Regulation of ¹⁸F-FDG Accumulation in Colorectal Cancer Cells with Mutated KRAS

Abstract

KRAS gene mutations occur in approximately 40% of colorectal cancers (CRCs) and are associated with resistance to anti-epidermal growth factor receptor antibody therapy. We previously demonstrated that 18 F-FDG accumulation in PET was significantly higher in CRCs with mutated KRAS than in those with wild-type KRAS in a clinical setting. Here, we investigated the mechanisms by which mutated KRAS increased 18 F-FDG accumulation. Methods: Using paired isogenic human CRC cell lines that differ only in the mutational status of the KRAS gene, we measured 18 F-FDG accumulation in these cells in vitro and in vivo. We also investigated the roles of proteins that have a function in 18 F-FDG accumulation. Finally, we examined the relationship among mutated KRAS, hypoxia-inducible factor 1α (HIF-1α), and maximum standardized uptake value with 51 clinical CRC samples. Results: In the in vitro experiments, 18 F-FDG accumulation was significantly higher in KRAS-mutant cells than in wild-type controls under normoxic conditions. The expression levels of glucose transporter 1 (GLUT1) and hexokinase type 2 (HK2) were higher in KRAS-mutant cells, and 18 F-FDG accumulation was decreased by knockdown of GLUT1. Hypoxic induction of HIF-1α was higher in KRAS-mutant cells than in wild-type controls; in turn, elevated HIF-1α resulted in higher GLUT1 expression and 18 F-FDG accumulation. In addition, HIF-1α knockdown decreased 18 F-FDG accumulation under hypoxic conditions only in the KRAS-mutant cells. Small-animal PET scans showed in vivo 18 F-FDG accumulation to be significantly higher in xenografts with mutated KRAS than in those with wild-type KRAS. The immunohistochemistry of these xenograft tumors showed that staining of GLUT1 was consistent with that of HIF-1α and pimonidazole. In a retrospective analysis of clinical samples, KRAS mutation exhibited a significantly positive correlation with expressions of GLUT1 and HIF-1α and with maximum standardized uptake value. Conclusion: Mutated KRAS caused higher 18 F-FDG accumulation possibly by upregulation of GLUT1; moreover, HIF-1α additively increased 18 F-FDG accumulation in hypoxic lesions. 18 F-FDG PET might be useful for predicting the KRAS status noninvasively.

Mouse model of proximal colon-specific tumorigenesis driven by microsatellite instability-induced Cre-mediated inactivation of Apc and activation of Kras

“…Moreover, this result was confirmed in cultured cells and xenograft models of thyroid and colon cancer, respectively, resulting in accumulation of 18F-FDG. [33,34] Consistent with these results, the correlation between Kras mutation status and Glut1 expression was confirmed in G22Cre;Apc flox/ flox ;Kras G12D mice with a potential MSI phenotype based on our previous observation in G22Cre;Apc flox/flox ;KrasWT mice [28]. Thus, the G22Cre;Apc flox/flox ;Kras G12D mouse model may recapitulate the human KRAS mutated colorectal cancer with MSI phonotype.…”

Relationship Between 18F-FDG PET/CT Scans and KRAS Mutations in Metastatic Colorectal Cancer

“…In this study, we investigated a possible association between KRAS status and HIF-1a expression by immunohistochemical analysis and found that HIF-1a did not correlate with KRAS status in metastatic CRC (data not shown). Our previous studies on primary CRC showed a significant correlation between HIF-1a and KRAS status (10). One possible reason for this discrepancy may be the difference in tumor size (primary CRC, 47.9 6 20 vs. metastatic CRC, 20.9 6 14.2 mm; P , 0.01).…”

“…When CRC cells were treated under hypoxic conditions, mutated KRAS enhanced the translation of HIF-1a through the phosphoinositide 3-kinase pathway (26). We recently reported that CRC cells with mutated KRAS increased 18 F-FDG accumulation by upregulating GLUT1 and at least partially by upregulating HIF-1a induction under hypoxic conditions (10). In this study, we investigated a possible association between KRAS status and HIF-1a expression by immunohistochemical analysis and found that HIF-1a did not correlate with KRAS status in metastatic CRC (data not shown).…”

“…In hypoxic cells, HIF-1a enhances glycolysis by inducing glucose transporter and several enzymes involved in glycolysis (9). In both in vitro and in vivo animal experiments, we recently showed that mutated KRAS caused higher 18 F-FDG accumulation possibly by upregulation of GLUT1 and at least partially by upregulating HIF-1a induction under hypoxic conditions (10).…”

A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics

“…Thei nvestigation of molecular uptake inside cells is valuable for the understanding of physiologic status (1,2), for the interpretation of molecular imaging results (3,4), and for the development of imaging agents and pharmaceuticals (5). The cellular uptake of a molecule is usually assessed by measuring labeling signals such as radioactivity (2,6), optical signal (7), or magnetic signal (8).…”