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Biomedical subjects

B K Bhuyan

Publications and source records attributed to B K Bhuyan.

At least 37 records · Page 2Linked to original sources
PubMed1987

Drug sensitivity of ten human tumor cell lines compared to mouse leukemia (L1210) cells.

L1210 leukemia cells, because of their rapid growth rate in suspension culture and high growth fraction, are ideally suited to screen in vitro for cytotoxic compounds. Although L1210 cells may mimic rapidly growing tumors, they have not been effective in selecting agents active against slow growing solid tumors. We expected that cell lines originating from human solid tumors, because of their slower growth rate and lower S phase fraction, would be more drug resistant than L1210. Therefore, we compared ten human tumor cell lines (5 melanomas, 4 colon carcinomas and 1 small cell lung carcinoma) to L1210 growth inhibition by 9 antitumor drugs. Not one human tumor cell line was consistently more resistant to all nine drugs than L1210 when the cells were exposed to drugs for about 2 doubling times. The drug sensitivity of 2 cell lines (L1210 and SK MEL 28) was again determined after a short term (2 hr) exposure and using growth inhibition and cell survival as end points. For both end points these two cell lines exhibited a random pattern of sensitivity to the drugs tested. Cell kill showed an order of sensitivity different than growth inhibition. The implication of these findings for drug-screening is discussed.

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PubMed1986

Cytotoxicity of combinations of prostaglandin D2 (PGD2) and antitumor drugs for B16 melanoma cells in culture.

Prostaglandin D2 (PGD2) is lethal to murine and human melanoma cells at high doses, but synchronizes cells at G1 at non-toxic doses (2.5 or 5 micrograms/ml). We tested the lethality to B16 mouse melanoma cells of combinations of PGD2 with anticancer drugs. The drugs selected were mostly those used in treating human melanoma: actinomycin D, Bleomycin, BCNU, cis-platin, melphalan, 5-fluorouracil, and 1-beta-D-arabinofuranosylcytosine (ara-C). PGD2 was combined with the drugs according to 3 different protocols: An asynchronous culture was given a long term (24 hr) exposure simultaneously to PGD2 + drug. Combinations with Bleomycin, ara-C or melphalan were additive or slightly antagonistic whereas PGD2 plus actinomycin D was significantly antagonistic. Cells synchronized in G1 by 24 hr PGD2 exposure were then given a short-term (2 hr) treatment with PGD2 + drug. Combinations with cis-platin, Bleomycin, BCNU or 5-fluorouracil were additive or slightly antagonistic, whereas melphalan and actinomycin D combinations were significantly antagonistic. Cells were released from a PGD2-induced G1 block and were exposed to drug at different times during cell progression. Actinomycin D was antagonistic when added immediately after release from the G1 block, but was significantly synergistic when added 10 to 12 hr later. The effect of the combinations cannot be explained by available cell cycle or biochemical information. The antagonism between PGD2 and several of the drugs resembles the "cytoprotective" effect of PGD2 towards various noxious agents.

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PubMed1986

Genotoxicity of the antitumor antibiotic CC-1065.

CC-1065, a very potent antitumor antibiotic, is active against several animal tumors, and against human tumors in the cloning assay at doses 50-1000 times lower than other agents such as adriamycin. It binds and alkylates DNA, and inhibits DNA synthesis, suggesting a potential for genotoxicity. Therefore, the genotoxic effects of CC-1065 were tested in several assay systems. CC-1065 was weakly mutagenic in the Ames Salmonella mutation assay (strain TA100) without S9 activation, but lacked mutagenic activity in TA98 with or without activation. CC-1065 was a very potent mutagen in the Salmonella forward mutation assay (induction of 8-azaguanine resistance), increasing the mutation frequency 19-fold over background at 0.1 ng/ml without activation. In mammalian (V79) cells it was a very potent mutagen without activation, increasing the mutation frequency 20-fold over background a 0.5 ng/ml. CC-1065 induced chromosome aberrations in V79 cells at very low (less than 0.1 ng/ml) doses, making this assay the most sensitive. CC-1065 increased the induction of micronuclei in rats 10- to 20-fold over the background at 200 and 400 micrograms/kg, but not at 100 micrograms/kg. CC-1065 failed to cause DNA breaks or DNA--protein cross-links as measured by the DNA damage/alkaline elution assay.

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PubMed1986

Effects of 7-R-O-methylnogarol (menogaril) on L1210 cell progression in vitro and in vivo.

Menogaril (7-R-O-methylnogarol) is an anthracycline which has significant antitumor activity in vivo and is in Phase II clinical trial. We report here the drug effect on growth and cell cycle progression of L1210 mouse leukemia cells in vitro and in vivo. At doses which inhibited the growth of L1210 cells in vitro, menogaril slowed the progression of cells through S phase and blocked cells in G2 + M. 7-R-O-Methyl-N-demethylnogarol, the major metabolite of menogaril had the same effects on cell progression in vitro. Menogaril effect on cell progression in vivo was studied with peritoneal L1210 ascites growing in CD2F1 mice. Early in infection, i.e., 3 days after inoculation of 10(5) L1210 cells, DNA histograms of cells from control and drug-treated mice showed only a G1 peak. This presumably represented host diploid G0-G1 cells which predominated in the peritoneal cavity and masked the histogram of L1210 cells. Later in infection, when about 10(8) or more cells were present in the ascites, L1210 cells predominated and DNA histograms were representative of L1210 cells. When menogaril was injected at this time, the cell cycle effects were similar to those seen in vitro. Therefore, the L1210 in vivo model can be used to study cell progression effects only late in infection (when L1210 cells predominate), and due consideration should be given to contamination of the L1210 cells with host G0-G1 cells.

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PubMed1986

Cell cycle effects of prostaglandins A1, A2, and D2 in human and murine melanoma cells in culture.

Our interest in prostaglandins (PGs) as antitumor agents stemmed from the report of Bregman and Meyskens (Cancer Res., 43: 1642-1645, 1983) that PGA1, PGA2, and PGD2 inhibited colony formation by human melanoma cells obtained from fresh biopsies of melanoma patients. We tested several PGs and found that PGA1, PGA2, and PGD2 were the most cytotoxic to L1210 cells in culture. Therefore, we studied these PGs for their effects on growth, cell survival, and cell progression of murine (B16) and human (RPMI7932,SK Mel 28) melanoma cells in culture. Although the three PGs equally inhibited the growth of B16 cells, PGD2 was more inhibitory to RPMI 7932 or SK Mel 28 than PGA1 or PGA2. Similarly the three PGs were almost equally active in inhibiting colony formation by B16 cells. However, against human melanoma cells, PGD2 was much more active than PGA1, whereas PGA2 was inactive. Towards the end of our study, we obtained PGJ2 and found that it was as cytotoxic as PGD2 for L1210 cells but was more lethal for human melanoma cells. The primary effect of all three PGs was to block cell progression from G1 to S. At 2.5 micrograms of PGD2 per ml, the blockade of cells in G1 and normal progression through the other phases resulted in accumulation of 80-90% of the cells in G1. At this dose, there was no inhibition of DNA synthesis, and cells in S progressed apparently normally through S, until all cells were blocked in G1. DNA synthesis was inhibited at 5 micrograms/ml which slowed cell progression through S and accumulated cells in G1. The partial synchronization of cells in G1 may be useful in devising new combinations of PGD2 with antitumor drugs.

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PubMed1985

Synergistic combination of menogarol and melphalan and other two drug combinations.

Menogarol is a new anthracycline undergoing phase I clinical trial. We report here the lethality after 2 hr exposure to 2 drug combinations of menogarol and several antitumor agents. A new statistical procedure was used to identify synergistic combinations. Most of these combinations were additive, except for menogarol plus melphalan, which was synergistic. Adriamycin plus melphalan was also synergistic. The menogarol-melphalan combination wa studied in detail with regard to the effect of dose and drug-schedule, lethality for exponential and plateau phase cells and effect on cell cycle progression. Although the combination was synergistic for exponential cells it was additive for plateau phase cells. The combination exerted a synergistic effect in inhibiting progression of cells through the cell cycle. After 2 hr menogarol exposure cells were blocked in G2 for about 12 hr following which the block was reversed. This reversal was inhibited when menogarol was combined with melphalan. The uptake of menogarol or melphalan was not changed in the presence of the other drug.

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PubMed1984

Biochemical and cellular effects of didemnins A and B.

Didemnins are a new class of cyclic depsipeptides in which didemnin A is the major component, didemnin B the minor component, and a trace of didemnin C is present. Didemnin B was more potent than was didemnin A against B16 melanoma and P388 leukemia in vivo, and B was also approximately 20 times more cytotoxic than was didemnin A in vitro. Therefore, didemnin B was studied in greater detail for its biochemical and cellular effects. Didemnin B inhibited the in vitro growth of B16 greater than L1210 greater than V-79 cells = human foreskin fibroblast = 9L greater than Chinese hamster ovary cells. Didemnin B was more lethal to exponentially growing B16 cells (50% lethal dose for a 2-hr exposure, 17.5 ng/ml) than to plateau-phase cells (50% lethal dose for a 2-hr exposure, 100 ng/ml). After a 24-hr exposure, the 50% lethal dose for exponential- and plateau-phase B16 cells was 8.8 and 59.6 ng/ml, respectively. Chinese hamster ovary cells were not killed even at 25,000 ng/ml. Mitotic cells were the least sensitive to didemnin B, and cells became more sensitive as they progressed into G1 and S phase. However, since cells in all phases were killed, didemnin B cannot be considered a phase-specific agent. Didemnin B inhibited the synthesis of protein more than that of DNA, with much less inhibition of RNA synthesis. Cell progression studies showed that high doses (300 ng/ml for 2 hr or 100 ng/ml for 24 hr) of didemnin B "froze" the cells in their respective phases with complete inhibition of cell progression or growth. At low doses (10 ng/ml for 2 hr or 3 ng/ml for 24 hr), the cells were blocked at the G1-S border thereby increasing the percentage of G1 cells and decreasing the percentage of S-phase cells. Cells continued to progress from S phase to G2 + M and from G2 + M to G1. The cytotoxicity to different cell lines and inhibition of macromolecule synthesis by didemnin A is also reported.

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PubMed1983

Comparative genotoxicity of adriamycin and menogarol, two anthracycline antitumor agents.

Adriamycin and menogarol are anthracyclines which cause more than 100% increase in life span of mice bearing P388 leukemia and B16 melanoma. Unlike Adriamycin, menogarol does not bind strongly to DNA, and it minimally inhibits DNA and RNA synthesis at lethal doses. Adriamycin is a clinically active drug, and menogarol is undergoing preclinical toxicology at National Cancer Institute. In view of the reported mutagenicity of Adriamycin, we have compared the genotoxicity of the two drugs. Our results show that, although Adriamycin and menogarol differ significantly in their bacterial mutagenicity (Ames assay), they have similar genotoxic activity in several mammalian systems. Adriamycin is strongly mutagenic in the Ames assay with TA98 and TA100. Menogarol is nonmutagenic to TA98 and TA100. For the mammalian cell culture systems, V79 (Chinese hamster) cells are exposed for 2 hr to drug, following which cell survival, induction of sister chromatid exchanges, chromosome damage, and production of mutants resistant to 6-thioguanine are measured. The percentage of survival obtained with the two drugs ranges between 25 and 50% at 0.15 microgram/ml and 5 to 15% at 0.3 microgram/ml. At 0.15 microgram/ml, Adriamycin and menogarol increase the percentage of cells with chromosome damage from a background level of 8.8 to 30 and 22.5%, respectively. The same drug concentration causes a small but significant increase in sister chromatid exchange rate. Both drugs are equally active (increase mutation frequency about 3- to 6-fold above background) in producing 6-thioguanine-resistant mutants. The induction of micronuclei in polychromatic erythrocytes of rats is the most sensitive assay system. Both drugs cause 10- to 15-fold increase in micronuclei at nontoxic doses.

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PubMed1983

Cell cycle effects of CC-1065.

CC-1065 is the most potent antitumor agent tested in our laboratory. It is lethal to B16 and CHO cells and to a variety of human tumors in the clonogenic assay at 1 ng/ml and is effective against L1210 leukemia and B16 melanoma in vivo at 1 to 50 micrograms/kg. CC-1065 inhibits DNA synthesis and binds to DNA in a nonintercalative manner in the minor groove. We report here the kinetics of inhibition of DNA synthesis and of cell progression and the phase-specific toxicity of the drug. To determine phase-specific toxicity, we started synchronous CHO cultures from mitotic cells harvested after Colcemid pretreatment. These cultures showed that mitotic cells were the most sensitive, and sensitivity decreased as the cells progressed through G1 to S and G2. Experiments with B16 and CHO mitotic cells harvested without Colcemid pretreatment also showed that mitotic cells were more sensitive than G1/S-phase cells. Cell progression studies showed that CC-1065 did not affect progression from mitosis to G1 or from G1 to S. Cells progressed slowly through S at low levels (1 ng/ml) of the drug but were blocked in S at 5 ng/ml. Cell progression from G2 to M was blocked by CC-1065. DNA synthesis in B16 cells was measured at different times after 2-hr exposure to CC-1065. The percentage of inhibition of DNA synthesis was minimum at 4 hr and maximum at 19 hr after drug exposure. Since B16 cell progression studies showed a marked change in percentage of S-phase cells during this time, the DNA synthesis rate was recalculated as cpm/S-phase cell. After this correction (i.e., expressing DNA synthesis as cpm/S-phase cell), the percentage of inhibition of DNA synthesis was minimum at 0 hr and gradually increased to maximum inhibition at 19 hr without the decrease seen previously at 4 hr.

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PubMed1982

CC-1065 (NSC 298223), a most potent antitumor agent: kinetics of inhibition of growth, DNA synthesis, and cell survival.

CC-1065 (NSC 298223) is the most cytotoxic agent tested against cells in culture in our laboratory. The 50% lethal doses for exponentially growing B16 melanoma and Chinese hamster ovary cells were 0.44 and 0.14 ng/ml, respectively, as compared to 35 and 500 ng/ml for Adriamycin. In the human tumor-cloning assay, 1-hr exposure to CC-1065 (0.1 ng/ml) caused greater than or equal to 50% lethality in a broad spectrum of tumors. The dose-survival curves for B16 and Chinese hamster ovary cells were characterized by an initial shoulder followed by an exponential decline with increasing dose. CC-1065 was more lethal to exponentially growing B16 cells (50% lethal dose = 0.44 ng/ml) than to plateau-phase cells (50% lethal dose = 1.2 ng/ml). CC-1065 inhibited DNA synthesis much more than did RNA or protein synthesis. After a 2-hr incubation with drug, inhibition of DNA synthesis was low immediately (0 hr) after drug exposure and reached maximum inhibition about 20 hr later. The doses for 50% inhibition of growth (0.18 ng/ml), survival (0.44 ng/ml), and DNA synthesis (0.15 ng/ml) were in the same range, whereas RNA synthesis was inhibited 50% at a much higher dose (5 ng/ml).

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PubMed1981

Changes in DNA distributions and ploidy of CHO cells as a function of time in culture.

Chinese hamster ovary (CHO) cells maintained in continuous culture for 3 to 5 months may undergo subtle changes in drug sensitivity response, growth kinetics, plating efficiencies, et cetera. Our studies done independently in two different laboratories, using flow cytometry, indicate that the DNA histogram patterns change at about 11 wk, from populations with an approximate diploid DNA content to populations also composed of triploid and tetraploid cells. Chromosome counts also change from distributions of 21 to 22 to populations of cells having 21 to 22, 34 to 35 and 44 to 46 chromosomes. These alterations occur earlier (at 8 to 9 wk) in cell populations previously treated with anticancer drugs.

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PubMed1981

Effect of 7-con-O-methylnogarol on DNA synthesis, survival, and cell cycle progression of Chinese hamster ovary cells.

The effect of 7-con-O-methylnogarol (7-OMEN) on the survival of exponentially growing and plateau-phase Chinese hamster ovary cells was determined in a cloning assay. After 2 hr of exposure, the 50% lethal dose for exponential and plateau-phase cells was 0.3 and 1.5 microgram/ml, respectively. Drug doses for cell progression studies were based upon drug lethality; therefore, higher doses were used for plateau than for exponential populations. The effect of 7-OMEN on cell progression was studied by DNA flow cytometry under the following conditions: (a) during 24 hr of continuous exposure of exponentially growing cells; (b) during recovery of exponential cells after 2 or 7 hr of drug exposure; and (c) during recovery of plateau-phase cells after 2 hr of exposure. Exponential cells exposed continuously for 24 hr progressed normally from M to G1 phase and from G1 to S phase, progression through S phase was slowed, and cells were ultimately blocked in G2 + M. Inhibition of S-phase progression was dose dependent, 0.2 microgram/ml having only slight effect and 1.0 microgram/ml accumulating a large fraction in S phase. Inhibition of S-phase progression correlated with DNA synthesis inhibition. Similar inhibitory effects were observed after pulsed (2- or 7-hr) exposure of exponential cells. 7-OMEN also blocked plateau-phase cells in G2 + M after 2 hr of exposure, but higher doses (3.0 microgram/ml) were required. Simultaneous exposure of exponential cells to Colcemid (which blocks cells in metaphase) and 1.0 microgram 7-OMEN per ml completely inhibited the expected increase in mitotic index, indicating that the G2 + M block observed by DNA flow cytometry was a block in G2 or prophase.

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