E. K. Choi

Ulsan University Hospital, Urusan, Ulsan, South Korea

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Publications (15)29.65 Total impact

  • Oral Oncology Supplement 01/2005; 1(1):148-148.
  • EJC Supplements 09/2004; 2(8):197-197. · 2.71 Impact Factor
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    ABSTRACT: It has been known that ATM plays a central role in response of cells to ionizing radiation by enhancing DNA repair. We have investigated the feasibility of increasing radiosensitivity of tumor cells with the use of ATM inhibitors such as caffeine, pentoxifylline and wortmannin. Human colorectal cancer RKO.C cells and RKO-ATM cells (RKO cells overexpressing ATM) were used in the present study. The clonogenic cell survival in vitro indicated that RKO-ATM cells were markdely radioresistant than RKO.C cells. Treatment with 3 mM of caffeine significantly increased the radiosensitivity of cells, particulary the RKO-ATM cells, so that the radiosensitivity of RKO.C cells and RKO-ATM cells were almost similar. The radiation induced G2/M arrest in RKO-ATM cells was noticeably longer than that in RKO.C cells and caffeine treatment significantly reduced the length of the radiation induced G2/M arrest in both RKO.C and RKO-ATM cells. Pentoxifylline and wortmannin were also less effective than caffeine to radiosensitize RKO.C or RKO-ATM cells. However, wortmannin was more effective than caffeine against human lung adenocarcinoma A549 cells indicating the efficacy of ATM inhibitor to increase radiosensitivity is cell line dependent. For in vivo study, RKO.C cells were injected s.c. into the hind-leg of BALB/C-nuslc nude mice, and allowed to grow to 130mm3 tumor. The mice were i.p. injected with caffeine solution or saline and the tumors irradiated with 10 Gy of X-rays. The radiation induced growth delay was markedly increased by 1-2 mg/g of caffeine. It was concluded that caffeine increases radiosensitivity of tumor cells by inhibiting ATM kinase function, thereby inhibiting DNA repair, that occurs during the G2/M arrest after radiation.
    Journal of Radiation Protection. 01/2003; 28(3).
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    ABSTRACT: This paper investigated the induction of apoptosis and perturbation of cell cycle progression caused by carboplatin (CPt) and hyperthermia alone or combined in WERI human retinoblastoma cells in vitro. An incubation of the cells with 25 or 50 microm of CPt at 37 degrees C caused apoptosis, which progressively increased during the 24-72 h treatment. Hyperthermia at 42.5 degrees C for 1 h induced apoptosis, which became significant from 24 h after the heating. Heating the cells in the presence of CPt and subsequent incubation with CPt was far more effective than treating the cells with hyperthermia or CPt treatment alone in inducing apoptosis in the WERI cells, indicating that the combination of these two modalities is potentially useful for the treatment of retinoblastoma. It appeared that the apoptosis in WERI cells caused by hyperthermia and CPt occurs during G1 phase. An interesting observation was that caspase 9 activation preceded the release of cytochrome C from mitochondria during apoptosis in WERI cells, contrary to the general notion that caspase 9 is activated by cytochrome C.
    International Journal of Hyperthermia 01/2003; 19(4):431-43. · 2.77 Impact Factor
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    ABSTRACT: To evaluate the local control rates, survival rates, and patterns of failure for esophageal cancer patients receiving preoperative concurrent chemotherapy and hyperfractionated radiotherapy followed by esophagectomy. From May 1993 through January 1997, 94 patients with resectable esophageal cancers received continuous hyperfractionated radiation (4,800 cGy/40 fx/4 weeks), with concurrent FP chemotherapy (5-FU 1 g/m(2)/day, days 2-6, 30-34, CDDP 60 mg/m(2)/day, days 1, 29) followed by esophagectomy 3-4 weeks later. If there was evidence of disease progression on preoperative re-evaluation work-up, or if the patient refused surgery, definitive chemoradiotherapy was delivered. Minimum follow-up time was 2 years. RESULTS; All patients successfully completed preoperative treatment and were then followed until death. Fifty-three patients received surgical resection, and another 30 were treated with definitive chemoradiotherapy. Eleven patients did not receive further treatment. Among 91 patients who received clinical reevaluation, we observed 35 having clinical complete response (CR) (38.5%). Pathologic CR rate was 49% (26 patients). Overall survival rate was 59.8% at 2 years and 40.3% at 5 years. Median survival time was 32 months. In 83 patients who were treated with surgery or definitive chemoradiotherapy, the esophagectomy group showed significantly higher survival, disease-free survival, and local disease-free survival rates than those in the definitive chemoradiation group. Preoperative chemoradiotherapy in this trial showed improved clinical and pathologic tumor response and survival when compared to historical results. Patients who underwent esophagectomy following chemoradiation showed decreased local recurrence and improved survival and disease-free survival rates compared to the definitive chemoradiation group.
    International Journal of Radiation OncologyBiologyPhysics 06/2001; 50(1):1-12. · 4.18 Impact Factor
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    ABSTRACT: The human genetic disorder ataxia-telangiectasia (AT) is a multisystem disease characterized by extreme radiosensitivity. Although ionizing radiation was known to induce c-fos transcription and cellular protein kinase C (PKC) induces the expression of this immediate response gene, little is known about how mutated AT (ATM) or PKC-mediated signal transduction pathway modulates the c-fos gene transcription and gene expression. Here we have studied the effect of PKC inhibitor (PKCI) on radiation sensitivity and c-fos transcription in normal and AT cells, and also studied whether PKCI effect on c-fos occurs in Ras-dependent pathway. Normal (LM217) and AT (AT5BIVA) cells were transfected with PKCI expression plasmid and integration and overexpression of PKCI was evaluated by polymerase chain reaction and northern blotting, respectively. Cells were irradiated at a dose of 5 Gy/min with 137Cs irradiator and harvested 48 h after irradiation and investigated apoptosis with TUNEL method. The c-fos transcription activity was studied by performing compute assisted tomography (CAT) assay of reporter gene after transfection of c-fos CAT plasmid into LM and AT cells. Overexpression of Ras protein in transfected cells was shown by western blotting. Our results demonstrated for the first time a role of PKCI on the radiation sensitivity and c-fos transcription in LM and AT cells. PKCI increased radiation induced apoptosis in LM cells (5% to 20%) but reduced apoptosis slightly in AT cells. The basal c-fos transcription activity is 70 times lower in AT cells than in LM cells. This c-fos transcription activity was repressed by overexpression of PKCI in LM cells but not in AT cells. After induction of c-fos by Ras protein, overexpression of PKCI repressed c-fos transcription in LM cells but not in AT cells. Overexpression of PKCI increased radiation sensitivity and repressed c-fos transcription in LM cells but not in AT cells, and this is related with Ras. These results suggest that the effect of PKCI on c-fos transcription activity is related with Ras dependent signal transduction pathways and these mechanisms are different between normal fibroblasts, LM and ATM mutated, AT cells. The data obtained by this study provided evidence for novel transcriptional difference between LM and AT cells and this may be a reason for increased radiation sensitivity of AT cells.
    International Journal of Radiation OncologyBiologyPhysics 03/2001; 49(2):397-405. · 4.18 Impact Factor
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    ABSTRACT: For practical use and cost-effectiveness, the authors have developed a PC-based virtual simulation method with custom-made DRR image and many new simulation functions. The method shows compatible reliability and effectiveness compared with commercial versions using a workstation in terms of DRR image quality, ease of use, handling of various simulation tools and simulation results of all the crucial parameters such as beam parameters and localization of target and critical organs
    01/2000; 3.
  • Lung Cancer. 01/2000; 29(1):158-159.
  • Lung Cancer. 01/1999; 25.
  • International Journal of Radiation OncologyBiologyPhysics 01/1999; 45(3):190-191. · 4.18 Impact Factor
  • Lung Cancer. 01/1999; 25.
  • International Journal of Radiation Oncology Biology Physics - INT J RADIAT ONCOL BIOL PHYS. 01/1997; 39(2):313-313.
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    ABSTRACT: Conventional treatment of esophageal cancer with surgery or radiation alone has afforded few long-term survivors. In order to improve outcome and determine the efficacy of a combined modality approach, this prospective study was performed. Between May 1993 and August 1994, 27 patients with loco-regional squamous cell carcinoma of the esophagus were treated with 2 courses of combined fluorouracil(1000mg per square meter of body-surface area daily for 5 days) and cisplatin(60mg per square meter on the first day)(D1 and D29) plus 48Gy of radiation therapy(RT) over 4 weeks. A transhiatal esophagectomy was planned 3-4 weeks after chemoradiotherapy. Twenty-seven patients completed a full course of therapy. Clinical response was evaluable in 26 patients: 22 patients showed improvement and relief from dysphagia, 2 patients stable disease, and 2 patients progression. One patient died of sepsis 1 week after completion of chemoradiotherapy and was excluded from the analysis. Ten patients underwent operation after chemoradiation. Of them, 5 showed complete histologic response. One of the complete responders died of recurred disease 8.5months after operation, the other 2 patients died of sudden death, and sepsis from wound deheiscence 7 days after operation, respectively. Nine patients refused operation because of excellent relief of their dysphagia and 6 patients were denied because of disease progression(2), fear of operations(2), old age and family member's disapprovement(1), and underlying liver cirrhosis(1). The last one patient was awaiting for operation. Of 13 patients who refused or denied operation, 6 patients finished further chemotherapy and radiatherapy(external radiation 1200 cGy+intracavitary radiation 900 cGy, 2 cycles of 5FU+cisplatin). This intensive preoperative chemoradiotherapy is feasible, and allows for a high rate of resectability and a high rate of complete pathologic response in a locoregional esophageal cancer. Toxicity is considerable but manageable. This study warrants further investigation.
    Journal of Korean Medical Science 05/1995; 10(2):111-20. · 1.25 Impact Factor
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    ABSTRACT: To study fluoroscopic placement of covered expandable stent tubes in patients with esophagogastric strictures. Under fluoroscopic guidance, 132 stent tubes were placed in 116 patients with malignant neoplasm; four, in three patients with benign lesions. All patients had aphagia or dysphagia to soft food or liquid. After placement (successful in 100% of cases), 93 (78%) of the patients could ingest solid food; 24 (20%), soft food. Complications in the 119 patients included blockage in 13, stent tube migration in 12, gastroesophageal reflux in nine, severe pain in nine, and delayed massive bleeding in four. Most major complications were managed by means of a balloon catheter, a second stent tube, or analgesics. One hundred four patients died 2-80 weeks after stent placement. Treatment with placement of a covered expandable stent tube is effective in most patients with dysphagia due to malignant esophogastric strictures and is less effective in patients with benign strictures.
    Radiology 01/1995; 193(3):689-95. · 6.21 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 01/1995; 32:267-267. · 4.18 Impact Factor

Publication Stats

115 Citations
29.65 Total Impact Points

Institutions

  • 1995–2003
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 2001
    • Asan Medical Center
      • Department of Radiation Oncology
      Seoul, Seoul, South Korea
  • 1995–2001
    • University of Ulsan
      • • College of Medicine
      • • Department of Medicine
      Urusan, Ulsan, South Korea