SummaryThe gene expression of glucose transporter type 4 isoform (GLUT4) is known to be controlled by metabolic, nutritional, or hormonal status. Understanding the molecular mechanisms governing GLUT4 gene expression is critical, because glucose disposal in the body depends on the activities of GLUT4 in the muscle and adipocytes. The GLUT4 activities are regulated by a variety of mechanisms. One of them is transcriptional regulation. GLUT4 gene expression is regulated by a variety of transcriptional factors in muscle and adipose tissue. These data are accumulating regarding the transcriptional factors regulating GLUT4 gene expression. These include MyoD, MEF2A, GEF, TNF-a, TR-1a, KLF15, SREBP-1c, C/EBP-a, O/E-1, free fatty acids, PAPRg, LXRa, NF-1, etc. These factors are involved in the positive or negative regulation of GLUT4 gene expression. In addition, there is a complex interplay between these factors in transactivating GLUT4 promoter activity. Understanding the mechanisms controlling GLUT4 gene transcription in these tissues will greatly promote the potential therapeutic drug development for obesity and T2DM.

Expression of the GLUT4 (glucose transporter type 4 isoform) gene in adipocytes is subject to hormonal or metabolic control. In the present study, we have characterized an adipose tissue transcription factor that is influenced by fasting/refeeding regimens and insulin. Northern blotting showed that refeeding increased GLUT4 mRNA levels for 24 h in adipose tissue. Consistent with an increased GLUT4 gene expression, the mRNA levels of SREBP (sterol-regulatory-element-binding protein)-1c in adipose tissue were also increased by refeeding. In streptozotocin-induced diabetic rats, insulin treatment increased the mRNA levels of GLUT4 in adipose tissue. Serial deletion, luciferase reporter assays and electrophoretic mobility-shift assay studies indicated that the putative sterol response element is located in the region between bases -109 and -100 of the human GLUT4 promoter. Transduction of the SREBP-1c dominant negative form to differentiated 3T3-L1 adipocytes caused a reduction in the mRNA levels of GLUT4, suggesting that SREBP-1c mediates the transcription of GLUT4. In vivo chromatin immunoprecipitation revealed that refeeding increased the binding of SREBP-1 to the putative sterol-response element in the GLUT4. Furthermore, treating streptozotocin-induced diabetic rats with insulin restored SREBP-1 binding. In addition, we have identified an Sp1 binding site adjacent to the functional sterol-response element in the GLUT4 promoter. The Sp1 site appears to play an additive role in SREBP-1c mediated GLUT4 gene upregulation. These results suggest that upregulation of GLUT4 gene transcription might be directly mediated by SREBP-1c in adipose tissue.

CG200745 can be safely administered at effective dose levels that inhibit HDAC in PBMCs and tumor tissue. Although MTD was not reached, further escalation was not performed because acetylated histone H4 plateaued at dose levels higher than 51 mg/m(2). Additional phase II trials are recommended at 250 mg/m(2).

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CG200745 is a HDAC inhibitor at the final stage of phase I clinical trial. In the current human studies with patient with terminal solid tumors, CG200745 is showing highly desirable PK and safety profiles. Actually, the AUC/dose of CG200745 is the highest among all the clinical stage HDAC inhibitors. CG200745 is more distributed in tumor tissue that in plasma. Moreover, SD's (stable disease) were observed even in single dose study. Currently, we are planning phase II studies using regimens combining CG200745 and existing therapy in patients with solid tumors. As a choice of indications, pancreatic cancer was considered based on biological studies and observation in phase I clinical studies.Thus, cellular and xenograft studies of CG200745 using pancreatic cancer cell lines have been carried out in our laboratories. In these studies, treatments of CG200745 combining with gemcitabine and/or erotinib show clear synergistic effects. These results indicate that the combination of CG200745 with existing therapy can be a promising intervention for pancreatic cancer. Citation Format: Seonggu Ro, Jang-Won Hong, Sool-Ki Kwon, Hyunju Cha, Dong Sub Jung, Ho-Jin Chang, Joong Myung Cho. Synergistic effects of CG200745 combining with Gemcitabine and/or Erotinib in pancreatic cancer. [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 682. doi:10.1158/1538-7445.AM2013-682