Kras mutation causes increased 18F-FDG uptake in experimental models of colorectal cancer

Objectives Ras proteins have been implicated in the regulation of aerobic glycolysis. However, there are controversial reports of the effect of Kras mutation on FDG uptake in the literature. We developed genetically engineered models of colorectal cancer with wild type or mutant Kras to specifically test the effect of Kras mutation on FDG uptake.

Methods To generate compound mutant mice, APCCKO, KrasLSL-G12D and p53flox/flox mice were crossed to generate APCCKOp53flox/flox (AP) mice and APCCKOKrasLSL-G12Dp53 flox/flox (AKP) mice. AdCre virus was administered focally in the colon to cause recombination; mice were followed by colonoscopy for tumor development. Tumors fragments were isolated and two AP lines (F62 and E75) and two AKP cell lines (A85, B17) were established. The AP and AKP cell lines were grown in 24-well plates, incubated for 1 hour with 25 μCi FDG and then collected and radioactive counts/cell was measured. The cell lines were also implanted in the flank of nu/nu mice. Once tumors grew they were imaged by PET 1 hour after injection of 400 µCi of FDG and SUVmax and SUVmean were measured. Tumors were then dissected and lactate was extracted and measured. Slc2a1 gene (Glut-1) expression was measured by microarray analysis. The statistical significance was tested using t-test.

Results We successfully developed two AP and two AKP cell lines. The results of the metabolic profiling of the cell lines showed that the FDG uptake was significantly higher in AKP compared to AP cell lines in both in vitro (Fig. 1A) and in vivo experiments (Fig. 1C, D and F). Analysis of the lactate content of the tumors after FDG-PET imaging showed higher lactate concentration in AKP tumors compared to AP tumors (Fig. 1B). A higher expression of Glut-1 was seen in AKP compare to AP cell lines (Fig. 1E).

Conclusions These findings are consistent with a metabolic shift towards increased aerobic glycolysis implicating a role for oncogenic Kras in a shift toward increased glycolysis and glucose consumption.

Research Support U01CA08430