Seog-Young Kim

Performance Measurement of the microPET Focus 120 Scanner

The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. Methods: A 68Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a 22Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an 18F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250∼750 keV or 350∼650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. Results: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250∼750 keV, 10 ns), 6.7% (250∼750 keV, 6 ns), 4.0% (350∼650 keV, 10 ns), and 3.8% (350∼650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250∼750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250∼750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. Conclusion: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.

Kinetic Modeling of 3′-Deoxy-3′-18F-Fluorothymidine for Quantitative Cell Proliferation Imaging in Subcutaneous Tumor Models in Mice

3′-Deoxy-3′-18F-fluorothymidine (18F-FLT) is a thymidine analog that was developed for measuring tumor proliferation with PET. The aim of this study was to establish a kinetic modeling analysis method for quantitative 18F-FLT PET studies in subcutaneous tumor models in mice. Methods: To explore the validity of an image-derived left ventricular input function, we measured equilibrium constants for plasma and whole blood and metabolite fractions in blood after 18F-FLT injection. In parallel, dynamic 18F-FLT PET scans were acquired in 24 mice with a small-animal dedicated PET scanner to compare arterial blood activities obtained by PET and blood sampling. We then investigated kinetic models for 18F-FLT in human epithelial carcinoma (A431) and Lewis lung carcinoma tumor models in mice. Three-compartment models with reversible phosphorylation (k4 ≠ 0, 3C5P) and irreversible phosphorylation (k4 = 0, 3C4P) and a 2-compartment model (2C3P) were examined. The Akaike information criterion and F statistics were used to select the best model for the dataset. Gjedde–Patlak graphic analysis was performed, and standardized uptake values in the last frame were calculated for comparison purposes. In addition, quantitative PET parameters were compared with Ki-67 immunostaining results. Results: 18F-FLT equilibrated rapidly (within 30 s) between plasma and whole blood, and metabolite fractions were negligible during PET scans. A high correlation between arterial blood sampling and PET data was observed. For 120-min dynamic PET data, the 3C5P model best described tissue time–activity curves for tumor regions. The net influx of 18F-FLT (KFLT) and k3 obtained with this model showed reasonable intersubject variability and discrimination ability for tumor models with different proliferation properties. The KFLT obtained from the 60- or 90-min data correlated well with that obtained from the 120-min data as well as with the Ki-67 results. Conclusion: The image-derived arterial input function was found to be feasible for kinetic modeling studies of 18F-FLT PET in mice, and kinetic modeling analysis with an adequate compartment model provided reliable kinetic parameters for measuring tumor proliferation.

Role of Bim in diallyl trisulfide-induced cytotoxicity in human cancer cells.

The aim of this study was to investigate the effect of garlic constituent diallyl trisulfide (DATS) on the cell‐death signaling pathway in a human breast cell line (MDA‐MB‐231). We observed that DATS (10–100 µM) treatment resulted in dose‐ and time‐dependent cytotoxicity. Treatment of MDA‐MB‐231 cells with a cytotoxicity inducing concentration of DATS (50–80 µM) resulted in an increase in the intracellular level of reactive oxygen species (ROS). Data from assay with MitoSOXTM Red reagent suggest that mitochondria are the main source of ROS generation during DATS treatment. DATS‐induced oxidative stress was detected through glutaredoxin (GRX), a redox‐sensing molecule, and subsequently GRX was dissociated from apoptosis signal‐regulating kinase 1 (ASK1). Dissociation of GRX from ASK1 resulted in the activation of ASK1. ASK1 activated a downstream signal transduction JNK (c‐Jun N‐terminal kinase)‐Bim pathway. SP600125, a JNK inhibitor, inhibited DATS‐induced Bim phosphorylation and protected cells from DATS‐induced cytotoxicity. Our results indicate that the cytotoxicity caused by DATS is mediated by the generation of ROS and subsequent activation of the ASK1‐JNK‐Bim signal transduction pathway in human breast carcinoma MDA‐MB‐231 cells. J. Cell. Biochem. 112: 118–127, 2011.

Curcumin protects against ovariectomy‐induced bone loss and decreases osteoclastogenesis

Curcumin has anti‐oxidative activity. In view of the increasing evidence for a biochemical link between increased oxidative stress and reduced bone density we hypothesized that curcumin might increase bone density by elevating antioxidant activity in some target cell type. We measured bone density by Micro‐CT, enzyme expression levels by quantitative PCR or enzyme activity, and osteoclast (OC) formation by tartrate‐resistant acid phosphatase staining. The bone mineral density of the femurs of curcumin‐administered mice was significantly higher than that of vehicle‐treated mice after ovariectomy (OVX) and this was accompanied by reduced amounts of serum collagen‐type I fragments, which are markers of bone resorption. Curcumin suppressed OC formation by increasing receptor activator of nuclear factor‐κB ligand (RANKL)‐induced glutathione peroxidase‐1, and reversed the stimulatory effect of homocysteine, a known H2O2 generator, on OC formation by restoring Gpx activity. Curcumin generated an aberrant RANKL signal characterized by reduced expression of nuclear factor of activated T cells 2 (NFAT2) and attenuated activation of mitogen‐activated protein kinases (ERK, JNK, and p38). Curcumin thus inhibited OVX‐induced bone loss, at least in part by reducing osteoclastogenesis as a result of increased antioxidant activity and impaired RANKL signaling. These findings suggest that bone loss associated with estrogen deficiency could be attenuated by curcumin administration. J. Cell. Biochem. 112: 3159–3166, 2011.

Exploratory Clinical Investigation of (4S)-4-(3-18F-Fluoropropyl)-l-Glutamate PET of Inflammatory and Infectious Lesions

We explored system xC− transporter activity and the detection of inflammatory or infectious lesions using (4S)-4-(3-18F-fluoropropyl)-l-glutamate (18F-FSPG) PET. Methods: In 10 patients with various inflammatory or infectious diseases, as many as 5 of the largest lesions were selected as reference lesions. 18F-FSPG images were assessed visually and quantitatively. Expression levels of xCT, CD44, and surface markers of inflammatory cells were evaluated by immunohistochemistry. Results: 18F-FSPG PET detected all reference lesions. 18F-FSPG uptake in sarcoidosis was significantly higher than that in nonsarcoidosis. The lesion–to–blood-pool SUV ratio for 18F-FSPG was comparable to that for 18F-FDG in sarcoidosis. In nonsarcoidosis, however, it was significantly lower. In 5 patients with available tissue samples, the SUVmax for 18F-FSPG and CD163 were negatively correlated (ρ = –0.872, P = 0.054). Conclusion: 18F-FSPG PET may detect inflammatory lesions when activated macrophages or monocytes are present, such as in sarcoidosis.

Cancer Stem Cells Protect Non-Stem Cells From Anoikis: Bystander Effects

Cancer stem cells (CSCs) are capable of initiation and metastasis of tumors. Therefore, understanding the biology of CSCs and the interaction between CSCs and their counterpart non‐stem cells is crucial for developing a novel cancer therapy. We used CSC‐like and non‐stem breast cancer MDA‐MB‐231 and MDA‐MB‐453 cells to investigate mammosphere formation. We investigated the role of the epithelial cadherin (E‐cadherin)‐extracellular signal‐regulated kinase (Erk) axis in anoikis. Data from E‐cadherin small hairpin RNA assay and mitogen‐activated protein kinase kinase (MEK) inhibitor study show that activation of Erk, but not modulation of E‐cadherin level, may play an important role in anoikis resistance. Next, the two cell subtypes were mixed and the interaction between them during mammosphere culture and xenograft tumor formation was investigated. Unlike CSC‐like cells, increased secretion of interleukin‐6 (IL‐6) and growth‐related oncogene (Gro) chemokines was detected during mammosphere culture in non‐stem cells. Similar results were observed in mixed cells. Interestingly, CSC‐like cells protected non‐stem cells from anoikis and promoted tumor growth. Our results suggest bystander effects between CSC‐like cells and non‐stem cells. J. Cell. Biochem. 117: 2289–2301, 2016.

Panax ginseng as an adjuvant treatment for Alzheimer's disease

Longevity in medicine can be defined as a long life without mental or physical deficits. This can be prevented by Alzheimers disease (AD). Current conventional AD treatments only alleviate the symptoms without reversing AD progression. Recent studies demonstrated that Panax ginseng extract improves AD symptoms in patients with AD, and the two main components of ginseng might contribute to AD amelioration. Ginsenosides show various AD-related neuroprotective effects. Gintonin is a newly identified ginseng constituent that contains lysophosphatidic acids and attenuates AD-related brain neuropathies. Ginsenosides decrease amyloid β-protein (Aβ) formation by inhibiting β- and γ-secretase activity or by activating the nonamyloidogenic pathway, inhibit acetylcholinesterase activity and Aβ-induced neurotoxicity, and decrease Aβ-induced production of reactive oxygen species and neuroinflammatory reactions. Oral administration of ginsenosides increases the expression levels of enzymes involved in acetylcholine synthesis in the brain and alleviates Aβ-induced cholinergic deficits in AD models. Similarly, gintonin inhibits Aβ-induced neurotoxicity and activates the nonamyloidogenic pathway to reduce Aβ formation and to increase acetylcholine and choline acetyltransferase expression in the brain through lysophosphatidic acid receptors. Oral administration of gintonin attenuates brain amyloid plaque deposits, boosting hippocampal cholinergic systems and neurogenesis, thereby ameliorating learning and memory impairments. It also improves cognitive functions in patients with AD. Ginsenosides and gintonin attenuate AD-related neuropathology through multiple routes. This review focuses research demonstrating that ginseng constituents could be a candidate as an adjuvant for AD treatment. However, clinical investigations including efficacy and tolerability analyses may be necessary for the clinical acceptance of ginseng components in combination with conventional AD drugs.

Abstract 1345: Role of AMP-activated protein kinase in crosstalk between apoptosis and autophagy in human colon cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Unresectable colorectal liver metastases remain major unsolved issues and more effective regimens are urgently needed. During screening synergistic drug combinations for colon cancer therapy, we identified a novel multimodality treatment for colon cancer cells-chemotherapeutic agent melphalan in combination with proteasome inhibitor bortezomib and mTOR (mammalian target of rapamycin) inhibitor rapamycin. We showed in this study that melphalan triggered apoptosis, bortezomib induced both apoptosis and autophagy, rapamycin caused autophagy, and the combinatorial treatment induced synergistic apoptosis which was mediated through an increase in caspase activation. We observed that mitochondrial dysfunction induced by the combination was linked with altered cellular metabolism and induced AMP-activated protein kinase (AMPK) activation, and thus resulted in Beclin-1 phosphorylated at Ser 93/96. Interestingly, Beclin-1 phosphorylated at Ser 93/96 is sufficient to induce Beclin-1 cleavage by caspase 8 for switching off autophagy to achieve the synergistic induction of apoptosis. The multimodality treatment-induced Beclin-1 cleavage was abolished in Beclin-1 double mutant (D133A/D149A) knock-in HCT116 cells, restoring the autophagy-promoting function of Beclin-1 and suppressing the apoptosis induced by the combination therapy. These observations provide a novel mechanism for AMPK induced apoptosis through interplay between autophagy and apoptosis. Citation Format: Xinxin Song, Seog-Young Kim, Lin Zhang, Yong J. Lee. Role of AMP-activated protein kinase in crosstalk between apoptosis and autophagy in human colon cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1345. doi:10.1158/1538-7445.AM2014-1345

Abstract 246: Role of the IL-6-JAK1-STAT3-Oct-4 pathway in the dynamic equilibrium between cancer stem cells and non-stem cancer cells.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Previous studies have demonstrated that a small subset of cancer cells is capable of tumor initiation. The existence of tumor initiating cancer stem cells (CSCs) has several implications in terms of future cancer treatment and therapies. However, recently, several researchers proposed that differentiated cancer cells (non-CSCs) can convert to stem-like cells to maintain equilibrium. These results imply that removing CSCs may prompt non-CSCs in the tumor to convert into stem cells to maintain the equilibrium. Interleukin-6 (IL-6) has been found to play an important role in the inducible formation of CSCs and their dynamic equilibrium with non-stem cells. In this study, we used CSC-like MDA-MB231 human breast adenocarcinoma cells and their alternate subset non-CSCs to investigate how IL-6 regulates the conversion of non-CSCs to CSCs. CSC-like cells formed mammospheres well, whereas most of non-stem cells died by anoikis and only part of the remaining non-stem cells produced viable mammospheres. Similar results were observed in xenograft tumor formation. Data from cytokine array assay show that IL-6 was secreted from non-CSCs when cells were cultured in ultra-low attachment plates. IL-6 regulates CSC-associated OCT-4 gene expression through the IL-6-JAK1-STAT3 signal transduction pathway in non-CSCs. Inhibiting this pathway by treatment with anti-IL-6 antibody (1 μg/ml) or niclosamide (0.5-2 μM)/LLL12 (5-10 μM) effectively prevented OCT-4 gene expression and suppressed mammosphere formation of non-stem cells. These results suggest that the IL-6-JAK1-STAT3 signal transduction pathway plays an important role in the conversion of non-CSCs into CSCs through regulation of OCT-4 gene expression. Citation Format: Seog-Young Kim, Jin W. Kang, Bokyoung Kim, Young D. Yoo, Yong T. Kwon, Yong J. Lee. Role of the IL-6-JAK1-STAT3-Oct-4 pathway in the dynamic equilibrium between cancer stem cells and non-stem cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 246. doi:10.1158/1538-7445.AM2013-246

Abstract 3367: Breast cancer stem cell-like cells are sensitive to ionizing radiation: Role of ATM

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL The aim of this study was to determine the radiosensitivity of cancer stem (tumor-initiating) cells (CSC), which are known to be responsible for tumorogenicity and metastasis. We used breast cancer stem cell (CSC)-like MDA-MB231 and MDA-MB453 cell lines which were established by Dr. Edward V. Prochownik (Sajithlal et al., Stem Cells, 28:1008, 2010). Interestingly, these cells can proliferate without differentiation and have characteristics of tumor-initiating cells. CSC-like cells and their alternate subset non-CSC cells were exposed to α-rays (1.25-8.75Gy) and survival curves were determined by colony formation. A final slope, D, of the survival curve for each cell line was determined to measure radiosensitivity. D of CSC-like MDA-MB453 cells and that of non-CSC MDA-MB453 cells were 1.16 Gy and 1.55 Gy, respectively. Similar results were observed in MDA-MB231 cells. We further examined whether CSC-like cells are relatively radiosensitive owing to different intrinsic factors including cell cycle distribution, free-radical scavengers and DNA repair. We observed that, unlike non-CSC cells, CSC-like cells have little/no sublethal damage repair and a low intracellular level of ATM. These results suggest that low DNA repair capability is responsible for the high radiosensitivity of these CSC-like cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3367. doi:1538-7445.AM2012-3367