Tianxing, Hang, Li, Yang, Xiujuan, Zhang, Jing, Li, Feng, Long, Ning, Zhu, Ying, Li, Jingwen, Xia, Youzhi, Zhang, Peng, Zhang, Yuanyuan, Zhang, Xiaomin, Wei, and Shengqing, Li
Objective: The folic acid analog pemetrexed (PMX) is recommended for the first-line chemotherapy for advanced non-squamous non-small cell lung cancer (NSCLC). However, the mechanisms underlying PMX cytotoxicity in NSCLC remain to be fully explored. Methods: PMX effect was evaluated in a urethane-induced lung adenocarcinoma mouse model. The interaction between PMX and intracellular proteins, particularly peroxisome proliferator-activated receptor γ (PPARγ), was investigated. The role of PPARγ in mediating pemetrexed cytotoxicity was investigated using NSCLC cell lines, mouse models and clinical specimens. Results: This study found that PPARγ expression was correlated with prolonged progression-free survival in NSCLC patients. PPARγ downregulated hypoxanthine-guanine phosphoribosyl transferase (HGPRT), a key enzyme for nucleotide salvage synthesis, thereby sensitizing cells to PMX inhibition on nucleotide de novo synthesis. PMX was also a candidate partial agonist of PPARγ, and PMX-activated PPARγ bound to NF-κB and transcriptionally suppressed the NF-κB target gene, c-Myc. PMX inhibited tumor growth by activating PPARγ in a urethane-induced lung cancer model characterized by elevated NF-κB activity. Conclusion: PPARγ improves pemetrexed therapeutic efficacy in non-squamous NSCLC. The cytotoxicity effect of PMX can be synergized by activating PPARγ and thereby inhibiting NF-κB pathway.