Biomedical subjects

Abhijit Guha

Publications and source records attributed to Abhijit Guha.

At least 19 recordsLinked to original sources

PubMed2007

Radiation induced peripheral nerve tumors: case series and review of the literature.

PURPOSE: Radiation induced peripheral nerve tumors (PNT) are a rare but known complication of radiotherapy. The clinical and pathologic features of six cases of post-radiation PNT's are reported here, more than doubling the number of known cases reported in the literature. METHODS: We reviewed six cases of radiation induced PNT and performed a review of the current literature on radiation induced neurofibromas. RESULTS: Patient's ranged in age from 18 months to 49 years at the time of their original diagnosis, with radiation doses to the primary tumor ranging from 24 to 40 Gy with post radiation intervals from 10 to 50 years. The majority of PNT's identified were neurofibromas (3) and schwannomas (3). Nuclear atypia, S100 positive staining and mild-moderate cellularity were common pathologic findings. CONCLUSIONS: There are only a handful of neurofibromas in the 60 cases of PNT's thus far reported. This case series broadens the post-radiation neurofibroma literature. While the pathology of PNT induced transformation is still poorly understood, experiments and pathology are congruent on the possibility of malignant transformation, especially for the "atypical neurofibroma". On the clinical level, this case series lends its support to some, but not all, of the risk factors thought to predispose to the formation of radiation induced neurofibromas. Though rare, the complication of radiation-induced neurofibroma cannot be ignored, especially with the increasing use of focused radiosurgical techniques.

Adult↗

PubMed2006

High-grade glioma formation results from postnatal pten loss or mutant epidermal growth factor receptor expression in a transgenic mouse glioma model.

High-grade gliomas are devastating brain tumors associated with a mean survival of <50 weeks. Two of the most common genetic changes observed in these tumors are overexpression/mutation of the epidermal growth factor receptor (EGFR) vIII and loss of PTEN/MMAC1 expression. To determine whether somatically acquired EGFRvIII expression or Pten loss accelerates high-grade glioma development, we used a previously characterized RasB8 glioma-prone mouse strain, in which these specific genetic changes were focally introduced at 4 weeks of age. We show that both postnatal EGFRvIII expression and Pten inactivation in RasB8 mice potentiate high-grade glioma development. Moreover, we observe a concordant loss of Pten and EGFR overexpression in nearly all high-grade gliomas induced by either EGFRvIII introduction or Pten inactivation. This novel preclinical model of high-grade glioma will be useful in evaluating brain tumor therapies targeted to the pathways specifically dysregulated by EGFR expression or Pten loss.

Animals↗

PubMed2006

Beta-catenin regulates wound size and mediates the effect of TGF-beta in cutaneous healing.

After cutaneous injury, a variety of cell types are activated to reconstitute the epithelial and dermal components of the skin. beta-Catenin plays disparate roles in keratinocytes and fibroblasts, inhibiting keratinocyte migration and activating fibroblast proliferation, suggesting that beta-catenin could either inhibit or enhance the healing process. How beta-catenin functions in concert with other signaling pathways important in the healing process is unknown. Wound size was examined in mice expressing conditional null or conditional stabilized alleles of beta-catenin, regulated by an adenovirus expressing cre-recombinase. The size of the wounds in the mice correlated with the protein level of beta-catenin. Using mice expressing these conditional alleles, we found that the wound phenotype imparted by Smad3 deficiency and by the injection of TGFbeta before wounding is mediated in part by beta-catenin. TGFbeta was not able to regulate proliferation in beta-catenin null fibroblasts, whereas keratinocyte proliferation rate was independent of beta-catenin. When mice are treated with lithium, beta-catenin-mediated signaling was activated in cutaneous wounds, which healed with a larger size. These results demonstrate a crucial role for beta-catenin in regulating cutaneous wound size. Furthermore, these data implicate mesenchymal cells as playing a critical role regulating wound size.

Animals↗

PubMed2005

Expression of GATA6 in the human and mouse central nervous system.

The mammalian GATA family of transcription factors comprises of 6 members that are involved in diverse roles. The expression profile of GATA6 has been poorly defined in the central nervous system (CNS). In this report, we identify GATA6 expression in the normal mouse and human CNS, using Northern blot analyses, immunohistochemistry (IHC), and immunofluorescence (IF). GATA6 is expressed as a 2.2 kb transcript in the adult mouse brain and several regions of the adult human brain. Furthermore, cellular characterization demonstrates GATA6 nuclear expression in neurons, astrocytes, choroids plexus epithelium, and endothelial cells.

Aging↗

PubMed2005

Radial glia cells are candidate stem cells of ependymoma.

Tumors of the same histologic type often comprise clinically and molecularly distinct subgroups; however, the etiology of these subgroups is unknown. Here, we report that histologically identical, but genetically distinct, ependymomas exhibit patterns of gene expression that recapitulate those of radial glia cells in the corresponding region of the central nervous system. Cancer stem cells isolated from ependymomas displayed a radial glia phenotype and formed tumors when orthotopically transplanted in mice. These findings identify restricted populations of radial glia cells as candidate stem cells of the different subgroups of ependymoma, and they support a general hypothesis that subgroups of the same histologic tumor type are generated by different populations of progenitor cells in the tissues of origin.

Animals↗

PubMed2005

Pathological and molecular progression of astrocytomas in a GFAP:12 V-Ha-Ras mouse astrocytoma model.

We previously characterized a genetically engineered mouse astrocytoma model with embryonic astrocyte-specific, activated (12)V-Ha-RAS (GFAP-RAS) transgenesis. The GFAP-RAS line Ras-B8 appears normal at birth, but 50% of mice die by 4 months from low- and high-grade astrocytomas. We examined the development and progression of astrocytomas in the Ras-B8 genetically engineered mouse. At embryonic day 16.5 (E16.5), there were no pathological differences compared to control littermates, aside from transgene expression. Diffuse astroglial hyperplasia was the first distinguishing feature in the 1-week-old Ras-B8 mice; however, these astrocytes were not transformed in vitro or in vivo. From 3 to 8 weeks the incidence of low-grade astrocytomas progressively increased with 85% of 12-week-old mice harboring low- or high-grade astrocytomas, the latter characterized by increased proliferation, nuclear atypia, and angiogenesis. Tp 53 mutations were detected in both astrocytoma grades, with high-grade astrocytomas expressing elevated levels of epidermal growth factor receptor and vascular endothelial growth factor, plus decreased levels of PTEN and p16, similar to human astrocytomas. We postulate that expression of (12)V-Ha-RAS in astroglial precursors induces astroglial hyperplasia, but transformation and subsequent progression requires additional molecular alterations resulting from aberrant activated p21-RAS. Of interest, many of these acquired alterations occur in human astrocytomas, further validating GFAP-RAS as a useful model for studying astrocytoma development and progression.

Animals↗

PubMed2005

Regulation of the pathological vasculature of malignant astrocytomas by angiopoietin-1.

Malignant astrocytomas are the most common and highly vascularized of all primary adult brain tumors. The histopathological hallmarks of malignant astrocytomas are microvascular proliferation and formation of vascular entities, which are referred to as "glomeruloid bodies." The significance of glomeruloid bodies and the molecular mechanisms driving the abnormal vascular architecture in malignant astrocytomas are not understood. We have observed that overexpression of angiopoietin-1 (Ang1) in both subcutaneous and intracranial xenograft models of malignant astrocytomas reproduces many of the vascular features of these tumors, including glomeruloid bodies. To confirm that the formation of glomeruloid bodies was directly dependent on Ang1, we performed experiments where levels of Ang1 expression were regulated under tetracycline control, and we found a direct correlation between levels of Ang1 expression and the occurrence of glomeruloid bodies in xenografts. Additionally, we inhibited the action of Ang1 by blocking its cognate receptor Tie2, and we found that the formation of glomeruloid bodies was inhibited. Collectively, these results support our hypothesis that Ang1 is a key molecular regulator of pathological vascularization characteristic of malignant astrocytomas.

Angiogenesis Inducing Agents↗

PubMed2005

A human transferrin-vascular endothelial growth factor (hnTf-VEGF) fusion protein containing an integrated binding site for (111)In for imaging tumor angiogenesis.

UNLABELLED: Our objective was to synthesize a recombinant protein (hnTf-VEGF [VEGF is vascular endothelial growth factor]) composed of VEGF(165) fused through a flexible polypeptide linker (GGGGS)(3) to the n-lobe of human transferrin (hnTf) for imaging angiogenesis. The hnTf domain allowed labeling with (111)In at a site remote from the VEGF receptor-binding domain. METHODS: DNA encoding hnTf, peptide linker (GGGGS)(3), and VEGF(165) genes were cloned into the Pichia pastoris vector pPICZalphaB to generate the pPICZalphaB-hnTF-VEGF plasmid. The expression vector was transformed into P. pastoris KM71H strain. The protein was purified using Co(2+) metal affinity resin. The growth-stimulatory effects of hnTf-VEGF on human umbilical vascular endothelial cells (HUVECs) and its binding to porcine aortic endothelial cells (PAECs) transfected with VEGF receptors were evaluated. hnTf-VEGF protein was labeled with (111)InCl(3) in 10 mmol/L HEPES/15 mmol/L NaHCO(3) buffer, pH 7.4 (HEPES is N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid). The loss of (111)In in vitro from (111)In-hnTf-VEGF to transferrin in human plasma and to diethylenetriaminepentaacetic acid (DTPA) in buffer was determined. Tumor and normal tissue distributions of (111)In-hnTf-VEGF were evaluated in athymic mice implanted subcutaneously with U87MG human glioblastoma xenografts. Tumor imaging was performed. RESULTS: Sodium dodecylsulfate-polyacrylamine gel electrophoresis under reducing and nonreducing conditions showed bands for hnTf-VEGF monomer (M(r) of 65 kDa) and dimer (M(r) of 130 kDa). hnTf-VEGF stimulated the growth of HUVECs 3-fold and demonstrated binding to PAECs displaced by a 50-fold excess of VEGF(165) but not by apotransferrin. There was 21.3% +/- 3.4% loss of (111)In per day from (111)In-hnTf-VEGF to transferrin in plasma, but <5% loss to DTPA over 4 h. (111)In-hnTf-VEGF accumulated in U87MG tumors (6.7% injected dose per gram at 72 h after injection) and its tumor uptake decreased 15-fold by coadministration of a 100-fold excess of VEGF but not by apotransferrin. The tumor-to-blood ratio was 4.9:1 at 72 h after injection and tumors were imaged at 24-72 h after injection. CONCLUSION: (111)In-hnTf-VEGF is a promising radiopharmaceutical for imaging tumor angiogenesis and represents a prototypic protein harboring the metal-binding site of transferrin for labeling with (111)In without introducing DTPA metal chelators.

Animals↗

PubMed2005

Fiber density index correlates with reduced fractional anisotropy in white matter of patients with glioblastoma.

A quantitative description of white matter fiber attenuation, the fiber density index (FDi) is described. This measure is derived from quantitative analysis of diffusion tensor imaging and reveals an index of the number of fiber paths traversing a region of interest. In this report, FDi is computed in 10 patients with glioblastoma multiforme, in white matter that is peritumoral and contralateral. FDi is shown to correlate significantly with fractional anisotropy.

Anisotropy↗

PubMed2004

Suppression of glioblastoma tumorigenicity by the Kruppel-like transcription factor KLF6.

The Kruppel-like transcription factor KLF6 is a novel tumor-suppressor gene mutated in a significant fraction of human prostate cancer. It is localized to human chromosome 10p14-15, a region that displays frequent loss of heterozygosity in glioblastoma multiforme (GBM). Indeed, mutations of the KLF6 gene have recently been reported in this tumor type. In this study, we report that the expression of KLF6 is attenuated in human GBM when compared with primary astrocytes. Expression of KLF6 in GBM cells reverts their tumorigenicity both in vitro and in vivo, which is correlated with its transactivation of the p21/CIP1/WAF1 promoter. Additionally, KLF6 inhibits cellular transformation induced by several oncogenes (c-sis/PDGF-B, v-src, H-Ras, and EGFR) that are components of signaling cascades implicated in GBM. Our results provide the first evidence of functional tumor suppression by KFL6, and its loss may contribute to glial tumor progression.

Animals↗

PubMed2004

Contrasting in vivo and in vitro fates of glioblastoma cell subpopulations with amplified EGFR.

Despite the high incidence of EGFR amplification in patient glioblastoma multiforme (GBM) tissues, only a single GBM cell line, of the many described in the literature, is known to contain and maintain amplified EGFR. Because EGFR mutations in GBM manifest primarily, if not exclusively, in amplified form, it follows that the availability of cell lines with mutation of endogenous EGFR would also be in short supply. In fact, there are no GBM cell lines harboring the common EGFR mutants described in patient GBMs. These observations suggest that in vivo environments select for EGFR amplification, whereas in vitro environments, specifically cell cultures, select against this gene alteration. To contrast directly the fates of EGFR amplification in vivo and in vitro, as well as to examine potential relationships between EGFR amplification and mutation, we have established and maintained GBM explants as xenografts by serial passaging in nude mice. Analysis of EGFR copy number and EGFR mutation status in 11 patient tumors and their corresponding xenografts, as well as the monitoring of EGFR copy number during the establishment of a GBM cell line from a xenograft with amplified EGFR, indicated that selection for EGFR amplification is an in vivo phenomenon. Furthermore, our data indicated that EGFR mutation occurs only in tumors with EGFR amplification and showed that the selection of amplified mutant EGFR over amplified wild-type EGFR as a xenograft occurred rapidly and completely during tumor propagation.

Animals↗

PubMed2004

Malignant peripheral nerve sheath tumors.

The rarity of MPNSTs and the lack of any singular diagnostic radiologic or pathologic signature lead to several management challenges. These tumors are best managed as part ofa multidisciplinary team so as to optimize patient care and facilitate research. Suspicion of an MPNST based on clinical or radiologic alteration of a soft tissue mass in proximity to a peripheral nerve, especially in the context of NF I, should lead to referral to such a tertiary center. Early diagnosis followed by oncologic surgery to obtain tumor-free margins provides the best chance for long-term cure. Psychologic support and occupational rehabilitation are vital components of the overall care of these relatively young patients faced with often disabling surgery. Current adjuvant therapy with radiation and chemotherapy is suboptimal. There have been major inroads toward the molecular biologic understanding of MPNSTs,with several biologic targets that are of potential therapeutic interest. Proper evaluation of these novel and promising management strategies requires a concerted effort to refer these patients to the tertiary centers through which multi-institutional clinical trials can be undertaken.

Humans↗

PubMed2004

Targeting the Tie2/Tek receptor in astrocytomas.

Tie2 is an endothelial cell-specific receptor tyrosine kinase, whose activation is positively and negatively modulated by angiopoietin-1 and angiopoietin-2, respectively. Angiopoietin-mediated modulation of Tie2 activation contributes to normal vessel development and stability, however, its role in tumor angiogenesis is not well known. We investigated the role of Tie2 activation in malignant astrocytomas, a common and highly vascularized primary human brain tumor. We found that Tie2 expression and activation increases with increasing malignancy grade of astrocytomas. Inhibition of Tie2, using a kinase-deficient Tie2 construct, decreases growth of malignant human astrocytoma subcutaneous and intracranial xenografts. Tie2 inactivation disrupted the tumor vascularity, with a decrease in microvascular density, increased presence of abnormally dilated vessels, and loss of interaction between endothelial cells and surrounding smooth muscle cells, all collectively resulting in increased tumor cell apoptosis. Overall, these findings strongly suggest that Tie2 activation contributes significantly to astrocytoma tumor angiogenesis and growth. We postulate that targeting Tie2 activation, either independently or in conjunction with other anti-angiogenic therapies, such as against vascular endothelial growth factor, is of potential clinical interest.

3T3 Cells↗

PubMed2004

Role of Ang1 and its interaction with VEGF-A in astrocytomas.

Angiopoietins (Ang1 and Ang2) modulate the activity of the endothelial cell (EC)-specific receptor tyrosine kinase Tie2, which together with vascular endothelial growth factor (VEGF-A) and its EC-specific receptors, VEGFR1 and VEGFR2, regulate normal physiological vessel development. The functional role of angiopoietins in tumor angiogenesis, in particular astrocytoma angiogenesis, remains unclear. In this study, we focus on the specific contribution of Ang1 to the vascular growth of glioblastoma multiforme (GBM) and its interactive role with VEGF-A. Subcutaneous and intracranial GBM xenografts were generated using 3 established astrocytoma cell lines (U87, U373, and U343) that were transfected to stably over-express Ang1. GBM xenografts were also generated to express low levels of VEGF-A and high Angl. We found that Ang1 increases the vascular growth of both subcutaneous and intracranial xenografts of GBM by approximately 3-fold. However, the increased vascular growth was only seen in xenografts with concurrent VEGF-A elevation, since decreasing VEGF-A expression resulted in a loss of the pro-angiogenic growth advantage seen with Ang1. Collectively, our data suggest that Ang1 regulates GBM vascularity in a VEGF-A dependent manner, synergizing the initial pro-angiogenic response that is triggered by VEGF-A and promoting the vascular growth of GBM.

Angiopoietin-1↗

PubMed2004

Advances in the biology of astrocytomas.

PURPOSE OF REVIEW: Conventional surgery, radio- and chemotherapy have failed to significantly improve the prognosis of patients with malignant astrocytomas--hence the need for understanding their molecular biology. Harvesting this understanding to yield novel biological targeted therapies has approached the clinical doorstep. Therapeutic efficacy will likely require combinatorial therapy involving biologicals and conventional therapies, with small incremental efficacy in selected sub-groups. This review highlights some of the findings over the past year (June 2003-2004) that have contributed to this slow but essential journey towards our understanding of the biology of astrocytomas. RECENT FINDINGS: The accumulation of loss and/or gain of function molecular alterations underlying astrocytoma formation, progression and key growth parameters including proliferation, angiogenesis, apoptosis, invasion and resistance are emerging. These alterations involve those regulating the growth factor/receptor and downstream signaling networks, cell cycle, immune modulators and other key biological processes. The advances are facilitated by interactions amongst clinician and basic scientists, in both academia and industry. They have incorporated high-throughput bioinformatics analysis of genomic and expression array data, the emerging field of proteomics and development of various genetically engineered models of astrocytomas. SUMMARY: Astrocytomas, like other cancers, are a result of several molecular alterations, some of which strongly correlate to their pathological grade. However, molecular heterogeneity exists between astrocytomas of similar grades and likely between varying micro-environmental regions of a single tumor. Characterization of the molecular signature of an astrocytoma and linking with the appropriate 'tailored' therapie(s) is the hope of the future.

Animals↗

PubMed2004

Gene expression profiling reveals unique molecular subtypes of Neurofibromatosis Type I-associated and sporadic malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive Schwann cell neoplasms that are frequently associated with Type I Neurofibromatosis (NF1) and respond poorly to current therapeutic regimens. To better understand the molecular heterogeneity of these tumors, we performed gene expression profiling on 25 NF1-associated and 17 sporadic MPNSTs using oligonucleotide microarrays representing approximately 8100 unique human gene transcripts. Using several previously reported statistical approaches, we were unable to identify a molecular signature that could reliably distinguish between NF1-associated and sporadic MPNSTs in independent training and test sample sets. However, using an unsupervised clustering approach, we identified an extensive gene expression signature that distinguished 9 of the 42 tumors analyzed. This signature corresponded to relative overexpression of transcripts associated with neuroglial differentiation (NCAM, MBP, L1CAM, P1P) and relative down-regulation of proliferation and growth factor associated transcripts (IGF2, FGFR1, MDK, Ki67). All tumors with this gene expression signature lacked expression of EGFR and all but one tumor were derived from patients with NF1. However, there were no other obvious associations with histological grade, tumor site, metastasis, recurrence, age, or patient survival. We conclude that distinct molecular classes of MPNST exist and that the ability to stratify these tumors based on unique and biologically relevant gene expression profiles may be important for future targeted therapeutics.

Adolescent↗

PubMed2004

The need to protect the thyroid gland during image intensifier use in orthopaedic procedures.

The image intensifier has become an essential part of the orthopaedic surgeon's armamentarium. Its increasing use, however, may expose medical staff and theatre personnel to high doses of radiation. The aim of this study was to assess the compliance of surgeons and staff with radiation protection protocols, especially the use of the thyroid shield and to calculate the radiation exposure dose during routine orthopaedic procedures. We carried out this prospective study of 44 consecutive cases at the Rochdale Infirmary. The total dose of radiation and the total number of images taken were found to be more during hip surgery such as dynamic hip screw fixation for intertrochanteric fracture (1,715.5 mGy.cm2) and the intramedullary nailing (4,357.5 mGy.cm2). However the total percentage of the theatre personnel wearing thyroid shield was as low as 4% (14 people out of total 345 people present in theatre in 44 procedures) in spite of its availability. The consistent neglect in the use of the thyroid shield by surgeons and nursing staff present in theatre during fluoroscopically assisted procedures is a matter for concern. The data presented in this study will emphasise the need to wear a thyroid collar during orthopaedic procedures and the need for better guidelines to protect theatre personnel as well as patients from radiation exposure hazards.

Adult↗

PubMed2003

Oligodendrogliomas result from the expression of an activated mutant epidermal growth factor receptor in a RAS transgenic mouse astrocytoma model.

A significant proportion of human malignant gliomas exhibit amplification, overexpression, or mutations of the epidermal growth factor receptor (EGFR). To define the functional role(s) of the EGFR in the pathogenesis of gliomas, we established transgenic mice that express both wild-type (wt) and mutant (EGFRvIII) EGFR molecules using the human glial fibrillary acidic protein (GFAP) promoter. Both GFAP-EGFR(wt) and GFAP-EGFRvIII transgenic mice demonstrated increased numbers of astrocytes compared with control littermates, however, developed normally without formation of gliomas. To determine whether EGFR overexpression could modify the tumor phenotype in our previously reported GFAP-V(12)Ha-ras transgenic mouse astrocytoma model, mice expressing both activated RAS and EGFR were developed. GFAP-V(12)Ha-ras;GFAP-EGFRvIII, but not GFAP-V(12)Ha-ras;GFAP-EGFR(wt) double transgenic mice, had decreased survival with fifty percent of the mice dead at 2-4 weeks from gliomas, compared with 12-16 weeks for the GFAP-V(12)Ha-ras mice. Furthermore, GFAP-V(12)Ha-ras;GFAP-EGFRvIII mice developed oligodendrogliomas and mixed oligoastrocytoma tumors, instead of the fibrillary astrocytomas observed in GFAP-V(12)Ha-ras mice. In addition to yielding a spontaneous model of infiltrating oligodendroglioma, this study demonstrates that astrocyte-specific expression of EGFRvIII alone is insufficient for gliomagenesis but rather contributes to glioma progression in the context of existing predisposing genetic changes.

Animals↗