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Biomedical subjects

K C Chow

Publications and source records attributed to K C Chow.

At least 55 records · Page 3Linked to original sources
PubMed1997

Expression of DNA topoisomerase II alpha and multidrug resistance p-glycoprotein in acute leukemia.

BACKGROUND: Drug resistance is a major cause of treatment failure in acute leukemia. Overexpression of multidrug resistance gene and decreased activity of topoisomerase II alpha are suggested as two important mechanisms for this resistance. METHODS: We used immunohistochemical method to determine the expressions of both topoisomerase II alpha (topo II alpha) and p-glycoprotein (gp-170) in bone marrow biopsy specimens from 68 cases of acute leukemia. Patients were divided into four groups: (1) leukemia cells with high score for topo II alpha and negative for gp-170; (2) leukemia cells with high score for topo II alpha and positive for gp-170; (3) leukemia cells with low score for topo II alpha and negative for gp-170; and (4) leukemia cells with low score for topo II alpha and positive for gp-170. The clinical responses were then followed as routine, and the clinical correlation was evaluated by analysis of variance and Pearson Chi-Square test. RESULTS: The measure of the single parameter (either topo II alpha or gp-170 alone) did not show a significant difference in the overall survival. However, the complete response rate was much higher in the first group patients whose bone marrow reading score was high in topo II alpha and negative for gp-170 expression. Survival duration increased with the increase in the complete response rate. CONCLUSIONS: Combined parameters of topo II alpha and gp-170 are more useful than any individual parameter for the prognosis of acute leukemia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Isolation and characterization of the Bacillus subtilis tryptophanyl-tRNA synthetase gene (trpS) conferring 5-fluorotryptophan resistance and temperature sensitivity.

The mutant trpS gene of Bacillus subtilis encoding a thermosensitive tryptophanyl-tRNA synthetase that also confers resistance to growth inhibition by 5-fluorotryptophan at permissive temperature has been isolated and characterized. A point mutation at codon 82 of the gene from a wild-type TCA codon for Ser to a TTA codon for Leu has been identified.

Bacillus subtilis↗
PubMed1996

Expression of Epstein-Barr virus-encoded RNAs as a marker for metastatic undifferentiated nasopharyngeal carcinoma.

BACKGROUND: Epstein-Barr virus (EBV) is associated with undifferentiated nasopharyngeal carcinoma (NPC). EBV-encoded nonpolyadenlyated RNAs (EBERs) are often used as a marker to detect EBV-infected NPC cells. This study was conducted to document the expression and determine the significance of EBERs in NPC cells at various metastatic sites. METHODS: An in situ hybridization (ISH) technique was used to identify the presence of EBERs in paraffin embedded tissues of primary and metastatic sites obtained from 21 patients with NPC. Nineteen of these patients had undifferentiated lesions, and 2 had squamous cell carcinoma. One hundred and fifty specimens of normal tissues and tissues from patients with a variety of benign and malignant diseases other than NPC served as controls. In the NPC specimens, the expression of latent membrane protein (LMP) and a lytic protein, BZLF-1, were also examined by immunohistochemistry. RESULTS: Tissues from all patients with undifferentiated NPC and one patient with squamous cell carcinoma contained EBERs in the malignant cells; the other case of squamous cell carcinoma was negative. In metastatic NPCs, LMP was expressed in 18% (4 of 22) of tissues whereas BZLF-1 was not expressed in any tissues. EBERs were not detected in the 43 patients with normal tissues and benign lesions. In malignant diseases other than NPC, EBERs were detected in only 2 of 12 cases of non-Hodgkin's lymphoma, 1 of 2 cases of Hodgkin's lymphoma, and 1 of 6 cases of gastric cancer. CONCLUSIONS: By virtue of the direct correlation between latent EBV infection and NPC, the authors conclude that EBERs can be used as a sensitive marker to identify NPC cells at various metastatic sites by techniques of in situ hybridization, and that demonstration of EBERs in lesions of undifferentiated histology may be useful as a diagnostic adjunct for NPC presenting as metastatic cancer of unknown origin.

Biomarkers, Tumor↗
PubMed1996

Patient-controlled sedation: a comparison of sedation prior to and until the end of minor oral surgery.

In order to find out whether patient-controlled sedation carried out only prior to surgery was sufficient for patients to undergo minor oral surgery, 30 patients of either sex between the ages of 16 and 30 years were selected. Each was scheduled to undergo bilateral third molar surgery, one side only at a visit. At the first visit each patient was randomly allocated to receive patient-controlled sedation with midazolam either only prior to, or to the end of surgery. At the second visit they received the alternative method of sedation when the operation was carried out on the opposite side. With both techniques the majority of the patients were relaxed and provided good operating conditions with stable vital signs and without loss of consciousness. However, when given the opportunity to sedate themselves until the end of surgery, 70 per cent obtained increments during surgery; four were assessed to have marked sedation and in five the button dropped off. When questioned at the end of both procedures, 87 per cent preferred to have increments during surgery.

Adolescent↗
PubMed1996

Intra-arterial fibrinolytic treatment for mesenteric arterial embolus: a case report.

The diagnosis of mesenteric ischemia is based on acute clinical awareness of the condition and confirmed by angiography or laparotomy. The standard treatment is abdominal exploration with resection of the gangrenous segment of the bowel or embolectomy of the superior mesentery artery, or both. Alternative treatment such as intra-arterial thrombolysis may be considered in selected patients. A 66-year-old man with a history of atrial fibrillation presented with abdominal pain. Angiography documented an embolus in both the ileocolic artery and a branch of the right renal artery. The patient was treated with selective intra-arterial infusion of streptokinase. The abdominal pain resolved. Repeat angiography showed lysis of both emboli.

Aged↗
PubMed1995

Expression of the Epstein-Barr virus DNA polymerase in Escherichia coli for use as antigen for the diagnosis of nasopharyngeal carcinoma.

Epstein-Barr virus (EBV) encoded DNA polymerase (POL) was cloned and over-expressed in Escherichia coli. Western blot analysis confirmed the presence of antibody to this POL protein in sera from nasopharyngeal carcinoma (NPC) patients. By Western blot analysis, moderate to high concentration of IgG POL-specific antibodies were present in 43 of 48 NPC sera and only 4 of 48 healthy, seropositive controls. The POL-specific IgG antibodies appear as early as stage I of NPC, suggesting that the recombinant POL protein can be a useful diagnostic marker for early diagnosis of the disease. It was also found that human sera containing high titer of cytomegalovirus (CMV) antibodies or herpes simplex virus type 1 (HSV-1) antibodies did not cross-react with the recombinant EBV POL, despite the homology shared by DNA polymerase proteins of these viruses.

Amino Acid Sequence↗
PubMed1995

A comparison of 1- and 3-minute lockout periods during patient-controlled sedation with midazolam.

PURPOSE: The maximum effect of midazolam injected intravenously occurs in about 3 minutes. Patient-controlled sedation carried out with 1-mg increments of midazolam at 3-minute intervals provides comparable conditions to that of doctor-controlled sedation carried out with 1-mg increments at 1-minute intervals, except for the longer duration taken for the patients to achieve satisfactory sedation prior to surgery. The purpose of this study was to find out how safe it would be to shorten the interval of increments of midazolam to 1 minute in patient-controlled sedation. PATIENTS AND METHODS: In a randomized crossover study, 26 patients undergoing bilateral lower third molar surgery at two visits had patient-controlled sedation with 1 mg midazolam increments at 1-minute or 3-minute intervals at one visit and the alternative at the other visit. RESULTS: The time taken for patients to achieve a degree of sedation that they thought was sufficient to tolerate the surgery was significantly longer when the increment interval was 3 minutes (t = -4.8; P < .05). Both techniques provided good operating conditions, stable vital signs, mild to moderate sedation, without loss of verbal contact. CONCLUSION: A significant majority preferred the sedation technique with 1-minute increment intervals (chi 2 = 4.6; P < .05).

Adolescent↗
PubMed1995

Effect of granulocyte-macrophage colony-stimulating factor on oral mucositis in head and neck cancer patients after cisplatin, fluorouracil, and leucovorin chemotherapy.

PURPOSE: To evaluate prospectively the efficacy of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the reduction of chemotherapy-induced oral mucositis. PATIENTS AND METHODS: Twenty patients with stage IV squamous cell carcinoma of head and neck were studied. Two-cycles (periods) of identical doses of cisplatin, fluorouracil (5-FU), and leucovorin (PFL) chemotherapy with cisplatin 20 mg/m2/d, 5-FU 800 mg/m2/d, leucovorin 90 mg/m2/d by 96-hour continuous intravenous infusion every 3 weeks were given to each patient. After PFL chemotherapy, GM-CSF 4 micrograms/kg subcutaneously from days 5 to 14 or no therapy was given by a randomized self-controlled crossover study design. Oral mucositis was graded with modified Radiation Therapy Oncology Group criteria. RESULTS: In the first cycle of PFL chemotherapy, GM-CSF significantly reduced the incidence, mean duration, and mean area under the curve (AUC) of severe oral gross mucositis (grade > or = 3) compared with no therapy. These beneficial effects continued into the second cycle of PFL chemotherapy after crossover to no GM-CSF. The incidence of severe mucositis was reduced when GM-CSF was given in the second cycle of PFL. Analysis of variance indicated significant direct GM-CSF treatment effects on the mean AUC of gross/functional scores and duration of moderate gross mucositis (grade > or = 2) over both periods. There was a significant period effect in favor of giving GM-CSF in the first cycle of chemotherapy. CONCLUSION: GM-CSF can significantly reduce the severity and duration of chemotherapy-induced oral mucositis after PFL chemotherapy.

Adult↗
PubMed1994

Differentiation between cutaneous form of adult T cell leukemia/lymphoma and cutaneous T cell lymphoma by in situ hybridization using a human T cell leukemia virus-1 DNA probe.

Adult T cell leukemia/lymphoma (ATLL) shares overlapping clinicopathological features with cutaneous T cell lymphoma (CTCL), requiring detection of monoclonal integration of proviral DNA of type 1 human T cell leukemia virus for its differential diagnosis from the latter. We applied in situ hybridization (ISH) and polymerase chain reaction (PCR) to paraffin sections from 63 Japanese autopsy cases that had been diagnosed as CTCL in earlier years when ATLL was still not widely known. Eleven and two cases with confirmed diagnoses of ATLL and CTCL served as positive and negative controls, respectively. It was found that ISH was positive in 7 of 63 test cases and 10 of 11 positive controls, whereas PCR was positive in none of the test cases and eight of the positive control cases. Two negative controls were negative for both ISH and PCR. We conclude that ISH is superior to PCR for detecting type 1 human T cell leukemia virus proviral DNA on paraffin sections and that the ISH method is useful for differentiating CTCL from the cutaneous form of ATLL.

Base Sequence↗
PubMed1992

Mutational identification of an essential tryptophan in tryptophanyl-tRNA synthetase of Bacillus subtilis.

The strongly conserved single tryptophan residue, Trp92, in Bacillus subtilis tryptophanyl-tRNA synthetase has been mutagenized via site direction singly into Gln, Ala, and Phe. All three mutant enzymes were inactive toward the catalysis of tRNA tryptophanylation. The Trp92----Phe mutant has been subcloned into the high expression plasmid pKK223-3 to yield the recombinant plasmid pKSW-F92. Growth of bacteria carrying the latter plasmid made possible the purification of the mutant TrpRS-F92 enzyme to homogeneity. This mutant enzyme was deficient in ultraviolet absorbance and fluorescence relative to the wild type enzyme and inactive in the partial reaction of Trp-activation as well as the overall reaction of tRNA tryptophanylation. Furthermore, unlike the wild type B. subtilis trpS gene, the mutant trpS-F92 gene upon transformation into Escherichia coli trpS 10343 failed to complement the temperature sensitive trpS mutation of the host cells. Trp92 therefore represents an essential residue both in vitro and in vivo for the function of the tryptophanyl-tRNA synthetase.

Amino Acid Sequence↗
PubMed1992

Is persistent polyclonal B lymphocytosis caused by Epstein-Barr virus? A study with polymerase chain reaction and in situ hybridization.

Previous reports of patients with persistent polyclonal B lymphocytosis have found associations with female sex, cigarette smoking, HLA-DR7 phenotype, and moderate elevation of peripheral blood polyclonal B lymphocytes. The presence of binucleated cells and atypical lymphocytes in the peripheral blood of these patients was highly suggestive of a viral infection, such as with the Epstein-Barr virus. We report a 47-year-old asymptomatic woman who was incidentally found to have persistent polyclonal B lymphocytosis and serum IgG against virus capsid antigen (VCA) and Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA) of EBV. The presence of EBV was investigated in the peripheral blood lymphocytes from this patient by in situ hybridization and polymerase chain reaction methods. EBV DNA was demonstrated in the lymphocyte fraction by polymerase chain reaction, and it was further located in lymphoid cells by in situ hybridization. These results indicate that persistent polyclonal B lymphocytosis is strongly associated with EBV.

B-Lymphocytes↗
PubMed1992

Heterogeneity of hairy cell tartrate-resistant acid phosphatase.

The human nonerythrocytic acid phosphatases (AcP) are composed of seven distinct activity bands in nondenaturing polyacrylamide gel electrophoresis (PAGE) when stained using either 1-naphthyl phosphate or naphthol ASBI phosphate as substrate. They are numbered 0, 1, 2, 3, 3b, 4, and 5 according to their increasing mobility toward the cathode in acidic conditions. Of these, only the most cationic "band 5" is tartrate resistant (TRAcP). When naphthol ASBI phosphate is used as substrate, AcP activity can also be stained in situ. In the presence of tartrate, activity remains strong in the hairy cells (HC) of hairy cell leukemia (HCL). Thus, the TRAcP stain has remained a reliable marker for HC. To investigate the function of TRAcP in HC, we purified two isoforms of TRAcP from HCL spleen tissue and found them to have similar substrate specificities and inhibitor sensitivities. In this report, we describe in detail the methods for TRAcP purification and compare some of the structural properties of the two isoforms to reinforce the concept that human TRAcP is a heterogeneous group of related enzymes. Band 5 represented only 15-20% of the total TRAcP extracted from HCL spleen. The remaining 80% of TRAcP hydrolyzed p-nitrophenyl phosphate but not naphthol ASBI phosphate and was not detectable in acidic, nondenaturing PAGE gels. Band 5 was solubilized from tissue using 500 mmol/L NaCl after previous extraction with 0.5% (v/v) NP-40 removed most other AcP and TRAcP activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Phosphatase↗
PubMed1990

High-level expression of Bacillus subtilis tryptophanyl-tRNA synthetase in Escherichia coli.

The trpS gene encoding Bacillus subtilis tryptophanyl-tRNA synthetase (TrpRS) was prepared from the pUC8-derived pTSQ2 plasmid, mutagenized to introduce an EcoRI site immediately in front of the ATG start codon, and inserted into the pKK223-3 vector downstream to the tac promoter to yield the pKSW1 plasmid. Upon induction with isopropyl-beta-D-thiogalactopyranoside, Escherichia coli JM109[pKSW1] cells synthesized TrpRS to a level corresponding to 45% of total cell proteins. This high level of gene expression facilitates large scale preparation of TrpRS for physical studies, detection of in vivo degradation of mutant forms of TrpRS, and comparative assays of TrpRS by [3H]Trp-tRNA formation and by Trp-hydroxamate formation for the purpose of mutant characterization. Finally, since pKSW1 could complement the temperature-sensitive TrpRS mutation on E. coli trpS 10343 cells, defective mutations of the trpS gene on pKSW1 would be deductible on the basis of complementation testing.

Amino Acyl-tRNA Synthetases↗
PubMed1988

Cloning and nucleotide sequence of the structural gene coding for Bacillus subtilis tryptophanyl-tRNA synthetase.

A 1.47-kb DNA fragment that carries the tryptophanyl-tRNA synthetase (TrpRS) gene of Bacillus subtilis has been cloned into the pUC8 plasmid. The recombinant plasmid, pTSQ2, conferred temperature-resistance to the temperature-sensitive trpS ts mutant of B. subtilis through chromosomal transformation, and to that of Escherichia coli through complementation. The pTSQ2 could be stably maintained in E. coli DH5 alpha, causing in the host cell a 200-fold amplification of TrpRS activity. The complete nucleotide sequence of the cloned fragment has been determined. A putative transcriptional promoter, a Shine-Dalgarno sequence, the 990-bp trpS gene proper, as well as a transcriptional terminator have been identified.

Amino Acid Sequence↗
PubMed1988

Abrogation of etoposide-mediated cytotoxicity by cycloheximide.

The antitumor agent etoposide interacts with DNA topoisomerase II to produce a unique form of DNA-enzyme intermediate referred to as a "cleavable complex". These drug-induced DNA strand breaks initiate poorly defined cell processes which result in lethality. To explore the mechanism of etoposide cytotoxicity, we studied the effect of protein synthesis inhibitor on Balb/C 3T3 fibroblasts and CCRF-CEM and L1210 leukemia cells by exposing these cell lines to cycloheximide for various periods of time prior to etoposide challenge. Cycloheximide alone during these periods of exposure was not cytotoxic; however, it conferred increasing cytoprotection from etoposide in a time-dependent fashion when it preceded etoposide. Although cycloheximide did cause a decrease in enzyme content and in etoposide-induced DNA cleavage of Balb/C 3T3 and the CCRF-CEM cell lines, cytoprotection by cycloheximide could not be accounted for completely by these phenomena since, in L1210 cells, cytoprotection was observed without significant change in DNA cleavage or enzyme content. Cycloheximide diminished DNA synthesis as well as protein synthesis. However, DNA synthesis resumed within 6 hr after removal of cycloheximide, in spite of the fact that cytoprotection persisted. Cycloheximide did not alter cell cycle distribution as measured by flow cytometry. Our data, therefore, clearly demonstrate that cycloheximide can diminish the cytotoxic potential of etoposide-mediated topoisomerase-DNA complexes. Elucidation of the mechanism by which cytoprotection occurs should shed light on the basis for the cytotoxic effect of topoisomerase II-active drugs.

Animals↗
PubMed1988

DNA binding by epipodophyllotoxins and N-acyl anthracyclines: implications for mechanism of topoisomerase II inhibition.

Previous evidence suggests that epipodophyllotoxins, such as etoposide and teniposide, and the N-acyl anthracycline AD41 inhibit topoisomerase II resealing even though they apparently do not bind to DNA. Using experimental conditions designed to detect limited numbers of DNA binding sites, we now report that both epipodophyllotoxins and the N-acyl anthracyclines AD41 and AD32 bind to DNA. Binding was greater to kinetoplast DNA than to pUC18 plasmid DNA. There was also greater etoposide binding to single-stranded DNA than to double-stranded linear or supercoiled DNA. Based on binding competition experiments, etoposide and teniposide appear to have equal affinity for DNA, in spite of the fact that the latter is more potent as a topoisomerase inhibitor. This suggests that the difference in the drugs relates to protein interaction. There are 3- to 7-fold more binding sites for AD41 than for AD32, depending on the DNA substrate employed, and both drugs, unlike adriamycin, exhibit saturation of binding sites over a concentration range of 0-50 microM when kinetoplast DNA is the substrate. Evidence for DNA intercalation by AD41 is provided by the observation that the drug introduces positive supercoils into covalently closed plasmid DNA. Based on these data, a hypothesis is proposed that would provide a general mechanism whereby intercalating agents and epipodophyllotoxins alter topoisomerase function and presumably exert their antitumor effects.

Antibiotics, Antineoplastic↗