A novel second-generation platinum derivative and evaluation of its anti-cancer potential

Abstract Cisplatin is the primary anti-cancer agent for the treatment of most solid tumors. However, platinum-based anti-cancer chemotherapy produces severe side effects due to its poor specificity. There are a broad interest and literature base for a novel mechanism of action on platinum derivatives. Additionally, combining cisplatin with histone deacetylase inhibitors (HDACi) such as 4-hydroxybenzoic acid derivatives showed promising results in treating solid tumors. Here we aimed to conjugate 4-hydroxybenzoic acid with platinum to obtain a novel platinum derivative that can overcome cisplatin resistance. Cis-4-hydroxyphenylplatinum(II)diamine compound was synthesized under mild conditions and characterized. Cytotoxicity assay was performed on SKOV3-Luc and A549-Luc cells. Hemocompatibility and serum protein binding analysis were performed. Treatment potential was evaluated in xenograft tumor models. Biodistribution was tested on tumor-bearing mice via Pt analysis in organs with ICP-MS, ex vivo. In this study, cis-4-hydroxyphenylplatinum (II) diamine was synthesized with a yield of 62%. The MTT assay on A549-Luc and SKOV3-Luc cell lines resulted in IC50 values of 17.82 and 7.81 µM, respectively. While tumor growth was continued in the control group, the tumor volume decreased in the treatment group. All results point to the conclusion that the new compound has the potential to treat solid tumors

Anticancer properties of phospholipase A2 fromDaboia siamensis venom on human skin melanoma cells

Phospholipase A2 (PLA2) is a major component of theDaboia siamensis venom, which is able to hydrolyse the membrane of various cells. For this reason, the activity of PLA2was investigated regarding its pharmaceutical properties. This study was conducted to explore the pharmacological properties of a PLA2from Daboia siamensis (dssPLA2) venom on human skin melanoma cell line (SK-MEL-28). Methods dssPLA2 was isolated by ion exchange and gel filtration columns. Various concentrations of dssPLA2were investigated for cytotoxic activity and inhibition of migration on SK-MEL-28 cells. Cell death analysis, mRNA expression levels of Notch I-III and BRAF V600E genes were also determined. Results dssPLA2 exhibited cytotoxicity on SK-MEL-28 for 24 and 72 h as compared with untreated cells. However, it had no toxic effects on CCD-1064sk cells under the same conditions. dssPLA2 (0.25 and 0.5 g/mL) induced 17.16 and 30.60 % of apoptosis, while activated 6.53 and 7.05 % of necrotic cells. dssPLA2 at 0.25, 0.5, 1 and 2 g/mL could inhibit migration on SK-MEL-28 cells for 24 h by 31.06, 41.66, 50 and 68.75 %, respectively. The action of dssPLA2 significantly reduced the levels of Notch I and BRAF V600E genes expression on SK-MEL-28 cells compared with untreated cells at 72 h. Conclusions This study indicates that dssPLA2 had potential effects of apoptosis, necrosis, cytotoxicity and inhibition of migration on SK-MEL-28 cells. dssPLA2 could possibly be a selective agent that targets cancer cells without affecting normal cells.

Prostate cancer prevention: agent development strategies.

Despite advances in surgery, radiation, and medical therapy over the past decade and the widespread adoption of PSA screening, prostate cancer continues to be the second leading cause of cancer death in men in the United States. Invasive cancer is the end result of carcinogenesis, a chronic process occurring over many years driven by genetic and epigenetic alterations. The protracted nature of this transformation to the malignant phenotype provides an opportunity to intervene pharmacologically to prevent, reverse, or delay carcinogenesis, i.e. chemoprevention. Herein, we describe the unique features of cancer prevention, as opposed to cancer treatment, agent development clinical trials, and provide a summary of the ongoing research in this field being supported by the National Cancer Institute.

Phytoestrogens and breast cancer prevention: possible mechanisms of action.

OBJECTIVE: Phytoestrogens display an array of pharmacologic properties, and in recent years investigation of their potential as anticancer agents has increased dramatically. In this article we review the published literature related to phytoestrogens and breast cancer as well as suggest the possible mechanisms that may underlie the relationship between phytoestrogens and breast cancer. DATA SOURCES: Electronic searches on phytoestrogens and breast cancer were performed on MEDLINE and EMBASE in June 2007. No date restriction was placed on the electronic search. DATA EXTRACTION: We focused on experimental data from published studies that examined the characteristics of phytoestrogens using in vivo or in vitro models. We also include human intervention studies in this review. DATA SYNTHESIS: We evaluated evidence regarding the possible mechanisms of phytoestrogen action. Discussions of these mechanisms were organized into those activities related to the estrogen receptor, cell growth and proliferation, tumor development, signaling pathways, and estrogen-metabolizing enzymes. CONCLUSIONS: We suggest that despite numerous investigations, the mechanisms of phytoestrogen action in breast cancer have yet to be elucidated. It remains uncertain whether these plant compounds are chemoprotective or whether they may produce adverse outcomes related to breast carcinogenesis.

Cucurbitane-type triterpenoids from the fruits of Momordica charantia and their cancer chemopreventive effects.

Thirteen cucurbitane-type triterpene glycosides, including eight new compounds named charantosides I (6), II (7), III (10), IV (11), V (12), VI (13), VII (16), and VIII (17), and five known compounds, 8, 9, 14, 15, and 18, were isolated from a methanol extract of the fruits of Japanese Momordica charantia. The structures of the new compounds were determined on the basis of spectroscopic methods. On evaluation of these triterpene glycosides and five other cucurbitane-type triterpenes, 1-5, also isolated from the extract of M. charantia fruits, for their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells, these compounds showed inhibitory effects on EBV-EA induction with IC(50) values of 200-409 mol ratio/32 pmol TPA. In addition, upon evaluation of compounds 1-5 for inhibitory effects against activation of (+/-)-(E)-methyl-2[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexemide (NOR 1), a nitrogen oxide (NO) donor, compounds 1-3 showed moderate inhibitory effects. Compounds 1 and 2 exhibited marked inhibitory effects in both 7,12-dimethylbenz[a]anthracene (DMBA)- and peroxynitrite (ONOO-; PN)-induced mouse skin carcinogenesis tests.

Acute, subchronic and chronic safety studies with genistein in rats.

Genistein is a phytoestrogen that occurs naturally in the diet, especially in soy based foods. There is wide spread interest in phytoestrogens as chemopreventive agents for a variety of diseases and cancers based on epidemiologic evidence. Although soy, and its constituents such as genistein, have been consumed at high levels in several Asian populations without apparent adverse effects, concern has been raised about potential adverse effects due to the estrogenic and other activities. Safety studies with genistein were conducted in the Wistar rat including two acute studies, two subchronic (4 weeks and 13 weeks) and a chronic 52-week dietary admix study. In the acute studies, genistein had a low order of toxicity. In the three repeated dose safety studies at doses up to 500 mg/kg/day, genistein was well tolerated. In all of the studies, decreased food consumption and body weight gain were observed at 500 mg/kg/day. The main hematological findings were decreased red blood cell parameters at 500 mg/kg/day with a compensatory increase in reticulocytes. For clinical chemistry, with the exception of a slight increase in gamma glutamyl transferase in male and female rats at the high dose, there were a number of other minor changes considered not toxicologically significant. At necropsy, there were relatively few macroscopic changes; in the 52-week study, dilation of the uterus with fluid at the high dose and cysts of the ovaries in treated animals were observed. Organ weight changes in male rats at the high dose of 500 mg/kg/day included increased kidney, spleen, adrenal and testes weights and for females included, increased liver, kidney, spleen, ovary and uterus weights. After 4 and 13 weeks of treatment with genistein, there were no treatment related histopathologic findings. After 26 and 52 weeks of treatment, histological changes were seen in the female reproductive organs (ovaries and uterus), and in males (epididymides and prostate), and bone, kidneys, heart, liver and spleen in both sexes. After 52 weeks of treatment of males, vacuolation of the epididymal epithelium at 500 mg/kg/day and inflammation of the prostate were recorded at a higher incidence at 50 and 500 mg/kg/day. In females, cytological changes in the uterus, squamous metaplasia at 50 and 500 mg/kg/day and hyperplasia at 500 mg/kg/day were observed. Furthermore, hydrometra of the uterus and findings in the vagina consisting of anestric or diestrus vaginal mucosa with vaginal mucification, hyperplastic epithelium and multifocal cystic degeneration were noted at 500 mg/kg/day. Atrophy of the ovaries increased in severity in animals at 50 and 500 mg/kg/day. Osteopetrosis (hyperostosis) was observed in male and female rats at 50 and 500 mg/kg/day along with a compensatory increase in extramedullary hemopoiesis in the spleen; females were more affected than males. Hepatocellular hypertrophy and minimal bile duct proliferation were recorded at a higher incidence in animals at 500 mg/kg/day. It is concluded that almost all of the treatment related findings in these studies are related to the estrogenic properties of genistein as a phytoestrogen and would be expected to occur with a compound with estrogenic activity. The hormonally related changes were considered to be functional in nature and thus not adverse effects. Most of the findings in these studies were limited to the high dose of 500 mg/kg/day and were reversible. The few findings observed at 50 mg/kg/day were relatively minor and in view of the functional (hormonally mediated) nature of the effects, were considered not adverse effects. The increased incidence of minimal bile duct proliferation and slightly increased gamma glutamyl transferase are indicative of a mild hepatic effect at the high dose of 500 mg/kg/day. The no observed adverse effect level (NOAEL) of genistein is considered to be 50 mg/kg/day based on the presence of mild hepatic effects at the high dose of 500 mg/kg/day. The no observed effect level (NOEL) is considered to be 5 mg/kg/day based on the hormonally induced functional changes at higher doses.

Genetic toxicity studies with genistein.

Genistein is a phytoestrogen that occurs naturally in the diet especially in soybeans and soy-based foods. Genistein and related phytoestrogens are of interest as chemopreventive agents for a variety of diseases and cancers based on epidemiologic evidence of reduced cancer rates in populations with a high intake of soy. Although soy and its constituents have been consumed at high levels in Asian populations without apparent adverse effects, concern has been raised of potential adverse effects due to estrogenic and other activities of the isoflavones. In these studies, genistein was evaluated for mutagenicity and clastogenicity in vitro in the S. typhimurium assay (Ames Test), the mouse lymphoma assay and in vivo in the micronucleus test in mice and rats. There was no evidence for a mutagenic effect in the in vitro S. typhimurium assay with and without metabolic activation (S9). In the in vitro mouse lymphoma assay, genistein increased resistant mutants with and without metabolic activation (S9), which were predominantly small colonies indicating that genistein acts as a clastogen. Three independent in vivo micronucleus tests were performed in Moro mice, RAIf rats and Wistar rats. MORO male and female mice were treated orally for 14 days at doses up to 20 mg/kg/day. RAIf and Wistar male and female rats were treated orally at doses up to 2000 mg/kg without an increase in micronuclei in treated mice or rats. It is concluded that genistein was not mutagenic in the S. typhimurium assay or mutagenic or clastogenic in vivo in the mouse and rat micronucleus test. In the mouse lymphoma assay, genistein induced an increase of predominantly small colonies indicating that genistein acts as a clastogen. This observation is in agreement with published data on the inhibitory action of genistein on topoisomerase II, which is known to lead to chromosomal damage with a threshold dose response.

Assessment of antioxidant / anticarcinogenic activity of plant extracts by a combination of molecular methods.

Cancer chemoprevention is considered to be a promising approach for cancer control, as it has been identified by both epidemiological and molecular studies that environmental factors are the major causes of cancer. Chemoprevention can be defined as the use of agents to prevent, inhibit or reverse the process of carcinogenesis. Several epidemiological studies have shown that fruits, vegetables and common beverages, as well as herbs and plants, are rich sources of chemopreventive compounds. In the present report, a battery of in vitro methods for the identification of chemopreventive agents are presented. These methods include: i) inhibition of bleomycin-induced mutations in Salmonella typhimurium TA102 cells, ii) inhibition of bleomycin-induced sister chromatid exchanges (SCEs) in human peripheral blood lymphocytes, iii) protection from mitomycin C-induced DNA strand breakage and iv) inhibition of topoisomerase I DNA relaxation. The first three methods are also used for the identification of agents which prevent reactive oxygen species (ROS)-mediated DNA damage.

Mouse models incorporating alterations in the major tumor suppressor genes P53 and P16: their use in screening for potential carcinogens, developing further relevant mouse models, and screening for potential chemopreventive and chemotherapetutic agents.

This review is primarily a follow up to an initial review on this subject that the authors published 4 years ago [Lubet et al., Exp Lung Res. 2000; 581-593]. The present review gives a brief discussion of certain background points and rationale for development of these specific models, which had been presented in greater detail in the earlier article. In that initial article the authors identified the potential use of mutant mice in screening for carcinogens as well as preventive or therapeutic agents, discussed the relevance of the dominant-negative P53 mutation, as contrasted with knockout P53 mice, and briefly discussed the pros and cons of mice with a germline mutation in tumor suppressor genes in developing mouse models. The primary objective of the present review is to describe more recent studies using mice the dominant-negative P53 mutation as well as to introduce studies with mice with a heterozygous knockout of the P16/Ink4A ARF locus.

TICAREX: Exposiciones laborales a agentes cancerígenos y plaguicidas en Costa Rica / TICAREX: occupational exposure to carcinogens and pesticides in Costa Rica

El sistema europeo de datos CAREX (CARcinogen Exposure) considera la fuerza laboral de un país agrupada en 55 sectores económicos según la Clasificación Internacional de Actividades Económicas de las Naciones Unidas, segunda revisión de 1968, y mediante la aplicación de proporciones de trabajadores expuestos a partir de datos generados en estudios de higiene industrial para 139 agentes carcinógenos, los convierte en fuerza laboral expuesta y número de trabajadores expuestos a agentes carcinogénicos, según rama de actividad. En este artículo se describe una modificación y extensión del sistema CAREX para calcular los números de trabajadores expuestos a agentes cancerígenos y plaguicidas en Costa Rica. Esta primera aplicación de CAREX fuera de Europa (TICAREX) fue realizada en Costa Rica, Centroamérica, para 27 agentes cancerígenos y 7 grupos de plaguicidas, considerados de interés para el país, realizando estimaciones por separado para mujeres y hombres. Los agentes cancerígenos más frecuentes a los que se expone la fuerza laboral de Costa Rica de 1.3 millones fueron la radiación solar (333,000 trabajadores), las emisiones de diesel (278,000), paraquat y diquat (175,000), el humo de tabaco ambiental (71,000), los compuestos de cromo hexavalente (55,000), el benceno (52,000), mancozeb, maneb y zineb (49,000), clorotalonil (38,000), el polvo de madera (32,000), el cuarzo (27,000), benomil (19,000), el plomo y sus compuestos inorgánicos (19,000), tetracloroetileno (18,000), y los compuestos aromáticos policíclicos (17,000). En los hombres, la distribución se mantuvo muy ajustada a los anteriores rangos, sin embargo en las mujeres, debido a su diferente distribución en los sectores, el formaldehído, el radón y el cloruro de metileno superaron a los plaguicidas, el cromo (VI), el polvo de madera y el cuarzo. La agricultura, la construcción, los servicios personales y domésticos, el transporte terrestre y acuático y los servicios asociados al transporte, la fabricación de productos cerámicos y similares, la manufactura de productos de madera, la minería, la silvicultura, la pesca, la fabricación de maquinaria y aparatos eléctricos, bares y restaurantes fueron sectores de donde las exposiciones son frecuentes. Una reducción drástica de exposiciones laborales y ambientales a estos agentes daría por resultado mejoras sustanciales en los niveles de salud pública y ocupacional. La vigilancia de las exposiciones laborales y de la salud en el trabajo son esenciales para el control de la contaminación y de las exposiciones a los agentes cancerígenos

The European data system CAREX takes the workforce of a country grouped into 55 economic sectors according to the International Economic Activity Classification of the United Nations, the second 1968 revision and through the application of proportions of workers exposed to 139 carcinogenic agents based on data from industrial hygiene studies, converting it into the total workforce exposed to carcinogens by sector. . In this article we describe a modification and extension of of the CAREX system in order to calculate the number of workers exposed to carcinogens in Costa Rica. It is the first use of CAREX outside Europe (TICAREX) in Costa Rica, Central America, for 27carcinogens and 7 groups of pesticides thought to be of interest for the country, with separate estimations for men and women. The most frequent agents of exposure for the 1.3 million workers of Costa Rica were solar radiation (333,000 workers); diesel exhaust (278,000); paraquat and diquat (175,000); environmental tobacco smoke (71,000); hexavalent chromium compounds (55,000); benzene (52,000); mancozeb, maneb and zineb (49,000); chlorothalonil (38,000); wood dust (32,000); quartz (27,000); benomyl (19,000); lead and its inorganic compounds (19,000); tetrachloroethylene (18,000); and polycyclic aromatic hydrocarbons (17,000). Owing to the different occupational distribution between the genders, exposures to formaldehyde, radon and methylene chloride were more frequent than pesticides, hexavalent chromium, wood dust, and quartz in women. Agriculture, construction, personal and domestic services, manufacture of wood products, mining, forestry, fishing, manufacture of electrical products, and bars and restaurants were sectors with frequent exposures. Substantial reduction of occupational and environmental exposures to these agents would significantly improve public and occupational health. Reduction of occupational exposures is usually also followed by improvement of environmental quality. Monitoring of exposures and health of workers and the general public is an essential element in the control of environmental contamination and human exposures

Semisynthesis of new sarcophine derivatives with chemopreventive activity.

The natural cembranolide sarcophine (3) and its lactone ring-opened analogue (10) were oxidized using selenium dioxide under different reaction temperatures to prepare hydroxylated derivatives. Nine new compounds were obtained, six of them targeted hydroxylated derivatives. The determination of regio- and stereochemistry as well as the mechanistic considerations on the selectivity observed in these reactions are discussed on the basis of 2D NMR and molecular modeling. In preliminary in vitro tests on inhibition of EBV-EA activation, compounds 10 and 12-15 have shown higher activity than the known chemopreventive agent sarcophytol A.

Modulation of heterocyclic amine-induced mutagenicity and carcinogenicity: an 'A-to-Z' guide to chemopreventive agents, promoters, and transgenic models.

A landmark report by Widmark in 1939 describing "cancer-producing substances in roasted food", and the seminal work of Sugimura and colleagues in the 1970s on the isolation of potent mutagens from cooked meat and fish stimulated a major international effort on the study of heterocyclic amines and their modulators. The latter term is used in its broadest context to mean agents or conditions that positively or negatively influence the mutagenic or carcinogenic activities of heterocyclic amines in vitro or in vivo. An 'A-to-Z' list of these modulators includes well over 150 natural or synthetic phytochemicals, micronutrients and antioxidants, as well as several large chemical classes (polyphenols, flavones, retinoids, porphyrins), food fractions, and food preparation methods. In many cases, the findings reported in the literature can be regarded as descriptive, but for a number of specific agents there is sufficient evidence to glean some understanding of the inhibitory or promotional mechanisms of action. These mechanisms can be divided into 11 separate sub-categories, arranged within a general classification scheme that encompasses such terms as 'blocking agents', 'suppressing agents', 'desmutagens', 'bioantimutagens', 'interceptor molecules' and 'tumor promoters'. In addition, new research directions, most notably during the past 2-3 years or so, have led to the use of novel dosing protocols and unique animal models (including transgenic species) that provide insight into exposure conditions and genetic background as modulators of heterocyclic amine activity in vitro and in vivo. Overall, the more than 250 citations on the subject give ample evidence of the growing interest in modulators of heterocyclic amine carcinogenesis and mutagenesis, and their possible importance in determining human cancer risk in defined populations.

New opportunities in chemoprevention research.

The importance of prevention in reducing the morbidity and mortality from cancer has been widely recognized. With the demonstration of tamoxifen's ability to prevent breast cancer in women, the feasibility of cancer chemoprevention in humans is now established. Future clinical chemoprevention studies should focus on phytochemicals, cancer preventive compounds in fruits, vegetables and other plants. Many phytochemicals are excellent potential chemopreventive agents, because, in addition to their cancer preventive effects, they are relatively non-toxic and inexpensive, they can be taken orally and some of them have other health benefits as well. New opportunities in clinical chemoprevention research include investigating chemopreventive effects of phytochemicals and conducting studies in patients with cancer. There is also a great need to investigate potential benefits and risks of administering phytochemicals before, during or after conventional therapies, such as surgery, chemotherapy, radiation or hormonal therapy. In addition, administration of chemopreventive agents prior to surgery provides an opportunity to investigate the modulation of genetic and epigenetic pathways by putative cancer preventive compounds and nutrients.

Evaluation of cancer-preventive agents and strategies a new program at the International Agency for Research on Cancer.

About five years ago, the International Agency for Research on Cancer (IARC) initiated a new program, IARC Handbooks of Cancer Prevention, aimed at evaluating the evidence base for the cancer-preventive activity of various agents and strategies. To date (2001) 5 volumes have been published--1. Non-steroidalAnti-inflammatory Drugs, 2. Carotenoids, 3. Vitamin A, 4. Retinoids, and 5. Sunscreens--and volume 6 (Weight Control and Physical Activity) is in press. Future volumes will include evaluations of breast cancer screening (vol. 7) and fruits and vegetables (vol. 8).

Primary cancer prevention trials.

Great progress has been made in cancer chemoprevention during the past 2 decades. Nevertheless, the field could benefit from the experiences of investigators studying the prevention of cardiovascular disease. During the past 50 years, prevention of cardiovascular disease has gone from a dream to a reality, with major clinical impact. The trend during the last 30 years has been impressive and sustained. From 1987 to 1994, there was a sustained major decrease in age-adjusted mortality from coronary heart disease in both men (from 3.1 to 2.2 per thousand persons) and women (from 1.1 to 0.9 per thousand persons). This trend is believed to have resulted from improvements in the treatment of myocardial infarction and, more substantively, from improvements in secondary prevention. This explanation is consistent with earlier computer simulations of trends in cardiovascular mortality during the 1980s, which estimated that 25% of the declines were attributable to primary prevention and 70% were caused by reductions in risk factors or treatment. The greatest effect of primary prevention had previously been noted in the late 1960s and 1970s. Most of these important findings occurred before cholesterol-lowering drugs became widely available, so further improvements are expected. Researchers in cancer prevention should follow in the footsteps of their cardiovascular colleagues. The tools are now available to make prevention of cancer a clinical reality. As the science of prevention improves, it must be remembered that effective and efficient preventive services do not help if they are not used. It is difficult to motivate practitioners and patients to implement preventive services. Also, preventive services are often considered a luxury. Persons without health insurance and those covered by Medicaid are much more likely to be diagnosed with late-stage cancer; therefore, they are key cohorts to target for effective preventive approaches. Finally, the most effective cancer prevention program will probably use both rational drug therapy targeting specific risk factors and public health efforts to promote healthy lifestyle choices in the population at large.

Mechanistic considerations in the evaluation of chemopreventive data.

Possible chemopreventive mechanisms include carcinogen-blocking activities, antioxidant/anti-inflammatory activities and antiproliferation/antiprogression activities. Carcinogen-blocking activities encompass inhibition of carcinogen uptake, inhibition of carcinogen formation or activation, deactivation or detoxification of carcinogens, prevention of carcinogen binding to DNA, and enhancement of the level or fidelity of DNA repair. Antioxidant/anti-inflammatory activities include scavenging of reactive electrophiles and oxygen radicals, and inhibition of arachidonic acid metabolism. Antiproliferation/antiprogression activities comprise modulation of signal transduction, modulation of hormonal and growth factor activity, inhibition of aberrant oncogene activity, inhibition of polyamine metabolism, induction of terminal differentiation, restoration of immune responses, enhancement of intercellular communication, restoration of tumour suppressor function, induction of apoptosis, telomerase inhibition, correction of DNA methylation imbalances, inhibition of angiogenesis, inhibition of basement membrane degradation, and activation of antimetastasis genes. In evaluating the potential efficacy of chemopreventive agents several mechanistic parameters are weighed: (1) the number of chemoprevention-related pharmacological activities, (2) the impact of the agent on likely carcinogenesis pathways to the targeted cancer, (3) pharmacodynamics, and (4) specificity for chemopreventive activity compared with interference with normal cellular function. Mechanistic data are important throughout the development process for chemopreventive drugs, and they are particularly important in the earlier phases of identifying promising candidate agents and characterizing efficacy. In vitro mechanistic assays are a first step in evaluating chemopreventive potential. Mechanistic considerations are also useful in defining animal efficacy models and in interpreting the results of assays in these models. Mechanistic data are also applied in designing short-term Phase II clinical chemoprevention trials that use reductions in intermediate biomarkers of cancer rather than cancer incidence as end points. The basis for identifying and evaluating these biomarkers is in understanding carcinogenesis and chemopreventive mechanisms.

Evaluation of chemopreventive agents in different mechanistic classes using a rat tracheal epithelial cell culture transformation assay.

The rat tracheal epithelial (RTE) cell focus inhibition assay was used to identify potential chemopreventive agents. Ninety-nine agents were evaluated for their ability to inhibit benzo[a]pyrene-induced transformation of RTE cells. Freshly isolated RTE cells were exposed to benzo[a]pyrene alone or in combination with a chemopreventive agent. After 30 days in culture, transformed foci were scored and inhibition was quantitated. In these studies, foci formation was inhibited mainly by agents which modulate the initiation of carcinogenesis by altering drug-metabolizing enzymes, inhibiting the binding of benzo[a]pyrene to DNA, enhancing detoxification of activated carcinogens, or by inducing epithelial cell differentiation. Such agents include antioxidants, free radical scavengers, glutathione S-transferase enhancers, vitamins, retinoids, and sulfhydryl compounds. Agents which inhibit ornithine decarboxylase and arachidonic acid metabolism were not as effective. The RTE assay provides important data for agent selection prior to whole animal-screening assays in the development of chemoprevention drugs.