New Data Integrating Multitargeted Antifolates into Treatment of First-line and Relapsed Non–Small-Cell Lung Cancer

Non–small-cell lung cancer (NSCLC) represents approximately 80% of all lung cancers. With modern platinum-based combination regimens, overall median survival has reached 9–12 months. Antifolates are active against several solid tumors and hematologic malignancies. The cytotoxic action of antifolates is mainly related to their ability to inhibit several different folate-dependent enzymes involved in DNA synthesis. Pemetrexed is a novel multitargeted antifolate that inhibits at least 3 of the enzymes involved in purine and pyrimidine synthesis: thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT). Pemetrexed was approved for the treatment of relapsed NSCLC as it produced equivalent response and survival rates and less toxicity compared with docetaxel. Pemetrexed in combination with platinum analogues or with gemcitabine showed equivalent clinical impact compared with standard combinations of platinum plus third-generation agents. We analyze the potential implications of pemetrexed's role in first-line chemotherapy of NSCLC as well as hints of differential cytotoxic action according to histology, new schedules of vitamin supplementation, and target enzymes expression levels. Issues of pharmacogenomics are becoming relevant in defining pemetrexed efficacy. Chemosensitivity was significantly linked to low levels of TS, GARFT, and DHFR in preclinical models. Consequently, the differential expression of TS according to histology might explain the different activity of pemetrexed according to histology, as recently postulated.