Perspectives on cancer chemoprevention research and drug development

Chemoprevention of DMBA-induced UV-B promoted, NOR-1-induced TPA promoted skin carcinogenesis, and DEN-induced phenobarbital promoted liver tumors in mice by extract of beetroot

Our previous studies identified the extract of Beta vulgaris (beetroot), commercially also known as betanin, as a potent cancer chemopreventive agent in both in vitro Epstein-Barr early antigen activation assay and in an in vivo two-stage mouse lung and skin carcinogenesis. To explore this issue further, we have now investigated its cancer chemopreventive potentials in three different chemical carcinogen initiation-promotion experimental tumor models in mice. Following tumor initiation with 390 nmol of 7,12-dimethylbenz(a)anthracene (DMBA) in 100 microl of acetone, the mouse skin tumor promotion with 3430 J/m(2) of ultraviolet light-B (UV-B) as well as splenomegaly was significantly inhibited by oral administration of 0.0025% betanin. At the same dose, betanin also afforded significant protection in the mouse skin cancer model following the topical application of 390 nmol of (+/-)-(E)-4-methyl-2-[(E)-hydroxyamino]-5-nitro-6-methoxy-3-hexanamide (NOR-1) in 100 microl of acetone and promoted by topical administration of 1.7 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA). In the two-stage model of hepatocarcinogenesis in mice with N-nitrosodiethylamine (DEN, 30 mg/kg) as the initiator and phenobarbital as the promoter, oral administration of 0.0025% betanin also showed a very significant inhibition of both the incidence and multiplicity of the liver tumors. These findings along with our initial reports suggest that betanin which is a regularly consumed natural product colorant is an effective cancer chemopreventive agent in mice. The most interesting observation is that the cancer chemopreventive effect was exhibited at a very low dose used in the study and thus indicating that beetroot warrants more attention for possible human applications in the control of malignancy.

Novel agents for chemoprevention, screening methods, and sampling issues

An aggressive approach to breast cancer control based on preventing the disease must complement efforts at effective treatment. To date clinical trials testing new chemopreventative agents have not generally met with the kind of success expected. A wide range of new breast cancer chemopreventative agents are poised to be tested in clinical trials. We review these novel agents and approaches, including those for which clinical trials have been initiated and those that are promising in the preclinical arena. Further progress in this area requires not only new agents, but novel methods for screening for risk assessment, sampling and development of intermediate biomarkers. We review these novel potential surrogate endpoints, including new imaging-techniques, breast sampling approaches, and methods to assess biomarkers in breast epithelium. Factors that could contribute to a meaningful choice of the chemopreventive agents and the design of clinical trials are discussed.

Lung cancer. 2: screening and early diagnosis of lung cancer

Technical developments in spiral CT scanning mean that considerably smaller lung cancers can now be identified than with previous methods of detection. Only time will tell whether this enhanced capability will result in a reduction in the number of deaths from lung cancer. The implications and problems of screening for lung cancer are discussed. Screening implies a careful refinement of a range of clinical activities that must be routinely delivered in a carefully coordinated fashion to allow for the possibility of improved outcome. Critical analyses of the nuances of this process are essential if the field is to move forward.

Chemopreventive agents induce suppression of nuclear factor-kappaB leading to chemosensitization

Nuclear factor-kappaB (NF-kappaB), a transcription factor, is present normally in the cytoplasm as an inactive heterotrimer consisting of p50, p65, and IkappaBalpha subunits. When activated, NF-kappaB translocates to the nucleus as a p50-p65 heterodimer. This factor regulates the expression of various genes that control apoptosis, viral replication, tumorigenesis, various autoimmune diseases, and inflammation. NF-kappaB has been linked to the development of carcinogenesis for several reasons. First, various carcinogens and tumor promoters have been shown to activate NF-kappaB. Second, activation of NF-kappaB has been shown to block apoptosis and promote proliferation. Third, the tumor microenvironment can induce NF-kappaB activation. Fourth, constitutive expression of NF-kappaB is frequently found in tumor cells. Fifth, NF-kappaB activation induces resistance to chemotherapeutic agents. Sixth, several genes involved in tumor initiation, promotion, and metastasis are regulated by NF-kappaB. Seventh, various chemopreventive agents have been found to down-regulate the NF-kappaB activation. All these observation suggest that NF-kappaB could mediate tumorigenesis and thus can be used as a target for chemoprevention and for the treatment of cancer. Agents that suppress NF-kappaB activation can suppress the expression of genes involved in carcinogenesis and tumorigenesis in vivo.

Antiproliferative and apoptotic effects of silibinin in rat prostate cancer cells

BACKGROUND

The tremendous impact of prostate cancer (PCA) on the US male population has led to an increased attention on its prevention and on therapeutic intervention. Short-term models are needed to quickly screen the efficacy of promising agents against PCA. We have established recently several rat PCA cell lines from primary PCA in rats induced by a MNU-testosterone protocol, but their usefulness as a model for screening PCA preventive and therapeutic agents remains to be established. With the rationale that agents found effective in these cells could be promising for efficacy testing in long-term in vivo experiments, e.g., with MNU-testosterone-induced PCA in rats, the major goal of our study was to assess the antiproliferative and apoptotic efficacy in rat PCA cell lines of silibinin, a major active flavonoid component of silymarin, which consists of a group of flavonoid antioxidants occurring in milk thistle (Silybum marianum).

METHODS

Three rat PCA cell lines, namely H-7, I-8, and I-26, were treated with silibinin or silymarin, a crude silibinin-containing preparation, at various doses for varying lengths of time. Cell growth and viability studies were carried out by using hemocytometer and Trypan blue dye exclusion methods. Cell cycle distribution studies were conducted by using PI staining and flow cytometry analysis, and DNA synthesis was assessed by bromodeoxyuridine incorporation. Apoptotic cell death was assessed as DNA damage by using an enzyme-linked immunosorbent assay method and by annexin V and PI staining followed by flow cytometry analysis.

RESULTS

Silibinin resulted in a significant growth inhibition and reduction in cell viability in each cell line studied in both a dose- and a time-dependent manner. Silibinin treatment of H-7 and I-8 cells at 100 microM dose for 12 and 24 hr resulted in a G1 arrest but caused S phase arrest after a 48-hr treatment period in each cell line studied. Similar silibinin treatment of I-26 cells resulted in a slight S phase arrest at all time points studied. Consistent with these findings, silibinin showed a strong inhibition of DNA synthesis. Silibinin also induced a substantial apoptotic death in each cell line studied. Similar to silibinin, silymarin induced growth inhibition and reduced viability in a dose- and time-dependent manner.

CONCLUSION

This study demonstrates that silibinin as well as silymarin induce growth inhibition and apoptosis in rat PCA cells. These results form a strong rationale for PCA prevention and therapeutic intervention studies with silibinin and silymarin in animal models, such as the MNU-testosterone rat PCA model, to establish their efficacy and to further define their mechanisms of action under in vivo conditions.

Genistein and vitamin D synergistically inhibit human prostatic epithelial cell growth

We performed studies to test synergism between the growth inhibitory effects of genistein and vitamin D compounds on prostatic epithelial cells. Isobolographic analysis demonstrated that genistein, in combination with the hormonally active form of cholecalciferol, 1alpha,25-dihydroxycholecalciferol, synergistically inhibited the growth of primary human prostatic epithelial cells (HPEC) and prostate cancer cells. Synergistic growth inhibition of HPEC was also observed between genistein and the low-calcemic vitamin D compound 25-hydroxycholecalciferol. Flow cytometry with HPEC indicated that genistein induced arrest in the G(2)M phase, whereas 1alpha,25-dihydroxycholecalciferol or 25-hydroxycholecalciferol induced arrest in the G(1/0) phase of the cell cycle. Combining genistein with either vitamin D compound resulted in both G(2)M and G(1/0) arrest in HPEC. In contrast, flow cytometry of prostate cancer cells indicated that both genistein and 1alpha,25-dihydroxycholecalciferol induced a G(1/0) arrest either alone or in combination. These are the first studies that demonstrate synergism between the prostatic cell growth inhibition elicited by genistein and that elicited by vitamin D compounds.

Bioavailability of the isomer mixture of phytoene and phytofluene-rich alga Dunaliella bardawil in rat plasma and tissues

Dunaliella bardawil, a beta-carotene-accumulating alga was treated by the bleaching herbicide norflurazon to select sub-species rich with a mixture of 9-cis and all-trans stereoisomers of phytoene and phytofluene. The present study determines the bioavailability of phytoene and phytofluene with their stereoisomers in rats fed on a diet supplemented with Dunaliella phytoene-rich spray dried powder. Three groups of female weanling rats, eight animals each, were fed AIN diets for two weeks. The control consumed the diet as is. The experimental group was supplemented with 50 g Dunaliella powder to give phytoene/phytofluene at a level of 1 g/kg diet, and the placebo was provided with the oxidized algae free of carotenoids at the same amount. Weight gain and tissues weight of rats fed on the control diet, or on the experimental diets were statistically same. Tissue analyses were carried out by liquid chromatography at the end of two weeks feeding for vitamin A, carotenoids, phytoene and phytofluene and theirs stereoisomers. Liver analyses revealed high hepatic storage of phytoene in the experimental group. Analysis of the other tissues, adrenal, brain, heart, kidney, lung, and spleen detected small amounts of phytoene in the adrenal, kidney and spleen and in the plasma. High-pressure liquid chromatography for stereoisomeric composition was performed to all phytoene-containing tissues. The original algal diet content of 9-cis-to-all-trans ratio of 1:1 was maintained in the plasma and adrenal while in the liver, spleen and kidney the ratio was reduced to 1:3. The preferential accumulation of all-trans phytoene over 9-cis phytoene in the liver, spleen and kidney may be interpreted as indicating stronger antioxidative effect of 9-cis phytoene over the all-trans isomer or alternatively, in vivo streoisomerization of 9-cis phytoene to the all-trans structure.

Apoptosis induction by S-allylcysteine, a garlic constituent, during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The apoptosis-inducing capacity of S-allylcysteine (SAC), a water-soluble garlic constituent, during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch (HBP) carcinogenesis was investigated in male Syrian hamsters using DNA fragmentation and the apoptosis-associated proteins, tissue transglutaminase (tTG) and Bcl-2. Hamsters were divided into four groups of six animals each. Animals in group 1 were painted with a 0.5% solution of DMBA in liquid paraffin on the right buccal pouches three times a week for 14 weeks. Group 2 animals painted with DMBA as in group 1, in addition received 200 mg kg(-1) body weight SAC orally on days alternate to DMBA application. Group 3 animals received SAC as in group 2. Group 4 animals received neither DMBA nor SAC and served as the control. The experiment was terminated at the end of 14 weeks. Administration of SAC (200 mg kg(-1) body weight) to animals painted with DMBA inhibited DMBA-induced HBP carcinogenesis as revealed by the absence of neoplasms, induction of tTG and inhibition of Bcl-2 expression. The results of the present study suggest that SAC may exert its chemopreventive effect by inducing apoptosis.

Chemoprevention: an essential approach to controlling cancer

Mortality that results from the common forms of cancer is still unacceptably high. Despite immense advances in the understanding of the mechanisms of carcinogenesis, in bringing potent new drugs to the clinic and in treating several relatively rare forms of cancer, overall mortality statistics are unlikely to change in a fundamental way until there has been a re-orientation of emphasis in cancer research that will direct greater resources towards prevention of new disease, rather than treatment of end-stage disease.

Garlic induces apoptosis during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The apoptosis-inducing capacity of aqueous garlic extract during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch (HBP) carcinogenesis was investigated in male Syrian hamsters using DNA fragmentation and the apoptosis-associated proteins, tissue transglutaminase (tTG) and Bcl-2. Hamsters were divided into four groups of six animals each. Animals in group 1 were painted with a 0.5% solution of DMBA in liquid paraffin on the right buccal pouches three times a week for 14 weeks. Group 2 animals painted with DMBA as in group 1, in addition received 250 mg/kg body weight aqueous garlic extract orally on days alternate to DMBA application. Group 3 animals received garlic extract as in group 2. Group 4 animals received neither DMBA nor garlic extract and served as the control. The experiment was terminated at the end of 14 weeks. Administration of aqueous garlic extract (250 mg/kg body weight) to animals painted with DMBA inhibited DMBA-induced oral carcinogenesis as revealed by the absence of neoplasms, induction of tTG and inhibition of Bcl-2 expression. The results of the present study suggest that garlic may exert its chemopreventive effect by inducing apoptosis.

Effects of N-acetylcysteine in an esophageal carcinogenesis model in rats treated with diethylnitrosamine and diethyldithiocarbamate

Due to the increasing role of esophageal tumors in human cancer pathology, there is need for animal models evaluating the mechanisms of esophageal carcinogenesis and investigating protective factors toward this disease. Several N-nitrosamines have been shown to induce esophageal tumors in rats. We designed a study in BD(6) rats treated with N-diethylnitrosamine (DEN) according to a simple protocol involving weekly i.p. injections of this carcinogen for 8 consecutive weeks. This treatment resulted in a high incidence and multiplicity of liver tumors and in occurrence of preneoplastic lesions and papillomas in the esophagus. Intraperitoneal injections of diethyldithiocarbamate (DEDTC), 4 hr after each DEN injection, i.e., during the period of DEN metabolization, improved survival of rats and did not affect the liver tumor yield but doubled the incidence of esophageal tumors and enhanced 4.9x their multiplicity. Moreover, 15% of rats developed esophageal squamocellular carcinomas. The oral administration of the thiol N-acetyl-L-cysteine (NAC), a precursor and analogue of reduced glutathione, to rats treated with the DEN/DEDTC combination did not change the liver tumor yield but attenuated esophageal carcinogenesis by producing a significant shift of preneoplastic lesions to milder forms as well as a significant decrease of tumor multiplicity. Therefore, the DEN/DEDTC protocol appears to provide an interesting 2-organ model of N-nitrosamine-induced carcinogenesis in rats, in which NAC is moderately effective as an inhibitor. The mechanisms underlying enhancement of DEN-induced esophageal carcinogenesis by DEDTC and the protective effects of NAC are discussed.

Angioprevention': angiogenesis is a common and key target for cancer chemopreventive agents

The potential to block tumor growth by inhibition of the neoangiogenic process represents an intriguing approach to the treatment of solid tumors. The high proliferation rate in the tumor deprived of proper vascularization would be balanced by cell death due to lack of diffusion of nutrients and oxygen. Matrix metalloproteinases (MMPs), angiogenic growth factors, and their receptors are the main targets of an increasing number of clinical trials approved to test the tolerance and therapeutic efficacy of antiangiogenic agents. We observed that a series of substances proposed as possible cancer chemopreventive agents show antiangiogenic properties when tested in in vitro and in vivo angiogenesis models. We demonstrated that N-acetyl-l-cysteine is able to reduce the invasive and metastatic potential of melanoma cells, and to inhibit endothelial cell invasion by direct inhibition of MMP activity. We also showed that epigallocatechin gallate (EGCG), a flavonoid from green tea that possesses chemopreventive activity in experimental and epidemiological studies, is a potent inhibitor of MMP-2 and MMP-9. Angiogenesis has also been demonstrated to be a target for nonsteroidal anti-inflammatory drug chemopreventive activity. Based on these data, we hypothesize that other chemopreventive agents, including natural or synthetic retinoids, steroid hormone antagonists, peroxisome proliferator-activated receptor gamma ligands, vitamin D, and protease inhibitors, might have antiangiogenesis as an important mechanism of action, a novel concept we will term 'angioprevention'. We analyze the mechanisms on how and why chemopreventive agents could exert antiangiogenic effects aimed at controlling tumor growth, and their potential use in the clinic.

Retinoic acid prevents experimental Cushing syndrome

Cushing syndrome is caused by an excess of adrenocorticotropic hormone (ACTH) production by neuroendocrine tumors, which subsequently results in chronic glucocorticoid excess. We found that retinoic acid inhibits the transcriptional activity of AP-1 and the orphan receptors Nur77 and Nurr1 in ACTH-secreting tumor cells. Retinoic acid treatment resulted in reduced pro-opiomelanocortin transcription and ACTH production. ACTH inhibition was also observed in human pituitary ACTH-secreting tumor cells and a small-cell lung cancer cell line, but not in normal cells. This correlated with the expression of the orphan receptor COUP-TFI, which was found in normal corticotrophs but not in pituitary Cushing tumors. COUP-TFI expression in ACTH-secreting tumor cells blocked retinoic acid action. Retinoic acid also inhibited cell proliferation and, after prolonged treatment, increased caspase-3 activity and induced cell death in ACTH-secreting cells. In adrenal cortex cells, retinoic acid inhibited corticosterone production and cell proliferation. The antiproliferative action and the inhibition of ACTH and corticosterone produced by retinoic acid were confirmed in vivo in experimental ACTH-secreting tumors in nude mice. Thus, we conclude that the effects of retinoic acid combine in vivo to reverse the endocrine alterations and symptoms observed in experimental Cushing syndrome.

Cancer chemoprevention by dietary constituents: a tale of failure and promise

Although the results of clinical intervention trials of beta-carotene to prevent lung cancer, and of dietary augmentation with fibre or fruit and vegetables to reduce the occurrence of colonic polyps have so far been negative, a structured path for the development of diet-derived constituents as cancer chemopreventive agents is emerging. Putative agents are identified on the basis of epidemiological and preclinical mechanistic studies. Some examples of promising diet-derived chemopreventive agents are folate, curcumin, genistein, and tea catechins. Long-term supplementation of the diet with folate seems to lower the risk of colorectal cancer. Curcumin in the spice turmeric, genistein in soya, and catechins in tea have tumour-suppressing properties in rodent models of carcinogenesis, and they interfere with cellular processes involved in tumour promotion and progression. Kinases, telomerase, cyclooxygenase-2, triggers of apoptosis, and transcription factors AP1 and nuclear factor kappaB are among the cellular targets. The investigation of dietary constituents should follow a structured design, incorporating parallel preclinical studies of the food source and the isolated agent in terms of efficacy, toxicity, biological mechanisms, and pharmacokinetics. Either the food source or the isolated agent should be selected for further development on the basis of dose-efficacy and toxicity data. Pilot clinical trials on the pharmacokinetics and mechanism-based markers of efficacy of the selected intervention should precede phase I-III development in suitable populations.

Treatment prospects for autosomal-dominant polycystic kidney disease

An increased understanding of the molecular genetic and cellular pathophysiologic mechanisms responsible for the development of autosomal-dominant polycystic kidney disease (ADPKD), made possible by the advances in molecular biology and genetics of the last three decades, has laid the foundation for the development of effective therapies. As the concept that a polycystic kidney is a neoplasm in disguise is becoming increasingly accepted, the development of therapies for ADPKD may benefit greatly from the expanding body of information on cancer chemoprevention and chemosuppression. This review summarizes the observations that already have been made and discusses therapies for PKD that deserve investigation.

Anti-genotoxicity of galangin as a cancer chemopreventive agent candidate

Flavonoids are polyphenolic compounds that are present in plants. They have been shown to possess a variety of biological activities at non-toxic concentrations in organisms. Galangin, a member of the flavonol class of flavonoid, is present in high concentrations in medicinal plants (e.g. Alpinia officinarum) and propolis, a natural beehive product. Results from in vitro and in vivo studies indicate that galangin with anti-oxidative and free radical scavenging activities is capable of modulating enzyme activities and suppressing the genotoxicity of chemicals. These activities will be discussed in this review. Based on our review, galangin may be a promising candidate for cancer chemoprevention.

Development of a green fluorescent protein microplate assay for the screening of chemopreventive agents

Here we develop a rapid, cell-based, functional assay to screen and identify naturally occurring or synthetic chemicals with chemopreventive activity. We constructed a reporter gene that consists of the gene-encoding green fluorescent protein (GFP) under the transcriptional control of the thymidine kinase (TK) promoter adjacent to which concatamerized EpRE regulatory elements were inserted. Human hepatoma HepG2 cells were transfected with the EpRE/TK-GFP reporter plasmid, and clones with low GFP background expression and high tBHQ-induced GFP expression were isolated. These GFP reporter cells were seeded into a 96-well microtiter plate, incubated for 24 h, and then treated with test compounds for an additional 24 h. The GFP level and DNA content (as an internal cell survival control) of cells in the 96-well plate were measured subsequently using a fluorescence plate reader. Known inducers of phase II enzymes, such as tert-butylhydroquinone, beta-naphthoflavone, and sulforaphane, significantly increased the GFP level in the HepG2 reporter cells. In an initial screening of a chemical library, we identified a synthetic compound whose inducing ability significantly exceeds (1.6-fold) that of the best currently known phase II enzyme inducers. The experimental results indicate that this cell system makes possible a new high throughput screening approach to identify novel chemopreventive molecules.

Retinoids in chemoprevention and differentiation therapy

Retinoids are essential for the maintenance of epithelial differentiation. As such, they play a fundamental role in chemoprevention of epithelial carcinogenesis and in differentiation therapy. Physiological retinoic acid is obtained through two oxidation steps from dietary retinol, i.e. retinol-->retinal-->retinoic acid. The latter retinal-->retinoic acid step is irreversible and eventually marks disposal of this essential nutrient, through cytochrome P450-dependent oxidative steps. Mutant mice deficient in aryl hydrocarbon receptor (AHR) accumulate retinyl palmitate, retinol and retinoic acid. This suggests a direct connection between the AHR and retinoid homeostasis. Retinoids control gene expression through the nuclear retinoic acid receptors (RARs) alpha, beta and gamma and 9-cis-retinoic acid receptors alpha, beta and gamma, which bind with high affinity the natural ligands all-trans-retinoic acid and 9-cis-retinoic acid, respectively. Retinoids are effective chemopreventive agents against skin, head and neck, breast, liver and other forms of cancer. Differentiation therapy of acute promyelocytic leukemia (APL) is based on the ability of retinoic acid to induce differentiation of leukemic promyelocytes. Patients with relapsed, retinoid-resistant APL are now being treated with arsenic oxide, which results in apoptosis of the leukemic cells. Interestingly, induction of differentiation in promyelocytes and consequent remission of APL following retinoid therapy depends on expression of a chimeric PML-RAR alpha fusion protein resulting from a t(15;17) chromosomal translocation. This protein functions as a dominant negative against the function of both PML and RARs and its overexpression is able to recreate the phenotypes of the disease in transgenic mice. The development of new, more effective and less toxic retinoids, alone or in combination with other drugs, may provide additional avenues for cancer chemoprevention and differentiation therapy.

Colon cancer: a role for cyclo-oxygenase-2-specific nonsteroidal anti-inflammatory drugs

Large bowel cancer is not only the third most frequent cancer in the world but is one of the most common human malignancies in Western countries, including North America. In recent years, multidisciplinary research in epidemiology, molecular biology, and laboratory animal model studies have contributed much to our understanding of the aetiology of this cancer; more importantly, it has enabled us to devise preventive strategies. Several epidemiological studies have detected a 40 to 50% decrease in risk of colorectal cancer in individuals who regularly use aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs). Clinical trials with NSAIDs in patients with familial adenomatous polyposis have demonstrated that treatment with NSAIDs caused regression of pre-existing adenomas. Preclinical efficacy studies have provided scientifically sound evidence as to how NSAIDs act to retard, block, or reverse colonic carcinogenesis. Equally exciting are opportunities for effective chemoprevention with selective cyclo-oxygenase-2 inhibitors in a variety of animal models of colon cancer. Selective cyclo-oxygenase-2 inhibitors such as celecoxib have been proven to be effective chemopreventive agents against colonic carcinogenesis with minimal gastrointestinal toxicity. Our exploration of the multistep process of carcinogenesis has provided substantial insights into the mechanisms by which anti-inflammatory agents modulate these events. There is growing optimism for the view that realisation of preventive concepts in large bowel cancer will also serve as a model for preventing malignancies of the prostate and breast.

Chemoprevention of cancer

In this short article, we review the conceptual basis for chemoprevention of cancer, the proven clinical efficacy of this concept, and current trends to develop new chemopreventive agents based on understanding of their mechanisms of action. Four classes of new agents, namely selective inhibitors of cyclooxygenase-2, selective estrogen receptor modulators, rexinoids (retinoids that bind selectively to the receptors known as RXRs) and ligands for the peroxisome proliferator-activated receptor-gamma are discussed in detail. The importance of developing totally new classes of chemopreventive agents is stressed, with particular emphasis on the potential usefulness of new synthetic triterpenoids derived from naturally occurring molecules.

Cancer chemoprevention: progress and promise

Cancer chemoprevention is the use of agents to inhibit, delay or reverse carcinogenesis. The focus of chemoprevention research in the next millennium will include defining the genotypic and phenotypic (functional and histological) changes during carcinogenesis, the cancer risk conferred by these changes, their modulation in preclinical experimentation and randomised clinical trials by chemopreventive drugs, dietary agents and regimens and treatments resulting from early detection. The key elements of this research effort will be basic and translational risk evaluation programmes; chemopreventive and dietary agent drug discovery and development; development of transgenic animal models; required safety and pharmacology studies; well-designed phase I, II and III chemoprevention studies; and much expanded early detection programmes. The large number of chemoprevention research programmes now ongoing ensures that the promise of chemoprevention will continue to be realised in the next decade.

Cancer chemoprevention: progress and promise

Cancer chemoprevention is the use of agents to inhibit, delay or reverse carcinogenesis. The focus of chemoprevention research in the next millennium will include defining the genotypic and phenotypic (functional and histological) changes during carcinogenesis, the cancer risk conferred by these changes, their modulation in preclinical experimentation and randomised clinical trials by chemopreventive drugs, dietary agents and regimens and treatments resulting from early detection. The key elements of this research effort will be basic and translational risk evaluation programmes; chemopreventive and dietary agent drug discovery and development; development of transgenic animal models; required safety and pharmacology studies; well-designed phase I, II and III chemoprevention studies; and much expanded early detection programmes. The large number of chemoprevention research programmes now ongoing ensures that the promise of chemoprevention will continue to be realised in the next decade.