Biomedical subjects

L Szeto

Publications and source records attributed to L Szeto.

11 recordsLinked to original sources

PubMed2003

Phase I/II investigation of paclitaxel, ifosfamide and carboplatin for advanced non-small-cell lung cancer.

BACKGROUND: The aim of this study was to evaluate feasibility and tolerability of the three-drug combination of paclitaxel, ifosfamide and carboplatin (TIC) in patients with advanced non-small-cell lung cancer. The specific objectives of the study were: (i) to define the dose-limiting toxicities (DLTs) and the maximum-tolerated dose of ifosfamide administered as part of the combination; and (ii) to determine the overall response rate and overall survival of patients treated with this regimen. PATIENTS AND METHODS: Patients with untreated, stage IIIB (pleural effusion) or stage IV non-small-cell lung cancer were enrolled in one of three cohorts. Patients received paclitaxel 200 mg/m(2) as a 1-h infusion on day 1 with carboplatin at an area under the concentration-time curve (AUC) of 6 mg.min/ml on day 2. For dose level I, ifosfamide was administered at a dose of 2 g/m(2) on days 1 and 2. For dose levels II and III, the dose of ifosfamide was decreased to 1.5 g/m(2) on days 1 and 2 and the dose of carboplatin was decreased to AUC 5 mg.ml/min. Therapy for dose levels I and III included filgrastim support (5 micro g/kg/day), which was initiated on day 3 and continued until after day 11 or until an absolute neutrophil count >10 000/ micro l. Treatment cycles were repeated every 21 days. Once the phase II dose was established, a full cohort of patients received therapy at this dose level to examine further the regimen's activity and tolerability. RESULTS: Neutropenia was the DLT encountered for dose levels I and II. No DLT was encountered in the initial six patients treated at dose level III, and therefore this dose level was declared the recommended phase II dose. A total of 49 patients were treated at the recommended phase II dose. The predominant non-hematological toxicity encountered with this triplet regimen was cumulative peripheral neuropathy. Of the 65 eligible patients enrolled in this study, 17 (26%) responded. There were 15 patients with partial responses (23%), two with regression, and 26 with stabilization of disease (40%). Median progression-free and overall survival were 4.8 and 9.4 months, respectively. CONCLUSIONS: The combination TIC is well-tolerated. This triplet regimen produced response and survival rates in advanced non-small-cell lung cancer similar to those of other current combination chemotherapy regimens.

Adult↗

PubMed2002

A pilot trial of G3139, a bcl-2 antisense oligonucleotide, and paclitaxel in patients with chemorefractory small-cell lung cancer.

BACKGROUND: Chemorefractory small-cell lung cancer (SCLC) is defined as disease that progresses during primary therapy or within 3 months of completion of primary therapy. Patients with chemorefractory SCLC have a very poor prognosis, and no treatment has been shown to be of significant clinical benefit. Elevated expression of Bcl-2 is found in the majority of SCLCs and has been associated with therapeutic resistance. Suppression of Bcl-2 levels through the use of G3139, an antisense oligonucleotide complementary to the mRNA encoding Bcl-2, might increase the antitumor efficacy of cytotoxic therapy. PATIENTS AND METHODS: Twelve patients with chemorefractory SCLC participated in this pilot trial of paclitaxel combined with G3139. G3139 was given by continuous i.v. infusion over 7 days at a fixed dose of 3 mg/kg/day. Paclitaxel dose was initially 175 mg/m2 on day 6, but was decreased to 150 mg/m2 due to myelosuppression observed in two of the three patients treated in the first dose cohort. RESULTS: The combination of paclitaxel at 150 mg/m2 and G3139 at 3 mg/kg/day was found to be feasible and well tolerated. No objective responses were observed, but two patients had stable disease, one remaining stable on therapy for >30 weeks. Plasma G3139 levels were determined, and were found to be highest in the patient with prolonged stable disease, suggesting that individual variation in metabolism and clearance of the antisense oligonucleotide may influence activity. CONCLUSIONS: This study demonstrates that G3139 can be combined with paclitaxel in a cytotoxic dose range, and suggests that a similar combination be tested for activity in the context of chemoresponsive disease.

Adult↗

PubMed2001

A phase I trial of the oral platinum analogue JM216 with concomitant radiotherapy in advanced malignancies of the chest.

JM216 is an orally administered platinum analogue. We undertook this study to determine the maximally tolerated dose (MTD) of JM216 when administered with concomitant radiotherapy to the chest (200 cGy daily, 5 x/week) in patients with locoregionally advanced non-small cell lung (NSCLC) or esophageal cancer. Patients were excluded for inadequate bone marrow reserve, prior radiotherapy to the primary tumor or previous treatment with platinum drugs. A dose-limiting toxicity (DLT) was defined using the National Cancer Institute (NCI) Common Toxicity Criteria (CTC) and consisted of grade > or = 2 renal, hepatic, cardiac, or pulmonary toxicity or grade > or = 3 hematologic, neurological, or gastrointestinal toxicity. A total of 23 patients were registered; two never received treatment and are excluded from analyses. Six patients were treated at a dose of 30 mg/m2/day for 5 days with two grade 2 DLT's: cough (1 pt) and elevated trans-aminases (1 pt). Seven evaluable patients were treated at 60 mg/m2/day and seven experienced grade 3 or 4 toxicity, five related to myelosuppression. The dose was then reduced to 45 mg/m2/d. Eight patients were evaluable for toxicity, of which 5 experienced DLT: myelosuppression (3 pts), esophagitis (2 pts), dyspnea (1 pt), and elevated creatinine (1 pt). Fourteen patients were evaluable for efficacy, of which 6 had an objective response, including one complete response. The recommended phase II dose of JM216 with concurrent radiation therapy is 30 mg/m2/d for 5 days. The major DLT is myelosuppression with only limited increased toxicity within the field of radiation. This conceivably may limit the use of JM216 as a radiation sensitizer.

Administration, Oral↗

PubMed1997

Alpha2p controls donor preference during mating type interconversion in yeast by inactivating a recombinational enhancer of chromosome III.

Homothallic strains of Saccharomyces cerevisiae can change mating type as often as every generation by replacing the allele at the MAT locus with a copy of mating type information present at one of two storage loci, HML and HMR, located on either end of chromosome III. Selection of the appropriate donor locus is dictated by a mating type-specific repressor protein, alpha2p: Cells containing alpha2p select HMR, whereas those lacking alpha2p select HML. As a repressor protein, alpha2p binds to DNA cooperatively with the transcriptional activator Mcm1p. Here we show that two alpha2p/Mcm1p-binding sites, DPS1 and DPS2, control donor selection. DPS1 and DPS2 are located approximately 30 kb from the left arm of chromosome III, well removed from HML, HMR, and MAT. Precise deletion of only DPS1 and DPS2 results in random selection of donor loci and in a cells without affecting selection in alpha cells. Reciprocally, deletion of only the alpha2p binding segments in each of these two sites results in selection of the wrong donor loci in alpha cells without affecting preference in a cells. These results suggest that Mcm1p, bound to these two sites in the absence of alpha2p, activates HML as donor. Binding of alpha2p blocks the ability of Mcm1p bound to DPS1 and DPS2 to activate HML, resulting in default selection of HMR as donor. DPS1 and DPS2 also regulate expression of several noncoding RNAs, although deletion of at least one of these RNA loci does not affect donor preference. This suggests that transcriptional activation, rather than transcription of a specific product, is the initiating event in activating the left arm of chromosome III for donor selection.

Binding Sites↗

PubMed1997

Role of alpha2 protein in donor locus selection during mating type interconversion.

The homeodomain protein alpha2p plays a role both in transcriptional repression in the process of cell type determination and in donor selection during mating interconversion. We have explored the mechanism of alpha2p-directed donor selection by examining the effects on donor preference of mutants deficient in alpha2p-mediated transcriptional repression. As a transcriptional regulator, alpha2p interacts with Mcm1p, Tup1p, and Ssn6p to repress a-specific genes and with a1p, Tup1p, and Ssn6p to repress haploid-specific genes. We have found that mutant alleles of MATalpha2 that specifically diminish the interaction of alpha2p with Mcm1p or Tup1p behave as null alleles with regard to donor preference, while mutations of MATalpha2 that specifically diminish interaction of alpha2p with a1p behave as wild-type MATalpha2 in this capacity. Tup1p plays an essential role in alpha2p-mediated transcriptional repression, while Ssn6p has only a modest effect in repression. In a similar vein, we find that TUP1, but not SSN6, is required for proper donor selection. These results suggest that, in addition to regulating a-specific gene expression to establish the mating type of the cell, alpha2p-Mcm1p-Tup1p complex may indirectly regulate donor preference through transcriptional control of an a-specific gene. Alternatively, this complex may play a direct role in establishing donor preference via its DNA binding and chromatin organization capacity.

Alleles↗

PubMed1995

Mutations affecting donor preference during mating type interconversion in Saccharomyces cerevisiae.

Homothallic strains of Saccharomyces cerevisiae can convert mating type from a to alpha or alpha to a as often as every generation, by replacing genetic information specifying one mating type at the expressor locus, MAT, with information specifying the opposite mating type. The cryptic mating type information that is copied and inserted at MAT is contained in either of two loci, HML or HMR. The particular locus selected as donor during mating type interconversion is regulated by the allele expressed at MAT. MATa cells usually select HML, and MAT alpha cells usually select HMR, a process referred to as donor preference. To identify factors required for donor preference, we isolated and characterized a number of mutants that frequently selected the nonpreferred donor locus during mating type interconversion. Many of these mutants were found to harbor chromosome rearrangements or mutations at MAT or HML that interfered with the switching process. However, one mutant carried a recessive allele of CHL1, a gene previously shown to be required for efficient chromosome segregation during mitosis. Homothallic strains of yeast containing a null allele of CHL1 exhibited almost random selection of the donor locus in a MATa background but were normal in their ability to select HMR in a MAT alpha background. Our results indicate that Chl1p participates in the process of donor selection and are consistent with a model in which Chl1p helps establish an intrinsic bias in donor preference.

Alleles↗

PubMed1994

VLDL production is decreased to a similar extent by acute portal vs. peripheral venous insulin.

Acute changes in very low-density lipoprotein (VLDL) triglyceride (TG) and VLDL apolipoprotein (apo) B production were examined in 11 healthy young males in response to insulin delivered either by the peripheral venous route or secreted directly by the pancreas. Steady rates of pancreatic insulin secretion were achieved for 5 h by a programmed intravenous tolbutamide infusion, while euglycemia was maintained with a dextrose infusion. Insulin secretory rate was calculated from peripheral C-peptide levels by deconvolution, and, in a subsequent study, exogenous insulin was infused peripherally to match this pancreatic insulin secretory rate in each subject. Changes in VLDL TG and VLDL apo B production were determined semiquantitatively on each occasion by examining the change in slope of the specific activity (SA) of 3H-labeled triglyceride glycerol ([3H]TGG) and 131I-VLDL apo B vs. time curves, respectively, occurring with acute hyperinsulinemia. Plasma-free fatty acids (FFA), TG, apo B, and VLDL TG/VLDL apo B ratio decreased to a similar extent in both studies after the onset of hyperinsulinemia. VLDL TG production decreased significantly in both the tolbutamide (-47.1 +/- 7.3%, P < 0.002) and the exogenous insulin infusion study (-52.8 +/- 12.4%, P < 0.005). VLDL apo B production also decreased significantly in both studies (-58.9 +/- 7.5%, P = 0.0007 and -52.1 +/- 6.8%, P < 0.006, respectively), and there were no significant differences between studies. Tolbutamide was shown to have no independent effect on VLDL TG or VLDL apo B production in four insulin-deficient diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Partial characterization of the fructose-induced defect in very-low-density lipoprotein triglyceride metabolism.

Very-low-density lipoprotein triglyceride (VLDL-TG) catabolism was studied in rats receiving either fructose or glucose as a 10% drinking solution. Consumption of either of the hexoses for 16 hours significantly elevated postheparin plasma (PHP) lipoprotein lipase (LPL) activity compared with normal control animals. Prolonged feeding of the carbohydrates for 14 days abolished the higher LPL activities, which were similar to control levels. PHP hepatic lipase (HL) activity was significantly reduced in carbohydrate-fed rats compared with control animals despite the duration of feeding. The kinetic parameters Km and Vmax cannot be obtained with lipoproteins and so the first-order rate constant (k1) of triglyceride hydrolysis was used to assess the effectiveness of VLDL-TG as substrates for endothelial lipases. VLDL-TG from fructose and VLDL-TG from glucose donors was lipolyzed with PHP LPL and HL from normal rats. The k1 (fraction of VLDL-TG lipolyzed) of VLDL-TG was found to be lower when donors had been fed fructose compared with VLDL that had come from glucose-fed donors. Rates of VLDL-TG removal from fructose and glucose donors were determined simultaneously in perfused livers of normal control, fructose-fed, and glucose-fed animals. Livers of fructose-fed animals cleared VLDL-TG at a slower rate than livers from glucose-fed or control rats. VLDL-TG from fructose-fed rats was cleared less effectively than VLDL-TG from glucose-fed rats in livers of both control and glucose-fed animals. We conclude that an impairment in the ability of fructose-fed rats to hydrolyze VLDL-TG, and of their livers to remove VLDL-TG, may in part explain fructose-induced hypertriglyceridemia.

Animals↗

PubMed1990

Glycation of very low density lipoprotein from rat plasma impairs its catabolism.

Rat VLDL were glycated in vitro in the presence or absence of a reducing agent. Prior to glycation, the VLDL triglyceride was endogenously radiolabelled with [3H]-oleic acid. Post glycation the VLDL B-apoprotein was exogenously radiolabelled with [131]I. The double labelled VLDL was then injected into normal rats and the decline in plasma radioactivity of the two isotopes was used as a measure of triglyceride and particle clearance. VLDL glycated in either the presence or absence of reducing agent exhibited a significantly slower removal of triglyceride and apoprotein B compared to normal VLDL. The ability of glycated VLDL triglyceride to act as substrate for lipoprotein lipase and hepatic lipase was examined. Increasing concentrations of normal and glycated VLDL triglyceride were incubated with post-heparin plasma. The kinetics of triglyceride hydrolysis were determined in a manner analogous to Michaelis-Menten analysis. Glycated VLDL was found to be poorer than normal VLDL as a substrate for lipoprotein lipase. Glycation of VLDL appears to interfere with the lipolysis of its triglyceride. This may explain the delayed clearance of glycated VLDL triglyceride in vivo. Glycation also extended the mean plasma residence time of the VLDL particle. These factors may, in part, contribute to the hypertriglyceridaemia observed in subjects with diabetes mellitus.

Animals↗

PubMed1990

The Legionella pneumophila major secretory protein, a protease, is not required for intracellular growth or cell killing.

The Legionella pneumophila major secretory protein (Msp) is a Zn2+ metalloprotease whose function in pathogenesis is unknown. The structural gene for the Msp protease, mspA, was isolated from an L. pneumophila genomic library. In Escherichia coli which contain plasmids with the mspA gene, Msp protein and activity are found in the periplasmic space and the cytoplasm. Transposon mutagenesis with Tn9 of an mspA-containing plasmid in E. coli yielded mutants which no longer expressed protease activity and others with increased protease activity. These results suggested that mspA expression might be regulated. Msp was shown to be produced at a much higher level in L. pneumophila grown in rich compared to semidefined media. A Tn9 insertion which abolishes Msp expression was introduced into the L. pneumophila genome. This mspA::Tn9 L. pneumophila strain showed no detectable production of Msp by immunoblot analysis, and it had less than 0.1% of the protease activity found in the wild-type strain. This mutant was fully capable of growing within and killing human macrophages derived from the HL-60 cell line.

Bacterial Proteins↗

PubMed1990

An immunoprotective molecule, the major secretory protein of Legionella pneumophila, is not a virulence factor in a guinea pig model of Legionnaires' disease.

We have examined whether a molecule that is capable of inducing immune protection, the major secretory protein (MSP) of Legionella pneumophila, is required for virulence in a guinea pig model of Legionnaires' disease. To do so, we have compared the virulence in guinea pigs of an isogenic pair of L. pneumophila, Philadelphia 1 strain, one of which produces MSP (MSP+) and one of which does not (MSP-). Both the MSP- strain and the MSP+ strain of L. pneumophila are highly virulent for guinea pigs, inducing similar signs and progression of illness. Both strains are lethal and have comparable LD50s and LD100s. Both strains multiply in the lungs of guinea pigs at a similar rate, and both strains produce indistinguishable pathological lesions in the lungs. Both strains maintain a stable phenotype with guinea pig passage, i.e., the MSP- strain does not regain the capacity to secrete MSP and the MSP+ strain retains its capacity to secrete MSP after lung passage. Although vaccination with MSP induces strong protective immunity in the guinea pig against lethal aerosol challenge with L. pneumophila, this protective immunogen is not required in its intact proteolytically active form for the expression of virulence by the intracellular pathogen L. pneumophila. This demonstrates that a protective immune response need not necessarily be directed against a virulence determinant and suggests that any molecule that allows the host immune system to detect and act against an intracellularly sequestered pathogen may potentially serve as a protective immunogen against such a pathogen.

Animals↗