PubMed Health⌕ Search

Biomedical subjects

M A Shibata

Publications and source records attributed to M A Shibata.

At least 19 recordsLinked to original sources
PubMed1998

Development and characterization of a mouse prostate adenocarcinoma cell line: ductal formation determined by extracellular matrix.

BACKGROUND: Tumor vaccines show promise as a new approach for treating cancer. We have developed a murine prostate cancer cell line which can be used to study growth factor and extracellular matrix regulation of prostate differentiation and will be useful for generating tumor vaccines using the C3(1)/TAG transgenic model of prostate cancer. METHODS: Pr-14 cells were established in defined growth media (GM) and grown in GM, GM + 2% fetal bovine serum (FBS) or DMEM + 10% FBS on plastic, collagen, or Matrigel. Immunofluorescence and Western blot analyses were performed using antibodies to cytokeratin, vimentin, SV40 large T-antigen, and androgen receptor (AR). RESULTS: Pr-14 cells are cytokeratin-positive, vimentin-negative, and express SV40 large T-antigen. These cells are tumorigenic when injected into athymic nude mice and appear to be androgen-independent. Pr-14 cell lines are nontumorigenic when injected into syngeneic FVB/N mice, but form tumors in transgenic TAG-expressing FVB/N mice. Cell growth and morphology are dependent on media composition which determines whether ductal or acinar structures form when grown on Matrigel. CONCLUSIONS: The mouse prostate adenocarcinoma cell line, Pr-14, undergoes alterations in the state of differentiation dependent upon serum concentration when grown on Matrigel. The Pr-14 cell line is a useful reagent to study prostate cell/extracellular matrix interactions, and for immunotherapy and cancer vaccine studies in C3(1)/TAG transgenic mice.

3T3 Cells↗
PubMed1998

Altered expression of transforming growth factor betas during urethral and bulbourethral gland tumor progression in transgenic mice carrying the androgen-responsive C3(1) 5' flanking region fused to SV40 large T antigen.

We demonstrate that targeted expression of SV40 large T antigen (TAg) to the urethral (periurethral) and bulbourethral gland epithelium leads to adenocarcinoma formation in these tissues after 7 months of age, which are extremely rare sites for spontaneous tumor formation in humans. The development of proliferative lesions in the urethral gland predictably follows a temporal course of progression with approximately one third of male animals developing urethral tumors by 1 year of age. Tumor progression in these organs correlates to the level of TAg and p53 expression. Immunoprecipitation confirmed that SV40 TAg protein was bound to p53 and Rb p110 in vivo. Expression of transforming growth factor beta (TGFbetas) was evaluated during tumor progression of urethral gland carcinomas. Elevations of intracellular and extracellular TGFbeta1 and extracellular TGFbeta3 were found in preneoplastic and neoplastic lesions, suggesting that increased TGFbetas may augment tumor growth. c-Met expression showed a tendency for increased expression in the urethral gland carcinomas. We speculate that the directed expression of SV40 TAg by the hormone responsive C3(1) gene and subsequent tumor formation in these organs is influenced by androgens, since these tissues and carcinomas express androgen receptor (AR) and arise only in male transgenic mice. Several cell lines established from the urethral carcinomas were also shown to express AR, but are not androgen dependent in culture. To our knowledge, this is the first transgenic animal model for urethral and bulbourethral carcinomas. This transgenic mouse model and the cell lines derived from it may provide a unique opportunity for dissecting molecular mechanisms involved in the tumorigenesis of these organs which otherwise rarely develop cancer.

Aging↗
PubMed1998

Genetic alterations in the development of mammary and prostate cancer in the C3(1)/Tag transgenic mouse model.

We have generated a transgenic mouse model in which female mice develop ductal mammary adenocarcinomas and male mice develop prostatic adenocarcinomas by using a transgene containing the hormone-responsive rat prostatic steroid binding protein 5' flanking region C3(1) fused to the simian virus 40 (SV40) large T antigen. We have identified some genetic alterations during mammary and prostate tumor progression: (i) p53 is functionally inactivated during mammary cancer development without p53 mutations; (ii) Alterations in apoptosis during mammary tumor progression are p53 and bcl-2 independent; (iii) Ha-ras mutations occur early in the development of prostate cancer. This unique animal model offers the opportunity to study multistep tumorigenesis in these organs.

Adenocarcinoma↗
PubMed1997

Lack of involvement of p53 gene mutations in N-methyl-N-nitrosourea-induced bladder tumor progression in N-butyl-N-(4-hydroxybutyl)nitrosamine-treated rats and no suppression by indomethacin.

The relevance of p53 mutations to rat bladder cancer progression induced by a single injection of N-methyl-N-nitrosourea (MNU) and the chemopreventive effects of indomethacin (IM) were investigated in male F344 rats, initially given N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) at a dose of 500 ppm in the drinking water for 10 weeks. The animals were subsequently treated with a single intraperitoneal injection of MNU at a dose of 50 mg/kg b.w. at week 20. A subgroup was then given IM dissolved in the drinking water at a concentration of 20 ppm for 20 weeks. The experiment was terminated at week 40 when transitional cell carcinomas (TCC) were observed in all animals given BBN, regardless of the administration of MNU and/or IM (incidences ranged from 80 to 100%). The extent of invasion was significantly greater with the additional MNU treatment but no inhibitory effects of IM were noted. A low frequency of p53 mutations was detected without relation to the extent of tumor invasion. Thus, only two mutations were found, one in a Ta and the other in a T1 carcinoma. The present study thus demonstrated that p53 mutations are not involved in MNU-induced progression in rat urinary bladder cancers, suggesting that they are not critical for malignancy.

Animals↗
PubMed1997

Enhanced sensitivity to tumor growth and development in multistage skin carcinogenesis by transforming growth factor-alpha-induced epidermal growth factor receptor activation but not p53 inactivation.

Transforming growth factor-alpha (TGF alpha) can stimulate keratinocyte proliferation and function as an autocrine tumor promoter in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated TGF alpha-transgenic mouse skin. In this study, we examined the effect of ectopic TGF alpha transgene expression on skin tumor growth and progression after DMBA initiation in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA). Both the multiplicity and size of skin tumors arising in TGF alpha-transgenic mice were significantly higher than those of the nontransgenic parental CD-1 strain. There were more dysplastic papillomas and squamous cell carcinomas (SCCs) in the transgenic animals as well. ProTGF alpha protein was expressed in transgenic papillomas, but mature TGF alpha was not detected. The epidermal growth factor receptor (EGFR) appeared to be downregulated and was associated with enhanced tyrosine phosphorylation of several substrates in TGF alpha-transgenic mouse tumors. Characteristic codon 61 mutations in the Ha-ras gene were found in most of the papillomas and SCCs induced by DMBA and TPA in transgenic as well as nontransgenic mice. However, no p53 gene mutations were found in any skin tumors from either transgenic or control animals. Analysis of cellular proliferation in both DMBA-TPA-induced papillomas and in skin 48 h after TPA treatment alone revealed significantly more DNA synthesis in TGF alpha-transgenic mice relative to controls. These results demonstrate that TGF alpha, through EGFR overstimulation, can act synergistically with TPA to induce the formation, growth, and development of DMBA-initiated skin tumors containing classic Ha-ras gene mutations but not p53 gene inactivation.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

Reduced p53 dosage associated with mammary tumor metastases in C3(1)/TAG transgenic mice.

Transgenic mice expressing the simian virus 40 large T-antigen (TAG) under the regulatory control of the rat prostatic steroid binding protein C3(1) gene develop mammary carcinomas (in females) and prostate carcinomas (in males). The development of carcinomas occurs several months after the appearance of dysplastic lesions, suggesting that TAG is necessary but insufficient for tumor formation and that other genetic events are involved in this process. TAG is known to bind to p53 and to result in its functional inactivation, which is believed to be a critical step in TAG-induced transformation. We investigated whether the TAG-p53 interaction is rate limiting in the development of phenotypic changes in these transgenic mice by crossing C3(1)/TAG transgenics with mice carrying null mutations of the p53 gene. TAG-expressing animals with a p53+/- genotype developed much more aggressive mammary tumors, as evidenced by increased numbers and size of metastases, than did TAG-expressing animals carrying two wild-type p53 alleles. While p53 was expressed in primary tumors, p53 expression appeared to be reduced or lost in many metastases in mice carrying either the p53+/+ or p53+/- genotypes. The tumorigenic process did not appear to be due to the loss of the second wild-type p53 allele or the gain of dominant oncogenic mutations in p53, as no mutations were detected in either primary or metastatic tumors by polymerase chain reaction--single-strand conformation polymorphism analyses. These findings suggest that despite the presence of TAG, p53 levels influence the characteristics of the late stages of mammary tumor growth and accelerate metastases. Functional loss of p53 and not p53 mutations participates in TAG-induced mammary carcinoma development and progression.

Adenocarcinoma↗
PubMed1997

Decrease of prostaglandin E2 and 5-bromo-2'-deoxyuridine labeling but not prostate tumor development by indomethacin treatment of rats given 3,2'-dimethyl-4-aminobiphenyl and testosterone propionate.

The modifying effects of indomethacin (IM) on rat prostate carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) were investigated. F344 rats were given 50 mg/kg body weight of DMAB at 2-week intervals for 20 weeks and then received IM at a dose of 20 ppm in the drinking water for 37 weeks. Separate groups additionally received testosterone propionate (TP) in Silastic tubes throughout the experiment. DMAB alone induced carcinomas in situ in the ventral lobe and in combination with TP caused invasive carcinomas of the dorso-lateral and anterior lobes and seminal vesicles. No clear suppression by IM of development of in situ carcinomas or invasive carcinomas was observed. In a short-term satellite experiment, it was revealed that prostaglandin E2 (PGE2) levels in the dorso-lateral prostate and seminal vesicles, but not the ventral prostate, were significantly reduced by IM and that TP itself also suppressed PGE2 levels. The 5-bromo-2'-deoxyuridine labeling index in the ventral prostate was significantly decreased by IM administration. These results indicate that while IM can efficiently suppress tissue PGE2 levels, it does not inhibit tumor development in the prostate or seminal vesicles of rats in the present model.

Aminobiphenyl Compounds↗
PubMed1996

Progression of prostatic intraepithelial neoplasia to invasive carcinoma in C3(1)/SV40 large T antigen transgenic mice: histopathological and molecular biological alterations.

The progression of prostatic intraepithelial neoplasia (PIN) to invasive prostate carcinoma has been analyzed in the C3(1)/T(AG) transgenic mouse model and appears very similar to the process proposed to occur in humans. PIN lesions in these transgenic mice histologically resemble those found in human PIN. Low-grade PIN was observed in the ventral and dorsolateral lobes at 2 months of age, whereas high-grade PIN was found in both lobes by 5 months of age. A progressive increase in the number of PIN lesions was observed with age. Prostate carcinomas, which appeared to arise from PIN lesions, were found by 7 months of age in the ventral lobe and 11 months of age in the dorsolateral lobe. Expression of T(AG) mRNA and protein in these lesions correlated with the development of PIN and carcinomas, as did the overexpression of p53 protein. Apoptosis levels were quite low in normal epithelial cells, moderate in low-grade PIN, and high in high-grade PIN and carcinomas. Levels of expression of proliferating cell nuclear antigen correlated with the degree of severity of the prostate lesions. Eighteen % of PIN lesions were found to already harbor Ha-ras mutations, whereas 33% of carcinomas showed various mutations in Ha-ras, Ki-ras, and/or p53. Mutations in Ha-ras may, therefore, be an early event in a significant portion of PIN lesions. Because high-grade PIN showed many characteristics similar to those observed in carcinomas and high-grade PIN was often found contiguous to carcinomas, we conclude that high-grade PIN is a precursor lesion of prostate carcinoma in this transgenic model. These transgenic mice will be useful to study mechanisms responsible for the progression of invasive carcinomas from PIN precursor lesions, as may occur during the development of prostate cancer in humans.

Animals↗
PubMed1996

Lack of tumor promoting effects of KCB-1, a recombinant human basic fibroblast growth factor, on two-stage skin carcinogenesis in female CD-1 (ICR) mice.

Skin tumor promoting and co-promoting potentials of KCB-1, a recombinant human basic fibroblast growth factor, were investigated in a two-stage skin carcinogenesis model using female ICR mice. Animals were allocated to either normal (non-injured) or injured skin groups, and given a single topical application of dimethylbenz[alpha]anthracene (DMBA) at 100 micrograms/mouse to fur-clipped back skin. One week after the DMBA initiation step, mice were injected with KCB-1 (0.4, 4.0 and 40 micrograms/mouse, s.c.) and/or 12-O-tetradecanoylphorbol-13-acetate (TPA) at 4.0 micrograms/mouse twice a week until the termination at week 20. The treatment with KCB-1 was not associated with any increases of papillomas and hyperplasias in either the normal or the wounded skin cases. High incidences and multiplicities of skin papillomas and hyperplasias developed in TPA-treated groups. The positive control TPA promotion was not influenced by the KCB-1 treatment in the present initiation/promotion protocol. Thus, KCB-1 exerted no tumor promoting effects on mouse skin two-stage carcinogenesis, and also no amplification activity for the established skin tumor promoter TPA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1996

p53-independent apoptosis during mammary tumor progression in C3(1)/SV40 large T antigen transgenic mice: suppression of apoptosis during the transition from preneoplasia to carcinoma.

Alterations in apoptosis and associated mechanisms during mammary tumor progression were investigated in transgenic mice expressing the SV40 large T antigen (T(AG)) driven by the rat prostatic steroid-binding protein C3(1) 5'-flanking region. Apoptosis levels, assessed by in situ end labeling, were low in normal mammary epithelial cells, highest in atypical hyperplasias (preneoplastic lesions), and less pronounced in adenocarcinomas. Preneoplastic cells maintain the ability to undergo apoptosis as a mechanism of tumor growth suppression, but this critical control of apoptosis is lost as these lesions progress to carcinomas. These alterations in apoptosis occur during mammary tumor progression in mice containing wild-type p53+/+ genotype as well as in mice with the p53-/- genotype. Thus, apoptosis in this tumor model occurs through a p53-independent mechanism. Because other studies have demonstrated p53-dependent apoptosis in T(AG)-induced choroid plexus tumors of transgenic mice, we propose that the role of p53 in apoptosis may be tissue-specific. In addition, bcl-2 protein was not expressed in any mammary lesions. SV40 T(AG) expression, which correlated with the nuclear p53 protein at all stages of tumor progression, was low in normal mammary epithelial cells, moderately high in atypical hyperplasias, and strongly expressed in adenocarcinomas. No p53 mutations were found at any stage of mammary adenocarcinoma development, suggesting that tumor progression does not require a dominantly acting p53 mutation in this transgenic model. p2l(Waf1/Cip1), a cyclin-dependent kinase inhibitor, was expressed in normal mammary tissue but was not detected in the mammary carcinomas, despite high nuclear accumulation of wild-type p53 protein, suggesting functional loss of p53 due to binding of SV40 T(AG), to p53. These findings suggest that suppression of apoptosis during the transition from atypical hyperplasia to adenocarcinoma appears to be a critical event for mammary cancer development in C3(1)/T(AG) transgenic mice and occurs by p53- and bcl-2-independent pathways.

Androgen-Binding Protein↗
PubMed1996

Non-carcinogenicity of 2,2'--(4-aminophenyl)imino-bisethanol sulfate in a long-term feeding study in Fischer 344 rats.

2,2'-[(4-aminophenyl)imino]bisethanol sulfate (4APE) was administered at dietary levels of 0 (control), 300, 1000 and 3000 ppm to groups of 50 male and 50 female Fischer 344/DuCrj rats for 104 wk. As slight body weight retardation was observed in the male 3000 ppm group in the preliminary 13-wk feeding study, this dose was selected for the highest exposure level. Mean body weights of both sexes in the 3000 ppm group were lower than those of the controls from wk 2 to termination. However, there were no treatment-related clinical signs or adverse effects on survival rate, food consumption or haematology data. Very slight but statistically significant increases in relative thyroid weights were found in males of the 3000 ppm group, but there was no significant treatment-related increase in the incidence of any non-neoplastic or neoplastic lesions. Thus, under the experimental conditions used, 4APE was not carcinogenic in Fischer 344 rats of either sex.

Animals↗
PubMed1995

Cancer induction by an organic arsenic compound, dimethylarsinic acid (cacodylic acid), in F344/DuCrj rats after pretreatment with five carcinogens.

Arsenic (As) is environmentally ubiquitous and an epidemiologically significant chemical related to certain human cancers. Dimethylarsinic acid (cacodylic acid; DMA) is one of the major methylated metabolites of ingested arsenicals in most mammals. To evaluate the effects of DMA on chemical carcinogenesis, we conducted a multiorgan bioassay in rats given various doses of DMA. One-hundred twenty-four male F344/DuCrj rats were divided randomly into 7 groups (20 rats each for groups 1-5; 12 rats each for groups 6 and 7). To initiate multiple organs and tissues, animals in groups 1-5 were treated sequentially with diethylnitrosamine (100 mg/kg body weight, i.p., single dose at the commencement) and N-methyl-N-nitrosourea (20 mg/kg body weight, i.p., 4 times, on days 5, 8, 11, and 14). Thereafter, rats received 1,2-dimethylhydrazine (40 mg/kg body weight, s.c., 4 times, on days 18, 22, 26, and 30). During the same period, the animals were sequentially administered N-butyl-N-(4-hydroxybutyl)nitrosamine (0.05% in the drinking water, during weeks 1 and 2) and N-bis(2-hydroxypropyl)nitrosamine (0.1% in the drinking water, during weeks 3 and 4; DMBDD treatment). After a 2-week interval, groups 2-5 were given 50, 100, 200, or 400 ppm DMA, respectively, in the drinking water. Groups 6 and 7, which were not given DMBDD treatment, received 100 and 400 ppm DMA during weeks 6-30. All rats were killed at the end of week 30. In the initiated groups (groups 1-5), DMA significantly enhanced the tumor induction in the urinary bladder, kidney, liver, and thyroid gland, with respective incidences in group 5 (400 ppm DMA) being 80, 65, 65, and 45%. Induction of preneoplastic lesions (glutathione S-transferase placental form-positive foci in the liver and atypical tubules in the kidney) was also significantly increased in DMA-treated groups. Ornithine decarboxylase activity in the kidneys of rats treated with 100 ppm DMA was significantly increased compared with control values (P < 0.001). In conclusion, DMA is acting as a promoter of urinary bladder, kidney, liver, and thyroid gland carcinogenesis in rats, and we speculate that this may be related to cancer induction by As in humans.

Acetyltransferases↗
PubMed1995

Lack of carcinogenicity of monosodium L-glutamate in Fischer 344 rats.

Monosodium L-glutamate (MSG) was administered to groups of 50 male and 50 female Fischer 344 rats in the diet at levels of 0, 0.6, 1.25, 2.5 and 5.0% for a 2-yr period. Survival of dosed and control rats of both sexes was comparable, although animals receiving 5.0% MSG showed a trend towards (or significant) growth retardation. Urinary biochemistry values indicated increased pH and Na+ levels and decreased K+ in rats of both sexes given 2.5 or 5.0%. However, no significant increases in proliferative or neoplastic lesion development in the urinary tract were observed in any MSG-treated animals. In addition, occurrences of neoplastic lesions in other organs did not differ between treated and control groups. The present study thus did not demonstrate any long-term carcinogenic effect of MSG administered to rats at levels up to 5.0% in the diet.

Animals↗
PubMed1995

Modification by analgesics of lesion development in the urinary tract and various other organs of rats pretreated with dihydroxy-di-N-propylnitrosamine and uracil.

Effects of the analgesics phenacetin, acetaminophen and antipyrine on lesion development in the urinary tract and other organs in male F344 rats were investigated. Animals were concurrently administered with 0.1% dihydroxy-di-N-propylnitrosamine (DHPN) in drinking water and 3.0% uracil in the diet for 4 weeks and then, starting 1 week after the cessation of this treatment, received basal diet or diet containing phenacetin, acetaminophen or antipyrine for 35 weeks. The occurrences of renal cell tumors were increased in the groups given phenacetin or antipyrine, as compared with the DHPN + uracil alone controls. Antipyrine, but not the two other compounds, also enhanced development of hyperplastic lesions in the renal pelvis and ureter. In the urinary bladder, phenacetin and antipyrine treatments were both associated with increased incidence of preneoplastic or neoplastic lesions. Furthermore, phenacetin alone, without the initiating agent pretreatments, induced simple hyperplasias of the urinary bladder at high incidence. Antipyrine enhanced induction of hyperplastic lesions in the ureter and was also found to increase the incidences of preneoplastic and neoplastic lesions in the liver. Although decreased incidences of tumor development of lung and thyroid were observed for the group given phenacetin, this might have been linked to the decreased weight gain. The results confirmed that combination treatment with DHPN + uracil is effective for wide-spectrum initiation of carcinogenesis in the urological tract and demonstrated significant modification potential for both phenacetin and antipyrine.

Acetaminophen↗
PubMed1994

Progressive growth of rat bladder carcinomas after exposure to prolonged uracil-induced urolithiasis.

Dietary uracil at the 3% level induces urinary bladder tumors in rats through urolithiasis-dependent mechanical irritation. In the present study, comparison of lesions induced by uracil administration over the different periods of 36 weeks (middle-term) and up to 103 weeks (long-term) revealed significant elevation of both incidences and multiplicity of transitional cell carcinomas (TCCs) in the long-term group. Histopathological assessment in terms of tumor biology further demonstrated significantly higher grading on the basis of the degree of cellular and structural atypia, and greater depth of invasion in the long-term group. Application of markers for cell proliferation activities including proliferating cell nuclear antigen (PCNA) and silver-binding nucleolar organizer regions (AgNORs) also revealed significantly elevated AgNOR counts in the long-term group TCC. AgNOR counts and PCNA rates in TCCs showed relation to the histological grades. Thus the present study demonstrated that prolonged uracil-induced urolithiasis causes more biologically aggressive bladder carcinomas with invasive potential. Continuous stimulation of cell proliferation presumably has the potential to facilitate multiple genetic alterations leading to development of more malignant carcinomas. However, it should be borne in mind that the difference in bladder cancer development might also be related to the fact that the animals survived longer and that the early lesions therefore had more time to progress to more advanced stages.

Animals↗
PubMed1994

DNA methylation adduct formation and H-ras gene mutations in progression of N-butyl-N-(4-hydroxybutyl)nitrosamine-induced bladder tumors caused by a single exposure to N-methyl-N-nitrosourea.

After receiving 500 p.p.m. N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in their drinking water for an initial 10 weeks, rats were given a single i.p. injection of N-methyl-N-nitrosourea (MNU) at a dose of 50 mg/kg body wt at week 20 (at a stage when bladder tumor development had already occurred), and then maintained until they were killed at week 40. Three and six hours after the MNU injection, the DNA methylation adducts, O6-methyldeoxyguanine (O6-medG) and 7-methyldeoxyguanine (7-medG), were immunohistochemically revealed to be markedly more frequent in urothelial preneoplasias or neoplasias than in normal cells. These adducts were rapidly repaired, and although 7-dmeG in tumor cells still persisted after 72 h, they appeared essentially to have returned to normal levels. At the termination, conversion of transitional cell carcinomas (TCC) to squamous cell carcinomas (SCC) of the urinary bladder was significantly increased in the BBN+MNU group. The extent of invasion was also significantly greater with the additional MNU treatment. Expression of p21 protein, detected by immunohistochemistry, was comparable between the groups. Mutations in the H-ras gene were observed in one case each of the BBN and BBN+MNU groups, and both cases showed a G:C to A:T transition at codon 12. The present study thus suggested that while an additional single treatment with MNU of rats bearing BBN-induced bladder neoplasias is associated with significant, possibly mutation-dependent tumor progression, H-ras mutations are not necessary events.

Administration, Oral↗
PubMed1993

Chemoprevention by indomethacin of tumor promotion in a rat urinary bladder carcinogenesis model.

The chemopreventive effects of indomethacin (IM) on the enhancement of bladder carcinogenesis and transitional-epithelial-cell proliferation by butylated hydroxyanisole (BHA) or sodium L-ascorbate (Na-AsA) were investigated. All animals were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for 4 weeks. They then received 2% BHA or 5% Na-AsA for 20 weeks, followed by 20 ppm IM in the drinking water or normal tap water without supplement for a further 20 weeks, or BHA or Na-AsA alone or concomitantly with IM for 40 weeks. No differences in bladder-tumor development were found when IM was administered after cessation of BHA or Na-AsA exposure. However, IM in combination with either BHA or Na-AsA significantly reduced both the incidence and the multiplicity of papillomas and carcinomas as compared with the values of groups receiving BHA or Na-AsA alone. This was associated with decreased DNA synthesis and prostaglandin (PG) E2 levels in the existing bladder tumors. Combined treatment with IM did not exert any effects on BHA forestomach carcinogenesis. A separate 8-week combination study demonstrated that IM diminished the increase in expression of proliferation nuclear-cell antigen (PCNA) induced by BHA or Na-AsA alone. The present results suggest that PGE2 may be involved in promotion of rat bladder carcinogenesis and that the PG synthesis blocker IM might exert preventive effects on the development of bladder cancer in humans.

Animals↗