PubMed Health⌕ Search

Biomedical subjects

W C Tang

Publications and source records attributed to W C Tang.

11 recordsLinked to original sources
PubMed2001

Lycobetaine acts as a selective topoisomerase II beta poison and inhibits the growth of human tumour cells.

The phenanthridine alkaloid lycobetaine is a minor constituent of Amaryllidaceae. Inhibition of cell growth was studied in the clonogenic assay on 21 human tumour xenografts (mean IC(50) = 0.8 microM). The growth of human leukaemia cell lines was also potently inhibited (mean IC(50) = 1.3 microM). Athymic nude mice, carrying s.c. implanted human gastric tumour xenograft GXF251, were treated i.p. with lycobetaine for 4 weeks, resulting in a marked tumour growth delay. Lycobetaine was found to act as a specific topoisomerase II beta poison. In the presence of calf thymus DNA, pure recombinant human topoisomerase II beta protein was selectively depleted from SDS-gels, whereas no depletion of topoisomerase II alpha protein was observed. In A431 cells immunoband-depletion of topoisomerase II beta was induced, suggesting stabilization of the covalent catalytic DNA-intermediate in living cells. It is reasonable to assume that this mechanism will cause or at least contribute significantly to the antitumour activity.

Alkaloids↗
PubMed2000

[The development of a double point sensor for the pulse].

This article has introduced the research and design on a double point sensor for the comprehensive pulse. The difference of this sensor from the single point sensor is that it is able to obtain a mechanics parameter from the pulse signals of the traditional Chinese medicine. This would be a great help for the more detailed quantitative analysis of the pulse signals of the traditional Chinese medicine. It has also explored the contribution of the double point sensor to the clinical medicine.

Equipment Design↗
PubMed1998

Utilization of sorbed compounds by microorganisms specifically isolated for that purpose.

A bacterium obtained by enrichment on nonsorbed phenanthrene was unable to degrade phenanthrene sorbed to polyacrylic beads and had little activity on phenanthrene sorbed to lake-bottom sediment. A bacterium obtained by enrichment on phenanthrene sorbed to polyacrylic beads readily mineralized the compound sorbed to the beads or the sediment. Degradation by the second bacterium of phenanthrene sorbed to beads 38-63 microns or 63-150 microns in diameter was more rapid than the rate of desorption of the hydrocarbon in the absence of the bacterium. Little degradation of sorbed, nonleachable phenanthrene in soil was effected by another isolate obtained by enrichment with the nonsorbed hydrocarbon, but a mixed culture and the bacterium obtained by enrichment on the sorbed compound extensively degraded phenanthrene. Because microorganisms specifically obtained for their capacity to degrade sorbed phenanthrene are more active than species not specialized for use of the bound compound, we suggest that microorganisms enriched on nonsorbed compounds may not be appropriate for evaluation of biodegradation and bioremediation of sorbed compounds.

Bacteria↗
PubMed1991

Reversible impairment of myocardial contractility due to hypercarbic acidosis in the isolated perfused rat heart.

BACKGROUND AND METHODS: Striking increases in PCO2 of the myocardium have recently been documented during cardiac arrest. The purpose of the present study was to investigate selective effects of hypercarbia as distinct from acidosis on left ventricular contractile function and oxygen utilization. An isolated, spontaneously beating rat heart preparation was utilized. The perfusate was equilibrated with gases containing 5%, 10%, 20%, and 30% CO2. In a subset of experiments, the [H+] was adjusted independently of PCO2 by decreasing the concentration of HCO3-. RESULTS: When the PCO2 of the perfusate was progressively increased from 36 to 146 torr (4.8 to 29.5 kPa), the left ventricular systolic pressure (LVSP) generated by the isolated heart and the maximum rate of pressure change in the left ventricle (dP/dt) were decreased to 20% of their control values. However, comparable acidosis in the absence of hypercarbia produced only minimal decreases in the LVSP or dP/dt such that contractility remained at greater than or equal to 88%. Increases in the perfusate PCO2 but not in the perfusate H+ were highly correlated with decreases in both myocardial contractility and oxygen consumption (r2 = .88). CONCLUSION: Hypercarbia rather than acidosis accounts for decreased contractility and oxygen utilization in the isolated perfused rat heart.

Acidosis↗
PubMed1990

Androgen-linked alkylating agents: biological activity in methylnitrosourea-induced rat mammary carcinoma.

This article gives a comprehensive survey on the anticancer activity of nitrosoureas linked to steroidal androgens in methylnitrosourea (MMU)-induced rat mammary carcinoma. cis-Androsterone, testosterone, 19-nortestosterone and 5-alpha-dihydrotestosterone were used as carrier hormones and were linked to various cytotoxic N-[N'-(2-chloroethyl)-N'-nitrosocarbamoyl] (CNC)-aminoacids and to N-(2-hydroxyethyl)-N'-(2-chloroethyl)-N'-nitrosourea hemisuccinate (HECNU-hemisuccinate). In the MNU-model used esters of dihydrotestosterone (DHT) invariably were more active and less toxic than those of testosterone, nortestosterone and cis-androsterone. Within the DHT esters of CNC-aminoacids those of CNC-glycine, CNC-methionine and CNC-alanine showed the highest antineoplastic activities and superiority compared with equimolar dosages of their unlinked mixtures. Additionally, CNC-alanine-DHT ester had the highest therapeutic ratio of all agents investigated. HECNU-hemisuccinate-DHT ester, on the other hand, achieved even higher antitumor activity at the optimal dose but had a narrower therapeutic ratio. No obvious correlation between antineoplastic efficacy and receptor binding affinity could be demonstrated, but, to be active, a conjugate apparently had to have some receptor binding affinity for both androgen and progesterone receptors. The results obtained indicate that linking antineoplastic agents to transport molecules with affinity to steroid receptors is a highly promising approach to obtain drugs with specific activity in steroid receptor containing tumors.

Alkylating Agents↗
PubMed1986

Synthesis and antineoplastic activity of CNC-cysteamine and related compounds.

N'-[N-(2-Chloroethyl)-N-nitroso]carbamoyl cysteamine (CNC-cysteamine) and several related compounds have been synthesized and tested against L 1210 leukemia in mice. Reaction of N-(2-chloroethyl)-N-nitrosocarbamoyl azide (CNC-azide) with cysteamine yielded CNC-cysteamine and bis(CNC)cystamine. Reaction of CNC-azide with cystamine in the presence of triethylamine gave bis(CNC)cystamine. Unexpectedly, formation of CNC-cystamine carboxylazide as a minor reaction product was also observed. N-(2-Chloroethyl)carbamoyl cysteamine 2-chloroethylcarbamate was formed when 2-chloroethyl isocyanate was reacted with cysteamine. Nitrosation of this cysteamine N,S-dicarbamoyl derivative led to formation of a mixture of two dinitroso isomers. Preliminary testing of the newly synthesized CNC-derivatives against L 1210 leukemia in mice revealed that CNC-cysteamine, its disulfide bis(CNC)cystamine and CNC-cystamine carboxylazide were highly active against L 1210 leukemia.

Animals↗
PubMed1984

Metabolism of, and DNA methylation by, N-nitrosomethylbenzylamine in chicken.

The metabolism of 14C-nitrosomethylbenzylamine (NMBA) was studied in chicken. Following a single IV dose of 2 mg/kg, 14C-NMBA was cleared from the blood with a half-life of 3.8 min. At 10 min after administration 14C-NMBA was totally metabolized in the liver, whereas in the esophagus no measurable metabolic degradation had taken place. Maximum exhalation of radioactive CO2 occurred 1 h after IV administration of NMBA, and 11% of the total radioactivity had been exhaled as CO2 by 8 h. These results are compared with data on the metabolism of NMBA in the rat. The analysis of methylated bases in the DNA of different organs of chicken revealed that 7-me guanine was formed in all organs. The highest amount of 0(6)-me guanine was found in liver DNA, followed by kidney DNA. O6-me guanine was not detectable in any other organ. The O6-/7-me guanine ratio in DNA was calculated to be 0.05 and 0.02 for liver and 0.01 for kidneys.

Animals↗