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Biomedical subjects

T C Chou

Publications and source records attributed to T C Chou.

At least 181 records · Page 10Linked to original sources
PubMed1986

When is the vectorcardiogram superior to the scalar electrocardiogram?

The clinical usefulness of the vectorcardiogram is well documented by the numerous reports published in the last 3 decades. It has been found more reliable than the electrocardiogram for the diagnosis of atrial enlargement and right ventricular hypertrophy. It is more sensitive than the electrocardiogram in the recognition of myocardial infarction, especially if the infarction is inferior or if it occurs in the presence of left bundle branch block or left anterior hemiblock. It is helpful in the diagnosis of ventricular pre-excitation and in the localization of the bypass tract. Some repolarization abnormalities are more clearly demonstrated by the vector display. However, some information, such as that on cardiac chamber size and myocardial damage, can also be obtained by other noninvasive tests that are often performed on the same patients. With the increasing awareness of cost-effectiveness of various laboratory procedures in medicine, the vectorcardiogram should no longer be considered a routine cardiac test and should be requested only for a specific clinical purpose. When properly utilized, vectorcardiography should remain a valuable diagnostic as well as teaching tool.

Cardiomegaly↗
PubMed1986

Delayed treatment with combinations of antiviral drugs in mice infected with herpes simplex virus and application of the median effect method of analysis.

Mice were inoculated intracerebrally with a lethal dose of herpes simplex virus type 2. Three days later, the mice were treated intraperitoneally, twice daily for 4 days, with the following drugs alone or in combination: acyclovir (ACV), vidarabine (ara-A), 2'-fluoro-5-iodoaracytosine (FIAC), and 2'-fluoro-5-methylarauracil (FMAU). Despite delayed treatment, most of the animals receiving low doses of FMAU alone or in combination with ACV or ara-A survived. In contrast, significantly higher mortality rates were noted in mice receiving ara-A, ACV, or FIAC alone. The data were analyzed for quantitation of synergism, additivity, and antagonism of multiple drug effect by the median effect method. The median effective doses (in nanomoles per kilogram per day) calculated in this manner were: FMAU, 22.5; FIAC, 510; ara-A, 901; ACV, 7,587; ACV-ara-A (drug ratio, 1:1), 550; FIAC-ara-A (1:1), 376; FIAC-ACV (1:1), 133; FMAU-ACV (1:8), 60.3; and FMAU-ara-A (1:8), 65.2. Marked synergy was found throughout a wide range of effect levels with the five different combinations, with no increased toxicity over the single-drug treatments. Similar results were obtained when the data were analyzed by the isobologram method. Since many patients with severe herpetic infections, such as herpes encephalitis, have a poor prognosis despite single-drug therapy, the possible use of combinations including low doses of FMAU deserves further investigation.

Animals↗
PubMed1985

Biologic and pharmacologic effects of harringtonine on human leukemia-lymphoma cells.

Ten human leukemia-lymphoma cell lines were tested for the growth-inhibitory effects of harringtonine (HT). HT was most active against HL-60 acute promyelocytic leukemia cells and least active against DND-41 acute lymphoblastic leukemia cells, with a 70-fold differential activity. Sensitivity of the cell lines is, in decreasing order: HL-60 greater than RPMI-8402 greater than DND-39A congruent to ML-2 congruent to MOLT-3 congruent to KG-1 greater than Daudi congruent to NALL-1 greater than BALM-2 greater than DND-41. The cell lines with rapid cell growth tended to be more sensitive to HT. To further elucidate the selectivity of the differential sensitivity, uptake and release of HT were compared in HL-60 and DND-41 cells. Uptake of [3H]HT into HL-60 and DND-41 cells showed no difference; however, the binding of [3H]HT to cellular components was greater than 16-fold higher in HL-60 cells than DND-41 cells. There were also minor, but significant differences in the inhibition of [3H]leucine incorporation into proteins of these two cell lines in the presence of 1 microgram/ml HT. To test whether the biological effects of HT are related to the concentration of, or exposure time to, HT, KG-1 cells were exposed to HT for different periods of time and the growth-inhibitory effects were compared. Increasing exposure time from 1 h to 3 h resulted in a 100-fold decrease in concentration X exposure time (c X t) at ID50; from 3 h to 6 h, in a 20-fold decrease at ID70; and from 6 h to 24 h, in a 16-fold decrease at ID90. HT was not inactivated by cells up to 24 h. These results indicate that (a) the sensitivity of different cell lines to HT may be related to the degree of HT binding; and (b) the effects of HT are more dependent on exposure time than concentration. Continuous infusion is thus rational for clinical trials of this drug, and the degree of HT binding to leukemic cells may be predictive of clinical response.

Alkaloids↗
PubMed1985

Synergistic effect of 4-hydroperoxycyclophosphamide and etoposide on a human promyelocytic leukemia cell line (HL-60) demonstrated by computer analysis.

Autologous stem cell transplantation using cryopreserved bone marrow offers the opportunity to rescue patients from hematopoietic toxicity caused by intensive chemotherapy. This approach is potentially useful for high-risk leukemias as well as for other cancers. The development of suitable methods for purging malignant cells from the bone marrow will offer a better chance of success for autologous stem cell transplantation. In this paper, we describe our efforts at purging myeloid cells. HL-60, a promyelocytic leukemia cell line, was used as a model. 4-Hydroperoxycyclophosphamide (4-HC) and VP-16-213 (VP-16) (either alone or in combination) were used to treat HL-60 cells and normal bone marrow. The cytotoxic effect of 4-HC (29.2 micrograms/ml; 100 microM) upon the HL-60 cell line was 99.8 +/- 0.12% (SE), and the colony-forming units-granulocyte, macrophage (CFU-cs) of normal bone marrow was inhibited by 82.5%. VP-16, at a concentration of 25 micrograms/ml (42.5 microM), can kill 99% of HL-60 cells and inhibit 72.7% of the CFU-cs. A drug mixture containing 4-HC (29.2 micrograms/ml) and VP-16 (10 micrograms/ml) (combination ratio, 1:0.342) reduces HL-60 cells to an undetectable number, and the CFU-cs were inhibited by 87.2%. The laboratory data were further analyzed for the synergistic effect of these two drugs by quantitative determination of the median effect plot and the multiple drug equation recently described by Chou and Talalay (Adv. Enz. Regul., 22: 27-55, 1984). Interactions of two drugs at different effect levels and at different combination ratios were then determined by computer simulation. At high effect levels, 4-HC and VP-16 in combination gave a synergistic cytocidal effect on HL-60 leukemic cells and gave an antagonistic inhibitory effect on normal bone marrow CFU-cs. This combination greatly increases the safety margin. Computer simulation of a dose effect relationship has also shown that the 4-HC:VP-16 combination ratio of 1:0.342 yields a better selective effect than a ratio of 1:0.856. This quantitative analysis suggests that the combination of these two drugs at the selected dose level offers a good method for purging nonlymphoblastic leukemia cells.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

The proliferative response of low-density human cell cultures to tumor promoters and its relevance to carcinogenic mechanisms in vitro.

The effects of the tumor promoter -12-O-tetradecanoyl phorbol-13-acetate, its analogues, and other tumor promoters, on the proliferation of human skin fibroblasts (SF) have been investigated. We have previously shown (Kopelovich and Bias, 1979), that TPA caused a biphasic (upward concave) dose effect in the cloning efficiency assay of normal and mutant human fibroblastic cell strains. Here we report that the biphasic dose response pattern, consisting of an inhibitory phase and a stimulatory phase, was shared by the active analogues of TPA, e.g., phorbol-12,13-dibutyrate and phorbol-12,13-dibenzoate. This biphasic dose effect relationship, however, was not seen with phorbol-12,13-diacetate or the inactive analogues of TPA such as phorbol and 4-O-methyl-12-O-tetradecanoyl phorbol-13-acetate, nor was it seen with mezerein, teleocidin, or bile-acid derivatives of humans. An analysis of the cloning efficiency data by the median-effect equation (Chou and Talalay, 1981) showed that in low-density cultures both the inhibitory phase and the stimulatory phase of the dose-effect relationships of TPA, its analogues, mezerein, and teleocidin exhibited a linear median-effect plot and thus closely followed the basic mass-action principle. The median-effect plot of these data allowed quantitative determination of growth curve characteristic such as regression coefficient, slope (a measure of sigmoidicity), median-effect concentrations such as I50 for the inhibitory effect, and A50 for the stimulatory effect (i.e., the relative potency of the analogues) and the transition point of the biphasic phenomenon in the case of the phorbol esters. In addition, we have demonstrated a relationship between the dose response effect of TPA on the proliferation of various human cells and tumor progression in vitro.

Caenorhabditis elegans Proteins↗
PubMed1984

Quantitative analysis of dose-effect relationships: the combined effects of multiple drugs or enzyme inhibitors.

A generalized method for analyzing the effects of multiple drugs and for determining summation, synergism and antagonism has been proposed. The derived, generalized equations are based on kinetic principles. The method is relatively simple and is not limited by whether the dose-effect relationships are hyperbolic or sigmoidal, whether the effects of the drugs are mutually exclusive or nonexclusive, whether the ligand interactions are competitive, noncompetitive or uncompetitive, whether the drugs are agonists or antagonists, or the number of drugs involved. The equations for the two most widely used methods for analyzing synergism, antagonism and summation of effects of multiple drugs, the isobologram and fractional product concepts, have been derived and been shown to have limitations in their applications. These two methods cannot be used indiscriminately. The equations underlying these two methods can be derived from a more generalized equation previously developed by us (59). It can be shown that the isobologram is valid only for drugs whose effects are mutually exclusive, whereas the fractional product method is valid only for mutually nonexclusive drugs which have hyperbolic dose-effect curves. Furthermore, in the isobol method, it is laborious to find proper combinations of drugs that would produce an iso-effective curve, and the fractional product method tends to give indication of synergism, since it underestimates the summation of the effect of mutually nonexclusive drugs that have sigmoidal dose-effect curves. The method described herein is devoid of these deficiencies and limitations. The simplified experimental design proposed for multiple drug-effect analysis has the following advantages: It provides a simple diagnostic plot (i.e., the median-effect plot) for evaluating the applicability of the data, and provides parameters that can be directly used to obtain a general equation for the dose-effect relation; the analysis which involves logarithmic conversion and linear regression can be readily carried out with a simple programmable electronic calculator and does not require special graph paper or tables; and the simplicity of the equation allows flexibility of application and the use of a minimum number of data points. This method has been used to analyze experimental data obtained from enzymatic, cellular and animal systems.

Adenosine Diphosphate↗
PubMed1984

Metabolic competition studies of 2'-fluoro-5-iodo-1-beta-d-arabinofuranosylcytosine in vero cells and herpes simplex type 1-infected vero cells.

2'-Fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine (FIAC) is a potent antiviral agent with minimal cytotoxicity. In Vero cells, incorporation of labeled dCyd and dThd into the acid-insoluble DNA fraction was, respectively, competitively and noncompetitively inhibited by FIAC. In herpes simplex type 1 (HSV-1) infected Vero cells, these inhibition patterns became noncompetitive. The inhibition constants of FIAC on dThd and dCyd incorporation into the acid-insoluble fraction during a 15-min period were greater than 30 microM which were much higher than the antiviral concentration of FIAC (ED90 = 0.003-0.013 microM) for continuous exposure. Incorporation of dUrd into acid-insoluble DNA was inhibited by 10 microM FIAC in HSV-1-infected Vero cells, but not in uninfected cells. The radioactivity of [2-14C]FIAC was incorporated into the acid-insoluble DNA fraction, and this incorporation in uninfected cells was strongly inhibited by 10 microM dCyd but not by dThd. By contrast, the incorporation in HSV-1-infected Vero cells was strongly inhibited by 10 microM dThd but not by dCyd. These data indicate that FIAC behaves metabolically like dThd, dUrd, or 5-iodo-dUrd in HSV-1-infected cells but like dCyd in noninfected cells. Thus, combined use of dCyd and FIAC may reduce cytotoxicity of FIAC or incorporation of FIAC into host cell DNA without affecting its antiviral activity. This finding is of significance since, for practical reasons, incorporation of FIAC into host cell DNA needs to be reduced as much as possible.

Animals↗
PubMed1984

Thymidine as a kinetic and biochemical modulator of 1-beta-D-arabinofuranosylcytosine in human acute nonlymphocytic leukemia.

We have carried out a clinical trial in which patients with relapsed leukemia were treated with thymidine (dThd) prior to and concomitantly with the administration of 1-beta-D-arabinofuranosylcytosine (ara-C) in an effort to kinetically and biochemically modulate the leukemic cells with two objectives: (a) to increase the S-phase fraction before giving ara-C; and (b) to increase the uptake and phosphorylation of ara-C. Six patients with acute nonlymphocytic leukemia who had relapsed after conventional or experimental therapy were given continuous i.v. infusions of dThd in conjunction with ara-C. dThd was started at 75 g/sq m/day (producing 1 mM plasma levels) and was given for 5 to 8 days until the proportion of bone marrow cells in S-phase (measured by autoradiography and flow cytometry) had increased and/or stabilized; then ara-C at 200 mg/sq m/day was begun. Twenty-four hr after initiation of ara-C therapy, the dThd dose was reduced to 30 g/sq m/day (plasma dThd, 0.1 to 0.6 mM). Both drugs were continued for 6 to 12 days until marrow aplasia or unacceptable toxicity occurred. Four patients with a base-line labeling index lower than 30% experienced a sustained increase in the S-phase fraction; two patients with a base-line labeling index higher than 30% experienced a reduction in the S-phase compartment during dThd infusion, in one case followed by an increase. The degree of S-phase arrest did not correlate with remission induction. In 5 patients, the flash incorporation of labeled ara-C into nucleoside triphosphate and deoxycytidine into DNA of bone marrow cells was measured. Three patients had a significant increase in the incorporation of deoxycytidine into DNA. Two of them achieved a complete remission. Increases in ara-C uptake were less impressive. A new technique was used to measure the absolute number of blasts present in the bone marrow. A decrease in leukemic cells between 0.9 and 2.6 logs10/mm was found at the end of the infusions. Three patients experienced greater than 2-log reduction. Two of them entered complete remission that lasted 6 weeks and 3 months, respectively. These correlations should be interpreted with caution because of the small number of patients treated. This study suggests that dThd, although of very limited therapeutic value by itself, may have potentiated the antitumor activity of ara-C to some extent. Whether this effect is of significance can only be determined by further studies.

Acute Disease↗
PubMed1984

Effect of very high-dose thymidine infusions on leukemia and lymphoma patients.

The physiological pyrimidine nucleoside thymidine (dThd) is cytotoxic to normal and neoplastic cells in culture that are exposed to concentrations in excess of 1 mM for prolonged periods. In order to explore the antileukemic potential of the compound, we have treated six patients with relapsed leukemia or lymphoma with marrow and blood involvement, by prolonged infusions of dThd, at dosages of 90 to 240 g/sq m/day for 14 to 29 days. Mean plasma dThd concentration ranged from 3.8 to 5.5 mM. Cerebrospinal fluid levels were measured on three occasions and ranged from 2 to 23.5% of simultaneous plasma levels. Diarrhea was dose limiting in one patient. The other side effects included nausea and vomiting in all patients, hepatotoxicity in two patients, electrolyte imbalance in one, progression of a pericardial effusion to tamponade in one, and mild central nervous system toxicity in five. In all cases, this therapy produced bone marrow aplasia. One patient with acute lymphoblastic leukemia, refractory to prior treatment, achieved a complete remission which lasted for 16 weeks. Another patient with lymphoblastic lymphoma had a greater than 50% reduction in his mediastinal mass which lasted for less than 1 month. At multiple points during therapy, the bone marrow S-phase fraction was measured by flow cytometry and autoradiography. In five patients, the proportion of cells in S phase increased during the first few days of the infusion but then returned to base line, concomitant with an overall reduction in the number of bone marrow blasts. Cytoreduction was evaluated by the technique of W. Hiddemann, B. D. Clarkson, T. Buchener, M. R. Melamed, and M. Andreeff (Blood, 59: 216-225, 1982). The magnitude of tumor cell kill ranged from 0.7 to 3.6 logs of blasts/cu mm of bone marrow. The data demonstrate that dThd is able to induce a complete remission in a patient with acute leukemia previously refractory to treatment. However, because of the very large drug quantities, fluid volumes, and the prolonged course required to produce the necessary tumor cell kill, this treatment approach is too impractical to be used extensively.

Adult↗
PubMed1983

Kinetic properties and inhibition of Acinetobacter glutaminase-asparaginase.

Kinetic parameters, substrate specificity and exclusivity of ligands at binding sites of L-glutaminase-L-asparaginase purified from Acinetobacter glutaminasificans were studied in order to gain knowledge about the dual activities of this enzyme and its inhibition by structural analogs. Both L-glutamine and L-asparagine, which showed similar Km (4 approximately 7 X 10(-5) M) and Vmax (molecular activity 1.0 min-1) values, were competitive with each other for the substrate binding site. The products, L-glutamic acid and L-aspartic acid, showed competitive inhibition with respect to either L-glutamine or L-asparagine as substrates. Multiple inhibition of the glutaminase activity by L-glutamic acid and L-aspartic acid indicated that these ligands are mutually exclusive at the product-releasing site. The initial rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in decreasing order of activity): 6-diazo-5-oxo-L-norleucine (DON), L-methionine sulfoximine, azaserine, and Acivicin. DON and azaserine inhibited both the asparaginase and glutaminase activities in a time-dependent and irreversible manner. The kinetic data suggest an ordered mechanism with glutamine or asparagine as the first substrate and glutamic acid or aspartic acid, respectively, as the last product. These results also suggest that a single mechanism and a single set of binding sites are responsible for catalyzing both of the enzyme's activities. The data also showed that succinylated enzyme, which has a 10-fold increase of plasma half-life in animals and humans and, thus, has benefit as a cancer chemotherapeutic agent, retained its catalytic activity and maintained Km and Vmax values similar to the native enzyme.

Acinetobacter↗
PubMed1983

Synthesis of an N-aminopyrazinonium analogue of cytidine.

An N-aminated pyrazine analogue of cytidine, in which the pyrimidine N(3) ring nitrogen and C(4) amino group were replaced by a C-amino and an N-amino function, respectively, was prepared as a potential deaminase-resistant cytidine antimetabolite. The nucleoside 1,2-diamino-4-beta-D-ribofuranosylpyrazin-2-onium chloride (6) was a mild cytostatic agent but was neither a substrate for nor an inhibitor of mouse kidney cytidine deaminase. It ionized with a lower pKa than expected. The anion did not undergo the dimerization usually observed with N-imino heterocyclic ylides but unerwent hydrolysis of the 2-amino group to yield a 1-aminopyrazine-2,3-dione nucleoside.

Animals↗
PubMed1983

Electrocardiographic and hemodynamic changes in experimental right ventricular infarction.

To investigate the electrocardiographic and hemodynamic changes in isolated right ventricular infarction, 0.25 ml or 0.5 ml of metallic mercury was injected into the right coronary artery of 14 closed-chest dogs. At autopsy, at least 60% of the right ventricle was necrotic in every dog. Hemodynamic observations were made in 11 and electrocardiographic mapping was performed in all 14 dogs. Right atrial pressure rose in 10 and left atrial pressure in nine of the 11 dogs; early right atrial pressure did not exceed left atrial pressure, but late right atrial pressure was greater in four dogs. Although cardiac output and blood pressure fell significantly, circulation was maintained. Twelve of 14 dogs had transient ST-segment elevation in the right precordial leads, and 12 developed right bundle branch block. Abnormal Q waves or R waves of 1 mm or less appeared in the right precordial leads in 13 of the 14 dogs. Since right bundle branch block and abnormal Q waves in the right precordial leads have not been recognized as useful signs in human right ventricular infarction, further investigations are warranted to determine their value in clinical applications.

Animals↗
PubMed1983

Uptake, initial effects, and chemotherapeutic efficacy of harringtonine in murine leukemic cells sensitive and resistant to vincristine and other chemotherapeutic agents.

[3H]Harringtonine was shown to be taken up rapidly by L1210/0 cells using a fast-mixing, fast-separating technique and was retained with a slow rate of limited release to the medium. Cells resistant to vincristine (L1210/VCR) showed impaired capability to take up the drug at 20 degrees. Its initial uptake in L1210 sublines in vitro was: L1210/0 greater than L1210/cyclophosphamide, L1210/1-beta-D-arabinofuranosylcytosine, L1210/6-mercaptopurine greater than L1210/5-fluorouracil, L1210/Adriamycin greater than L1210/VCR. In [3H]harringtonine-preloaded cells, L1210/0 retained significantly more radioactivity than did L1210/VCR cells after repeated washing with fresh medium at 37 degrees. The radioactivity appeared to be predominantly bound to the microsomal fractions. [3H]Leucine incorporation into protein in L1210/0 cells was inhibited 90% within 15 min by harringtonine (0.5 micrograms/ml); incorporation of [3H]thymidine into DNA and [3H]cytidine into RNA was much less inhibited and showed an apparent lag of onset for 5 and 10 min, respectively. The relative potency of harringtonine to inhibit [3H]leucine incorporation in the above sublines in vitro follows an order similar to their rates of uptake of harringtonine by these sublines of cells. The efficacy of harringtonine, 2.4 or 3.6 mg/kg i.p., in increasing the life span of C57BL/6 X DBA/2 F1 mice bearing the sublines of leukemic cells, on the average, was: L1210/0 greater than L1210/cyclophosphamide, L1210/6-mercaptopurine greater than L1210/1-beta-D-arabinofuranosylcytosine, L1210/5-fluorouracil greater than L1210/Adriamycin, L1210/VCR. These results suggest that: (a) protein synthesis is the major initial target for the effect of harringtonine; (b) harringtonine bound more tightly to the cellular components of VCR-sensitive leukemic cells than to VCR-resistant cells; and (c) cellular uptake of harringtonine and the relative potency of inhibiting protein synthesis in sublines have a rank order similar to the chemotherapeutic efficacy of harringtonine in these cells.

Alkaloids↗
PubMed1983

Modification by nitrobenzylthioinosine-5'-monophosphate of pseudoisocytidine pharmacokinetics in mice and rats through inhibition of membrane transport.

In isolated, perfused mouse livers, initial rates of uptake of [2-14C]pseudoisocytidine (PIC), measured during the first 15 secs of perfusion were markedly reduced when the perfusion medium contained 5 X 10(-6) M nitrobenzylthioinosine (NBMPR), a potent inhibitor of nucleoside transport. A similar inhibition of PIC uptake occurred when mice were treated with NBMPR-P (the 5'-monophosphate of NBMPR) at doses greater than 0.2 mg/kg ip injected 30 mins prior to the liver perfusion assay. However, in vivo studies showed that a late effect of NBMPR-P was enhancement in PIC levels in liver and other tissues in mice and rats, relative to levels in animals that had not received NBMPR-P. Increases in incorporation of PIC into RNA reflected the NBMPR-P-induced increases in tissue levels of PIC. NBMPR-P and other inhibitors of nucleoside transport may have therapeutic applications in manipulation of the pharmacokinetic behavior and toxicity of nucleoside drugs.

Animals↗