In vitro activity: Methotrexate (0.1-10 mM) induces apoptosis of in vitro activated T cells from human peripheral blood. Methotrexate achieves clonal deletion of activated T cells in mixed lymphocyte reactions. Methotrexate can selectively delete activated peripheral blood T cells by a CD95-independent pathway. Methotrexate is taken up by cells via the reduced folate carrier and then is converted within the cells to polyglutamates. Methotrexate leads to diminished production of leukotriene B4 by neutrophils stimulated ex vivo. Methotrexate polyglutamates inhibit the enzyme aminoimidazolecarboxamidoadenosineribonucleotide (AICAR) transformylase more potently than the other enzymes involved in purine biosynthesis. Methotrexate is also known to suppress TNF activity by suppressing TNF-induced nuclear factor-κB activation in vitro, in part related to a reduction in the degradation and inactivation of an inhibitor of this factor, IκBα, and probably related to the release of adenosine. Methotrexate suppresses the production of both TNF and IFN-γ by T-cell-receptor-primed T lymphocytes from both healthy human donors and RA patients. Methotrexate treatment is associated with a significant decrease of TNF-α-positive CD4+ T cells, while the number of T cells expressing the anti-inflammatory cytokine IL-10 increased.

Cell Assay: Each cell line is studied in growth inhibition experiments using 96-well microtiter plates. As antifols are schedule dependent, preliminary experiments are aimed at defining the longest duration of exposure that would allow for continuous logarithmic phase growth of cells without changing of the culture media while maintaining a linear relationship between SRB optical density and cell number. Twenty-four hours after cell plating, the cell lines are exposed to the antifol for 120 h (three replicates per experiment). To ensure that a complete sigmoidal survival-concentration curve could be observed, the following drug concentrations are studied: Methotrexate (0.002-5 μM), AMT (0.0001-1 μM), PXD (0.0003-10 μM), TLX (0.0002-0.5 μM). Experiments are repeated at least twice.

J Clin Invest. 1998 Jul 15;102(2):322-8; J Clin Invest. 1993 Dec;92(6):2675-82.