Prostate intraepithelial neoplasia in Noble rats, a potential intermediate endpoint for chemoprevention studies

In most prostate chemoprevention studies conducted with animal models, the incidence and multiplicity of tumours have been used as endpoints for efficacy. However, the latency of tumours is usually over 1 year, making these studies costly and time consuming. The main purpose of this study was to assess the utility of prostate intraepithelial neoplasia (PIN), induced in Noble rats by continuous testosterone + oestradiol (T + E) administration, as a potential intermediate endpoint biomarker of efficacy in chemoprevention studies. Noble rats at the age of 12 weeks were treated for 36 weeks with T + E given subcutaneously via Silastic capsules. The incidence and multiplicity of PIN were assessed in various prostate glands by serial sections generated at three separate tissue levels. The efficacy of dehydroepiandrosterone (DHEA) and DHEA 8354 (1000 and 2000 mg/kg diet), difluoromethylornithine (DFMO) (1000 and 2000 mg/kg diet) and oltipraz (125 and 250 mg/kg diet) to inhibit PIN was assessed in two independent sets of experiments. T + E induced multiple PIN in the dorsolateral prostate (DLP) of 80-100% of the animals. DHEA and DHEA 8354 did not affect the incidence but decreased the multiplicity of PIN in the DLP, from 3.2 +/- 1.0 in control group to 1.5 +/- 1.0 in the low-dose and to 1.6 +/- 0.6 in the high-dose group for DHEA (P<0.05 and P<0.02, respectively), and to 1.9 +/- 0.8 in the high-dose (P<0.05) DHEA 8354. Both agents did not affect PIN in anterior prostate, seminal vesicles or ventral prostate. In a second experiment, DFMO and oltipraz were found not effective in inhibiting PIN. In this study, we provide new evidence that PIN in Noble rats, induced by continuous T + E treatment, is a useful intermediate endpoint for determining the efficacy of DHEA and other potential chemopreventive agents. The hormonal pathogenesis, high multiplicity, short latency, preferential location in the DLP, similarity in morphology and biology to PIN of human prostate, and the sensitivity to agents that suppress prostate carcinogenesis, makes PIN in Noble rats a promising intermediate endpoint for chemoprevention studies.

How curcumin works preferentially with water soluble antioxidants

In this study we investigated physicochemical characteristics of the curcumin radical by pulse radiolysis and laser flash photolysis. Two methylated curcumin derivatives, methylcurcumin and trimethylcurcumin, were synthesized to explore the role of phenol hydroxy and beta-diketone moieties in the free radical chemistry of curcumin. Our results show that the initially generated beta-oxo-alkyl transforms rapidly, probably via an intramolecular H-atom shift, into the phenoxyl-type curcumin radical. This phenoxyl does not react with oxygen, k < 10(5) M(-1) s(-1), and can be repaired by any water-soluble antioxidant with appropriate redox potential, E(6) < 0.83 V, for example, with vitamin C, k = (6 +/- 1) x 10(6) M(-1) s(-1). A molecular mechanism of cancer chemoprevention by curcumin is proposed, with special emphasis on the synergism with water-soluble antioxidants.

Computer-assisted image analysis-derived intermediate endpoints

The development of prostatic lesions undergoes a slow progression. To establish efficacy of chemopreventive intervention it is therefore necessary to define surrogate endpoint biomarkers. Such biomarkers should be sensitive in their ability to indicate response. They should be objective, ie, the result of measurement, and numerically defined so that a statistical validation of response is possible. They should be able to indicate not only a halt of progression of a lesion, but also a reversal of progression. The spatial and statistical distribution of nuclear chromatin in the secretory and luminal cells in prostatic intraepithelial neoplastic lesions has been shown to be well defined. It can be represented by a set of features. These have been used to define a progression curve along which progression or regression of a lesion can be assessed. One could define a fixed endpoint, or one might choose to accept a statistically significant regression along the progression curve as criterion for chemopreventive efficacy. Expected difficulties could arise from lesion heterogeneity, as it would affect the sampling, and from multifocal lesions of differing progressions. Lesion heterogeneity thus limits the precision with which regression could be detected. These problems might be partially overcome by observations taken in histologically normal appearing regions of the prostate. The nuclear chromatin pattern of secretory cell nuclei measured in such tissue regions from prostates harboring intraepithelial or malignant lesions has been shown to exhibit distinctive changes from the chromatin pattern seen in secretory cell nuclei from prostates free from any such lesions. These changes appear to be expressed in the tissue up to a substantial distance from a lesion. The expression of changes in the nuclear chromatin suggests the existence of an intraepithelial preneoplastic lesion that can be detected by biomarkers, but which is not apparent from visual microscopic inspection. Since chemoprevention might be expected to be most effective at the earliest stages of lesion development, the assessment of such early alterations is seen as highly relevant to efforts to validate the efficacy of chemopreventive intervention.

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.

Quantitative nuclear morphometry by image analysis for prediction of recurrence of ductal carcinoma in situ of the breast

Clinical management of ductal carcinoma in situ (DCIS) remains a challenge because significant proportions of patients experience recurrence after conservative surgical treatment. Unfortunately, it is difficult to prospectively identify, using objective criteria, patients who are at high risk of recurrence and might benefit from additional treatment. We conducted a multi-institutional, collaborative case-control study to identify nuclear morphometric features that would be useful for identifying women with DCIS at the highest risk of recurrence. Tissue sections of archival breast tissue of 29 women with recurrent and 73 matched women with nonrecurrent DCIS were stained for DNA, and nuclei in the DCIS lesions were evaluated by image analysis. A clear correlation between mean fractal2_area (FA2) and nuclear grade was observed (P < 0.001), allowing an objective determination of nuclear grade. Several nuclear morphometric features, including mean and variance of variation of radius, mean area, mean and variance of frequency of high boundary harmonics (FQH), and variance in sphericity, were found to be useful in discriminating recurrent from nonrecurrent DCIS subjects. However, the nuclear features associated with recurrence differed between high- and low-grade lesions. For lesions with high FA2 (nuclear grade 3), mean variation of radius, mean FQH, and mean area alone yielded recurrence odds ratios of 4.55 [95% confidence interval (CI) 0.45-45.96], 3.86 (95% CI, 0.88-16.98), 2.90 (95% CI, 0.31-27.2), respectively. Using a summed feature model, high-FA2 lesions showing three poor prognostic features had an odds ratio of 15.63 (95% CI, 1.22-200), compared with those with zero or one poor prognostic feature. Lesions with low mean FA2 (nuclear grade 1 or 2) showing high variances in sphericity and FQH had an odds ratio of 7.71 (95% CI, 1.77-33.60). Addition of other features did not enhance the odds ratio or its significance. These results suggest that nuclear image analysis of DCIS lesions may provide an adjunctive tool to conventional pathological analysis, both for the objective assessment of nuclear grade and for the identification of features that predict patient outcome.

Chromosome 3p tumor-suppressor gene alterations in cervical carcinomas

Loss of heterozygosity (LOH) on chromosome 3p is a common event in cervical cancer and typically occurs in a dispersed pattern involving several loci. This implies that more than one resident tumor-suppressor gene is involved in the genesis of these tumors; however, specific targets remain to be identified. The region of 3p14.2-pter encompasses a region of frequent loss and contains at least three tumor-suppressor genes: fragile histidine triad (FHIT), transforming growth factor-beta receptor II (T beta R-II), and Von Hippel-Lindau. To identify those loci within 3p14.2-pter that are important in cervical cancer, invasive tumors were first subjected to high-density LOH analysis. With 25 microsatellite markers, LOH was detected in seven of 15 cervical carcinomas (47%). Losses always included markers mapping to 3p22, and markers at this location were exclusively lost in two tumors, implicating this as a site of a cervical tumor-suppressor gene. Because it is a known tumor-suppressor gene located at 3p22 and thus a potential target for inactivation in these tumors, the T beta R-II gene was subsequently screened for mutation and altered expression levels. Whereas no tumor-derived mutations were detected in any of the tumors, six of ten tumors showed T beta R-II transcript levels reduced by > or = 50% when compared with normal cervical epithelium. Nine of 15 (60%) tumors exhibited LOH at 3p22 or reduced expression of T beta R-II, suggesting that reduced T beta R-II levels contribute to cervical tumorigenesis. Two cases exhibited silent germline polymorphisms of T beta R-II: one corresponding to a C1167T transversion and the other to an A1266G transition. The FHIT gene, which is located at 3p14.2, also frequently incurred LOH and abnormal transcription in these tumors. LOH of FHIT was observed in five of the 15 tumors analyzed. Neither mutations nor homozygous deletions of FHIT were detected in the tumors. However, aberrantly short transcripts of the FHIT gene were evident in six of nine (67%) tumors. Only one of these also displayed LOH, indicating that this gene was altered in at least 10 of 15 (67%) tumors. These results provide evidence that the inactivation of two known tumor-suppressor genes, TbetaR-II and FHIT, on chromosome 3p is involved in cervical carcinogenesis. Mol. Carcinog. 30:159--168, 2001.

Detection of genetic alterations in mouse lung adenocarcinomas by two-dimensional gel electrophoresis

DNA from 14 mouse lung adenocarcinomas and 7 normal lungs were examined by 2-dimensional gel electrophoresis (2-DGE) for genetic alterations. 2-DGE profiles from tumor samples were compared with those profiles from normal lung tissues through a computer-assisted color overlay system. Compared to the profiles in normal lung DNA, 6 spots were amplified and 16 spots were partially reduced in their intensity in tumors. Two spots were detectable only in tumor tissues. These altered spots indicate genetic changes in mouse lung tumor development. The identification of these genetic alterations is probably important in understanding mouse lung carcinogenesis.

Chemoprevention with theaflavins of rat esophageal intraepithelial neoplasia quantitatively monitored by image tile analysis

The objective of the study was to compare three methods of monitoring the inhibition by dietary theaflavins of N-nitrosomethylbenzylamine (NMBA)-induced rat esophageal intraepithelial neoplasia: the mean tile grade, measured by computer-assisted quantitative image tile analysis; tumor multiplicity; and mean tumor size. A "tile" is defined as a small portion of a microscopic image at x 40, 87 x 292 microm in size. The computer divided the image of esophageal intraepithelial neoplasia into a grid of contiguous tiles and measured four tissue features within each tile based on cytonuclear and tissue architectural changes used by pathologists to diagnose intraepithelial neoplasia. The tile grade is defined as the weighted sum of the four feature measurements within a tile, the weights being determined by Fisher linear discriminant analysis. The mean tile grade of 300 tiles is used to grade rat esophageal intraepithelial neoplasia. NMBA was given s.c., 0.5 mg/kg, three times a week for 5 weeks. Theaflavins were given in the drinking water at 360 ppm (low dose) and 1200 ppm (high dose) throughout the experiment. In a given set of four groups of rats, one group received theaflavins alone, one NMBA alone, one NMBA plus low-dose theaflavins, and one NMBA plus high-dose theaflavins. One set of four groups, four rats/group, was sacrificed at the 15th week and another at the 20th week after starting NMBA; a final set with 15 rats/group was sacrificed at 25 weeks. At the 15th and 20th weeks, the mean tumor grade was the only variable that responded significantly (P < 0.01) to the low dose of dietary theaflavins. In fact, tumor multiplicity and mean tumor size sometimes showed enhancement at these doses. At the 25th week, when there were 15 instead of 4 rats/group, the mean tile grade, tumor multiplicity, and mean tumor size were all significantly (P < 0.01) decreased by both low and high doses of theaflavins. The mean tile grade is a more sensitive and reproducible variable than tumor multiplicity and mean tumor size in detecting the chemopreventive effects of theaflavins on intraepithelial neoplasia in the rat esophagus. This suggests that the mean tile grade may be a useful intermediate end point for use in human chemoprevention trials.

Chemoprevention of prostate cancer: concepts and strategies

Chemoprevention is the administration of agents to prevent induction and inhibit or delay progression of cancers. For prostate, as for other cancer targets, successful chemopreventive strategies require well-characterized agents, suitable cohorts, and reliable intermediate biomarkers of cancer for evaluating chemopreventive efficacy. Agent requirements are experimental or epidemiological data showing chemopreventive efficacy, safety on chronic administration, and a mechanistic rationale for the observed chemopreventive activity. On this basis, promising chemopreventive drugs in prostate include retinoids, antiandrogens, antiestrogens, steroid aromatase inhibitors, 5alpha-reductase inhibitors, vitamins D and E, selenium, lycopene, and 2-difluoromethylornithine. Phase II trials are critical for evaluating chemopreventive efficacy. Cohorts in these trials should be suitable for measuring the chemopreventive activity of the agent and the intermediate biomarkers chosen as endpoints. Many cohorts proposed for phase II trials are patients with previous cancers or premalignant lesions. For such patients, trials should be conducted within the context of standard treatment. Two cohorts currently used in phase II prostate cancer chemoprevention trials are patients with PIN and patients scheduled for prostate cancer surgery. Biomarkers should fit expected biological mechanisms, be assayed reliably and quantitatively, measured easily, and correlate to decreased cancer incidence. Protocols for adequately sampling tissue are essential. Changes in PIN provide prostate biomarkers with the ability to be quantified and a high correlation to cancer. PIN measurements include nuclear polymorphism, nucleolar size and number of nucleoli/nuclei, and DNA ploidy. Other potentially useful biomarkers are associated with cellular proliferation kinetics (e.g. PCNA and apoptosis), differentiation (e.g. blood group antigens, vimentin), genetic damage (e.g. LOH on chromosome 8), signal transduction (e.g. TGFalpha, TGFbeta, IGF-I, c-erbB-2 expression), angiogenesis, and biochemical changes (e.g. PSA levels).

Endpoint markers for cancer chemoprevention trials derived from the lesion of precancer (intraepithelial neoplasia) measured by computer-assisted quantitative image analysis

Endpoint markers for cancer chemoprevention clinical trials are described that are developed from the morphological properties of the precancerous lesion of intraepithelial neoplasia itself, as measured by computer-assisted quantitative image analysis. The markers include increased proliferative fraction (percentage MIB-1 positive nuclear area); nuclear DNA content (DNA ploidy), including DNA content exceeding fivefold the haploid amount (5C-exceeding rate); nuclear/nucleolar morphometry; and disorganization of nuclear chromatin pattern as characterized by Markovian parameters and other functions. A significant new advance in image analysis is the process of "tiling," in which hundreds of full monitor image fields of a given histological section at x40 magnification are reduced in size and fused seamlessly to produce a single image of the histological section at x1.25 magnification. The operator may review the low-power image and retrieve x40 magnification of any desired area by point/clicking with a mouse.

Quantitative grading of rat esophageal carcinogenesis using computer-assisted image tile analysis

Our objective was to grade, by computer-assisted quantitative image tile analysis, the intraepithelial neoplasia (also called dysplasia) that develops in esophagi of rats given N-nitrosomethybenzylamine (NMBA) for 5 weeks. To perform image tile analysis, the computer divides the video image of the neoplastic epithelium into a row of contiguous small rectangular images, or "tiles," 84 x 292 microm in size, and quantitatively measures four selected tissue features within each image tile. The computer then calculates a tile grade for each image tile as the weighted sum of the four feature measurements, transformed into statistical Z-scores, the weights being determined by Fisher linear discriminant analysis of 300 tile grades of the neoplastic epithelium referenced to the mean tile grade (MTG) of 300 image tiles of normal epithelium. The two grading parameters, MTG and the percentage of tile grades exceeding the MTG of normal epithelium by >4 SD units (%TG>4SD), were validated as endpoints for screening chemopreventive agents in the rat NMBA-induced esophageal carcinogenesis model in two ways: (a) after NMBA treatment, %TG>4SD developed in parallel with tumor incidence and tumor multiplicity (number of papillomas/tumor-bearing rat); and (b) placing the chemopreventive phenethylisothiocyanate in the food of NMBA-treated rats produced parallel reductions in MTG, tumor incidence, and tumor multiplicity. Both MTG and %TG>4SD, measured by quantitative image tile analysis, are sensitive and objective continuous parametric response variables expressed to three significant figures, with wide dynamic range, that may be evaluated by t tests to compare tissue neoplastic changes before and after treatment with a chemopreventive agent.

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).

Perspectives on surrogate end points in the development of drugs that reduce the risk of cancer

This paper proposes a scientific basis and possible strategy for applying surrogate end points in chemopreventive drug development. The potential surrogate end points for cancer incidence described are both phenotypic (at the tissue, cellular, and molecular levels) and genotypic biomarkers. To establish chemopreventive efficacy in randomized, placebo-controlled clinical trials, it is expected that in most cases it will be critical to ensure that virtually all of the biomarker lesions are prevented or that the lesions prevented are those with the potential to progress. This would require that both the phenotype and genotype of the target tissue in agent-treated subjects, especially in any new or remaining precancers, are equivalent to or show less progression than those of placebo-treated subjects. In the National Cancer Institute chemoprevention program, histological modulation of a precancer (intraepithelial neoplasia) has thus far been the primary phenotypic surrogate end point in chemoprevention trials. Additionally, we give high priority to biomarkers measuring specific and general genotypic changes correlating to the carcinogenesis progression model for the targeted cancer (e.g., progressive genomic instability as measured by loss of heterozygosity or amplification at a specific microsatellite loci). Other potential surrogate end points that may occur earlier in carcinogenesis are being analyzed in these precancers and in nearby normal appearing tissues. These biomarkers include proliferation and differentiation indices, specific gene and general chromosome damage, cell growth regulatory molecules, and biochemical activities (e.g., enzyme inhibition). Serum biomarkers also may be monitored (e.g., prostate-specific antigen) because of their accessibility. Potentially chemopreventive drug effects of the test agent also may be measured (e.g., tissue and serum estrogen levels in studies of steroid aromatase inhibitors). These initial studies are expected to expand the list of validated surrogate end points for future use. Continued discussion and research among the National Cancer Institute, the Food and Drug Administration, industry, and academia are needed to ensure that surrogate end point-based chemoprevention indications are feasible.

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.

Comparative chemopreventive mechanisms of green tea, black tea and selected polyphenol extracts measured by in vitro bioassays

Black tea extracts (hot aqueous, polyphenols and theaflavins) and green tea extracts (hot aqueous, polyphenols, epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate) were tested in nine standardized cell culture assays for comparative cancer chemopreventive properties. Most black and green tea extracts strongly inhibited neoplastic transformation in mouse mammary organ cultures, rat tracheal epithelial cells and human lung tumor epithelial cells. Nearly all tea fractions strongly inhibited benzo[a]pyrene adduct formation with human DNA. Induction of phase II enzymes, glutathione-S-transferase and quinone reductase, were enhanced by nearly all tea fractions, while glutathione was induced by only a few fractions. Ornithine decarboxylase activity was inhibited by nearly all the green tea fractions, but none of the black tea fractions. 12-O-tetradecanoylphorbol-13-acetate-induced free radicals were inhibited by most tea fractions. These results provide strong evidence of both anti-mutagenic, anti-proliferative and anti-neoplastic activities for both black and green tea extracts. Such anticancer mechanisms may well be responsible for the cancer preventive efficacies seen in both experimental and human studies.

Image morphometric nuclear grading of intraepithelial neoplastic lesions with applications to cancer chemoprevention trials

A new image morphometric method of nuclear grading is described and assessed in the context of the evaluation of histological samples from ductal carcinoma in situ of the breast and cervical intraepithelial neoplasia. The method results in a continuous scaled variable, or nuclear grading scale, expressed in SD units from measured normal nuclei from breast or cervix. For a given histological preinvasive neoplastic lesion, the mean nuclear grade of measured nuclei was shown to be analogous to the histopathological nuclear grade of the same lesion assigned subjectively by the pathologist. In a chemoprevention trial of the effect of difluoromethylornithine given for 1 month to subjects with cervical intraepithelial neoplasia grade 3, pathologists could see no difference in 14 histological sections taken before and after difluoromethylornithine treatment. However, the image morphometric method detected a systematic effect of lowered mean nuclear grade and a decrease in the variability of nuclear grade expression. Twelve of 14 samples showed a lower posttreatment mean nuclear grade (P<0.05), and 13 of the 14 samples showed a decrease in the SD of their nuclear grade distributions (P<0.01). This study demonstrates the use of image morphometric nuclear grading in a chemoprevention setting. It may be very useful in supplementing the pathologist's histopathological grading by providing objective, quantitative assessments.

Endpoint markers for clinical trials of chemopreventive agents derived from the properties of epithelial precancer (intraepithelial neoplasia) measured by computer-assisted image analysis

The Chemoprevention Branch, NCI, is supporting over 80 clinical trials of chemopreventive agents and has dozens of drugs under development. The structural and functional properties of epithelial precancer (also called preinvasive or IEN), such as increasingly aberrant nuclear size, shape and rates of cellular proliferation and apoptosis, measured by CAQIA, form the basis for specific and quantitative end markers in short term clinical trials of chemopreventive agents. IEN very frequently, if not invariably, is preceded by two conditions diffusely affecting the epithelium: genomic instability and chronic hyperplasia. Chronic subepithelial inflammation is also commonly present. Multicentricity and multipath genetic progression of individual lesions are important characteristics that must be considered when designing endpoint markers and planning for adequate biopsy sampling in clinical trials of chemopreventive agents. Use of CAQIA provides increased sensitivity and specificity when measuring the cellular changes of IEN, such as increasingly aberrant nuclear size, nuclear shape, integrated optical density of nuclear DNA and nuclear chromatin texture features. A software program called the Deep Valley Detector, which measures the optical density gradient at the margins of chromatin clumps in cell nuclei of histological sections stained for DNA, is one example of many nuclear chromatin texture features measured. In the image of the nucleus of a neoplastic cell from high grade IEN of the cervix, 111 deep valley sites were counted, whereas the nucleus of a non-neoplastic hyperplastic cell showed only 16 sites. The modulating effects of chemopreventive agents on IEN may be quantitated by the change they produce in the average number of deep valley sites per nucleus.

Oltipraz, a novel inhibitor of hepatitis B virus transcription through elevation of p53 protein

Molecular epidemiological studies of populations at high risk for liver cancer have shown that hepatitis B virus (HBV) and aflatoxin B1 exposures are two major risk factors for this disease. Oltipraz is currently being considered for clinical trial to protect against aflatoxin B1-induced hepatocarcinogenesis based on its proven protective effect in many different animal models. In addition, oltipraz inhibits human immunodeficiency virus (HIV) replication. The inactivation of reverse transcriptase of HIV appears to be the antiviral mechanism. It has been demonstrated that a number of compounds that inhibit HIV replication also inhibit HBV replication in vitro. Therefore, we tested the possibility of oltipraz blocking HBV replication in 2.2.15 cells (clonal cells derived from HepG2 cells that were transfected with a plasmid containing HBV DNA) in vitro. Results of the experiments indicate that oltipraz has a dose-dependent inhibitory effect on HBV replication and specifically blocks HBV transcription in 2.2.15 cells. In addition, oltipraz induces endogenous wild-type p53 protein in a dose- and time-course-dependent manner. Taken together, we speculate that the effects of oltipraz against replication of HBV and specific blocking of HBV transcription may be through the induction of p53-mediated pathway in 2.2.15 cells. In addition to its known chemopreventive action on aflatoxin B1 hepatocarcinogenesis, oltipraz was shown here to inhibit HBV replication. These dual effects put oltipraz as the excellent candidate for the chemopreventive agent of human hepatocellular carcinoma.

Preclinical drug development paradigms for chemopreventives

Preclinical screening studies and animal efficacy testing models currently are used by the National Cancer Institute's chemoprevention drug discovery program to assess and identify chemical agents and natural products that may have the potential to prevent human cancer. Identification of potential cancer preventing agents begins by subjecting each compound to a sequential series of short-term, in vitro prescreens of mechanistic, biochemical assays to provide quantitative data to help establish an early indication of chemopreventive efficacy and to assist in prioritizing agents for further evaluation in longer-term, in vitro transformation bioassays and whole animal models. Promising chemical agents or combinations of agents that work through different inhibitory mechanisms subsequently are tested in well-established, chemically induced, animal tumor models, which include models of the lung, bladder, mammaries, prostate, and skin. These preclinical bioassays afford a strategic framework for evaluating agents according to defined criteria, and not only provide evidence of agent efficacy, but also serve to generate valuable dose-response, toxicity, and pharmacokinetic data required prior to phase I clinical safety testing. Based on preclinical efficacy and toxicity screening studies, only the most successful agents considered to have potential as human chemopreventives progress into clinical chemoprevention trials.

Protective action of plant polyphenols on radiation-induced chromatid breaks in cultured human cells

The present study was performed to determine whether plant polyphenols can protect human cells against radiation-induced DNA damage manifested as chromatid breaks. Since each chromatid contains a single continuous molecule of double stranded DNA, chromatid breaks represent unrepaired DNA strand breaks. The addition of green or black tea extracts, their polyphenols or curcumin to cultures of human skin fibroblasts or PHA-stimulated blood lymphocytes significantly reduced the frequencies of radiation-induced chromatid breaks. An exception to this general finding was that the green tea polyphenol, (-)epigallocatechin gallate, had no effect. The protective action of these plant polyphenols seems to result from their known antioxidant properties, particularly the scavaging of hydroxyl free radicals. Frequencies of chromatid breaks in cells arrested immediately after irradiation or 0.5 to 1.5 hours post-irradiation in the presence or absence of a DNA repair inhibitor, provide a measure of DNA damage. The results of the present study show that tea and other plant polyphenols can protect human cells against radiation-induced DNA damage.

Use of Druckrey analysis to quantitatively evaluate the chemopreventive efficacy of N-difluoromethylornithine (DFMO), a prototype proliferation inhibitor

Druckrey analysis of the results of skin painting TG.AC transgenic mice with three different doses of benzo[a]pyrene was used to obtain quantitative estimates of the in vivo cancer chemopreventive efficacy of N-difluoromethylornithine. The percent decrease in mean rate of subvisible tumor development during the tumor latent period produced by 2000 ppm and 4000 ppm DFMO in the diet was 39% and 50%, respectively. Druckrey analysis was also successfully applied to transformations of published data on human cigarette smokers. The time before onset of lung cancer in 2% of smokers was prolonged 17 weeks for every cigarette per day not smoked. The Druckrey model, of substantiated validity because of the results in human smokers, provides a rapid quantitative screening method applicable to large numbers of candidate chemopreventive agents.

Quantitation of preinvasive neoplastic progression in animal models of chemical carcinogenesis

An assay method that precisely quantitates the cellular and tissue changes associated with early, preinvasive neoplasia is much needed as a surrogate endpoint biomarker (SEB) in clinical trials to predict the potential efficacy of chemopreventive agents in bringing about cancer incidence reduction. Quantification of histological changes at the tissue level are potentially powerful SEB's since these visually apparent changes are common in all neoplastic development, regardless of tissue type or neoplastic cause. Currently, subjective inspection of the histological appearance of sectioned and stained material, or "grading," by experienced pathologists is used to evaluate neoplastic progression. This has well-known limitations of reproducibility, accuracy, and resolution of grading scale. Since neoplastic changes are visually apparent and morphologic in nature, quantification by image analysis is a measurement modality of choice. Image analysis was implemented through the use of high-resolution "tiled" images of complete tissue sections. A histological grading system, or "scale," was developed that could be expressed in terms of normal deviate units of multiple and different morphometric descriptors. Neoplastic growth was characterized quantitatively with multiple measurements on each tissue image tile, which were combined into a single number for each tile, i.e., a histologic grade per tile, and parameters from the distributions of these measurements were used to represent the histologic grade for the entire region considered. This concept provided a uniform final scale in similar units of measurement, regardless of which tissues were graded. Also, the grading scale automatically adjusted measurement variance for different tissues by using normal tissue for each different type to obtain the normalization to standard deviation (z) units. This further defined a uniform final scale and maintained standard references. Using this method, results from two well-known animal models of carcinogenesis, squamous cell carcinoma of SENCAR mouse skin induced by benzo(a)pyrene (B[a]P), and squamous cell carcinoma of the rat esophagus induced by N-nitrosomethylbenzylamine (NMBA), were compared to each other. Image analysis was performed on skin tissue sections from a total of 64 SENCAR mice, and esophagus tissue sections from 96 Fischer-344 rats. In both cases, a quantitative expression of the preinvasive neoplastic response to the carcinogen as a function of time of exposure was expressed along a continuous grading scale in standard deviation units (z). In the SENCAR mouse skin animal model, similar cohorts of 4 mice at 20 weeks showed significant modulation of B[a]P-induced neoplasia by treatment with the antiproliferative agent difluoromethylornithine, P < .05. In the rat esophagus animal model, similar cohorts of 6 rats at 10 and 15 weeks showed significant modulation of NMBA-induced neoplasia by treatment with the antimutagen phenethyl isothiocyanate, P < .05.

Properties of intraepithelial neoplasia relevant to the development of cancer chemopreventive agents

Cancer chemoprevention is concerned with the development of drugs or diet supplements that will avert the onset or stop the progression of the intraepithelial neoplasia which precedes invasive cancer. Two basic processes underlie the onset and development of intraepithelial neoplasia. First is genomic instability (often associated with chronic diffuse epithelial hyperplasia), which is the increased production of genomic structural variants due to unrepaired DNA breaks with secondary formation of abnormal structures, including "mutator" mutations in genes responsible for genomic stability, gene copy amplification or loss from DNA breakage-fusion-anaphase bridge cycles, unequal sister chromatid exchange, and accumulation of double minutes. Second is the development within an epithelium having genomic instability of multicentric neoplastic lesions that independently progress through each of the following processes at a continuously accelerating rate: clonal evolution, hyperproliferation, production of genomic structural variants, and apoptosis. Recommended chemoprevention strategies based on these mechanisms are (1) early diagnosis and treatment of genomic instability before the appearance of intraepithelial neoplasia, i.e., during the "predysplastic" or "premorphologic" phase, (2) development of multiple agents that block intralesional proliferation at steps along the "command" pathways of mitotic signal transduction and along the "execute" pathways of synthesis of daughter cell components, (3) development of nontoxic antiinflammatory agents, antioxidants, antimutagens, and proapoptotics, (4) avoidance of "clonal escape" through use of drug combinations, and (5) use of computer-assisted quantitative image analysis to assay modulation of surrogate endpoints in chemoprevention clinical trials.

Effects of theaflavins on N-nitrosomethylbenzylamine-induced esophageal tumorigenesis

The purpose of this experiment was to compare the inhibitory effects of the polyphenol fraction of black tea, theaflavins (TF), the polyphenol fraction of green tea, and (-)-epigallocatechin-3-gallate (EGCG) in the rat esophageal tumor model. The tea fractions were administered in the drinking water at concentrations of 360 and 1,200 ppm for two weeks before administration of the esophageal carcinogen N-nitrosomethylbenzylamine (NMBA). NMBA was administered subcutaneously in 10% dimethyl sulfoxide three times weekly for five weeks. Additional groups of rats received only vehicle and plain drinking water or vehicle and drinking water containing 1,200 ppm of each tea fraction. Twenty-five weeks after NMBA administration began, the experiment was terminated and esophagi were excised and scored for tumors. Rats that were not dosed with NMBA had no tumors. Rats treated with NMBA only had an esophageal tumor incidence of 100% and a multiplicity of 3.3 +/- 0.4 tumors/rat. The proportion of rats developing tumors was not significantly reduced by any of the four tea fractions at the concentrations tested. However, the 1,200 ppm concentrations of each tea fraction in the drinking water produced some reduction in esophageal tumor multiplicity, although only TF significantly reduced tumor multiplicity compared with rats treated with NMBA only. The rates of esophageal tumor formation were significantly reduced at 360 and 1,200 ppm by TF and EGCG.

Development of new cancer chemoprevention agents: role of pharmacokinetic/pharmacodynamic and intermediate endpoint biomarker monitoring

Recently, several promising strategies have been advanced for improving the efficiency of new agent development. These include pharmacokinetic/pharmacodynamic (PK/PD) and intermediate endpoint biomarker (IEB) monitoring. Here, we review their essential role as practical tools for guiding the evaluation of agents for cancer chemoprevention (CP) and provide examples of CP agents that utilize these approaches. Several important categories of IEBs are delineated, including histologically based (intraepithelial neoplasias and nuclear morphometry). The use of select IEBs combined with a Bayesian method for clinical trial monitoring for rapid identification of ineffective or promising agents is discussed. The similarities between IEB and TDM are described. Finally, we present future tools for enhanced monitoring of CP agents that will impact on laboratory medicine and are also applicable to many other drug classes, e.g., laser capture microdissection and cDNA chip microarrays that assess gene expression patterns of precancerous and cancerous lesions.

Effect of tea extracts, polyphenols, and epigallocatechin gallate on azoxymethane-induced colon cancer

Studies were conducted to determine the chemopreventive efficacy of several types of tea extracts on azoxymethane-induced colon cancer in male F344 rats. After determining the maximally tolerated dosage of the tea products, their effect in a colon cancer model was investigated. Groups of 36 male F344 rats received 2 subcutaneous doses of 15 mg/kg azoxymethane (AOM) at Weeks 6 and 7. Experimental groups also received as drinking fluids 3600 ppm of black or green tea extracts, 1800 ppm of EGCG, or 1800 ppm of black or green tea polyphenols beginning at 5 weeks of age. Additional groups drank a lower dose of 360 ppm of the five tea products. The experiments were terminated 43 weeks after the first tea exposure. No evidence of toxicity was observed since the body weight gain of all groups was similar. The rats given AOM had carcinoma of the small intestine and of the colon, classified histologically as in situ carcinoma, exophytic, invasive, and Peyer's patch carcinoma. In the small intestine, most of the neoplasms were classified as invasive, but in the colon, most were exophytic. The various tea products failed to produce a significant difference in the incidence of the several types of colon and small intestine carcinoma. The multiplicity of colon cancers ranged from 1.2-2.8 in all groups. The group on 3600 ppm of green tea had a significantly higher tumor multiplicity than the control group on AOM and water. Also, the group on 3600 ppm of green tea had a significantly higher tumor multiplicity than the group on 360 ppm. The tea products did not affect the development aspects of the tumors in most groups. The mechanisms underlying these findings rest on the fact that azoxymethane is metabolized mainly by cytochrome P450 2E1, and this enzyme system is not affected by tea.

Aromatase inhibitors as potential cancer chemopreventives

Epidemiological and experimental evidence strongly supports a role for estrogens in the development and growth of breast tumors. A role for estrogen in prostate neoplasia has also been postulated. Therefore, one chemopreventive strategy for breast and prostate cancers is to decrease estrogen production. This can be accomplished by inhibiting aromatase, the enzyme that catalyzes the final, rate-limiting step in estrogen biosynthesis. The use of aromatase inhibitors is of clinical interest for cancer therapy, and selective, potent aromatase inhibitors have been developed. Several of these agents have demonstrated chemopreventive efficacy in animal models. The rationale for the use of aromatase inhibitors as chemopreventives and identification of inhibitors to serve as potential chemopreventive agents are the subjects of this review. After background information regarding aromatase is presented, the data for each inhibitor are summarized separately. The discussion focuses on those inhibitors that are clinically available or in clinical trials, including: aminoglutethimide (Cytadren), rogletimide, fadrozole hydrochloride, liarozole hydrochloride, anastrozole (Arimidex), letrozole, vorozole, formestane, exemestane, and atamestane. On the basis of results from preclinical studies, aromatase inhibitors may be promising agents for clinical trials in populations at high risk for developing estrogen-dependent cancers. Total suppression of aromatase may have adverse effects, as is evident in postmenopausal women (increased osteoporosis, cardiovascular disease, and urogenital atrophy). However, on the basis of preclinical studies of chemopreventive efficacy and chemotherapeutic applications of aromatase inhibitors showing dose-response efficacy, it may be possible to obtain chemopreventive effects without total suppression of aromatase and circulating estrogen levels. Suppressing local estrogen production may be an alternative strategy, as suggested by the discovery of a unique transcriptional promoter of aromatase gene expression, I.4, in breast adipose tissue. The development of drugs that target this promoter region may be possible.

Biomarker end-points in cancer chemoprevention trials

Over the last decade, the Chemoprevention Branch, Division of Cancer Prevention and Control, National Cancer Institute, USA, has been developing drugs that will slow or stop the progression to invasive cancer of precancerous (pre-invasive) lesions generally termed 'intraepithelial dysplasia' or 'dysplasia'. Over 40 short-term clinical trials are in progress, testing the following classes of agents on precancerous lesions in the different major organ systems: antimutagens (N-acetylcysteine, oltipraz), antiproliferatives (difluoromethylornithine, dehydroepiandrosterone, selenomethionine), antioxidants (vitamin E, curcumin), anti-inflammatories (aspirin, piroxicam, ibuprofen, sulindac sulfone) and hormonally active agents (tamoxifen in breast ductal carcinoma in situ and finasteride in prostatic intraepithelial neoplasia). Because of the strong practical need to keep so many clinical trials as short-term as possible, certain tissue changes known to be associated with high cancer risk were selected for use as biomarker end-points in the trials, such changes being quantitatively assayed by computer-assisted image analysis. These 'surrogate end-point biomarkers' (SEBs) are based on the individual cellular morphological and functional changes universally used by histopathologists to diagnose the lesion of intraepithelial neoplasia (Riddell, 1984; Boone et al., 1992; Wright et al., 1994). High grades of this lesion precede invasive cancer in the great majority of cases, and therefore SEBs based on them are linked to high cancer risk. Table 1 summarizes some of the short-term clinical trials now being monitored by the Chemoprevention Branch. The SEBs abbreviated 'PPNN' in the figure are: proliferative index (P); ploidy (DNA histogram) (P); nuclear morphometry and chromatin texture (N); and nucleolar size and frequency (N). Computer-assisted image analysis is used to assay these features quantitatively, which gives the SEBs increased objectivity, reproducibility and sensitivity. Further details concerned with cancer chemoprevention trials using SEBs, and their relation to the field of cancer epidemiology, are given below.

Properties of intraepithelial neoplasia relevant to cancer chemoprevention and to the development of surrogate end points for clinical trials

Cancer chemoprevention is defined as the prevention of cancer by the administration of diet supplements or drugs. A drug discovery effort should therefore focus on finding agents that will avert the process of intraepithelial neoplasia which precedes invasive cancer. Over 30 agents developed by the chemoprevention program at the National Cancer Institute are being tested against intraepithelial neoplasia of many organ sites in more than 80 clinical trials. Two basic mechanisms underlie the onset and development of intraepithelial neoplasia. First is the development of the two precursor lesions of chronic diffuse epithelial hyperplasia and genomic instability, the latter being produced by "mutator" mutations in genes responsible for genomic stability, by gene copy amplification or loss from DNA breakage-fusion-anaphase-bridge cycles, by unequal sister chromatid exchange, and by accumulation of double minutes. Second is the development of multicentric intraepithelial neoplastic lesions which independently progress through each of the following processes at a continuously accelerating rate: clonal evolution, hyperproliferation, production of genomic structural variants, and apoptosis. Recommended chemoprevention strategies based on these mechanisms are (i) the development of better technology for early diagnosis, (ii) the development of multiple agents that block intralesional proliferation at steps along the signal pathway of mitotic signal transduction and along the signal pathway of synthesis of daughter cell components, (iii) the development of nontoxic anti-inflammatory agents, anitoxidants, antimutagens, and proapoptotics, (iv) the avoidance of "clonal escape" through use of drug combinations, and (v) the use of computer-assisted quantitative image analysis to assay modulation of surrogate end points in chemoprevention clinical trials.

DNA image cytometric measurement as a surrogate end point biomarker in a phase I trial of alpha-difluoromethylornithine for cervical intraepithelial neoplasia

Cervical intraepithelial neoplasia grade 3 (CIN 3) is considered a high-risk precursor of invasive cervical cancer. alpha-Difluoromethylornithine (DFMO) is a promising antiproliferative chemopreventive agent. The purpose of this study was to evaluate image cytometric measurement of nuclear DNA (ICM-DNA) as a surrogate end point biomarker (SEB) in a Phase I trial of DFMO for CIN. Thirty patients with CIN 3 were treated with DFMO at five doses, ranging from 0.0625 to 1.0 g/m2/day, for 1 month. Half of the patients had histological responses. Twenty-five pre- and posttreatment cervical biopsy specimens (from 11 responders and 14 nonresponders) were available for this analysis. ICM-DNA was performed on 4-micron sections cut from formalin-fixed tissue blocks and stained with a thionin-SO2 Feulgen reaction. ICM-DNAs for each case were expressed as normalized measurements (against the nuclear modal absorbance of lymphocytes) of the absorbance of each cell of interest and were presented in bar histograms. The mean normalized summed absorbance (sigma ODn) was obtained as a mean histogram of the cell population of interest. Nineteen (76%) of 25 patients had a significant decrease in sigma ODn after DFMO treatment. Posttreatment values were significantly lower than pretreatment values in a paired analysis, and responders had significantly lower values than nonresponders. Analyses of different ICM-DNA references, including percentile values of sigma ODn distribution, DNA malignancy grade, and 5c exceeding rate, showed a decrease of mean sigma ODn during DFMO treatment. In addition, the summed posttreatment sigma ODn histograms also showed progressively shorter right shoulders compared with pretreatment histograms in both responders and nonresponders. We concluded that the modulation of sigma ODn reflected the chemoprevention effect of DFMO even before morphological changes appeared, and thus, ICM-DNA may be useful as a SEB in chemoprevention trials of DFMO. Additional reasons for using ICM-DNA as a SEB are the relative simplicity of its use, the high accuracy of the results, the low cost of the reagents, the ability to use small tissue samples, and the objectivity and reproducibility of the procedure.

Farnesyl protein transferase inhibitors as potential cancer chemopreventives

Among the most important targets for chemopreventive intervention and drug development are deregulated signal transduction pathways. Ras proteins serve as central connectors between signals generated at the plasma membrane and nuclear effectors; thus, disrupting the Ras signaling pathway could have significant potential as a cancer chemopreventive strategy. Target organs for Ras-based chemopreventive strategies include those associated with activating ras mutations (e.g., colorectum, pancreas, and lung) and those carrying aberrations in upstream element(s), such as growth factors and their receptors. Ras proteins require posttranslational modification with a farnesyl moiety for both normal and oncogenic activity. Inhibitors of the enzyme that catalyzes this reaction, farnesyl protein transferase (FPT) should, therefore, inhibit Ras-dependent proliferative activity in cancerous and precancerous lesions (J. B. Gibbs et al., Cell, 77: 175-178, 1994). Because growth factor networks are redundant, selective inhibition of signaling pathways activated in precancerous and cancerous cells should be possible. Requirements for Ras farnesylation inhibitors include: specificity for FPT compared with other prenyl transferases; specificity for FPT compared with other farnesyl PPi-utilizing enzymes; ability to specifically inhibit processing of mutant K-ras (the most commonly mutated ras gene in human cancers); high potency; selective activity in intact cells; activity in vivo; and lack of toxicity. Numerous FPT inhibitors have been identified through random screening of natural products and by rational design of analogues of the two substrates, farnesyl PPi and the COOH-terminal CAAX motif of Ras tetrapeptides. A possible testing strategy for developing FPT inhibitors as chemopreventive agents includes the following steps: (a) determine FPT inhibitory activity in vitro; (b) evaluate selectivity (relative to other protein prenyl transferases and FPT-utilizing enzymes); (c) determine inhibition of Ras-mediated effects in intact cells; (d) determine inhibition of Ras-mediated effects in vivo (e.g., in nude mouse tumor xenografts); and (e) determine chemopreventive efficacy in vivo (e.g., in carcinogen-induced A/J mouse lung, rat colon, or hamster pancreas).

Progress in clinical chemoprevention

Chemoprevention has four goals: (1) inhibition of carcinogens, (2) logical intervention for persons at genetic risk for cancer, (3) treatment of precancerous lesions, and (4) confirmation and translation of leads from dietary epidemiology into intervention strategies. The National Cancer Institute has described a multidisciplinary, cancer science-based program for chemopreventive drug development that addresses these objectives, and has collaborated with the US Food and Drug Administration to provide consensus guidance for applying this approach. A critical component is the identification and characterization of intermediate biomarkers of cancer and their validation as surrogate end points for cancer incidence in clinical chemoprevention trials. More than 40 agents in the program are currently on the clinical development path (preclinical toxicology and phase I clinical safety studies or phase II/III efficacy trials), with the major effort in phase II studies to identify and characterize intermediate biomarkers. The continually advancing knowledge of molecular and tissue-based carcinogenesis mechanisms will provide leads to new chemopreventive agents with increased specificity for carcinogenesis-related activities and, hence, reduced toxicity by virtue of minimal effects on normal cell and tissue functions. Results from the Human Genome Project will help identify and evaluate the potential for chemopreventive intervention in cohorts at genetic risk and will provide specific target lesions for intervention strategies.

Apoptosis, cell replication, and Western-style diet-induced tumorigenesis in mouse colon

In this study, feeding Western-style diets (WDs) to mice for a duration of two years without any chemical carcinogen led to the development of gross colonic lesions that were histologically classified as dysplastic crypts and focal hyperplasias with or without atypical nuclei. To better understand early biological events contributing to the development of colonic neoplasia, grossly normal colonic mucosa was investigated; mitotic and apoptotic colonic epithelial cells, atypical mitosis, and atypical nuclei were studied. A significant and transient increase of mitotic activity in the basal and intermediate portions of the colonic crypts was seen in young mice after feeding them the WDs. This was accompanied by diffuse activation of apoptosis of the colonic epithelial cells. In the middle of the rodents' life span, after administration of both the WDs and control diet, the rodents developed a marked depletion of apoptotic epithelial cells in the mid-region of the colonic crypts; this was followed by the expansion of an epithelial cell population containing atypical nuclei, and the emergence of the gross lesions noted above. With this sequence of events, prolonged feeding of WDs to mice produced single-crypt dysplastic lesions and focal hyperplasias indicative of tumorigenesis.

Strategies for identification and clinical evaluation of promising chemopreventive agents

Strategies for chemopreventative drug development are based on the use of well-characterized agents, intermediate biomarkers correlating to cancer incidence, and suitable cohorts for efficacy studies. Since chemoprevention is applied over the long-term, chemopreventive drugs must have low toxicity. Strategies for enhancing chemopreventive drug efficacy and minimizing toxicity include combinations of drugs with complementary mechanisms and/or synergistic activity; coadministration of drugs to counter the toxicity of the chemopreventive agents; and pursuit of related compounds that retain efficacy with reduced side effects. Because of its slow development, cancer is not a feasible end point for clinical evaluation of chemoprevention, and so intermediate biomarkers that can serve as surrogate end points are crucial. Particularly important biomarkers are the morphometric and cytometric changes defining intraepithelial neoplasia (IEN). Cohorts for chemoprevention trials should have high incidences of the cancer or intermediate biomarker(s) under study within the trial duration.

Epidermal growth factor receptor tyrosine kinase inhibitors as potential cancer chemopreventives

Among the most important targets for chemopreventive intervention and drug development are deregulated signal transduction pathways, and protein tyrosine kinases are key components of these pathways. Loss of tyrosine kinase regulatory mechanisms has been implicated in neoplastic growth; indeed, many oncogenes code for either receptor or cellular tyrosine kinases. Because of its deregulation in many cancers (bladder, breast, cervix, colon, esophagus, head and neck, lung, and prostate), the epidermal growth factor receptor (EGFR) has been selected as a potential target for chemoprevention. Because growth factor networks are redundant, selective inhibition of signaling pathways activated in precancerous and cancerous cells should be possible. Requirements for specific EGFR inhibitors include specificity for EGFR, high potency, activity in intact cells, and activity in vivo. Inhibition of autophosphorylation is preferred, because it should result in total blockade of the signaling pathway. Inhibitors that compete with substrate rather than at the ATP-binding site are also preferable, because they are not as likely to inhibit other ATP-using cellular enzymes. Several classes of specific EGFR inhibitors have been synthesized recently, including structures such as benzylidene malononitriles, dianilinophthalimides, quinazolines, pyrimidines, [(alkylamino)methyl]-acrylophenones, enollactones, dihydroxybenzylaminosalicylates, 2-thioindoles, aminoflavones, and tyrosine analogue-containing peptides. A possible testing strategy for the development of these and other EGFR inhibitors as chemopreventive agents includes the following steps: (a) determine EGFR tyrosine kinase inhibitory activity in vitro; (b) evaluate EGFR specificity and selectivity (relative to other tyrosine kinases and other protein kinases); (c) determine inhibition of EGFR-mediated effects in intact cells; (d) determine inhibition of EGFR-mediated effects in vivo (e.g., in nude mouse tumor xenografts); and (e) determine chemopreventive efficacy in vivo (e.g., in the hamster buccal pouch or mouse or rat bladder).

Strategy and planning for chemopreventive drug development: clinical development plans II

This is the second publication of Clinical Development Plans from the National Cancer Institute, Division of Cancer Prevention and Control, Chemoprevention Branch and Agent Development Committee. The Clinical Development Plans summarize the status of promising chemopreventive agents regarding evidence for safety and chemopreventive efficacy in preclinical and clinical studies. They also contain the strategy for further development of these drugs, addressing pharmacodynamics, drug effect measurements, intermediate biomarkers for monitoring efficacy, toxicity, supply and formulation, regulatory approval, and proposed clinical trials. Sixteen new Clinical Development Plans are presented here: curcumin, dehydroepiandrosterone, folic acid, genistein, indole-3-carbinol, perillyl alcohol, phenethyl isothiocyanate, 9-cis-retinoic acid, 13-cis-retinoic acid, l-selenomethionine and 1, 4-phenylenebis(methylene)selenocyanate, sulindac sulfone, tea, ursodiol, vitamin A, and (+)-vorozole. The objective of publishing these plans is to stimulate interest and thinking among the scientific community on the prospects for developing these and future generations of chemopreventive drugs.

Detection of genomic alterations in human cervical cancer by two-dimensional gel electrophoresis

Two-dimensional gel electrophoresis was used to comprehensively scan the whole genome of 6 cervical intraepithelial neoplasia (CIN) lesions, 7 cervical squamous cell carcinomas, 1 cervical adenosquamous cell carcinoma, and 2 cervical adenocarcinomas for multiple genetic alterations, such as DNA amplification, chromosome deletion, loss of heterozygosity, and chromosome translocation, as compared with the paired normal tissues. DNA spot analysis of the genomic 2-dimensional gels was performed by a computer color overlay system and by spot recognition software allowing for objective spot comparison and quantitation. Nine spots were found to be amplified in the cervical carcinomas while two amplified spots were detected in the CIN III lesions. Fourteen DNA spots were either reduced in their intensity or absent in cervical carcinomas as compared to their normal paired tissues. Reduction of intensity in 6 spots was observed in the 5 CIN III lesions. These genetic alterations may represent changes in cancer genes that are associated with human cervical carcinogenesis. Further characterization of these alterations may be significant to the understanding of cervical tumorigenesis and to the development of biomarkers for clinical trials in cancer chemoprevention.

Risk biomarkers and current strategies for cancer chemoprevention

Quantifiable, well-characterized cancer risk factors demonstrate the need for chemoprevention and define cohorts for chemopreventive intervention. For chemoprevention, the important cancer risk factors are those that can be measured quantitatively in the subject at risk. These factors, called risk biomarkers, can be used to identify cohorts for chemoprevention. Those modulated by chemopreventive agents may also be used as endpoints in chemoprevention studies. Generally, the risk biomarkers fit into categories based on those previously defined by Hulka: 1) carcinogen exposure, 2) carcinogen exposure/effect, 3) genetic predisposition, 4) intermediate biomarkers of cancer, and 5) previous cancers. Besides their use in characterizing cohorts for chemoprevention trials, some risk biomarkers can be modulated by chemopreventive agents. These biomarkers may be suitable surrogate endpoints for cancer incidence in chemoprevention intervention trials. The criteria for risk biomarkers defining cohorts and serving as endpoints are the same, except that those defining cohorts are not necessarily modulated by chemopreventive agents. A primary criterion is that the biomarkers fit expected biological mechanisms of early carcinogenesis-i.e., differential expression in normal and high-risk tissue, on or closely linked to the causal pathway for the cancer, and short latency compared with cancer. They must occur in sufficient number to allow their biological and statistical evaluation. Further, the biomarkers should be assayed reliably and quantitatively, measured easily, and correlated to cancer incidence. Particularly important for cancer risk screening in normal subjects is the ability to use noninvasive techniques that are highly specific, sensitive, and quantitative. Since carcinogenesis is a multipath process, single biomarkers are difficult to correlate to cancer, as they may appear on only one or a few of the many possible causal pathways. As shown in colorectal carcinogenesis, the risks associated with the presence of biomarkers may be additive or synergistic. That is, the accumulation of genetic lesions is the more important determinant of colorectal cancer compared with the presence of any single lesion. Thus, batteries of biomarker abnormalities, particularly those representing the range of carcinogenesis pathways, may prove more useful than single biomarkers both in characterizing cohorts at risk and defining modulatable risks. Risk biomarkers are already being integrated into many chemoprevention intervention trials. One example is the phase II trial of oltipraz inhibition of carcinogen-DNA adducts in a Chinese population exposed to aflatoxin B1. Also, urine samples from subjects in this trial will be screened for the effect of oltipraz on urinary mutagens. A second example is a chemoprevention protocol developed for patients at high risk for breast cancer; the cohort is defined both by hereditary risk and the presence of biomarker abnormalities. Modulation of the biomarker abnormalities is a proposed endpoint. Also, dysplastic lesions, such as prostatic intraepithelial neoplasia, oral leukoplakia and colorectal adenomas, have been used to define high-risk cohorts and as potential modulatable surrogate endpoints in chemoprevention trials.

New agents for cancer chemoprevention

Clinical chemoprevention trials of more than 30 agents and agent combinations are now in progress or being planned. The most advanced agents are well known and are in large Phase III chemoprevention intervention trials or epidemiological studies. These drugs include several retinoids [e.g., retinol, retinyl palmitate, all-trans-retinoic acid, and 13-cis-retinoic acid], calcium, Beta carotene, vitamin E, tamoxifen, and finasteride. Other newer agents are currently being evaluated in or being considered for Phase II and early Phase III chemoprevention trials. Prominent in this group are all-trans-N-(4-hydroxy phenyl)retinamide (4-HPR) (alone and in combination with tamoxifen), 2-difluoromethylornithine (DFMO), nonsteroidal antiinflammatory drugs (aspirin, piroxicam, sulindac), oltipraz, and dehydroepiandrostenedione (DHEA). A third group is new agents showing chemopreventive activity in animal models, epidemiological studies, or in pilot clinical intervention studies. They are now in preclinical toxicology testing or Phase I safety and pharmacokinetics trials preparatory to chemoprevention efficacy trials. These agents include S-allyl-l-cysteine, curcumin, DHEA analog 8354 (fluasterone), genistein, ibuprofen, indole-3-carbinol, perillyl alcohol, phenethyl isothiocyanate, 9-cis-retinoic acid, sulindac sulfone, tea extracts, ursodiol, vitamin D analogs, and p-xylyl selenocyanate. A new generation of agents and agent combinations will soon enter clinical chemoprevention studies based primarily on promising chemopreventive activity in animal models and in mechanistic studies. Among these agents are more efficacious analogs of known chemopreventive drugs including novel carotenoids (e.g., alpha-carotene and lutein). Also included are safer analogs which retain the chemopreventive efficacy of the parent drug such as vitamin D3 analogs. Other agents of high interest are aromatase inhibitors (e.g., (+)-vorozole), and protease inhibitors (e.g., Bowman-Birk soybean trypsin inhibitor). Combinations are also being considered, such as vitamin E with l-selenomethionine. Analysis of signal transduction pathways is beginning to yield classes of potentially active and selective chemopreventive drugs. Examples are ras isoprenylation and epidermal growth factor receptor inhibitors.

DNA quantification in cervical intraepithelial neoplasia thick tissue sections by confocal laser scanning microscopy

Image analysis of tissue biopsies for determination of DNA content as an early marker of neoplasia is hampered by the complexity of corrections necessary to dea with nuclear truncation and overlap in thin sections. The use of confocal laser scanning microscopy (CLSM) for measurement of cellular DNA content on whole cells within thick tissue sections offers the advantage of preservation of cellular architecture, capacity for 3-dimensional analysis, and absence of sectioning artifacts. We have applied this technique to pararosaniline-Feulgen stained human cervical tissues graded from normal to cervical intraepithelial neoplasia (CIN) III. For the purpose of comparison, 15 microns sections were stained and mapped so that the same cell population could be analyzed by both integrated optical density and fluorescence intensity. Distribution of DNA content from normal cervical epithelial cells 2-3 layers out from the basal cell layer measured by both methodologies showed a stable G0/G1 population with no observable S-phase or G2 cells. Cells measured from areas of increasing CIN grade showed progressively higher DNA content values that were not observable in normal tissue. Although these data are preliminary they suggest that CLSM can be used to identify aneuploid states within defined structural areas of pre-invasive neoplasia.

Genetic and cellular changes in colorectal cancer: proposed targets of chemopreventive agents

Progress in development of a genetic model for colorectal tumorigenesis and human chemoprevention research may allow the mechanism-based identification of targets and chemopreventive agents that will protect against colorectal cancer. For example, numerous mutagenic events can occur throughout colorectal carcinogenesis, including loss of heterozygosity in tumor suppressor genes such as APC, MCC, DCC, and p53, as well as in oncogenes such as K-ras. Chemopreventive agents that inhibit mutagenic activity such as N-acetyl-l-cysteine, oltipraz, and nonsteroidal anti-inflammatory drugs may protect against these mutations. Also, agents such as perillyl alcohol and lovastatin that interfere with protein isoprenylation and, hence, inhibit oncogene activation may protect against aberrant K-ras expression. Hyperproliferation in normal mucosa, leading to growth and progression of neoplasia, are also aspects of colorectal carcinogenesis that can be controlled by chemopreventive agents. Calcium is a chemopreventive agent for which there is both clinical and experimental evidence of inhibition of cell proliferation in colon mucosa. Other examples of antiproliferative agents with potential chemopreventive efficacy in colon are 2-difluoromethylornithine, dehydroepiandrosterone, and selenium. Differentiating agents such as retinoids and deltanoids also may slow proliferation and progression. Antioxidants have potential for interfering with both mutagenicity and proliferation (e.g., by preventing oxidative activation of carcinogens and scavenging activated oxygen species generated during inflammation). The same mechanistic principles apply to identification of dietary chemopreventive intervention for colorectal carcinogenesis. For example, lowering dietary fat and increasing dietary fiber lead to lower colorectal mucosal proliferation, and cruciferous vegetables contain agents such as indoles and dithiolthiones that have shown antimutagenic activity.

Strategies for phase II cancer chemoprevention trials: cervix, endometrium, and ovary

Well-designed and conducted Phase II clinical trials are very important to cancer chemoprevention drug development. Three critical aspects govern the design and conduct of these trials--well-characterized agents, suitable cohorts, and reliable biomarkers for measuring efficacy that can serve as surrogate endpoints for cancer incidence. Requirements for the agent are experimental or epidemiological data showing chemopreventive efficacy, safety on chronic administration, and a mechanistic rationale for the chemopreventive activity observed. Agents that meet these criteria for chemoprevention of cervical cancer include antiproliferative drugs (e.g., 2-difluoromethylornithine), retinoids, folic acid, antioxidant vitamins and other agents that prevent cellular oxidative damage. Because of the significant cervical cancer risk associated with human papilloma virus (HPV) infection, agents that interfere with the activity of HPV products may also prove to be effective chemopreventives. In endometrium, unopposed estrogen exposure has been associated with cancer incidence. Thus, pure antiestrogens and progestins may be chemopreventive in this tissue. Ovarian cancer risk is correlated to ovulation frequency; therefore, oral contraceptives are potentially chemopreventive in the ovary. Recent clinical observations also suggest that retinoids, particularly all-trans-N-4-hydroxyphenylretinamide, may be chemopreventive in this tissue. The cohort should be suitable for measuring the chemopreventive activity of the agent and the intermediate biomarkers chosen. In the cervix, patients with cervical intraepithelial neoplasia (CIN) and in endometrium, patients with atypical hyperplasia, fit these criteria. Defining a cohort for a Phase II trial in the ovary is more difficult. This tissue is less accessible for biopsy; consequently, the presence of precancerous lesions is more difficult to confirm. The criteria for biomarkers are that they fit expected biological mechanisms (i.e., differential expression in normal and high-risk tissue, on or closely linked to the causal pathway for the cancer, modulated by chemopreventive agents, and short latency compared with cancer), may be assayed reliably and quantitatively, measured easily, and correlate to decrease cancer incidence. They must occur in sufficient incidence to allow their biological and statistical evaluation relevant to cancer. Since carcinogenesis is a multipath process, single biomarkers are difficult to validate as surrogate endpoints, perhaps appearing on only one or a few of the many possible causal pathways. Panels of biomarkers, particularly those representing the range of carcinogenesis pathways, may prove more useful as surrogate endpoints. It is important to avoid solely on biomarkers that do not describe cancer but represent isolated events that may or may not be on the causal pathway or otherwise associated with carcinogenesis. These include markers of normal cellular processes that may be increased or expressed during carcinogenesis. Chemoprevention trials should be designed to evaluate fully the two or three biomarkers that appear to be the best models of the cancer. Additional biomarkers should be considered only if they can be analyzed efficiently and the sample size allows more important biomarkers to be evaluated completely. Two types of biomarkers that stand out regarding their high correlation to cancer and their ability to be quantified are measures of intraepithelial neoplasia and indicators of cellular proliferation. Measurements made by computer-assisted image analysis that are potentially useful as surrogate endpoint biomarkers include nuclear polymorphism comprising nuclear size, shape (roundness), and texture (DNA distribution patterns); nucleolar size and number of nucleoli/nuclei; DNA ploidy, and proliferation biomarkers such as S-phase fraction and PCNA...

Approaches to the development and marketing approval of drugs that prevent cancer

The broad concept of chemoprevention applies to the prevention of clinical cancer by the administration of chemical agents. Current approaches to the development and marketing approval of drugs to prevent cancer are described by a Working Group from the National Cancer Institute and the Food and Drug Administration. A strategy is presented that identifies candidate drugs, with examples that illustrate how drugs are characterized for efficacy through in vitro transformation modulation and mechanistic assays, and in vivo tumor modulation models of carcinogenesis. Requirements and recommendations for safety evaluation in toxicology testing are given, and the evaluation of pharmacokinetic and pharmacodynamic drug effects and potential surrogate end point biomarkers in Phase I trials are discussed. Appropriate subject populations are identified. Phase II trials should emphasize the evaluation of surrogate end point biomarkers that are highly correlated with cancer incidence and may serve as an estimate of cancer incidence reduction. In Phase III trials the interim analysis of a validated surrogate end point of cancer incidence may facilitate timely and cost-effective marketing of efficacious drugs.

Chronic toxicity studies of the potential cancer preventive 2-(difluoromethyl)-dl-ornithine

The synthetic compound 2-(difluoromethyl)-dl-ornithine irreversibly inhibits ornithine decarboxylase and reduces the intracellular levels of the polyamine cell cycle factors putrescine and spermidine. The drug has shown chemopreventive efficacy in numerous laboratory epithelial cancer models and is a prototype for antiproliferative agents. Chronic toxicity studies in rats and dogs were performed to characterize the toxicities of the compound at high dosages and to support its further development in clinical trials as a potential chemopreventive agent. Chronic administration (52 weeks) by gavage to Charles River CD rats at dosages of 400, 800, and 1600 mg/kg produced weight loss, increased platelets, alopecia and skin abrasions, dermatitis, liver necrosis, and gastric inflammation. The no-effect dose in this study was considered 400 mg/kg. Chronic administration by capsule to dogs at dosages of 50, 100, and 200 mg/kg produced conjunctivitis, hyperkeratosis and alopecia, and cystic intestinal crypts. A no-effect dose was not determined in this study. The toxicities demonstrated in these studies may be minimized at lower dosages and support the further development of this compound in chemopreventive clinical investigations.