Search PubMed⌕ Search

Biomedical subjects

T C Chou

Publications and source records attributed to T C Chou.

At least 163 records · Page 9Linked to original sources
PubMed1988

Incorporation and metabolism of 2'-fluoro-5-substituted arabinosyl pyrimidines and their selective inhibition of viral DNA synthesis in herpes simplex virus type 1 (HSV-1)-infected and mock-infected Vero cells.

The incorporation and metabolism of 2'-fluoro-5-substituted arabinosyl pyrimidine analogs, and their selective inhibition of viral DNA synthesis in herpes simplex virus type 1 (HSV-1)-infected and mock-infected Vero cells were studied by HPLC and CsCl isopycnic density gradient analysis of isolated DNAs. The amounts of radiolabeled analogs incorporated as parent compound following 10 microM exposure for 4 h were 10-fold higher in HSV-1-infected vs mock-infected cells for 2'-fluoro-5-difluoromethyl-Ara-U (F2FMAU); 4.3-fold higher for 5-ethyl deoxyuridine (EdU); 2.6-fold higher for 2'-fluoro-5-methyl-Ara-U (FMAU) and 1.7-fold higher for dThd. For 2'-fluoro-5-ethyl-Ara-U (FEAU), 3.0 pmole of unchanged moiety was incorporated per 10(6) HSV-1-infected cells but no incorporation was detected in mock-infected cells. HPLC profiles showed that the percentages of radiolabeled analogs incorporated as parent compound in the DNA extracted from HSV-1-infected cells were 31.0% for F2FMAU, 99.6% for EdU, 83.5% for FEAU and 98.3% for FMAU; from mock-infected cells, they were 63.6% for F2FMAU, 96.7% for EdU, 97.3% for FMAU and no incorporation into DNA for FEAU was detected. CsCl density gradient analyses of isolated DNA showed that viral DNA synthesis was inhibited 98% by 10 microM FEAU, 92% by 10 microM F2FMAU, 90% by 2 microM FMAU and 80% by 50 microM EdU, whereas cellular DNA synthesis was inhibited by 53, 44, 61, 66 and 54%, respectively. We conclude that: (a) FEAU incorporation into host-cell DNA was not detectable but FEAU was selectively incorporated into HSV-infected cells; (b) FMAU and FEAU were metabolically stable; however, F2FMAU was extensively metabolized; (c) FEAU and F2FMAU were among the most selective inhibitors of HSV-1 DNA synthesis while allowing cellular DNA synthesis to continue.

Animals↗
PubMed1988

Antagonistic interactions of hexamethylene bisacetamide in combination with 1-beta-D-arabinofuranosylcytosine, adriamycin and harringtonine on the growth and differentiation of HL-60 cells in vitro.

Selective killing of cancer cells by cytotoxic agents and the conversion of cancerous cells to normal state by differentiation agents represent two basically different approaches in chemotherapy. In this study, we examined the combination of the cell differentiation inducer, hexamethylene bisacetamide (HMBA), and the cytotoxic agents, 1-beta-D-arabinofuranosylcytosine (Ara-C), adriamycin (Adr) and harringtonine (HT), for cytotoxicity and induction of cell differentiation in HL-60 cells by measuring cell growth inhibition, morphological maturation and nitroblue tetrazolium (NBT) reduction. To determine quantitatively whether the effects produced by these combinations were additive, synergistic or antagonistic, we used a computer program based on the median-effect principle and isobologram equations (Adv. Enz. Reg. 22, 27-55, 1984), After 5-day exposure to each drug alone we found that the ED50s for cell growth inhibition were 0.01 microM for Ara-C, 0.012 microM for Adr, 0.017 microM for HT and 2.53 mM for HMBA. ED50s for differentiation were 0.089 microM (morphology), 0.06 microM (NBT) for Ara-C; 0.12 microM (morphology), 0.09 microM (NBT) for Adr; 0.04 microM (morphology) 0.06 microM (NBT) for HT; and 2.55 mM (morphology), 2.43 mM (NBT) for HMBA, respectively. At dose levels from ED50 to ED95, the combinations of Adr/HMBA and HT/HMBA produced antagonistic cytotoxic and cell differentiation effects. The combination of Ara-C/HMBA produced antagonistic cytotoxic and cell differentiation effects. The combination of Ara-C/HMBA produced antagonistic cytotoxic effects but slight synergistic cell differentiation effects. On the basis of this study, we conclude that the equipotency combinations of the above three pairs of drugs do not synergistically enhance cytotoxicity or cell differentiation effects in vitro at effect levels high enough for the successful treatment of acute leukemia. Other combinations of cell differentiation agents with cytotoxic agents or biological response modifiers remain to be explored.

Acetamides↗
PubMed1988

Chemical synthesis and biological activities of 5-deazaaminopterin analogues bearing substituent(s) at the 5- and/or 7-position(s).

Condensation of cyanothioacetamide (4) with ethyl alpha-(ethoxymethylene)acetoacetate (5b), ethyl 4-ethoxy-2-(ethoxymethylene)-3-oxobutanoate (5c), ethyl 2-(ethoxymethylene)-3-oxo-4-phenylpropanoate (5d) afforded exclusively the corresponding 6-substituted pyridines (6b-d). Cyclization of 4 with 3-carbethoxybutane-2,4-dione (5e) gave 3-cyano-5-(ethoxycarbonyl)-4,6-dimethylpyridine-2(1H)-thione (6e), whereas reaction of 4 with 3-carbethoxy-1-phenylpropane-1,3-dione (5f) yielded two products, 3-cyano-5-(ethoxycarbonyl)-4-methyl-6-phenylpyridine-2(1H)-thione (6f) and the 6-methyl-4-phenyl isomer 6g. The structural assignments for 6f and 6g are made on the basis of 1H and 13C NMR spectral analyses of the 2-(methylthio)nicotinates (7f,g) prepared from 6f and 6g by treatment with MeI/K2CO3. Nicotinates 7b,d-g were converted into their corresponding 2,4-diaminopyrido[2,3-d]pyrimidines 12b,d-g in five steps, via reduction, protection, oxidation, condensation with guanidine, and deprotection. The 7-mono- and 5,7-disubstituted-5-deazaaminopterins (1b,d-g) were prepared from the respective pyrido[2,3-d]pyrimidines 12b,d-g. Preliminary biological studies showed that 7-methyl and 5,7-dimethyl analogues (1b and 1e) were less active than methotrexate against human leukemic HL-60 and murine L-1210 cells in tissue culture. Compound 1e produced an ILS of 71% at 100 mg/kg per day X 5 (ip) in BDF mice inoculated ip with 10(6) L-1210 cells.

Aminopterin↗
PubMed1988

Nucleosides. 150. Synthesis and some biological properties of 5-monofluoromethyl, 5-difluoromethyl, and 5-trifluoromethyl derivatives of 2'-deoxyuridine and 2'-deoxy-2'-fluoro-beta-D-arabinofuranosyluracil.

A new synthesis of 5-(monofluoromethyl)- and 5-(difluoromethyl)-2'-deoxy-2'-fluoro-beta-D-arabinofuranosyluracil (F-FMAU and F2-FMAU) is reported. 3',5'-Di-O-(tert-butyldiphenyl)silylated thymidine or FMAU was photochemically brominated with NBS to the corresponding alpha-monobromide, which was hydrolyzed to the 5-hydroxymethyl derivative. Further oxidation of the latter with MnO2 afforded the 5-formyluracil nucleoside. Treatment of these nucleosides with DAST in CH2Cl2 gave the protected alpha-fluorinated nucleosides. Desiylation with TBAF afforded the desired free nucleosides. Also, 5-(trifluoromethyl)-2'-deoxy-2'-fluoro-beta-D-arabinofuranosyluracil (F3-FMAU) was synthesized by copper-catalyzed trifluoromethylation of 5-iodo-2'-fluoro-ara-U (FIAU). These new nucleosides were studied in comparison with the corresponding 2'-deoxy-erythro-pentofuranosyl derivatives, for their inhibitory activity against cellular thymidylate synthase (TS) and [3H]TdR incorporation into DNA, cytotoxicity against HL-60 cells, and antiviral activity against herpes simplex types 1 and 2 (HSV-1 and -2). F2-TDR and F3-TDR strongly inhibited TS and were also quite cytotoxic and antiherpetic, whereas FTDR was only active in the antiviral assay. In the 2'-fluoroarabino series, fluorine substitution at the alpha-methyl function did not alter significantly the antiherpetic activity. Although FMAU and F-FMAU did not inhibit TS to any significant extent, F2-FMAU and F3-FMAU were weakly inhibitory. The latter nucleosides did not inhibit [3H]TDR incorporation into DNA, while all the other alpha-fluorinated thymine nucleosides inhibited the incorporation of radioactivity of [3H]TDR into DNA to various extents. F2-FMAU and F3-FMAU were about 2 orders of magnitude less cytotoxic against HL-60 cells than were F2-TDR and F3-TDR. The results strongly suggest that in both the 2'-deoxy-2'-fluoroarabino and the 2'-deoxy-erythro-pentofurano series the cytotoxic action of the alpha,alpha-difluoro and alpha,alpha,alpha-trifluoro derivatives may involve the inhibition of TS. The synthesis of [2-14C]F2-FMAU, as an experimental imaging agent, is also described. Unfortunately, the highly selective uptake of the labeled compound within infected brain regions previously noted with [2-14C]FMAU was not detected with the derivative [2-14C]F2-FMAU.

Animals↗
PubMed1988

Synergistic interaction of 2',3'-dideoxycytidine and recombinant interferon-alpha-A on replication of human immunodeficiency virus type 1.

Effective treatment of infections with human immunodeficiency virus type 1 (HIV-1) may require a combination of antiviral drugs that act by different mechanisms. We report that the combination of 2',3'-dideoxycytidine (ddCyd) and recombinant interferon-alpha-A (rIFN-alpha-A) acts synergistically against HIV-1 replication in vitro. Various cell types (peripheral blood leukocytes, a CD4-positive T cell line, and two monocyte-macrophage lines) have been studied. For each set of dose-effect data, the degree of drug interaction was quantitatively assessed with the median-effect principle and the isobologram equation by using a computer analysis. Under various culture conditions using several concentrations of drugs, multiplicities of infectious virus, and assay systems, antiviral synergism was consistently observed against HIV-1 replication without enhanced cell toxicity. Synergism was seen at concentrations as low as 0.02 microM ddCyd plus 4 U of rIFN-alpha-A/mL or 0.01 microM ddCyd plus 8 U of rIFN-alpha-A/mL, whereas 10-fold higher concentrations were usually required to achieve similar effects with single drugs.

Antiviral Agents↗
PubMed1988

Recurrent ventricular tachycardia due to pentamidine-induced cardiotoxicity.

Although pentamidine isethionate is effective in the treatment of Pneumocystis carinii pneumonia, it frequently causes serious adverse reactions. We report a case of reversible pentamidine-induced cardiotoxicity, characterized electrocardiographically by prolongation of the QT interval, T-wave inversion, and electrical alternans of the U-wave. In addition, the patient had repeated episodes of ventricular tachycardia that culminated in torsades de pointes. Our case re-emphasizes the need for close patient monitoring during pentamidine therapy.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Phase I and clinical pharmacology study of trimetrexate administered weekly for three weeks.

Trimetrexate, a new antifolate compound, was administered by 30-min infusions weekly for 3 weeks to 29 patients with solid tumors in a Phase I study. Thrombocytopenia was dose limiting, but highly variable among patients at a given dose level; other toxicity was mild and uncommon. Twenty-three patients participated in pharmacokinetic studies and five patients participated in a study of the effects of trimetrexate on [6-3H]-deoxyuridine incorporation into hematopoietic cell DNA. The median total body clearance of trimetrexate for each dose level was independent of dose but the total body clearance varied widely among patients at a given dose level. The magnitude of the fall in platelet count in individual patients correlated well with the amount of exposure to trimetrexate, but not with the extent of prior therapy. The amount of [6-3H]deoxyuridine incorporation into hematopoietic cell DNA at 72 h after drug administration correlated with the total body clearance of trimetrexate. The total body clearance of trimetrexate was reduced in patients with impaired hepatic synthetic function, as judged by low pretreatment serum albumin concentrations. The recommended Phase II starting dose on this schedule is 130 mg/m2 weekly for 3 weeks; patients with hypoalbuminemia should be treated at lower doses.

Adenocarcinoma↗
PubMed1987

Toxicity, elimination, and metabolism of 10-ethyl-10-deazaaminopterin in rats and dogs.

10-Ethyl-10-deazaaminopterin (10-EdAM) is an antifolate compound with greater therapeutic activity than methotrexate against transplanted tumors in mice. When given weekly for 3 weeks, the 10% lethal dose in rats was 125 mg/kg (i.p.) and in dogs it was 2.5 mg/kg (i.v.). The major histopathological findings in intoxicated animals were damage to the mucosa of the gastrointestinal tract in rats and dogs and hypocellularity of the marrow in rats. The elimination of 50 mg/kg of 10-EdAM from the plasma of rats was triexponential with a terminal phase t1/2 of 18.5 h but a mean residence time of 0.7 h. The primary route of elimination in rats was biliary secretion of parent compound and eventual excretion of the parent compound and the deglutamate metabolite in the feces; the 7-hydroxy metabolite was also present in plasma, bile, and feces. Biliary elimination was independent of dose over a 5-fold range. The elimination of 10-EdAM from the plasma of dogs was also triexponential with a mean terminal phase t1/2 of 9.1 h and a mean residence time of 2.5 h; nonrenal clearance was the primary route of elimination. The pharmacokinetic parameters were independent of dose over the range of 0.25 to 5.0 mg/kg. High tissue concentrations of 10-EdAM were observed initially in liver, kidney, and small intestine of rats, while concentrations in bone marrow were low. Some polyglutamate formation was observed in these tissues as early as 0.5 h after drug administration but declined over 72 h.

Aminopterin↗
PubMed1987

Schedule-dependent interaction of alpha-difluoromethylornithine and cis-diamminedichloroplatinum(II) against human and hamster pancreatic cancer cell lines.

The interaction of cis-diamminedichloroplatinum (cisplatin) and alpha-difluoromethylornithine (DFMO) has been previously shown by us to be roughly additive in enhancing the growth-inhibitory effects of cisplatin and by another group of investigators to be antagonistic. Since two different schedules of administration were used, we sought to investigate systematically the role of schedule dependence in the interaction of cisplatin and DFMO in a panel of pancreatic adenocarcinoma cell lines (PANC-1, of human origin, and WD PaCa and PD PaCa, both of hamster origin). Dose-effect relationships of single drug alone and in combination were analyzed by the median-effect principle and by the combination indices for the quantitation of synergism or antagonism with the aid of a microcomputer. Pre-cisplatin administration of DFMO for 2 or 5 to 6 days at concentrations of 50 or 100 micrograms/ml (0.21 or 0.42 mM) was found to antagonize the effects of cisplatin to various degrees in the cell lines. In contrast, whenever post-cisplatin DFMO was administered, marked enhancement, which was synergistic in most instances, of cisplatin's inhibition of colony formation was found. Thus, the interaction of cisplatin and DFMO is felt to be schedule dependent with deleterious effects found only when DFMO is administered prior to and not following cisplatin. Furthermore, the combination shows promise as an approach to overcoming drug resistance in pancreatic cancer.

Adenocarcinoma↗
PubMed1987

Ribavirin antagonizes the effect of azidothymidine on HIV replication.

Azidothymidine and ribavirin both inhibit replication of human immunodeficiency virus in vitro and show promise of clinical utility in patients infected with this virus. In this study, the possible interactions of these drugs were examined in vitro, and a reproducible antagonism between azidothymidine and ribavirin was found to occur under a variety of experimental conditions. The mechanism responsible for this antagonism appeared to be inhibition of azidothymidine phosphorylation by ribavirin. Because similar effects may occur in vivo, clinical trials of these two drugs in combination must be performed only under carefully controlled conditions.

Cell Line↗
PubMed1987

Comparative cytotoxicity of various drug combinations for human leukemic cells and normal hematopoietic precursors.

The development of suitable methods for purging the malignant cells contaminating the bone marrow of patients with cancer may offer a better chance of success for autologous bone marrow transplantation. In this paper, we further describe our efforts at purging acute myelogenous leukemia cells. HL-60, a promyelocytic leukemia cell line, was used as a model. 4-Hydroperoxycyclophosphamide (4-HC), VP-16-213 (VP-16), and Adriamycin were used alone or in combination to develop the best method to purge HL-60 cells. The cytotoxicity of 29.2 micrograms/ml (100 microM) of 4-HC was 99.8 +/- 0.12% (SD) on HL-60 cells and 82.5% on colony forming units-granulocyte, macrophage. Ninety-nine % of HL-60 cells and 72.7% of colony forming units-granulocyte, macrophage were inhibited by VP-16 at a concentration of 25 micrograms/ml (42.5 microM). The cytotoxicity of 1.5 micrograms/ml (2.76 microM) of Adriamycin on HL-60 cells was 98.6 +/- 0.8% and inhibited colony forming units-granulocyte, macrophage by 50.8%. The cytotoxicity and interactions of any two drug combinations at different combination ratios and the different effect levels were quantitatively determined by median effect plot and the multiple drug effect equation (T-C. Chou and P. Talalay. Adv. Enzyme Regul. 22: 27-55, 1984). The combination of 4-HC and VP-16 at a 4-HC:VP-16 drug ratio of 1:0.342 was found to be the best for selective toxicity towards HL-60 cells and was superior to the 4-HC-Adriamycin or VP-16 Adriamycin combination for usefulness in purging bone marrow.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1987

Cell differentiation effects of 2'-fluoro-1-beta-D-arabinofuranosyl pyrimidines in HL-60 cells.

A group of 2'-fluoro and 5-substituted arabinosyl pyrimidines and a group of base-substituted pseudoisocytidine analogs were evaluated for their capacity to induce differentiation in the human promyelocytic leukemia cell line, HL-60. These compounds were compared to 1-beta-D-arabinofuranosylcytosine (Ara-C) by monitoring: (1) inhibition of cell growth; (2) morphological maturation; (3) nitroblue tetrazolium (NBT) reduction; (4) expression of a myeloid differentiation antigen, Mo1; and (5) inhibition of colony formation. Exposure of logarithmically growing cells for 5 days to Ara-C, 2'-fluoro-Ara-C (FAC), 2'-fluoro-5-methyl-Ara-C (FMAC) and 2'-fluoro-5-ethyl-Ara-C (FEAC) resulted in cell growth inhibition at ED50 concentrations of 0.007, 0.11, 1.7 and 18 microM, and at cytostatic concentrations of 0.1, 0.5, 5.0 and 50 microM, respectively. These compounds induced granulocytic and monocytic maturation, reduction of NBT, increased expression of Mo1 antigen and a decrease or loss of both cell proliferation and colony formation in semisolid medium. There were few, if any, cell differentiation effects for the uracil nucleosides and pseudoisonucleosides tested. We found that Ara-C was the most cytotoxic of the compounds, and that when comparing absolute numbers of differentiated cells, i.e. percent of positive cells multiplied by the number of viable cells, FAC, FMAC and FEAC were superior to Ara-C inducing differentiation of HL-60 cells.

Antigens, Differentiation↗
PubMed1987

Effect of 9-(1,3-dihydroxy-2-propoxymethyl)guanine and recombinant human beta interferon alone and in combination on simian varicella virus infection in monkeys.

Treatment of viral infections with combinations of antiviral agents may permit administration of reduced doses of either or both drugs. Lowered doses may reduce associated toxicity. Intravenous administration of substantial doses of either human recombinant beta interferon (rHuIFN-beta) or 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) prevents development of simian varicella virus infection in African green monkeys. Daily doses of 2 X 10(6) U of rHuIFN-beta/kg inhibited clinical disease in monkeys inoculated with simian varicella virus, and doses of DHPG between 20 and 60 mg/kg per day were necessary for similar antiviral effects. Intravenous administration of combinations of rHuIFN-beta and DHPG permitted an approximately 100-fold reduction in the effective dose of rHuIFN-beta and a 10-fold reduction in the effective dose of DHPG. Analysis of data relating to viremia by using the method of the median-effect principle showed the combination of rHuIFN-beta and DHPG was strongly synergistic in treatment of this infection.

Acyclovir↗
PubMed1987

Synergistic inhibition of human immunodeficiency virus in vitro by azidothymidine and recombinant alpha A interferon.

Both recombinant alpha A interferon and azidothymidine inhibit the replication of human immunodeficiency virus in peripheral blood mononuclear cells. Combinations of recombinant alpha A interferon and azidothymidine at concentrations that are easily achievable in patients synergistically inhibit human immunodeficiency virus in vitro with minimal toxicity. Combinations of antiretroviral compounds that act by different mechanisms may prove useful in the treatment of acquired immunodeficiency syndrome-related disorders.

Antiviral Agents↗
PubMed1987

Synthesis and biological effects of 2'-fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil.

2'-Fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil (FEAU) was synthesized, and its biological activities were compared with those of 2'-fluoro-5-methyl-1-beta-D-arabinofuranosyluracil (FMAU). Earlier studies indicated that both compounds showed potent anti-herpes simplex virus activity, with a 50% effective dose (ED50) of less than 0.25 microM. In the present study the cell growth inhibitory activity of FEAU (ED50, 200 to 2,060 microM) was found to be about 100-fold less than that of FMAU. With an ED50 ranging from 630 to 3,700 microM, FEAU only weakly inhibited thymidine incorporation into DNA, as compared with FMAU with an ED50 of 9 to 28 microM. Following exposure to [2-14C]FEAU (100 microM), 0.48 pmol/10(6) cells per h was incorporated into the DNA of herpes simplex virus type 1-infected Vero cells, whereas no detectable incorporation was found in uninfected Vero cells or L1210 cells. The Ki of FEAU for thymidine kinase purified from human leukemic cells was greater than 150 microM. For herpes simplex virus type 1- and 2-encoded thymidine kinases, the Kis were 0.6 and 0.74 microM, respectively. Both FEAU and FMAU were relatively nontoxic for mice, with a 50% lethal dose of greater than 800 mg/kg per day (four intraperitoneal doses). However, the lethal dose of FEAU for dogs was 100 mg/kg per day (10 intravenous doses), a dose which is 40- to 80-fold greater than the toxic dose of FMAU. These results suggest that FEAU is a worthy candidate for further development as an antiherpetic agent.

Antiviral Agents↗