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Biomedical subjects

P K Chakravarty

Publications and source records attributed to P K Chakravarty.

At least 19 recordsLinked to original sources
PubMed2000

Pregnancy induced mammary tumor specific effector cells are present long after parturition in a breast cancer model in rats.

Pregnancy is known to provide protection against 7,12 dimethylbenz[a]anthracene-(DMBA) induced mammary carcinogenesis in rats. We observed in earlier studies that splenocytes of parous rats have significant cytotoxicity against mammary tumor cells both in vitro and in vivo. However, it remains to be established how long these cytolytic cells persist after parturition in parous host. The present study was designed using parous rats, 36 or more days after parturition. We observed that fresh splenocytes from these rats had low cytolytic activity against mammary tumor cells. However, when these cells were re-stimulated with irradiated mammary tumor cells in vitro, they had significantly higher cytotoxicity against mammary tumor cells. These studies show for the first time that pregnancy induced cytotoxic splenocytes are present long after parturition and they can be restimulated in vitro to enhance the cytotoxic effect.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1999

Flt3-ligand administration after radiation therapy prolongs survival in a murine model of metastatic lung cancer.

An ineffective tumor-specific immune response from inadequate/incompetent antigen presentation could contribute to the failure in tumor control and its dissemination. Dendritic cells (DCs) have been shown to present antigen from apoptotic cells. We hypothesized that Flt3-ligand (Flt3L) therapy, which expands DCs in vivo, in combination with local tumor radiotherapy (RT), should improve antigen presentation from dying, irradiated tumor cells. RT + Flt3L reduced pulmonary metastases in a murine model of Lewis lung carcinoma and significantly improved survival in C57Bl/6 mice with established footpad tumors. Mice treated with Flt3L alone showed delayed tumor growth but eventually succumbed to tumor progression. The combination therapy of RT + Flt3L failed to impact survival in immunodeficient athymic mice, implicating the role of T cells in prolonging survival. These results support an attractive strategy of sequential RT and immunotherapy with Flt3L to enhance tumor antigen presentation, which may produce therapeutic responses against disseminated cancer and improvement in survival.

Animals↗
PubMed1996

Pharmacology of L-744,453, a novel nonpeptidyl endothelin antagonist.

L-744,453 ((+/-)3-[4-(1-carboxy-1-(3,4-methylenedioxyphenyl)methoxy)-3,5-diprop ylphenyl methyl]-3H-imidazo[4,5-c]pyridine) is an endothelin (ET) receptor antagonist from a new structural class, the dipropyl-alpha-phenoxyphenylacetic acid derivatives. L-744,453 competitively and reversibly inhibits [125I]-ET-1 binding to Chinese Hamster Ovary cells expressing cloned human ET receptors (K(i)s: hET(A)=4.3 nM; hET(B)=232 nM), and is selective for endothelin receptors compared to other peptide receptors. It is an antagonist of ET-1 stimulated phosphatidyl inositol hydrolysis in rat uterine slices (IC50=220 nM) and exhibits no agonist activity. This compound also inhibits ET-1 stimulated contraction of rat aortic rings with a K(b) value of 50 nM. L-744,453 protects against ET-1 induced lethality in mice after i.v. (AD50=13 mg/kg i.v.) or oral administration. This compound also antagonizes ET-1 induced increases in diastolic blood pressure in conscious normotensive rats (AD50=0.67 mg/kg i.v.) and anesthetized ferrets (AD50=1.6 mg/kg i.v.). L-744,453 is a potent, selective, orally active endothelin antagonist which may be useful in elucidating the role of endothelin in normal and pathophysiological states.

Animals↗
PubMed1996

In vivo effect of chemically induced fibrosarcoma on copper metabolism of liver in mice.

Copper and ceruloplasmin concentrations were determined in different subcellular fractions of liver of mice bearing benzo(a)pyrene induced fibrosarcoma. Though the copper content was elevated in the nuclear, mitochondrial and lysosomal fractions of tumor bearing mice, the microsomal and soluble supernatant fractions showed a downward trend in their copper concentration when compared to the controls. Similarly, ceruloplasmin concentration in the different subcellular fractions also showed variable results. This study was aimed to ascertain the distribution of copper. The incorporation of radioactive copper in different fractions was also monitored. The possible reasons for the variation in copper and ceruloplasmin concentrations observed during malignancy in the tumor bearing animals, has been discussed.

Animals↗
PubMed1995

In vivo pharmacology of a novel AT1 selective angiotensin II receptor antagonist, MK-996.

MK-996, N-(4'-(5,7-dimethyl-2-ethyl-3H-imidazo[4,5-b]pyridin-3-yl- methyl)1,1'-biphenyl-2-yl)-sulfonylbenzamide, is a potent, orally active, highly selective, nonpeptide angiotensin II (AII) receptor antagonist. MK-996 prevents the pressor response to intravenous AII in the conscious rat, dog, and rhesus monkey (ED50, mg/kg; oral/intravenous = 0.067/0.014, 0.035/0.017, and 0.1/0.036, respectively). In the anesthetized chimpanzee, MK-996 (1 mg/kg, iv) produces 100% (peak) inhibition of the AII pressor response and is still active (52%) at 24 h. To our knowledge this pharmacologic profile in the rat, dog, rhesus monkey, and chimpanzee presents the least species variability of any AII receptor antagonist yet described. Responses to methoxamine and arginine vasopressin are not affected by MK-996. In aortic coarcted (high renin) rats, MK-996 (3 mg/kg, by mouth) reduces blood pressure to normotensive (< 120 mm Hg) levels without reflex tachycardia. This dose of MK-996 reduces blood pressure to approximately the same level as both losartan (3 mg/kg, by mouth) and enalapril (3 mg/kg, by mouth) in this model. The duration of antihypertensive activity of MK-996 is similar to enalapril and shorter than losartan at the doses tested. Additionally, in the rat MK-996 does not potentiate the vasodepressor response to bradykinin and completely prevents the ability of AII to stimulate an increase in plasma levels of aldosterone. Therefore, MK-996 is a potent, orally active, nonpeptide AII receptor antagonist with a long duration of action, little species variability, and anti-hypertensive activity.

Administration, Oral↗
PubMed1995

Biotransformation of losartan to its active carboxylic acid metabolite in human liver microsomes. Role of cytochrome P4502C and 3A subfamily members.

Losartan is a 4-chloro-5-hydroxymethylimidazole derivative that is a potent and highly selective angiotensin II receptor antagonist. Losartan is metabolized in vivo in rats, monkeys, and humans to a carboxylic acid derivative E3174 that is pharmacologically more active than the parent compound. We have investigated the mechanism of this biotransformation in human liver preparations. The oxidation of both losartan and the putative aldehyde intermediate E3179 was catalyzed by the microsomal fraction, required both NADPH and molecular oxygen, and was inhibited by SKF 525-A, implicating cytochrome P450 (CYP). When incubations with each substrate were performed under an atmosphere of 18O2, the extent of 18O incorporation into the carboxylic acid product was consistent with a mechanism for losartan oxidation involving an aldehyde intermediate. To substantiate the involvement of CYP in these reactions, incubations with losartan and the aldehyde E3179 were performed in the presence of isoform-selective inhibitors. Inhibitors of CYP3A4/5 (gestodene and ketoconazole) and CYP2C9/10 (sulfaphenazole) attenuated the oxidation of both substrates. It was then demonstrated that microsomes containing either recombinant human liver CYP2C9 or CYP3A4 were capable of oxidizing both losartan and the aldehyde E3179 to the carboxylic acid E3174. Subsequently, it was shown that rabbit anti-CYP2C9 and anti-CYP3A3/4 inhibited the oxidation of losartan to E3174 in incubations with human liver microsomes. These studies support the hypothesis that the aldehyde E3179 is an intermediate in the oxidation of losartan and that this two-step reaction is catalyzed in human liver microsomes by members of the CYP3A and CYP2C subfamilies.

Adult↗
PubMed1994

Plasma and erythrocyte copper level as an indicator of disease activity during malignancy.

Copper and zinc concentrations in erythrocytes, plasma and whole blood were determined in mice bearing spontaneous-, transplanted- and benezo[a]pyrene-induced-tumour. The transplanted tumours studied were Sarcoma 180, Ehrlich carcinoma, and Dalton's lymphoma. Copper concentration in the malignant-tumour-bearing mice showed significant increases in erythrocytes and plasma, when compared with their normal controls. However, the zinc concentrations, although depressed in the different constituents of blood, were not significant enough to warrant any attention. Utilization of erythrocyte copper level as an additional marker of cancer activity is discussed.

Animals↗
PubMed1994

Triazolinone biphenylsulfonamide derivatives as orally active angiotensin II antagonists with potent AT1 receptor affinity and enhanced AT2 affinity.

Several series of 2,4-dihydro-2,4,5-trisubstituted-3H-1,2,4-triazol-3-ones with acidic sulfonamide replacements of tetrazole at the 2'-position of the biphenyl-4-ylmethyl side chain at N4 were prepared and tested as angiotensin II (AII) antagonists. Preferred substituents on the triazolinone ring were n-butyl at C5 and 2-(trifluoromethyl)phenyl at N2. Subnanomolar IC50 values at the AT1 receptor subtype were observed for a variety of acylsulfonamides, including aroyl, heteroaroyl, and cycloalkylcarbonyl derivatives. Certain other acidic sulfonamides, such as sulfonylcarbamates and disulfimides also displayed high affinity for the AT1 receptor. In addition, AT2 binding for some of these compounds was increased by as much as 1000-fold over the corresponding tetrazole (e.g., AT2 IC50 17 nM for the tert-butyl sulfonylcarbamate 92). When evaluated for inhibition of the AII pressor response, the benchmark benzoylsulfonamide 9 (L-159,913) was efficacious in several species and was superior to losartan (1a) in conscious rhesus monkeys. Several subsequent analogues, including the 2-chlorobenzoyl (18), (3-chlorothiophene-2-yl)carbonyl (51), ((S)-2,2-dimethylcyclopropyl)carbonyl (80), and tert-butoxycarbonyl (92) derivatives, were highly effective in rats, surpassing 9 and losartan in duration of action and/or potency. Compound 18 (L-162,223) displayed very prolonged AII antagonism in the rat model (> 24 h at 1 mg/kg iv). At 1 mg/kg po in rats, 18 and 92 (L-162,234) produced 85-87% peak inhibition of the AII pressor response with duration exceeding 6 h. The identification of triazolinone-based sulfonamide derivatives combining high AT1 affinity, considerably enhanced AT2 potency, and favorable in vivo properties provides insights relevant to the design of dual AT1/AT2 receptor antagonists.

Angiotensin II↗
PubMed1994

Effect of fibrosarcoma induction on copper and ceruloplasmin concentration in different organs of the host.

The copper content and ceruloplasmin activity were determined in mice bearing benzo(a)pyrene induced fibrosarcoma. The copper level and ceruloplasmin activity in different organs of fibrosarcomatous mice varied when compared to their controls. Significant changes in copper and ceruloplasmin concentration were observed in the liver and tumor tissue of host mice bearing fibrosarcoma compared to controls. Disturbed copper metabolism at the hepatic level may account for the hypercupremia observed during malignancy.

Animals↗
PubMed1992

Tumorigenicity of interleukin-2 (IL-2)-cDNA-transfected L1210 lymphoma and its in vivo variants is modulated by changes in IL-2 expression; potential therapeutic implications.

To study parameters that affect the tumorigenicity of L1210 lymphoma we have analyzed the structure of MHC class I antigens of this tumor. In addition this tumor was transfected with interleukin-2 (IL-2) cDNA in order to determine the effects of high concentrations of IL-2 within the tumor environment. The nucleotide sequence of the class I Kd, Dd and Ld mRNAs from this tumor showed that the encoded amino acid sequence of the corresponding antigens is normal, thus suggesting that the tumorigenicity of L1210 lymphoma is not due to defective antigen presentation to tumor-specific cytotoxic T cells. In contrast, induction of IL-2 expression by cDNA transfection led to loss of tumorigenicity of the IL-2-secreting tumor cells. However, a fraction of long-term-surviving mice developed progressively growing variant tumors that showed substantial decrease or loss of IL-2 expression. These results suggest that IL-2 secretion by tumors is suicidal but, because of tumor heterogeneity, IL-2-loss-variant tumors may arise that are able to escape the immune defenses of the host. The observed consistent loss of IL-2 expression in variant tumors implies that specific targeting of large quantities of IL-2 to tumor cells may be a valuable approach to immunotherapy of cancer. In addition we find that under specific gamma ray irradiation IL-2-secreting tumor cells lose their ability to multiply yet continue to secrete IL-2 at levels equivalent to those secreted by unirradiated cells. Such IL-2-secreting irradiated tumor cells were found to be superior immunogens in comparison to the irradiated parental tumor cells, suggesting their use as tumor vaccines.

Animals↗
PubMed1992

Pregnancy-induced antitumor cytotoxicity of T cell-rich fraction against mammary adenocarcinoma cells in rats.

Our earlier observations indicated that splenocytes from parous rats have high cytotoxic activity against mammary tumor cells in vitro. It has also been observed that this cytotoxic activity of splenocytes from parous rats can be adoptively transferred to virgin rats of same age. The present investigation is an attempt to determine the cell type in spleens of parous rats that cause the cytotoxicity against mammary tumors. The spleens from both virgin and parous rats were removed aseptically and T and B cell-rich fractions were separated. 7,12-Dimethylbenz[a]anthracene-induced rat mammary tumor epithelial cells were used as targets and the T and B cell-rich fractions from either virgin or parous rats were used as effectors. The parous rats were divided into two groups according to the time period after parturition. Group I contained rats that were 5-13 days after delivery, while the rats in group II were 14 or more days post parturition. In vitro cytotoxicity was determined by incubating the tumor cells with spleen cells in the target/effector ratio of 1:3, 1:10 and 1:30 and using the standard 51Cr release assay. In all ratio groups of T cell-rich fractions particularly in group II, there was significantly higher cytotoxicity against mammary tumor cells. None of the B cell-rich fractions from parous rats were significantly more cytotoxic than those from virgin controls.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1992

In vitro pharmacology of L-158,809, a new highly potent and selective angiotensin II receptor antagonist.

L-158,809 interacted in a competitive manner with rabbit aortic angiotensin II (AII) receptors as determined by Scatchard analysis of the specific binding of [125I]Sar1Ile8-AII. The affinity of L-158,809 (IC50 = 0.3 nM) for AII receptors in this tissue was appreciably greater than that of other reported nonpeptide AII antagonists such as DuP-753 (IC50 = 54 nM) and EXP3174 (IC50 = 6 nM) and similar to the natural ligand, AII. L-158,809 also exhibited a high potency at AII receptors in several other tissues from different animal species (IC50 = 0.2-0.8 nM). In vitro functional assays utilizing AII-induced aldosterone release in rat adrenal cortical cells demonstrated further that L-158,809 acts as a competitive, high affinity antagonist of AII (pA2 = 10.5) and lacks agonist activity. L-158,809 also potently inhibited AII-induced inositol phosphate accumulation in vascular smooth muscle cells and contractile responses to AII in isolated blood vessels. The specificity of L-158,809 for AII receptors was demonstrated by its lack of activity (IC50 greater than 1 microM) in several other receptor binding assays and its inability to affect in vitro functional responses produced by other agonists. L-158,809 demonstrated a very high selectivity for the AT1 compared to the AT2 receptor subtype (AT2 IC50 greater than or equal to 10 microM). The high affinity and selectivity makes L-158,809 a valuable new tool for investigating the physiological and pharmacological actions of AII.

Aldosterone↗
PubMed1992

In vivo pharmacology of L-158,809, a new highly potent and selective nonpeptide angiotensin II receptor antagonist.

L-158,809 (5,7-dimethyl-2-ethyl-3-[[2'-(1H-tetrazol-5yl)[1,1']-bi- phenyl-4-yl]-methyl]-3H-imidazo[4,5-b]pyridine) is a potent, competitive and specific antagonist of AT1 subtype of angiotensin II (AII) receptors in in vitro radioligand binding and functional isolated tissue assays. The present study was carried out to characterize the in vivo pharmacology of this potent AII receptor antagonist. In conscious, normotensive and anesthetized pithed rats, L-158,809 inhibits AII (0.1 microgram/kg i.v.) elevations in blood pressure without altering pressor responses to methoxamine or arginine vasopressin. In conscious rats, the relative potencies (ED50) were 29 micrograms/kg i.v. and 23 micrograms/kg p.o. Duration of action with single i.v. or p.o. doses exceeded 6 hr in rats. In similar experiments using rhesus monkeys, the potencies of L-158,809 were 10 micrograms/kg i.v. and approximately 100 micrograms/kg p.o. In these rats and monkeys, L-158,809 was 10 to 100 times more potent than DuP-753 (losartan) and approximately 3 times more potent than the metabolite, EXP3174. AII-induced elevation of plasma aldosterone in rats was also inhibited by L-158,809. Unlike angiotensin converting enzyme inhibitors, L-158,809 did not potentiate the hypotensive responses to i.v. bradykinin. L-158,809 was antihypertensive in high renin hypertensive rats (aortic coarction) and volume-depleted rhesus monkeys. The maximum hypotensive responses with acute doses of L-158,809 were equal to those with an angiotensin converting enzyme inhibitor in these renin-dependent animal models. From these in vivo data, L-158,809 is a selective AII receptor antagonist with high potency, good p.o. absorption, long duration and antihypertensive efficacy equal to angiotensin converting enzyme inhibition after single doses.

Administration, Oral↗
PubMed1991

Inhibition of mammary tumorigenesis in virgin rats by adoptive transfer of splenocytes from parous donors.

Splenocytes from parous rats have been previously found to have cytotoxic activity against mammary tumor cells in vitro. Experiments were carried out to determine if this pregnancy-induced cytotoxic nature of the splenocytes is inherent and transferable. Splenocytes from parous rats wer adoptively transferred to a group of virgin rats. Another group of age-matched, virgin rats received splenocytes from virgin donors in a similar way. After a period of rest, at the age of 55 days, the rats belonging to both of the groups, received 7,12-dimethylbenz(a)anthracene (DMBA) intragastrically. A third group of untreated virgin rats were also given the chemical carcinogen the same way as above and were considered as intact controls. The rats were monitored for development and growth of mammary tumor from 60 days of DMBA administration. After 4 months of DMBA administration the rats were sacrificed and mammary glands were examined for tumors. Mammary glands with no visible tumors were taken for whole mount preparation, to be examined for microscopic lesions. The results showed that 33 of 41 intact control rats, developed tumor and 27 of the 34 rats that received spleen cells from virgin rats developed tumors. Of the rats that received spleen cells from parous rats, only 18 out of 37 rats developed tumors, indicating an inhibition of tumor induction in these rats. Growth rate of the tumors in this group was also slower than in the control groups.

Animals↗
PubMed1991

Pregnancy-induced cytotoxicity of splenocytes against mammary tumor cells in rats.

Our earlier observations indicate the possibility of involvement of a 'host factor' in pregnancy-induced protection against mammary carcinogenesis. The present investigation is an attempt to determine if this "host factor" is of immunological nature. Rat mammary tumors induced by 7,12-dimethylbenz[a]anthracene were used as target, and splenocytes from parous rats of the same strain were used as effector cells. The parous rats were divided into two groups according to the time period after parturition. Group 1 contained rats which were 5-13 days after delivery, group 2 had rats 14 or more days after parturition. In vitro cytotoxicity was determined by incubating the tumor cells with spleen cells in the target:effector ratios of 1:3, 1:10 and 1:30. Both groups 1 and 2 showed significant lysis of mammary tumor cells. These results were confirmed by the trypan blue exclusion test. The results showed a significantly higher cytotoxic capability of the spleen cells from parous rats against mammary tumor cells as compared to spleen cells from age-matched nulliparous rats.

Animals↗