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Biomedical subjects

J A Quinn

Publications and source records attributed to J A Quinn.

At least 19 recordsLinked to original sources
PubMed2001

Analysis of the pobA and pobR genes controlling expression of p-hydroxybenzoate hydroxylase in Azotobacter chroococcum.

We report the cloning and analysis of a gene and its cognate regulatory element from a member of the Azotobacteriaceae which are involved in the breakdown of an aromatic compound. The genes from Azotobacter chroococcum encoding p-hydroxybenzoate hydroxylase (pobA) and its regulatory protein (pobR) were cloned from a genomic library and sequenced. Sequence analysis of pobA revealed homology with other bacterial p-hydroxybenzoate hydroxylase enzymes. Residues essential to the structure and function of the enzyme have been conserved. The pobR gene encodes a DNA binding regulatory protein with similarity to proteins from the AraC/XylS family of transcriptional activators. A fragment containing both pobA and pobR was cloned into pUC19 and p-hydroxybenzoate hydroxylase activity was induced in Escherichia coli by the addition of p-hydroxybenzoate. A frame-shift mutation introduced into the pobR gene prevented expression of p-hydroxybenzoate hydroxylase, indicating that PobR is the protein required for transcription of pobA. Interestingly, A. chroococcum PobR has no homology to the PobR protein that is the transcriptional activator of pobA in Acinetobacter strain ADP1, a protein that is homologous to the IclR family of transcriptional regulators. However, PobR from A. chroococcum is homologous to several other proteins, suggesting that these proteins will also function as transcriptional activators of pobA.

4-Hydroxybenzoate-3-Monooxygenase↗
PubMed2001

What about the other breast? A review of a series of bilateral breast carcinomas.

The BreastScreen Queensland Brisbane Southside BreastScreen Service reports on a study of 10 cases of bilateral breast carcinomas from a total cancer population of 217 cases. All cases were patients of screening examinations that were recalled for a suspicious lesion in one breast. Two cases were mammographically suspicious of bilateral tumours. In eight cases, tumours were ultrasonically visible in both breasts and in two further cases, the suspicion of bilateral malignancy was raised by the presence of bilateral microcalcification. It is not the purpose of this paper to provide a statistical analysis of the occurrence of bilateral breast cancer. This is a radiological paper from a breast screening service reporting on findings that conventional wisdom may find unusual. The incidence of bilateral breast malignancy in the study was found to be somewhat higher than expected. These cases have been diagnosed by the utilization of a particularly high standard of ultrasound and mammography, performed and interpreted by diagnosticians possessing an elevated level of suspicion of the possible presence of a second primary lesion. It is therefore proposed that an increased rate of diagnosis of bilateral tumours is possible with an evolution of assessment protocols, combined with quality ultrasound and mammography.

Journal Article↗
PubMed2001

Phase I study of Gliadel wafers plus temozolomide in adults with recurrent supratentorial high-grade gliomas.

Both Gliadel wafers [1,3-bis(2-chloroethyl)-1-nitrosourea] and temozolomide (TEMO) have been shown in independent studies to prolong survival of patients with recurrent malignant glioma following surgery and radiotherapy. On the basis of preclinical evidence of synergism between Gliadel wafers and TEMO, a phase I study was designed to evaluate the toxicity of combining these 2 agents in the treatment of patients with recurrent supratentorial malignant glioma. All patients had surgical resection of the tumor at relapse, and up to 8 Gliadel (3.85%) wafers were placed in the surgical cavity following resection. Two weeks after surgery, TEMO was given orally daily for 5 days. Cohorts of 3 patients received TEMO at daily doses of 100 mg/m2, 150 mg/m2, and 200 mg/m2, respectively. Patients were assessed for toxicity 4 weeks after start of the first course of TEMO. Contrast-enhanced MRI of the brain was used to assesstumor response after the first cycle of TEMO. Patients with stable disease or response after the first cycle of TEMO were allowed to continue treatment at the same dose every 4 weeks for 12 cycles or until disease progression or unacceptable toxicity. Ten patients with a median age of 47 years (range, 22-66 years) were enrolled in this study. There were 7 patients with glioblastoma multiforme and 3 patients with anaplastic astrocytoma. Three patients were treated with TEMO at the first dose level of 100 mg/m2, 4 at the second dose level of 150 mg/m2, and 3 at the third dose level of 200 mg/m2. The 10 patients received a median of 3 cycles (range, 1-12 cycles) of TEMO following placement of Gliadel wafers. The treatment was well tolerated, with only 1 patient suffering grade III thrombocytopenia at the highest dose level. Two patients at each dose level had no evidence of disease progression after treatment. Four patients suffered progressive disease on therapy. Our study demonstrates that TEMO can be given safely after placement of Gliadel (3.85%) wafers. The recommended dosage for TEMO for a phase II study of this combination is 200 mg/m2 per day for 5 days.

Adult↗
PubMed2000

Phase I trial of carmustine plus O6-benzylguanine for patients with recurrent or progressive malignant glioma.

PURPOSE: The major mechanism of resistance to alkylnitrosourea therapy involves the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT), which removes chloroethylation or methylation damage from the O(6) position of guanine. O(6)-benzylguanine (O(6)-BG) is an AGT substrate that inhibits AGT by suicide inactivation. We conducted a phase I trial of carmustine (BCNU) plus O(6)-BG to define the toxicity and maximum-tolerated dose (MTD) of BCNU in conjunction with the preadministration of O(6)-BG with recurrent or progressive malignant glioma. PATIENTS AND METHODS: Patients were treated with O(6)-BG at a dose of 100 mg/m(2) followed 1 hour later by BCNU. Cohorts of three to six patients were treated with escalating doses of BCNU, and patients were observed for at least 6 weeks before being considered assessable for toxicity. Plasma samples were collected and analyzed for O(6)-BG, 8-oxo-O(6)-BG, and 8-oxoguanine concentration. RESULTS: Twenty-three patients were treated (22 with glioblastoma multiforme and one with anaplastic astrocytoma). Four dose levels of BCNU (13.5, 27, 40, and 55 mg/m(2)) were evaluated, with the highest dose level being complicated by grade 3 or 4 thrombocytopenia and neutropenia. O(6)-BG rapidly disappeared from plasma (elimination half-life = 0. 54 +/- 0.14 hours) and was converted to a longer-lived metabolite, 8-oxo-O(6)-BG (elimination half-life = 5.6 +/- 2.7 hours) and further to 8-oxoguanine. There was no detectable O(6)-BG 5 hours after the start of the O(6)-BG infusion; however, 8-oxo-O(6)-BG and 8-oxoguanine concentrations were detected 25 hours after O(6)-BG infusion. The mean area under the concentration-time curve (AUC) of 8-oxo-O(6)-BG was 17.5 times greater than the mean AUC for O(6)-BG. CONCLUSION: These results indicate that the MTD of BCNU when given in combination with O(6)-BG at a dose of 100 mg/m(2) is 40 mg/m(2) administered at 6-week intervals. This study provides the foundation for a phase II trial of O(6)-BG plus BCNU in nitrosourea-resistant malignant glioma.

Adult↗
PubMed2000

Estrogen-induced activation of Erk-1 and Erk-2 requires the G protein-coupled receptor homolog, GPR30, and occurs via trans-activation of the epidermal growth factor receptor through release of HB-EGF.

Estrogen rapidly activates the mitogen-activated protein kinases, Erk-1 and Erk-2, via an as yet unknown mechanism. Here, evidence is provided that estrogen-induced Erk-1/-2 activation occurs independently of known estrogen receptors, but requires the expression of the G protein-coupled receptor homolog, GPR30. We show that 17beta-estradiol activates Erk-1/-2 not only in MCF-7 cells, which express both estrogen receptor alpha (ER alpha) and ER beta, but also in SKBR3 breast cancer cells, which fail to express either receptor. Immunoblot analysis using GPR30 peptide antibodies showed that this estrogen response was associated with the presence of GPR30 protein in these cells. MDA-MB-231 breast cancer cells (ER alpha-, ER beta+) are GPR30 deficient and insensitive to Erk-1/-2 activation by 17beta-estradiol. Transfection of MDA-MB-231 cells with a GPR30 complementary DNA resulted in overexpression of GPR30 protein and conversion to an estrogen-responsive phenotype. In addition, GPR30-dependent Erk-1/-2 activation was triggered by ER antagonists, including ICI 182,780, yet not by 17alpha-estradiol or progesterone. Consistent with acting through a G protein-coupled receptor, estradiol signaling to Erk-1/-2 occurred via a Gbetagamma-dependent, pertussis toxin-sensitive pathway that required Src-related tyrosine kinase activity and tyrosine phosphorylation of tyrosine 317 of the Shc adapter protein. Reinforcing this idea, estradiol signaling to Erk-1/-2 was dependent upon trans-activation of the epidermal growth factor (EGF) receptor via release of heparan-bound EGF (HB-EGF). Estradiol signaling to Erk-1/-2 could be blocked by: 1) inhibiting EGF-receptor tyrosine kinase activity, 2) neutralizing HB-EGF with antibodies, or 3) down-modulating HB-EGF from the cell surface with the diphtheria toxin mutant, CRM-197. Our data imply that ER-negative breast tumors that continue to express GPR30 may use estrogen to drive growth factor-dependent cellular responses.

Breast Neoplasms↗
PubMed2000

Neurologic emergencies in the cancer patient.

Neurologic complications of cancer and its therapy are varied and common, but there are few true neurologic emergencies. However, when a neurologic emergency does occur, rapid diagnosis and treatment can preserve neurologic function and, in some circumstances, save a life. Epidural spinal cord compression, raised intracranial pressure (ICP), status epilepticus, and intracerebral hemorrhage (ICH) are the most common neurologic emergencies in the cancer patient. This chapter details the clinical features, possible etiologies, diagnostic tests, and treatment options for each of these complications.

Antineoplastic Agents↗
PubMed2000

Sex expression, sex-specific traits, and the effects of salinity on growth and reproduction of Amaranthus cannabinus (Amaranthaceae), a dioecious annual.

Amaranthus cannabinus was studied to investigate some of the ecological factors thought to be involved in the evolution of dioecy and to investigate the effects of salinity on sex expression and sex-specific selection. In the field portion of this study, sex ratios, stability of sex expression, spatial distribution, allocation strategies, and phenologies of the sexes were investigated in New Jersey freshwater and salt marsh populations of water hemp. To examine the effects of salinity on vegetative and reproductive development of males and females, plants were grown in the greenhouse at three salinity levels. Adult sex ratios were found to be 1:1. Temporal deviations from a 1:1 sex ratio varied by population and were due to differences in flowering phenology and mortality between the sexes. No plants were observed to change sex expression, and there was no evidence of spatial segregation of the sexes in the field. In both the field and the greenhouse, females allocated more resources to vegetative tissues and had a longer growing period than males. The results of this study suggest that increased reproductive efficiency through sex-specific growth patterns may have been an important selective factor involved in the evolution of dioecy in A. cannabinus.

Journal Article↗
PubMed1993

Maximal migration of human smooth muscle cells on fibronectin and type IV collagen occurs at an intermediate attachment strength.

Although a biphasic dependence of cell migration speed on cell-substratum adhesiveness has been predicted theoretically, experimental data directly demonstrating a relationship between these two phenomena have been lacking. To determine whether an optimal strength of cell-substratum adhesive interactions exists for cell migration, we measured quantitatively both the initial attachment strength and migration speed of human smooth muscle cells (HSMCs) on a range of surface concentrations of fibronectin (Fn) and type IV collagen (CnIV). Initial attachment strength was measured in order to characterize short time-scale cell-substratum interactions, which may be representative of dynamic interactions involved in cell migration. The critical fluid shear stress for cell detachment, determined in a radial-flow detachment assay, increased linearly with the surface concentrations of adsorbed Fn and CnIV. The detachment stress required for cells on Fn, 3.6 +/- 0.2 x 10(-3) mu dynes/absorbed molecule, was much greater than that on CnIV, 5.0 +/- 1.4 x 10(-5) mu dynes/absorbed molecule. Time-lapse videomicroscopy of individual cell movement paths showed that the migration behavior of HSMCs on these substrates varied with the absorbed concentration of each matrix protein, exhibiting biphasic dependence. Cell speed reached a maximum at intermediate concentrations of both proteins, with optimal concentrations for migration at 1 x 10(3) molecules/micron2 and 1 x 10(4) molecules/micron2 on Fn and CnIV, respectively. These optimal protein concentrations represent optimal initial attachment strengths corresponding to detachment shear stresses of 3.8 mu dyne/micron2 on Fn and 1.5 mu dyne/micron2 on CnIV. Thus, while the optimal absorbed protein concentrations for migration on Fn and CnIV differed by an order of magnitude, the optimal initial attachment strengths for migration on these two proteins were very similar. Further, the same minimum strength of initial attachment, corresponding to a detachment shear stress of approximately 1 mu dyne/micron2, was required for movement on either protein. These results suggest that initial cell-substratum attachment strength is a central variable governing cell migration speed, able to correlate observations of motility on substrata differing in adhesiveness. They also demonstrate that migration speed depends in biphasic manner on attachment strength, with maximal migration at an intermediate level of cell-substratum adhesiveness.

Cell Adhesion↗
PubMed1990

Receptor-mediated adhesion phenomena. Model studies with the Radical-Flow Detachment Assay.

Receptor-mediated cell adhesion phenomena play a vital role in many physiological and biotechnology-related processes. To investigate the physical and chemical factors that influence the cell/surface interaction, we have used a radial flow device, a so-called Radial-Flow Detachment Assay (RFDA). The RFDA allows us to make direct observations of the detachment process under specified experimental conditions. In results reported here, we have studied the detachment of receptor-coated latex beads (prototype cells) from ligand-coated glass surfaces. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine several aspects of the adhesion process with particles having uniform properties that can be varied systematically. Advantages of the RFDA are many, especially direct observation of cell detachment over a range of shear stresses with quantitative measurement of the adhesive force. We focus our studies on the effects of ligand and receptor densities, along with the influence of pH and ionic strength of the medium. These data are analyzed with a mathematical model based on the theoretical framework of Bell, G. I. (1978. Science [Wash. DC]. 200:618-627) and Hammer, D. A. and D. A. Lauffenburger (1987. Biophys. J. 52:475-487). We demonstrate experimental validation of a theoretical expression for the critical shear stress for particle detachment, and show that it is consistent with reasonable estimates for the receptor-ligand bond affinity.

Antibodies↗
PubMed1990

Receptor-mediated cell attachment and detachment kinetics. I. Probabilistic model and analysis.

The kinetics of receptor-mediated cell adhesion to a ligand-coated surface play a key role in many physiological and biotechnology-related processes. We present a probabilistic model of receptor-ligand bond formation between a cell and surface to describe the probability of adhesion in a fluid shear field. Our model extends the deterministic model of Hammer and Lauffenburger (Hammer, D.A., and D.A. Lauffenburger. 1987. Biophys. J. 52:475-487) to a probabilistic framework, in which we calculate the probability that a certain number of bonds between a cell and surface exists at any given time. The probabilistic framework is used to account for deviations from ideal, deterministic behavior, inherent in chemical reactions involving relatively small numbers of reacting molecules. Two situations are investigated: first, cell attachment in the absence of fluid stress; and, second, cell detachment in the presence of fluid stress. In the attachment case, we examine the expected variance in bond formation as a function of attachment time; this also provides an initial condition for the detachment case. Focusing then on detachment, we predict transient behavior as a function of key system parameters, such as the distractive fluid force, the receptor-ligand bond affinity and rate constants, and the receptor and ligand densities. We compare the predictions of the probabilistic model with those of a deterministic model, and show how a deterministic approach can yield some inaccurate results; e.g., it cannot account for temporally continuous cell attach mentor detachment, it can underestimate the time needed for cell attachment, it can overestimate the time required for cell detachment for a given level of force, and it can overestimate the force necessary for cell detachment.

Biophysical Phenomena↗
PubMed1990

Receptor-mediated cell attachment and detachment kinetics. II. Experimental model studies with the radial-flow detachment assay.

Quantitative information regarding the kinetics of receptor-mediated cell adhesion to a ligand-coated surface are crucial for understanding the role of certain key parameters in many physiological and biotechnology-related processes. Here, we use the probabilistic attachment and detachment models developed in the preceding paper to interpret transient data from well-defined experiments. These data are obtained with a simple model cell system that consists of receptor-coated latex beads (prototype cells) and a Radial-Flow Detachment Assay (RFDA) using a ligand-coated glass disc. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine transient behavior with particles that possess fairly uniform properties that can be varied systematically, and the RFDA is designed for direct observation of adhesion to the ligand-coated glass surface over a range of shear stresses. Our experiments focus on the effects of surface shear stress, receptor density, and ligand density. These data provide a crucial test of the probabilistic framework. We show that these data can be explained with the probabilistic analyses, whereas they cannot be readily interpreted on the basis of a deterministic analysis. In addition, we examine transient data on cell adhesion reported from other assays, demonstrating the consistency of these data with the predictions of the probabilistic models.

Biophysical Phenomena↗
PubMed1989

Permeation of inert gases through human skin: modeling the effect of skin blood flow.

We present an analytic method for determining the effects of skin perfusion--vasculature and flow rates--on the flux of inert gases through human skin. We systematically specify the underlying blood flow and examine the resulting fluxes of several gases, allowing for the appropriate tissue resistances. For physiological flows, the stratum corneum has an effect equivalent to a series resistance. Helium flux at low total flow depends primarily on subdermal perfusion, but at higher flow, middermal and subpapillary effects become important. The fluxes of less permeable gases, such as argon and xenon, depend on middermal and subpapillary flow at lower total flows. From any single measurement of gas flux, it is difficult to establish an unambiguous value for the underlying blood flow, but the simultaneous measurement of different gases narrows the range of plausible conditions.

Argon↗