66), associated with patients smoking history and overall survival. At multivariate analysis, TS gene expression was an independent prognostic factor (relative risk (RR) = 1.78, from 1.16 to 2.72; p < 0.01). Immunohistochemical detection in tumor specimens confirmed that Src kinase activation, evaluated by phospho-specific antibody, was associated to a higher TS expression. In cell lines, dasatinib, a Src-inhibiting agent, synergistically enhanced pemetrexed-cytotoxicity of A549 cells, as evaluated by MTT and apoptosis assays. The biological explanation for this interaction was based on the upregulation of TS messenger RNA and protein levels induced by pemetrexed, which was significantly prevented by dasatinib cotreatment. The data of our study suggest that TS and Src may belong to a common pathway that bears prognostic significance Sunitinib
in NSCLC, and that Src represents a potential target to improve the efficacy of TS-inhibiting agents. Cytotoxic chemotherapy is the standard of care for locally advanced and metastatic nonsmall cell lung cancer (NSCLC) even though the efficacy of the currently available therapeutic armamentarium is limited,1, 2 and new therapeutic strategies are clearly needed to improve patients quality of life, response rates and overall survival. Thymidylate synthase (TS) is the enzyme which catalyzes the reaction that provides the sole de novo intracellular source of deoxythymidine monophosphate, or thymidylate, which is essential for DNA replication and repair.3, 4 TS protein Selleckchem BAY-61-3606
and messenger RNA (mRNA) levels have been found elevated in many human cancers, and correlated with poor prognosis in patients with colorectal,5 breast,6 head and neck,7 pancreatic8 and in NSCL cancers.9, 10 Transfection of catalytically active TS has been shown to induce a transformed phenotype in human cells, as manifested by foci formation, anchorage independent growth and tumor formation in nude mice, suggesting that TS itself could be considered as an oncogene.11 TS is also the cellular target of 5-fluorouracil (5-FU)4 and of pemetrexed.12 Pemetrexed is a multitargeted antifolate that prevents the formation of DNA Q-VD-Oph mouse
and RNA, blocking the growth of cancer cells, by inhibiting the activity of four enzymes in the folate pathway, being TS the most important target.13�C15 In lung cancer, it was previously reported an higher TS mRNA and protein level in squamous cell carcinoma, as opposed to adenocarcinoma,10 and a 10-fold higher TS expression in small-cell lung cancer (SCLC) as compared to NSCLC16 and to carcinoid tumors.17 More recently, it was shown a consistency between the aforementioned findings and TS enzymatic activity in lung cancer cell lines of different histotypes,18 and these findings led to a rationale interpretation of the outcome of the clinical trials which investigated the role of pemetrexed in NSCLC and SCLC.