Chemoprevention of OH-BBN-induced bladder cancer in mice by piroxicam

The Effect of Acetylsalicylic Acid, as a Representative Non-Steroidal Anti-Inflammatory Drug, on the Activity of Myeloperoxidase

BACKGROUND

Acetylsalicylic acid (ASA or aspirin) is one of the world's most widely used non-steroidal anti-inflammatory drug (NSAID). Numerous studies have shown that the long-term use of aspirin may contribute to longer survival among patients with various types of cancer, including ovarian cancer.

AIM

The aim of this study was to investigate the effect of ASA on myeloperoxidase (MPO), which is found at an elevated level in women with ovarian cancer, among others.

METHODS

The influence of different concentrations of ASA on the chlorinating and peroxidase activity of MPO was analysed. The relationship between the concentration of ASA and the degree of inhibition of MPO activity was determined based on the results.

CONCLUSIONS

Aspirin has a significant effect on MPO activity. The use of 50 mM ASA resulted in the enzyme activity being inhibited by more than 90%.

Cranberry: A Promising Natural Source of Potential Nutraceuticals with Anticancer Activity

Studies have shown that cranberry and its components may exert anticancer properties. The present study aims to critically summarise the existing experimental studies evaluating the potential effects of cranberry on cancer prevention and treatment. PubMed database was searched to identify relevant studies. Current in vitro studies have indicated that cranberry and/or its components may act as chemopreventive agents, diminishing the risk for cancer by inhibiting cells oxidation and inflammatory-related processes, while they may also exert chemotherapeutic effects by inhibiting cell proliferation and angiogenesis, inducing cell apoptosis and attenuating the ability of tumour cells to invade and metastasis. Limited in vivo studies have further documented potential anticancer activity. Cranberry could be considered as a conglomeration of potential effective anticancer druglike compounds.

Enhanced inhibition of urinary bladder cancer growth and muscle invasion by allyl isothiocyanate and celecoxib in combination

Allyl isothiocyanate (AITC) occurs in cruciferous vegetables that are commonly consumed by humans and has been shown to inhibit urinary bladder cancer growth and progression in previous preclinical studies. However, AITC does not significantly modulate cyclooxygenase-2 (Cox-2), whose oncogenic activity has been well documented in bladder cancer and other cancers. Celecoxib is a selective Cox-2 inhibitor and has been widely used for treatment of several diseases. Celecoxib has also been evaluated in bladder cancer patients, but its efficacy against bladder cancer as a single agent remains unclear. In a syngeneic rat model of orthotopic bladder cancer, treatment of the animals with the combination of AITC and celecoxib at low dose levels (AITC at 1 mg/kg and celecoxib at 10 mg/kg) led to increased or perhaps synergistic inhibition of bladder cancer growth and muscle invasion, compared with each agent used alone. The combination regime was also more effective than each single agent in inhibiting microvessel formation and stimulating microvessel maturation in the tumor tissues. The anticancer efficacy of the combination regime was associated with depletion of prostaglandin E2, a key downstream signaling molecule of Cox-2, caspase activation and downregulation of vascular endothelial growth factor in the tumor tissues. These data show that AITC and celecoxib complement each other for inhibition of bladder cancer and provide a novel combination approach for potential use for prevention or treatment of human bladder cancer.

Natural products for chemopreventive and adjunctive therapy in oncologic disease

Nutritional supplements or complementary and alternative medicines (CAM) are currently being investigated for their use in preventing, inhibiting, and reversing the progression of cancer. Natural agents and their derivatives such as vitamin A, selenium, green tea, resveratrol, aspirin, and probiotics have potential benefits in chemoprevention. There is also growing evidence for the use of natural products as adjunctive therapy alongside conventional cancer treatments. Nutritional supplements expenditures demonstrated greater growth than pharmaceuticals, with approximately 80% of cancer patients using natural products. Current issues with nutritional supplements use in cancer treatment include insufficient or conflicting evidence, poor quality control, potential interactions with chemotherapy, and potential efficacy in relation to changes in certain biomarkers, but long-term implications remain largely unresolved. Continued research is needed to lend credibility to these potentially valuable naturally driven supplements in the prevention and potentially in the treatment of cancer in conjunction with standard pharmaceuticals.

Dithiolethiones for cancer chemoprevention: where do we stand?

Dithiolethiones are a well-known class of cancer chemopreventive agents; the key mechanism of action of dithiolethiones involves activation of Nrf2 signaling and induction of phase II enzymes. In the past, attention has been focused mainly on 4-methyl-5-pyrazinyl-3H-1,2-dithiole-3-thione (oltipraz), which showed ability as a wide-spectrum inhibitor of chemical carcinogenesis in preclinical models. However, clinical trials of oltipraz have shown questionable efficacy, and at the high doses employed in such studies, significant side effects were observed. Dithiolethiones that are markedly more effective and potent than oltipraz in both induction of phase II enzymes and inhibition of chemical carcinogenesis in preclinical studies have been identified, and these compounds have shown pronounced organ specificity in vivo. Further investigation of these compounds may lead to development of effective and safe agents for cancer prevention in humans.

Non-steroidal anti-inflammatory drugs in the treatment of genitourinary malignancies: focus on clinical data

The antitumour activity of NSAIDs in preclinical trials has lead to their evaluation in the management of various malignancies in humans. Evidence regarding their use in the treatment of genitourinary tumours is reviewed here, focusing primarily on clinical data. The majority of available evidence comes from meeting abstracts and only a few published manuscripts were detected. The efficacy of selective COX-2 inhibitors, a subcategory of anti-inflammatory drugs, is promising in prostate cancer, in either biochemical recurrence after initial treatment or advanced disease. This does not seem to be the case for renal tumours in which efficacy in the advanced disease setting is not satisfactory. Despite the well-documented rationale for the application of NSAIDs in bladder cancer management, clinical evidence is not available. More studies are needed to assess the efficacy of anti-inflammatory agents in bladder cancer treatment and further clarify their therapeutic benefit in patients with prostate cancer, in which initial results are encouraging.

Chemopreventive property of dietary ginger in rat urinary bladder chemical carcinogenesis

The modifying potential of ginger on the development of preneoplasia and tumors in the male Wistar rat urinary bladder was investigated in a 36-week-long initiation-promotion assay for chemical carcinogenesis. Groups G1 to G3 were given 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) in drinking water for 5 weeks and a 3% uracil meal for the subsequent 3 weeks. Groups G4 and G5 were treated with 3% uracil only for the same period. After these steps, groups G2, and G3 and G4 were fed for 26 weeks a ginger extract mixed at 0.5 and 1.0% in a basal diet, respectively. Thirty six weeks after the beginning of the experiment all rats were killed. The multiplicity of urothelial lesions (hyperplasia and neoplasia) was significantly lower (P = 0.013) in group G3 than in groups G1 and G2. The results suggest that 1.0% ginger meal exerts a protective effect on the post-initiation stage of rat chemically-induced urothelial carcinogenesis.

Effects of ginger (Zingiber officinale Roscoe) on DNA damage and development of urothelial tumors in a mouse bladder carcinogenesis model

Extracts of the spice ginger (Zingiber officinale Roscoe) are rich in gingerols and shogaols, which exhibit antioxidant, anti-inflammatory, antifungal, antimycobacterial, and anticarcinogenic proprieties. The present study evaluated the chemoprotective effects of a ginger extract on the DNA damage and the development of bladder cancer induced by N-butyl-N-(4-hydroxibutyl) nitrosamine (BBN)/N-methyl-N-nitrosourea (MNU) in male Swiss mice. Groups G1-G3 were given 0.05% BBN in drinking water for 18 weeks and four i.p. injections of 30 mg/kg body weight MNU at 1, 3, 10, and 18 weeks. Group G4 and G5 received only the BBN or MNU treatments, respectively, and groups G6 and G7 were not treated with BBN or MNU. Additionally, Groups G2, G3, and G6 were fed diets containing 1, 2, and 2% ginger extract, respectively, while Groups G1, G4, G5, and G7 were fed basal diet. Samples of peripheral blood were collected during the experiment for genotoxicity analysis; blood collected 4 hr after each MNU dose was used for the analysis of DNA damage with the Comet assay (assay performed on leukocytes from all groups), while reticulocytes collected 24 hr after the last MNU treatment of Groups G5-G7 were used for the micronucleus assay. At the end of the experiment, the urinary bladder was removed, fixed, and prepared for histopathological, cell proliferation, and apoptosis evaluations. Ginger by itself was not genotoxic, and it did not alter the DNA damage levels induced by the BBN/MNU treatment during the course of the exposure. The incidence and multiplicity of simple and nodular hyperplasia and transitional cell carcinoma (TCC) were increased by the BBN/MNU treatment, but dietary ginger had no significant effect on these responses. However, in Group G2 (BBN/MNU/2% ginger-treated group), there was an increased incidence of Grade 2 TCC. The results suggest that ginger extract does not inhibit the development of BBN-induced mouse bladder tumors.

Chemopreventive effects of cyclooxygenase-2 inhibitor and epidermal growth factor-receptor kinase inhibitor on rat urinary bladder carcinogenesis

OBJECTIVE

To examine the chemopreventive effects of a selective cyclooxygenase (COX)-2 inhibitor, meloxicam, and a selective epidermal growth factor (EGF)-receptor tyrosine kinase inhibitor, gefitinib (as a single agent) on a carcinogen-induced rodent bladder carcinogenesis model.

MATERIALS AND METHODS

The study comprised 103 male Fisher-344 rats (8 weeks old); after initial carcinogen treatment for 8 weeks with 0.05%N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in drinking water, the rats were divided into five groups, i.e. group 1, control (vehicle only); group 2, gefitinib high-dose (15 mg/kg by gavage once daily); group 3, gefitinib low-dose (5 mg/kg); group 4, meloxicam high-dose (1.8 mg/kg by gavage once daily); and group 5, meloxicam low-dose (0.6 mg/kg). Twelve weeks later the rats were killed; after fixing the bladder in 10% formalin, the number and size of hyperplasia and carcinoma foci were recorded microscopically in sections stained with haematoxylin and eosin, submitted entirely as multiple strips.

RESULTS

The incidence of carcinoma, confirmed microscopically, was: control 14/20 (70%); high-dose gefitinib, 7/20 (35%); low-dose gefitinib, 7/20 (35%); high-dose meloxicam 7/21 (33%); and low-dose meloxicam, 12/20 (60%). The mean numbers of carcinomas per bladder in groups 1-5 were 1.2, 0.5, 0.4, 0.5 and 1.1, respectively. The incidence and the mean number of carcinomas per bladder were significantly lower in the treatment groups (P < 0.05) than in the control group, except in the low-dose meloxicam group. There were no significant adverse effects.

CONCLUSION

Both meloxicam and gefitinib have inhibitory effects on rat bladder carcinogenesis with no significant adverse effects. A combination of these drugs would be worth studying for their synergistic effects.

Multiple dose pharmacokinetics and acute safety of piroxicam and cimetidine in the cat

The purpose of this study was to evaluate the multiple dose pharmacokinetics and acute safety of piroxicam and cimetidine alone and in combination in cats. Seven healthy cats were included in this randomized-crossover study. The cats were assigned to groups designated to receive cimetidine alone (15 mg/kg, p.o., q12 h), piroxicam alone (0.3 mg/kg, p.o., q24 h), and piroxicam combined with cimetidine (both at aforementioned doses). The cats were dosed for 10 days followed by at least a 2-week washout period between trials. Serial blood samples were collected following the first and last doses and analyzed utilizing a high-performance liquid chromatography with mass spectrometry detection (LC/MS) assay. Pharmacokinetic parameters were determined using noncompartmental analysis. Endoscopic evaluation of the gastric mucosa was performed and serum urea nitrogen (SUN), creatinine, alkaline phosphatase (ALP), and alanine transaminase (ALT) activities were evaluated. There were not a clinically relevant difference between the pharmacokinetic parameters of piroxicam administered alone or in combination with cimetidine after either the first or last dose. Gastric ulcers were not observed in any cats although gastric erosions were. The SUN, creatinine, ALP, and ALT activities remained within reference ranges for all cats. It appears that once daily, short-term use of piroxicam alone and in combination with cimetidine in cats is relatively safe based on the parameters evaluated in this study. However, further studies are necessary to determine the long-term gastrointestinal safety of piroxicam.

Fenretinide: a prototype cancer prevention drug

Fenretinide (N-4-hydroxyphenylretinamide [4-HPR]) is a synthetic retinoid that has been examined in in vitro assays, preclinical animal models and clinical trials as a cancer chemopreventive agent. Its pharmacology, toxicity and mechanisms of action initially suggested an increased therapeutic index relative to native retinoids for the control of tumours of the breast, prostate, bladder, colon, cervix and head and neck. Although fenretinide at the doses and schedules used in several pivotal Phase II and III clinical trials has not been proven to be efficacious in reducing the incidence of cancer or in retarding the development of preneoplastic lesions, encouraging observations regarding unanticipated preventative activity, such as for ovarian cancer control, have arisen from these studies. Research in cancer therapy and the elucidation of molecular pathways activated by fenretinide have also yielded clues about how this agent might be better used in a prevention setting. Current trials are underway to re-examine both dose and schedule of fenretinide administration as well as the target tissues of interest. Investigations of potential synergism between fenretinide and other candidate chemopreventative molecules with complementary mechanisms of action may support future assessments of this prototype cancer prevention drug or its newer analogues.

Correlation of in vitro chemopreventive efficacy data from the human epidermal cell assay with animal efficacy data and clinical trial plasma levels

The human epidermal cell (HEC) assay, which uses carcinogen exposed normal skin keratinocytes to screen for cancer prevention efficacy, was used to screen possible preventive agents. The endpoints measured were inhibition of carcinogen-induced growth and induction of involucrin, an early marker of differentiation. Sixteen of twenty agents (apigenin, apomine, budesonide, N-(2-carboxyphenyl)retinamide, ellagic acid, ibuprofen, indomethacin, melatonin, (-)-2-oxo-4-thiazolidine carboxylic acid, polyphenon E, resveratrol, beta-sitosterol, sulfasalazine, vitamin E acetate, and zileuton) were positive in at least one of the two assay endpoints. Four agents (4-methoxyphenol, naringenin, palmitoylcarnitine chloride, and silymarin) were negative in the assay. Nine of the sixteen agents were positive for both endpoints. Agents that showed the greatest response included: ellagic acid > budesonide, ibuprofen > apigenin, and quinicrine dihydrochloride. Fifty-eight of sixty-five agents that have been evaluated in the HEC assay have also been evaluated in one or more rodent bioassays for cancer prevention and several are in clinical trials for cancer prevention. The assay has an overall predictive accuracy of approximately 91.4% for efficacy in rodent cancer prevention irrespective of the species used, the tissue model, or the carcinogen used. Comparison of the efficacious concentrations in vitro to plasma levels in clinical trials show that concentrations that produced efficacy in the HEC assay were achieved in clinical studies for 31 of 33 agents for which plasma levels and/or C(max) levels were available. For two agents, 9-cis-retinoic acid (RA) and dehydroepiandrosterone (DHEA), the plasma levels greatly exceeded the highest concentration (HC) found to have efficacy in vitro. Thus, the HEC assay has an excellent predictive potential for animal efficacy and is responsive at clinically achievable concentrations.

Analgesic therapy and the prevention of bladder cancer

The aim of this study was to measure the association between analgesic use and risk of bladder cancer among patients seen at the James A. Haley Veterans' Administration (VA) Hospital in Tampa, FL. A total of 330 cases were obtained using a combination of computerized pathology records, and inpatient and outpatient diagnoses. Controls were randomly selected from the VA computerized administrative database, and 1293 controls were included for analysis. Unconditional logistic regression analysis was performed to assess the risk of bladder cancer after adjusting for age, gender, and cigarette smoking. Among analgesic users, we were able to identify a nearly 20% reduction in risk potentially consistent with a protective role (OR = 0.81, 95% CI = 0.63, 1.05). Nonsmokers had a 43% decrease in risk (OR = 0.57, 95% CI = 0.33, 0.98). While smoking is a strong and recognized cause of bladder cancer, 50% of bladder cancer cases are not attributable to tobacco consumption. Given that nonsmokers prescribed nonsteroidal anti-inflammatory drugs (NSAIDs) were observed to have a 43% reduction in risk, it is important to study whether nonsmokers may benefit from therapy with NSAIDs.

Nrf2 Is Essential for the Chemopreventive Efficacy of Oltipraz against Urinary Bladder Carcinogenesis

The induction of phase 2 detoxifying enzymes, such as UDP-glucuronosyltransferases (UGTs), in response to an array of naturally occurring and synthetic agents, such as oltipraz (4-methyl-5-[2-pyrazinyl]-1,2-dithiole-3-thione), provides an effective means of protection against a variety of carcinogens. Transcription factor Nrf2 is an essential regulator of the inducible expression of detoxifying enzyme genes by chemopreventive agents. In this study, we investigated in Nrf2-deficient mice the susceptibility to the urinary bladder-specific carcinogen N-nitrosobutyl(4-hydroxybutyl)amine (BBN) and the chemopreventive efficacy of oltipraz. The incidence of urinary bladder carcinoma by BBN was significantly higher in Nrf2-/- mice than in wild-type mice; invasive carcinoma was found in 24.0 and 38.5% of wild-type and Nrf2-/- mice, respectively. Oltipraz induced the phase 2 enzymes responsible for BBN detoxification in the liver and urinary bladder in an Nrf2-dependent manner. As expected, therefore, oltipraz decreased the incidence of urinary bladder carcinoma by BBN in wild-type mice but had little effect in Nrf2-/- mice. In wild-type mouse liver, oltipraz significantly induced BBN glucuronidation and decreased the urinary concentration of N-nitrosobutyl(3-carboxypropyl)amine, a proximate carcinogen of BBN. Importantly, BBN was found to suppress the expression of UGT1A specifically in the urinary bladder. This suppression was counteracted by oltipraz in wild-type mice but not in Nrf2-/- mice. These results show that Nrf2 and its downstream target genes are responsible for BBN detoxification. Furthermore, oltipraz prevents carcinogenesis by BBN by enhancing detoxification of this carcinogen in the liver and urinary bladder.

COX-2 inhibitors and other nonsteroidal anti-inflammatory drugs in genitourinary cancer

Selective cyclooxygenase (COX)-2-inhibiting and other nonsteroidal anti-inflammatory drugs (NSAIDs) show promise for preventing and treating bladder and prostate cancers. In contrast to the strong NSAID epidemiology in colorectal cancer, the epidemiologic data on NSAIDs and genitourinary (GU) cancers are limited and mixed. However, a substantial body of preclinical in vitro and in vivo animal model data shows consistent NSAID activity in treating, and in some cases preventing, GU cancers and begins to address the mechanisms behind this activity (eg, involving Akt and ERK2 in the prostate). Many preclinical and clinical NSAID studies currently under way are helping to resolve the best type (selective or nonselective COX inhibitors or non-COX inhibitors), dose and duration of NSAID treatment for prevention in the GU setting. Future studies likely will focus on clarifying the NSAID mechanisms behind and developing NSAID combinations for both treating and preventing GU cancers.

The expression of cyclooxygenase in transitional cell carcinoma cell lines: its correlation with tumor differentiation, invasiveness and prostanoids production

OBJECTIVE

To evaluate the isozyme activities of COX-1 and COX-2 in TCC cells and correlate with cellular differentiation and tumor behavior.

MATERIAL AND METHODS

Various TCC cell lines were characterized through several aspects: (1). to measure the content and the mRNA amount of COX-1 and COX-2, (2). to characterize the proteins of COX-1 and COX-2 by Western immunoblotting, (3). to measure the production of prostaglandin E2 and thromboxane B2 in culture media, and (4). to correlate these parameters with tumor differentiation and invasiveness.

RESULTS

Seven out of 10 cell lines (70%) had significantly higher COX expression than normal urothelium. Tumors with lower-grade differentiation and less invasiveness had significantly higher content of COX-1 and COX-2 than those tumors with higher-grade differentiation and more invasive behavior (p<0.01). The expression of COX mRNA in TSGH8301, TCC8702 and RT4 were much higher than J82 which has minimal expression of COXs. Similarly, the COX-2 protein was much higher in TSGH8301, TCC8702 and RT4 when compared with J82. TSGH8301, TCC8702, and RT4 had high production of PGE2 and thromboxane B2 in their culture media. Increased secretions of PGE2 and thromboxane B2 were also observed in TCC8701, TCC9101, HT1376, and T24. The production of prostanoids is closely related to cytoplasmic COX expression of tumor cells.

CONCLUSIONS

The expression of COX-1 and COX-2 is a common phenomenon in TCC cells and closely related to cellular differentiation and tumor invasiveness. The COX-2 inhibitors may play an important role in the control of TCC growth.

Bladder cancer prevention. Part I: what do I tell my patients about lifestyle changes and dietary supplements?

PURPOSE OF REVIEW

Comprehensive reviews of lifestyle changes and dietary supplements that may prevent bladder cancer are needed in order to facilitate discussions between clinicians and patients.

RECENT FINDINGS

Novel data exist that numerous lifestyle/diet and dietary supplements may lower the risk of this disease. For example, reducing arsenic exposure, incorporating dietary changes, and vitamin E supplements continue to accumulate research that supports their use with some patients at a higher risk for this disease. Regardless, smoking cessation seems to have the largest impact on reducing risk and incorporating these other changes after smoking cessation may reduce an individual's risk to an even greater extent.

SUMMARY

However, a large percentage of cases of individuals diagnosed with this cancer apparently have no known etiology. Diets lower in calories or possibly specific sub-types of fat, and higher in fruits and especially vegetables, seem to provide some protection. Other dietary/supplement options may affect risk, but these benefits could be seriously attenuated by smoking. Dietary selenium, but currently not selenium supplements, may also affect risk, especially in non-smokers. Dietary vitamin E, and vitamin E supplements, may provide some protection. Non-selective (e.g. non-steroidal anti-inflammatory drugs) and selective cyclooxygenase-2 inhibitors are generating interest because bladder tumors seem to contain higher concentrations of this enzyme. Drinking-water quality, especially arsenic concentrations, may seriously affect risk. Providing recommendations for patients with regard to some of these lifestyle modifications is currently recommended because the majority of these alterations are also recommended currently for cardiovascular or general oncology disease reduction.

Development of COX inhibitors in cancer prevention and therapy

On the strength of in vitro, in vivo, observational, and clinical data, nonsteroidal antiinflammatory drugs (NSAIDs)-also referred to as COX inhibitors-have emerged as lead compounds for cancer prevention, and possible adjuncts to cancer therapy. Thus far, the routine use of NSAIDs for these indications is limited, largely owing to toxicity concerns, the paucity of efficacy data for any specific target organ, and uncertainties with regard to the most appropriate regimen (i.e., the best agent, formulation, dose, route of administration, and duration). Strategies to address these concerns primarily aim to improve the therapeutic index (i.e., benefit:risk ratio) of COX inhibitors by 1) minimizing systemic exposures whenever feasible, 2) achieving greater mechanistic specificity, 3) coadministering agents that provide prophylaxis against common toxicities, and 4) coadministering other effective anticancer agents. Clinical trials testing most of these strategies have been completed or are under way. The National Cancer Institute has a substantial research portfolio dedicated to the identification, testing, and development of NSAIDs as preventive and therapeutic anticancer agents. Discovering how to apply NSAIDs in persons with-or at risk for-cancer, although challenging, has the potential for considerable clinical and public health benefits.

Mechanisms and applications of non-steroidal anti-inflammatory drugs in the chemoprevention of cancer

Biological and chemical irritants can be the cause of irritation in a variety of organ sites. It is becoming well understood that chronic irritation in any form can initiate and accelerate the cancer process in these same organs. This understanding comes in part from the many epidemiologic studies which point out that chronic inflammation correlates with increased risk of developing cancer in that organ which is affected. One of the hallmarks of chronic irritation is the increased activity in the arachidonic acid pathway which provides many of the necessary inflammatory biochemical mediators to this process. Arachidonic acid metabolism diverges down two main pathways, the cyclooxygenase (COX) and the lipoxygenase (LOX) pathways. The COX pathway leads to prostaglandin and thromboxane production and the LOX pathway leads to the leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs). These classes of inflammatory molecules exert profound biological effects which enhance the development and progression of human cancers. A large number of synthetic drugs and natural products have been discovered that block many of these key pathways. Much experimental evidence in animals has shown that inhibition of the key enzymes which drive these pathways can, in fact, prevent, slow or reverse the cancer process. The data are convincing in a number of organ sites including colon, breast, lung, bladder and skin. More recently, double-blinded randomize clinical trials in humans have shown the prevention of colonic polyps by anti-inflammatory agents. These studies have primarily used non-steroidal anti-inflammatory drugs (NSAIDS) which block the COX pathways. Recent preclinical studies indicate that the LOX pathway also may be an important target for cancer prevention strategy. The expression of high levels of these enzymes in cancerous tissues make them an obvious first target for cancer prevention strategies. As newer more specific drugs are developed with few adverse effects this important prevention strategy may become a reality.

COX-2 inhibitors in cancer treatment and prevention, a recent development

Epidemiological and experimental studies have demonstrated the effect of non-steroidal anti-inflammatory drugs (NSAIDs) in the prevention of human cancers. NSAIDs block endogenous prostaglandin synthesis through inhibition of cyclooxygenase (COX) enzymatic activity. COX-2, a key isoenzyme in conversion of arachidonic acid to prostaglandins, is inducible by various agents such as growth factors and tumor promoters, and is frequently overexpressed in various tumors. The contribution of COX-2 to carcinogenesis and the malignant phenotype of tumor cells has been thought to be related to its abilities to (i) increase production of prostaglandins, (ii) convert procarcinogens to carcinogens, (iii) inhibit apoptosis, (iv) promote angiogenesis, (v) modulate inflammation and immune function, and (vi) increase tumor cell invasiveness, although some studies indicated that NSAIDs have COX-2-independent effects. A number of clinical trials using COX-2 inhibitors are in progress, and the results from these studies will increase our understanding of COX-2 inhibition in both cancer treatment and prevention. The combination of COX-2 inhibitors with radiation or other anti-cancer or cancer prevention drugs may reduce their side effects in future cancer prevention and treatment. Recent progress in the treatment and prevention of cancers of the colon, esophagus, lung, bladder, breast and prostate with NSAIDs, especially COX-2 inhibitors, is also discussed.

Potential lifestyle and dietary supplement options for the prevention and postdiagnosis of bladder cancer

Apart from smoking, certain occupational exposures, and schistosomiasis, little is known about other potential lifestyle risk factors for bladder cancer. Other investigations thus far have also been important because of the large number of individuals who are diagnosed with this cancer that apparently have no known risk factors. Preventing the recurrence of bladder cancer has generated some interest because several preliminary trials have found that a combination dietary supplement of vitamins and minerals or a probiotic agent (Lactobacillus casei) may impact this outcome favorably. Advising patients on some of these lifestyle modifications is currently recommended because the majority of them are also currently recommended for cardiovascular disease reduction.

Expression of cyclooxygenase-1 and -2 in urinary bladder carcinomas in vivo and in vitro and prostaglandin E2 synthesis in cultured bladder cancer cells

Cyclooxygenases (Coxs) are the rate-limiting enzymes catalysing the formation of prostaglandins, which are involved in various of physiological processes. Increased Cox-2 expression has been observed in several malignancies, but the exact role of Cox-2 in carcinogenesis remains unsolved. We studied the expression of both Cox-1 and Cox-2 by immunohistochemistry in 29 transitional cell carcinomas of the urinary bladder. Diffuse cytoplasmic immunosignal for Cox-2 was detected in all cancer specimens. The expression was moderate in 55% and strong in 31% of the carcinomas. The normal urothelium in the samples stained also for Cox-2, but the intensity of the immunosignal was weak in most specimens. Cox-1 was expressed in the stroma of bladder wall, whereas in the tumour cells, Cox-1 immunosignal was either absent or weak. No correlation was detected between Cox-1 or Cox-2 expression and tumour differentiation or stage of invasion. We also evaluated the mRNA expression of Cox-1 and Cox-2 and synthesis of prostaglandin E2 (PGE2) in three bladder carcinoma cell lines (RT4, 5637, and T24). All cell lines expressed high levels of Cox-2 mRNA, whereas Cox-1 mRNA expression was detected only in T24 cells. There was great variation in the basal levels of PGE2 synthesis in these cell lines. Indomethacin inhibited the synthesis of PGE2 in all three cell lines, although the level of Cox-2 mRNA tended to increase by indomethacin. These results indicate that Cox-2 is widely expressed in human bladder carcinomas and that the role of Cox-2 inhibition in bladder cancer should be further studied.

Cyclo-oxygenase 2: a pharmacological target for the prevention of cancer

Understanding the mechanisms underlying carcinogenesis provides insights that are necessary for the development of therapeutic strategies to prevent cancer. Chemoprevention--the use of drugs or natural substances to inhibit carcinogenesis - is an important and rapidly evolving aspect of cancer research. We discuss evidence that cyclooxygenase 2 (COX 2), an inducible form of the enzyme, is a potential pharmacological target to prevent cancer. Key data implicating a causal relation between increased activity of COX 2 and carcinogenesis and possible mechanisms of action of COX 2 in this context are covered. Importantly, selective COX 2 inhibitors appear to be safe enough in human beings to allow large-scale clinical testing in healthy people. Several chemoprevention trials using selective COX 2 inhibitors are underway.

The role of cyclooxygenase and lipoxygenase in cancer chemoprevention

The involvement of prostaglandins (PGs) and other eicosanoids in the development of human cancer has been known for over two decades. Importantly, an increase in PG synthesis may influence tumor growth in human beings and experimental animals, and numerous studies have illustrated the effect of PG synthesis on carcinogen metabolism, tumor cell proliferation and metastatic potential. PGs produced by cyclooxygenases (COXs) are represented by a large series of compounds that mainly enhance cancer development and progression, acting as carcinogens or tumor promoters, with profound effects on carcinogenesis. Further investigations suggest that arachidonic acid (AA) metabolites derived from lipoxygenase (LOX) pathways play an important role in growth-related signal transduction, implying that intervention through these pathways should be useful for arresting cancer progression. We discuss here the implications of COX and LOX in colon, pancreatic, breast, prostate, lung, skin, urinary bladder and liver cancers. Select inhibitors of COX and LOX are described, including nonsteroidal antiinflammatory drugs (NSAIDs), selective COX-2 inhibitors, curcumin, tea, silymarin and resveratrol, as well as a method useful for evaluating inhibitors of COX. Although a substantial amount of additional work is required to yield a better understanding of the role of COX and LOX in cancer chemoprevention, it is clear that beneficial therapeutic effects can be realized through drug-mediated modulation of these metabolic pathways.

Non-steroidal anti-inflammatory drugs and bladder cancer prevention

Inclusion of phenacetin among 'proven' human carcinogens by the IARC in 1987, raised concerns about the carcinogenic potential of acetaminophen, its major metabolite. Acetaminophen has been implicated as a possible causal agent in the development of cancer of the renal pelvis. The bladder and renal pelvis, which derive from the same embryological structure, share the same transitional type of epithelium. Past studies have been inconclusive on the possible relationship among these analgesics and bladder cancer but no large, highly detailed study of this association has been conducted. A population-based case-control study conducted in Los Angeles, California, involved 1514 incident bladder cancer cases and an equal number of controls who were matched to the index cases by sex, date of birth (within 5 years) and race. Detailed information on medication use and prior medical conditions was collected through in-person interviews. Regular use of analgesics was not associated with an increased risk of bladder cancer in either men or women. In fact, compared with non- or irregular users, regular analgesic users were at a decreased risk of bladder cancer overall (odds ratio (OR) = 0.81, 95% confidence interval (CI) = 0.68-0.96). However, there were clear differences in both the direction and strength of the associations between the different formulation classes of analgesics and bladder cancer risk. Intake of phenacetin was positively related to bladder cancer risk in a dose-dependent manner while intake of its major metabolite in humans, acetaminophen, was unrelated to risk. Intake of all classes of NSAIDs, except pyrazolon derivatives, were negatively associated with bladder cancer risk, with suggestive evidence that the protective effect varies in strength by subcategories of formulation. Acetic acids seemed to exhibit the strongest protective effect, whereas aspirin/other salicylic acids and oxicam showed the weakest protection.

Potential utility of COX-2 inhibitors in chemoprevention and chemotherapy

Increased prostaglandin (PG) production is associated with many inflammatory pathophysiological conditions; it is derived from arachidonic acid by either of two enzymes: cyclooxygenase-1 or -2 (COX-1 or COX-2). In addition to its role in inflammation, recent work suggests COX-2 derived prostaglandins may play a pivotal part in the maintenance of tumour viability, growth and metastasis. In this review, we summarise the non-steroidal anti-inflammatory drug (NSAID) epidemiological evidence, studies demonstrating overexpression of COX-2 in multiple human tumours and the pharmacological evidence in animal models which also support this hypothesis. We also discuss the potential functional roles of COX-2 activity during tumourigenesis, and speculate on the mechanism by which COX-2 inhibitors may exert their anticancer effects.

Chemopreventive efficacy of piroxicam administered alone or in combination with lycopene and beta-carotene on the development of rat urinary bladder carcinoma after N-butyl-N-(4-hydroxybutyl)nitrosamine treatment

The effects of the non-steroidal anti-inflammatory drug (NSAID) piroxicam and the carotenoids lycopene and beta-carotene, alone or in combination, on the development of rat superficial urinary bladder carcinomas induced by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were studied. Male Fischer 344 rats, 6 weeks old, were given 0.05% BBN in the drinking water for 8 weeks followed by administration of piroxicam (0.0075% in the diet), lycopene (0.0025% in the drinking water) and/or beta-carotene (0.0025% in the drinking water) for 12 weeks, then killed for histological analysis of urinary bladder lesions. Cell proliferation potential was analyzed by immunohistochemical staining of the proliferative cell nuclear antigen (PCNA). Piroxicam alone, piroxicam+lycopene, and piroxicam +lycopene+ beta-carotene all significantly decreased the incidences and numbers of transitional cell carcinomas (TCCs), but the combination of piroxicam with carotenoids did not result in a clear improvement in the preventive potential of piroxicam. Piroxicam+ beta-carotene also caused a significant reduction and lycopene alone a slight but not significant reduction in the number of TCCs. In contrast, beta-carotene alone and lycopene+ beta-carotene were without inhibitory influence on any of the lesion categories examined, and the latter significantly increased the proportion of high-grade TCCs. Nevertheless, all of the chemopreventive agents, either alone or in combination, significantly decreased the TCC PCNA index, the effect extending to the surrounding epithelium in the piroxicam+lycopene and piroxicam+lycopene+beta-carotene groups. These results indicate that the NSAID piroxicam may be a more effective chemopreventive agent than lycopene and beta-carotene for superficial urinary bladder carcinogenesis.

Prevention of lipid peroxidation induced by ochratoxin A in Vero cells in culture by several agents

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus ochraceus as well as other moulds. This mycotoxin contaminates animal feed and food and is nephrotoxic for all animal species studied so far. OTA is immunosuppressive, genotoxic, teratogenic and carcinogenic. It is a structural analogue of phenylalanine and contains a chlorinated dihydroisocoumarinic moiety. Ochratoxin A inhibits protein synthesis by competition with phenylalanine in the phenylalanine-tRNA aminoacylation reaction. Recently lipid peroxidation induced by OTA has been reported, indicating that the lesions induced by this toxin could also be related to oxidative damage. An attempt to prevent its toxic effect, mainly the lipid peroxidation, has been made using aspartame (L-aspartyl-L-phenylalanine methyl ester) a structural analogue of both OTA and phenylalanine, piroxicam, a non steroidal anti-inflammatory drug and superoxide dismutase+catalase (endogenous oxygen radical scavengers). Lipid peroxidation was assayed in monkey kidney cells (Vero cells) treated by increasing concentrations of OTA (5-50 microM). After 24 h incubation OTA induced lipid peroxidation in Vero cells in a concentration dependent manner, as measured by malonaldehyde (MDA) production. The MDA production, in Vero cells, was significantly increased by 50.5% from 694.1 +/- 21.0 to 1041.5 +/- 23.5 pmol/mg of protein. In the presence of superoxide dismutase (SOD)+catalase (25 micrograms/ml each) the MDA production induced by OTA was significantly decreased. At 50 microM of OTA concentration (optimal production of MDA) the MDA production decreased from 1041.5 +/- 23.5 to 827.5 +/- 21.3 pmol/mg of protein. SOD and catalase, when applied prior to the toxin, seemed to prevent lipid peroxidation more efficiently than piroxicam (at a ten-fold higher concentration than OTA) and aspartame (at equimolar concentration). These molecules also partially prevented the OTA-induced leakage of MDA in the culture medium.

Effect of piroxicam on the nephrotoxicity induced by ochratoxin A in rats

Ochratoxin A (OTA) is a mycotoxin which contaminates animal feed and human food and is nephrotoxic for all animal species studied so far. It binds to plasma proteins and is transported into target organs, especially the kidney. An attempt to prevent its toxic effects has been made using piroxicam, a non-steroidal anti-inflammatory drug (NSAID). Piroxicam also binds strongly to plasma proteins and our hypothesis is that this drug could stop OTA-binding and transport into target organs, thereby preventing its nephrotoxicity. Our experiments on rats given OTA (289 micrograms/kg/48 h for 2 weeks) show that piroxicam prevents the enzymuria induced by OTA and increases renal elimination of OTA. In vivo, piroxicam could prove useful in preventing the chronic effects of ochratoxin A, mainly nephrotoxicity, at doses 5 mg/kg/48 h, which were not found to be nephrotoxic in experimental animals.

Mechanistic considerations in chemopreventive drug development

This overview of the potential mechanisms of chemopreventive activity will provide the conceptual groundwork for chemopreventive drug discovery, leading to structure-activity and mechanistic studies that identify and evaluate new agents. Possible mechanisms of chemopreventive activity with examples of promising agents include carcinogen blocking activities such as inhibition of carcinogen uptake (calcium), inhibition of formation or activation of carcinogen (arylalkyl isothiocyanates, DHEA, NSAIDs, polyphenols), deactivation or detoxification of carcinogen (oltipraz, other GSH-enhancing agents), preventing carcinogen binding to DNA (oltipraz, polyphenols), and enhancing the level or fidelity of DNA repair (NAC, protease inhibitors). Chemopreventive antioxidant activities include scavenging reactive electrophiles (GSH-enhancing agents), scavenging oxygen radicals (polyphenols, vitamin E), and inhibiting arachidonic acid metabolism (glycyrrhetinic acid, NAC, NSAIDs, polyphenols, tamoxifen). Antiproliferation/antiprogression activities include modulation of signal transduction (glycyrrhetinic acid, NSAIDs, polyphenols, retinoids, tamoxifen), modulation of hormonal and growth factor activity (NSAIDs, retinoids, tamoxifen), inhibition of aberrant oncogene activity (genistein, NSAIDs, monoterpenes), inhibition of polyamine metabolism (DFMO, retinoids, tamoxifen), induction of terminal differentiation (calcium, retinoids, vitamin D3), restoration of immune response (NSAIDs, selenium, vitamin E), enhancing intercellular communication (carotenoids, retinoids), restoration of tumor suppressor function, induction of programmed cell death (apoptosis) (butyric acid, genistein, retinoids, tamoxifen), correction of DNA methylation imbalances (folic acid), inhibition of angiogenesis (genistein, retinoids, tamoxifen), inhibition of basement membrane degradation (protease inhibitors), and activation of antimetastasis genes. A systematic drug development program for chemopreventive agents is only possible with continuing research into mechanisms of action and thoughtful application of the mechanisms to new drug design and discovery. One approach is to construct pharmacological activity profiles for promising agents. These profiles are compared among the promising agents and with untested compounds to identify similarities. Classical structure-activity studies are used to find optimal agents (high efficacy with low toxicity) based on good lead agents. Studies evaluating tissue-specific and pharmacokinetic parameters are very important. A final approach is design of mechanism-based assays and identification of mechanism-based intermediate biomarkers for evaluation of chemopreventive efficacy.

Preclinical efficacy evaluation of potential chemopreventive agents in animal carcinogenesis models: methods and results from the NCI Chemoprevention Drug Development Program

In the NCI, Chemoprevention Branch drug development program, potential chemopreventive agents are evaluated for efficacy against chemical carcinogen-induced tumors in animal models. This paper summarizes the results of 144 agents in 352 tests using various animal efficacy models. Of these results, 146 were positive, representing 85 different agents. The target organs selected for the animals model are representative of high-incidence human cancers. The assays include inhibition of tumors induced by MNU in hamster trachea, DEN in hamster lung, AOM in rat colon (including inhibition of AOM-induced aberrant crypts), MAM in mouse colon, DMBA and MNU in rat mammary glands, DMBA promoted by TPA in mouse skin, and OH-BBN in mouse bladder. The agents tested may be classified into various pharmacological and chemical structural categories that are relevant to their chemopreventive potential. These categories include antiestrogens, antiinflammatories (e.g., NSAIDs), antioxidants, arachidonic acid metabolism inhibitors, GST and GSH enhancers, ODC inhibitors, protein kinase C inhibitors, retinoids and carotenoids, organosulfur compounds, calcium compounds, vitamin D3 and analogs, and phenolic compounds (e.g., flavonoids). The various categories of compounds have different spectra of efficacy in animal models. In hamster lung, GSH-enhancing agents and antioxidants appear to have high potential for inhibiting carcinogenesis. In the colon, NSAIDs and other antiinflammatory agents appear particularly promising. Likewise, NSAIDs are very active in mouse bladder. In rat mammary glands, retinoids and antiestrogens (as would be expected) are efficacious. Several of the chemicals evaluated also appear to be promising chemopreventive agents based on their activity in several of the animal models. Particularly, the ODC inhibitor DFMO was active in the colon, mammary glands, and bladder models, while the dithiolthione, oltipraz, was efficacious in all the models listed above (i.e., lung, colon, mammary glands, skin, and bladder).

Strategy and planning for chemopreventive drug development: clinical development plans. Chemoprevention Branch and Agent Development Committee. National Cancer Institute

At the National Cancer Institute, Division of Cancer Prevention and Control, the Chemoprevention Branch and Agent Development Committee develop strategies for efficiently identifying, procuring, and advancing the most promising drugs into clinical trials. Scientific expertise is applied at each phase of development to critically review the testing methods and results, and to establish and apply criteria for evaluating the agents for further development. The Clinical Development Plan, prepared by the Chemoprevention Branch and the Agent Development Committee, is a summary of the status of the agent regarding evidence for safety and chemopreventive efficacy in preclinical and clinical studies. It also contains the strategy for further development of the drug that addresses pharmacodynamics, drug effect measurements, intermediate biomarkers for monitoring efficacy, toxicity, supply and formulation, regulatory approval, and proposed clinical trials. Sixteen Clinical Development Plans are presented here: N-acetyl-l-cysteine (NAC), aspirin, calcium, beta-carotene, 2-difluoromethylornithine (DFMO), DHEA analog 8354, 18 beta-glycyrrhetinic acid, N-(4-hydroxyphenyl)retinamide (4-HPR), ibuprofen, oltipraz, piroxicam, Proscar, sulindac, tamoxifen, vitamin D3 and analogs, and vitamin E. The objective of publishing these plans is to stimulate interest and thinking among the scientific community on the prospects for developing chemopreventive drugs.