Search PubMed⌕ Search

Biomedical subjects

M S Chapekar

Publications and source records attributed to M S Chapekar.

25 records · Page 2Linked to original sources
PubMed1985

Synergistic effect of human immune interferon and double-stranded RNA against human colon carcinoma cells in vitro.

The cytocidal activity of human immune interferon (IFN-gamma) in combination with the synthetic double-stranded RNA, poly(I).poly(C), was investigated in human colon carcinoma cell line HT-29. Three days of treatment with IFN-gamma (10 to 25 units/ml) resulted in 30 to 40% reduction in colony formation, whereas poly(I).poly(C) (25 to 100 micrograms/ml) reduced cell viability by 10 to 20% of control. The lethal effect of the combination of IFN-gamma and poly(I).poly(C) was synergistic wherein 70 to 90% reduction in colony formation was observed. Measurements of DNA, RNA, and protein synthesis after IFN-gamma and poly(I).poly(C) treatment showed a dose-dependent reduction in all three parameters. Recombinant IFN-gamma in combination with poly(I).poly(C) exhibited a similar effect. Studies evaluating the molecular mechanism of IFN-gamma and poly(I).poly(C) toxicity indicate a lack of involvement of the double-stranded RNA-dependent (2',5')oligoadenylate-RNase L and protein kinase pathways; however, the effect appears to be related to the inhibition of ribosomal RNA transcription in this cell line.

2',5'-Oligoadenylate Synthetase↗
PubMed1984

Effects of human immune interferon on cell viability, (2',5')oligoadenylate synthesis, and polyamine-dependent protein phosphorylation in human colon carcinoma cells in vitro.

The growth-inhibitory effect of human immune interferon (IFN-gamma) was investigated in human colon carcinoma cell line HT-29. Three-day treatment of HT-29 cells with IFN-gamma (10 to 200 units/ml) resulted in 30 to 90% growth inhibition and 40 to 99% reduction in colony formation. Measurement of DNA, RNA, and protein synthesis following IFN-gamma treatment showed a dose-dependent reduction in all 3 parameters. The associated changes in (2',5')oligoadenylate [(2',5')oligo(A)] pathway were measured under growth-inhibitory conditions. Upon 1-day exposure to 25 to 200 units/ml of IFN-gamma, (2',5')oligo(A) synthetase activity was induced 10- to 15-fold and remained elevated for 3 days, whereas (2',5')oligo(A) phosphodiesterase activity remained unchanged. There was no detectable increase in intracellular (2',5')oligo(A) levels after IFN-gamma treatment, and ribosomal RNA degradation was not observed. Accompanying 1-day treatment with IFN-gamma (100 units/ml) was an induction of a polyamine-dependent protein kinase, which was double-stranded RNA-independent and phosphorylated endogenous polypeptides with molecular weights of 68,000 and 72,000. A similar exposure of cells to IFN-gamma (25 to 100 units/ml) resulted in 30 to 70% inhibition of ornithine decarboxylase activity; however, no significant alteration in intracellular polyamine levels was observed. These data suggest that IFN-gamma-dependent toxicity is not related to (2',5')oligo(A) activation of a latent endoribonuclease but is accompanied by protein phosphorylation, which is, in part, stimulated by exogenous polyamines.

2',5'-Oligoadenylate Synthetase↗
PubMed1983

Cordycepin analog of (A2'p)2A: evidence that it functions as a prodrug of cordycepin.

The effect of the cordycepin trimer analog of (A2'p)2A on cell growth, cell viability and nucleic acid synthesis was assessed in human colon carcinoma cell line HT-29 in vitro. The cordycepin analog, (3'dA2'p)2(3)'dA reduced 24 hr cell growth by 50% at 10(-4)M and decreased cell viability by 98% under these conditions. The cytotoxicity and inhibitory effects of (3'dA2'p)2(3)'dA on DNA and RNA synthesis were potentiated 5-10-fold by the presence of the adenosine deaminase inhibitor, 2'-deoxycoformycin, and closely resembled those of the parent drug, cordycepin. Chromatographic analyses of the stability of (3'dA2'p)2(3)'dA in the tissue culture medium indicated that it was hydrolyzed to the dimer and monomer forms with a half life of approximately 2 hr. No intact (3'dA2'p)2(3)'dA was detectable intracellularly, but large concentrations of cordycepin nucleotide metabolites were formed, particularly in the presence of 2'-deoxycoformycin.

Adenocarcinoma↗
PubMed1983

Role of antibody response helper factors in immunosuppressive effects of friend leukemia virus.

The primary antibody response of BALB/c splenocytes to sheep erythrocytes in vitro was suppressed by infection with Friend leukemia virus (FLV), with the response capacity decreasing with increasing duration of infection. The acquisition of normal antibody responses was amplified by macrophage-produced antibody response helper factor(s). FLV-infected mice were treated with bacterial lipopolysaccharide to induce the release of these helper factors into the serum. Similar to the loss of antibody response capacity by their splenocytes, the FLV-infected mice progressively lost the ability to produce helper factors in response to lipopolysaccharide. In vitro cultures of FLV-infected cells also showed a depressed ability to produce helper factor activity both spontaneously and in response to lipopolysaccharide stimulation. The reconstitution of normal levels of exogenous helper factors to FLV-infected splenocytes restored the antibody response to normal or even elevated levels. These studies indicate that the mechanism for suppression of antibody responses by FLV involves the depression of antibody response helper factor production.

Animals↗
PubMed1983

Effects of fibroblast and recombinant leukocyte interferons and double-stranded RNA on ppp(2'-5')An synthesis and cell proliferation in human colon carcinoma cells in vitro.

The antiproliferative effect of human fibroblast interferon (IFN-beta), human recombinant leukocyte interferon (IFN-alpha A), and polyinosinic . polycytidylic acid [poly(I) . poly(C)] was investigated in human colon carcinoma cell line HT-29. Exposure of HT-29 cells for 1 to 3 days with 100 to 2000 units of either interferon preparation resulted in a 30 to 50% inhibition of growth after 3 days. Similar treatment of cells with 100 micrograms per ml poly(I) . poly(C) resulted in progressive inhibition of growth by 50 to 60% in 2 to 3 days. The inhibitory effects of combination of either IFN-beta or IFN-alpha A with poly(I) . poly(C) were additive with up to 80 to 90% inhibition of cell growth after 3 days of exposure. None of the treatment regimens was markedly cytocidal, and only 25 to 30% reduction in colony formation was noted under optimal treatment conditions following 2 to 3 days of drug exposure. Measurements of DNA, RNA, and protein synthesis following interferon treatment indicated a dose-dependent reduction in all three parameters, particularly when interferon was administered with poly(I) . poly(C). The associated changes in the (2',5')oligoadenylate [(2',5')oligo(A)] pathway produced by IFN-beta and IFL-alpha A were measured under growth-inhibitory conditions. A concentration-dependent induction of (2',5')oligo(A) synthetase was produced by IFN-beta or IFL-alpha A with a concomitant decrease in (2',5')oligo(A) phosphodiesterase. Poly(I) . poly(C) alone induced (2',5')oligo(A) synthetase activity but had no effect on the associated activity of phosphodiesterase. The combination of either IFN-beta or IFL-alpha A and poly(I) . poly(C) further reduced (2',5')oligo(A) phosphodiesterase activity. There was no general dose-response correlation between the induction of (2',5')oligo(A) synthetase and the cytostatic activity of interferon treatment alone or in combination with double-stranded RNA.

2',5'-Oligoadenylate Synthetase↗