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A Guha

Publications and source records attributed to A Guha.

At least 55 records · Page 3Linked to original sources
PubMed1999

Expression of activated epidermal growth factor receptors, Ras-guanosine triphosphate, and mitogen-activated protein kinase in human glioblastoma multiforme specimens.

OBJECTIVE: Amplification of the epidermal growth factor receptor (EGFR) is a common event in the molecular pathogenesis of high-grade astrocytic tumors, occurring in 50% of glioblastoma multiforme (GBM) cases. A subset of GBMs also express a constitutively phosphorylated truncated receptor (EGFRvIII). Expression of transfected EGFRvIII in cells has been reported to activate the Ras-mitogen-activated protein kinase pathway and to provide a growth advantage. Novel therapeutic agents targeting signal transduction pathways are entering early clinical trials; determination of which GBMs express EGFRvIII might help identify patients who might benefit from these biological agents. METHODS: A cohort of 15 flash-frozen surgical specimens (12 GBMs, 2 gliosarcomas, and 1 adult low-grade glioma) were evaluated for EGFR and EGFRvIII expression and for EGFR activation status using immunohistochemical (IHC) analysis, Western blotting, and reverse transcription-polymerase chain reaction assays. Levels of activated Ras-guanosine triphosphate were measured using a nonradioactive luciferase-based technique. Mitogen-activated protein kinase activation was determined using a myelin basic protein assay. IHC analysis was performed on paraffin-embedded, formalin-fixed, pathological specimens. Normal control samples included white matter specimens distal to tumors (n = 5), a sample obtained during a lobectomy for treatment of epilepsy (n = 1), and cultured fetal human astrocytes (n = 1). RESULTS: We demonstrated higher levels of activated Ras and mitogen-activated protein kinase in GBM specimens, compared with normal brain tissue or the low-grade glioma. There was a very good correlation between results obtained using specialized molecular techniques and those obtained using routine IHC techniques. Screening for EGFRvIII expression may be of prognostic importance, because patients with EGFRvIII-positive tumors exhibited shorter life expectancies (mean survival time for patients with EGFRvIII-positive tumors, 4.5 +/- 0.6 mo; mean survival time for patients with EGFRvIII-negative tumors, 11.2 +/- 0.9 mo). CONCLUSION: We demonstrated that routine IHC techniques using commercially available antibodies are capable of identifying which GBM specimens express EGFRvIII and whether the EGFRs are activated. Such a molecular classification of GBMs might allow us to determine which patients might benefit from biologically targeted therapies. In addition, characterization of specimens with respect to their EGFRvIII status seems to be of prognostic value.

Adult↗
PubMed1998

Screening for loss of heterozygosity and microsatellite instability in oligodendrogliomas.

To assess the frequency of loss of heterozygosity (LOH) and microsatellite instability (MI) in oligodendrogliomas, we performed an extensive screening of 16 oligodendrogliomas and nine anaplastic oligodendrogliomas by using 132 microsatellite markers on chromosomes 1 through 12 and 15 through 21. In total, 3,135 loci were examined in 25 tumor samples. Only 33/1,965 (1.7%) of oligodendroglioma (low-grade) and 11/1,070 (1.0%) of anaplastic oligodendroglioma (high-grade) loci exhibited MI. High-frequency LOH regions were identified on chromosome arms 1p (31-73% for oligodendrogliomas and 60-100% for anaplastic oligodendrogliomas) and 19q (23-69% for oligodendrogliomas and 100% for anaplastic oligodendrogliomas). In addition, regions on chromosomes 4, 6, and 11 were found to be lost in 30-80% of both oligodendrogliomas and anaplastic oligodendrogliomas. Increased LOH frequency of chromosome 17 (38-40%) was found only in high-grade oligodendrogliomas. The differences in LOH frequencies between low-grade and high-grade oligodendrogliomas in all loci combined and at three loci (DIS447, DIS226, and DIS252) on chromosome arm 1p were determined to be statistically significant [chi 2(1) = 20.2, P < 0.0001, and Fisher's exact test respective P values: 0.01, 0.03, and 0.02]. Our results provide evidence that microsatellite instability does not play an important role in the development of oligodendrogliomas. Furthermore, high LOH frequency on chromosomes 6 and 11 in addition to that identified previously on chromosomes 1, 19, and 4 suggests that multiple candidate tumor suppressor genes on these chromosomes may underlie the processes of initiation and/or progression in oligodendroglioma tumorigenesis.

Adult↗
PubMed1998

Degradation of fenitrothion by Bacillus stearothermophilus adhering to silica.

B. stearothermophilus strain AG-49, when cultivated in mineral medium in the presence of silica (SA), adhered to SA. Adhesion depended on age of culture, contact time and glucose concentration of the culture medium. Mid-exponential phase culture (5 h) required minimum contact time (30 min) for maximum adhesion. 0.6% glucose concentration was optimum. Quantitative variation in protein and saccharide extractable in sodium chloride and sodium dodecyl sulfate (SDS) was observed. Five % degradation of fenitrothion by adherent B. stearothermophilus could be achieved in 4 d.

Bacterial Adhesion↗
PubMed1998

Experimental biofilm and its application in malathion degradation.

Mixed bacterial culture consisting of three different strains of Micrococcus sp. (AG 36, AG 94 and AG 98) and two strains of Pseudomonas sp. (AG 7 and AG 52) and its individual components was passed through a sand column and 25.5-92% of cell dry mass was found to be retained (adsorbed) on it. Incubation of sand soaked in mineral medium containing glucose as a sole carbon source resulted in formation of a biofilm with 1.2-2.5-fold increase in biomass. A 61% degradation of malathion by the mixed culture biofilm could be achieved in 4 d.

Bacterial Adhesion↗
PubMed1998

In vitro transformation of ampicillin to cephalexin by free and immobilized cells of Streptomyces sp.

In vitro transformation of ampicillin to cephalexin was studied using calcium alginate-immobilized and free Streptomyces sp. strain DRS-1 packed in glass columns. Tris-HCl buffer containing ampicillin was continuously circulated through the columns for four cycles, each cycle (with fresh ampicillin) being continued for 5 h. The pattern of product formation was identical in both cases, i.e. in each cycle, after reaching a certain concentration, its formation did not increase. Product formation was always higher with immobilized cells. Conversion of ampicillin to cephalexin by the strain was affected by cell and substrate concentration.

Alginates↗
PubMed1998

Neurofibromatosis type 1: piecing the puzzle together.

Neurofibromatosis type 1 (NF1) was first described in 1882 and is characterized by a diverse spectrum of clinical manifestations, including neurofibromas, café au lait spots, and Lisch nodules. NF1 is also noted for the higher risk of associated malignancies, making it the most common tumour-predisposing disease in humans. Transmitted in an autosomal dominant manner, the NF1 gene was cloned in 1990, and belongs to the family of tumour suppressor genes. Since then, there has been an explosion in our understanding of how the gene product, neurofibromin, functions in normal cellular physiology, and how its loss in NF1 relates to the wide spectrum of clinical findings, including NF1-associated tumours. Neurofibromin is a major negative regulator of a key signal transduction pathway in cells, the Ras pathway, which transmits mitogenic signals to the nucleus. Loss of neurofibromin leads to increased levels of activated Ras (bound to GTP), and thus increased downstream mitogenic signaling. Our understanding of neurofibromin's role within cells has allowed for the development of pharmacological therapies which target the specific molecular abnormalities in NF1 tumours. These include the farnesyl transferase inhibitors, which inhibit the post-translational modification of Ras, and other agents which modulate Ras-mediated signaling pathways.

Genes, Neurofibromatosis 1↗
PubMed1998

Ras activation in astrocytomas and neurofibromas.

Oncogenic mutations resulting in activated Ras Guanosine Triphosphate (GTP) are prevalent in 30% of all human cancers, but not primary nervous system tumors. Several growth factors/receptors are implicated in the pathogenesis of malignant astrocytomas including epidermal growth factor (EGFR) and platelet derived growth factor (PDGF-R) receptors, plus the highly potent and specific angiogenic vascular endothelial growth factor (VEGF). A significant proportion of these tumors also express a truncated EGFR, which is constitutively activated. Our work demonstrates that the mitogenic signals from both the normal PDGF-R and EGFR and the truncated EGFR activate Ras. Inhibition of Ras by genetic or pharmacological strategies leads to decreased astrocytoma tumorgenic growth in vitro and decreased expression of VEGF. This suggests that these agents may be potentially important as novel anti-proliferative and anti-angiogenic therapies for human malignant astrocytomas. In contrast to astrocytomas, where increased levels of activated Ras GTP results from transmitted signals from activated growth factor receptors, the loss of neurofibromin is postulated to lead to functional up-regulation of the Ras pathway in neurofibromatosis-1(NF-1). We have demonstrated that NF-1 neurofibromas and neurogenic sarcomas, compared to non-NF-1 Schwannomas, have markedly elevated levels of activated Ras GTP. Increased Ras GTP was associated with increased tumor vascularity in the NF-1 neurogenic sarcomas, perhaps related to increased VEGF secretion. The role of Ras inhibitors as potential therapy in this tumor is also under study.

Astrocytoma↗
PubMed1998

Neurogenic sarcomas: experience at the University of Toronto.

OBJECTIVE: Elucidation of the natural history and optimal management of neurogenic sarcomas is not straightforward, because of diagnostic difficulties and the low incidence of this disease. The majority of neurogenic sarcomas are categorized and treated as soft tissue sarcomas, and only a few centers have sufficient experience to add to our understanding of these malignant tumors. This article proposes an algorithm for the management of these tumors. METHODS: A cohort of 18 cases of neurogenic sarcoma (overall mean follow-up period after oncological diagnosis, 33.7 mo), representing approximately 3% of all soft tissue sarcomas treated at the University of Toronto Musculoskeletal Oncology Unit (Toronto, Canada) between 1989 and 1995, were reviewed. The clinical and pathological criteria used to establish the diagnosis of neurogenic sarcoma, the presenting symptoms, the tumor size and grade, the ability to obtain tumor-free margins during en bloc resection, the time to recurrence, and the overall survival rates were noted. A centralized pathological review of the biopsy was undertaken in all cases. RESULTS: A metastatic survey demonstrated localized disease for 16 of the 18 patients. The overall management strategy for these 16 neurogenic sarcomas with localized disease was to obtain local control by en bloc resection. Tumor size, tumor grade, and, most importantly, the ability to obtain tumor-free margins were all relevant prognostic factors for survival. Tumor-free surgical margins were obtained for 11 of 16 patients, with 9 of these 11 patients remaining disease-free. In contrast, all patients for whom tumor-free margins could not ultimately be achieved died as a result of their disease. CONCLUSION: Based on our experience, we propose an algorithm for the management of these rare tumors, for both optimal patient care and oncological research.

Adolescent↗
PubMed1998

Incidence of silent hemorrhage and delayed deterioration after stereotactic brain biopsy.

OBJECT: Many neurosurgeons routinely obtain computerized tomography (CT) scans to rule out hemorrhage in patients after stereotactic procedures. In the present prospective study, the authors investigated the rate of silent hemorrhage and delayed deterioration after stereotactic biopsy sampling and the role of postbiopsy CT scanning. METHODS: A subset of patients (the last 102 of approximately 800 patients) who underwent stereotactic brain biopsies at the Toronto Hospital prospectively underwent routine postoperative CT scanning within hours of the biopsy procedure. Their medical charts and CT scans were then reviewed. A postoperative CT scan was obtained in 102 patients (aged 17-87 years) who underwent stereotactic biopsy between June 1994 and September 1996. Sixty-one patients (59.8%) exhibited hemorrhages, mostly intracerebral (54.9%), on the immediate postoperative scan. Only six of these patients were clinically suspected to have suffered a hemorrhage based on immediate postoperative neurological deficit: in the remaining 55 (53.9%) of 102 patients, the hemorrhage was clinically silent and unsuspected. Among the clinically silent intracerebral hemorrhages, 22 measured less than 5 mm. 20 between 5 and 10 mm, five between 10 and 30 mm, and four between 30 and 40 mm. Of the 55 patients with clinically silent hemorrhages, only three demonstrated a delayed neurological deficit (one case of seizure and two cases of progressive loss of consciousness) and these all occurred within the first 2 postoperative days. Of the neurologically well patients in whom no hemorrhage was demonstrated on initial postoperative CT scan, none experienced delayed deterioration. CONCLUSIONS: Clinically silent hemorrhage after stereotactic biopsy is very common. However, the authors did not find that knowledge of its existence ultimately affected individual patient management or outcome. The authors, therefore, suggest that the most important role of postoperative CT scanning is to screen for those neurologically well patients with no hemorrhage. These patients could safely be discharged on the same day they underwent biopsy.

Adolescent↗
PubMed1998

Manson's schistosomiasis presenting as a brain tumor. Case report.

Neurological complications arising from schistosomiasis are uncommon, and reports of Manson's schistosomiasis presenting as an intracerebral mass lesion are particularly rare. The authors describe the case of a 26-year-old man with a 3-month history of headaches and visual abnormalities. He had immigrated to Canada from Brazil 4 years previously. The patient's general physical and neurological examinations were unremarkable. Magnetic resonance (MR) imaging revealed an enhancing lesion with surrounding edema and mild mass effect in the right occipital lobe. A stereotactic brain biopsy demonstrated intraparenchymal granulomas surrounding Schistosoma masoni eggs. The patient's symptoms resolved following treatment with praziquantel and steroid medications; follow-up MR imaging yielded normal findings. This case demonstrates that neuroschistosomiasis should be considered when an individual presenting with an intracerebral mass has lived in a region in which this disease is endemic.

Adult↗
PubMed1997

Proliferation of human malignant astrocytomas is dependent on Ras activation.

Overexpression and activation of receptor tyrosine kinases, such as platelet derived growth factor receptors (PDGFRs) and epidermal growth factor receptor (EGFR), leads to proliferation of human malignant astrocytoma cells. Although oncogenic mutations affecting Ras are not prevalent in human malignant astrocytomas, we have investigated whether levels of activated Ras.GTP might be elevated in these tumors secondary to the mitogenic signals originating from activated receptor tyrosine kinases. In support of this hypothesis high levels of Ras.GTP, similar to those found in oncogenic Ras transformed fibroblasts, were present in four established human malignant astrocytoma cell lines which express PDGFRs and EGFR, and 20 operative malignant astrocytoma specimens. Stimulation of PDGFR's and EGFR's induced tyrosine phosphorylation of the Shc adaptor protein and its association with Grb2, suggesting a mechanism by which Ras may be activated in human malignant astrocytoma cells. Furthermore, blocking Ras activation by expression of the Ha-Ras-Asn17 dominant-negative mutant, or by farnesyl transferase inhibitors, decreased in vitro proliferation of the human astrocytoma cell lines. These results support the hypothesis that proliferative signals from receptor tyrosine kinases expressed by human malignant astrocytoma cells utilize the Ras mitogenic pathway. Pharmacological inhibitors of the Ras pathway may therefore be of therapeutic value in these presently terminal tumors.

Alkyl and Aryl Transferases↗
PubMed1997

Alterations in the rap1 signaling pathway are common in human gliomas.

Several inherited predisposition to cancer syndromes are associated with the development of nervous system tumors. Tuberous sclerosis complex (TSC) is an autosomal dominant disorder in which affected individuals are at risk for developing astrocytomas. One of the genes responsible for this disorder is TSC2, located on chromosome 16p, and encoding a 180 kDa protein (tuberin) that functions in part as a negative regulator of rap1. Previous studies from our laboratory demonstrated that 30% of sporadic astrocytomas have reduced or absent tuberin expression. In addition to loss of tuberin in sporadic astrocytomas, aberrant rap1 mediated signaling may also result from overexpression of rap1. In this study, we test the hypothesis that alterations in the rap1 signaling pathway are frequently observed in certain subsets of gliomas compared to other tumors of the nervous system. Analysis of sporadic astrocytomas and ependymomas demonstrated either increased rap1 or reduced/absent tuberin protein expression in 50-60% of different cohorts of these gliomas, compared to 30-33% of sporadic schwannomas and meningiomas and none of eight oligodendrocyte tumors. These results suggest that alterations in the rap1 signaling pathway are important in the development of certain sporadic human gliomas.

Adult↗
PubMed1997

Detection of activated platelet-derived growth factor receptors in human meningioma.

The beta receptor subunit of platelet-derived growth factor (PDGF) and its corresponding ligand (PDGF-BB) are coordinately expressed in fresh surgical isolates of human meningioma. These observations imply that PDGF autocrine loops are engaged in human meningioma and suggest that activated PDGF-beta receptors might contribute to the pathology of this common brain neoplasm. The study of PDGF autocrine loops and human meningioma has been slowed by the scarcity of meningioma cell culture model systems. Furthermore, in meningioma tumor tissue, the activation state of PDGF receptors is difficult to assess with conventional reagents, because the tumor is intermixed with normal stroma. In fact, there is no evidence that PDGF receptors within the tumor are activated by ligand. We used a synthetic tyrosine phosphopeptide to raise an antibody that reports the phosphorylation state of tyrosine 751 in the human PDGF-beta receptor. Phosphorylated tyrosine 751 is a recognition site for phosphatidylinositol 3'-kinase, a cytoplasmic effector of PDGF-induced mitogenesis, chemotaxis, and membrane ruffling. Immunoblotting and immunostaining analyses with this antibody show that the PDGF-beta receptor is constitutively phosphorylated at tyrosine 751 within multiple fresh surgical isolates of human meningioma. These findings are consistent with a role for activated PDGF receptors in the proliferation of human meningiomas.

3T3 Cells↗
PubMed1997

Reduced TSC2 RNA and protein in sporadic astrocytomas and ependymomas.

Individuals affected with tuberous sclerosis complex (TSC) develop several benign and malignant tumors at increased frequency, including astrocytomas. Tuberin, the protein product of the tuberous sclerosis complex-2 (TSC2) tumor suppressor gene, has been shown to directly inhibit cell growth and is expressed at high levels in normal central nervous system neurons and astrocytes. To determine whether TSC2 RNA and protein are reduced in astrocytomas from individuals without tuberous sclerosis, reverse transcriptase-polymerase chain reaction and immunoblotting analyses were performed on 49 adult astrocytomas, 10 pediatric astrocytomas, and 13 ependymomas. Eighteen of 40 (45%) high-grade (World Health Organization [WHO] grade III/IV) astrocytomas and 4 of 8 (50%) adult low-grade (WHO grade II) astrocytomas demonstrated reduced or absent TSC2 expression, including 1 giant cell astrocytoma, whereas none of the 10 pediatric low-grade astrocytomas analyzed showed a reduction in TSC2 expression. Reduced or absent tuberin was observed in 2 of 6 (33%) ependymomas analyzed. These data demonstrate, for the first time, that reduced or absent TSC2 expression may represent one of the critical genetic events associated with the development of sporadic adult, but not pediatric, astrocytomas.

Adult↗
PubMed1997

Possible involvement of plasmids in degradation of malathion and chlorpyriphos by Micrococcus sp.

Two plasmid-harboring strains of Micrococcus sp. (M-36 and AG-43) degrade malathion and chlorpyriphos. Derivatives of the strains (SDS-36 and AO-43) treated with acridine orange and sodium dodecyl sulfate could not utilize malathion and chlorpyriphos for growth as the sole carbon source. Agarose gel electrophoresis of cell extracts of M-36 and AG-43 revealed the presence of a plasmid which was absent in SDS-36 and AO-43--suggesting probable involvement of plasmids in the degradation of malathion and chlorpyriphos by M-36 and AG-43. Nalidixic acid resistance in M-36 was also lost upon elimination of plasmids.

Acridine Orange↗
PubMed1997

Primary intracranial fibrosarcoma with intratumoral hemorrhage: neuropathological diagnosis with review of the literature.

Primary intracranial sarcomas are rare tumors of mesenchymal origin in the central nervous system (CNS). Spontaneous hemorrhage, while not an uncommon presentation of brain tumors, has not been described in primary cerebral sarcoma. We report the case of a 43 year old woman presenting with spontaneous hemorrhage into a primary cerebral fibrosarcoma, and discuss this case in the context of the diagnostic criterions of these rare tumors previous reports of intracranial sarcomas and mechanisms of intratumoral hemorrhage.

Adult↗
PubMed1997

Signal transduction pathways and their relevance in human astrocytomas.

Aberrations in a number of signal transduction pathways have been identified as playing a key role in the molecular pathogenesis of astrocytomas and their progression to high grade glioblastoma multiforme (GBM). GBMs are characterized by overexpression of the Platelet Derived Growth Factor Receptors (PDGFR) and their ligands (PDGF), as well as the Epidermal Growth Factor Receptor (EGF-R). These receptors activate the Ras pathway, a key cellular signal transduction pathway, culminating in the activation of a wide range of Ras-dependent cellular events. GBMs have also been found to either overexpression or lose expression of various Protein Kinase C (PKC) isoforms. Major strides are being made in developing pharmacological agents which specifically inhibit these growth factor receptors and intracellular signal transduction pathways. Elucidating the role of these pathways in GBMs is thus of major clinical importance, as these novel molecularly-targeted agents may prove of use in the clinical management of GBMs in the future.

Astrocytoma↗