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Biomedical subjects

M J Browne

Publications and source records attributed to M J Browne.

At least 19 recordsLinked to original sources
PubMed1992

A recombinant, chimeric enzyme with a novel mechanism of action leading to greater potency and selectivity than tissue-type plasminogen activator.

BACKGROUND: Early intervention with thrombolytic agents has been shown unequivocally to reduce mortality after acute myocardial infarction. Presently used agents have disadvantages such as short half-life, immunogenicity, hypotension, and bleeding complications. Therefore, there is a need to develop improved thrombolytic drugs with novel mechanisms of action leading to improved properties. METHODS AND RESULTS: Hybrid plasminogen/tissue-type plasminogen activator (t-PA) complementary DNA was constructed and expressed in Chinese hamster ovary cells. The chimeric protein, comprising the fibrin-binding domains of plasminogen covalently linked to the catalytic domain of t-PA, was purified and evaluated in vitro and in vivo. The hybrid was inhibited rapidly in human and animal plasmas. The mediator of this rapid inhibition was shown to be alpha 2-antiplasmin. The active center of the hybrid could be protected by reversible active center acylation with a novel inverse acylating agent, 4'-amidinophenyl-4-chloroanthranilic acid (AP-CLAN). An acylated (CLAN-) hybrid was cleared from the bloodstream of guinea pigs at 0.35 +/- 0.02 ml/min.kg-1 compared with a clearance rate of 36 +/- 4 ml/min.kg-1 for t-PA. The CLAN-plasminogen/t-PA hybrid was evaluated in a quantitative, "humanized" guinea pig pulmonary embolism model and shown to be approximately threefold more potent when given by bolus than an infusion of t-PA. Furthermore, the acylated hybrid was more fibrin selective than t-PA as determined by the relation between clot lysis and fibrinogen degradation. CONCLUSIONS: An acylated, recombinant plasminogen/t-PA hybrid has sufficiently slow clearance to be administered by bolus and is more potent and fibrin selective than t-PA in vivo.

Acylation↗
PubMed1991

Redesigning t-PA for improved thrombolytic therapy.

Attempts are being made to redesign the structure of tissue-type plasminogen activator (t-PA) in order to increase its plasma half-life, increase its fibrin affinity or decrease its rate of interaction with plasma inhibitors. The principal strategies employed so far have been to construct hybrid enzymes, to mutate the polypeptide sequence of t-PA or to add extra fibrin-binding elements. It has been relatively easy to alter the half-life of t-PA but more difficult to do this with retention of the full specific activity of the molecule; the most promising molecules will have to be evaluated in the clinic before we know whether the redesign of t-PA has been truly successful.

Amino Acids↗
PubMed1990

Oral zidovudine, continuous-infusion fluorouracil, and oral leucovorin calcium: a phase I study.

A phase I clinical, pharmacologic, and biochemical evaluation of escalating oral zidovudine (AZT) given over 2 days with a fixed dose of continuous-infusion fluorouracil (800 mg/m2 per day X 3 days) and oral leucovorin calcium was performed. Eighteen patients were treated with doses of AZT ranging from 1.0 to 9.0 g/m2 per day. Nausea and vomiting were dose limiting, with a maximally tolerated dose of 7.5 g/m2 per day. Rash and mucositis occurred but were not dose limiting. A dose-related increase in peak plasma levels of AZT was observed, and the alpha half-life of AZT in plasma (75 min) was unaffected by these high doses. At doses above 4.0 g/m2 per day, trough levels significantly increased, perhaps reflecting prolonged absorption from the gut. No responses were observed; however, a significant increase in DNA single-strand breaks was observed in peripheral blood cells after a threshold dose of 4.0 g/m2 per day, confirming a biological effect of AZT in this regimen. Further trials with an intravenous formulation capable of maintaining plasma levels and circumventing dose-limiting toxicity are warranted.

Administration, Oral↗
PubMed1990

A phase I-II trial of continuous-infusion cisplatin, continuous-infusion 5-fluorouracil, and VP-16 in colorectal carcinoma.

Twenty-nine evaluable patients with colorectal adenocarcinoma were treated in a phase I-II trial of combination chemotherapy with a 72-h continuous infusion of cisplatin (CDDP) and 5-fluorouracil (5-FU) with an infusion of VP-16 given at 24 and 48 h after the start of therapy. There were five (17 +/- 14%) partial responses lasting 2-6 months (median, 3). Three of these responses occurred among the 10 previously untreated patients. The toxicity of this regimen was pronounced. Four of eight patients with severe neutropenia required hospitalization for infections, two of which were life-threatening; one of six patients with severe thrombocytopenia had a life-threatening hemorrhagic complication; and four patients experienced severe, dose-limiting fatigue. These complications occurred principally with CDDP and VP-16 at doses above 27.5 mg/m2/day and 110 mg/m2/dose, respectively. Mucositis occurred in six patients and limited the dose of 5-FU to 1,300 mg/m2/day. Although the response rate appeared to be high in previously untreated patients, the minimal palliative benefit of treatment and the brief duration of the responses do not compensate for the toxicity observed.

Adenocarcinoma↗
PubMed1990

A randomized trial of open lung biopsy versus empiric antimicrobial therapy in cancer patients with diffuse pulmonary infiltrates.

Twenty-four cancer patients with diffuse interstitial pneumonitis (DIP) were randomized to undergo an open lung biopsy (OLB) within 8 hours of presentation (12 patients) or to receive empiric antimicrobial therapy (ET) with trimethoprim-sulfamethoxazole (TMP-SMX) erythromycin for a minimum of 4 days (12 patients). Patients whose condition deteriorated underwent an OLB on day 4. Eight of 12 patients (67%) having OLB survived versus 10 of 12 (83%) receiving ET (P = .64). Morbidity occurred in nine of 12 (75%) having OLB versus eight of 12 (67%) receiving ET (P = 1.0). Concurrently, there were 14 additional cancer patients with DIP who were not randomized (nine refused, three had a coagulopathy contraindicating surgery, two were excluded by primary care physicians) and who were comparable demographically to the randomized group. Two received OLB and 12 ET. Combining the randomized and nonrandomized groups, eight of 14 (57%) having an initial OLB survived versus 18 of 24 (75%) of ET-treated patients (P2 = .19). Results of the OLB were seven Pneumocystis carinii pneumonia (PCP), five nonspecific pneumonitis (NSP), one cytomegalovirus, and one lymphoma. Results of OLB led to discontinuation of antibiotics in three patients. Of the 24 ET patients, eight failed to improve by day 4 and had an OLB. Results were two NSP, two PCP, two cancer, one blastomycosis, and one Candida pneumonia. Complications were seen in 10 of 14 (72%) initial OLB patients versus 14 of 24 (58%) patients on the ET arm (P = .65). When the complication rate between patients receiving only empiric antibiotics was compared with all patients having an OLB (initially or on day 4), the difference was greater in patients undergoing OLB (37% v 72%, respectively) (P2 = .14). ET with TMP-SMX plus erythromycin and broad spectrum antibiotics in granulocytopenic patients appeared to be as successful and potentially less toxic than an OLB in this study. Although the number of patients in this study was small, these data suggest that a trial of empiric antibiotic management may be reasonable in cancer patients presenting with DIP, especially if they are nonneutropenic.

Adult↗
PubMed1988

A tissue-type plasminogen activator mutant with prolonged clearance in vivo. Effect of removal of the growth factor domain.

The complete cDNA for human tissue-type plasminogen activator (t-PA) was cloned and sequenced. A mutant was constructed by using in vitro site-specific mutagenesis to delete the region encoding the growth factor domain (amino acids 51-87 inclusive). Normal and mutant t-PA species were produced using two mammalian expression systems (in human HeLa cells and mouse C127 cells). The clearance of mutant and normal t-PA from plasma was examined in vivo using a guinea pig model. Mutant t-PA derived from HeLa or C127 cells was cleared much more slowly than the cognate normal t-PA. The potential role of the growth factor domain in the recognition of t-PA by the hepatic clearance mechanism is discussed.

Animals↗
PubMed1987

Infectious complications of intraventricular reservoirs in cancer patients.

Drug administration via an intraventricular reservoir is useful in the treatment of leukemic and carcinomatous meningitis that occurs in patients who have previously received lumbar intrathecal chemotherapy. The intraventricular route, however, is associated with a higher incidence of infectious complications compared with therapy given by the lumbar route. To characterize the infectious complications associated with such reservoirs, we reviewed the 10-year experience of the Pediatric Branch, National Cancer Institute, National Institutes of Health, and Children's Orthopedic Hospital, Seattle, WA, with 61 patients (49 with leukemia, 8 with lymphoma, 4 with solid tumors) who had intraventricular reservoirs placed for administration of chemotherapy. The reservoirs were in place for a median of 36 weeks and were punctured a median of 29.5 times, Infectious complications occurred in 14 of 61 patients (23%) and Propionibacterium acnes was the most common organism recovered from cultures. Twelve patients (19.7%) had 19 episodes of clinically suspected and microbiologically documented meningitis or of positive intraventricular reservoir cerebrospinal fluid cultures without symptoms which were treated successfully. Local cellulitis occurred at the site of intraventricular reservoir placement in 2 patients (3.3%) and removal of the intraventricular reservoir was necessary for successful management. Nine patients had their intraventricular reservoir removed (5 because of associated infection and 4 because of malfunction unassociated with infection).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Large scale, rapid purification of recombinant tissue-type plasminogen activator.

Recombinant tissue-type plasminogen activator (rt-PA) from cultures of a genetically manipulated Bowes melanoma cell line (TRBM6) was purified in batches of average volume 451 using an autoclavable, reusable, continuous chromatography system comprising zinc chelate-Sepharose CL4B and lysine-Sepharose CL4B. After eight successive purifications the rt-PA was ultrafiltered to yield a preparation containing 4.9 mg protein/ml and 2.7 X 10(6) IU/ml. Analysis by SDS-polyacrylamide gel electrophoresis followed by staining with Coomassie brilliant blue R250 showed major protein bands at Mr = 63,000 and 65,000; most of the material was in the 1-chain form. The potential usefulness of a simple, rapid continuous chromatography system that can be operated under aseptic conditions is discussed.

Animals↗
PubMed1986

Excess prevalence of Pneumocystis carinii pneumonia in patients treated for lymphoma with combination chemotherapy.

A significantly greater prevalence of interstitial pulmonary infiltrates and Pneumocystis carinii pneumonitis occurred on one arm of a randomized study comparing ProMACE-CytaBOM (prednisone, methotrexate with leucovorin, doxorubicin, cyclophosphamide, etoposide; cytarabine, bleomycin, vincristine, methotrexate with leucovorin) to ProMACE-MOPP (ProMACE, mechlorethamine, vincristine, prednisone, procarbazine) chemotherapy in patients with lymphoma. Of the 37 patients receiving ProMACE-CytaBOM, 13 (35.1%) developed an interstitial pulmonary infiltrate compared with 3 of 32 (9.4%) patients receiving ProMACE-MOPP (p2 = 0.02). Of the 13 patients receiving ProMACE-CytaBOM who had infiltrates, open lung biopsy in 7 showed P. carinii; 5 others had clinically suspected P. carinii pneumonia, and 1 had blastomycosis. No patient receiving ProMACE-MOPP had documented or suspected P. carinii pneumonia. Of patients with infiltrates, 3 of 13 on ProMACE-CytaBOM but 0 of 3 on ProMACE-MOPP died. Two other patients on ProMACE-CytaBOM who had P. carinii pneumonia died. Groups did not differ in predisposing risk factors or patient history. The exact cause for the increased prevalence of P. carinii infection in patients receiving ProMACE-CytaBOM was not ascertained. These data emphasize that new drug regimens may lead to unanticipated complications.

Adult↗
PubMed1985

Identification of the calcium-inducible plasminogen activators secreted by a human diploid fibroblast cell line (MRC-5).

Human embryonic lung fibroblast (MRC5) cells secreted small amounts of plasminogen activators into normal, serum-free harvest medium. Stimulation with calcium led to markedly enhanced levels of activator. The major species of plasminogen activator in the harvest medium of the stimulated cultures resembled u-PA when analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis followed by fibrin zymography. This activator was partially-purified using controlled-pore glass and Blue Sepharose CL6B. Characterisation by fibrin zymography in the presence of specific antibody, by 3H-DFP labelling and by fibrin-binding ability indicated that the activator was indistinguishable from high molecular weight u-PA. The possible physiological role of the production of relatively large amounts of u-PA by a lung cell capable of producing both u-PA and t-PA is discussed.

Calcium↗
PubMed1985

Increased yield of human tissue-type plasminogen activator obtained by means of recombinant DNA technology.

Extra copies of the human tissue-type plasminogen activator (t-PA) gene were introduced into the Bowes melanoma cell line. We obtained a recombinant cell line (TRBM6) which secretes approximately ten-fold more t-PA than the parent cell line. The identity of the plasminogen activator made by the new cell line was confirmed by sizing on sodium dodecyl sulphate polyacrylamide gels and by specific quenching using anti-t-PA antibody. We estimate that the recombinant line produces t-PA at a rate of approximately 3 pg/cell/24 hr and that t-PA accumulates in the harvest medium at a rate of approximately 4000 International t-PA Units/ml/24 hr.

Cell Line↗
PubMed1985

Isolation of a human tissue-type plasminogen-activator genomic DNA clone and its expression in mouse L cells.

We have isolated a cDNA clone corresponding to a substantial portion of the human tissue-type plasminogen activator (t-PA) protein. It encodes almost all of the protein B chain and part of the 3' untranslated region. We have used this clone to screen bacteriophage lambda and cosmid libraries of human genomic DNA. Several related genomic clones were isolated. One of these, a cosmid clone, carried approx. 40 kb of human DNA. Mapping experiments indicate that the region containing the protein-coding exons is approx. 20 kb in length. The cosmid, containing the t-PA gene and the aminoglycosyl-3'-phosphotransferase dominant-selection marker, was introduced into mouse L cells. Approximately half of the transformants were shown to produce human t-PA. We demonstrated that the fibrinolytic t-PA activity could be specifically quenched by anti-t-PA antibody and that the recombinant t-PA was of similar size (by SDS-polyacrylamide gel electrophoresis) to the t-PA produced by the human Bowes melanoma cell line. Our results suggest that the cosmid clone carries the whole t-PA coding region together with the regulatory elements necessary for its expression.

Amino Acid Sequence↗
PubMed1985

Segments of chromosomal DNA from Rhynchosciara americana that undergo additional rounds of DNA replication in the salivary gland DNA puffs have only weak ARS activity in yeast.

We have constructed a library of recombinant phage containing DNA from salivary gland chromosomes of Rhynchosciara americana. We have isolated phage from this library that carry sequences homologous to cDNA clones that hybridize in situ to the DNA puffs at the polytene chromosome regions C3 and C8. This has enabled us to demonstrate a 16-fold amplification of the genomic DNA sequences at these regions during DNA-puffing. At the C8 site there is a sequence element that has characteristics of 'scrambled' moderately repetitive DNA. This is located within 3 kb from the gene encoding a 1.95-kb mRNA. We have assayed restriction fragments from the two DNA puffs for Ars activity in yeast. The only strong Ars activity is associated with a part of the moderately repetitive DNA element from the C8 puff which is not present at this site in all animals.

Animals↗