldosterone and hydrocortisone. Quantitative determination of the cellular concentration of the respective mRNA was ascertained by molecular hybridization of RNA to the specific cloned cDNA probes using both the solution and the filter hybridization methods. Selenium at 100 nm concentration caused a pronounced inhibition of accumulation of the respective mRNAs. The retinoid, 4-HPR, also caused a dose-dependent inhibition of expression of these mRNA sequences. In contrast, concentrations of the 3 mRNAs in beta-carotene-treated glands remained similar to those observed in glands cultured in medium containing the hormones and hexane (the latter being the solvent for beta-carotene). The significant antagonistic action of selenium and 4-HPR, however, was reversible after removal of the chemicals from the culture medium. Thus, among the 3 chemicals tested, selenium and retinoid can cause an adverse effect on functional differentiation (lactogenesis) of the mammary cells. This inhibitory effect, however, was reversible. beta-Carotene, on the other hand, caused no apparent antagonistic effect on expression of the milk-protein genes in the isolated whole mammary organ in culture.

Topics: Actins; Animals; beta Carotene; Carotenoids; Cell Transformation, Neoplastic; Female; Fenretinide; Hormones; In Vitro Techniques; Mammary Glands, Animal; Mice; Milk Proteins; RNA, Messenger; Selenium; Tretinoin

Present studies in the mammary epithelial cell transformation model in organ culture showed that presence of beta-carotene during the 24 hr treatment (initiation stage) of the glands with the carcinogens, 7,12-dimethylbenz[a]anthracene (DMBA), N-nitrosodiethylamine (DENA) and N-methylnitrosourea (MNU), caused a highly significant (P less than 0.001-0.01) reduction of SCE induced by the same carcinogens. In contrast, 4-hydroxyphenyl retinamide (4-HPR) which is known to act at the promotional stage of carcinogenesis did not show any significant reduction of SCE. Thus findings suggest that beta-carotene can modify the DNA damaging effect of the carcinogens and thereby may also prevent the initiation of the carcinogenic process.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; beta Carotene; Carcinogens; Carotenoids; Cell Transformation, Neoplastic; Diethylnitrosamine; Female; Fenretinide; Mammary Glands, Animal; Methylnitrosourea; Mice; Organ Culture Techniques; Retinoids; Sister Chromatid Exchange; Tretinoin

The effects of N-(4-hydroxyphenyl)retinamide (HPR), a synthetic analogue of vitamin A, on cell morphology, cell cycle kinetics, cytoplasmic matrix, and expression of murine mammary tumor virus (MuMTV) in MuMTV-infected murine mammary tumor cells (GR-3A) were determined. Cellular uptake of HPR was rapid and linear, with zero-order kinetics, during the first 30 minutes of incubation. Flow cytometric analysis of cells treated with nontoxic levels of HPR (10 microM) for 48 hours revealed a reduction in percent cells in the DNA synthetic (S) phase of the cell cycle with a concomitant increase in percent cells in the G1 phase of the cell cycle. Dexamethasone-stimulated MuMTV expression was not affected after 48 hours of HPR exposure, whereas the virus expression was significantly reduced in cells treated with HPR for seven days. The reduction in MuMTV expression was preceded by changes in cell morphology (decreased cell-cell contact and reduced cell flattening) and altered F-actin aggregation. Continuous exposure to HPR (10 microM) for 14 days resulted in reduced cell proliferation rates and decreased cell plating efficiency of GR-3A cells. Taken together, these results indicate that HPR is rapidly incorporated into GR-3A cells and that the effects of HPR on cell profileration, cytoskeletal organization, and cell morphology appear to precede the effects of this retinoid on the expression of the etiological agent of murine mammary tumorigenesis, MuMTV.

Topics: Actin Cytoskeleton; Actins; Animals; Cell Cycle; Cell Division; Cell Line; Cell Survival; Cell Transformation, Neoplastic; Female; Fenretinide; Mammary Neoplasms, Experimental; Mammary Tumor Virus, Mouse; Mice; Microscopy, Electron, Scanning; Tretinoin

The ability of N-nitrosodiethylamine (DENA) to induce transformation of the mammary cells was studied in culture of the whole mammary organ from BALB/c female mice. Incidence of nodule-like alveolar lesions (NLAL) in the glands in vitro has been as a measure of transformation. NLALs are analogous to the precancerous hyperplastic alveolar nodules (HAN) of mouse mammary gland in vivo. The mammary glands were treated with graded concentrations (0.1-2.5 microgram/ml) of DENA during lobuloalveolar morphogenesis in medium (Waymouth's MB752/1) containing insulin, prolactin, hydrocortisone and aldosterone. DENA treatment caused a dose-related increased occurrence of NLAL in the glands in vitro and concentration of 1.5 microgram/ml produced the highest incidence of 85%. The high incidence of NLAL was accompanied by a 3-fold increase of DNA repair activity in the DENA treated glands. Incubation of the glands for 6 days after DENA treatment in medium containing N-4-hydroxyphenyl)retinamide and the same hormone mixture caused 61% inhibition of NLAL incidence. The results indicate that DENA is capable of inducing a high level of transformation of the mammary epithelial cells in vitro and that this retinoid can inhibit expression of the transformed cells acting at the promotional level.

Topics: Animals; Cell Transformation, Neoplastic; Diethylnitrosamine; DNA Repair; Female; Fenretinide; Mammary Neoplasms, Experimental; Mice; Mice, Inbred BALB C; Nitrosamines; Organ Culture Techniques; Tretinoin

Influence of estrogen and progesterone on the inhibitory action of N-(4-hydroxyphenyl) retinamide (4-HPR) was examined during the promotional stage of 7,12-dimethylbenz[alpha]anthracene (DMBA) transformation of the epithelial cells in culture of the whole mammary organs of BALB/c mice. In medium containing insulin, prolactin, hydrocortisone, and aldosterone, 4-HPR caused 68% inhibition of transformation as determined by the presence of nodule-like alveolar structures in the glands exposed to DMBA in vitro. Addition of estrogen and progesterone to the medium reduced this pronounced inhibitory action of 4-HPR to only 15%. While the medium containing insulin, prolactin, growth hormone, estrogen and progesterone was highly conducive to DMBA transformation, 4-HPR inhibition of transformation was limited to only 21%. The antagonistic action of the ovarian steroid hormones was present also at the level of frequency of nodule-like alveolar lesions (NLAL) per gland. Although both ovarian hormones reduced the inhibitory action of 4-HPR, on mammary cell transformation, the antagonistic action of estrogen was noticeably more pronounced.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Benz(a)Anthracenes; Castration; Cell Transformation, Neoplastic; Estrogens; Female; Fenretinide; Hormones; Mammary Glands, Animal; Mammary Neoplasms, Experimental; Mice; Mice, Inbred BALB C; Organ Culture Techniques; Progesterone; Tretinoin

Various natural and synthetic retinoids have been studied for their activity in two biological systems: (a) their activity as inhibitors of methylcholanthrene-induced neoplastic transformation in the C3H/10T1/2 clone 8 mouse fibroblast line (System 1); and (b) their ability to increase the degree of adhesion of C3H/10T1/2 clone 8 cells to a plastic substrate (System 2). These activities were then compared with their known activity in maintaining epithelial differentiation (System 3). With the notable exception of retinoic acid and 13-cis-retinoic acid, which were inactive in Systems 1 and 2, an excellent correlation was observed between activities in Systems 1 and 3 for retinyl acetate, N-(4-hydroxyphenyl)retinamide, retinylidene dimedone, N-ethylretinamide, and N-benzoylretinylamine. Compounds shown to be inactive in System 1 had little or no activity in System 2. However, the ability of retinoids to cause increased adhesion could not be correlated with Systems 1 or 3 in all cases. For instance, retinyl acetate was highly active in Systems 1, 2, and 3, whereas retinylidene dimedone was highly active in Systems 1 and 3 but weakly active in System 2. Conversely, N-(4-hydroxyphenyl)retinylamide was highly active in Systems 1 and 3 but caused a decrease in System 2. The lack of activity of 3 but caused a decrease in System 2. The lack of activity of retinoic acid isomers in the C3H/10T1/2 clone 8 system is paradoxical and may provide important information on requirements for their activation and/or transport.

Topics: Amides; Animals; Cell Adhesion; Cell Line; Cell Transformation, Neoplastic; Diterpenes; Fenretinide; Isotretinoin; Methylcholanthrene; Mice; Neoplasms, Experimental; Retinoids; Retinyl Esters; Structure-Activity Relationship; Tretinoin; Vitamin A