The Application of Metabolic Markers (GLUT1, GLUT4, TKTL1/2) to Formulate Novel Risk Stratification Strategies Against Colorectal Cancer

Abstract

Background: Tumors ferment glucose to lactate even in the presence of oxygen (aerobic glycolysis; Warburg effect). This nonoxidative conversion of glucose to lactate is activated by transketolase, an enzyme of the pentose phosphate pathway. For maintaining accelerated metabolism, tumors are known to have high requirements for glucose and thus have increased transport of glucose across the plasma membrane. Metabolic dependence of tumors on glucose utilization has been characterized by three genes; GLUT1, GLUT 4 and TKTL1/2. However, the expression patterns of the genes have not been explored fully for early stages of colorectal carcinogenesis. In this study we studied the expression pattern of these genes in colonic carcinogenesis (rat-AOM model and human CRC) and chemoprevention (by studying the effect of celecoxib in, Caco-2 and HCT-116 cell lines).Methods: Immunohistochemical expression of GLUT1, GLUT4, and TKTL1/2 was analyzed in human colon caner tissue array (consisting of 36 cases of colonic cancers and 12 cases each of normal, inflammatory and benign tumor tissues of the colon). In addition we analyzed 14 week AOM-treated rat colon tissue samples (early stage of colorectal carcinogenesis model) and saline-treated samples. Caco-2 and HCT-116 CRC cells were treated with 50μM celecoxib for 72hrs. Further analysis was carried out through real-time PCR using TKTL (1 & 2), GLUT (1 &4), PCNA and β-actin (control) Taqman probes. Results: Our results reveal an increased expression of GLUT1, GLUT4 and TKTL1/2 during CRC progression from adenoma to mucinous adenocarcinoma (Table 1). Increased expression of these genes was evident during early onset of carcinogenesis as shown in 14 week AOM-treated rat colon. Lastly, the cell culture data revealed that celecoxib caused a significant reduction in the expression of these metabolic markers in Caco-2 (p<.01) or HCT-116 (p<.05). These changes corresponded to the reduction in the proliferation marker PCNA in Caco-2 (95%) or in HCT-116 cells (39%) (Table 2). Conclusions: We, herein, demonstrate that expression of GLUT 1, GLUT4, and TKTL1/2 is significantly altered during early CRC and are key factors in cancer progression. Our studies show a significant increase in the glucose transporter 1 and 4, in relationship to cancer progression and early stages of colorectal carcinogenesis, thereby proposing potential biomarker role for these markers. TKTL1/2, on the other hand, seems to be up regulated in only a few of human colorectal tumors, which portends it to be a subset-specific biomarker. We further demonstrate that chemopreventive properties of celecoxib against colorectal cancer (Caco-2 and HCT-116 cells) may be modulated by the metabolic mediators involved in glycolysis. Further studies are needed to access the clinical application of these receptors as potential biomarkers for colorectal cancer. Table 1. Colon Tumor Tissue Array