Time course tests showed that optimal antiproliferative results were achieved when cells were subjected to pralatrexate for 72h (Body 1A). Outcomes: == Pralatrexate and methotrexate got a similar design of cytotoxicity, pralatrexate getting stronger. Pralatrexate potentiated the consequences of platinum medications, eGFR and antimetabolites inhibitors. Dosage- and time-dependent cytotoxicity of pralatrexate correlated with high mRNA appearance of FPGS. Obtained level of resistance to pralatrexate was connected with reduced RFC-1 appearance, whereas methotrexate level of resistance correlated with an increase of DHFR appearance, suggesting different systems of acquired resistance. == Conclusion: == Pralatrexate was more potent than methotrexate in a panel of solid tumour lines. Our findings support the further clinical development of pralatrexate in combination with certain cytotoxics and targeted therapies, and suggest that RFC-1, FPGS and DHFR may be potential biomarkers of outcome. Keywords:methotrexate, antimetabolites, antifolates, drug resistance, combination chemotherapy, folate transporters The folate pathway has a key role in cell growth and proliferation (Appling, 1991;Odinet al, 2003). Folic acid (folate) enters cells through reduced folate carrier 1 (RFC-1), P300/CBP-IN-3 is polyglutamated by folylpolyglutamate synthetase (FPGS), and is reduced to dihydrofolate, which is further converted to tetrahydrofolate (THF) by dihydrofolate reductase (DHFR). The different enzymes and transporters involved in this pathway are targets for an important class of cytotoxic agents, antifolates. Methotrexate was one of the first agents of this class and was first used in the treatment of childhood acute lymphoblastic leukaemia (Farberet al, 1948). Since then, methotrexate has been widely used in haematologic and solid cancers, and new generations of antifolates have been rationally designed to exploit multiple aspects of the folate pathway (e.g., raltitrexed in colorectal cancer (Cocconiet al, 1998), and pemetrexed in malignant pleural mesotheliomas (Vogelzanget al, 2003) and non-small-cell lung carcinomas (NSCLC) (Hannaet al, 2004)). Pralatrexate ((RS)-10-propargyl-10-deazaaminopterin) is a synthetic anti-DHFR antifolate, rationally designed to have greater affinity for RFC-1 and FPGS, resulting in increased cytotoxic activity as compared with methotrexate (DeGrawet al, 1993;Sirotnaket al, 1998). The cytotoxicity of pralatrexate was shown to be correlated with RFC-1 mRNA expression in human lymphoma cells (Wanget al, 2003). Pralatrexate is undergoing clinical evaluation as a single agent or in combination in several tumour types, including lymphoma TNFRSF10D (OConnoret al, 2007;Marneroset al, 2009), and has received accelerated approval by the US Food and Drug Administration (FDA) for patients with refractory or relapsed peripheral T-cell lymphoma. In this study, we have compared the antiproliferative activity of pralatrexate with that of methotrexate and other antimetabolites in several human solid tumour cell lines. In addition, we further evaluated molecular mechanisms of action of pralatrexate, and screened for markers of sensitivity and acquired resistance to pralatrexate, knowledge of which could be of potential use for designing future clinical trials. Finally, possible sequence-dependent synergy or additive effects of pralatrexate with various cytotoxic and targeted agents were also investigated. == Materials and methods == == Cell lines == A panel of colon (HT29, HCT116, COLO205 and HCC2998), breast (MCF7), melanoma (MDA-MB-435, formerly designated as a breast cancer line), NSCLC (HOP62 (adenocarcinoma) and HOP92 (large cell carcinoma)), ovarian (OVCAR3, IGROV1), prostate (DU145, PC3) and head and neck (SCC61, HEP2 and SQ20B) cancer cell lines was purchased from the ATCC (Rockville, MD, USA) and National Cancer Institute collections. Cells were grown as monolayers in RPMI medium supplemented with 10% fetal calf serum (Invitrogen, Cergy-Pontoise, France), 2 mMglutamine, 100 U ml1penicillin and 100Mml1streptomycin. In this study, we used unpurified media potentially containing glycine, hypoxanthine and thymidine, which may have theoretically reduced drug activity. However, considering P300/CBP-IN-3 the high levels of resistance developed in our cell lines and taking into account that both parental and derived resistant counterpart were grown in similar media, it remains unlikely that this would have severely impact on data. == Cytotoxicity assays == Cell viability was determined using the MTT assay, which was carried out as described previously (Hansenet al, 1989). Briefly, P300/CBP-IN-3 cells were seeded in 96-well plates at a density of 2 103cells per well. Cells were incubated for 120 h and then 0.4 mg ml1of MTT dye (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide; Sigma, Saint-Quentin Fallavier, France), was added for 4 h at 37C. Media was removed and the monolayer suspended in 0.1 ml of DMSO, after which the absorbance at 560 nm was measured using a microplate reader (Thermo, Saint-Herblain, France). The control value corresponding to untreated cells was defined as 100% and the viability of treated samples was expressed.
