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M Dalal

Publications and source records attributed to M Dalal.

29 records · Page 2Linked to original sources
PubMed1987

A simple method for the rapid determination of the stereospecificity of NAD-dependent dehydrogenases applied to mammalian IMP dehydrogenase and bacterial NADH peroxidase.

The stereospecificity of IMP dehydrogenase (IMP:NAD+ oxidoreductase, EC 1.1.1.205) from two different sources was determined. The enzyme preparations were obtained from murine lymphoblasts and from Escherichia coli. Both enzymes transferred the 2-3H of IMP to the pro-S position of carbon atom C-4 of the nicotinamide ring in NAD. Thus, B-sided stereospecificity is common to the enzyme from two very different species. In addition, the studies described here demonstrate that alcohol dehydrogenase and NADH peroxidase, used as auxiliary enzymes, in combination with a microdistillation procedure, should permit rapid determination of the stereospecificity of any NAD-dependent dehydrogenase for which the appropriate tritiated substrate is available.

Alcohol Dehydrogenase↗
PubMed1987

2',3'-Dideoxycytidine: regulation of its metabolism and anti-retroviral potency by natural pyrimidine nucleosides and by inhibitors of pyrimidine nucleotide synthesis.

The antiretroviral action of 2',3'-dideoxycytidine (ddCyd) depends on its intracellular conversion to the 5'-triphosphate metabolite ddCTP. The effect of natural pyrimidines and pyrimidine nucleosides, as well as of a number of inhibitors of pyrimidine nucleotide synthesis (i.e., N-(phosphonacetyl)-L-aspartate, 6-azauridine, pyrazofurin, 3-deazauridine, and hydroxyurea) on the metabolism of the potent anti-human immunodeficiency virus drug ddCyd has been investigated in human and murine cell lines. Deoxycytidine (dCyd) and cytidine (Cyd) effectively blocked the intracellular phosphorylation of ddCyd: dCyd by competition with ddCyd for 2'-deoxycytidine kinase, and Cyd probably by competition with the higher nucleoside mono- and diphosphate kinases. These conclusions are supported by the observations that (i) the cytostatic effects of ddCyd against human Molt/4F cells are significantly reversed by dCyd; (ii) the antiviral effects of ddCyd against hman immunodeficiency virus-infected human ATH8 cells are reversed by dCyd and Cyd; (iii) phosphorylated metabolites of ddCyd could not be detected in a 2'-deoxycytidine kinase-deficient murine leukemia (L1210)/araC cell line; and (iv) ddCyd lacked any cytostatic effect against this araC-resistant L1210 cell line. In contrast to dCyd and Cyd, thymidine (dThd) stimulated formation of phosphorylated ddCyd metabolites. The degree of this stimulation proved dependent on preincubation time and dThd concentration. There was a correlation between the increased ddCTP levels upon preincubation of the cells with dThd, and decreased dCyd-5'-triphosphate pools, presumably caused by inhibition of cytidine-5' -diphosphate reductase by dThd-5'-triphosphate. In an attempt to discover compounds other than dThd that are able to stimulate ddCTP formation, a number of inhibitors of pyrimidine nucleotide metabolism were also studied. Under our experimental conditions, 3-deazauridine and hydroxyurea proved equally as effective as dThd in stimulating ddCyd phosphorylation. Finally, we could demonstrate that dThd significantly enhanced the protective effect of ddCyd against human immunodeficiency virus-infected ATH8 cells.

Animals↗
PubMed1987

The anti-HTLV-III (anti-HIV) and cytotoxic activity of 2',3'-didehydro-2',3'-dideoxyribonucleosides: a comparison with their parental 2',3'-dideoxyribonucleosides.

A series of 2',3'-didehydro-2',3'-dideoxyribonucleosides (ddeNs) [i.e., 2',3'-dideoxythymidinene (ddeThd), 2',3'-dideoxyuridinene (ddeUrd), 2',3'-dideoxycytidinene (ddeCyd), and 2',3'-dideoxyadenosinene (ddeAdo)] has been synthesized and the individual members compared in terms of their in vitro antiviral, antimetabolic, and cytostatic properties to their 2',3'-saturated counterparts (ddNs) (i.e., ddThd, ddUrd, ddCyd and ddAdo). All ddeNs except ddeUrd are potent and/or selective inhibitors of human immunodeficiency virus (HIV) in vitro, ddeCyd being the most potent (MIC50, 0.30 microM). The inhibitory effect of ddeCyd on ATH8 cell proliferation and HIV-induced cytopathogenicity is comparable to that of ddCyd. ddeThd is a more potent anti-HIV agent than ddThd (MIC50, 3.4 microM and 84 microM, respectively), but also more cytostatic (ID50, 172 microM and greater than 2000 microM, respectively). However, its in vitro chemotherapeutic index is higher than that of 3'-azido-2',3'-dideoxythymidine, a drug which has recently proven effective in the treatment of acquired immunodeficiency syndrome. ddeAdo has a weaker anti-HIV and a stronger cytostatic effect than ddAdo. Neither ddeUrd nor ddUrd shows significant anti-retroviral activity at 500 microM. In contrast to their anti-retroviral activity, both ddNs and ddeNs lack any appreciable inhibitory activity against a series of nononcogenic RNA and DNA viruses, pointing to their selectivity as anti-retroviral agents. All ddeNs show a progressive loss of anti-retroviral effect upon prolonged incubation with virus-infected cells. This phenomenon is most likely due to the chemical instability of these compounds, and not to a preferential enzymatic phosphorolytic cleavage of the ddeNs. Evidence is presented that ddeCyd and ddCyd, and ddeThd and ddThd are phosphorylated by cellular dCyd kinase and dThd kinase, respectively. However, the Ki values as alternate substrate inhibitors for their respective kinases are high (greater than 500 microM), indicating poor substrate activity and, thus, poor anabolism in ATH8 cells.

Animals↗
PubMed1986

Potent and selective anti-HTLV-III/LAV activity of 2',3'-dideoxycytidinene, the 2',3'-unsaturated derivative of 2',3'-dideoxycytidine.

2',3'-Dideoxycytidinene (ddeCyd), the 2',3'-unsaturated derivative of 2',3'-dideoxycytidine (ddCyd) is, like ddCyd itself, a potent and selective inhibitor of HTLV-III/LAV in vitro. This conclusion is based on the relatively high ratio of effective antiviral dose (0.3 microM) versus cell growth inhibitory concentration (20-35 microM) and the lack of any appreciable inhibitory activity against a series of non-oncogenic RNA and DNA viruses. Both compounds were considerably more inhibitory to human lymphoid cell lines than human nonlymphoid or murine cell lines. They were highly dependent on prior activation by deoxycytidine kinase to exert their anti-HTLV-III/LAV and cytostatic effects. In contrast with ddCyd, ddeCyd lost part of its anti-retrovirus effect upon prolonged incubation (10 days) with the virus-infected cells in culture.

Animals↗
PubMed1986

Thiazole-4-carboxamide adenine dinucleotide (TAD). Analogues stable to phosphodiesterase hydrolysis.

Thiazole-4-carboxamide adenine dinucleotide (TAD), the active metabolite of the oncolytic C-nucleoside tiazofurin (TR), is susceptible to phosphodiesteratic breakdown by a unique phosphodiesterase present at high levels in TR-resistant tumors. Since accumulation of TAD, as regulated by its synthetic and degradative enzymes, appears to be an important determinant for sensitivity to the drug, a series of hydrolytically resistant phosphonate analogues of TAD were synthesized with the intent of producing more stable compounds with an ability to inhibit IMP dehydrogenase equivalent to TAD itself. Isosteric phosphonic acid analogues of TR and adenosine nucleotides were coupled with activated forms of AMP and TR monophosphate to give dinucleotides 2 and 4. Coupling of protected adenosine 5'-(alpha, beta-methylene)diphosphate with isopropylidene-TR in the presence of DCC afforded compound 3 after deprotection. These compounds are more resistant than TAD toward hydrolysis and still retain potent activity against IMP dehydrogenase in vitro. beta-Methylene-TAD (3), the most stable of the TAD phosphonate analogues, produced a depletion of guanine nucleotide pools in an experimentally induced TR-resistant P388 tumor variant that was superior to that obtained with TR in the corresponding sensitive line.

Adenine Nucleotides↗
PubMed1986

Arabinofuranosyl-5-azacytosine: antitumor and cytotoxic properties.

Arabinofuranosyl-5-azacytosine (ara-AC), a nucleoside combining the structural elements of 5-azacytidine and arabinofuranosylcytosine, exhibited unusually wide therapeutic activity against several murine leukemias and all three human xenografts of the National Cancer Institute tumor panel. Activity was observed following either a daily or an intermittent regimen of treatment in the i.p. L1210 model. However, when multiple doses were administered on each treatment day, a greater therapeutic effect was produced and the total dose was reduced. Extensive necrosis was observed by light and electron microscopy in P388 tumors treated with ara-AC. Following s.c. administration, ara-AC caused regression of the mammary and lung xenografts (MX-1 and LX-1) and a 93% inhibition of the human colon tumor (CX-1); other analogues of this drug failed to demonstrate a comparably broad spectrum of activity. Morphological assessment of treated xenografts revealed a general loss of cell-to-cell contact and abundant necrosis 24 h after the administration of ara-AC. In culture, the 50% inhibitory concentrations of ara-AC for P388 and L1210 cells at 24 h were 1.9 and 4.5 microM, respectively, and the decline in replication rates was dependent on drug concentration. The cytocidal nature of the drug was demonstrated by cloning experiments in which it was observed that ara-AC abolished the clonogenicity of lymphoblasts but was only minimally cytotoxic to normal murine bone marrow progenitor cells. As adjudged by flow cytometry, the drug induced a distinct slowing of cell cycle traverse through S phase. Induction of the differentiation of HL-60 cells in culture was another cytotropic effect of this drug. At 44% differentiation (10 microM ara-AC), 50% of the cultured cells were viable. Its broad spectrum antitumor activity, its selective toxicity to tumor cells, and its ability to produce cytodifferentiation render ara-AC of interest as a potential antineoplastic agent in humans.

Animals↗
PubMed1986

Arabinosyl-5-azacytosine: mechanisms of native and acquired resistance.

Factors influencing the activity of the nucleoside analogue arabinosyl-5-azacytosine (ara-AC) were studied in P388 murine lymphoblasts in vitro and in vivo, in variants of these cells with artificially acquired resistance, in the naturally resistant colon 38 carcinoma in vivo, and in a panel of six human tumors maintained in continuous culture. Differences were noted not only between the sensitive and artificially developed resistant variants of P388, but also between the naturally sensitive (P388) and naturally resistant (colon 38) tumors. The artificially developed resistant P388 cell lines showed an inhibited capacity to accumulate nucleotides derived from ara-AC and deoxycytidine, whereas the accumulation of cytidine nucleotides remained unchanged. Studies of the initial velocity of facilitated diffusion of ara-AC showed only minor differences between parental and resistant lines, while the nucleotide formation rates from both ara-AC and deoxycytidine were markedly depressed in the latter cells. It is concluded, therefore, that the failure of resistant P388 cells to accumulate these compounds results not from a transport deficit per se but rather from a failure to convert the nucleosides to nondiffusible (i.e., phosphorylated) species inside the cell. This failure was accompanied by a substantial reduction in the incorporation of a radiolabeled product derived from deoxycytidine into the nucleic acids of the resistant clones. The common factor responsible for the resistance of P388 variants toward ara-AC appears to be a markedly decreased level of deoxycytidine kinase activity. The naturally resistant colon 38 carcinoma, on the other hand, in addition to a decrease in the activity of its deoxycytidine kinase, showed a lower level of activity of all its purine and pyrimidine kinases, along with a notably elevated nucleoside triphosphatase activity (with ATP as substrate) when compared to P388. These differences were reflected in lower endogenous nucleoside triphosphate pool sizes in colon 38, and in a lower level of ara-AC-5'-triphosphate accumulation in colon 38 than in P388 after comparable drug exposure. In the six human tumor lines, a positive correlation was established between sensitivity to ara-AC (as determined by its median inhibitory concentration) and cellular content of deoxycytidine kinase. It is concluded that this latter enzyme is a generally important determinant of sensitivity to arabinosyl-5-azacytosine.

Animals↗
PubMedDate not supplied

Epidemiological aspects of school dropouts in children between 7-15 years in rural Maharashtra.

A study on school dropouts from primary and secondary school children was undertaken in September '91 from 16 schools at the headquarters of 8 Primary Health Centres, where 172 school dropouts were identified. A home visit was paid and information about socio-economic and cultural aspects was collected and a psychological screening was undertaken. Although there was no significant difference in overall dropout rates for both sexes, it increased sharply at 11 years of age in girls. The majority of children dropped out due to financial problems or unsatisfactory scholastic performance, and 142 (82.5%) of the 172 children studied were poor performers in one or more function tests. Maximum difficulty was observed in concept formation 87 (50.5%), followed by numerical ability in 78 (45%). Identification of children with learning difficulties and intervention using special educational methods within the framework of existing network of primary and secondary schools in rural areas is suggested.

Adolescent↗