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At least 127 records · Page 7Linked to original sources
PubMed1992

Novel expression of gastrin (cholecystokinin-B) receptors in azaserine-induced rat pancreatic carcinoma: receptor determination and characterization.

Many reports have emphasized the role of gastrin as a growth factor for normal gastrointestinal mucosa and gastrointestinal cancers. Recent studies have pointed out that this peptide acts also as a growth factor for the pancreatic cancer cell line AR42J. This effect is mediated by gastrin [cholecystokinin (CCK)-B] receptors. In the present study, we investigated gastrin (CCK-B) receptor expression in the azaserine-induced rat pancreatic carcinoma DSL-6, comparing it to normal rat pancreas, and we also characterized CCK receptor subtypes in this tumor. The results showed that there is extensive gastrin binding to the DSL-6 pancreatic carcinoma. No evidence of specific gastrin binding to normal pancreas was found. Analysis of the ability of gastrin-17-I to inhibit 125I-gastrin-I binding demonstrated that gastrin bound to a single class of receptors with a Kd of 0.21 +/- 0.04 nM and a binding capacity of 184 +/- 29 fmol/mg protein. 125I-Gastrin-I binding was inhibited by the specific CCK-B receptor antagonist L365,260 approximately 40 times more effectively than by the specific CCK-A receptor antagonist L364,718. Analysis of the ability of cholecystokinin octapeptide (CCK-8) to inhibit 125I-Bolton-Hunter-CCK-8 binding revealed two CCK binding sites, i.e., a high affinity site and a low affinity site. The observed binding affinities of CCK-8 were then introduced into the computer analysis of the dose-inhibition curve of the ability of gastrin-17-I to inhibit binding of 125I-Bolton-Hunter-CCK-8, which was significantly better fit by a three-site model than by a two-site model. The three sites meet the criteria for CCK-B, high affinity CCK-A, and low affinity CCK-A receptors. The binding capacity of CCK-B receptors constitutes 34% of the total high affinity CCK binding sites. This study demonstrated that DSL-6 pancreatic carcinoma expresses three subtypes of CCK receptors. Gastrin (CCK-B) receptors, which were not detected in normal rat pancreas, constitute about one third of the total high affinity CCK receptors. We suggest that novel expression of gastrin (CCK-B) receptors may be generated by gene mutation or amplification during carcinogenesis and may play an important role in promoting tumor growth.

Animals↗
PubMed1986

6-diazo-5-oxo-L-norleucine and azaserine as affinity inhibitors of glutamin(asparagin)ase.

Incubation of homogeneous glutamin(asparagin)ase from Pseudomonas aurantiaca with 6-diazo-5-oxo-L-norleucine (DON) and azaserine leads to an almost complete inactivation of the enzyme. The inactivation process in both cases involves the step of reversible binding of the enzyme with the inhibitor into a complex and subsequent modification of the enzyme within this complex. The data on saturation of the enzyme by low concentrations of inhibitors, the protective effect of substrate and its analogs as well as of the competitive inhibitor and product of the enzymatic reaction, L-aspartate, suggest that the modification of functional groups takes place in the enzyme active site. The presence of essential threonine hydroxyl groups in/or near the enzyme active site is surmised.

Affinity Labels↗
PubMed1979

Azaserine, DON, and azotomycin: three diazo analogs of L-glutamine with clinical antitumor activity.

A review of the clinical data on azaserine, DON, and azotomycin reveals that these agents have limited but definite antitumor activity. All three drugs are analogs of L-glutamine and contain a diazo group. They have been studied as single agents in a wide variety of human malignancies and have also been included in trials using combination chemotherapy. Most of these studies were performed early in the history of clinical trials and, therefore, the method of reporting results and the evaluation criteria were quite different from those in use today. A renewed interest in these agents has been triggered by the remarkable activity of DON and azotomycin against human tumor lines implanted into nude mice. On the basis of this activity and the clinical data we have compiled, we feel that new clinical trials with these agents are warranted.

Animals↗
PubMed1987

Effects of dietary fats and soybean protein on azaserine-induced pancreatic carcinogenesis and plasma cholecystokinin in the rat.

Both dietary unsaturated fat and raw soybean products are known to enhance pancreatic carcinogenesis when fed during the postinitiation phase. A comparison of these two dietary components was made to evaluate the relative potency of each ingredient for enhancing pancreatic carcinogenesis and to determine if this enhancement was correlated with an increase in plasma cholecystokinin (CCK) levels. Male Wistar rats were initiated with a single dose of azaserine (30 mg/kg body weight) at 14 days of age. The rats were weaned to test diets formulated from purified ingredients. Dietary protein at 20% by weight was either casein or soy protein isolate (heat treated or raw). Corn oil was the unsaturated fat of major interest and it was fed at either 5 or 20% by weight. Pancreases were quantitatively evaluated for carcinogen-induced lesions at 2- and 4-month postinitiation. In a second experiment designed to closely mimic the above experiment, rats were implanted with cannulae which allowed plasma to be repetitively sampled over a 2.5-week period during which the test diets were fed. Plasma was collected both prior to introduction of the test diets and afterwards. Plasma CCK was measured by a specific radioimmunoassay. Both the 20% corn oil diet and the raw soy protein isolate diet enhanced pancreatic carcinogenesis. The effects of the raw soy protein isolate on the growth of the carcinogen-induced lesions were significantly greater than the effects of the 20% corn oil diet. Plasma CCK values were not elevated in the rats fed the 20% corn oil diet, but they were significantly elevated in the rats fed the raw soy protein isolate. Heat-treated soy protein isolate neither enhanced carcinogenesis nor elevated the plasma CCK level. This study demonstrates that certain plant proteins enhance the growth of carcinogen-induced pancreatic foci and that this effect is considerably greater than the enhancement by high levels of dietary unsaturated fat. Furthermore, the enhancement by the raw soy protein isolate may be mediated by CCK; but this does not appear to be the mechanism by which the unsaturated fat, corn oil, enhances pancreatic carcinogenesis.

Animals↗
PubMed1985

Monoclonal antibodies against tumour-associated antigens: mycoplasma as a major technical obstacle and its possible circumvention by azaserine selection medium.

In experiments aimed at generating monoclonal antibodies against tumour associated antigens, mice are usually immunized with cancer cells (or membrane fractions prepared from it) obtained from surgery or cultured in vitro. In both situations there is the danger of introducing mycoplasmas into the hybridoma cultures even if the myeloma cell line and the mice used for immunization or feeder cell preparation are not infected. Mycoplasmas kill hybridoma cells during HAT selection because they excessively degrade thymidine. The use of azaserine instead of aminopterin in hybrid selection circumvents the necessity for thymidine and therefore may allow survival and growth of hybridomas in the presence of mycoplasmas.

Animals↗
PubMed1985

[Inactivation of microbial glutamin-(asparagin-)ase by azaserine and 6-diazo-5-oxo-L-norleucine].

The effect of substrate analogues on glutamin-(asparagin-)ase from Pseudomonas aurantiaca-548 has been studied. The enzyme was demonstrated to be highly sensitive to the the action of 6-diazo-5-oxo-L-norleucine and azaserine. L-isomers of glutamine, aspartate, glutamate and several other substrate analogues with free alpha-amino groups protected the enzyme against the inhibitory DON effect. Thus, thorough preliminary selection of appropriate inhibitors, their dosage and treatment duration is needed for the recommendation of combined enzyme-inhibitor application in anti-tumour chemotherapy.

Amidohydrolases↗
PubMed1983

Exclusion of cellular iron and reduced gamma-glutamyl transpeptidase activity in rat pancreas acinar cell hyperplastic nodules and adenomas induced by azaserine.

Rat acinar cells in the azaserine-induced hyperplastic nodules or adenomas in the siderotic pancreas produced by repeated iron injections were found to be resistant to iron accumulation. These iron-resistant acinar cell lesions coincided rather well with the lesions having markedly decreased activity of gamma-glutamyl transpeptidase. These properties of the acinar cells could be useful for the identification of early lesions in pancreatic carcinogenesis.

Adenoma↗
PubMed1981

Dietary modulation of azaserine-induced pancreatic carcinogenesis in the rat.

Because diet has been shown to modulate the incidence of a wide variety of chemically induced cancers in experimental animals, various dietary constituents were evaluated for their ability to modulate the incidence of pancreatic exocrine cancer in male Wistar/Lewis rats given injections of the pancreatic carcinogen, azaserine. Ten different diet regimens were fed. The incidence of pancreatic cancers in rats fed a control diet was compared to that in groups fed diets formulated to evaluate the effect of caloric restriction, high protein, low protein, low fat, cyclopropenoid fatty acids, lipotrope deficiency, high unsaturated fat, and high saturated fat. The incidence of pancreatic adenomas and carcinomas was evaluated by light microscopy. The number of pancreatic neoplasms was reduced in carcinogen-treated groups which were underfed the control diet or fed the diet high in protein. Pancreatic carcinogenesis appeared to be enhanced in two groups which were fed diets containing 20% corn oil, i.e., high in unsaturated fat; whereas, the group fed a diet high in saturated fat had the same incidence of neoplasms as did the group fed the control diet. The pancreatic neoplasms from groups in which the incidence was enhanced by diet showed less evidence of acinar cell differentiation and displayed diverse histological types. In the lipotrope-deficient group, there was a significantly increased incidence of hepatocellular carcinoma; however, a low incidence of liver tumors was encountered in all other dietary groups.

Adenocarcinoma↗