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G Abel

Publications and source records attributed to G Abel.

At least 37 records · Page 2Linked to original sources
PubMed1993

Histidine2 of the alpha-factor of Saccharomyces cerevisiae is not essential for binding to its receptor or for biological activity.

Seven His2 analogs of the Saccharomyces cerevisiae [Nle12]alpha-factor, WXWLQLKPGQP(Nle)Y, where X = beta-D-thienylalanine, beta-L-thienylalanine, 1-D-methylhistidine, 1-L-methylhistidine, 3-D-methylhistidine, 3-L-methylhistidine, and beta-3-L-pyridylalanine, were synthesized and purified to homogeneity. Assays were carried out on binding to the alpha-factor receptor and of biological activity determined by either growth arrest or morphological changes in target cells. In the L-isomer, replacement of the imidazole of histidine by thiophene or 3-pyridyl groups or derivatization of either nitrogen of the imidazole ring by methylation resulted in a 2-100-fold decrease in bioactivity. D-Isomers of the beta-thienylalanyl-, 1-methylhistidinyl-, or 3-methylhistidinyl-alpha-factors did not possess measurable bioactivity with the exception of comparatively low activity of the 3-D-methylhistidinyl and 1-D-methylhistidinyl-alpha-factors in the morphogenesis assay. In contrast, both active and inactive analogs demonstrated binding affinities 10-20-fold less than that of [Nle12]alpha-factor. These results indicate that the histidine residue of alpha-factor is not required for binding to the receptor or for biological activity and that bioactivity and binding can be dissociated through the use of pheromone analogs.

Amino Acid Sequence↗
PubMed1993

Preclinical antitumor evaluation of bis-acetato-ammine-dichloro-cyclohexylamine platinum(IV): an orally active platinum drug.

The cytotoxicity of a novel platinum(IV) complex, bis-acetato-amminedichloro-cyclohexylamine platinum(IV) (JM216), has been evaluated in vitro against a panel of human tumor cell lines (predominantly ovarian) representative of models of intrinsic and acquired to cisplatin. In addition, the activity of JM216 administered by the p.o. route has been determined in vivo using the murine ADJ/PC6 plasmacytoma and four human ovarian carcinoma xenograft lines. In vitro, against seven human ovarian carcinoma cell lines, JM216 showed similar cytotoxicity and pattern of cytotoxicity to cisplatin (mean 50% inhibitory concentrations of 3.5 microM for cisplatin and 1.7 microM for JM216). The cytotoxicity of JM216 was more dependent on the time of drug exposure than that of cisplatin, suggesting that extended split-dosing rather than a single bolus administration might be a more appropriate schedule in patients. Using six pairs of acquired cisplatin-resistant and parent human tumor cell lines (four ovarian, one testicular, and one cervical) JM216 exhibited non-cross-resistance (resistance factor of < 1.5) in three whereas tetraplatin exhibited partial or full cross-resistance in all six pairs. Notably, in two of the acquired cisplatin-resistant lines (41McisR and HX/155cisR) where JM216 retained activity, resistance has previously shown to be due primarily to reduced platinum uptake. In vivo, following p.o. administration using the cisplatin-sensitive murine ADJ/PC6 plasmacytoma, JM216 showed antitumor selectivity far superior to that observed for either cisplatin, carboplatin, or tetraplatin. Across four human ovarian carcinoma xenografts of widely differing sensitivity to cisplatin and carboplatin, JM216 exhibited p.o. activity, broadly comparable to that observed for i.v. administered cisplatin and carboplatin and markedly superior to i.p. administered tetraplatin. These antitumor properties suggest that JM216 provides a structural lead to platinum complexes which may circumvent transport-determined acquired resistance to cisplatin and is a suitable candidate as an p.o. administrable platinum complex for phase I clinical trial.

Animals↗
PubMed1992

Comparison of cellular accumulation and cytotoxicity of cisplatin with that of tetraplatin and amminedibutyratodichloro(cyclohexylamine)platinum(IV) (JM221) in human ovarian carcinoma cell lines.

We have compared the cellular accumulation and cytotoxicity of three platinum compounds in a panel of five human ovarian carcinoma cell lines. The cell lines, which were established from both untreated and pretreated patients, showed a wide range in sensitivity to cisplatin and other platinum drugs. The panel consisted of two sensitive (41M, CH1), one in vivo acquired resistant (PXN/94) with moderate sensitivity, and two intrinsically resistant (SKOV-3, HX/62) cell lines. The cisplatin 2-h concentration of drug required to inhibit cell growth by 50% compared with vehicle treated control cells (IC50 values) for these cell lines were in the following order: CH1 < 41M < PXN/94 < SKOV-3 < HX/62. None of the cell lines showed saturation of platinum accumulation (per mg protein) at 2 h after exposure to cisplatin concentrations of up to 500 microM. The highest cellular platinum accumulation was observed in the sensitive 41M cell line which was established from an untreated patient. The lowest accumulation was found in the intrinsically resistant HX/62 cell line. The rate of platinum accumulation at an equimolar concentration of cisplatin was 41M > SKOV-3 > CH1 > PXN/94 > HX/62. The relationship between drug accumulation and cytotoxicity was evaluated by comparing 2-h IC50 values with platinum accumulation following exposure to both equimolar and equitoxic doses of the agent. The results suggest that reduced drug accumulation may play a partial role in the mechanism of intrinsic resistance to cisplatin in one cell line (SKOV-3) and a major role in another (HX/62), where reduced accumulation is attributable to reduced uptake rather than enhanced efflux. Decreased drug accumulation may also contribute significantly to the lower sensitivity of the PXN/94 cell line to cisplatin. Interestingly, both the PXN/94 and the sensitive CH1 cell lines, which were established from patients pretreated with platinum drugs, showed reduced drug accumulation relative to the 41M cell line. Cellular accumulation of tetraplatin and JM221 [(ammine)dibutyratodichloro(cyclohexylamine)platinum(IV)], a novel platinum(IV) dicarboxylate complex exhibiting enhanced cytotoxicity compared to cisplatin, was also examined. Comparison with platinum accumulation from cisplatin suggests that the increased cytotoxicity of tetraplatin and JM221 may be related to their increased accumulation. Significantly both agents are more lipophilic than cisplatin, which may account partially for their improved uptake in cisplatin resistant cells.

Antineoplastic Agents↗
PubMed1992

Mechanism-related circumvention of acquired cis-diamminedichloroplatinum(II) resistance using two pairs of human ovarian carcinoma cell lines by ammine/amine platinum(IV) dicarboxylates.

Acquired resistance to cisplatin has been generated in vitro in two human ovarian carcinoma cell lines: 41M, established from a previously untreated patient; and CH1, from a patient previously treated with cisplatin and cis-diammine-1,1-cyclobutane dicarboxylatoplatinum(II) (carboplatin). In neither cell line with acquired resistance did intracellular detoxification (via increased glutathione or metallothioneins) appear to be a major determinant of resistance. Resistance in 41McisR (resistance factor of 4.7) appeared to be due predominantly to a reduced platinum accumulation (levels were only 23.8% in 41McisR versus 41M). This was also reflected at the DNA level by a similar level of reduced DNA interstrand cross-links and total platinum-DNA adducts measured immediately after a 2-h exposure to cisplatin in 41McisR versus 41M. Conversely, for CH1cisR (resistance factor of 6.5), platinum accumulation, and initial numbers of DNA-interstrand cross-links and total DNA-platinum adducts were not significantly different from the parent CH1 line. This is suggestive of a resistance mechanism involving increased DNA repair or tolerance to platinum-DNA adducts operating in the CH1cisR/CH1 pair of lines. Cross-resistance to carboplatin and partial cross-resistance to the 1,2-diaminocyclohexane-containing agent, (trans-d,l)-1,2-diaminocyclohexane tetrachloroplatinum(IV) (tetraplatin), was observed in both pairs. However, two novel platinum(IV) ammine/amine dicarboxylates, ammine dibutyratodichloro(cyclohexylamine)platinum(IV) (JM221) and ammine dibenzoatodichloro(propylamine)platinum(IV) (JM244), completely circumvented resistance in 41McisR to produce some collateral sensitivity (resistance factors of 0.67 and 0.54, respectively) but showed cross-resistance in CH1cisR (resistance factors of 3.7 and 4.6). In contrast to the data for cisplatin, intracellular platinum levels were not significantly different between the 41M and 41McisR pair of cell lines after exposure to JM244. These results suggest that the ammine/amine platinum(IV) dicarboxylates, which show considerably greater in vitro cytotoxicity than cisplatin, are capable of circumventing acquired cisplatin resistance which is due to decreased intracellular accumulation but are not able to overcome resistance at the level of DNA platination and removal.

Antineoplastic Agents↗
PubMed1992

Establishment and characterization of an in vitro model of acquired resistance to cisplatin in a human testicular nonseminomatous germ cell line.

Clinically, human testicular nonseminomatous germ cell tumors exhibit remarkable sensitivity to platinum-based chemotherapy. To define better the mechanistic basis for this unusual sensitivity, the biochemical determinants of platinum-induced cytotoxicity have been investigated in a human testicular tumor cell line (GCT27) established from a previously untreated patient and in an in vitro derived 5.6-fold cisplatin-resistant stable variant (GCT27cisR). Compared to 12 ovarian and 5 cervical human tumor cell lines, the parent GCT27 line was among the most sensitive to the cytotoxic effects of both cisplatin (dosage producing 50% inhibition, 0.2 microM) and carboplatin (dosage producing 50% inhibition, 2.9 microM), thus reflecting clinical data. A 4-day exposure sulforhodamine B-staining assay was used to determine that GCT27cisR was cross-resistant to carboplatin and iproplatin and the classical bifunctional alkylating agents melphalan and chlorambucil. Partial cross-resistance was observed to tetraplatin, methotrexate, and mitomycin C. No cross-resistance was observed to Adriamycin, etoposide, vinblastine, bleomycin, 1-beta-D-arabinofuranosylcytosine, and 5-fluorouracil. Intracellular cisplatin accumulation across the dose range 2.5-100 microM (for 2 h) was 1.6 +/- 0.39-fold (mean +/- SD) greater for the parent line. There was no significant difference in glutathione levels between the two lines. The acquired resistance line was 1.9-fold more resistant than the parent line to the cytotoxic effects of cadmium chloride. There was no significant difference between the two lines, however, in the total amounts of platinum bound to DNA after cisplatin exposure (25, 50, or 100 microM for 2 h). The removal of total platinum adducts from DNA was significantly faster for GCT27cisR compared to the parent line (half-times of removal, 32 and 67 h, respectively). These data suggest that the abnormal sensitivity of the parent testicular tumor cell line to platinum-containing anticancer drugs may be due predominantly to an inherent defect in the ability of these cells to remove platinum from their DNA. This defect is apparently lost in the acquired resistance counterpart. Reduced intracellular accumulation and increased cytoplasmic concentrations of metallothionein may also contribute, in part, to the acquisition of cisplatin resistance in this model.

Antineoplastic Agents↗
PubMed1992

Ammine/amine platinum(IV) dicarboxylates: a novel class of platinum complex exhibiting selective cytotoxicity to intrinsically cisplatin-resistant human ovarian carcinoma cell lines.

Using a panel of six human ovarian carcinoma cell lines varying by two orders of magnitude in terms of cisplatin cytotoxicity, we have investigated the in vitro antitumor activity of a series of novel alkylamine ammine dicarboxylatodichloroplatinum(IV) complexes of the general formula c,t,c-[PtCl2(OCOR1)2NH3(RNH2)]. A clear relationship existed between increasing the number of carbons in the R1 substituent and increasing cytotoxicity up to R1 = C5H11. In terms of changing the R group, maximum cytotoxic effects were conferred by alicyclic substituents. Furthermore, increasing the alicyclic ring size from cyclobutane through to cycloheptane resulted in increasing cytotoxicity. The agents with longer axial chains (e.g., JM300, R = cyclohexyl, R1 = C6H13) were significantly more cytotoxic than cisplatin and, moreover, exhibited a selective cytotoxic effect against the most intrinsically cisplatin-resistant cell lines (e.g., for HX/62, cisplatin 50% inhibitory concentration, 12.6 microM; SKOV-3, cisplatin 50% inhibitory concentration, 4.4 microM and 41 M; cisplatin 50% inhibitory concentration, 0.23 microM; JM300 was 840-, 440-, and only 34-fold more active, respectively). The dicarboxylates JM221 (R = cyclohexyl, R1 = C3H7) and JM244 (R = n-propyl, R1 = C6H5) also retained activity against a 4-fold cisplatin-acquired resistant variant of the 41M cell line. At least part of the increased cytotoxicity of the dicarboxylate, JM221, over cisplatin appeared to be attributable to an increased intracellular accumulation. This novel class of platinum compound represents a valuable lead in the development of a "third-generation" agent capable of exhibiting activity against clinical disease currently resistant to cisplatin.

Antineoplastic Agents↗
PubMed1992

Comparative in vitro cytotoxicity of taxol and Taxotere against cisplatin-sensitive and -resistant human ovarian carcinoma cell lines.

Using the sulforhodamine B assay, we compared the cytotoxic properties of the novel microtubule agent taxol and the semi-synthetic related compound Taxotere in nine human ovarian-carcinoma cell lines, including three pairs of cell lines rendered resistant to cisplatin or carboplatin. In addition, the cytotoxicity of the commonly used anticancer drugs cisplatin and adriamycin and the topoisomerase II inhibitor etoposide was determined. The results of continuous drug exposure showed that taxol [mean concentration producing 50% growth inhibition (IC50), 1.1 x 10(-9) M; range, 2.8 x 10(-9)-5 x 10(-10) M and Taxotere (mean IC50, 5.1 x 10(-10) M; range, 7.2-3.3 x 10(-10) M) were greater than 1,000 times more cytotoxic than either cisplatin (mean IC50, 3.1 x 10(-6) M; P less than 0.05) or etoposide (mean IC50, 2.3 x 10(-6) M; P less than 0.05) and greater than 100 times more cytotoxic than Adriamycin (mean IC50, 6.9 x 10(-8) M; P less than 0.05). Taxotere was more cytotoxic than taxol; following continuous exposure, the mean difference across the cell lines was 2 orders of magnitude (range, 1.1-3.9 orders of magnitude for individual lines). Although this difference did not reach statistical significance for any individual cell line (P values ranged from 0.17 for HX/62 to 0.9 for OVCAR-3), when all IC50 values for the 96-h experiments were pooled, Taxotere was found to be significantly more potent than taxol (P = 0.05). Following 2 h exposure, the mean cytotoxicity of Taxotere was 3.9-fold greater than that of taxol across the nine lines (range, 0.75- to 10-fold; P less than 0.05 for the CH1 cell line; overall pooled IC50 data, P = 0.05). Although a 71-fold range of sensitivity to cisplatin was observed across the six parent cell lines (IC50 most resistant line/IC50 most sensitive line), this was largely abolished by treatment with taxol (5.6-fold range) and Taxotere (2.2-fold range). Following continuous exposure of the three pairs of lines exhibiting acquired resistance to platinum, no cross-resistance with either Taxotere or taxol was found (resistance factors, less than 1.5). In the 41M and 41McisR pair of lines, in which previous studies have shown resistance to be due to reduced platinum accumulation, taxol and Taxotere exhibited some collateral sensitivity (resistance factors, 0.69 and 0.66, respectively). Taxotere and, particularly, taxol showed a pronounced concentration times exposure duration (C x T) dependence as compared with cisplatin (P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Antineoplastic Agents, Phytogenic↗
PubMed1992

Human ovarian-carcinoma cell lines and companion xenografts: a disease-oriented approach to new platinum anticancer drug discovery.

A disease-oriented approach to the discovery of novel platinum anticancer drugs has been established through the setting up of parallel human ovarian-carcinoma cell lines and xenografts. The correlation between in vitro and in vivo antitumour activity was determined for four reference platinum agents (cisplatin, carboplatin, iproplatin and tetraplatin) in eight companion lines. Two methods of assessing antitumour effect were used in vitro (tritiated thymidine incorporation and sulforhodamine B staining) and three were applied in vivo [28-day treated/control (T/C) ratio, growth delay and specific growth delay]. In vitro, large differences in cytotoxicity across the cell lines were observed for each drug. This was also reflected in the xenografts for cisplatin and carboplatin and, to a lesser extent, for iproplatin. A correlation analysis of in vitro vs in vivo data revealed a high, statistically significant positive correlation for cisplatin and a strong positive correlation for carboplatin. However, for the two platinum(IV) drugs, the correlation was less good. In particular, tetraplatin was markedly less active in vivo (showing a general lack of activity against all of the tumour lines) than its in vitro potency against the cell lines predicted, resulting in poor correlation coefficients. These human tumour panels may be valuable for the elucidation of both cellular/molecular and corresponding in vivo pharmacological mechanisms of platinum drug resistance. Moreover, the HX/62 and SKOV-3 tumour lines, which exhibit a level of intrinsic resistance to the four reference agents both in vitro and in vivo (and which were derived from patients who had not received prior platinum therapy), represent particularly useful evaluation models for the discovery of novel broad-spectrum platinum drugs.

Antineoplastic Agents↗
PubMed1992

Stimulation of human monocyte beta-glucan receptors by glucan particles induces production of TNF-alpha and IL-1 beta.

beta-glucans are pharmacologic agents that rapidly enhance host resistance to a variety of biologic insults through mechanisms involving macrophage activation. To determine whether stimulation of the beta-glucan receptors on human monocytes resulted in cytokine production, monolayers of monocytes were incubated with purified yeast glucan particles and measured for tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) mRNA and protein. By Northern blot analysis, TNF-alpha mRNA was detected within 30 min of incubation with glucan particles, peaked at 2 h, and remained elevated for at least 8 h. Glucan induction of IL-1 beta mRNA followed a similar time-course of initiation and accumulation. By enzyme-linked immunosorbent assays (ELISAs), significant levels of TNF-alpha and IL-1 beta were present in supernatants of glucan-treated cells within 1 h and plateau levels of both cytokines were approached within 4 h. At particle-to-cell ratios of from 0.4 to 18, glucan particles induced dose-dependent increases in TNF-alpha and IL-1 beta mRNA and corresponding increases in TNF-alpha and IL-1 beta proteins. Exposure of monocytes to glucan particles for 0-30 min and washing before continued incubation for 4 h in particle-free buffer induced production and secretion of TNF-alpha and IL-1 beta in a time-dependent fashion compatible with phagocytosis. The pretreatment of monocyte monolayers with trypsin reduced glucan-induced production of TNF-alpha and IL-1 beta in a dose-dependent manner with 5 micrograms/ml of trypsin effecting reductions of greater than 50%. Thus, glucan particles induce human monocyte production of TNF-alpha and IL-1 beta by a mechanism that is dependent on trypsin-sensitive beta-glucan receptors.

Cells, Cultured↗
PubMed1992

Reduced drug accumulation as a major mechanism of acquired resistance to cisplatin in a human ovarian carcinoma cell line: circumvention studies using novel platinum (II) and (IV) ammine/amine complexes.

Acquired resistance to cisplatin (cis-diamminedichloroplatinum (II)) has been generated in vitro in the 41M human ovarian carcinoma cell line, established from a previously untreated patient. Three cisplatin-resistant variants were selected at approximately 2, 4 and 6-fold resistance (in terms of 50% inhibitory concentrations), in order to study the underlying mechanisms of acquired cisplatin resistance. Compared to the parent line, platinum accumulation following exposure to equimolar concentrations of cisplatin was on average (across the entire concentration range) 2.9, 3.6 and 4.8-fold lower in the 41McisR2, 41McisR4 and 41McisR6 cell lines, respectively. Thus the difference in uptake corresponded closely with their resistance factor in the three resistant variants. Moreover, a significant reduction in platinum accumulation was observed as early as 5 min after exposure to cisplatin in the 41M vs 41McisR6 cell lines. Platinum accumulation was similar in all cell lines following exposure to equitoxic concentrations (2 h IC50) of cisplatin. Enhanced efflux of drug was not observed between the 41M and 41McisR6 cells. In addition, there was no difference in intracellular glutathione (GSH) levels. Our previous studies have shown no indication of metallothionein involvement and the decrease in cisplatin uptake in the 41McisR6 cells was reflected by a similar reduction in DNA interstrand cross-links (ISC) formation. These results suggest that the mechanism of acquired resistance to cisplatin in the 41McisR6 cell line may be predominantly due to reduced drug uptake. The 41McisR6 cells were not found to be cross-resistant to ouabain, a postulated specific inhibitor of sodium-potassium adenosine triphosphatase (Na+, K(+)-ATPase), suggesting that decreased cisplatin accumulation in these cells is probably not regulated by alterations in their Na+, K(+)-ATPase levels, and Na+ potential across the plasma membrane. Cellular accumulation of a novel class of platinum (IV) ammine/cyclohexylamine dicarboxylates, which exhibit enhanced cytotoxicity over cisplatin and completely circumvent resistance to cisplatin in the 41McisR line, was also examined. The data suggests that increased accumulation of these compounds, as a result of their enhanced lipophilicity, could account for the dramatic increase in their potency over cisplatin.

Carcinoma↗
PubMed1991

The relationships between glutathione, glutathione-S-transferase and cytotoxicity of platinum drugs and melphalan in eight human ovarian carcinoma cell lines.

The role of glutathione (GSH) and GSH-S-transferase (GST) activity in modulating the cytotoxicity of four platinum drugs and melphalan was evaluated in eight human ovarian carcinoma cell lines. The cell lines were established from solid and ascitic tumours from pretreated and untreated patients, and showed a wide spectrum of sensitivity to several platinum II and platinum IV drugs; cisplatin, carboplatin, CHIP and tetraplatin. Intracellular glutathione concentration measured in the cell lines showed a significant (P = 0.05) correlation with IC50 values for cisplatin (r = 0.91), carboplatin (r = 0.87) and CHIP (r = 0.88). The correlation between GSH levels and IC50 values for melphalan (r = 0.76) or tetraplatin (r = 0.60) was not as significant. GST activity showed no correlation with IC50 values, for the four platinum drugs. To determine the significance of the elevated GSH concentration in the refractory cell lines, the effect of D,L-buthionine-S, R-sulfoximine (BSO) mediated GSH depletion on platinum drug cytotoxicity was examined in one of the most sensitive (CH1) and two of the least sensitive (relatively resistant; SKOV-3, HX/62) cell lines. Comparison was made with the effect of GSH depletion on melphalan cytotoxicity in these three lines. These lines were differentially sensitive to BSO, with the two most platinum drug resistant lines being more tolerant to BSO than the sensitive CH1 line. Depletion of cellular GSH, ranging between 61 and 88%, had a differential effect on the sensitivity to PtII vs PtIV drugs in the three cell lines: cytotoxicity of the PtIV drugs, tetraplatin and CHIP, was substantially enhanced in both the resistant and sensitive cell lines; in contrast, the cytotoxicity of the PtII drugs, cisplatin and carboplatin, was only significantly increased in one of the two relatively resistant lines (SKOV-3) and in the sensitive (CH1) line after GSH depletion. Moreover the dose modification factor (DMF) for the PtII agents were lower than those for PtIV agents in the three cell lines. The dose modification factor for tetraplatin after BSO treatment was similar to that observed for melphalan in all three cell lines. In the SKOV-3 cell line extending the BSO pretreatment period to 48 h from 24 h marginally reduced the cytotoxicity of cisplatin, whereas the cytotoxicity of the other three drugs remained similar to that observed after 24 h BSO pretreatment. In contrast, extending the BSO treatment to 24 h after drug exposure potentiated the cytotoxicity of cisplatin, CHIP and tetraplatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Carboplatin↗
PubMed1991

Purification and Characterization of Chorismate Synthase from Euglena gracilis: Comparison with Chorismate Synthases of Plant and Microbial Origin.

Chorismate synthase was purified 1200-fold from Euglena gracilis. The molecular mass of the native enzyme is in the range of 110 to 138 kilodaltons as judged by gel filtration. The molecular mass of the subunit was determined to be 41.7 kilodaltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purified chorismate synthase is associated with an NADPH-dependent flavin mononucleotide reductase that provides in vivo the reduced flavin necessary for catalytic activity. In vitro, flavin reduction can be mediated by either dithionite or light. The enzyme obtained from E. gracilis was compared with chorismate synthases purified from a higher plant (Corydalis sempervirens), a bacterium (Escherichia coli), and a fungus (Neurospora crassa). These four chorismate synthases were found to be very similar in terms of cofactor specificity, kinetic properties, isoelectric points, and pH optima. All four enzymes react with polyclonal antisera directed against chorismate synthases from C. sempervirens and E. coli. The closely associated flavin mononucleotide reductase that is present in chorismate synthase preparations from E. gracilis and N. crassa is the main difference between those synthases and the monofunctional enzymes from C. sempervirens and E. coli.

Journal Article↗
PubMed1991

Phagocytosis of fluorescent latex microbeads by peritoneal macrophages in different strains of mice: a flow cytometric study.

The phagocytosis of uniform fluorescent latex particles by resident and thioglycollate-elicited macrophages was analysed by flow cytometry. The percentage of phagocytosing macrophages and the number of internalized microspheres per cell was determined from cell size and fluorescence histograms. Results were corrected for the adherence of microbeads to the cells in the presence of sodium azide in the medium. Human C3b- or murine monoclonal IgG-coated microspheres were applied to assess receptor-mediated phagocytosis in different inbred strains of mice. Phagocytic activity of thioglycollate-elicited macrophages was consequently higher than that of resident macrophages. A decreasing gradient of C3b and Fc receptor-mediated phagocytosis was established in the following order: B10.BR, B10, C3H/Di and C3H.SW strains. Our results indicate that the phagocytic function of murine macrophages is under control of both the somatic (non-H-2) and H-2 genes.

Animals↗
PubMed1989

Phase I trial and pharmacokinetics of trimelamol (N2,N4,N6-trihydroxymethyl-N2,N4,N6-trimethylmelamine).

Trimelamol is an analogue of hexamethylmelamine and pentamethylmelamine which does not require metabolic activation and is sufficiently soluble to allow parenteral administration. A Phase I trial has been performed at the Royal Marsden Hospital in which two schedules of administration have been evaluated, a single i.v. infusion repeated every 3 weeks and 3 daily doses repeated every 3 weeks. Pharmacokinetic analysis was performed at all dose levels on both schedules and a linear correlation was demonstrated between dose and area under the curve. Myelosuppression was dose limiting for single dose administration with a maximum tolerated dose of 2400 mg/m2. Median leukocyte nadirs at 1800, 2100, and 2400 mg/m2 were 3.2, 2.6, and 1.5 x 10(9)/liter. Thrombocytopenia and anemia also occurred but were not dose limiting. Doses greater than 1500 mg/m2 caused WHO grade 3 nausea and vomiting but no acute sedation. Three day administration appeared to be less myelosuppressive, giving a maximum tolerated dose of 1000 mg/m2. Median leukocyte nadirs at 800, 900, and 1000 mg/m2 daily for 3 days were 3.0, 2.3, and 1.5 x 10(9)/liter. Nonhematological toxicities were also less marked on the fractionated schedule. Antitumor effects were observed including 1 complete and 9 partial responses. Demonstration of activity in ovarian cancer has led to further evaluation in this disease using the 3-day schedule at a dose of 800 mg/m2 daily for 3 days.

Adult↗
PubMed1989

Effect of lentinan and mannan on phagocytosis of fluorescent latex microbeads by mouse peritoneal macrophages: a flow cytometric study.

Lentinan, an immunopotentiating beta-1,3-glucan polysaccharide stimulated the in vitro phagocytosis of BSA-coated, C3b- or monoclonal immunoglobulin (IgG2b)-coated fluorescent microspheres by resident or thioglycollate-elicited mouse macrophages in a dose-dependent manner. Analysis of flow cytometric data has shown that microbead phagocytosis of resident macrophages, which exhibit a lower basic phagocytic activity than the thioglycollate elicited ones, has been augmented by up to 900% due to lentinan. The percent ratio of phagocytes among peritoneal exudate cells, however, remained unchanged after short-term lentinan stimulation. Preincubation of the cells with lentinan resulted in increased ingestion of the microbeads. Activation of phagocytosis by lentinan is therefore due in part to the direct stimulation of the cells, however, lentinan also serves as supplementary opsonin for C3b-coated beads. Mannan inhibited the ingestion of C3b-coated microspheres by 75%, which was abolished in part when lentinan was also added to the cells. Mannan did not influence the phagocytosis of BSA-coated or IgG-coated beads. Our data, based solely on in vitro studies, suggest a beta-glucan receptor mediated activation of phagocytes by lentinan. These receptors are different from the C3b, Fc or mannose receptors. It is very likely that stimulation of phagocytic activity of macrophages by lentinan may contribute to the antitumor action of this immunopotentiating polysaccharide.

Animals↗
PubMed1989

Biological properties of ten human ovarian carcinoma cell lines: calibration in vitro against four platinum complexes.

Ten human ovarian carcinoma cell lines have been studied as a potential in vitro screen for the development of novel anticancer platinum complexes. Lines have been established and developed both from solid and ascitic tumours, from pretreated and untreated patients, and are available at a range of in vitro passage numbers. The biological properties of the lines were consistent with them being human, epithelial and of ovarian carcinoma origin. Using a tritiated thymidine or leucine uptake method, and a 96 hour continuous drug exposure, the lines have been calibrated against four platinum-containing chemotherapeutic agents: cisplatin, iproplatin, carboplatin and tetraplatin. Striking differences in cytotoxicity were observed across the lines for each agent. Some lines were consistently resistant, others generally sensitive, whereas some showed clear evidence of differential sensitivity to a particular agent. Statistical analysis (Spearman rank correlation) involving the six possible pairings of drugs showed that cisplatin, iproplatin and carboplatin elicit a very similar pattern of response in these lines whereas tetraplatin elicits a completely different response pattern. Similar cytotoxicity values were obtained using a soft agar cloning assay. Results using a tetrazolium dye reduction assay, however, gave somewhat higher and more variable values, particularly with tetraplatin. The thymidine uptake assay will be adopted in further studies on a selected panel of six lines. This panel encompasses the spectra of sensitivities identified for each of the four agents against the original ten lines and may provide a useful screening facility for the development of novel platinum drugs, in that it detects both cell line-determined and structure-determined differences in cytotoxicity.

Antigens, Neoplasm↗
PubMed1989

[Studies on the effect of an alkaloid extract of Symphytum officinale on human lymphocyte cultures].

An alkaloid extract of Symphytum officinale was investigated for its chromosome-damaging effect in human lymphocytes in vitro. In concentrations of 1.4 micrograms/ml and 14 micrograms/ml the alkaloids had no effect, in concentrations of 140 micrograms/ml and 1400 micrograms/ml the alkaloids induced sister chromatid exchanges (SCE) as well as chromosome aberrations. Additionally, the influence of rat liver enzymes (S9) was tested. The SCE-inducing capacity and the clastogenic effect of Symphytum alkaloids was increased by simultaneous application of S9-Mix.

Alkaloids↗