Inhibitory effects of sulfation inhibitors on initiation of pancreatic ductal carcinogenesis by N-nitrosobis(2-oxopropyl)amine in hamsters

A new medium-term rat colon bioassay applying neoplastic lesions as endpoints for detection of carcinogenesis modifiers–validation with known modifiers

We have established a medium-term colorectal carcinogenesis rat model initiated with 1,2-dimethylhydrazine (DMH) followed by dextran sodium sulfate (DSS) treatment, featuring induction of neoplastic lesions within 10 weeks. In the present study, we examined its ability to detect modification of colon lesion development with 10- or 20-week experimental periods. F344 male rats were given three subcutaneous injections of DMH (40 mg/kg b.w.) in a week followed by free access to drinking water containing 1% DSS for a week. One week after this regimen, basal diet alone, basal diet containing 0.04% nimesulide or 2% lactoferrin as known inhibitors, 0.3% deoxycholic acid (DCA) as a promoter or 1.5% 1-hydroxyanthraquinone (1-HA) as a carcinogen were supplied. At week 10, the incidence and multiplicity of combined adenomas and adenocarcinomas were significantly (P < 0.05 or 0.01) decreased by nimesulide and lactoferrin, and values for adenomas were significantly (P < 0.01) increased in the 1-HA group. There was no clear change in the DCA group. At week 20, multiplicity and volume of the tumors were significantly (P < 0.01 or 0.05) decreased by nimesulide, but no effect was now evident with lactoferrin. Multiplicity and volume of tumors were significantly (P < 0.01) increased in 1-HA group and a similar tendency was apparent (P = 0.08) with DCA. It is concluded that this system offers a useful tool for detection of colorectal carcinogenesis modifiers within 10-20 weeks, pending further studies for verification employing other model chemicals.

Curcumin is a potent inhibitor of phenol sulfotransferase (SULT1A1) in human liver and extrahepatic tissues

1. Curcumin has anti-carcinogen effects and is under clinical evaluation as a potential colon cancer chemopreventive agent. The first aim was to see whether curcumin inhibited phenol sulfotransferase (SULT1A1) and, if so, to study the variability of the IC(50) of curcumin for SULT1A1 in 50 human liver samples. For comparative purposes, the inhibition of catechol sulfotransferase (SULT1A3) in five human liver specimens was studied. The second aim was to measure the IC(50) of curcumin against SULT1A1 in five samples of human duodenum, colon, kidney and lung. 2. Curcumin was a potent inhibitor of SULT1A1 in human liver; the mean +/- SD and median of IC(50) were 14.1 +/- 7.3 nM and 12.8 nM, respectively. The IC(50) ranged from 6.2 to 30.6 nM between the 5th and 95th percentiles and the fold of variation was 4.9. The distribution of IC(50) was positively skewed (skewness 1.2) and deviated from normality (p = 0.0004). 3. Curcumin inhibited human SULT1A3, and the inhibition was studied in five liver specimens with an IC(50) of 4324 +/- 1026 nM. This inhibition was greater than the IC(50) of curcumin for SULT1A1 (p < 0.0001). 4. In the extrahepatic tissues, the IC(50) of curcumin for SULT1A1 was 25.9 +/- 4.8 nM (duodenum), 25.4 +/- 6.8 nM (colon), 23.4 +/- 2.2 nM (kidney) and 25.6 +/- 5.6 nM (lung). Inhibition in these tissues is greater than that of curcumin for SULT1A1 in human liver (p < 0.0001). 5. In conclusion, curcumin is a potent inhibitor of SULT1A1 in human liver, duodenum, colon, kidney and lung. The IC(50) of curcumin for SULT1A1 varied 4.9-fold in human liver. The comparison of the present data with those of the literature revealed that the IC(50) of curcumin in the liver and extrahepatic tissues is one order of magnitude lower that the peak serum concentration of curcumin after therapeutic doses of 4 g to humans.

The role of aspirin in carcinogenesis

British Journal of Cancer (2002) 87, 1337–1338. doi:10.1038/sj.bjc.6600670www.bjcancer.com

© 2002 Cancer Research UK

Oral dehydroepiandrosterone inhibits the growth of human pancreatic cancer in nude mice

BACKGROUND

Dehydroepiandrosterone (DHEA), an androgen precursor, inhibits the induction of pancreatic cancer in some animal models. Our laboratory has previously demonstrated that the sulfated form of DHEA (DHAS), when administered by intraperitoneal injection, inhibits the growth of pancreatic cancer xenografts in nude mice. In the present study, we hypothesize that DHEA-mediated pancreatic cancer growth inhibition is associated with alterations in plasma sex hormone concentrations.

MATERIALS AND METHODS

Forty male, nude, athymic mice were fed either Teklad 22/5 rodent diet or diet supplemented with 0.6% DHEA ad libitum. Four weeks following the institution of the experimental diets, 1 x 10(6) MiaPaCa-2 cells were injected into the right flank of each animal. Tumor area was recorded weekly and tumor weights were measured after 5 weeks. Plasma DHAS, testosterone, and progesterone concentrations were determined by radioimmunoassay.

RESULTS

Plasma DHAS, testosterone, and progesterone concentrations were all significantly elevated in the DHEA-treated group. DHEA-treated mouse plasma DHAS concentrations were approximately 50-fold higher than controls. Mean tumor weight was significantly reduced in the DHEA group (68.9 +/- 39.1 vs 121.0 +/- 64.3). DHEA treatment did not result in significant animal weight reductions and toxic side effects were not observed.

CONCLUSIONS

Dietary supplementation with 0.6% DHEA causes significant elevations in plasma DHAS concentration. DHEA administration significantly inhibits pancreatic cancer cell growth at plasma concentrations 1 x 10(5)-fold lower than previously reported. The mechanism of action may involve elevated concentrations of sex hormones.

Inhibition of phenolsulphotransferase by salicylic acid: a possible mechanism by which aspirin may reduce carcinogenesis

BACKGROUND

Recent epidemiological evidence has shown that chronic use of aspirin decreases susceptibility to bowel cancer. Animal studies have shown that sulphotransferase inhibitors coadministered with sulphation activated carcinogens dramatically reduce the incidence of cancer.

AIMS

To investigate the effect of the main aspirin breakdown product, salicylic acid, on the P and M isoforms of phenolsulphotransferase from human platelets and colonic mucosa.

METHODS

Platelets were obtained from healthy blood donors and isolated within 24 hours after donation. Samples of colonic mucosa were obtained at resection for non-malignant disease. Phenolsulphotransferase activity was measured in cellular homogenates using a standard radiolabelling assay.

RESULTS

Salicylic acid consistently and selectively inhibited the P form of phenolsulphotransferase at subtherapeutic concentrations in both tissue samples. A 50% inhibition of sulphation by the P phenolsulphotransferase occurred at salicylic acid concentrations of about 40 and 130 microM in platelets and bowel mucosa respectively. M phenolsulphotransferase was virtually unaffected by salicylic acid up to a concentration of 1.5 mM (the therapeutic plasma concentration for salicylates when treating rheumatoid arthritis is about 1-2 mM).

CONCLUSION

The action of salicylic acid on P phenolsulphotransferase, by preventing the excessive activation of carcinogens, is a possible additional pathway by which aspirin can reduce cancer risk.

Dietary modulation of human platelet phenolsulphotransferase activity

1. The mammalian phenolsulphotransferase enzymes are known to play a major role in both the detoxification and possibly the activation of pre-carcinogenic phenols and aromatic amines. 2. Vegetable cytosol preparations were tested in vitro for their ability to affect the sulphation of two reference compounds (rho-nitrophenol and dopamine, which are selective substrates for the phenol and monoamine forms of phenolsulphotransferase respectively), and to act as substrates for the enzymes in comparison with the same reference compounds. 3. The majority of cytosols greatly decreased (> 80%) the sulphation of either or both the reference compounds. This effect may have been due to either enzyme inhibition or substrate binding. 4. Whereas some of the cytosols were sulphated under the assay conditions, most were not. Additionally, it was found that a cytosol that decreased the sulphation of the two reference compounds was not necessarily poorly sulphated itself. 5. It is concluded that dietary factors have the potential to play a major role in modulating the sulphation detoxification pathway, and have wide ranging implications with regard to adverse drug reactions.