Mechanism of growth inhibition of mammary carcinomas by glucarate and the glucarate: retinoid combination

In synergistic combination 0.75 mmol/kg diet of N-(4-hydroxyphenyl) retinamide and 32 mmol/kg diet of glucarate inhibits the growth of primary rat mammary tumors, but are equally effective as single agents at 1.5 and 128 mmol/kg diet, respectively. Dose-response studies suggest that like retinoids, glucarate acts directly on tumor cells, rather than having an adjuvant effect. Although synergism is maintained down to at least 0.38 mmol/kg diet of the retinoid, experiments using Vitamin A-deficient diets indicates 128 mmol/kg glucarate acts independent of retinoid. Both alone and in combination, glucarate and retinoid inhibited the growth of human mammary tumor cells grown in the athymic mouse, the growth of rat mammary tumors in germfree rats and the hormone-independent MTW 9a/R rat mammary tumor. Like retinoids, glucarate suppresses protein kinase C and induces transforming growth factor-beta, in the mammary tumor cells.

In vivo use of N-(4-hydroxyphenyl retinamide)-0-glucuronide as a breast cancer chemopreventive agent

The inhibitory effects of N-(4-hydroxyphenyl) retinamide and its glucuronide derivative on the development and growth of 7,12-dimethylbenz (a) anthracene - induced rat mammary tumors in vivo were compared. The results indicate that the glucuronide had a greater chemopreventive potency than equimolar concentration of the free retinoid by all the criteria measured, mainly the inhibition of tumor incidence, multiplicity and tumor growth. HPLC analysis of the blood of the rats showed no hydrolysis of the glucuronide during its chronic consumption, indicating that the retinoid glucuronide is probably acting in vivo per se rather than through hydrolysis to the free retinoid. The higher potency and lower toxicity of the glucuronide suggests, for the first time, that the conjugate may have an in vivo chemopreventive advantage over the parent retinamide.

Cloning and functional expression of a brain G-protein-coupled ATP receptor

A cDNA encoding a novel member of the G-protein-coupled receptor (GCR) superfamily, an ATP receptor, has been isolated from an embryonic chick whole brain cDNA library by hybridization screening. The encoded protein has a sequence of 362 amino acids (41 kDa) and shares no more than 27% amino acid identity with any known GCR. When expressed as a complementary RNA (cRNA) in Xenopus oocytes a slowly-developing inward current was observed in response to application of ATP. The pharmacology of this expressed protein defines it as a P2Y purinoceptor.

Basis for the anti-tumor and chemopreventive activities of glucarate and the glucarate:retinoid combination

The biochemical basis for the cancer chemopreventive and anti-cancer activities of glucarate, retinoids (13-cis-retinoic acid, hydroxyphenyl retinamide) and their synergistic combination, has been evaluated. Neither alone nor in combination did these agents affect the level in the rat, of enzymes which are (a) known to correlate with reduced risk of carcinogenesis (detoxification enzyme, catalase, glutathione reductase) nor (b) enzymes which correlate with increased risk of carcinogenesis (beta-glucuronidase, xanthine oxidase, glucose-6-phosphate dehydrogenase). Retinoids, but neither glucarate nor its lactone inhibited free radical-induced lipid peroxidation. Both agents alone and synergistically in combination, raise cellular cAMP levels, repress protein kinase C and more generally inhibited DNA synthesis.

Dietary glucarate-mediated inhibition of initiation of diethylnitrosamine-induced hepatocarcinogenesis

Previously, it has been reported that calcium glucarate is a potent inhibitor of chemical carcinogenesis, including phenobarbital-promoted diethylnitrosamine-initiated hepatic toxicity expressed as altered hepatic foci in rats. The purpose of the present study was to determine whether calcium glucarate could inhibit the immediate and delayed appearance of altered hepatic foci when fed to rats during the initiation phase of diethylnitrosamine-induced hepatocarcinogenesis. The effects of dietary mode of administration of calcium glucarate on the initiation phase of hepatocarcinogenesis were also examined. Since diethylnitrosamine is not known to undergo glucuronidation and calcium glucarate has been shown to enhance clearance of circulating estrogens, an indirect mechanism of action of calcium glucarate was also evaluated by pretreating rats with an anti-estrogen, tamoxifen, prior to partial hepatectomy and administration of diethylnitrosamine. Calcium glucarate significantly inhibited both the early and delayed appearance of altered hepatic foci and exerted maximal inhibition when administered by gavage prior to diethylnitrosamine. Maximal inhibition was obtained when calcium glucarate was provided continuously in the diet of animals up to 5 and 7 months. Pretreatment of animals with tamoxifen before partial hepatectomy and diethylnitrosamine resulted in maximal inhibition of the initiation phase of hepatocarcinogenesis. This suggests but does not prove that the anti-carcinogenic activity of calcium glucarate was due to decreased liver proliferation. In the present study, the proliferation of ductular epithelial and oval cells appeared to be associated with the administration of diethylnitrosamine. Collectively, our data suggest that calcium glucarate inhibited the initiation phase of diethylnitrosamine-induced hepatocarcinogenesis.

Antitumour synergism between non-toxic dietary combinations of isotretinoin and glucarate

Dietary calcium glucarate (CGT) increased the activity of non-toxic levels of dietary isotretinoin against pre-established tumors in the chemically-induced rat mammary tumour model. In the range of 1.0-1.5 mmol/kg diet, isotretinoin enhanced tumour growth by 20% over a 4 week course of treatment. Tumour growth inhibition not exceeding 15% was observed only at dosages as high as 2.0 mmol/kg, i.e. in the cumulative toxicity range. Growth inhibition by 64 mmol/kg diet of CGT alone was marginal, varying from zero to 8%. In contrast, the combination of 1.0 mmol/kg of isotretinoin and 64 mmol/kg of CGT caused a reversible inhibition of tumour growth, culminating in a net decrease in tumour volume of 20%. This study documents the marginal enhancement of tumour growth by high sub-optimal concentrations of isotretinoin alone, and describes conditions for inhibition of tumour growth by sub-optimal concentrations of the natural retinoid. Related in vitro studies on retinoid sensitive and insensitive cell lines suggest that the anticancer activity of the combination is dependent on sensitivity of the cells to retinoids.

Effect of dietary soybean and licorice on the male F344 rat: an integrated study of some parameters relevant to cancer chemoprevention

The individual and combined effects of dietary toasted soybean meal (3.13-25%) and dietary licorice root extract (0.38-3.0%) on selected liver and intestinal enzyme levels and on clinical chemistry and histopathological parameters were evaluated on male F344 rats. All parameters were measured one and three months after the 50-day-old rats were started on the diets. By use of newly developed high-performance liquid chromatography-based analytic methods, measurable levels of daidzein (2.67 micrograms/ml) and glycyrrhetinic acid (7.87 micrograms/ml) were detected in the sera of rats on the 25% soybean and 3% licorice diets, respectively. Histopathological evaluations of organs and tissues yielded only nonsignificant strain-related changes. At all dosages, there were no significant soybean- or licorice-related anatomic lesions or hematologic changes. In the clinical biochemistry profile, soybean meal caused moderate but significant dose-dependent decreases in serum cholesterol and increases in alkaline phosphatase, blood urea nitrogen, and phosphorus, which remained within the normal range. Liver glutathione transferase, catalase, and protein kinase C showed significant inductions (up to 50%) in response to increasing doses of soybean meal and licorice extract, with evidence for only marginal interaction between the two additives. Their effects on the intestinal mucosa were not significant. Ornithine decarboxylase levels, an indicator of promotional activity, were unchanged or repressed by the additives. The favorable effects of up to 25% toasted soybean meal and 3% licorice root extract on the levels of the four enzymes, without unfavorable changes in clinical parameters, might account in part for the chemopreventive activities of these additives. These effects would be in addition to direct inhibitory effects of known components in these additives on these or other enzymes or modulation of hormone activity that is not evaluated in this study.

Effects of 5-fluorouracil, leucovorin, and glucarate in rat colon-tumor explants

In a previous study, we showed that 5-fluorouracil (FU) is active against the dimethylhydrazine-induced colon tumor in rats; a 7-day infusion of FU at 30 mg/kg daily produced 85% tumor-free cures. The present study examined the effects of FU alone and in combination with leucovorin (LV) or D-glucarate (GT) using an ex vivo system that maintained the growth of the rat colon-tumor explants on collagen gels. The labeling index (LI) was determined by the incorporation of [3H]-thymidine and autoradiography. The mean LI of the untreated control was 64.8% +/- 19.8%. The IC50, IC90, and IC95 values following a 7-day exposure to FU were 0.36, 0.75, and 1.22 microM, respectively. In comparison, the steady-state FU concentration required to produce 67% tumor-free cures in rats following a 7-day infusion is 1.54 microM. LV alone did not produce any antiproliferative effect at concentrations as high as 10 microM. The addition of LV at concentrations of 0.001-10 microM did not significantly reduce the IC50 of FU. The lack of effect of LV may have been due to tissue saturation with folate provided in the culture medium. GT alone reduced the tumor LI by 20%-30% at concentrations of 0.1-10 microM. GT enhanced the effect of FU. As compared with FU alone, the addition of GT at concentrations of 0.1 and 1.0 microM reduced the IC50 of FU by 47% and 60% to 0.21 and 0.16 microM, respectively. Assessment of the potentiation of the inhibitory effect of FU by GT using two-way analysis of variance and the isobologram method indicated a significant synergistic interaction between FU and GT. This interaction occurred within the FU concentration range of 0.08 and 0.4 microM. In summary, these data indicate that (a) the IC values for FU are comparable in tumor explants and in rats, suggesting that the effects in cultured tumors reflect those in intact animals; (b) GT alone showed antitumor activity, albeit relatively minor as compared with FU; (c) FU and GT exhibited synergistic activity, which was most pronounced at FU concentrations that produced submaximal activity (less than 30% inhibition of tumor LI); and (d) GT and LV had different effects on the growth inhibition by FU, suggesting that GT acts by a mechanism different from the thymidylate synthase-directed effect of FU and LV.

Development and use of monoclonal antibodies against an oncofetal protein associated with carcinogenesis and tumorigenesis

An oncofetal protein (OFP) studied in our laboratory associated with embryogenesis, carcinogenesis and tumorigenesis has as its known biological function the modification of RNA release from isolated nuclei. In the present study, we have developed and investigated the use of monoclonal antibodies against OFP. Six hybridoma cell lines (A-F) were isolated by screening the hybridoma culture media for anti-OFP antibodies (MOFP) with an indirect ELISA and by testing the ability of these antibodies complexed with anti-mouse IgG-agarose to bind to rat OFP and remove its associated RNA transport activity from solution (Immunobioassay). An inhibition ELISA developed to measure OFP gave a linear response up to 20 ng of plasma protein from a tumor-bearing rat. Western blot analysis using these monoclonals showed that OFP from a rat tumor (H7777) cytosol that shed to the blood consisted of two species exhibiting molecular weights of 50 and 55 kD respectively. In order to show the usefulness of our assays, a preliminary study showing the ability of the immunobioassay to detect the expression of OFP in the plasma of carcinogen treated rats in a dosage dependent manner has been presented. Since OFP is produced in the target organ of rats shortly after treatment with carcinogens and persists in the preneoplastic foci and subsequent tumors, these monoclonal antibodies will be valuable in studying its involvement in chemical carcinogenesis and tumorigenesis.

Growth suppression of human breast carcinoma cells in culture by N-(4-hydroxyphenyl)retinamide and its glucuronide and through synergism with glucarate

The inhibitory effects of N-(4-hydroxyphenyl)retinamide (HPR) and its glucuronide derivative on the growth of MCF-7 human breast cancer cells in vitro were compared. The results indicate that the glucuronide had slightly greater potency and much less cytotoxicity than the free retinoid. At a concentration of 10(-6) M, HPR inhibited MCF-7 cell growth by approximately 25%, whereas an equimolar concentration of the glucuronide caused a 40% growth inhibition. Higher concentrations of HPR were highly cytotoxic. At a 10(-5) M concentration of the glucuronide, cell viability was 77%, and 65% of the cells were able to resume growth. On the other hand, at 10(-5) M HPR, cell viability dropped to 49%, and only 15% of the cells were capable of resuming growth. The lower cytotoxicity and higher potency of the retinoid glucuronide compared to the parent retinamide suggest that the conjugate may have a chemotherapeutic advantage over the parent compound. The apparent higher efficacy of HPR in combination with glucarate (GT) compared to the single agents could be due to increased net formation of HPR glucuronide conjugate following conversion of GT to the beta-glucuronidase inhibitor, D-glucaro-1,4-lactone. However, HPLC analysis of the cell metabolites did not show any detectable levels of the retinoid glucuronide upon treatment of MCF-7 cells with HPR and GT.

Expression of an oncofetal protein (OFP) in rat and human leukemia cells

A unique oncofetal protein (OFP) previously identified in rat fetal tissue and rat and human solid tumors, is now shown to be present in rat and human leukemia cells by use of a monoclonal antibody-based assay. Using a highly specific anti-rat OFP monoclonal antibody OFP has been unquivocally immunolocalized to the cytoplasm of the rat leukemia cells. The factor is rapidly released to the circulation as 50 and 55 kD species which share the immunological determinants. When leukemia cells are transplanted to normal rats, OFP increases in the circulation in a biphasic manner which may be due to immune clearance since circulating anti-OFP antibodies have been demonstrated. Induction of differentiation in the human HL-60 leukemia cell line by 13-cis-retinoic acid caused a down regulation of OFP synthesis, both intra- and extra-cellular levels dropping to essentially zero. Induction of differentiation with dibutyryl cyclic AMP caused a cessation of secretion of OFP, with a marked increase in its intracellular concentration, a condition resembling the retention in fetal cells. Leukemia cells add to a growing list of tumors previously shown to produce OFP, suggesting that OFP is intimately involved in some facet of tumorigenesis.

Effect of calcium glucarate on beta-glucuronidase activity and glucarate content of certain vegetables and fruits

Glucarate is normally present in tissues and body fluids and is in equilibrium with D-glucaro-1,4-lactone, a natural inhibitor of beta-glucuronidase activity. Dietary calcium glucarate, a sustained-release from of glucarate, elevates the blood level of D-glucaro-1,4-lactone which suppresses blood and tissue beta-glucuronidase activity. A single dose of CaG (4.5 mmole/kg body weight) inhibited beta-glucuronidase activity in serum and liver, lung, and intestinal microsomes by 57, 44, 37, and 39%, respectively. A chronic administration of calcium glucarate (4% in diet) also decreased beta-glucuronidase activity in intestinal and liver microsomes. Maximal inhibition of beta-glucuronidase activity in serum was observed from 12 noon to 2:00 PM. In contrast, maximum inhibition of beta-glucuronidase activity in intestinal and liver microsomes occurred during mornings, although a secondary depression in intestinal microsomes also occurred around 4 PM. A 4% calcium glucarate supplemented diet also inhibited beta-glucuronidase activity by 70% and 54%, of the bacterial flora obtained from proximal (small intestine) and distal (colon) segments of intestine, respectively. Due to the potential effect of dietary glucarate on net glucuronidation and on other metabolic pathways, glucaric acid levels in various foods were determined. The glucaric acid content varied from a low of 1.12-1.73 mg/100 g for broccoli and potatoes to a high of 4.53 mg/100 g for oranges.

Chemotherapeutic evaluation of glucarate and N-(4-hydroxyphenyl)retinamide alone and in combination in the rat mammary tumor model

We evaluated calcium glucarate (CGT) and N-(4-hydroxyphenyl)retinamide (HPR) for their effectiveness as anti-tumor agents. For this evaluation, we tested the effects of CGT and HPR given alone or combined in the diet on the growth of established 7,12-dimethylbenz[a]anthracene-induced rat mammary tumors. When given alone, optimal doses of CGT (128.0 mmol/kg in the diet) or HPR (2.0 mmol/kg in the diet) administered daily for 25 days reduced mammary tumor sizes by approximately 15% or 20%, respectively. Suboptimal doses of CGT (64.0 mmol/kg) or HPR (0.75 mmol/kg) administered daily for 25 days only slightly inhibited tumor growth; over the 25-day period, the tumor sizes in rats on the CGT diet and in rats on the HPR diet increased by 55% and 70%, respectively, compared with a 98% increase in tumor sizes in the rats on the control diet. In contrast, the combination of suboptimal doses of CGT (64.0 mmol/kg) and HPR (0.75 mmol/kg) administered daily for 25 days decreased tumor sizes by 33%. These results are statistically significant. They show that CGT and HPR act synergistically. Consequently, lower concentrations of these agents can be used to inhibit mammary tumor development and growth.

A carcinogenesis- and tumorigenesis-associated rat fetal protein: an immuno-histochemical and immuno-biochemical study utilizing a new monoclonal antibody, MOFP

An oncofetal protein (OFP), which is a potential marker for carcinogenesis and tumorigenesis, was evaluated with monoclonal antibodies shown to be specific for the antigen. Treatment of partially hepatectomized rats with a single non-necrogenic dose of diethylnitrosamine induced OFP in the liver. Its concentration, as measured by a dual immuno/bioassay, increased steadily over a 5-week period of observation before reaching a constant level. Immunohistochemical localization of OFP in liver sections from rats treated with N-nitroso-N-diethyl-nitrosamine showed that the factor was primarily localized to the cell cytoplasm in cells of most of the altered hepatic foci although some of this shedding antigen was also extracellular. Monoclonal antibody 17-1A specific for 17-1A antigen, an established surface marker for adenocarcinomas of the gastrointestinal tract, showed a similar distribution in liver from the carcinogen-treated rats, but localized to the cell membrane and cytoplasm. Scattered cells surrounding the altered hepatic foci were also positive for both monoclonal antibodies. Immunolocalization studies showed fetal rat liver and hepatoma were positive for OFP but adult normal or regenerating liver was negative. It was not detected in cells which morphologically could be classified as oval cells. As assessed by immuno/bioassay, the OFP released to the peripheral blood (plasma) of hepato-carcinogen-treated rats increased for 3 weeks, before undergoing a transitory decrease. Circulating antibodies specific for the factor were detected in the blood around 3-5 weeks post-treatment. Development of Western blots of the OFP with antiphosphotyrosine IgG indicates that the marker protein contains phosphotyrosine.

Induction of an oncofetal marker protein upon X-radiation of rat mammary glands

Fifty-day-old female Sprague--Dawley rats were given carcinogenic and sub-carcinogenic doses of X-radiation to the mammary glands to evaluate the induction of a 60-kDa oncofetal protein (OFP-60). This protein has previously been shown to be produced in the target organ and released to circulation during chemical carcinogenesis and tumorigenesis. In a time course experiment, the mammary glands of the rats were irradiated with a single dose of 1.85 gray (Gy). The OFP-60 marker protein was detected in peripheral blood at 21 days post-irradiation. Irradiation of the mammary gland with single X-ray doses ranging from 0.22 to 1.85 Gy produced a linear relationship between X-ray dose and plasma concentration of OFP-60 determined at 21 days post-treatment. This initiation-related parameter correlates with the known linear relationship between dose of X-radiation and potential tumor incidence.

Developmental changes in expression of a tumor-associated protein in the rat fetus

Monoclonal antibodies specific for a rat tumor-associated protein cross-react with a similar protein present in the cytosol of the rat fetus. The oncofetal protein exists as two species of approximate molecular weight 50 and 55 kDa which promote the transport of RNA from isolated nuclei. During rat fetal development, the protein first increases in concentration from approximately 12 to 16 days gestation and then drops to non-detectable levels perinatally.

Synergistic interaction between 13-cis-retinoic acid and glucarate: activity against rat mammary tumor induction and MCF-7 cells

At high dietary levels in vivo, both 13-cis-retinoic acid and calcium glucarate inhibit the induction of rat mammary tumors by 7,12-dimethylbenz(a)anthracene. The present study shows that sub-optimal dietary levels of each, which individually have no effect on tumor induction, when combined together in the diet, significantly increases tumor latency and suppresses tumor frequency in the rat system. Weight gain of animals was similar in control and experimental groups. Furthermore, ineffective sub-optimal dosages of glucarate and 13-cis-retinoic acid interacted synergistically to inhibit the growth in vitro of the MCF-7 human breast cancer cells. By varying the concentrations of glucarate and 13-cis-retinoic acid independently, evidence was obtained that in combination glucarate may play an adjuvant role, with the retinoid as the effector. Thus, the results of this experimental animal study demonstrate for the first time the potential use in synergistic combination of 2 normal metabolites in non-toxic chemoprevention and chemotherapy.

Hybridization analysis of RNA transported from rat liver nuclei in response to 35 kDa normal and 60 kDa messenger RNA transport factors

The transport of messenger RNA (mRNA) in response to normal adult (35 kDa) and oncofetal (60 kDa) transport factors has been studied in a reconstituted cell-free system. Poly(A)+ mRNA sequences transported by the 35 kDa and 60 kDa transport factors were compared by cDNA:RNA hybridization kinetics. Heterologous hybridization reactions indicated that a proportion of messengers transported in response to the 35 kDa factor were absent or at a markedly reduced abundance in the mRNA released by the 60 kDa factor. Recombinant DNA probes containing cDNA inserts were used to quantitate transport of rat-liver-specific alpha 2 mu-globulin and albumin mRNA from isolated nuclei in presence of the normal and tumor-specific transport factors. More alpha 2 mu-globulin and albumin messenger sequences were transported in response to the 35 kDa transport factor as compared to the 60 kDa factor. These results indicate that the 35 kDa transport protein isolated from rat liver cytosol and the 60 kDa transport protein isolated from hepatoma cytosol, differ significantly in specificity for the classes of RNA sequences released from nuclei. Monoclonal antibodies against the 60 kDa factor do not cross-react with the 35 kDa factor or other proteins as determined by the immunobioassay and by the Western blot technique.

Chemopreventative activity of dietary glucarate on azoxymethane-induced altered hepatic foci in rats

Previous studies have shown that dietary calcium glucarate, an inhibitor of beta-glucuronidase, is a potent inhibitor of promotion of diethylnitrosamine-induced altered hepatic foci, 7,12-dimethylbenzanthracene-induced mammary tumorigenesis and benzo(a)pyrene-induced lung carcinogenesis. The present study was undertaken to test the chemopreventative activity of calcium glucarate on azoxymethane-induced hepatocarcinogenesis in female Fischer 344 rats. A series of experiments were carried out over 36 weeks to evaluate the effects of calcium glucarate on the initiation and promotion phases separately and also in combination with each other. A calcium gluconate group was included and used as a negative calcium control. Histopathologic evaluation of H&E stained liver sections of all animals in this study showed that a statistically significant inhibition of hepatocarcinogenesis only occurred when dietary calcium glucarate supplementation was provided throughout the combined initiation and promotion phases. This inhibitory effect approximately equaled the summation of that obtained when calcium glucarate was fed only during initiation phase and only during promotion phase.

Effects of the experimental chemopreventative agent, glucarate, on intestinal carcinogenesis in rats

Dietary calcium glucarate was previously shown to protect effectively against chemically-induced mammary, lung, liver and skin carcinogenesis in rodents, whereas the negative dietary calcium control, calcium gluconate, had no effect. In the present study the chemopreventative activity of dietary calcium glucarate was evaluated in the azoxymethane intestinal carcinogenesis model using the Fischer strain rat. The protocol limited the duration of azoxymethane treatment to 3 weeks to permit the evaluation of the separate effects of glucarate on the initiation and promotion phases. Control rats, treated with azoxymethane and maintained on a low fat chow diet throughout the 32-week experiment had an intestinal adenocarcinoma incidence of 55%, with an equal incidence of 27.7% in the small and large intestines. There was no significant difference between this control group and a negative calcium control group fed 128 mmol/kg chow of calcium as calcium gluconate. In contrast to these two control groups, supplementation of the diet of azoxymethane-treated rats with 128 mmol/kg diet of calcium glucarate during both the initiation and promotion phases significantly inhibited the overall induction of adenocarcinomas in the intestine, the incidence in the entire intestine and in the small and large intestines being 11.8, 5.8 and 5.8%, respectively. When fed only during the initiation phase, the inhibition again was statistically significant, the corresponding values being 11.8%, 5.8 and 5.8%. When calcium glucarate was fed during the promotion phase, a statistically significant inhibition of adenocarcinoma induction was observed only in the colon where the incidence was 5.5%. Weight gain was similar in all groups. These and related data indicate that dietary glucarate exerts a significant inhibitory effect on azoxymethane-induced intestinal and in particular colon carcinogenesis in the rat, decreasing their incidence and size and reducing their metastic potential.

Modulation of chemically initiated and promoted skin tumorigenesis in CD-1 mice by dietary glucarate

The efficacy of dietary calcium glucarate as a chemopreventative agent has been tested in the mouse skin tumorigenesis system. Skin tumorigenesis was initiated in mice of the CD-1 strain with 7,12-dimethylbenz(a)anthracene (DMBA), then promoted with twice weekly applications of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) for 13 weeks. The mice were fed a regular chow diet, or a chow diet fortified with calcium glucarate (128 mmol/kg diet), or with equimolar calcium as calcium gluconate (negative calcium control). When mice were fed calcium glucarate throughout both the initiation and promotion phases papilloma formation was inhibited by over 30%. Transfer of these DMBA-initiated, TPA promoted CD-1 mice to chow diet after 13 weeks on the calcium glucarate-supplemented diet, resulted in an increase in the number of skin papillomas within 3 weeks to the level of those seen in control animals maintained exclusively on the chow diet. When calcium glucarate feeding was restricted to either the initiation or promotion phases, papilloma formation was inhibited by 25%. Dietary calcium gluconate had no effect on papilloma formation in the CD-1 mouse system, but increased the calcium concentration in the skin to the same extent as that of calcium glucarate. The data indicate that the elevation of the normally low levels of glucarate in the body through supplementation, results in a marked alteration in the retention, activity and/or metabolism of xenobiotics.

Repression by sustained-release beta-glucuronidase inhibitors of chemical carcinogen-mediated induction of a marker oncofetal protein in rodents

The degree of induction of an oncofetal protein marker in rodents by selected chemical carcinogens has been correlated with changes in carcinogenicity induced by dietary D-glucaro-1,4-lactone (GL) based anticarcinogens. These potent anticarcinogens may act to increase the clearance of carcinogens as glucuronides through the inhibition of beta-glucuronidase. The sustained-release forms are particularly effective, 1.5 mmol/kg of GL maintaining serum beta-glucuronidase activity at or below 50% for only 1 h, while an equivalent amount of calcium glucarate (CGT) maintained this level of inhibition for over 5 h. CGT or other sustained-release inhibitors, when fed to rodents during administration of carcinogens that undergo glucuronidation, caused a marked reduction in the induction of the marker protein. For those systems where other markers of carcinogenesis were also assessed, it was determined that the inhibition of marker-protein induction was quantitatively similar to both the inhibition of binding of the carcinogen to DNA and the subsequent induction of tumors in target organs.

Effects of calcium glucarate on the promotion of diethylnitrosamine-initiated altered hepatic foci in rats

Calcium glucarate (CGT), an inhibitor of beta-glucuronidase, is a potent inhibitor of chemically-induced tumors when administered orally. The present study was undertaken to determine the effects of CGT on the promotion of hepatocarcinogenesis by phenobarbital following initiation with diethylnitrosamine (DENA). Partially hepatectomized, DENA-initiated female Sprague-Dawley rats, previously maintained only on chow diet for 2 months, were supplemented with either 0.05% phenobarbital alone or 0.05% phenobarbital plus 4% dietary CGT, for varying time intervals up to 6 months. Histopathologic evaluation of the liver sections showed that CGT significantly delayed the development of altered hepatic foci (AHF). By the seventh month post-initiation, however, the frequency and severity of changes seen in the livers of experimental animals approximated those of the controls.