Cancer Prevention Research Online First Articles

Finasteride Does Not Increase the Risk of High-Grade Prostate Cancer: A Bias-Adjusted Modeling Approach

2008-03-01

Finasteride taken for 7 years in the Prostate Cancer Prevention Trial (PCPT) reduced the risk of prostate cancer by 25%, but with an apparent increased risk of high-grade disease. Subsequent analyses found that finasteride biases toward improved prostate cancer detection and accuracy in prostate cancer grading at biopsy. In our first analysis of the present study, we accounted for these biases in estimating the effect of finasteride on the risk of overall and high-grade prostate cancer. This analysis used PCPT data that included 3-month longer collection of endpoints than in the original report with observed prostate cancer rates of 22.9% (4.8% with high grade; placebo) versus 16.6% (5.8% with high grade; finasteride). Based on these updated results, the bias-adjusted prostate cancer rates are estimated to be 21.1% (4.2% high grade; placebo) and 14.7% (4.8% high grade; finasteride), a 30% risk reduction in prostate cancer [relative risk (RR), 0.70; 95% confidence interval (95% CI), 0.64-0.76; P < 0.0001] and a nonsignificant 14% increase in high-grade cancer (RR, 1.14; 95% CI, 0.96-1.35; P = 0.12) with finasteride. We then estimated rates of high-grade prostate cancer based on an analysis that incorporated grading information from radical prostatectomies in 500 subjects diagnosed with cancer. The resulting estimates were high-grade cancer rates of 8.2% (placebo) versus 6.0% (finasteride), a 27% risk reduction (RR, 0.73; 95% CI, 0.56-0.96; P = 0.02) with finasteride. Our third analysis examined the impact of biopsy sensitivity on the risk relative of high-grade prostate cancer and found that differential sensitivity of biopsy between the treatment arms can have a significant impact on risk ratio estimates. These collective results suggest that the observed, unadjusted higher risk of high-grade disease with finasteride seems to have been due to facilitated diagnosis resulting primarily from increased biopsy sensitivity with finasteride. Therefore, men undergoing regular prostate cancer screening or who express an interest in cancer prevention should be informed of the opportunity to take finasteride for preventing prostate cancer.

High-Grade Prostate Cancer and the Prostate Cancer Prevention Trial

Logothetis, C. J., Schellhammer, P. F. — 2008-03-01

Pathologic Characteristics of Cancers Detected in the Prostate Cancer Prevention Trial: Implications for Prostate Cancer Detection and Chemoprevention

2008-03-01

The Prostate Cancer Prevention Trial (PCPT) showed a risk of prostate cancer at prostate-specific antigen (PSA) <4.0 ng/mL and that prostate cancer risk is reduced by finasteride. A major concern about early detection by PSA and prevention by finasteride is that they may involve biologically inconsequential tumors. We reviewed the pathologic characteristics of prostate biopsies from men in the placebo and finasteride groups of the PCPT. We examined tumor pathology characteristics stratified by level of PSA for men in the placebo group who underwent radical prostatectomy. Seventy-five percent of all cancers and 62% of Gleason score ≤6 cancers in the PCPT met the biopsy criteria for clinically significant tumors. Surrogate measures for tumor volume (number of cores positive, percent cores positive, linear extent, and bilaterality) and risk of perineural invasion were lower in men who received finasteride. The PSA-associated risks of insignificant cancer were 51.7% (PSA, 0-1.0 ng/mL), 33.7% (1.1-2.5 ng/mL), 17.8% (2.6-4.0 ng/mL), and 11.7% (4.1-10 ng/mL). Conversely, the risks of high-grade (Gleason score ≥7) tumors for the same PSA strata were 15.6%, 37.9%, 49.1%, and 52.4%, respectively. These data highlight the dilemma of PSA when used for screening: Lower cutoff levels increase detection of insignificant disease, but cure is more likely, whereas higher cutoff levels make detection of significant cancer more likely, but cure is less likely. Therefore, the effectiveness of finasteride in preventing prostate cancer, including Gleason score ≤6 cancer, with meaningful rates of significant disease in the PCPT suggests that cutoff values for PSA screening should be individualized and that men undergoing screening should be informed of the opportunity to reduce their risk of disease with finasteride.

Estimating Rates of True High-Grade Disease in the Prostate Cancer Prevention Trial

Pinsky, P., Parnes, H., Ford, L. — 2008-03-01

The Prostate Cancer Prevention Trial (PCPT) showed a decreased prostate cancer rate but an increased rate of high Gleason grade disease on biopsy for finasteride versus placebo. The results from radical prostatectomy (RP) on 25% of the men undergoing RP have recently been reported and suggest that grading artifacts in biopsy Gleason scoring may have occurred. We used a statistical model to extrapolate the RP Gleason results to all men in the PCPT using a missing-at-random assumption. We estimated the rates of true high-grade (Gleason 7-10) and true low-grade disease, where true Gleason grade is what is (or would have been) found on RP. We also estimated misclassification rates on biopsy of true high-grade and low-grade disease. We show that the rate of upgrading of biopsy low-grade disease to high-grade on RP is a function of misclassification rates as well as the ratio of true low-grade to high-grade disease. The estimated relative risks for true low-grade and true high-grade disease for finasteride compared with placebo were 0.61 (95% confidence interval, 0.51-0.71) and 0.84 (95% confidence interval, 0.68-1.05), respectively. The misclassification rate of true high-grade disease (to low-grade disease on biopsy) was significantly lower for finasteride (34.6%) than for placebo (52.6%). Although misclassification rates differed, upgrading rates were similar in each arm due to the different ratios of true low-grade to high-grade disease in each arm. Results from RP show that misclassification rates on biopsy were higher in the placebo arm and that the rate of true high-grade disease may have been lower in the finasteride arm.

Impact of Economic, Regulatory, and Patent Policies on Innovation in Cancer Chemoprevention

Grabowski, H. G., Moe, J. L. — 2008-03-01

Chemoprevention agents are an emerging new scientific area that holds out the promise of delaying or avoiding a number of common cancers. These new agents face significant scientific, regulatory, and economic barriers, however, which have limited investment in their research and development (R&D). These barriers include above-average clinical trial scales, lengthy time frames between discovery and Food and Drug Administration approval, liability risks (because they are given to healthy individuals), and a growing funding gap for early-stage candidates. The longer time frames and risks associated with chemoprevention also cause exclusivity time on core patents to be limited or subject to significant uncertainties. We conclude that chemoprevention uniquely challenges the structure of incentives embodied in the economic, regulatory, and patent policies for the biopharmaceutical industry. Many of these policy issues are illustrated by the recently Food and Drug Administration–approved preventive agents Gardasil® and raloxifene. Our recommendations to increase R&D investment in chemoprevention agents include (a) increased data exclusivity times on new biological and chemical drugs to compensate for longer gestation periods and increasing R&D costs; chemoprevention is at the far end of the distribution in this regard; (b) policies such as early-stage research grants and clinical development tax credits targeted specifically to chemoprevention agents (these are policies that have been very successful in increasing R&D investment for orphan drugs); and (c) a no-fault liability insurance program like that currently in place for children's vaccines.

Genomics of Smoking Exposure and Cessation: Lessons for Cancer Prevention and Treatment

Penning, T. M., Lerman, C. — 2008-03-01

Tobacco use is the greatest preventable cause of cancer in the United States, accounting for almost one third of all cancer-related deaths and 90% of deaths from lung cancer. Despite widespread knowledge of these risks, tobacco use prevalence rates are 20% in the United States and up to 30% to 50% in the developing world (1, 2). Nicotine, the addictive chemical in tobacco, produces a biological dependence (3), and therefore, even with the most efficacious medications available, only one in four smokers is able to maintain long-term abstinence (4). Persistent tobacco use is common even following a diagnosis of tobacco-related cancer and is associated with poorer outcomes of radiation therapy and chemotherapy and with increased risk of second primary malignancies (5). Although smoking cessation is optimal, it may not be realistic for all patients. Therefore, it is essential to gain a better understanding of the cellular and molecular mechanisms through which tobacco exposure contributes to cancer pathogenesis and outcomes, and to develop targeted prevention and therapeutic approaches.

Increased Susceptibility of Nrf2 Knockout Mice to Colitis-Associated Colorectal Cancer

2008-03-01

The nuclear factor-erythroid 2-related factor 2 (Nrf2) plays a critical role in protecting various tissues against inflammation, which is a potential risk factor for colorectal and other cancers. Our previously published mouse model work showed that Nrf2 helps protect against dextran sulfate sodium (DSS)–induced colitis/inflammation, and others have shown that Nrf2 helps protect against inflammation-associated colorectal carcinogenesis (aberrant crypt foci). The present study extended these important earlier findings by exploring the role of Nrf2 in colitis-associated colorectal cancer in a mouse model involving azoxymethane/DSS–induced colorectal carcinogenesis in Nrf2 knockout mice. Azoxymethane/DSS–treated Nrf2 knockout mice had increased incidence, multiplicity, and size of all colorectal tumors, including adenomas, versus treated wild-type (WT) mice, and the proportion of tumors that were adenocarcinoma was much higher in knockout (80%) versus WT (29%) mice. Compared with WT mice, knockout mice also had increased markers of inflammation in tumor tissue (cyclooxygenase-2 and 5-lipoxygenase expressions and prostaglandin E₂ and leukotriene B₄ levels) and in inflamed colonic mucosa (nitrotyrosine expression), supporting the association of knockout mouse tumor formation with inflammation. The phase II detoxifying/antioxidant enzymes NAD(P)H-quinone reductase 1 and UDP-glucurosyltransferase 1A1 were elevated in the normal mucosa of WT, but not Nrf 2 knockout, mice treated with azoxymethane/DSS. Our findings show that Nrf2 plays a critical role in protecting against inflammation-associated colorectal cancer.

Targeting Transcription Factors for Cancer Prevention--the Case of Nrf2

Colburn, N. H., Kensler, T. W. — 2008-03-01

NF-E2-related factor 2 (Nrf2) is one of several transcription factors that are altered in human cancer and that modulate susceptibility to carcinogenesis in mouse models (1–3). Nrf2 up-regulates transcription of a number of oxidant and electrophile detoxication genes through an antioxidant response element present in their transcriptional promoters. In this issue of the journal, Khor et al. (4) follow up their own and others' previous findings that Nrf2 protects against dextran sodium sulfate–induced colitis, inflammation, and aberrant crypt foci with a study now showing that tumor incidence, multiplicity, size, and stage of progression are increased in Nrf2-deficient mice in an azoxymethane-dextran sodium sulfate colon carcinogenesis model. Expressions of the proinflammatory genes cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) and their products prostaglandin E₂ and leukotriene B₄ were increased in tumors induced in the knockout mice compared with wild-type tumors and with normal mucosa. Induction of prototypic protective enzymes UDP-glucuronosyl transferase 1A and NAD(P)H:quinone oxidoreductase 1 following azoxymethane-dextran sodium sulfate failed to occur in Nrf2-deficient mice. Although the association between chronic inflammation and cancer has been noted for several cancer sites including liver, pancreas, stomach, bladder, and colon, the molecular basis for this association is not well understood. Khor et al. now implicate activation of pro-oxidant enzymes such as COX-2 and 5-LOX and lowered expression of antioxidant enzymes such as NAD(P)H:quinone oxidoreductase 1 as likely mediators of the inflammation-associated colon tumor promotion and progression in Nrf2-deficient mice. This suggests that activation of Nrf2 or Nrf2 signaling might be a promising strategy for prevention of inflammation-associated cancer.

Intratumoral Epiregulin Is a Marker of Advanced Disease in Non-Small Cell Lung Cancer Patients and Confers Invasive Properties on EGFR-Mutant Cells

2008-03-01

Non–small cell lung cancer (NSCLC) cells with activating epidermal growth factor receptor (EGFR) somatic mutations have unique biological properties, including high expression of the ErbB ligand epiregulin; however, the biological role of epiregulin in these cells has not been elucidated. To examine its role, we used an immunohistochemical approach to detect epiregulin expression in NSCLC biopsy samples and pharmacologic and genetic approachesto inhibit epiregulin in cultured NSCLC cells. In NSCLC biopsy samples, epiregulin was detected in 237 of 366 (64.7%) tumors, which correlated with nodal metastasis and a shorter duration of survival. In EGFR-mutant NSCLC cell lines, treatment with a small-molecule EGFR tyrosine kinase inhibitor diminished mRNA levels of the gene encoding epiregulin (EREG). The ability of EGFR-mutant NSCLC cells to invade through Matrigel in vitro was inhibited by treatment with an anti-epiregulin neutralizing antibody or by transfection with an EREG short hairpin RNA. Collectively, these findings show that epiregulin expressioncorrelated with advanced disease, was EGFR dependent, and conferred invasive properties on NSCLC cells. Additional studies are warranted in NSCLC patients to evaluate whether epiregulin expression predicts the metastatic potential of primary tumors and whether anti-epiregulin treatment strategies are efficacious in the prevention of metastasis.

Effects of Tobacco Smoke on Gene Expression and Cellular Pathways in a Cellular Model of Oral Leukoplakia

2008-03-01

In addition to being causally linked to the formation of multiple tumor types, tobacco use has been associated with decreased efficacy of anticancer treatment and reduced survival time. A detailed understanding of the cellular mechanisms that are affected by tobacco smoke (TS) should facilitate the development of improved preventive and therapeutic strategies. We have investigated the effects of a TS extract on the transcriptome of MSK-Leuk1 cells, a cellular model of oral leukoplakia. Using Affymetrix HGU133 Plus 2 arrays, 411 differentially expressed probe sets were identified. The observed transcriptome changes were grouped according to functional information and translated into molecular interaction network maps and signaling pathways. Pathways related to cellular proliferation, inflammation, apoptosis, and tissue injury seemed to be perturbed. Analysis of networks connecting the affected genes identified specific modulated molecular interactions, hubs, and key transcription regulators. Thus, TS was found to induce several epidermal growth factor receptor (EGFR) ligands forming an EGFR-centered molecular interaction network, as well as several aryl hydrocarbon receptor–dependent genes, including the xenobiotic metabolizing enzymes CYP1A1 and CYP1B1. Notably, the latter findings in vitro are consistent with our parallel finding that CYP1A1 and CYP1B1 levels were increased in oral mucosa of smokers. Collectively, these results offer insights into the mechanisms underlying the procarcinogenic effects of TS and raise the possibility that inhibitors of EGFR or aryl hydrocarbon receptor signaling will prevent or delay the development of TS-related tumors. Moreover, the inductive effects of TS on xenobiotic metabolizing enzymes may help explain the reduced efficacy of chemotherapy, and suggest targets for chemopreventive agents in smokers.

Impact of Smoking Cessation on Global Gene Expression in the Bronchial Epithelium of Chronic Smokers

2008-03-01

Cigarette smoke is the major cause of lung cancer and can interact in complex ways with drugs for lung cancer prevention or therapy. Molecular genetic research promises to elucidate the biological mechanisms underlying divergent drug effects in smokers versus nonsmokers and to help in developing new approaches for controlling lung cancer. The present study compared global gene expression profiles (determined via Affymetrix microarray measurements in bronchial epithelial cells) between chronic smokers, former smokers, and never smokers. Smoking effects on global gene expression were determined from a combined analysis of three independent data sets. Differential expression between current and never smokers occurred in 591 of 13,902 measured genes (P < 0.01 and >2-fold change; pooled data)—a profound effect. In contrast, differential expression between current and former smokers occurred in only 145 of the measured genes (P < 0.01 and >2-fold change; pooled data). Nine of these 145 genes showed consistent and significant changes in each of the three data sets (P < 0.01 and >2-fold change), with eight being down-regulated in former smokers. Seven of the eight down-regulated genes, including CYP1B1 and three AKR genes, influence the metabolism of carcinogens and/or therapeutic/chemopreventive agents. Our data comparing former and current smokers allowed us to pinpoint the genes involved in smoking-drug interactions in lung cancer prevention and therapy. These findings have important implications for developing new targeted and dosing approaches for prevention and therapy in the lung and other sites, highlighting the importance of monitoring smoking status in patients receiving oncologic drug interventions.

Cancer Prevention: Epigenetics Steps Up to the Plate

Issa, J.-P. — 2008-03-01

The fields both of cancer prevention and epigenetics have matured to a point where their intersection deserves sustained attention. There now is strong evidence for an epigenetic component of early neoplasia, and data on the cancer preventive properties of epigenetic modulation are emerging. With preclinical proof of principle at hand, the challenge is to translate these epigenetic findings into testable clinical hypotheses.

Colorectal Neoplasia Goes with the Flow: Prostaglandin Transport and Termination

Markowitz, S. D. — 2008-03-01

The past 10 to 15 years have witnessed major advances in our understanding of polyunsaturated fatty acid metabolism involving synthesis, activity, and degradation of prostaglandin (PG), especially prostaglandin E₂ (PGE₂), in neoplasia, in particular colorectal neoplasia. Little is known, however, about the role of PG transport in these processes. The flow of PGs in and out of colorectal cells involves highly coordinated activities of PG transporters that become highly dysregulated in colorectal neoplasia. Recent work by various investigators supports key components of this flow for novel molecular-targeted approaches to prevent or treat colorectal neoplasia.

Regulation of Prostaglandin Transporters in Colorectal Neoplasia

Holla, V. R., Backlund, M. G., Yang, P., Newman, R. A., DuBois, R. N. — 2008-03-01

Prostaglandin E₂ (PGE₂) promotes cancer progression by affecting cell proliferation, apoptosis, angiogenesis, and the immune response. It has been reported that PGE₂ is transported or passes through the cell membrane via prostaglandin-specific transporters including the prostaglandin transporter (PGT, an influx transporter) and the multidrug resistance-associated protein 4 (an efflux transporter). PGT can facilitate the removal of PGE₂ from the extracellular milieu by transporting it into the cell, where 15-hydroxyprostaglandin dehydrogenase (15-PGDH) then oxidizes PGE₂ into 15-keto PGE₂. We previously reported that 15-PGDH expression is reduced in most colorectal cancers, indicating the tumor suppressor role of this gene. In the present study, we show that PGT expression is also decreased (whereas multidrug resistance-associated protein 4 expression is elevated) in human colorectal cancer specimens (compared with expression in normal mucosa) and in colorectal cancer cell lines. Furthermore, we found that PGT expression decreased in premalignant adenomas in Apc^min mice and was partially restored (in human colorectal cancer cell lines) by treatment with a DNA demethylating agent or histone deacetylase inhibitor. Forced PGT overexpression in vitro reduced extracellular PGE₂ levels and increased intracellular levels of its catabolic product 15-keto PGE₂. Our data suggest that the existing model to explain increased PGE₂ in colorectal neoplasia should be modified to include the novel mechanism of coordinated up- and down-regulation of genes involved in PGE₂ transport.

Long-term Epigenetic Therapy with Oral Zebularine Has Minimal Side Effects and Prevents Intestinal Tumors in Mice

2008-03-01

Recent successes in the application of epigenetic drugs for the treatment of myelodysplastic syndrome have raised questions on the safety of long-term administration of DNA methylation inhibitors. We treated preweaned cancer prone Apc^Min/+ (Min) mice continuously with the DNA methylation inhibitor zebularine in their drinking water to determine the effects of the drug on normal mouse development as well as cancer prevention. Zebularine caused a tissue-specific reduction in DNA methylation at B1 short interspersed nucleotide elements in the small and large intestines of female Min mice but not in other organs examined after chronic oral treatment. No significant difference in the average weights of mice was observed during the treatment. In addition, analysis of global gene expression of colonic epithelial cells from the females indicated that only 3% to 6% of the genes were affected in their expression. We did not detect toxicity and abnormalities from the histopathologic analysis of liver and intestinal tissues. Lastly, we tested whether prevention of tumorigenesis can be achieved with chronic oral administration of zebularine in Min mice. The average number of polyps in Min females decreased from 58 to 1, whereas the average polyp number remained unaffected in Min males possibly due to differential activity of aldehyde oxidase. Taken together, our results show for the first time that long-term oral administration of zebularine causes a gender-specific abrogation of intestinal tumors while causing a tissue-specific DNA demethylation. Importantly, prolonged treatment of mice with epigenetic drugs resulted in only minor developmental and histologic changes.

Fetal Mouse Cyp1b1 and Transplacental Carcinogenesis from Maternal Exposure to Dibenzo(a,l)pyrene

2008-03-01

Dibenzo(a,l)pyrene (DBP) is among the most potent carcinogenic polycyclic aromatic hydrocarbons. Previously, we showed that DBP administration to pregnant mice resulted in high mortality of offspring from an aggressive T-cell lymphoma. All mice that survive to 10 months of age exhibit lung tumors with high multiplicity. Recombinant cytochrome P450 (cyp) 1b1 from mice and the homologue 1B1 in humans exhibit high activity toward the metabolic activation of DBP. Targeted disruption of the cyp1b1 gene protects against most DBP-dependent cancers. Mice heterozygous for the disrupted cyp1b1 allele were used to examine the effect of cyp1b1 gene dosage on DBP transplacental carcinogenesis. Dams were treated with 1 or 15 mg/kg of DBP or 50 mg/kg of benzo(a)pyrene. Cyp1b1-null offspring did not develop lymphoma, whereas wild-type and heterozygous siblings, born to dams given the high dose of DBP, exhibited significant mortalities between 10 and 30 weeks of age. At 10 months, all groups had lung adenomas or carcinomas [9.5%, 40.3%, 25.6%, and 100% incidences for controls, benzo(a)pyrene, 1 and 15 mg/kg DBP, respectively]. Cyp1b1 status did not alter benzo(a)pyrene-dependent carcinogenesis. At 1 mg/kg DBP, cyp1b1 status altered the incidence of lung tumors (19.0, 27.8, and 28.6% for nulls, heterozygous, and wild-type, respectively). At 15 mg/kg, tumor multiplicities in cyp1b1 wild-type (9.3) and heterozygous (9.5) offspring were nearly twice that of cyp1b1-null siblings (5.0). These data confirm that cyp1b1 bioactivation of DBP occurs in fetal target tissues, following transplacental exposure, with the thymus and lung as primary and secondary targets, respectively.