In vitro activity: Foscarnet Sodium is able to penetrate into cells and inhibit viral replication by inhibiting viral DNA synthesis. Foscarnet Sodium (300 μM) displays a more than 95% inhibition on HTLV-III reverse transcriptase activity in H9 cells infected with HTLV-III. Foscarnet Sodium has a low cellular toxicity, but shows an inhibition of cell proliferation at high concentrations, which is reversed after drug removal. Incubation 0.5-1 mM Foscarnet Sodium with HeLa cells or primary human lung fibroblast for 24-48 hr inhibited 50% DNA synthesis and/or cell proliferation. Foscarnet Sodium is able to bind with the heparin-binding domain of FGF2 and inhibits FGF2 induced cell proliferation. Foscarnet Sodium (25 μM) treating HUVEC cells for 48 hr reduced FGF2-induced cellular proliferation by 20%. Foscarnet Sodium (0.5-1 mM) reduced the 24h proliferation rate of CAL-62 cell, a Human thyroid anaplastic carcinoma cell line which expresses FGF2, to nearly 80%.

Kinase Assay: Reverse transcriptase assays are carried out in a reaction mixture (50 μL) containing 50 mM Tris-HCl (pH 7.5), 5 mM DTT, 100 mM potassium chloride, 0.01% Triton X-100 or NP40, 10 μg/ml (dT)15.(A)n as template primer and [3H] deoxythymidine triphospahate. The reaction mixture is incubated for 1 hr at 37 ℃ and stopped by the addition of 50 μg of yeast tRNA and 2 mL of 10% solution of trichloroacetic acid containing 1 mM sodium pyrophosphate. The samples are filtered on filters (0.45 μm), washed first with 5% TCA solution for 5 times and then with 2 ml of 70% ethanol. The filters are dried, scintillation fluid is added and the radioactivity counted in a counter. 

Cell Assay: CAL-62 cells are placed on 96 well plates at 8×103 cells/well in 100 μL DMEM for 24 h. Then medium is replaced by fresh DMEM with or without foscarnet. After 48 h of incubation, 20 μL of CellTiter 96AQ solution is added to the cells and incubated for 2-4 h. The quantity of formazan product as measured by the absorbance at 492 nm.