The clinical significance of L-type amino acid transporter 1 (LAT1) expression remains unclear, whereas many experimental studies have demonstrated that LAT1 is associated with the proliferation of cancer cells. The purpose of this study was to evaluate the prognostic value of LAT1 in patients with nonsmall cell lung cancer (NSCLC). A total of 321 consecutive patients with completely resected pathologic stage I–III NSCLC were retrospectively reviewed. Expression of LAT1 and proliferative activity, as determined by the Ki-67 labelling index, was also evaluated immunohistochemically and correlated with the prognosis of patients who underwent complete resection of the tumour. Expression of LAT1 was positive in 163 patients (51%) (29% of adenocaricnoma (58 of 200 patients), 91% of squamous cell carcinoma (91 of 100 patients), and 67% of large cell carcinoma (14 of 21 patients)). The 5-year survival rate of LAT1-positive patients (51.8%) was significantly worse than that of LAT1-negative patients (87.8%; P<0.001). L-type amino acid transporter 1 expression was significantly associated with lymph node metastasis and disease stage. Multivariate analysis confirmed that positive expression of LAT1 was an independent factor for predicting a poor prognosis. There was a significant correlation between LAT1 expression and Ki-67 labelling index. LAT1 expression is a promising pathological factor to predict the prognosis in patients with resectable stage I–III NSCLC.

Oncogenic KRAS is found in more than 25% of lung adenocarcinomas, the major histologic subtype of non–small cell lung cancer (NSCLC), and is an important target for drug development. To this end, we generated four NSCLC lines with stable knockdown selective for oncogenic KRAS. As expected, stable knockdown of oncogenic KRAS led to inhibition of in vitro and in vivo tumor growth in the KRAS-mutant NSCLC cells, but not in NSCLC cells that have wild-type KRAS (but mutant NRAS). Surprisingly, we did not see large-scale induction of cell death and the growth inhibitory effect was not complete. To further understand the ability of NSCLCs to grow despite selective removal of mutant KRAS expression, we conducted microarray expression profiling of NSCLC cell lines with or without mutant KRAS knockdown and isogenic human bronchial epithelial cell lines with and without oncogenic KRAS. We found that although the mitogen-activated protein kinase pathway is significantly downregulated after mutant KRAS knockdown, these NSCLCs showed increased levels of phospho-STAT3 and phospho–epidermal growth factor receptor, and variable changes in phospho-Akt. In addition, mutant KRAS knockdown sensitized the NSCLCs to p38 and EGFR inhibitors. Our findings suggest that targeting oncogenic KRAS by itself will not be sufficient treatment, but may offer possibilities of combining anti-KRAS strategies with other targeted drugs. Mol Cancer Ther; 10(2); 336–46. ©2011 AACR.

Purpose:l-[3-¹⁸F]-α-Methyltyrosine ([¹⁸F]FMT) is an amino acid tracer for positron emission tomography (PET). We evaluated the diagnostic usefulness of [¹⁸F]FMT PET in non–small-cell lung cancer (NSCLC) patients. Tumor uptake of [¹⁸F]FMT was compared with that of 2-[¹⁸F]-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) and correlated with L-type amino acid transporter 1 (LAT1) expression. Experimental Design: Fifty NSCLC patients were enrolled in this study, and a pair of PET study with [¹⁸F]FMT and [¹⁸F]FDG was done. LAT1 expression and Ki-67 labeling index of the resected tumors were analyzed by immunohistochemical staining. Results: For the primary tumor detection, [¹⁸F]FMT PET exhibited a sensitivity of 90% whereas the sensitivity for [¹⁸F]FDG PET was 94%. For lymph node staging, the sensitivity and specificity of [¹⁸F]FMT PET were 57.8% and 100%, and those of [¹⁸F]FDG PET were 65.7% and 91%, respectively. The expression of LAT1 in squamous cell carcinoma and large cell carcinoma was significantly higher than that in adenocarcinoma. [¹⁸F]FMT uptake was also higher in squamous cell carcinoma and large cell carcinoma than in adenocarcinoma. Uptake of [¹⁸F]FMT in the tumor is closely correlated with LAT1 expression (ρ = 0.890). Conclusion: [¹⁸F]FMT PET had no false-positives in the detection of primary tumor and lymph node metastasis and could improve the diagnostic performance in NSCLC. Uptake of [¹⁸F]FMT correlated with the expression of LAT1 that showed a significant association with cellular proliferation.

The CXC chemokine interleukin‐8 (IL‐8) is an angiogenic growth factor that is overexpressed in various cancers, including non‐small cell lung cancer (NSCLC). Previously, IL‐8 was shown as a transcriptional target of RAS signaling, raising the possibility of its role in oncogenic KRAS‐driven NSCLC. Using microarray analysis, we identified IL‐8 as the most downregulated gene by shRNA‐mediated KRAS knockdown in NCI‐H1792 NSCLC cells where IL‐8 is overexpressed. NSCLC cell lines harboring KRAS or EGFR mutations overexpressed IL‐8, while IL‐8 levels were more prominent in KRAS mutants compared to EGFR mutants. IL‐8 expression was downregulated by shRNA‐mediated KRAS knockdown in KRAS mutants or by treatment with EGFR tyrosine kinase inhibitors and EGFR siRNAs in EGFR mutants. In our analysis of the relationship of IL‐8 expression with clinical parameters and mutation status of KRAS or EGFR in 89 NSCLC surgical specimens, IL‐8 expression was shown to be significantly higher in NSCLCs of males, smokers, and elderly patients and those with pleural involvement and KRAS mutated adenocarcinomas. In KRAS mutant cells, the MEK inhibitor markedly decreased IL‐8 expression, while the p38 inhibitor increased IL‐8 expression. Attenuation of IL‐8 function by siRNAs or a neutralizing antibody inhibited cell proliferation and migration of KRAS mutant/IL‐8 overexpressing NSCLC cells. These results indicate that activating mutations of KRAS or EGFR upregulate IL‐8 expression in NSCLC; IL‐8 is highly expressed in NSCLCs from males, smokers, elderly patients, NSCLCs with pleural involvement, and KRAS‐mutated adenocarcinomas; and IL‐8 plays a role in cell growth and migration in oncogenic KRAS‐driven NSCLC.