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Biomedical subjects

K Luk

Publications and source records attributed to K Luk.

15 recordsLinked to original sources
PubMed2001

Protein phosphatase methyltransferase 1 (Ppm1p) is the sole activity responsible for modification of the major forms of protein phosphatase 2A in yeast.

Protein phosphatase 2A (PP2A) is a major threonine/serine phosphatase that is involved in regulating a variety of cellular processes. It has been shown in both yeast and mammals that the PP2A catalytic subunit (PP2Ac) is methyl-esterified at the conserved C-terminal Leu residue. The recent characterization of a mammalian PP2A carboxyl methyltransferase has led to the identification of two ORFs in Saccharomyces cerevisiae as potential orthologues of the mammalian PP2A methyltransferase: protein phosphatase methyltransferase 1 (PPM1) and protein phosphatase methyltransferase 2 (PPM2). To experimentally identify the PP2A methyltransferase in yeast, we obtained deletion mutants of PPM1 and PPM2 and then constructed double mutants. Using in vivo-labeling techniques, we demonstrate that only the PPM1 gene is required for PP2Ac methylation at the C-terminus. Because yeast has at least three homologues of PP2Ac (PPH21, PPH22, and PPH3), we then asked whether all of these catalytic subunits are methylated by the PPM1 and/or PPM2 putative methyltransferases. We modified the segment corresponding to the N-terminal coding region of all three PP2Ac genomic genes with a hemagglutinin (HA) tag in the parent, ppm1, ppm2, and ppm1ppm2 mutant genetic backgrounds. Using immuoprecipitation with anti-HA antibodies followed by methyl ester analysis, we showed that only in the ppm1 mutant were both Pph21p and Pph22p not methylated. We did not detect any methylesterification of Pph3p under our conditions. Our results indicate that PPM1 is the sole methyltransferase responsible for methylating the two major homologues of PP2Ac in yeast. The function of the PPM2 gene product remains unclear.

DNA Methylation↗
PubMed1997

Unilateral rotational path removable partial dentures for tilted mandibular molars: design and clinical applications.

This article describes the design of a unilateral rotational path removable partial denture to restore a single edentulous space with a tilted mandibular molar. It is modified from an original bilateral rotational path design and consists of several components, which are (1) the rotation axis, (2) the long occlusal rest, (3) the short bracing arms, (4) the rigid retainer and extended proximal plates, (5) the conventional direct retainer assembly, and (6) optional auxiliary rest. The stability and retention of the denture are controlled anteriorly by the buccal retentive clasp and lingual guide plate of the conventional direct retainer, and posteriorly by the rigid retainer and its buccally and lingually extended proximal plates. The clinical results of the dentures used in strictly selected situations are excellent; however, it is emphasized that a unilateral denture is only an alternative rather than a routine application. The risk of accidental aspiration is also of concern.

Deglutition↗
PubMed1993

Interstitial thermoradiotherapy with ferromagnetic implants for locally advanced and recurrent neoplasms.

PURPOSE: The University of Arizona, University of California at San Francisco, City of Hope Medical Center, and University of Wisconsin participated in a Phase I/II protocol to assess the heating ability and the toxicity of interstitial thermoradiotherapy using ferromagnetic implantation. METHODS AND MATERIALS: Forty-four patients with advanced primary or recurrent extra-cranial solid malignancies were enrolled in this study. Fourteen gauge catheters were implanted into tumors and, once in the department of Radiation Oncology, loaded with ferromagnetic seeds to deliver a 60 min hyperthermia treatment. Multi-point thermometry was continuously used throughout the heating sessions for all patients, sampling the periphery as well as the core of the tumor. After 192Iridium brachytherapy, 18 patients then had an additional treatment. The mean radiation dose while on protocol was 50.0 Gy, with total doses (including prior radiotherapy) ranging from 20.3-151.8 Gy (median = 88.7 Gy). Response and toxicity were assessed by inspection, palpation, and/or radiologic studies. Forty-one patients were evaluable for response, and there were 55 analyzable hyperthermia treatment sessions. RESULTS: The complete response rate was 61% (25/41). The partial response rate was 31.7% and only 7.3% failed to respond. Median duration of local control has not yet been reached. The mean maximum, minimum, and mean time-averaged temperatures for all in-tissue sensors were 43.7 degrees C, 38.7 degrees C, and 41.0 degrees C, respectively. Tumor size was the only factor significantly correlated with temperatures or with complete response rate; larger tumors attained higher temperatures but smaller tumors had a higher response probability. Nineteen patients (43%) experienced toxicities, however there was only a 7% (3/44) rate of serious complications (Grade 3 or 4). Prior treatment with hyperthermia was the only factor significantly correlated with serious toxicity. CONCLUSION: These results, a 93% total response with only 7% serious toxicity, are encouraging especially in the context of the patient population treated. Phase II/III studies involving ferromagnetic implantation are warranted.

Adult↗
PubMed1990

MM 46115, a new antiviral antibiotic from Actinomadura pelletieri. Characteristics of the producing cultures, fermentation, isolation, physico-chemical and biological properties.

Six strains of Actinomadura pelletieri were shown to produce a novel macrolide antibiotic, designated MM 46115. MM 46115 was active against parainfluenza virus 1 and 2 and Gram-positive bacteria. Methods are described for the production of MM 46115 by strain IP 729.63, and for the isolation of the compound from a butanol extract of the culture filtrate.

Animals↗
PubMed1989

Hyperthermia quality assurance guidelines.

These Hyperthermia Quality Assurance guidelines are a result of a joint workshop of the Hyperthermia Committee of the American College of Radiology and the Hyperthermia Physics Center, which is the national quality assurance program under Contract No. N01-CM-37512 with the National Cancer Institute. Hyperthermia technology presently lacks the kind of standardization in equipment, treatment procedures, patient monitoring, and treatment documentation available in radiotherapy. Therefore, preventing unacceptable variability in treatment data demands a strong commitment to in-house quality control procedures and to centralized quality assurance reviews in cooperative multi-institutional trials. This paper presents a set of test procedures necessary to ensure proper operation of equipment, suggests a frequency for such tests, and also includes guidelines on quality control procedures to be used during treatment to improve the safety, effectiveness, and reproducibility of hyperthermia treatments. A set of forms are presented to indicate the minimum data, albeit incomplete, that must be collected for acceptable documentation of treatment. These guidelines should be valuable not only to the new entrants in the field but also to those participating in multi-institutional cooperative hyperthermia trials. They have been approved by the Hyperthermia Committees of American College of Radiology, American Society for Therapeutic Radiology and Oncology, Radiation Therapy Oncology Group and the American Association of Physicists in Medicine.

Forms and Records Control↗
PubMed1987

Induction of hepatic veno-occlusive disease in dogs.

The authors attempted to induce hepatic veno-occlusive disease (VOD) in 64 dogs. Preparative treatments included combinations of total-body irradiation (TBI) or localized hepatic irradiation (LI) or both and chemotherapy consisting of dimethylbusulfan (DMB), L-phenylalanine mustard (L-PAM), methotrexate, or monocrotaline. VOD occurred infrequently in those dogs given 9.2 Gy TBI and DMB (1/10), TBI and/or LI (9.2-27 Gy) with L-PAM (2/36) or high dose methotrexate and LI (0/2). Specifically, VOD occurred in the dogs with a shorter interval between TBI and DMB or in the dog that received the glutathione reductase inhibitor, buthionine sulfoximide (BSO) before L-PAM. In contrast, among 17 dogs given monocrotaline, 8 developed VOD, particularly when used with L-PAM +/- irradiation (7/13). The major cause of death, early gastrointestinal toxicity, was further augmented by higher doses of irradiation, by shortening the interval between LI and L-PAM administration to less than 4 weeks, and administering BSO or monocrotaline before L-PAM. Gastrointestinal toxicity was lessened by giving low dose cyclophosphamide given before L-PAM. VOD can be produced in dogs especially with monocrotaline or BSO given before and L-PAM +/- irradiation. However, gastrointestinal toxicity renders the study of VOD beyond the acute phase difficult. Nevertheless, this approach appears useful for the study of VOD in other animals and for developing agents aimed at preventing VOD.

Animals↗
PubMed1986

Improvement of the bioavailability of the anti-herpes virus agent BVDU by use of 5'-O-alkoxycarbonyl derivatives with increased metabolic stability.

(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) was found by HPLC analysis to be rapidly metabolized in mice and in liver homogenates from mouse and man to the antivirally inactive (E)-5-(2-bromovinyl) uracil (BVU) but was comparatively stable in blood from both species. Of a series of 5'-O-alkoxycarbonyl derivatives of BVDU, the 5'-O-tert.-butoxycarbonyl derivative (BRL 37000) was the most stable in mouse and human blood and liver homogenates, neither its ester bond nor its N-glycosidic linkage being readily cleaved enzymically. Oral administration of BRL 37000 and the 5'-O-ethoxycarbonyl derivative (BRL 36101) to mice gave prolonged serum concentrations of BVDU and delayed the appearance of BVU compared with the BVDU control. BRL 36101 was more active than BVDU when administered orally to mice infected cutaneously with herpes simplex virus type 1.

Animals↗
PubMedDate not supplied

A pilot study of intracavitary hyperthermia combined with radiation in the treatment of oesophageal carcinoma.

Twenty-five patients with primary squamous cell carcinoma of the oesophagus were treated with intracavitary hyperthermia combined with external beam radiation and intraluminal radiation at Nanjing Jinling Hospital, China. External beam radiation was given with a 6-MV X-ray; 1.8-2.0 Gy per fraction and five fractions per week; this brought the total dose to 60 Gy. Two weeks later, hyperthermia was applied with 915 MHz microwave intracavitary applicators, which were designed at the City of Hope. Temperature measurements were obtained while moving fibreoptic temperature sensors at 1.0 cm intervals in each of the six peripheral channels of the applicator. Hyperthermia was applied for 1 h before and after the intraluminal radiation. Intraluminal radiation was provided by low dose-rate iridium-192 ribbons in the same intracavitary applicator, giving 30 Gy at 0.75 cm from the applicator surface. The 3-month post-treatment responses showing complete response, partial response, no change and progressive disease were 60% (15/25), 24% (6/25), 8% (2/25) and 8% (2/25) respectively. The median follow-up time was 17 months (range 4-29 months). The 1- and 2-year overall survival rates were 72% (18/25) and 32% (8/25) respectively, and disease-free survival rates were 47 and 30% respectively. The median overall survival and disease-free survival periods were 17 and 10 months respectively. Fourteen patients had local recurrence (either at the primary site or in the lymph node) or had local progression, and five developed metastases. The median duration of the onset of local recurrence or of local progression was 9.5 months (range 0-20 months); the median of distant metastases was 8 months (range 2-16 months). Seventeen patients died. Of these, 15 died of cancer: six with local recurrence alone, four with local progression primary cancer alone, three with distant metastases alone, and two with both local and distant failure. Two patients with complete response of the primary disease died of other diseases. The toxicity was mild. According to the mucous reaction scoring criteria of the Radiation Therapy Oncology Group, the acute toxicity grades I, II, III and IV were 0% (0/25), 20% (5/25), 48% (12/25) and 32% (8/25) respectively. The major late complication was a mild oesophagus fibrosis and difficult swallowing. No serious side effects (grade IV), fistulas or perforations were seen. These results indicate that this method is safe and feasible for treating oesophageal carcinoma.

Combined Modality Therapy↗