Chemoprevention of respiratory-tract neoplasia in the hamster by oltipraz, alone and in combination

Two doses of oltipraz (300, 600 mg/kg diet) and alpha-difluoromethylornithine DFMO; 1600, 3200 mg/kg diet), alone and in combinations with N-(4-hydroxyphenyl) retinamide (4-HPR; 98, 196 mg/kg diet) and/or beta-carotene (3, 1.5 mg; sc, 2x/week), were investigated for prevention of hamster respiratory carcinogenesis. After 25 weeks, only high dose oltipraz (-100%) inhibited the incidence of DEN-induced (17.8 mg/kg BW, sc, 2x/week, 20 weeks) bronchial carcinomas when given alone. Low dose oltipraz (-34%, n.s.) synergistically decreased carcinoma incidence in combinations with 4-HPR (-80%), beta-carotene (-90%) or both (-100%). Other effective combinations were low dose DFMO + beta-carotene (-64%) and high dose DFMO with 4-HPR (-56%), beta-carotene (-63%) or both (-67%).

A randomised, double blind, placebo controlled study of celecoxib, a selective cyclooxygenase 2 inhibitor, on duodenal polyposis in familial adenomatous polyposis

BACKGROUND

Non-selective cyclooxygenase (COX) inhibitors (non-steroidal anti-inflammatory drugs) inhibit large bowel carcinogenesis in patients with familial adenomatous polyposis (FAP). Their role in the duodenum of these patients is less certain. The disease modifying activity of specific COX-2 inhibitors has not been explored in humans.

PATIENTS AND METHODS

This was a randomised, double blind, placebo controlled study of celecoxib (100 mg twice daily (n=34) or 400 mg twice daily (n=32)) versus placebo (n=17), given orally twice daily for six months to patients with FAP. Efficacy was assessed qualitatively by blinded review of shuffled endoscopy videotapes comparing the extent of duodenal polyposis at entry and at six months and quantitatively by measurement of the percentage change in duodenal area covered by discrete and plaque-like adenomas from photographs of high and low density polyposis.

RESULTS

Shuffled and blinded video review showed a statistically significant effect of 400 mg twice daily celecoxib compared with placebo treatment (p=0.033) with all five independent observers scoring a beneficial effect. Overall, patients taking celecoxib 400 mg twice daily showed a 14.5% reduction in involved areas compared with a 1.4% for placebo (p=0.436). However, patients with clinically significant disease at baseline (greater than 5% covered by polyps) showed a 31% reduction in involved areas with celecoxib 400 mg twice daily compared with 8% on placebo (p=0.049).

CONCLUSIONS

A panel of five endoscopists found a significant reduction in duodenal polyposis after six months of treatment with celecoxib 400 mg twice daily. COX-2 inhibition may help this otherwise untreatable condition.

2-difluoromethylornithine and dehydroepiandrosterone inhibit mammary tumor progression but not mammary or prostate tumor initiation in C3(1)/SV40 T/t-antigen transgenic mice

Female transgenic mice that express SV40 T/t antigens under the regulatory control of the rat C3(1) gene spontaneously develop multifocal mammary lesions that predictably evolve into invasive, hormone-independent carcinomas, whereas male mice are prone to develop prostate cancer. Chemopreventive agents were administered to female C3(1)/SV40 large T-antigen mice from 7 to 19 weeks of age, during which time the mammary lesions developed and progressed to invasive carcinomas. No significant differences in the numbers of preinvasive mammary intraepithelial neoplasia lesions (histologically similar to human ductal carcinoma in situ) were observed after 2 or 8 weeks of treatment between mice receiving either vehicle alone, dehydroepiandrosterone (DHEA), or 2-difluoromethylornithine (DFMO). However, a dose-response reduction in invasive carcinoma growth was observed for both DFMO, an inhibitor of ornithine decarboxylase, and DHEA, the primary steroid precursor to both androgens and estrogens in primates. Despite unaltered expression of the transgene, tumor incidence was reduced approximately 20% by DFMO (8000 mg/kg) and 30% by DHEA (4000 mg/kg; P < 0.05). Tumor multiplicity was reduced by approximately 50% by both DFMO and DHEA (P < 0.05). DFMO had a dose-dependent effect on total tumor burden, which was reduced by 25% at low doses (4000 mg/kg) and 70% at high doses (8000 mg/kg). DHEA reduced tumor burden by 50% and 66% at low (2000 mg/kg) and high (4000 mg/kg) doses, respectively. Interestingly, despite its inhibitory effects on tumor development, DHEA caused a dose-dependent increase of serum estradiol levels that we have previously shown to increase mammary tumor formation in this model. No effect on the development of the prostate cancer precursor lesions (prostate intraepithelial neoplasia) was observed when mice were treated with DHEA, DFMO, tocopherol acetate, selenomethionine, or 9-cis-retinoic acid, although the effects on late-stage prostate cancer development were not determined. These results demonstrate that despite the expression of the highly transforming C3(1)/SV40 large T-antigen transgene, this transgenic model can be used to study the effects of chemopreventive agents on mammary cancer progression. The tumor-inhibitory effects of DHEA and DFMO on mammary cancer growth appear to occur after the development of preinvasive lesions, suggesting that these agents inhibit tumor progression but not initiation.

Novel translational model for breast cancer chemoprevention study: accrual to a presurgical intervention with tamoxifen and N-[4-hydroxyphenyl] retinamide

Surrogate end point biomarkers for risk assessment and efficacy of potential chemopreventive agents are needed to improve the efficiency and reduce the cost of chemoprevention trials. It is imperative to develop the best clinical breast model for translational surrogate end point biomarker studies, especially with respect to accrual feasibility. We have initiated a prospective study to develop biomarkers for tamoxifen and N-[4-hydroxyphenyl] retinamide by administering either a placebo or both drugs for 2-4 weeks to women with ductal carcinoma in situ or early invasive cancers in the interval between the initial diagnostic core biopsy and definitive surgery. The principle end point is pretreatment versus posttreatment tumor levels of Ki-67; a number of other exploratory markers will also be examined. The planned target sample size is 100 patients. Between February 1997 and February 2000, 4514 women who had either an abnormal mammogram or a diagnosed breast cancer were screened for the study. Of these 4514 screened patients, 52 (1%) were registered on the study. Major factors of nonparticipation in the remaining 4462 women were as follows: (a) no evidence of malignancy (2081 patients; 46%); (b) ineligible per protocol criteria (575 patients; 13%); (c) preoperative chemotherapy/tamoxifen (520 patients; 11%); (d) surgery scheduling conflict (360 patients; 8%); (e) outside needle biopsy (221 patients; 5%); (f) no residual disease after excisional biopsy (345 patients; 8%); and (g) second opinion only (123 patients; 3%). Other nonparticipation factors included fine needle aspiration only, refusal, tumor size > 2 cm, and estrogen replacement therapy (35 patients each; 2% each). The protocol was amended in midstudy to allow outside needle biopsy, tumor > 2 cm, and estrogen replacement therapy. Accrual to biomarker (nontherapeutic) protocols with delay in definitive cancer surgery is challenging but feasible. Although some accrual problems remain, we have nonetheless succeeded in recruiting 50% of our target sample size in a 3-year period.

The cyclooxygenase-2 inhibitor celecoxib is a potent preventive and therapeutic agent in the min mouse model of adenomatous polyposis

Epidemiological and animal studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce colon cancer risk. NSAIDs nonselectively inhibit both the constitutive cyclooxygenase (COX) 1 associated with side effects and the desired therapeutic target COX-2, which is induced in inflammation and neoplasia. We used the adenomatous polyposis coli (Apc) mutant Min mouse model to determine whether the selective COX-2 inhibitor celecoxib is effective for adenoma prevention and/or regression, and whether it might be safer than the nonselective NSAID previously shown to be most effective in this model, piroxicam. Min mice (n = 120) were randomized to treatment with celecoxib (0, 150, 500, or 1500 ppm celecoxib mixed in the diet) or piroxicam. To distinguish prevention from regression effects, groups were treated either "early" (before adenomas develop) or "late" (after most adenomas are established). Celecoxib caused dramatic reductions in both the multiplicity and size of tumors in a dose-dependent manner (P < 0.01). Early treatment with 1500 ppm of celecoxib was effective for prevention, decreasing tumor multiplicity to 29% and tumor size to only 17% of controls (P < 0.01). Late treatment demonstrated regression effects, reducing tumor multiplicity and size by about half. In contrast to the significant toxicity of piroxicam, which caused ulcers complicated by perforation and bleeding, celecoxib caused no gastrointestinal side effects and did not inhibit platelet thromboxane B2 at plasma drug levels similar to those obtained in early clinical trials in humans. These results provide the first evidence that selective inhibitors of COX-2 are safe and effective for the prevention and regression of adenomas in a mouse model of adenomatous polyposis and strongly support ongoing clinical trials in humans with the same syndrome. The broader population of patients with common sporadic adenomas that have somatic mutations of the same gene (APC) may also benefit from this treatment approach.

Evaluation of biomarker modulation by fenretinide in prostate cancer patients

An NCI-sponsored, phase II trial of N-(4-hydroxyphenyl)- retinamide (4-HPR) in patients with organ-confined prostate cancer in the period prior to radical prostatectomy was carried out. Thirty-seven men with the histologic diagnosis of prostate cancer planning to have radical prostatectomy entered the study after informed consent and were given 4-HPR (or matching placebo) as a single daily dose (two 100-mg capsules of 4-HPR or two capsules of placebo daily) for 3 weeks prior to surgery. Four men dropped out for unrelated reasons. Thirty-three men completed the study. At the time of surgery, repeat biopsies of the prostate were performed to study the effects of the drug on potential surrogate endpoint biomarkers (SEBs) of malignancy within the tissue. The panel of potential SEBs of malignancy include p53, cytomorphometric indices, ploidy, PNCA, erbB-2, erbB-3, EGF receptor, TGF-alpha tumor-associated glycoprotein-72, fatty acid synthetase and Lewis Y antigen. Twenty-three patients had matching pre- and posttherapy lesions and were considered informative. Results from the patients indicate significant differential expression of biomarkers in pretreatment specimens of uninvolved prostatic tissue (normal-appearing epithelia) prostatic intraepithelial neoplasia (PIN) and prostate cancer. The mean erbB-2 expression was 0.58 in uninvolved vs. 1.04 in PIN (p = 0.002); while the mean erbB-2 expression was 1.35 in prostate cancer (p = 0.0007, uninvolved vs. prostate cancer). A similar pattern of increased biomarker expression between uninvolved and PIN or prostate cancer tissues can be observed for EGF receptor (mean = 1.21, 1.87 and 1.76 for uninvolved, PIN and prostate cancer, respectively) and erbB-3 (mean = 0.81, 1.59 and 1.30 for uninvolved, PIN and prostate cancer, respectively). There were no statistically significant differences in biomarkers observed in the 4-HPR-treated patients when compared with placebo-treated control patients. There was a posttreatment up-regulation of biomarkers observed in both groups of patients. This observation is most likely explained by an effect due to the diagnostic sextant biopsy equally affecting both groups of patients. Results from this study do not demonstrate a chemoprevention effect of 4-HPR on tissue-based SEBs at the dose given.

Bcl-2 and Bax are differentially expressed in hyperplastic, premalignant, and malignant lesions of mammary carcinogenesis

Previously, we found that vorozole (Vz), a nonsteroidal aromatase inhibitor, suppresses the development and progression of mammary tumors in rats. Here we evaluated for the first time the expression of cell death-related proteins Bcl-2 and Bax in hyperplastic, premalignant (carcinoma in situ), or malignant (carcinoma) lesions of mammary carcinogenesis; we also assessed whether these proteins are involved in mediating Vz-induced cell death in tumors. We found that Bcl-2 and Bax were equally expressed in epithelial cells of terminal end buds, ducts, and alveoli. However, in myoepithelial cells, the level of Bax expression was much higher than the level of Bcl-2 expression. Bcl-2 and Bax levels in hyperplastic lesions were similar to those of normal mammary epithelial cells but lower in most carcinomas in situ and carcinomas. In animals with established mammary tumors, Vz induced apoptotic cell death, which was primarily associated with a decrease in Bcl-2 and, to a lesser extent, with a decrease in Bax. These data support the hypothesis that Bcl-2 loss is more potent than Bax gain in regulating apoptotic cell death in mammary tumors.

The effect of celecoxib, a cyclooxygenase-2 inhibitor, in familial adenomatous polyposis

BACKGROUND

Patients with familial adenomatous polyposis have a nearly 100 percent risk of colorectal cancer. In this disease, the chemopreventive effects of nonsteroidal antiinflammatory drugs may be related to their inhibition of cyclooxygenase-2.

METHODS

We studied the effect of celecoxib, a selective cyclooxygenase-2 inhibitor, on colorectal polyps in patients with familial adenomatous polyposis. In a double-blind, placebo-controlled study, we randomly assigned 77 patients to treatment with celecoxib (100 or 400 mg twice daily) or placebo for six months. Patients underwent endoscopy at the beginning and end of the study. We determined the number and size of polyps from photographs and videotapes; the response to treatment was expressed as the mean percent change from base line.

RESULTS

At base line, the mean (+/-SD) number of polyps in focal areas where polyps were counted was 15.5+/-13.4 in the 15 patients assigned to placebo, 11.5+/-8.5 in the 32 patients assigned to 100 mg of celecoxib twice a day, and 12.3+/-8.2 in the 30 patients assigned to 400 mg of celecoxib twice a day (P=0.66 for the comparison among groups). After six months, the patients receiving 400 mg of celecoxib twice a day had a 28.0 percent reduction in the mean number of colorectal polyps (P=0.003 for the comparison with placebo) and a 30.7 percent reduction in the polyp burden (the sum of polyp diameters) (P=0.001), as compared with reductions of 4.5 and 4.9 percent, respectively, in the placebo group. The improvement in the extent of colorectal polyposis in the group receiving 400 mg twice a day was confirmed by a panel of endoscopists who reviewed the videotapes. The reductions in the group receiving 100 mg of celecoxib twice a day were 11.9 percent (P=0.33 for the comparison with placebo) and 14.6 percent (P=0.09), respectively. The incidence of adverse events was similar among the groups.

CONCLUSIONS

In patients with familial adenomatous polyposis, six months of twice-daily treatment with 400 mg of celecoxib, a cyclooxygenase-2 inhibitor, leads to a significant reduction in the number of colorectal polyps.

Chemopreventive efficacy of combined piroxicam and difluoromethylornithine treatment of Apc mutant Min mouse adenomas, and selective toxicity against Apc mutant embryos

Genetic knockout or pharmacological inhibition of cyclooxygenase-2 decreases the number and size of adenomas in mouse models of familial adenomatous polyposis. Epidemiological and clinical studies in humans indicate that the entire class of nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit both COX-1 and COX-2 enzymes are promising colon cancer chemopreventive agents. We used the Apc mutant Min mouse model to test combinations of agents that might maximize preventive benefit with minimal toxicity because they act via different mechanisms. Min mice (n = 144) were exposed to low doses of the nonselective COX inhibitor piroxicam and the ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO), beginning at the time they were weaned and continuing throughout the duration of the experiment. Piroxicam at 12, 25, and 50 ppm in the diet caused dose-dependent decreases in the number of tumors in the middle and distal portions of the small intestine. This decrease in tumor multiplicity was associated with a striking decrease in the size of those tumors that did grow out. In contrast, none of the doses of piroxicam alone decreased tumor multiplicity in the proximal portion of the intestine (duodenum). Exposure to DFMO (0.5 or 1.0% in water) caused a dose-dependent decrease in tumor multiplicity in the middle and distal portions of the small intestine. However, this decreased multiplicity was not associated with a striking decrease in the size of the tumors. Combined treatment of mice with piroxicam plus DFMO was much more effective than either agent alone and resulted in a significant number of mice totally free of any intestinal adenomas (P < 0.001), in contrast to the 100% incidence and high multiplicity in control Min mice. In addition to this profound effectiveness in reducing tumor number, the few residual tumors in mice treated with the combined drugs were markedly smaller in size than tumors that arose from control Min mice. These experiments suggest that selective COX-2 inhibition combined with ODC inhibition is a very promising approach for colon cancer prevention. These COX-2 and ODC inhibitor drugs were not overtly toxic at the doses used when administered to mice after weaning. However, when treatment was begun in utero, the Mendelian expected progeny ratio of 1:1 that we routinely obtained in untreated control litters was no longer observed. Apc(min)/+ progeny of pregnant dams treated with piroxicam and/or DFMO were reduced in number and their ratio to Apc+/+ progeny was decreased to approximately 0.28:1. Thus, these agents are effective against adenomas that have homozygous mutation of the APC gene and also select against fetuses bearing a heterozygous mutation in the APC gene.

Sulindac sulfone induced regression of rectal polyps in patients with familial adenomatous polyposis

Sulindac sulfone (Exisulind), a metabolite of the non-steroidal anti-inflammatory drug, sulindac, was evalauted for its effects on the development of rectal polyps in patients with familial adenomatous polyposis. Three cohorts of 6 patients each were given doses of 200, 300, or 400 mg Exisulind twice daily. Hepatotoxicity, shown by elevation in blood transaminase levels, was the dose-limiting toxicity and occurred at the 400 mg bid dose. Due to this toxicity, all patients treated with the 400 mg dose were subsequently reduced to the 200 mg dose level. Subsequently, 2 of the 6 patients were dose-escalated to 400 mg bid dose. The patients were treated with Exisulind for a period of six months. Sixteen of 18 patients had regression of small polyps (> or = 6 mm in diameter) characterized by a flattening of the polyps and a macular "halo" appearance. Histopathologic examination of the polyp biopsy specimens showed a marked increase in the proportion of mucin producing cells in the glands after treatment with Exisulind at all dose levels. Ki-67 staining, a measure of cell proliferation, was higher in the polyps than in normal mucosa. There was no significant change in the proliferation index between baseline and six month values in any of the groups treated with Exisulind or in normal tissues. The median apoptotic labeling index, as determined by the TUNEL technique, was higher in the polyps than in normal-appearing mucosa. Overall, there was no significant change in the apoptotic labeling index between base-line and 6 months in normal-appearing mucosa however, the index in polyps was increased. These results suggest that treatment of FAP patients with Exisulind for a period of six months may lead to regression of small polyps, and that the mechanisms of Exisulind--induced regression appear to be through stimulation of mucus differentiation and apoptosis in glandular epithelium.

Cellular responses of mammary carcinomas to aromatase inhibitors: effects of vorozole

Vorozole (Vz) is a competitive non-steroidal inhibitor of aromatase, which has been used to treat breast cancer in postmenopausal women and in various chemoprevention pre-clinical studies. Recently, we assessed the inhibitory effect of Vz on MNU-induced mammary carcinogenesis (Lubet et al., 1994), as well as on the progression of mammary tumors (Lubet et al., 1998). In this study we evaluated the effects of Vz on tumor growth, serum estradiol, cell proliferation, apoptotic and non-apoptotic cell death to determine whether any of these 'surrogate' markers might reflect the efficacy of various doses of Vz. Vz at doses of 2.5 (Hi), 0.32 (Md), and 0.08 (Lo) mg/kg body weight induced complete (100%), 60%, and 20% regression of mammary tumors, respectively. Vz at Hi and Md doses caused a decrease in serum estradiol within the first two days of treatment, and the estradiol values remained low with additional treatment for 4 and 10 days. When Vz was administered to animals bearing palpable tumors a time and dose-dependent decrease in the proliferating cells (BrdU-L1) was observed. The percentage of apoptotic cells (A1) sharply increased 2 days after initiation of Vz treatment and then decreased followed by an increase in non-apoptotic dead cells. Interestingly even the Lo dose of Vz, which was only moderately effective in suppressing tumor growth, decreased cell proliferation and increased cell death in the peripheral tumor areas at 4 and 10 days after initiation of treatment. The time- and dose-dependent alterations in various cell parameters suggest two different phases of Vz-induced cellular responses: (1) an early phase (2-4 days of treatment) with a sharp increase in apoptotic cells and decrease in proliferating cells, and (2) a later phase (10 days) with disintegration of tumor parenchyma, increase in non-apoptotic dead cells, and decrease in apoptotic cells. The dose-dependent decrease in proliferating cells and increase in apoptotic and non-apoptotic cell death in Vz-treated animals suggest that these biomarkers might be used as potential surrogate endpoints for efficacy in breast cancer chemoprevention and therapy studies with aromatase inhibitors.

Neoplastic transformation of mammary epithelial cells in rats is associated with decreased apoptotic cell death

Previous studies have shown that terminal end buds (TEBs) in the murine mammary gland have high proliferative activity and demonstrate apoptotic cell death (ACD). Since TEBs are considered the place of origin of most chemically induced mammary carcinomas, we hypothesized that the development of hyperplastic and premalignant (carcinoma in situ, CIS) lesions in TEBs is associated with either a further increase in cell proliferation and/or with a decrease in ACD. To test this hypothesis we used the N-methyl-N-nitorosourea (MNU) carcinogenesis model in rats, where the occurrence of mammary tumors is preceded by hyperplastic and premalignant lesions arising mostly in TEBs, as well as in ducts and alveoli. The percentage of proliferating cells, as evaluated by 5-bromodeoxyuridine labeling (BrdU-LI), was similar in TEBs to those in terminal endbud hyperplasia (TEBH), CIS, and carcinomas (CA), whereas the percentage of apoptotic cells (apoptotic index, AI) was relatively high in TEBs and decreased in TEBH, CIS, and CA. This indicates that neoplastic transformation of mammary epithelial cells in TEBs is not associated with an increase in cell proliferation, but with a decrease in ACD. In addition to TEBH, hyperplastic lesions developed in ductal branching areas (ductal hyperplasia, DH) and alveolar structures (alveolar hyperplasia, AH). However, BrdU-LI in both DH and AH was lower than in TEBH, whereas the AI values were similar, suggesting that TEBH has a higher potential for progression and malignant transformation than DH and AH. In mammary tumors apoptotic cells were rare in the peripheral, proliferative areas, but frequent close to the necrotic areas, suggesting that intratumoral factors may significantly affect ACD. Thus, it appears that dissociation between cell proliferation and apoptosis occurs in the hyperplastic stages of mammary carcinogenesis and that neoplastic transformation of mammary epithelial cells is associated with decreased ACD but not with increased cell proliferation.

Chemoprevention of colon cancer by specific cyclooxygenase-2 inhibitor, celecoxib, administered during different stages of carcinogenesis

Epidemiological observations and laboratory research have suggested that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colon cancer and that the inhibition of colon carcinogenesis by NSAIDs is mediated through the modulation of prostaglandin production by rate-limiting enzymes known as cyclooxygenases (COXs). Because traditional NSAIDs inhibit both COX-1 and COX-2, these drugs induce side effects, such as gastrointestinal ulceration and renal toxicity, through the inhibition of the constitutive COX-1. Overexpression of COX-2 has been observed in colon tumors; therefore, specific inhibitors of COX-2 could serve as chemopreventive agents. Our previous study has shown that celecoxib, an inhibitor of COX-2, while sparing COX-1, inhibited azoxymethane (AOM)-induced colon tumorigenesis when administered during both initiation and postinitiation stages, ie., celecoxib administered continuously before, during, and after carcinogen treatment. This study examined the dose-response effect of celecoxib when administered during the initiation and postinitiation stages. In addition, the chemopreventive effects of high-dose celecoxib administered during the promotion/progression stage of colon carcinogenesis, ie., continuous celecoxib administration beginning 14 weeks after the carcinogen treatment, was determined in male F344 rats. We also measured the steady-state levels of celecoxib in the plasma of animals given this inhibitor. Groups of 5-week-old male F344 rats were fed either a control diet or experimental diets containing 500, 1000, or 1500 ppm celecoxib. At 7 and 8 weeks of age, rats scheduled for carcinogen treatment were injected s.c. with AOM at a dose rate of 15 mg/kg body weight/week. Groups of animals destined for the promotion/ progression study and initially receiving the control diet were switched to a diet containing 1500 ppm celecoxib beginning 14 weeks after the second AOM treatment. All rats remained on their respective dietary regimens until the termination of the study, ie., 52 weeks, and were then sacrificed. Colon tumors were evaluated histopathologically. Administration of 500, 1000, or 1500 ppm celecoxib during the initiation and postinitiation stages significantly inhibited the incidence (P < 0.01 to P < 0.0001) as well as the multiplicity (P < 0.01 to P < 0.0001) of adenocarcinomas of the colon in a dose-dependent manner. Importantly, administration of 1500 ppm celecoxib during the promotion/progression stage also significantly suppressed the incidence and multiplicity of adenocarcinomas of the colon (P < 0.01). Also, administration of celecoxib to the rats during the initiation and postinitiation periods and throughout the promotion/progression stage strongly suppressed colon tumor volume (P < 0.0002 to P < 0.001). The steady-state plasma concentration of celecoxib increases somewhat with the dose. Thus, in this model system, the chemopreventive efficacy of celecoxib is dose-dependent when this COX-2 inhibitor is administered during the initiation and postinitiation periods. This study provides the first evidence that celecoxib is also very effective when it is given during the promotion/progression stage of colon carcinogenesis, indicating that the chemopreventive efficacy is achieved during the later stages of colon tumor development. This suggests that celecoxib may potentially be an effective chemopreventive agent for the secondary prevention of colon cancer in patients with familial adenomatous polyposis and sporadic polyps.

Phase I trial of exisulind (sulindac sulfone, FGN-1) as a chemopreventive agent in patients with familial adenomatous polyposis

Exisulind (sulindac sulfone; FGN-1), a metabolite of sulindac without known effects on prostaglandin synthesis, can promote apoptosis and inhibit tumorigenesis in preclinical systems. We performed a Phase I trial of this compound in patients with familial adenomatous polyposis (FAP) to examine the tolerability and safety of this drug in the cancer chemoprevention setting. Six patients each were treated with exisulind at doses of 200, 300, and 400 mg p.o. twice a day. Reversible hepatic dysfunction was noted in four of six patients treated at the 400-mg p.o., twice-a-day dose level, but in only one to two of six patients treated at each of the lower dose levels. The serum half-life of exisulind was 6-9 h; little drug accumulation was noted over time. A nonsignificant trend toward increased apoptosis in polyps was noted at the maximum tolerated dose, but no decrease in polyp numbers or significant effects on cellular proliferation was noted. After treatment, polyps tended to display a "halo" appearance grossly and mucinous differentiation histologically. The maximum safe dose of exisulind is 300 mg p.o. twice a day in patients with subtotal colectomies. Reversible hepatic dysfunction limits further dose escalation. A decrease in polyp numbers could not be demonstrated, but the trend toward increased apoptosis at the MTD and the observation of mucinous change histologically suggest that further investigation of drugs of this class might be warranted.

Chemopreventive activity of celecoxib, a specific cyclooxygenase-2 inhibitor, and indomethacin against ultraviolet light-induced skin carcinogenesis

Epidemiological and dietary studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colon cancer, possibly through a mechanism involving inhibition of cyclooxygenase (COX)-2, which is overexpressed in premalignant adenomatous polyps and colon cancer. Because ultraviolet light (UV) can induce COX-2 and nonspecific NSAIDs can decrease UV-induced skin cancer, we evaluated the ability of two compounds, celecoxib (a specific COX-2 inhibitor) and indomethacin (a nonspecific NSAID), to block UV-induced skin tumor development in SKH:HR-1-hrBr hairless mice. Mice fed 150 or 500 ppm celecoxib showed a dose-dependent reduction (60% and 89%, respectively) in tumor yield. Indomethacin (4ppm) reduced tumor yield by 78%. Although both acute and chronic UV exposure increased cell proliferation and edema, neither compound reduced these parameters. In contrast, UV-induced prostaglandin synthesis in the epidermis was effectively blocked by both compounds. UV-induced increases in COX-2 expression in skin were also not altered in any of the treatment groups. Similarly, tumors that constitutively express high levels of COX-2 displayed no reduction by treatment with celecoxib or indomethacin. The dramatic protective effects of celecoxib suggests that specific COX-2 inhibitors may offer a way to safely reduce the risk of skin cancer in humans.

Chemopreventive effect of S-methylmethane thiosulfonate and sulindac administered together during the promotion/progression stages of colon carcinogenesis

S-methylmethane thiosulfonate (S-MMTS), isolated from cauliflower and having antiproliferative activity, and the non-steroidal anti-inflammatory drug sulindac have been shown to inhibit chemically induced colon carcinogenesis when they are administered during the initiation and/ or post-initiation stages. The present study was designed to investigate the chemopreventive efficacy of 80 p.p.m. S-MMTS administered during the initiation and post-initiation stages and of S-MMTS and sulindac administered together at low doses (40 and 160 p.p.m., respectively) during the promotion/progression phases (late in the premalignant stage) of colon carcinogenesis. At 5 weeks of age, groups of male F344 rats were fed diets containing 0 (control diet) or 80 p.p.m. S-MMTS. At 7 and 8 weeks of age all rats except those in the vehicle-treated groups were given s.c. injections of 15 mg/kg body wt azoxymethane (AOM). Rats receiving the control diet and intended for the study of inhibition of colon carcinogenesis during the promotion/progression phases were continued on the control diet for 14 weeks after the second AOM treatment; they were then switched to experimental diets containing 80 p.p.m. S-MMTS, 160 p.p.m. sulindac or 40 p.p.m. S-MMTS plus 160 p. p.m. sulindac. The rats were maintained on their respective dietary regimens until 52 weeks after carcinogen treatment and were then killed. Colon tumors were evaluated histopathologically. Administration of 80 p.p.m. S-MMTS alone during the initiation and post-initiation stages and promotion/progression stages had no significant effect on colon tumor inhibition. In contrast, the administration of 160 p.p.m. sulindac during the promotion/progression stages did significantly inhibit total colon tumor multiplicity (P < 0.05). Moreover, co-administration of 40 p.p. m. S-MMTS with 160 p.p.m. sulindac during the promotion/progression stages suppressed the incidence and multiplicity of non-invasive adenocarcinomas (P < 0.05-0.01) and multiplicity of invasive and total adenocarcinomas of the colon to a significant degree (P < 0. 05-0.01). These findings have potential clinical implications.

Difluoromethylornithine chemoprevention of epidermal carcinogenesis in K14-HPV16 transgenic mice

To be informative for chemoprevention, animal models must both closely emulate human disease and possess surrogate endpoint biomarkers that facilitate rapid drug screening. This study elucidated site-specific histopathological and biochemical surrogate endpoint biomarkers of spontaneous epidermal carcinogenesis in K14-HPV16 transgenic mice and demonstrated that the incidence and severity of these markers were decreased by the ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO). The cumulative incidence of visible epidermal cancers in 127 untreated transgenic mice was 42% by 52 weeks of age, most frequently affecting the chest as flat lesions in association with chronic ulcers, or in the ear as protuberant masses. Microscopic malignancies were detected in 39% of 32-week-old transgenic mice and were found to emerge from precursor lesions that were of two distinct types: dysplastic sessile ear papillomas and hyperproliferative follicular/interfollicular chest dysplasias. ODC activity and tissue polyamine contents were differentially elevated in ear and chest skin during carcinogenesis, such that there was a marked elevation of both parameters of polyamine metabolism as early as 4 weeks of age in the ear, whereas in the chest, polyamine metabolism was increased significantly only in the late stages of neoplastic progression and in epidermal cancers. Administration of 1.0% DFMO in the drinking water from 4 to 32 weeks of age prevented both visible and microscopic malignancies and significantly decreased the incidence of chest and ear precursor lesions. ODC activity and tissue putrescine content were markedly diminished by DFMO chemoprevention in ear skin, whereas there was a more modest decline of these parameters in chest skin. DFMO treatment of transgenic mice from 28 to 32 weeks of age was associated with an absence of ear cancer and a marked regression of dysplastic papillomas. In contrast, the results in chest skin were complex in that the severity of chest precursors diminished, but their incidence was unchanged, and microscopic cancers were still detectable within these lesions. Collectively, this study highlights the utility of multistage epidermal carcinogenesis in K14-HPV16 transgenic mice both for the study of the biology of, and as a screening tool for, novel drugs and chemopreventive regimens.

Suppression of cell proliferation and telomerase activity in 4-(hydroxyphenyl)retinamide-treated mammary tumors

The detection of telomerase activity has been proposed as a biomarker of breast cancer development and progression. In this study, we used cell proliferation and telomerase in MNU (N-methyl-N-nitrosourea)-induced mammary carcinomas as targets for assessing the response of tumor cells to 4-(hydroxyphenyl)retinamide (4-HPR), a known inhibitor of mammary carcinogenesis in animal models and premenopausal women. In mammary tumors of rats treated for 1, 2, 4 or 6 weeks with 4-HPR, we observed that telomerase activity decreased progressively with the extension of 4-HPR administration. A marked reduction in telomerase activity was already observed by 2 weeks after treatment and the lowest level was found at 6 weeks after initiation of 4-HPR treatment. The changes in telomerase activity were preceded and accompanied by a significant decrease in the percentage of proliferating cells as evaluated by 5-bromodeoxyuridine (BrdU)-labeling. However, when the values of telomerase activity in the individual tumors were compared with the percentage of proliferating cells, no significant correlation was found. These data suggest that the decreased telomerase activity in the animals treated with 4-HPR is not a simple consequence of the changes in cell proliferation, but a more complex phenomenon involving different cellular mechanisms and pathways. The time-dependent and consistent decrease of telomerase activity in the tumors treated with 4-HPR suggests that, in addition to the percentage of proliferating cells, telomerase activity could also be used as an endpoint in breast cancer chemotherapy studies.

Sex-related differences in bronchial epithelial changes associated with tobacco smoking

BACKGROUND

Lung cancer is the most common cause of cancer death in North American women. Because smoking-related changes in the bronchial epithelium and in lung function have not been studied in detail in women, we used fluorescence bronchoscopy-directed biopsy to determine the prevalence of high-grade preinvasive lesions in former and current smokers of both sexes.

METHODS

Spirometry, white-light bronchoscopy, and fluorescence bronchoscopy were performed in 189 women and 212 men older than 40 years of age who had smoked 20 pack-years or more (pack-years = number of packs of cigarettes smoked per day x number of years of smoking).

RESULTS

Carcinoma in situ was found in 1.8% of the subjects, severe dysplasia was found in 6.5%, and moderate dysplasia was found in 14% (all preinvasive lesions). Compared with men, women had a lower prevalence of high-grade preinvasive lesions in the observed airways (14% versus 31%; odds ratio = 0.18; 95% confidence interval = 0.04-0.88), and women with preinvasive lesions had fewer such lesions (two-sided P = .048). The prevalence of preinvasive lesions did not change substantially for more than 10 years after cessation of smoking. Lung function was associated with the prevalence of preinvasive lesions, but the association was weaker in women than in men. If the presence of airflow obstruction was defined by an FEV1/FVC (forced expiratory volume in 1 second/forced vital capacity) value of 70% or less, only 56% of the men and 44% of the women with preinvasive lesions had abnormal lung function.

CONCLUSION

In developing strategies for chemoprevention or early detection of lung cancer in high-risk populations, it is important to consider the effect of sex and arbitrarily chosen lung function values on the prevalence of preinvasive airway lesions.

Interobserver reproducibility of the Lagios nuclear grading system for ductal carcinoma in situ

Several studies have shown an association between high nuclear grade or necrosis of ductal carcinoma in situ (DCIS) lesions and the risk of local disease recurrence in patients with DCIS treated surgically with less than mastectomy. Although criteria for separating low from high nuclear grade lesions have been published, no information exists regarding interobserver reproducibility (IR). To assess IR in the classification of DCIS, six surgical pathologists from four institutions used the Lagios grading system to grade 125 DCIS lesions. Before meeting to evaluate the cases, a training set of 12 glass slides, including cases chosen to present conflicting cues for classification, was mailed to the participants with a written criteria summary. This was followed by a working session in which criteria were reviewed and agreed on. The pathologists then graded the lesions independently. The area of interest was marked on each slide before grading. After initial grading, the pathologists met again to resolve discrepant lesion classifications. A complete agreement among raters was achieved in 43 (35%) cases, with five of six raters agreeing in another 45 (36%) cases. In no case did two raters differ by more than one grade. The pairwise kappa agreement values ranged from fair to substantial (0.30 to 0.61). Generalized kappa value indicated moderate agreement (0.46, standard error = 0.02). Kappa statistics for the distinction between grades 1 and 2 and 2 and 3 were 0.29 and 0.48, respectively, (standard error = 0.02). Only one of the six raters differed significantly in scoring. With adherence to specific criteria, IR in the classification of DCIS cases can be obtained in most cases. Although these pathologists made a few grading system modifications, further refinements are needed, especially if grading will influence future therapy.

Enhancement of experimental colon cancer by genistein

Several phytochemicals and micronutrients that are present in fruits and vegetables are known to exert cancer chemopreventive effects in several organs, including the colon. Among them, the soybean isoflavonoid genistein received much attention due to its potential anticarcinogenic, antiproliferative effects and its potential role in several signal transduction pathways. The present study was designed to investigate the effect of genistein on azoxymethane (AOM)-induced colon carcinogenesis and to study its modulatory role on the levels of activity of 8-isoprostane, cyclooxygenase (COX), and 15-hydroxyprostaglandin F2alpha dehydrogenase (15-PGDH) in the colonic mucosa and colon tumors of male F344 rats. At 5 weeks of age, groups of male F344 rats were fed control (AIN-76A) diet or a diet containing 250 ppm genistein. Beginning 2 weeks later, all animals except those in the vehicle-treated groups were given weekly s.c. injections of AOM (15 mg/kg body weight) for 2 successive weeks. All rats were continued on their respective dietary regimen for 52 weeks after AOM treatment and were then sacrificed. Colon tumors were evaluated histopathologically. Colonic mucosae and tumors were analyzed for COX, 15-PGDH, and 8-isoprostane levels. Administration of genistein significantly increased noninvasive and total adenocarcinoma multiplicity (P < 0.01) in the colon, compared to the control diet, but it had no effect on the colon adenocarcinoma incidence nor on the multiplicity of invasive adenocarcinoma (P > 0.05). Also, genistein significantly inhibited the 15-PGDH activity (>35%) and levels of 8-iosoprostane (50%) in colonic mucosa and in tumors. In contrast, genistein had no significant effect on the COX synthetic activity, as measured by the rate of formation of prostaglandins and thromboxane B2 from [14C]arachidonic acid. The results of this investigation emphasize that the biological effects of genistein may be organ specific, inhibiting cancer development in some sites yet showing no effect or an enhancing effect on the tumorigenesis at other sites, such as the colon. The inhibition of 8-isoprostane levels by genistein indicates its possible antioxidant potential, which is independent of the observed colon tumor enhancement, yet this agent may also possess several biological effects that overshadow its antioxidant potential. The exact mechanism(s) of colon tumor enhancement by genistein remain to be elucidated; it is likely that its colon tumor-enhancing effects may, at least in part, be related to inhibition of prostaglandin catabolic enzyme activities.

Suppression of human colorectal mucosal prostaglandins: determining the lowest effective aspirin dose

BACKGROUND

A variety of studies have supported the finding that regular intake of aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory agents can affect colorectal cancer carcinogenesis. These agents inhibit the synthesis of prostaglandins. High levels of prostaglandins are observed in colon cancer tissues.

PURPOSE

Experiments were planned to determine the lowest dose of aspirin that can markedly suppress the levels of mucosal prostaglandins E2 and F(2alpha) in colorectal mucosa and to determine whether a relationship exists between these levels and plasma levels of both acetylsalicylic acid and its metabolite, salicylic acid.

METHODS

Healthy men and women aged 18 years or older participated in the study. The participants took a single, daily dose of aspirin (40.5, 81, 162, 324, or 648 mg) or a placebo for 14 days. Colorectal biopsy specimens were taken at baseline, 24 hours after the first dose of aspirin, and 24-30 hours and 72-78 hours after the last, i.e., fourteenth, daily dose of aspirin. The biopsy specimens were assayed for prostaglandins E2 and F(2alpha) by use of a competitive enzyme immunoassay. Plasma concentrations of acetylsalicylic acid and salicylic acid were determined by use of high-performance liquid chromatography. All P values are two-sided.

RESULTS

A total of 65 subjects (10 receiving placebo, groups of 10 each receiving 40.5, 81, 162, or 324 mg of aspirin, and a group of 15 receiving 648 mg of aspirin) completed the protocol. One subject reported unacceptable drug-induced toxic effects and did not complete the protocol; other subjects reported acceptable side effects. The lowest dose to significantly suppress colorectal mucosal prostaglandin E2 concentrations from baseline at 24 hours after the first dose (by 22.6%; P = .002) and at 24-30 hours after the last dose (by 14.2%; P = .021) was 162 mg. At 72-78 hours after the last dose, there was significant suppression for subjects receiving 81 mg (by 23.7%; P = .008). The lowest dose to significantly suppress colorectal mucosal prostaglandin F(2alpha) concentrations from baseline at 24 hours after the first dose (by 18.3%; P = .032) was 324 mg. The lowest dose causing a marked reduction in the level of prostaglandin F(2alpha) at 24-30 hours (by 15.1%; P = .003) and 72-78 hours (by 23.0%; P = .0002) after the last dose was 40.5 mg. No detectable amounts of acetylsalicylic acid or salicylic acid were present in the plasma at any of the biopsy time points.

CONCLUSIONS

The lowest doses of aspirin taken daily for 14 days to significantly suppress concentrations of colorectal mucosal prostaglandins E2 and F(2alpha) were 81 and 40.5 mg, respectively. The suppression occurred without detectable amounts of aspirin or salicylic acid in the plasma at the time points studied. On the basis of these observations, we recommend a single, daily dose of 81 mg of aspirin in future studies of this drug as a chemopreventive agent for colorectal cancer.

Modulation of alterations in p53 tumor suppressor gene and its association with activation of ras proto-oncogenes during chemoprevention of colon cancer

Previously, we reported (Carcinogenesis 15: 1317-1323, 1994) a high rate of activating point mutations in I ns proto-oncogenes in azoxymethane (AOM)-induced colon tumors, and a significant suppression of these mutations by dietary administration of chemopreventive agents, D,L-alpha-difluoromethylornithine (DFMO) and piroxicam. To understand the role of p53 tumor suppressor gene in chemoprevention of colon cancer and to study the association of p53 gene alterations with activation of ras genes, we determined point mutations in conserved regions (exons 5-9) of p53 gene and analyzed the occurrence of double event of ms activation acid p53 mutation. Groups of male F344 rats were fed the modified AIN-76A diet containing 0, 4000 ppm DFMO, or 150 ppm piroxicam and administered s.c. AOM at a dose rate of 15 mg/kg body wt, once weekly, for 4 weeks. Vehicle controls received s.c. equal volume of normal saline. Animals were sacrificed 32 weeks after the last AOM or saline injection and their grossly visible colon tumors were analyzed to determine p53 mutations by PCR amplification based single strand conformation polymorphism (SSCP) and direct DNA sequencing. Our results demonstrate that about 57% tumors from animals fed the control diet contained predominantly missense but also nonsense mutations, whereas only 30% tumors from animals on piroxicam diet, and none (0%) from animals fed the DFMO diet had similar mutations. Analysis of data revealed that about half of the tumors from animals on control diet possessed both ms and p53 mutations together, only 27% of colon tumors from animals on piroxicam diet and none of the tumors from animals on DFMO diet exhibited both ms and p53 mutations. These results indicate that the administration of piroxicam, a non-steroidal anti-inflammatory drug, and DFMO, a irreversible inhibitor of ornithine decarboxylase, may inhibit selective proliferation of initiated cells containing activated las and/or mutant p53. Dietary DFMO exerted more pronounced inhibition of selective amplification of initiated cells containing mutated ras and/or p53.

Inhibition of 2-Amino-1-methyl-6-phenylimidazo[4,5]pyridine-induced lymphoma formation by oltipraz

2-Amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mutagenic and carcinogenic heterocyclic amine present in pyrolysate products of meat and fish and has been shown to induce tumors in the colon, mammary gland, and possibly lymphatic system. Experiments were designed to examine the lymphoma-inducing capacity of PhIP and to test the inhibitory effects of oltipraz on PhIP-induced lymphomas in male F344 rats. Beginning at 5 weeks of age, groups of rats were fed the diets containing 0, 200, and 400 ppm oltipraz with or without 100-400 ppm PhIP. All animals were continued on this regimen until the 58th week. The results indicate that administration of PhIP produced lymphomas in 75% of rats. Most of the large lymphomas were thymomas (65%), and these lymphomas developed in less than 6 months. Death of animals during the course of the study was due to suffocation produced by a large lymphoma that filled the entire thoracic cavity, resulting in collapse of the lungs. Administration of 200-400 ppm oltipraz significantly protected rats from PhIP-induced toxicity; most of the rats survived until termination of the experiments. It is noteworthy that the addition of oltipraz at 200 and 400 ppm in the diet suppressed the PhIP-induced lymphomas to 90-100%. In conclusion, PhIP-induced lymphomas in the laboratory rat appears to be a very useful model to analyze the genesis of lymphomas, and oltipraz serves as a potential chemopreventive agent for lymphomas.

Chemopreventive efficacy of arylalkyl isothiocyanates and N-acetylcysteine for lung tumorigenesis in Fischer rats

The purpose of this study is to evaluate the efficacy of three promising sulfur-containing compounds, 6-phenylhexyl isothiocyanate (PHITC), phenethyl isothiocyanate (PEITC), and N-acetylcysteine (NAC), as chemopreventive agents in a long-term bioassay for lung tumorigenesis in F344 rats. PEITC occurs as a constituent of certain cruciferous vegetables, PHITC is a synthetic homologue, and NAC is an endogenous substance. Male F344 rats were treated with the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by s.c. injection at a dose of 1.5 mg/kg body weight three times weekly for 20 weeks. This dose regimen induced a 67% tumor incidence in the lung, a major target organ of NNK. PHITC or PEITC administered in the diet for 22 weeks, a period covering from 1 week before to 1 week after the NNK treatment, exhibited significant inhibition of lung tumorigenesis induced by NNK. The lung tumor incidences in the NNK-treated groups, fed a diet containing 4 mmol/kg (876 ppm) or 2 mmol/kg (438 ppm) PHITC, were 24 and 19% and were 9 and 17% in groups fed PEITC at concentrations of 8 mmol/kg (1304 ppm) or 4 mmol/kg (652 ppm), respectively. In contrast to isothiocyanates, NAC given in the diet at 80 mmol/kg (13056 ppm) or 40 mmol/kg (6528 ppm) exerted no inhibitory effects on the NNK-induced lung tumorigenesis. At the dose studied, NNK did not induce liver and pancreatic tumors in the treated animals, but a significant increase of nasal cavity tumor incidence was observed in the NNK-treated group. However, none of the test compounds showed any effect on the tumorigenesis in this tissue. This study demonstrated that PHITC and PEITC were potent chemopreventive agents for the NNK-induced lung tumorigenesis in F344 rats, whereas NAC was not active at all. These results support further evaluation of these compounds in chemoprevention studies.

Chemo- and dietary prevention of colorectal cancer

Because of the substantial morbidity and mortality associated with colorectal cancer, and the limitations and costs of treating this disease, prevention remains a desirable (if elusive) goal. In this paper, we discuss both chemo- and dietary prevention strategies for colorectal cancer, recognising the overlap and cross-fertilisation between these two approaches. Chemopreventive compounds are drugs and are developed for clinical use like other pharmaceuticals. A formal sequential multi-phase programme for development of chemopreventive agents has been instituted by the National Cancer Institute, U.S.A. This involves both preclinical efficacy and clinical studies. Such studies increasingly employ preneoplastic intermediate markers (such as proliferation measures) as well as neoplastic adenomas as endpoints. Promising chemopreventive agents include calcium, aspirin and other non-steroidal anti-inflammatory drugs, vitamins (such as vitamin E and folate), 2-dimethylfluorornithine (DFMO), oltipraz and ursodeoxycholic acid. Several lines of evidence implicate diet in colorectal carcinogenesis. Key hypotheses in diet and colorectal cancer (which are amenable to prevention, research and action), in addition to those pertaining to the micronutrient chemopreventives, include dietary fat and fibre, food mutagens, red meat, and overall low-fat, high-fibre, high fruit and vegetable dietary patterns and cuisines. Several adenomatous polyp recurrence studies with fibre supplement, macronutrient or dietary pattern interventions have been undertaken internationally. We review early findings from this new generation of studies, and anticipate the future results from these investigations and the ambitious Women's Health initiative in the U.S.A. Results from these studies may convert the promise of colorectal cancer prevention into reality.

Chemoprevention of colon carcinogenesis by sulindac, a nonsteroidal anti-inflammatory agent

Epidemiological and laboratory animal model studies have suggested that nonsteroidal anti-inflammatory drugs reduce the risk of development of colon cancer. The present study was designed to investigate the chemopreventive action of 160 and 320 ppm (equivalent to 40 and 80% maximum tolerated doses) sulindac, a nonsteroidal anti-inflammatory drug, fed during initiation and postinitiation stages and 320 ppm sulindac fed during promotion/progression stages of azoxymethane-induced colon carcinogenesis in male F344 rats. Also investigated was the modulating effect of this agent on the colonic mucosal and tumor phospholipase A2, phosphatidylinositol-specific phospholipase C, lipoxygenase, and cyclooxygenase activities. At 5 weeks of age, groups of male F344 rats were fed control diet or diets containing 160 and 320 ppm of sulindac. At 7 weeks of age, all animals except those in the vehicle-treated groups were given two weekly s.c. injections of azoxymethane at a dose rate of 15 mg/kg body weight/week. Animals intended for tumor promotion/progression study were administered 320 ppm of sulindac in diet starting at 14 weeks after a second azoxymethane treatment. All animals continued on their respective dietary regimen until the termination of the experiment at 52 weeks after the carcinogen treatment. Colonic tumors were evaluated histopathologically. Colonic mucosa and tumors were analyzed for phospholipase A2, phosphatidylinositol-specific phospholipase C, prostaglandin E2, cyclooxygenase, and lipoxygenase activities. The levels of sulindac and its metabolites in stomach, cecal, and fecal contents and in serum were analyzed. The results indicate that dietary sulindac at 160 and 320 ppm levels inhibited the incidence of invasive and noninvasive adenocarcinomas of the colon (P < 0.01-0.001) as well as their multiplicity (P < 0.01-0.0001) in a dose-dependent manner. Also, feeding sulindac during promotion/progression stages significantly suppressed the incidence (P < 0.0001) and multiplicity (P < 0.0001) of colonic adenocarcinomas. Dietary sulindac also suppressed the colon tumor volume by > 52-62% compared to the control diet. Dietary sulindac significantly decreased the activities of phosphatidylinositol-specific phospholipase C (32-51%) and levels of prostaglandin E2 (> 40%) in the colonic mucosa and tumors, but it had no significant (P > 0.05) effect on phospholipase A2 activity. The formation of cyclooxygenase metabolites, particularly prostaglandin E2, prostaglandin F2 alpha, prostaglandin D2, 6-ketoprostaglandin F1 alpha, and thromboxane B2, and lipoxygenase metabolites such as 8(S)- and 12(S)-hydroxyeicosatetraenoic acids were significantly reduced in colonic mucosa and tumors of animals fed 320 ppm sulindac.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemoprevention

Chemoprevention has been shown to be an extremely promising approach to the prevention of invasive cancer. Through the identification of chemopreventive agents that inhibit or reverse the process of carcinogenesis, new strategies of early intervention can be developed for patients at high risk that potentially prevent the onset of invasive and metastatic phases of cancer. This articles reviews the present efforts in chemoprevention research, including the identification of promising agents, screening, and preclinical and clinical evaluations.

New directions in dietary studies in cancer: the National Cancer Institute

Through an orderly sequence incorporating epidemiologic and laboratory research, human clinical/metabolic studies, and clinical intervention trials, the NCI develops and maintains cancer prevention and control programs that are directed toward the overall goal to reduce cancer incidence, morbidity, and mortality. Epidemiologic studies have shown correlations between consumption of numerous dietary constituents and cancer risk. Results of in vitro and animal studies have reinforced many of these epidemiologic associations and data from clinical/metabolic studies are being used to evaluate the relevance of these associations in humans. Although much remains to be learned about the influence of specific dietary constituents and dietary patterns on cancer risk, it is clear that diet can have a significant impact in cancer prevention and control. Investigations on the cellular and molecular effects of dietary constituents, as well as their metabolic and physiologic effects should provide better insight on the mechanisms of action of these dietary constituents. There also is a need to develop biomarkers of dietary intake that could be used to monitor compliance in intervention studies, as well as biomarkers as clinical trial endpoints that can be used to predict the emergence and progression of cancer. Working with other agencies and the private sector, the NCI will continue to design and implement information programs that translate the knowledge gained from these diet and cancer prevention studies to help Americans adopt dietary patterns that may reduce cancer risk. Continued emphasis will be placed on intervention programs targeted toward high-risk and underserved segments of the U.S. population in an effort to reduce the high incidence of cancers in these groups.

Modulation of azoxymethane-induced mutational activation of ras protooncogenes by chemopreventive agents in colon carcinogenesis

In our previous study, we demonstrated that azoxymethane (AOM) treatment significantly enhanced the expression of ras p21, the protein product of ras genes, and that the dietary administration of chemopreventive agents such as D,L-alpha-difluoromethylornithine (DFMO), a irreversible inhibitor of ornithine decarboxylase, and piroxicam, a non-steroidal anti-inflammatory drug (NSAID), exerted a significant inhibitory effect on AOM-induced ras p21 expression. In the present study, which is an extension of our earlier investigation, we have determined the effect of DFMO and piroxicam on mutational activation of ras protooncogenes during AOM-induced colon carcinogenesis. Groups of male F344 rats were fed the modified AIN-76A diet containing 0 or 150 p.p.m. piroxicam, or 4000 p.p.m. DFMO and administered s.c. AOM dissolved in normal saline at a dose rate of 15 mg/kg body wt, once weekly, for 4 weeks. Vehicle control groups received s.c. equal volumes of normal saline. Groups of animals were then killed at 0, 4, 16, 24 or 32 weeks after last AOM or saline injection. AOM-induced colon tumors and colonic mucosa from AOM treated as well as saline treated animals were analyzed for point mutations in K- and H-ras protooncogenes by a combination of polymerase chain reaction mediated restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing. Our results demonstrate that of the total 65 AOM-induced colon tumors analyzed, 45/50 (90%) obtained from AOM-treated animals fed the control diet, 4/11 (36%) from AOM-treated animals fed piroxicam diet, and 1/4 (25%) from AOM-treated animals fed the DFMO diet, contained single-point mutations occurring specifically at the second nucleotide of codon 12 which were identified exclusively as G to A transitions in case of K-ras, and G to A transitions and also G to T transversions in H-ras. Similar point mutations were identified in colonic mucosa of 21/30 (70%) of AOM-treated animals fed the control diet, 10/30 (33%) of AOM-treated animals fed piroxicam diet, and none of 30 (0%) of AOM-treated animals fed DFMO diet. These results indicate that the administration of piroxicam and DFMO may inhibit the selective amplification of AOM-induced initiated cells carrying mutated ras genes. Dietary DFMO exerted more pronounced inhibition of selective amplification of initiated cells containing AOM-induced mutant ras. Data suggest that determination of ras activation may be a useful marker for chemoprevention of colon cancer.

Inhibitory effect of aspirin on azoxymethane-induced colon carcinogenesis in F344 rats

Epidemiologic studies suggest that sustained use of aspirin may reduce the risk of development of and mortality due to colon cancer. Previous preclinical studies have shown that several non-steroidal anti-inflammatory drugs act as potential chemopreventive agents in experimentally induced colon cancer models. The present study was designed to investigate the chemopreventive effect of 40 and 80% maximum tolerated dose (MTD) levels of aspirin administered in the diet on azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. The MTD of aspirin as determined in male F344 rats was 500 p.p.m. Beginning at 5 weeks of age, all animals were randomly divided into various experimental groups (48 rats/group) and fed one of the semipurified diets containing 0, 200 p.p.m. (40% MTD), or 400 ppm (80% MTD) of aspirin. Two weeks later, all animals (36 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM at a dose level of 15 mg/kg body wt, once weekly for 2 weeks. All animals were continued on their respective dietary regimen for additional 52 weeks and necropsied. Histopathologic evaluation of colon tumors was performed by routine procedures. Basal levels and ex vivo production of colonic mucosal and tumor prostaglandin E2 (PGE2) were measured in all groups. The results indicate that daily oral administration of 200 and 400 p.p.m. aspirin significantly inhibited the incidence (% animals with tumors) and multiplicity (tumors/animal) of invasive adenocarcinomas of the colon as well as the size of adenocarcinomas. Colonic mucosal and tumor PGE2 levels (basal and ex vivo production) were significantly reduced in animals administered 200 and 400 p.p.m. aspirin. The results of this study support the epidemiologic evidence that ingestion of aspirin inhibits colon carcinogenesis. Although the precise mechanisms of aspirin-induced colon tumor inhibition remain to be determined, it is likely that the effect may be mediated through the modulation of prostaglandin synthesis.

Chemoprevention of colon carcinogenesis by organosulfur compounds

It has been reported that several naturally occurring and related synthetic organosulfur compounds exert chemopreventive effects in several target organs in rodent models. The chemopreventive actions of 40 and 80% maximum tolerated doses (MTD) of organosulfur compounds, namely anethole trithione, diallyl disulfide, N-acetylcysteine, and taurine, administered in AIN-76A diet, on azoxymethane (AOM)-induced neoplasia were investigated in male F344 rats. Also, the effects of these agents on the activities of phase II enzymes, namely glutathione S-transferase (GST), NAD(P)H-dependent quinone reductase, and UDP-glucuronosyl transferase, in the liver and colonic mucosa and tumors were assessed. The MTD levels of anethole trithione, diallyl disulfide, N-acetylcysteine, and taurine were determined in male F344 rats and found to be 250, 250, 1500, and 1500 ppm, respectively. At 5 weeks of age, animals were fed the control diet (AIN-76A) or experimental diets containing 40 or 80% MTD levels of each test agent. All animals in each group, except those allotted for vehicle (saline) treatment, were administered AOM s.c. at a dose rate of 15 mg/kg body weight once weekly for 2 weeks. All animals were necropsied during week 52 after the second AOM injection. Colonic mucosal and tumor and liver enzyme activities were measured in animals fed 80% MTD levels of each test agent. Colon tumors were subjected to histopathological evaluation and classified as invasive or noninvasive adenocarcinomas. Colon tumor incidence (percentage of animals with tumors) and tumor multiplicity (tumors/animal) were compared among various dietary groups. The results indicated that administration of 200 ppm (80% MTD) anethole trithione significantly inhibited the incidence and multiplicity of both invasive and noninvasive adenocarcinomas, whereas feeding of 100 ppm (40% MTD) anethole trithione or 100 (40% MTD) or 200 ppm (80% MTD) diallyl disulfide suppressed only invasive adenocarcinomas of the colon. Although diets containing N-acetylcysteine and taurine inhibited colon tumor multiplicity, the effect was somewhat marginal. GST, NAD-(P)H-dependent quinone reductase, and UDP-glucuronosyl transferase activities in colonic mucosa and tumor and liver were significantly elevated in animals fed anethole trithione or diallyl disulfide, compared to those fed the control diet. N-Acetylcysteine and taurine slightly but significantly increased only the GST activity in the liver. Although other mechanisms are not excluded, inhibition of AOM-induced colon carcinogenesis by anethole trithione and diallyl disulfide may be associated, in part, with increased activities of phase II enzymes such as GST, NAD(P)H-dependent quinone reductase, and UDP-glucuronosyl transferase in the liver and colon.

Intermediate biomarkers of colon cancer: modulation of expression of ras oncogene by chemopreventive agents during azoxymethane induced colon carcinogenesis

In our attempts to evaluate the influence of chemopreventive agents on intermediate biomarkers of colon cancer, we have investigated the effect of D,L-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase and piroxicam, a non-steroidal anti-inflammatory drug (NSAID) on the expression levels of biochemically active p21ras, the protein product of cellular ras protooncogenes during the development of azoxymethane (AOM) induced colon carcinogenesis in male F344 rats in order to explore the plausibility of using p21ras as an intermediate biochemical marker of colon cancer. Groups of male F344 rats were fed the modified AIN-76A diets containing 0 or 150 p.p.m. piroxicam or 4000 p.p.m. DFMO and administered s.c. AOM dissolved in normal saline at a dose of 15 mg/kg body wt/week, once weekly, for 4 weeks. Vehicle control groups received s.c. equal vol of normal saline. Groups of animals were then killed at 0, 4, 16, 24 and 32 weeks after the last injection of AOM or saline and their colonic mucosa and tumors analyzed for biochemically active p21ras levels. AOM treatment significantly increased the expression of biochemically active p21ras. The AOM-induced expression of biochemically active p21ras was significantly suppressed by dietary DFMO and piroxicam. DFMO exerted a more pronounced inhibitory effect on AOM-induced colon tumor development as well as the expression of biochemically active p21ras. These results indicate that the determination of biochemically active p21ras may be effectively used in clinical chemoprevention trials as an intermediate end-point to monitor the colon carcinogenesis.

Effect of chemopreventive agents on intermediate biomarkers during different stages of azoxymethane-induced colon carcinogenesis

Chemoprevention of colon cancer is emerging as an alternative to therapy with a broad potential for reducing cancer incidence in defined high-risk groups and the general population. Besides several chemopreventive agents in use and under investigation, D,L-alpha-difluoromethylornithine (DFMO) and piroxicam have been shown to effectively inhibit colon carcinogenesis in rodents. A variety of proliferation-related parameters have been suggested as potential intermediate markers of cancer risk that could be used to monitor the progress of chemoprevention in clinical trials. We have investigated the effect of chemopreventive agents, DFMO, and piroxicam on mucosal ornithine decarboxylase (ODC) and tyrosine-specific protein kinase (TPK) activities during different stages of azoxymethane (AOM)-induced colonic carcinogenesis in male F344 rats in order to examine the plausibility of using these enzymes as intermediate biochemical markers of colon cancer. Groups of male F344 rats were fed modified AIN-76A diets containing 0 or 150 ppm piroxicam or 4000 ppm DFMO and given s.c. injections of AOM dissolved in normal saline at a dose of 15 mg/kg body weight/week, once weekly, for 4 weeks. Vehicle control groups received s.c. equal volumes of normal saline. Groups of animals were then sacrificed at 0, 4, 16, 24, and 32 weeks after AOM or saline treatment, and their colonic mucosa was analyzed for ODC and TPK activities. AOM treatment significantly increased mucosal ODC as well as TPK activities. AOM-induced ODC and TPK activities were significantly suppressed by dietary DFMO progressively at all stages of colon carcinogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of colon carcinogenesis by prostaglandin synthesis inhibitors and related compounds

The inhibitory effect of 40 and 80% maximum tolerated dose (MTD) levels of piroxicam, ibuprofen, ketoprofen and glycyrrhetinic acid on colon carcinogenesis was investigated in male F344 rats. The MTD levels of piroxicam, ibuprofen, ketoprofen and glycyrrhetinic acid as determined in male F344 rats were 500, 500, 250 and 3000 p.p.m. respectively. At 5 weeks of age, groups of male F344 rats were fed the control (AIN-76A) diet and 40 and 80% MTD levels of each test agent in AIN-76A diet. At 7 weeks of age, all animals except the vehicle (saline)-treated controls received azoxymethane (AOM) at a dose rate of 15 mg/kg body wt, once weekly for 2 weeks. All animals were necropsied 50 weeks after the second AOM injection and colon tumor incidences were compared among the groups fed the control diet and chemopreventive agents. Animals fed 400 (80% MTD) and 200 p.p.m. (40% MTD) of piroxicam, 400 p.p.m. (80% MTD) of ibuprofen and 200 p.p.m. (80% MTD) of ketoprofen showed a significant inhibition of colon tumorigenesis as compared to those fed the control diet. Results analyzed by the linear regression method suggested a dose-dependent inhibition of colon carcinogenesis with increasing levels of piroxicam or ibuprofen. In contrast, glycyrrhetinic acid had no measurable chemopreventive effect on colon carcinogenesis.

Effect of the chemopreventive agents piroxicam and D,L-alpha-difluoromethylornithine on intermediate biomarkers of colon carcinogenesis

Our previous studies have shown that dietary piroxicam, a non-steroidal anti-inflammatory drug (NSAID), and D,L-alpha-difluoromethylornithine (DFMO), an ornithine decarboxylase (ODC) inhibitor, act as potential chemopreventive agents in inhibiting azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. The present study was designed to determine the effect of these chemopreventive agents on intermediate biomarkers, namely colonic epithelial cell proliferation and levels of prostaglandins, which can be used as effective predictors of colon cancer. Starting at 6 weeks of age, groups of animals were fed the control diet and experimental diets containing piroxicam or DFMO. At 7 weeks of age, all animals, except the vehicle controls, were injected s.c. with AOM at a dose level of 15 mg/kg body wt/week for 4 weeks. Vehicle controls received an equal volume of normal saline. Groups of animals were then killed at the end of last AOM or saline injection (baseline) and at week 4, 16, 24 and 32 following the last AOM or saline treatment. Animals intended for cell proliferation study were injected with bromodeoxyuridine (BrdU) at a dose level of 20 mg/kg body wt 1 h prior to being killed. The rate of colonic cell proliferation at all time points was assessed immunohistochemically using anti-BrdU. The levels of colonic mucosal prostaglandins were estimated by radioimmunoassay. The results indicate that carcinogen treatment increased the colonic cell proliferation measured as the crypt labeling index in proximal and distal colons and the concentrations of colonic prostaglandin E2 (PGE2) and 6-keto PGF1 alpha. The data demonstrate that DFMO significantly inhibited the AOM-induced labeling index in the distal and proximal colon at all time points, whereas piroxicam slightly decreased the labeling index. On the other hand, piroxicam exerted a pronounced inhibitory effect on the levels of both PGE2 and 6-keto PGF1 alpha. DFMO suppressed the colonic PGE2 levels to a lesser degree than piroxicam. The results demonstrate that DFMO, an inhibitor of ODC, suppresses cell proliferation, whereas piroxicam, a NSAID, inhibits prostaglandins, and emphasize the need to develop agent-dependent intermediate biomarker(s) to validate the efficacy of chemopreventive agent(s) in colon carcinogenesis.

Chemoprevention of colon carcinogenesis by dietary administration of piroxicam, alpha-difluoromethylornithine, 16 alpha-fluoro-5-androsten-17-one, and ellagic acid individually and in combination

The chemopreventive action of 40 and 80% maximum tolerated dose (MTD) levels of piroxicam, D,L-alpha-difluoromethylornithine (DMFO), 16 alpha-fluoro-5-androsten-17-one (DHEA analogue 8354), and ellagic acid (EA) administered in diet individually and in combination before and during initiation and postinitiation phases of azoxymethane-induced neoplasia of the intestine was studied in male F344 rats. The MTD levels of piroxicam, DFMO, DHEA analogue, and EA were determined in male F344 rats and found to be 500, 5,000, 500, and 10,000 ppm, respectively, in modified AIN-76A diet. When these agents were fed in combination, the MTD levels were: piroxicam plus DFMO, 250 and 2500 ppm; piroxicam plus DHEA analogue, 250 and 250 ppm; piroxicam plus EA, 250 and 5000 ppm; piroxicam plus DFMO plus DHEA analogue, 250, 2500, and 250 ppm; and piroxicam plus DFMO plus EA, 250, 2500, and 5000 ppm. From these MTD values, 40 and 80% MTD levels were calculated and tested for their efficacy. At 5 weeks of age, animals were fed the modified AIN-76A (control) diet and experimental diets containing 40 and 80% MTD levels of piroxicam, DFMO, DHEA analogue, and EA individually and in combination. At 7 weeks of age, all animals except the vehicle-treated groups were administrated s.c. injections of azoxymethane (15 mg/kg body weight/week for 2 weeks). Animals intended for vehicle treatment received s.c. injections of an equal volume of normal saline. Fifty-two weeks after azoxymethane and saline treatment all the animals were necropsied, and colon and small intestinal tumor incidence (percentage of animals with tumors) and multiplicity (tumors/animal) were compared among various dietary groups. The results indicate that 40 and 80% MTD levels of dietary piroxicam and DFMO significantly (P less than 0.001) inhibited colon and small intestinal tumor incidence and multiplicity. DHEA analogue at 40% MTD level significantly decreased the small intestinal and colon tumor incidences (P less than 0.05), whereas 80% MTD of DHEA analogue inhibited only small intestinal tumor incidence. EA at 40 and 80% MTDs had no significant effect on colon tumor incidence (P greater than 0.05), but 80% MTD of EA showed a significant inhibitory effect on the incidence of small intestinal adenocarcinomas (P less than 0.01). In the combination study, 40 and 80% MTD levels of piroxicam plus DFMO significantly (P less than 0.001) inhibited colon adenocarcinoma incidence (8.3%) and multiplicity (0.08 +/- 0.04) (SE) when compared to colon adenocarcinoma incidence (72.2%) and multiplicity (1.14 +/- 0.18) in control diet-fed animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition by dietary oltipraz of experimental intestinal carcinogenesis induced by azoxymethane in male F344 rats

Epidemiological studies suggest that consumption of cruciferous vegetables rich in dithiolethiones is associated with a reduction in the incidence of cancer in man. The effect of two dose levels of dietary oltipraz [5-(2-pyrazinyl)-4-methyl-1, 2- dithiole-3-thione], a substituted dithiolethione, on azoxymethane (AOM)-induced intestinal carcinogenesis and on serum levels was studied in male F344 rats. The maximum tolerated dose (MTD) of oltipraz was determined in male F344 rats and found to be 500 p.p.m. Oltipraz at levels of 200 p.p.m. (40% MTD) and 400 p.p.m. (80% MTD) diet was tested as inhibitor of intestinal carcinogenesis. At 5 weeks of age, animals were fed the modified AIN-76A (control) diet and experimental diets containing oltipraz. At 7 weeks of age, all animals except the vehicle-treated animals were administered s.c. injection of AOM (15 mg/kg body wt/week for 2 weeks). Animals intended for vehicle treatment were administered s.c. with an equal volume of normal saline. Fifty-two weeks later, all animals were killed and colon and small intestinal tumor incidences and multiplicity were compared among the dietary groups. The results indicate that feeding of 200 and 400 p.p.m. of oltipraz significantly inhibited the incidence of adenocarcinomas in colon and small intestine and multiplicity of colon adenomas and small intestinal adenocarcinomas. Animals fed 400 p.p.m. oltipraz showed increased levels of oltipraz in the serum as compared to those fed 200 p.p.m. oltipraz. The results of this study indicate that dietary oltipraz inhibits intestinal carcinogenesis.

Chemoprevention of colon carcinogenesis by concurrent administration of piroxicam, a nonsteroidal antiinflammatory drug with D,L-alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor, in diet

The effect of three levels of piroxicam and three levels of D,L-alpha-difluoromethylornithine (DFMO) fed individually and in combination during the postinitiation phase of carcinogenesis was studied in male F344 rats to generate a data base on the efficacy and synergistic and additive effects of these compounds as inhibitors of colon carcinogenesis. The maximum tolerated dose of DFMO was determined in male F344 rats and found to be 5000 ppm in the AIN-76A diet. Piroxicam at levels of 25, 75, and 150 ppm and DFMO at concentrations of 400, 1000, and 4000 ppm (20, 50, and 80% maximum tolerated dose) in AIN-76 diet were tested individually and in combinations. At 7 weeks of age, while the rats were consuming the control diet (AIN-76A), all animals except the vehicle (saline)-treated controls were given a single s.c. injection of azoxymethane (CAS: 25843-45-2) at a dose level of 29.6 mg/kg body weight to induce intestinal tumors. One week after azoxymethane injection, animals were transferred to their respective experimental diets containing piroxicam and DFMO. Fifty-six weeks after azoxymethane injection, all animals were necropsied and colon and small intestinal tumor incidences and multiplicity were compared among the various dietary groups. Feeding of diets containing 75 and 150 ppm piroxicam or 1000 and 4000 ppm DFMO significantly inhibited the incidence (percentage of animals with tumors) of colon adenocarcinomas compared to that of control diet. The multiplicity (number of tumors/rat) of adenocarcinomas was significantly inhibited in animals fed the 25, 75, and 150 ppm piroxicam or 400, 1000, and 4000 ppm DFMO diets. Results analyzed by the linear regression method suggested a dose-dependent inhibition in colon adenocarcinoma incidence with increasing levels of piroxicam or DFMO. The incidence and multiplicity of colon adenocarcinomas were significantly inhibited in animals fed the diets containing combinations of 25, 75, and 150 ppm piroxicam and 400, 1000, and 4000 ppm DFMO. Piroxicam and DFMO administered together had a stronger inhibitory effect than did those given individually. Piroxicam and DFMO when administered individually had no significant inhibitory effect on colon adenoma incidence and multiplicity; in contrast, combinations of these compounds significantly inhibited colon adenomas. No consistent differences were found in the incidence and multiplicity of small intestinal tumors among the dietary groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose-related inhibition of colon carcinogenesis by dietary piroxicam, a nonsteroidal antiinflammatory drug, during different stages of rat colon tumor development

The effect of four dose levels of piroxicam administered during different stages of colon tumor development was studied in male F344 rats to obtain a data base on the efficacy of piroxicam as an inhibitor of colon carcinogenesis. Piroxicam was added at levels of 25, 50, 75, and 150 ppm to the NIH-07 open-formula diet and fed to male F344 rats starting 1, 13, and 23 wk after the carcinogen administration. At 7 wk of age, while the animals were consuming the control diet, all animals except the vehicle-treated controls were given s.c. injection of azoxymethane (CAS:25843-45-2; 29.6 mg/kg body weight, once) to induce intestinal tumors. Forty wk after AOM injection, all animals were necropsied, and tumor incidences were compared among the various dietary groups. Colon tumor incidence (percentage of animals with tumors) was inhibited in a dose-dependent manner in rats fed the diets containing 25, 50, 75, and 150 ppm piroxicam starting 1 and 13 wk after carcinogen treatment. The colon tumor incidences in animals fed the diets containing 0, 25, 50, 75, and 150 ppm of piroxicam starting at 1 wk after carcinogen treatment were 89, 61, 58, 50, and 39%, respectively. When the diets containing 0, 25, 50, 75, and 150 ppm were fed 13 wk after carcinogen treatment, the colon tumor incidences were 89, 69, 69, 44, and 33%, respectively. Colon tumor multiplicity (tumors/animal; tumors/tumor-bearing animal) was also significantly inhibited in animals fed the diets containing 25 to 150 ppm piroxicam starting 1 and 13 wk after carcinogen administration. The number of colon tumors/animal was inhibited by about 80 to 84% in animals fed the 150 ppm piroxicam diet. When the diets containing different levels of piroxicam were fed 23 wk after carcinogen treatment, the colon tumor incidence was significantly inhibited in animals fed the 75 and 150 ppm piroxicam diets. The colon tumor incidences in animals fed the diets containing 0, 25, 50, 75, and 150 ppm were 89, 78, 67, 64, and 64%, respectively. The colon tumor multiplicity (colon tumors/animal) was slightly but significantly inhibited in animals fed the diets containing 25 to 150 ppm piroxicam. The results of this study demonstrate that increasing levels of piroxicam in the diet, when fed 1 or 13 wk after carcinogen insult, inhibit colon tumor incidence in a dose-dependent manner.