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Biomedical subjects

W Kohler

Publications and source records attributed to W Kohler.

At least 37 records · Page 2Linked to original sources
PubMed1990

On the role of Ca2(+)-calmodulin-dependent and cAMP-dependent protein phosphorylation in the circadian rhythm of Neurospora crassa.

Pulses of some Ca2+ channel blockers (dantrolene, Co2+, nifedipine) and calmodulin inhibitors (chlorpromazine) lead to medium (maximally 5-9 h) phase shifts of the circadian conidiation rhythm of Neurospora crassa. Pulses of high Ca2+, or of low Ca2+, a Ca2+ ionophore (A23187) together with Ca2+, and other Ca2+ channel blockers (La3+, diltiazem), however, caused only minor phase shifts. The effect of these substances (A 23187) and of different temperatures on the Ca2+ release from isolated vacuoles was analyzed by using the fluorescent dye Fura-2. A 23187 and higher temperatures increased the release drastically, whereas dantrolene decreased the permeation of Ca2+ (Cornelius et al., 1989). Pulses of 8-PCTP-cAMP, IBMX and of the cAMP antagonist RP-cAMPS, also caused medium (maximally 6-9 h) phase shifts of the conidiation rhythm. The phase response curve of the agonist was almost 180 degrees out of phase with the antagonist PRC. In spite of some variability in the PRCs of these series of experiments all showed maximal shifts during ct 0-12. The variability of the response may be due to circadian changes in the activity of phosphodiesterases: After adding cAMP to mycelial extracts HPLC analysis of cAMP metabolites showed significant differences during a circadian period with a maximum at ct 0. Protein phosphorylation was tested mainly in an in vitro phosphorylation system (with 35S-thio gamma-ATP). The results showed circadian rhythmic changes predominantly in proteins of 47/48 kDa. Substances and treatments causing phase-shifts of the conidiation rhythm also caused changes in the phosphorylation of these proteins: an increase was observed when Ca2+ or cAMP were added, whereas a decrease occurred upon addition of a calmodulin inhibitor (TFP) or pretreatment of the mycelia with higher (42 degrees C) temperatures. Altogether, the results indicate that Ca2(+)-calmodulin-dependent and cAMP-dependent processes play an important, but perhaps not essential, role in the clock mechanism of Neurospora. Ca2+ calmodulin and the phosphorylation state of the 47/48-kDa proteins may have controlling or essential functions for this mechanism.

Calcium↗
PubMed1990

Phase I study of repeated cycles of high-dose cyclophosphamide, etoposide, and cisplatin administered without bone marrow transplantation.

Forty-two patients with advanced malignancy judged unlikely to respond to standard treatment received high-dose combination chemotherapy with cyclophosphamide, etoposide, and cisplatin in a phase I trial. Twenty-two of these patients who had at least a partial response (PR) to the first cycle of therapy received a second cycle, and eight patients received three or more cycles of therapy. Bone marrow replacement was not used. The maximum-tolerated doses (MTDs) were cyclophosphamide 2.5 g/m2 on days 1 and 2; etoposide 500 mg/m2 on days 1, 2, and 3; and cisplatin 50 mg/m2 on days 1, 2, and 3. Hematologic toxicity was not dose-limiting by study design. Recovery to an absolute granulocyte count above 100/microL occurred at a median of 9 days from onset (range, 3 to 23 days) at the MTD. Recovery was delayed after the third cycle. Only one patient on his third cycle failed to recover peripheral blood counts and died of sepsis an day 43. Hematologic toxicity was not dose-dependent. Nonhematologic toxicities included emesis, fatigue, alopecia, diarrhea, and anorexia and were generally well tolerated. The dose-limiting toxicities were fatal pulmonary or cardiac toxicities in five of nine patients treated at the highest dose level. Patients likely to do well can be selected by tumor type, response to prior therapy, and performance status. Nine of 36 assessable patients had a complete response (CR) and 13 a PR for a response rate of 61%. Five patients (12%) remain alive and free of disease at 15 to 32 months. Repeated cycles of dose-intensive combination therapy can produce long-term disease-free remissions in patients with refractory tumor types. The toxicity of the regimen is acceptable if patients are carefully selected.

Adolescent↗
PubMed1989

Comparison of the biological effects of selected 5,8-dideazafolate analogues with their 2-desamino counterparts.

Three new 5,8-dideaza analogues of folic acid devoid of an amino group at position 2 have been prepared by using synthetic routes patterned after earlier methodologies. They were 2-desamino-5,8-dideazaisofolic acid, 2b, 2-desamino-10-thia-5,8-dideazafolic acid, 2c, and 2-desamino-10-oxa-5,8-dideazafolic acid, 2d. These compounds were found to be 4-6-fold more cytoxic toward L1210 leukemia cells than their 2-NH2 counterparts and to be poor inhibitors of mammalian thymidylate synthase. However, they were only 1.5-3-fold less inhibitory toward dihydrofolate reductase than the analogous compounds containing a 2-NH2 group. The known thymidylate synthase inhibitors 2-desamino-10-propargyl-5,8-dideazafolic acid and 10-propargyl-5,8-dideazafolic acid were included in this study for purposes of comparison.

Animals↗
PubMed1989

Granulocyte colony-stimulating factor stimulates recovery of granulocytes in patients receiving dose-intensive chemotherapy without bone marrow transplantation.

Bone marrow colony-stimulating factors (CSF) ameliorate hematologic toxicity of standard chemotherapy regimens and may allow relatively safe use of intensive and more efficacious doses of anticancer drugs. Twenty-four patients with cancers for which no standard regimens were likely to be effective received repeated courses of a combination of cisplatin (150 mg/m2), etoposide (1,500 mg/m2), and cyclophosphamide (5,000 mg/m2) at doses for which bone marrow transplantation is usually used. A total of 10 patients received escalating doses of recombinant human granulocyte CSF (rhG-CSF); 11 patients receiving identical chemotherapy and supportive therapy without rhG-CSF served as controls for the first cycle of therapy. Five of these patients and 3 additional patients also served as their own controls, receiving rhG-CSF for all cycles after the first. No patient received bone marrow transplantation. rhG-CSF shortened the median duration of severe granulocytopenia (less than or equal to 100/mm3) in a dose-related fashion (P less than .03; Kruskal-Wallis test). Patients not receiving rhG-CSF had a median of 8.5 days of granulocytopenia. Those receiving 40 micrograms/kg of rhG-CSF for approximately 20 days from the third day after chemotherapy had a median of 7.0 days (P less than .23) and those receiving 60 micrograms/kg had a median of 5.5 days (P less than .007) of granulocytopenia. An rhG-CSF dose of 20 micrograms/kg had no effect. Recovery to a granulocyte count of at least 500/mm3 took a median of 12 days in the control group and 8 days (P less than .03) in patients receiving rhG-CSF at a dose of 60 mg/kg. The duration of antibiotic therapy (a median, 9.0 days v 5.0 days) was shortened with the two higher and effective doses of rhG-CSF compared with control patients. The duration of hospitalization (median of 20 days v 19 days) was not shortened. These findings that rhG-CSF decreases the risk of granulocytopenia associated with this particular dose-intensive chemotherapy regimen therapy administered without bone marrow transplantation.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1988

Methotrexate analogues. 32. Chain extension, alpha-carboxyl deletion, and gamma-carboxyl replacement by sulfonate and phosphonate: effect on enzyme binding and cell-growth inhibition.

Analogues of methotrexate (MTX) and aminopterin (AMT) with aminophosphonoalkanoic, aminoalkanesulfonic, and aminoalkanephosphonic acid side chains in place of glutamate were synthesized and tested as inhibitors of folylpolyglutamate synthetase (FPGS) from mouse liver. The aminophosphonoalkanoic acid analogues were also tested as inhibitors of dihydrofolate reductase (DHFR) from L1210 murine leukemia cells and as inhibitors of the growth of MTX-sensitive (L1210) and MTX-resistant (L1210/R81) cells in culture. The optimal number of CH2 groups in aminophosphonoalkanoic acid analogues of AMT was found to be two for both enzyme inhibition and cell growth inhibition but was especially critical for activity against FPGS. Deletion of the alpha-carboxyl also led to diminished anti-FPGS activity in comparison with previously studied homocysteic acid and 2-amino-4-phosphonobutyric acid analogues. In the aminoalkanesulfonic acid analogues of MTX without an alpha-carboxyl, anti-FPGS activity was low and showed minimal variation as the number of CH2 groups between the carboxamide and sulfonate moieties was changed from one to four. In similar aminoalkanephosphonic acid analogues of MTX, anti-FPGS activity was also low, was comparable for two and three CH2 groups between the carboxamide and phosphonate moieties, and was diminished by monoesterification of the phosphonate group. These effects demonstrate that the alpha-carboxyl group of folate analogues is involved in binding to the active site of FPGS, and that an alpha-carboxyl group should be retained as part of the structure of FPGS inhibitors.

Aminopterin↗
PubMed1988

Methotrexate analogues. 33. N delta-acyl-N alpha-(4-amino-4-deoxypteroyl)-L-ornithine derivatives: synthesis and in vitro antitumor activity.

N delta-Acyl derivatives of the potent folylpolyglutamate synthetase (FPGS) inhibitor N alpha-(4-amino-4-deoxypteroyl)-L-ornithine (APA-L-Orn) were synthesized from N alpha-(4-amino-4-deoxy-N10-formylpteroyl)-L-ornithine by reaction with an N-(acyloxy)succinimide or acyl anhydride, followed by deformylation with base. The N delta-hemiphthaloyl derivative was also prepared from 4-amino-4-deoxy-N10-formylpteroic acid by reaction with persilylated N delta-phthaloyl-L-ornithine, followed by simultaneous deformylation and ring opening of the N delta-phthaloyl moiety with base. The products were potent inhibitors of purified dihydrofolate reductase (DHFR) from L1210 murine leukemia cells, with IC50's ranging from 0.027 and 0.052 microM as compared with 0.072 microM for APA-L-Orn. Several of the N delta-acyl-N10-formyl intermediates also proved to be good DHFR inhibitors. One of them, N alpha-(4-amino-4-deoxy-N10-formylpteroyl)-N delta-(4-chlorobenzoyl)-L- ornithine, had a 2-fold lower IC50 than its deformylated product, confirming that the N10-formyl group is well tolerated for DHFR binding. While N delta-acylation of APA-L-Orn did not significantly alter anti-DHFR activity, inhibition of FPGS was dramatically diminished, supporting the view that the basic NH2 on the end of the APA-L-Orn side chain is essential for the activity of this compound against FPGS. N delta-Acylation of APA-L-Orn markedly enhanced toxicity to cultured tumor cells. However, N delta-acyl derivatives also containing an N10-formyl substituent were less cytotoxic than the corresponding N10-unsubstituted analogues even though their anti-DHFR activity was the same, suggesting that N10-formylation may be unfavorable for transport. Two compounds, the N delta-benzoyl and N delta-hemiphthaloyl derivatives of APA-L-Orn, with IC50's against L1210 cells of 0.89 and 0.75 nM, respectively, were more potent than either methotrexate (MTX) or aminopterin (AMT) in this system. These compounds were also more potent than MTX against CEM human lymphoblasts and two human head and neck squamous cell carcinoma cell lines (SCC15, SCC25) in culture. Moreover, in assays against SCC15/R1 and SCC25/R1 sublines with 10-20-fold MTX resistance, the N delta-hemiphthaloyl derivative of APA-L-Orn showed potency exceeding that of MTX itself against the parental cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Aminopterin↗
PubMed1988

Methotrexate analogues. 34. Replacement of the glutamate moiety in methotrexate and aminopterin by long-chain 2-aminoalkanedioic acids.

Eight previously unreported methotrexate (MTX) and aminopterin (AMT) analogues with the L-glutamate moiety replaced by DL-2-aminoalkanedioic acids containing up to 10 CH2 groups were synthesized from 4-amino-4-deoxy-N10-methylpteroic or 4-amino-4-deoxy-N10-formylpteroic acid. All the compounds were potent inhibitors of purified L1210 mouse leukemia dihydrofolate reductase (DHFR), with IC50's of 0.023-0.034 microM for the MTX analogues and 0.054-0.067 microM for the AMT analogues. The compounds were not substrates for, but were inhibitors of, partially purified mouse liver folylpolyglutamate synthetase (FPGS). Activity was correlated with the number of CH2 groups in the side chain. The IC50's for inhibition of cell growth in culture by the chain-extended MTX analogues were 0.016-0.64 microM against CEM human leukemic lymphoblasts and 0.0012-0.026 microM against L1210 mouse leukemia cells. However, the optimal chain length for growth-inhibitory activity was species-dependent. Our results suggested that CEM cells were inhibited most actively by the analogue with nine CH2 groups, while L1210 cells were most sensitive to the analogue with six CH2 groups. Among the AMT analogues, on the other hand, the most active compound against L1210 cells was the one with nine CH2 groups, which had an IC50 of 0.000 65 microM as compared with 0.0046 microM for MTX and 0.002 microM for AMT. A high degree of cross-resistance was observed between MTX and the chain-extended compounds in two MTX-resistant cell lines, CEM/MTX and L1210/R81. All the MTX analogues were active against L1210 leukemia in mice on a qd X 9 schedule, with optimal increases in lifespan (ILS) of 75-140%. Notwithstanding their high in vitro activity, the AMT analogues were more toxic and less therapeutically effective than MTX analogues of the same chain length even though neither series of compounds possessed FPGS substrate activity. These MTX and AMT analogues are an unusual group of compounds in that they retain the dicarboxylic acid structure of classical antifolates yet are more lipophilic than the parent compounds because they have more CH2 groups and are almost equivalent in vivo to MTX on the same schedule even though they do not form polyglutamates.

Amino Acids, Dicarboxylic↗
PubMed1987

Does smoking interfere with the effect of histamine H2-receptor antagonists on intragastric acidity in man?

The interaction between smoking and the effect of histamine H2-antagonists on intragastric acidity was examined in a double blind double dummy placebo controlled study. Healthy volunteers, 11 smokers and 10 non-smokers, were given, on four separate days at least one week apart, either placebo or cimetidine 800 mg nocte or ranitidine 2 X 150 mg per day or ranitidine 300 mg nocte. Tablets were taken at 2115 and 0900 h. Smokers smoked a cigarette hourly from 0700 to 2300 h. Breakfast, lunch, and dinner were standardised. Intragastric acidity was measured with a combined intragastric glass electrode and a solid state recorder. The subjects were fully ambulatory. The three histamine H2-receptor antagonist regimens were less effective (p = 0.04) in smokers than in non-smokers, but the difference between acidity of smokers and non-smokers was small. Means of medians of pH during a 24-h period with placebo, cimetidine 800 mg, ranitidine 2 X 150 mg and ranitidine 300 mg were 1.6, 2.3, 3.1, and 2.7 in smokers and 1.5, 2.7, 3.2, and 3.1 in non-smokers, respectively. In a second part of the study seven chronic smokers were reexamined after acutely stopping smoking: inhibition of gastric acidity by histamine H2-receptor antagonists was similar before and after withdrawal. Smoking does not affect intragastric acidity in untreated volunteers and only slightly decreases the effectiveness of histamine H2-receptor antagonists on intragastric acidity. This effect best in part explains the unfavourable effect of smoking on healing of peptic ulcer in patients treated with these drugs.

Adult↗
PubMed1987

Reduction of gastric acidity with ranitidine or famotidine: early evening dosage is more effective than late evening dosage.

The antisecretory effect of a once daily dose of ranitidine and famotidine was examined after administration of the drugs either immediately after dinner or 3 h after dinner. A placebo-controlled multiple cross-over study was performed in 7 healthy ambulatory volunteers. They were given, on 6 separate days at least 1 week apart, either placebo, ranitidine 300 mg or famotidine 40 mg, either immediately after dinner or 3 h later. Breakfast, lunch and dinner were standardized. 24-Hour intragastric acidity was measured with a combined glass electrode. Duration of secretory inhibition by a drug was defined as the nighttime period between the first rise of pH above and the final fall below 3.5. This value represents the 95% upper confidence limit of nighttime pH values during placebo treatment. Secretory inhibition with early and late administration of ranitidine lasted for 10.7 and 7.3 h, respectively (p = 0.012). With famotidine it lasted for 10.1 and 7.1 h, respectively (p = 0.005). Gastric acidity after dinner was decreased by early but not late intake of ranitidine and famotidine. Thus, both ranitidine and famotidine were more effective when taken early, immediately after dinner, than when taken late in the evening. This observation might affect the mode of ulcer treatment with these drugs.

Adult↗