Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan
J Nucl Med. 2014 Dec;55(12):2038-44. doi: 10.2967/jnumed.114.142927. Epub 2014 Nov 5.
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.
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.
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.
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.
KRAS 基因突变发生于约 40%的结直肠癌（CRC）中，与抗表皮生长因子受体抗体治疗的耐药性相关。我们先前在临床环境中证明，在 KRAS 突变型 CRC 中，（18）F-FDG 在 PET 中的聚集明显高于 KRAS 野生型。在此，我们研究了 KRAS 突变增加（18）F-FDG 聚集的机制。
使用配对的具有相同 KRAS 基因突变状态的同源人 CRC 细胞系，我们在体外和体内测量这些细胞中（18）F-FDG 的聚集。我们还研究了在（18）F-FDG 聚集中具有功能的蛋白质的作用。最后，我们检查了 51 例临床 CRC 样本中 KRAS 突变、缺氧诱导因子 1α（HIF-1α）和最大标准化摄取值之间的关系。
在体外实验中，在常氧条件下，KRAS 突变细胞中（18）F-FDG 的聚集明显高于野生型对照。KRAS 突变细胞中葡萄糖转运蛋白 1（GLUT1）和己糖激酶 2（HK2）的表达水平较高，并且 GLUT1 的敲低降低了（18）F-FDG 的聚集。KRAS 突变细胞中缺氧诱导的 HIF-1α较高，而野生型对照则较高；反过来，升高的 HIF-1α导致 GLUT1 表达和（18）F-FDG 聚集增加。此外，仅在 KRAS 突变细胞中，HIF-1α 的敲低降低了缺氧条件下的（18）F-FDG 聚集。小动物 PET 扫描显示，携带 KRAS 突变的异种移植物体内（18）F-FDG 的积累明显高于携带野生型 KRAS 的异种移植物。这些异种移植瘤的免疫组化染色显示 GLUT1 的染色与 HIF-1α和 pimonidazole 的染色一致。在对临床样本的回顾性分析中，KRAS 突变与 GLUT1 和 HIF-1α的表达以及最大标准化摄取值呈显著正相关。
KRAS 突变通过上调 GLUT1 导致更高的（18）F-FDG 聚集；此外，HIF-1α 在缺氧病变中附加增加（18）F-FDG 聚集。（18）F-FDG PET 可能有助于非侵入性地预测 KRAS 状态。
