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Biomedical subjects

A M Spence

Publications and source records attributed to A M Spence.

At least 37 records · Page 2Linked to original sources
PubMed1996

Caenorhabditis elegans sex-determining protein FEM-2 is a protein phosphatase that promotes male development and interacts directly with FEM-3.

Male sexual development in the nematode Caenorhabditis elegans requires the genes fem-1, fem-2, and fem-3. The current model of sex determination portrays the FEM proteins as components of a novel signal transduction pathway, but the mechanisms involved in signaling through the pathway are not understood. We report the isolation of fem-2 cDNAs in a yeast two-hybrid screen for clones encoding proteins that interact with FEM-3. Association of FEM-3 and FEM-2 in two independent in vitro binding assays substantiates the interaction detected in the two-hybrid system. FEM-2 is related in sequence to protein serine/threonine phosphatases of Type 2C (PP2C). We demonstrate that FEM-2 exhibits magnesium-dependent casein phosphatase activity, typical of PP2C, in vitro. Point mutations that abolish the casein phosphatase activity of FEM-2 without affecting its FEM-3-binding activity reduce severely its ability to rescue male development in fem-2 mutant nematodes. These results suggest that protein phosphorylation regulates sex determination in C. elegans.

Amino Acid Sequence↗
PubMed1996

Boron neutron capture therapy (BNCT) for high-grade gliomas of the brain: a cautionary note.

PURPOSE/OBJECTIVE: Boron neutron capture therapy (BNCT) is a method of treating high-grade gliomas of the brain that involves incorporating 10B into the tumor using appropriate pharmacological agents and then irradiating the tumor with thermal or epithermal neutron beams. To date, over 120 patients have been treated in this manner by Japanese investigators using a thermal neutron beam from a nuclear reactor. Favorable reports on outcome have motivated considerable current research in BNCT. The purpose of this study is to provide an independent analysis of the Japanese data by identifying the subset of patients from the United States who received this treatment in Japan and comparing their outcomes relative to a matched cohort who received conventional therapy in various Radiation Therapy Oncology Group (RTOG) studies. METHODS AND MATERIALS: The principal referral sources of patients to Japan for BNCT were identified and the names of patients sent for treatment obtained. The treating physicians in Japan were also contacted to see if additional patients from the United States had been treated. Either the patients or their next of kin were contacted, and permission was obtained to retrieve medical records including tumor pathology for central review. Prognostic variables according to an analysis of the RTOG brain tumor database by Curran et al. were determined from these records and used to construct a matched cohort of patients treated conventionally. RESULTS: A total of 14 patients were identified who had traveled to Japan for BNCT treatment between July, 1987 and June, 1994. In the case of one patient (deceased), it was not possible to contact the next of kin. Material was obtained on the other 13 patients and review of the pathology indicated that 1 patient had a central nervous system lymphoma rather than a high-grade glioma. Survival data was analyzed for the other 12 patients on an actuarial basis, and this showed no difference compared to survival data for a matched set of patients constructed according to the classification schema of Curran et al. Median survivals were 10.5 months for both groups; survival at 3 years was 22% for the BNCT group compared to 13% for the conventionally treated group (p = NS). The only long-term survivors in the BNCT group had anaplastic astrocytomas and favorable prognostic criteria (Classes I and II of Curran et al.). The actuarial survival curves for the patients with glioblastoma multiforme (strict histological criteria) who received BNCT and their counterparts who received conventional therapy are virtually superimposable. The respective 2-year survivals are 20 vs. 10% (p = NS). Patterns of failure, toxicity, and analysis of the results according to histology are discussed. CONCLUSIONS: Analysis of patients from the United States who received BNCT treatment in Japan does not support a clinically meaningful improvement in survival attributable to this form of therapy. The implications of this for future BNCT research directions are discussed.

Adult↗
PubMed1996

Operation and permanent low activity 125I brachytheraphy for recurrent high-grade astrocytomas.

Twenty-two adult patients with recurrent high grade astrocytomas [18 glioblastoma multiforme (GBM) and 4 anaplastic astrocytoma (AA) at time of implant] underwent therapy at the University of Washington from October 1991 through March 1995, with repeat craniotomy, maximal debulking of tumor, and placement of permanent low activity 125I seeds. Median age was 41 years and median Karnofsky performance status was 90. Median survival for the entire group was 65 weeks from the time of implant. For the subgroup of GBM patients, median survival was 64 weeks from the time of implant. One-year survival from the date of implant was 57% for the entire group and 59% for those with GBM. The site of first failure after implant was local (within 2 cm of the resection cavity) in 70%, distant (noncontiguous, beyond 2 cm) in 18% and concurrently local and distant in 12%. There was one case of symptomatic radiation injury that resolved with steroid therapy, and no patient required repeat craniotomy for parenchymal necrosis. For patients with recurrent GBM, treatment with resection and permanent low activity 125I brachytherapy yielded improved survival compared to an internal historical control group treated with resection and chemotherapy (p = 0.023). Craniotomy with maximal tumor debulking and placement of low activity 125I seeds yields encouraging results with minimal morbidity in patients with recurrent high-grade astrocytomas.

Adolescent↗
PubMed1996

Effects of gamma irradiation on the transduction of dividing and nondividing cells in brain and muscle of rats by adeno-associated virus vectors.

Vectors based on adeno-associated virus (AAV) are under investigation for use in gene therapy applications. Critical aspects of AAV vector biology remain undefined, in particular the intracellular events and activities mediating transduction and determining host cell permissiveness for transduction. Using cultured primary human fibroblasts, we previously showed that AAV vectors preferentially, but not exclusively, transduce cells in the S phase of the cell cycle, and that transduction can be markedly enhanced by pretreatment of target cells with physical and chemical agents that perturb DNA metabolism. In this study, we tested whether similar improvements in AAV vector performance might be achievable in vivo. The adult rat brain and overlying scalp muscle were selected for vector inoculation because of the presence of well-defined populations of dividing, quiescent, and post-mitotic cells, and gamma irradiation was chosen as a reproducible means of inducing DNA repair in these cells. We find that gamma irradiation markedly enhances the transduction of dividing cell populations in the pia-arachnoid and choroid epithelium within the central nervous system, and of mature nondividing muscle cells in the scalp, whereas gamma irradiation did not increase the basal transduction level of post-mitotic neurons in the hippocampus. These data confirm that replicative cellular DNA synthesis is not required for transduction by AAV vectors and show that the mitotic state of target cells is not necessarily predictive of responsiveness to transduction-enhancing treatments. Most importantly, these data demonstrate that target cells can be manipulated in vivo to render them more permissive for AAV vector transduction.

Age Factors↗
PubMed1996

Post-transcriptional regulation of sex determination in Caenorhabditis elegans: widespread expression of the sex-determining gene fem-1 in both sexes.

The fem-1 gene of C. elegans is one of three genes required for all aspects of male development in the nematode. Current models of sex determination propose that the products of the fem genes act in a novel signal-transduction pathway and that their activity is regulated primarily at the post-translational level in somatic tissues. We analyzed the expression of fem-1 to determine whether it revealed any additional levels of regulation. Both XX hermaphrodites and XO males express fem-1 at approximately constant levels throughout development. Somatic tissues in hermaphrodites adopt female fates, but they nonetheless express fem-1 mRNA and FEM-1 protein, suggesting that the regulation of fem-1 activity is post-transcriptional and probably post-translational. A compact promoter directs functional expression of fem-1 transgenes, as assayed by their masculinizing activity in fem-1 mutants. Activity also requires any two or more introns, suggesting that splicing may enhance fem-1 expression. The minimal noncoding sequences required for activity of fem-1 transgenes suffice to direct expression of a fem-1::lacZ reporter gene in all somatic tissues in both sexes. Many fem-1 transgenes, including those that rescue male somatic development in fem-1 mutants, paradoxically feminize the germline. We suggest that they do so by interfering with the germline expression of the endogenous fem-1 gene.

Animals↗
PubMed1996

Phase II study of paclitaxel in patients with recurrent malignant glioma.

PURPOSE: To assess the efficacy and toxicity of paclitaxel administered as a 3-hour infusion to patients with recurrent malignant glioma. PATIENTS AND METHODS: Adult patients with recurrent malignant glioma following radiation therapy, who had received no more than one prior chemotherapy regimen and who had a Karnofsky performance status (KPS) > or = 60, were treated with a 3-hour infusion of paclitaxel every 3 weeks. The initial dose was 210 mg/m2; dose escalation to 240 mg/m2 was allowed. Tumor response was assessed at 6-week intervals using radiographic and clinical criteria. Treatment was continued until documented tumor progression or a total of 12 paclitaxel infusions. RESULTS: Of 41 eligible patients, all were assessable for treatment toxicity and 40 (98%) were assessable for response. The response rate (disease stabilization or better) was 35%. Twenty-nine patients (71%) underwent dose escalation to 240 mg/m2 without the use of growth factors. Toxicities included alopecia (98%), nausea (22%), arthralgias (32%), CNS toxicity (24%), peripheral neuropathy (15%), cardiac toxicity (7%), and myelosuppression (10% grade 3 or 4 hematologic toxicity). No patient developed febrile neutropenia. There was one allergic reaction (2%). CONCLUSION: Paclitaxel is well tolerated at this dose schedule in patients with recurrent malignant glioma, and affords a modest response rate. Because minimal myelotoxicity was encountered in our patients, a dose-escalating phase I/II study of paclitaxel is planned to determine the maximal-tolerated dose (MTD).

Adult↗
PubMed1995

Toxicity, biodistribution and radioprotective capacity of L-homocysteine thiolactone in CNS tissues and tumors in rodents: comparison with prior results with phosphorothioates.

L-Homocysteine thiolactone (L-HCTL) was evaluated for its potential as an intravenously-administered central nervous system (CNS) radioprotector in C3H mice and F344 rats. Toxicity assessments in the mouse yielded a LD50 of 297 mg/kg and in the rat 389 mg/kg. Biodistribution studies in tumor-bearing mice showed that brain specimens contained more label at 10 min than the tumors but less at 30 or 60 min. Brain uptake relative to the tumors, the brain/tumor ratio, ranged between 0.5 and 3.3. The cervical spinal cord of non-tumor-bearing rats was irradiated with 32 Gy 137Cs with or without prior treatment with L-HCTL following which the time to forelimb or hindlimb paralysis was measured to determine the relative protective factors (RPFs) for this radiation dose. For forelimb paralysis the RPF was 1.9 (+/- 1.0, SD) and for hindlimb it was 2.0 (+/- 1.1, SD). 36B-10 glioma cells irradiated in vitro with or without L-HCTL and assayed for colony forming capacity demonstrated a dose modifying factor (DMF) of only 1.15 (+/- 0.16, SE). Rats bearing intracerebral 36B-10 glioma received 137Cs irradiation with or without L-HCTL after which the tumors were similarly assayed in vitro. From this the glioma DMF was 1.2 (+/- 0.30, SE). Compared to prior results with phosphorothioates our data show that the toxicity of L-HCTL is roughly the same as WR2721, WR77913 and WR3689 and that it distributes at higher levels in the CNS after systemic administration. L-HCTL may well equal these phosphorothioates at protecting normal CNS tissue without requiring administration directly into the cerebrospinal fluid-containing spaces and it does not protect the 36B-10 glioma.

Amifostine↗
PubMed1995

Radiation therapy for sarcoid of the thalamus/posterior third ventricle: case report.

There are a limited number of previously reported cases involving the use of radiation therapy for sarcoid of the brain. The case of a 22-year-old man with a thalamic/posterior third ventricle sarcoid mass that grew despite steroid medication is presented. The patient was treated with external beam radiation to a total dose of 20 Gy, with 2-Gy fractions over 14 elapsed days. A complete radiographic response was achieved 4 months after radiation was completed. Radiographic follow-up through 8 months postradiation shows no evidence of disease recurrence. Fractionated radiation therapy in low-to-moderate doses appears to be efficacious in steroid-refractory sarcoid of the brain.

Adult↗
PubMed1994

Gene therapy of rat 9L gliosarcoma tumors by transduction with selectable genes does not require drug selection.

9L rat glioma cells have been used as a model for brain tumor therapies. It has been reported that in vivo infection of 9L cells with a replication-defective retrovirus expressing the herpes simplex thymidine kinase gene resulted in decreased tumor formation following treatment with the antiviral drug ganciclovir. In the study reported here, rats were injected either intracerebrally or subcutaneously with 9L glioma cells expressing a chimeric hygromycin phosphotransferase-thymidine kinase fusion protein or with unmodified 9L cells. Tumor formation was decreased in the rats receiving modified cells, even in the absence of treatment with ganciclovir. Suppression of tumor growth was also observed with cells modified to express the intracellular selectable marker neomycin phosphotransferase. These results indicate that an intracellular selectable marker, in the absence of pharmacologic selection, can inhibit tumor growth of 9L cells. The demonstration that intracellular marker genes can negatively influence the survival of transplanted cells has important implications for in vivo studies that use genetically modified cells.

Animals↗
PubMed1994

Concomitant boron-neutron capture therapy during fast-neutron irradiation of a rat glioma.

PURPOSE: Fast-neutron irradiation and boron-neutron capture therapy (BNCT) have been independently investigated as treatments for malignant disease. This study tested the feasibility of enhancing fast-neutron irradiation with concomitant BNCT. MATERIALS AND METHODS: Seventeen male Fisher rats, each weighing 180-200 g and bearing 36B10 gliomas, were irradiated with graded doses of fast-neutron radiation. Half of the animals received an L-para-boronophenylalanine (BPA) fructose complex prior to treatment. An in vitro colony-forming assay was used to measure surviving fraction. RESULTS: A significantly lower surviving fraction was noted in the tumors from the BPA group compared with those receiving neutrons alone at the three lower neutron doses (P < .005). With use of a linear quadratic curve fit of cell survival, the dose modifying factor was 1.32 at the 0.10 surviving fraction. Mean tumor boron concentration was 68.4 micrograms/g. CONCLUSIONS: BNCT enhancement of fast-neutron irradiation is feasible in an in vivo tumor system.

Animals↗
PubMed1994

Multimodality management of recurrent adult malignant gliomas: results of a phase II multiagent chemotherapy study and analysis of cytoreductive surgery.

Fifty-one adult patients with recurrent malignant gliomas were treated in a Phase II trial of multidrug chemotherapy (6-thioguanine, dibromodulcitol, procarbazine, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 5-fluorouracil, and hydroxyurea). Thirty-one patients underwent radical tumor debulking, before the administration of chemotherapy. Fifty-seven percent of all patients had either an objective radiographic response or stabilization of disease after the institution of therapy. The overall median survival time (MST) was 40 weeks; it was 79 and 33 weeks for anaplastic astrocytoma and glioblastoma patients, respectively. The overall median time to tumor progression (MTP) was 19 weeks--32 weeks for anaplastic astrocytoma patients and 13 weeks for glioblastoma patients. Serious chemotoxicity occurred in 35% of patients without permanent morbidity or mortality. The factors that affected response (including disease stabilization), MTP, and MST were identified through a multivariate statistical analysis. A longer MTP was associated with higher Karnofsky scores, lower grade initial histology, lack of prior chemotherapy, greater degree of myelotoxicity, smaller postoperative tumor volumes, greater extent of surgical resection, and a local versus diffuse recurrence pattern. A longer MST was associated with higher Karnofsky scores, lower grade histology at the time of recurrence, greater degree of myelotoxicity, and lobar versus deep tumor location. Response (including disease stabilization) correlated with higher Karnofsky scores, lower grade histology (initial and current), prior lower grade histology, smaller preoperative tumor volume, longer intervals from the time of initial diagnosis, and absence of prior chemotherapy. These results suggest that, in addition to established prognostic factors such as Karnofsky scores, other factors including prior chemotherapy administration, patterns of tumor recurrence, and tumor location may be important variables to consider in future Phase II-III clinical trials. Of the treatment variables analyzed, greater surgical debulking and smaller postoperative tumor volumes were associated with prolonged MTP but not MST, and greater myelotoxicity had a positive association with all outcomes. The significance of this latter relationship and its relevance to chemotherapy dosing will require further study. Standardization in the design and reporting of clinical trials and the use of computer-assisted tumor volume calculations to assess the extent of surgical resection and the response to therapy are advocated.

Adult↗
PubMed1994

Enhanced optical imaging of rat gliomas and tumor margins.

Current intraoperative methods used to maximize the extent of tumor removal are limited to intraoperative biopsies, ultrasound, and stereotactic volumetric resections. A new technique involving the optical imaging of an intravenously injected dye has the potential to localize tumors and their margins with a high degree of accuracy. In a rat glioma model, enhanced optical imaging was performed and indocyanine green was used as the contrast-enhancing agent. In all 22 animals, the peak optical change in the tumor was greater than in the ipsilateral brain around the tumor and the contralateral normal hemisphere. The clearance of the dye was significantly delayed to a greater extent in the tumor than in the brain around the tumor and the normal brain. After attempts were made at complete microscopic resection, enhanced optical imaging of the tumor margins and the histological samples demonstrated a specificity of 93% and a sensitivity of 89.5%. Enhanced optical imaging was capable of outlining the tumor even when the imaging was done through the cranium. The optical imaging of rat gliomas with a contrast-enhancing dye is able to differentiate between normal brain and tumor tissue both at the cortical surface and at the tumor margins. The application of these studies in an intraoperative clinical setting may allow for the more accurate determination of tumor margins and may increase the extent of tumor removal.

Animals↗
PubMed1994

MR assessment of radiation-induced blood-brain barrier permeability changes in rat glioma model.

PURPOSE: To assess the potential of a T1-weighted, gadolinium-enhanced MR technique for quantifying radiation-induced changes of blood-brain barrier permeability in a model of stereotactically implanted intracerebral gliomas in rats. METHODS: We calculated the gadolinium blood-to-tissue transport coefficient for gadopentetate dimeglumine from signal intensities in sequential MR images in nine control animals that were not irradiated and in five and three animals that had received 2500 cGy and 1500 cGy whole-brain irradiation, respectively, at 2 days before imaging. RESULTS: The average blood-to-tissue transport coefficient values were 9.76 mL.kg-1.min-1 in the control group, 23.41 mL.kg-1.min-1 in the 2500 cGy group, and 25.63 mL.kg-1.min-1 in the 1500-cGy group. Blood-to-tissue transport coefficients were significantly higher after irradiation, indicating increased radiation-induced blood-brain barrier permeability. Similar increased blood-brain barrier leakiness in brain tumors after high-dose irradiation has been shown by previous nuclear medicine studies using quantitative autoradiography. CONCLUSION: Contrast-enhanced dynamic MR of brain gliomas is a sensitive method to document radiation-induced blood-brain barrier breakdown. Quantitative gadolinium-enhanced MR may become a useful tool for the management of patients with brain tumors undergoing radiation therapy.

Animals↗
PubMed1993

Indocyanine green (ICG) staining and demarcation of tumor margins in a rat glioma model.

The ability of indocyanine green (ICG) to stain and demarcate brain tumor margins was investigated using an intracerebral rat glioma model. Indocyanine green was injected intravenously into tumor-bearing rats and was found to stain the tumor intensely at 60 to 120 mg/kg for at least 1 hour after injection. Furthermore, gross tissue staining was found to coincide with the actual histologic tumor margins within 1 mm. After resection of stained tumor tissue, minimal residual tumor cells at the margins of the resection cavity were identified. This investigation established the capacity of indocyanine green to grossly delineate a rat brain tumor and its margins from adjacent normal parenchyma.

Animals↗
PubMed1992

UNC-5, a transmembrane protein with immunoglobulin and thrombospondin type 1 domains, guides cell and pioneer axon migrations in C. elegans.

The unc-5 gene is required for guiding pioneering axons and migrating cells along the body wall in C. elegans. In mutants, dorsal migrations are disrupted, but ventral and longitudinal movements are largely unaffected. The gene was tagged for molecular cloning by transposon insertions. Based on genomic and cDNA sequencing, the gene encodes UNC-5, a transmembrane protein of 919 aa. The predicted extracellular N-terminus comprises two immunoglobulin and two thrombospondin type 1 domains. Except for an SH3-like motif, the large intracellular C-terminus is novel. Mosaic analysis shows that unc-5 acts in migrating cells and pioneering neurons. We propose that UNC-5 is a transmembrane receptor expressed on the surface of motile cells and growth cones to guide dorsal movements.

Amino Acid Sequence↗
PubMed1992

Phase II evaluation of high-dose intravenous cisplatin for treatment of adult malignant gliomas recurrent after chloroethylnitrosourea failure.

Twenty-one patients with recurrent malignant glioma who had failed prior chemotherapy with nitrosoureas were treated with high-dose intravenous cisplatin on days 1 and 8 of successive 4 week cycles. Fourteen patients were evaluable for response. Four patients showed partial responses; mean time to tumor progression (MTP) was 8 weeks. Six patients stabilized; MTP was 11 weeks. Four patients showed no response. There were no infectious or hemorrhagic complications, but partial hearing loss occurred in 7 patients and severe vomiting in 8 patients. High-dose intravenous cisplatin demonstrates substantial activity against malignant gliomas recurrent after chloroethylnitrosourea (CENU) failure.

Adult↗
PubMed1992

Contribution of labeled carbon dioxide to PET imaging of carbon-11-labeled compounds.

11CO2 is one of the major metabolites of many [11C]-labeled radiopharmaceuticals, including glucose, thymidine, acetate, amino acids, and fatty acids. Our data contradict the notion that the contribution of labeled CO2 to PET images can be disregarded because of its rapid elimination through the lungs. We have measured the retention and excretion of 11CO2 in dogs after the intravenous injection of labeled CO2/HCO3-, which had been equilibrated ex vivo with blood. Only 58% of the label was exhaled as CO2 over the first 60 min after injection, with the rest retained in the body. The injection of [11C]thymidine labeled in the ring-2 position or [11C]acetate labeled in the carboxylate position resulted in the production of large amounts of labeled CO2 with the exhalation of about 47% and 23%, respectively, of the injected label over 60 min. At 10 min after injection of either [11C]thymidine and [11C] acetate, approximately 60% to 70% of total blood activity was in labeled CO2 or bicarbonate. On the other hand, the use of [1-11C]glucose only resulted in exhalation of 5% of the injected dose and CO2/HCO3- made up less than 10% of blood activity at 10 min. Our results indicate that retention and distribution of labeled CO2 needs to be considered when interpreting PET data obtained from 11C-labeled compounds.

Acetates↗