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Biomedical subjects

Thomas C Lee

Publications and source records attributed to Thomas C Lee.

16 recordsLinked to original sources
PubMed2006

Rb induces a proliferative arrest and curtails Brn-2 expression in retinoblastoma cells.

BACKGROUND: Retinoblastoma is caused by loss of the Rb protein in early retinal cells. Although numerous Rb functions have been identified, Rb effects that specifically relate to the suppression of retinoblastoma have not been defined. RESULTS: In this study, we examined the effects of restoring Rb to Y79 retinoblastoma cells, using novel retroviral and lentiviral vectors that co-express green fluorescent protein (GFP). The lentiviral vector permitted transduction with sufficient efficiency to perform biochemical analyses. Wild type Rb (RbWT) and to a lesser extent the low penetrance mutant Rb661W induced a G0/G1 arrest associated with induction of p27KIP1 and repression of cyclin E1 and cyclin E2. Microarray analyses revealed that in addition to down-regulating E2F-responsive genes, Rb repressed expression of Brn-2 (POU3F2), which is implicated as an important transcriptional regulator in retinal progenitor cells and other neuroendocrine cell types. The repression of Brn-2 was a specific Rb effect, as ectopic p27 induced a G0/G1 block, but enhanced, rather than repressed, Brn-2 expression. CONCLUSION: In addition to Rb effects that occur in many cell types, Rb regulates a gene that selectively governs the behavior of late retinal progenitors and related cells.

Cell Line, Tumor↗
PubMed2006

Small molecule inhibition of HDM2 leads to p53-mediated cell death in retinoblastoma cells.

PURPOSE: To determine the efficacy of inducing p53-mediated cell death in retinoblastoma cells by Nutlin 3A, a small molecule HDM2 inhibitor. METHODS: Retinoblastoma cell lines WERI-RB-1 and Y79 were treated with Nutlin 3A. Cell viability assays, Western blot analyses, confocal microscopy, and flow cytometry were performed to measure cell survival, p53 protein levels, activation of downstream targets, and apoptosis. To determine whether the effects of Nutlin 3A were p53-dependent, cell viability assays were performed on Y79 cells expressing short interfering RNA (siRNA) against p53. RESULTS: Nutlin 3A induced cell death in Y79 and WERI-RB-1 in the 5- to 10-microM dose range. Treated cells demonstrated increased protein levels of p53 and the p53 targets p21 and HDM2. Phosphorylation of p53-serine-15, a marker for activation of p53 via genotoxic mechanisms, was absent. Y79 cells expressing siRNA against p53 demonstrated resistance to Nutlin 3A. CONCLUSIONS: Nutlin 3A induced p53-mediated apoptosis in a dose-dependent, nongenotoxic fashion in 2 retinoblastoma cell lines. CLINICAL RELEVANCE: Nutlin 3A is effective against retinoblastoma cells in a nongenotoxic manner. Because the mutagenic effects of radiation and chemotherapy may increase risks of secondary tumor formation, targeted p53 activation may be a safer alternative treatment for retinoblastoma in the future.

Annexin A5↗
PubMed2006

Cell cycle-specific and cell type-specific expression of Rb in the developing human retina.

PURPOSE: To define the pattern of Rb expression relative to cell cycle position and cell type in the developing human retina. METHODS: Cryosections of fetal week 11-18 retinas were immunostained for Rb and cell cycle- or cell type-specific markers. RESULTS: Rb was prominent in retinal progenitor cells (RPCs) expressing the cyclin D1, cyclin A, and cytoplasmic cyclin B markers of G1, S, and early to mid G2 phases, but not in RPCs expressing the phosphohistone H3 marker of late G2 and M. Rb was not detected in the earliest postmitotic ganglion, amacrine, horizontal, and bipolar cell precursors migrating away from the ventricular layer, but was detected as such cells underwent further differentiation. Among photoreceptors, Rb was not detected in the earliest RXRgamma(+) cone precursors or in the earliest Nrl(+) rod precursors, but subsequently rose to high levels in cones and to low levels in rods. Rb was prominent at the time when Müller glia exit the cell cycle and was generally expressed in a pattern complementary to p27(Kip1). CONCLUSIONS: Rb exhibits cell cycle-specific expression in RPCs, with loss in late G2-M and restoration in G1. Rb is re-expressed after postmitotic ganglion, amacrine, horizontal, and bipolar cell precursors migrate away from the ventricular layer; after the appearance of early cone and rod markers; but coinciding with Müller glia cell cycle withdrawal. The results suggest that Rb does not mediate the initial proliferative arrest of retinal neurons, but may indirectly induce arrest in RPCs or maintain an arrest in postmitotic precursors.

Amacrine Cells↗
PubMed2005

Microdamage: a cell transducing mechanism based on ruptured osteocyte processes.

As a result of underlying pathological diseases, such as osteoporosis, osteopenia, or due to altered loading after joint replacements, bones become more susceptible to microdamage accumulation than those of normal human beings, as are those of athletes who undertake strenuous exercise [Stromsoe, 2004. Fracture fixation problems in osteoporosis. Injury 35, 107-113]. Experimental evidence has linked bone adaptation to microdamage, and to increased cell activity. In this work, we investigated whether microcrack detection is related to rupturing of the cellular material itself due to crack face displacements. Using specific cell staining techniques, it was confirmed that relative crack displacements are capable of tearing cell processes between neighbouring osteocytes. No ruptured cell processes were found near the crack tip where the displacements are less. Rupturing of cell processes due to crack opening and shear displacement is a feasible new mechanism by which bone can detect and estimate the size of a microcrack. Ruptured cell processes may directly secrete passive and active components in the extracellular matrix, triggering a repair response.

Adaptation, Physiological↗
PubMed2005

Time course of depression-symptom improvement during treatment with duloxetine.

The aim of this study was to examine the longitudinal response for overall and individual symptoms during the treatment of major depressive disorder. Data were pooled from two 9-week trials, which compared duloxetine 60-mg QD (n=251) with placebo (n=261) in the treatment of MDD. Changes from baseline in the 17-item Hamilton Depression Rating Scale (HAMD17) and in the Visual Analog Scales for pain were analyzed. Compared to placebo-treated patients, duloxetine-treated patients experienced greater improvement (P<.05) in the HAMD17 total score at Week 2. The individual symptoms showing the most rapid improvements (Week 1) were depressed mood, guilt, suicidal ideation, work/activities, and psychic anxiety as well as VAS back pain and shoulder pain. At subsequent visits, significant improvements were observed in retardation (Week 2); hypochondriasis (Week 3); general somatic symptoms (Week 5); middle and late insomnia (Week 7); and gastrointestinal (GI) symptoms, genital symptoms (level of sexual interest or ease of sexual arousal), insight, and early insomnia (Week 9). Significant advantages for duloxetine were not achieved at any visit for agitation, somatic anxiety, or weight loss. At Weeks 1 and 2, placebo-treated patients had significantly lower GI symptoms and reported less weight loss compared with duloxetine-treated patients; however, differences were not significant at subsequent visits. Furthermore, duloxetine was superior to placebo on GI symptoms at endpoint compared to placebo-treated patients; duloxetine-treated patients had a significantly higher response rate at Week 2 and a higher remission rate at Week 5. These results may help clinicians establish more accurate expectations regarding treatment with duloxetine.

Adult↗
PubMed2005

Duloxetine vs. placebo in patients with painful diabetic neuropathy.

The aim of this study was to examine the efficacy and safety of duloxetine, a balanced and potent dual reuptake inhibitor of serotonin and norepinephrine, in the management of diabetic peripheral neuropathic pain. Serotonin and norepinephrine are thought to inhibit pain via descending pain pathways. In a 12-week, multicenter, double-blind study, 457 patients experiencing pain due to polyneuropathy caused by Type 1 or Type 2 diabetes mellitus were randomly assigned to treatment with duloxetine 20 mg/d (20 mg QD), 60 mg/d (60 mg QD), 120 mg/d (60 mg BID), or placebo. The diagnosis was confirmed by a score of at least 3 on the Michigan Neuropathy Screening Instrument. The primary efficacy measure was the weekly mean score of the 24-h Average Pain Score, which was rated on an 11-point (0-10) Likert scale (no pain to worst possible pain) and computed from diary scores between two site visits. Duloxetine 60 and 120 mg/d demonstrated statistically significant greater improvement compared with placebo on the 24-h Average Pain Score, beginning 1 week after randomization and continuing through the 12-week trial. Duloxetine also separated from placebo on nearly all the secondary measures including health-related outcome measures. Significantly more patients in all three active-treatment groups achieved a 50% reduction in the 24-h Average Pain Score compared with placebo. Duloxetine treatment was considered to be safe and well tolerated with less than 20 percent discontinuation due to adverse events. Duloxetine at 60 and 120 mg/d was safe and effective in the management of diabetic peripheral neuropathic pain.

Aged↗
PubMed2005

The dual transporter inhibitor duloxetine: a review of its preclinical pharmacology, pharmacokinetic profile, and clinical results in depression.

Major depressive disorder (MDD) poses a significant health problem and is estimated to be the third most costly and disabling disorder in the United States. Pharmacotherapy of depression has been successful, but improvements in response rates, remission rates, side effects, compliance and faster onset of therapeutic action have become prime objectives in drug development. There is considerable support for the hypothesis that dysfunctional serotonergic or noradrenergic neurotransmission may be etiological in depressed patients. Duloxetine is a balanced and potent reuptake inhibitor of serotonin (5-HT) and norepinephrine (NE) being studied as an antidepressant medication. In this review, we highlight the preclinical pharmacology, pharmacokinetic profile, and effects of duloxetine in the pharmacotherapy of depression. Evidence for 5-HT and NE reuptake inhibition by duloxetine comes from in vitro and in vivo transporter binding and functional uptake studies. Taken together with efficacy data from in vivo microdialysis, electrophysiological and behavioral studies, it is evident that duloxetine is balanced as a dual serotonin norepinephrine uptake inhibitor in vivo. The clinical efficacy and safety of duloxetine in the treatment of MDD has been studied in 6 multicenter, randomized, double-blind, placebo-controlled trials. In these studies, duloxetine was found to be effective in the treatment of emotional/psychological and painful physical symptoms associated with depression. More importantly, duloxetine appears to have better response rates and remission from depressive symptoms, perhaps due to its ability to treat a wider range of symptoms.

Adrenergic Uptake Inhibitors↗
PubMed2005

The hypodense artery sign.

An acute intracranial embolus may be associated with a hyperdense artery sign on CT, related to acute thrombus within the affected artery, a phenomenon that is well known and has been extensively documented. We present an unusual case of a middle cerebral artery territory acute infarct with a hypodense artery on CT. The Hounsfield unit attenuation of the embolic lesion was fat density. CT angiography and MR imaging confirmed the fatty lesion to be within the middle cerebral artery.

Aged↗
PubMed2004

Treatment of conjunctival squamous cell carcinoma with photodynamic therapy.

PURPOSE: The aim of this study was to describe the clinical and angiographic response of squamous cell carcinoma (SCC) of the conjunctiva to treatment with photodynamic therapy (PDT). DESIGN: Interventional case series. METHODS: In a prospective study, three patients (62 to 86 years old) with SCC of the conjunctiva were treated with PDT. Patients received one to three treatments of verteporfin (6 mg/m(2) body surface area, intravenously). The light dose was calculated as 50 J/cm(2). All tumors were irradiated 1 minute after injection. The mean follow-up time was 8.6 months (7 to 12 months). Main outcome measurements were clinical and angiographic response and treatment-related side effects. RESULTS: One week after treatment, angiographic occlusion of tumor vasculature and normal conjunctival vessels was observed in all patients. Tumor regression was noted in all patients 1 month after treatment. Two patients had complete regression (clinical and angiographic observation) after one or two treatments for the entire follow-up time. One tumor involved large aspects of the conjunctiva and cornea. In this case, only the treated areas showed tumor regression. PDT caused minimal temporary local irritation in two patients, and small conjunctival hemorrhages and mild transient chemosis in the three eyes directly after treatment. One patient had infusion-related back pain. CONCLUSION: The preliminary results of this study suggest that PDT may be a valuable addition to the treatment of patients with SCC of the conjunctiva. However, longer follow-up is necessary to assess the duration and degree of tumor control.

Aged↗
PubMed2004

Chorioretinal scar growth after 810-nanometer laser treatment for retinoblastoma.

PURPOSE: To determine the extent of expansion of laser scars after single treatment with transpupillary thermotherapy (TTT) for retinoblastoma. DESIGN: We retrospectively reviewed medical records and RetCam (Massie Industries, Dublin, CA) digital fundus photographs of patients with retinoblastoma who received TTT by use of an 810-nm diode laser with large-spot indirect ophthalmoscope. Digital images were measured by use of RetCam software beginning immediately after treatment. Lesions were measured in both linear size and area by 2 observers. In addition, optic disc diameters were also measured for each image. PARTICIPANTS: We identified 9 patients with hereditary retinoblastoma who were treated from 1997 to 2000. MAIN OUTCOME MEASURES: Linear and area expansion of laser scars as a function of time. RESULTS: Fourteen tumors in 10 eyes were treated successfully with 1 session of TTT. Follow-up for all eyes was at least 16 months. Scars of 12 of the 14 lesions increased beyond their original borders (mean starting linear diameter, 2.02 mm; range 1.46-2.59 mm; mean increase, 0.72 mm [36%]) over time, most within 6 months to 1 year after treatment. CONCLUSIONS: Scars from TTT for retinoblastoma may increase in size after treatment. This expansion must be considered when applying TTT to tumors near vital macular structures, such as the fovea and optic nerve.

Choroid Diseases↗
PubMed2004

Microsatellite instability and MLH1 promoter methylation in human retinoblastoma.

PURPOSE: To investigate the link between microsatellite instability and epigenetic silencing of the MLH1 gene in the human retinoblastoma genome. METHODS: Methylation at the 5' region of MLH1 was studied, along with its protein expression level by using immunohistochemical staining in 51 retinoblastoma tumors and 2 retinoblastoma cell lines. Also assessed was the genomic stability of 26 retinoblastoma DNAs from microdissected tumor tissue and matched normal retina tissue obtained from the same patient by microsatellite instability (MSI) analysis. The National Cancer Institute-designed reference panel, and 85 markers on chromosomes 1, 6, 9, and 13 were used. RESULTS: Hypermethylation of the MLH1 promoter was detected in the WERI-Rb1 cell line and in 34 (67%) of the 51 tumors, but not in cell line Y79 and the other 17 tumors. MLH1 hypermethylation was associated with null MLH1 protein expression (P < 0.0005) and with well-differentiated histology (P < 0.05). MSI at three markers (D2S123, D6S470, and D13S265) was frequently identified among 26 retinoblastoma specimens with matched normal DNA. Among these 26 retinoblastomas, high-frequency MSI (MSI-H) tumors were detected in 19% (5/26) and low-frequency MSI (MSI-L) in another 19% (5/26). The remaining 62% (15/26) were genetically stable (MSS). MSI status (MSS, MSI-L, and MSI-H) was not associated with MLH1 promoter hypermethylation (P = 0.088; Kruskal-Wallis test). CONCLUSIONS: Epigenetic silencing of the DNA repair gene MLH1 by promoter hypermethylation is a frequent event in retinoblastoma. The results showed that somatic genetic changes involving MSI occur in a subset of retinoblastoma and implicated the presence of a defective DNA mismatch repair pathway resulting in MSI in retinoblastoma.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Treatment of choroidal melanoma using photodynamic therapy.

PURPOSE: To InternetAdvance publication at ajo.com Feb 26, 2002. investigate the effect of photodynamic therapy using verteporfin on choroidal melanoma. DESIGN: Interventional case series. METHOD: Four patients with choroidal melanoma who showed recurrence or no response after previous brachytherapy and transpupillary thermotherapy were treated with photodynamic therapy. RESULTS: One tumor decreased in size and remained stable for 18 months. One tumor had no growth for 11 months. Two melanomas continued to grow, necessitating enucleation. CONCLUSIONS: Of the four eyes that had failed conventional therapies, two would have been salvaged (to date) with photodynamic therapy. However, additional studies are needed to determine if photodynamic therapy can play a role in the management of choroidal melanoma.

Aged↗
PubMed2003

New retinoblastoma tumor formation in children initially treated with systemic carboplatin.

PURPOSE: To determine the frequency and timing of new intraocular tumor formation in children with hereditary retinoblastoma initially treated with systemic carboplatin. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: This study included 34 children (57 eyes) with hereditary bilateral retinoblastoma initially treated with systemic carboplatin at the Robert M. Ellsworth Ophthalmic Oncology Center at NewYork-Presbyterian Hospital from 1994 through 2000. MAIN OUTCOME MEASURES: New tumor formation after initial treatment with systemic carboplatin. RESULTS: There were a total of 165 tumors in 57 eyes. There were 63 new tumors in 27 eyes (47%) after administration of systemic carboplatin, for a mean of 1.1 new tumors per eye. The mean patient age at time of new tumor presentation was 9 months, with 57% of new tumors developing within 4 months of carboplatin treatment. Kaplan-Meier analysis showed that children who were treated when younger than 6 months of age were more likely to have new tumors (60%) compared with those treated after 6 months of age (31%; P = 0.0182). CONCLUSIONS: New intraocular tumors continue to develop after systemic carboplatin; most new tumors appeared within 4 months of treatment.

Antineoplastic Agents↗
PubMed2003

Screening for retinoblastoma: presenting signs as prognosticators of patient and ocular survival.

OBJECTIVE: To correlate 3 common presenting signs of retinoblastoma with patient and ocular survival and to assess the efficacy of current pediatric screening practices for retinoblastoma. METHODS: A retrospective study was conducted of 1831 retinoblastoma patients from our center (1914-June 2000). Patient survival (excluding deaths from other primary neoplasms) and ocular survival (presenting eyes) rates were calculated and analyzed using the Kaplan-Meier method. RESULTS: Leukocoria correlated with excellent patient survival (>86%, 5 years) but poor ocular survival in unilateral (4%, 5 years) and bilateral patients (29%, 5 years). A total of 308 (19%) of 1654 patients presented with strabismus: patient survival was excellent (90%, 5 years), and ocular survival was poor (17%, 5 years) yet better than leukocoria. Patients who had a family history of retinoblastoma and were clinically screened for retinal tumors from birth were diagnosed younger (8 months of age) and earlier (Reese Ellsworth group 1 = 26 [58%] of 45) and had better ocular survival than nonscreened patients with a family history. More patients were initially detected by family/friends (1315 [80%] of 1632) than pediatricians (123 [8%] of 1632) or ophthalmologists (156 [10%] of 1632). CONCLUSION: Most US children whose retinoblastoma is diagnosed initially present with leukocoria detected by a parent, despite routine pediatric screening for leukocoria via the red reflex test. Initial disease detection at the point of leukocoria or strabismus correlated with high patient survival rates and poor ocular survival rates for the presenting eye. Saving eyes and vision requires disease recognition before leukocoria, as demonstrated by the better ocular salvage rate among patients who had a positive family history and received clinical surveillance via early, routine dilated funduscopic examinations by an ophthalmologist.

Humans↗