Biomedical subjects

P C Phillips

Publications and source records attributed to P C Phillips.

At least 19 recordsLinked to original sources

PubMed2006

Exploring the evolution of environmental sex determination, especially in reptiles.

Environmental sex determination has been documented in a variety of organisms for many decades and the adaptive significance of this unusual sex-determining mechanism has been clarified empirically in most cases. In contrast, temperature-dependent sex determination (TSD) in amniote vertebrates, first noted 40 years ago in a lizard, has defied a general satisfactory evolutionary explanation despite considerable research effort. After briefly reviewing relevant theory and prior empirical work, we draw attention to recent comparative analyses that illuminate the evolutionary history of TSD in amniote vertebrates and point to clear avenues for future research on this challenging topic. To that end, we then highlight the latest empirical findings in lizards and turtles, as well as promising experimental results from a model organism, that portend an exciting future of progress in finally elucidating the evolutionary cause(s) and significance of TSD.

Adaptation, Biological↗

PubMed2003

Phase I study of thalidomide for the treatment of plexiform neurofibroma in neurofibromatosis 1.

An open-label phase I trial of thalidomide (TL) in 20 patients with neurofibromatosis 1 (NF1) treated symptomatic plexiform neurofibroma (PNF). TL was well tolerated in doses up to 200 mg/d. Adverse reactions included transient somnolence in four, evanescent rash in two, and reversible mild peripheral neuropathy in two patients. Four patients showed less than 25% reduction in the tumor size. TL may have a role in the treatment of PNF and should be explored in a larger controlled study, possibly using higher doses of TL.

Adolescent↗

PubMed2003

Molecular evolution and quantitative variation for chemosensory behaviour in the nematode genus Caenorhabditis.

Caenorhabditis elegans is a model organism in biology, yet despite the tremendous information generated from genetic, genomic and functional analyses, C. elegans has rarely been used to address questions in ecological genetics. Here, we analyse genetic variation for chemosensory behaviour, an ecologically important trait that is also genetically well characterized, at both the phenotypic and molecular levels within three species of the genus Caenorhabditis. We show that the G-protein ODR-3 plays an important role in chemosensory avoidance behaviour and identify orthologues of odr-3 in C. briggsae and C. remanei. Both quantitative genetic analysis of chemosensory behaviour and molecular population genetic analysis of odr-3 show that there is little genetic variation among a worldwide collection of isolates of the primarily selfing C. elegans, whereas there is substantially more variation within a single population of the outcrossing C. remanei. Although there are a large number of substitutions at silent sites within odr-3 among the three species, molecular evolution at the protein level is extremely conserved, suggesting that odr-3 plays an important role in cell signalling during chemosensation and/or neuronal cilia development in C. remanei and in C. briggsae as it does in C. elegans. Our results suggest that C. remanei may be a more suitable subject for ecological and evolutionary genetic studies than C. elegans.

Animals↗

PubMed2002

Loss of caspase-8 mRNA expression is common in childhood primitive neuroectodermal brain tumour/medulloblastoma.

Upon binding of tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), the agonistic TRAIL receptors DR4 and DR5 activate caspase-8 leading to apoptosis. In primitive neuroectodermal brain tumour (PNET) cell lines, TRAIL-induced apoptosis was recently shown to correlate with caspase-8 mRNA expression (Grotzer MA, Eggert A, Zuzak TJ, et al. Oncogene 2000, 19, 4604-4610). In this study, we analysed the expression of the TRAIL death pathway in 27 primary PNET/medulloblastoma. As shown by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), all PNET/medulloblastoma evaluated expressed DR5, the adapter protein FADD and caspase-3, but only 48% expressed caspase-8. The mRNA expression of caspase-8 was significantly lower in primary PNET/medulloblastoma compared with normal brain samples. PCR revealed >75% methylation of the caspase-8 promoter region in three of seven PNET cell lines and in 55% of the primary PNET/medulloblastoma evaluated. In the PNET cell lines, the methylation status correlated with the caspase-8 mRNA expression. We conclude that loss of caspase-8 gene expression is common in PNET/medulloblastoma suggesting that suppression of death receptor induced apoptosis may play an important role in the pathogenesis of this common childhood brain tumour.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Antitumor activity of the rapamycin analog CCI-779 in human primitive neuroectodermal tumor/medulloblastoma models as single agent and in combination chemotherapy.

We examined the cytotoxicity of the immunosuppressant agent rapamycin and its analogue CCI-779 in human brain tumor cell lines in vitro and in vivo as single agents and in combination with standard chemotherapeutic drugs. In the rapamycin-sensitive PNET/MB cell line DAOY, rapamycin exhibited additive cytotoxicity with cisplatin and with camptothecin. In vivo, CCI-779 delayed DAOY xenograft growth by 160% after 1 week and 240% after 2 weeks of systemic treatment, compared with controls. Single high-dose treatment induced 37% regression of tumor solume. Growth inhibition of DAOY xenografts was 1.3 times greater after simultaneous treatment with CCI-779 and cisplatin than after cisplatin alone. Interestingly, CCI-779 also produced growth inhibition of xenografts derived from U251 malignant glioma cells, a human cell line resistant to rapamycin in vitro. These studies suggest that the rapamycin analogue CCI-779 is an important new agent to investigate in the treatment of human brain tumors, particularly PNET/MB.

Animals↗

PubMed2001

Prognostic significance of Ki-67 (MIB-1) proliferation index in childhood primitive neuroectodermal tumors of the central nervous system.

BACKGROUND: Primitive neuroectodermal tumors (PNET) of the central nervous system, including medulloblastomas, are the most common malignant brain tumors of childhood. Whereas some patients experience prolonged disease control after surgery and adjuvant therapy, others with tumors that appear comparable will relapse and eventually die from progressive disease. PROCEDURE: Because proliferative activity may provide a potential correlate of biologic aggressiveness, PNETs of 78 well-characterized patients were evaluated by Ki-67 (MIB-1) immunohistochemistry. Proliferation indices (PI) were determined by counting Ki-67 (MIB-1) positive tumor cells either in the highest staining region (hot spot PI), or in at least 15 randomly chosen fields (random PI). RESULTS: Twenty-five of 78 PNETs showed amore than twofold higher value of hot spot PI (median 9.3%; range 0.6-56%), compared to random PI (median 5.6%; range 0.2-41.3%), Univariate Cox regression analysis revealed that PNETs with a high hot spot PI had a significantly greater risk of progression and death than PNETs with a low hot spot PI (hazard ratio 1.58, P = 0.04). The hazard ratio remained significant after adjusting for M-stage in multivariate analysis. In contrast to hot spot PI, random PI proved not to be a significant prognostic predictor. CONCLUSIONS: Hot spot PI is a significant and independent prognostic factor in PNETs. Its assessment is uncomplicated, reliable, and may supplement routine histologic examination as a means for improving the accuracy of predicting the biologic behavior of childhood PNETs.

Adolescent↗

PubMed2001

Visual loss in children with neurofibromatosis type 1 and optic pathway gliomas: relation to tumor location by magnetic resonance imaging.

PURPOSE: To examine the potential for visual acuity loss, and its relation to extent and location of optic pathway gliomas in a cohort of children with neurofibromatosis type 1 studied with magnetic resonance imaging. METHODS: We reviewed the neuro-ophthalmologic records and brain/orbital magnetic resonance imaging scans for 43 consecutive pediatric patients with neurofibromatosis type 1 and optic pathway gliomas who were followed at the Children's Hospital of Philadelphia. The presence of visual loss, defined as abnormal visual acuity for age in one or both eyes, was determined. Optic pathway gliomas were classified by tumor extent and location according to involvement of the optic nerves, chiasm, and postchiasmal structures by magnetic resonance imaging. RESULTS: Involvement of the optic tracts and other postchiasmal structures at tumor diagnosis was associated with a significantly higher probability of visual acuity loss (P =.048, chi-square test). Visual loss was noted in 20 of 43 patients (47%) at a median age of 4 years; however, three patients developed visual acuity loss for the first time during adolescence. CONCLUSIONS: In pediatric patients with neurofibromatosis type 1 and optic pathway gliomas, the likelihood of visual loss is dependent on the extent and location of the tumor by magnetic resonance imaging and is particularly associated with involvement of postchiasmal structures. Furthermore, older age during childhood (adolescence) does not preclude the occurrence of visual loss. Close follow-up beyond the early childhood years, particularly for those with postchiasmal tumor, is recommended.

Adolescent↗

PubMed2001

Angiogenic profile of childhood primitive neuroectodermal brain tumours/medulloblastomas.

Primitive neuroectodermal brain tumours (PNET) including medulloblastomas (PNET/MB) are the most common malignant brain tumours of childhood. Similar to many other brain tumours, PNET/MB often show marked neovascularisation. To determine which angiogenic factors contribute to PNET/MB angiogenesis, we examined the expression of eight angiogenic factors (vascular endothelial growth factors (VEGF, VEGF-B, VEGF-C), basic fibroblast growth factor (bFGF), angiopoetins (Ang-1, Ang-2), transforming growth factor (TGF-alpha), and platelet-derived endothelial growth factor (PDGF-A)) by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in six PNET cell lines and 28 primary PNET/MB. Expression levels of angiogenic factors were compared with microvessel density, TrkC mRNA expression, clinical variables and survival outcomes. Our results indicate that all PNET/MB tested produce a wide range of angiogenic factors that are, individually or together, likely to play a direct role in PNET/MB tumour growth. This suggests that anti-angiogenesis approaches targeting VEGF alone may be insufficient in PNET/MB.

Adolescent↗

PubMed2001

High microvessel density in primitive neuroectodermal brain tumors of childhood.

Microvessel density (MVD), a measure of tumor angiogenesis, has been shown to correlate significantly with overall and progression-free survival outcomes in various cancers including astrocytic brain tumors. To assess if the MVD is an independent prognostic factor in primitive neuroectodermal tumors (PNET) of the central nervous system, formalin-fixed paraffin-embedded tumor sections of 78 children with PNET were studied by CD34 immunohistochemistry to highlight endothelial cells. Microvessel density was determined in the most active area of neovascularization according to well-established methods. While it was shown that MVD showed considerable inter-tumor variability (median 75; range 20-345 microvessels per 0.7 mm2 field), no significant associations were found between MVD and metastasis or survival outcomes. We conclude that many PNETs are highly vascular CNS tumors, indicating potent angiogenic activity. Therefore, these tumors would be good candidates for antiangiogenic strategies. However, MVD determined in the most active area of neovascularization is not a predictor of metastatic potential or survival outcomes in childhood PNET.

Adolescent↗

PubMed2001

Neuropsychological functioning and social functioning of survivors of pediatric brain tumors: evidence of nonverbal learning disability.

The purpose of the study was to examine if survivors of pediatric brain tumors exhibit a pattern of performance consistent with nonverbal learning disability (NVLD) and to explore the relationship between neuropsychological and social functioning in these children. A comprehensive neuropsychological battery and objective measures of psychosocial function designed to assess NVLD were administered to 15 survivors of brain tumors, ages 8-12 years. Despite the small sample size, a trend for better verbal skills compared to nonverbal skills was found using composite scores. Parents reported significant social deficits and a tendency for greater internalizing behavior problems as expected in NVLD. Additionally, there was a trend for a positive association between nonverbal scores and social function. Further research is needed to determine if the NVLD pattern observed is attributable to white matter damage of the right hemisphere. Routine neuropsychological and psychosocial assessment and intervention are indicated.

Brain Damage, Chronic↗

PubMed2001

Inbreeding changes the shape of the genetic covariance matrix in Drosophila melanogaster.

The pattern of genetic covariation among traits (the G matrix) plays a central role in determining the pattern of evolutionary change from both natural selection and random genetic drift. Here we measure the effect of genetic drift on the shape of the G matrix using a large data set on the inheritance of wing characteristics in Drosophila melanogaster. Fifty-two inbred lines with a total of 4680 parent-offspring families were generated by one generation of brother-sister mating and compared to an outbred control population of 1945 families. In keeping with the theoretical expectation for a correlated set of additively determined traits, the average G matrix of the inbred lines remained proportional to the outbred control G matrix with a proportionality constant approximately equal to (1 - F), where F is the inbreeding coefficient. Further, the pattern of covariance among the means of the inbred lines induced by inbreeding was also proportional to the within-line G matrix of the control population with a constant very close to the expectation of 2F. Although the average G of the inbred lines did not show change in overall structure relative to the outbred controls, separate analysis revealed a great deal of variation among inbred lines around this expectation, including changes in the sign of genetic correlations. Since any given line can be quite different from the outbred control, it is likely that in nature unreplicated drift will lead to changes in the G matrix. Thus, the shape of G is malleable under genetic drift, and the evolutionary response of any particular population is likely to depend on the specifics of its evolutionary history.

Animals↗

PubMed2001

Decreased cyclin B1 expression contributes to G2 delay in human brain tumor cells after treatment with camptothecin.

DNA damage produces delayed mitosis (G2/M delay) in proliferating cells, and shortening the delay sensitizes human malignant glioma and medulloblastoma cells to cytotoxic chemotherapy. Although activation of the cyclin-dependent kinase CDC2 mediates G2/M transition in all tumor cells studied to date, regulation of CDC2 varies between tumor types. Persistent hyperphosphorylation of kinase and reduced cyclin expression have been implicated as mediators of treatment-induced G2 delay in different tumor models. To evaluate regulation of G2/M transition in human brain tumors, we studied the expression and/or activity of CDC2 kinase and cyclins A and B1 in U-251 MG and DAOY medulloblastoma cells after their treatment with camptothecin (CPT). Synchronized cells were treated during S phase, then harvested at predetermined intervals for evaluation of cell cycle kinetics, kinase activity mRNA, and protein expression. CPT produced G2 delay associated with decreased CDC2 kinase activity and cyclin B1 expression. Kinase activity was associated with CDC2 bound to cyclin B1, not cyclin A, in both cell lines. Cyclin A mRNA and protein expression were reduced after CPT treatment; however, decreased protein expression was short lived and moderate in the glioma and primitive neuroectodermal tumor/medulloblastoma cells, respectively. We conclude that G2 delay is a common response of brain tumor cells to chemotherapy with topoisomerase I inhibitors and that a mechanism of this delay may be reduced expression of cyclin B1.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Abundance of apoptotic neoplastic cells in diagnostic biopsy samples is not a prognostic factor in childhood primitive neuroectodermal tumors of the central nervous system.

PURPOSE: To assess if the abundance of apoptotic tumor cells is an independent prognostic factor in primitive neuroectodermal tumors (PNET) of the central nervous system. PATIENTS AND METHODS: Formalin-fixed paraffin-embedded tumor tissue sections from 78 clinically well-characterized children with PNET were evaluated by terminal deoxytransferase-mediated deoxyuridinie-5'-triphosphate (dUTP) nick-end labeling (TUNEL). Apoptotic indices (AI) were determined by counting TUNEL-positive tumor cells either in the highest staining region (AI hot spot) or in at least 15 randomly chosen fields (AI random). The AI hot spot and AI random were then correlated with clinical variables and survival outcome. RESULTS: AI hot spot (median 0.56%; range 0%-6.54%) and AI random (median 0.30%; range 0%-3.21%) showed considerable intertumor variability. Moreover, 53% of the evaluated PNET showed a more than two-fold difference between AI hot spot and AI random, showing important intratumoral variability of the abundance of apoptotic cells in a subset of the evaluated PNET. No significant associations were found between AI hot spot and AI random with clinical variables or survival outcome. CONCLUSION: The apoptotic index does not predict survival outcome and is not specifically associated with clinical variables of prognostic significance in childhood PNET.

Apoptosis↗

PubMed2001

MYC messenger RNA expression predicts survival outcome in childhood primitive neuroectodermal tumor/medulloblastoma.

PURPOSE AND EXPERIMENTAL DESIGN: Cerebellar primitive neuroectodermal tumors/medulloblastomas (PNET/MB) are the most common malignant brain tumors in childhood. To identify PNET/MB biological prognostic factors that define a patient group with a sufficiently good prognosis to permit a reduction in treatment intensity, we determined the expression levels of MYC mRNA in fresh frozen tumor samples from 26 PNET/MB patients using semiquantitative reverse transcription-PCR. RESULTS: MYC mRNA expression levels in primary PNET/MB showed a wide range with a 22-fold difference between the highest and lowest values and did not correlate with MYC gene amplification. MYC mRNA expression was an independent significant prognostic factor for progression-free survival outcome and was more predictive than standard clinical factors. The combination of low MYC mRNA expression and high TrkC mRNA expression identified a good outcome group of PNET/MB patients (n = 7) with 100% progression-free survival after a median follow-up time of 55 months (range, 15-91 months). Three of these seven good outcome patients survived without radiotherapy. CONCLUSIONS: Low MYC mRNA expression is a powerful independent predictor of favorable clinical outcome in PNET/MB. Assessment of MYC mRNA levels is feasible and may be incorporated in prospective PNET/MB clinical trials to aid in treatment planning for patients with PNET/MB on confirmation of our results in larger studies.

Cerebellar Neoplasms↗

PubMed2000

Resistance to TRAIL-induced apoptosis in primitive neuroectodermal brain tumor cells correlates with a loss of caspase-8 expression.

TNF-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in adult malignant glioma and various other human solid tumor models but not in normal tissues. To characterize the TRAIL death pathway in childhood primitive neuroectodermal brain tumor (PNET), 8 human PNET cell lines were tested for TRAIL-induced apoptosis. TRAIL-sensitivity of the PNET cell lines was correlated with mRNA expression levels of TRAIL, its agonistic (TRAIL-R1, TRAIL-R2) and antagonistic (TRAIL-R3, TRAIL-R4) receptors, cellular FLICE-like inhibitory protein (cFLIP), caspase-3 and caspase-8. Three of 8 PNET cell lines tested were susceptible to TRAIL-induced apoptosis. Sensitivity to TRAIL-induced apoptosis did not correlate with mRNA expression of TRAIL receptors or cFLIP. However, all TRAIL-sensitive PNET cell lines expressed caspase-8 mRNA and protein, while none of the five TRAIL-resistant PNET cell lines expressed caspase-8 protein. Treatment with the methyltransferase inhibitor 5-aza-2'-deoxycytidine restored mRNA expression of caspase-8 and TRAIL-sensitivity in formerly TRAIL-resistant PNET cells, suggesting that gene methylation inhibits caspase-8 transcription in these cells. We conclude, that loss of caspase-8 mRNA is an important mechanism of TRAIL-resistance in PNET cells. Treatment with recombinant soluble TRAIL, possibly in combination with methyltransferase inhibitors, represents a promising therapeutic approach for PNET that deserves further investigation.

Adult↗

PubMed2000

A novel kinase, AATYK induces and promotes neuronal differentiation in a human neuroblastoma (SH-SY5Y) cell line.

Apoptosis Associated Tyrosine Kinase (AATYK), a novel protein recently isolated from differentiating 32D mouse myeloid cells, contains a putative tyrosine kinase domain and several binding motifs for src homology 2 (SH-2) and src homology 3 (SH-3) domain containing proteins. We observed that AATYK is expressed in different regions of the brain. Although it might play a role in normal nervous system development by modulating apoptosis, little is known regarding its function in the brain or its intracellular localization and kinase activity. Recognizing its homology with Insulin like growth factor-I (IGF-I) receptor (IGF-IR) and the critical role of IGF-I in neuronal survival, we hypothesized that AATYK plays an important role in neuronal differentiation/apoptosis. To test this hypothesis, we transfected the human adrenergic neuroblastoma (NB):SH-SY5Y cells with AATYK cDNA under a tetracycline-repressible promoter and established stable cell lines that readily express AATYK on removal of tetracycline. AATYK immunoprecipitated from these cell lysates is an active kinase. Indirect immunofluorescent staining of the clones revealed AATYK to be localized in the cytoplasm. By itself, AATYK overexpression for short duration (2-3 days) did not induce differentiation in the stable SH-SY5Y clones. On the other hand, overexpression for longer periods (7-8 days) per se, significantly (P<0.05-0.001) increased the percent of differentiated cells as well as the neurite length. AATYK-induced differentiation was in the same range as the differentiation induced by agents like all-trans retinoic acid (RA), 12-O-Tetradecanoyl phorbol 13-acetate (TPA) and IGF-I. In addition, AATYK significantly promoted the neuronal differentiation induced by these agents. Our results demonstrate for the first time that AATYK is an active, non-receptor, cytosolic kinase which induces neuronal differentiation and also promotes differentiation induced by other agents in the SH-SY5Y cells.

Animals↗

PubMed2000

Outcome for children with supratentorial primitive neuroectodermal tumors treated with surgery, radiation, and chemotherapy.

BACKGROUND: The outcome of a child with a primitive neuroectodermal tumors arising supratentorially (SPNET) is not well characterized and may differ from the outcome of a patient with a histologically similar cerebellar tumor (medulloblastoma [MB]). Recently, 5-year progression free survival rates as high as 80% have been reported for children with MB treated with craniospinal radiation (CRT) and chemotherapy including cisplatin, lomustine (CCNU), and vincristine (VCR). METHODS: The authors reviewed the outcome of 22 consecutive patients age 3 years and older (mean age, 10 years; range, 3-18 years) with SPNET who were treated at the study institutions between 1981 and 1996. Tumor location included was 13 pineal, 6 cortical, and 3 thalamic or suprasellar. Five patients had disease dissemination at diagnosis. All patients underwent surgery and staging, followed by CRT and chemotherapy with cisplatin, CCNU, and VCR. RESULTS: Of the 22 patients, 13 had developed disease progression and 10 had died at the time of last follow-up. Overall progression free survival (PFS) was 47% +/- 11% at 3 years and 37% +/- 11% at 5 years. There was a significant difference in PFS between patients with localized disease versus those with disseminated disease (P = 0.04). There was no statistical association between tumor location and survival. Although not significant (P = 0.21), there was a trend toward better survival of those patients with complete or near-complete resection compared with those with partial resection or biopsy. CONCLUSIONS: The results of the current study demonstrate that the outcome for children with SPNET treated with radiation and chemotherapy appears worse than for children with MB treated with identical therapy. This suggests that there may be biologic differences between supratentorial and infratentorial primitive neuroectodermal tumors, thus requiring refinements in treatment.

Adolescent↗

PubMed2000

Biological stability of RNA isolated from RNAlater-treated brain tumor and neuroblastoma xenografts.

BACKGROUND: Advances in molecular biological research have led to identification of prognostic factors such as Trk mRNA expression in primitive neuroectodermal tumors of the CNS and neuroblastoma. To study prospectively the importance of these prognostic factors in large groups of homogeneously treated patients, tumor specimens of good quality must be acquired, preserved, and stored at multiple institutions. Immediate freezing of tumor biopsy samples in liquid nitrogen and storage at -70 degrees C are the most commonly used method of tissue preservation for future RNA analysis. PROCEDURE: To evaluate alternative methods of preserving tissue samples for subsequent RNA analysis, we tested a new RNA stabilization solution. Using tumor tissue of two CNS tumor and one neuroblastoma human xenografts, we compared total RNA isolated from tumor tissue stored for 7 days at room temperature in stabilization solution to that of snap-frozen tissue. The quality of the RNA was studied by spectrophotometry, gel electrophoresis, RT-PCR, and gene expression profiling. RESULTS: No major differences were observed in the quality of RNA isolated from tumor samples stored at room temperature in the RNA stabilization solution compared to snap-frozen tumor samples stored at -70 degrees C. CONCLUSIONS: High-quality RNA can be prepared from tumor tissue stored at room temperature. Whenever snap freezing is not feasible, pieces of tumor tissue can be treated with RNAlater for subsequent RNA analysis. Short-term storage and shipment of well-preserved tumor tissue are clearly feasible for all institutions, thereby facilitating large multiinstitutional studies of biological prognostic factors.

Animals↗