In vitro activity: Tenofovir is eliminated from systemic circulation renally through a combination of glomerular filtration and active tubular secretion. Tenofovir is not a substrate for human organic cation transporter type 1 (hOCT1) or hOCT2. Tenofovir accumulates to fivefold lower levels in MRP4-overexpressing cells, and its accumulation could be increased by an MRP inhibitor. Tenofovir produces no significant changes in mitochondrial DNA (mtDNA) levels in human hepatoblastoma (HepG2) cells, skeletal muscle cells (SkMCs), or renal proximal tubule epithelial cells. Tenofovir elevates lactate production by less than 20% in HepG2 cells or SkMCs. Tenofovir is efficiently phosphorylated to tenofovir diphosphate (TFV-DP) in both HepG2 cells and primary human hepatocytes. Tenofovir has a 50% effective concentration of 1.1 mM against HBV in cell-based assays, and potency is improved> 50-fold by the addition of bis-isoproxil progroups. Tenofovir has previously demonstrated full activity against lamivudine-resistant HBV in vitro and clinically. Tenofovir inhibits the proliferation of liver-derived HepG2 cells and normal skeletal muscle cells with CC(50) values of 398 mM and 870 mM, respectively. Tenofovir shows substantially weaker effects on proliferation and viability of renal proximal tubule epithelial cells than cidofovir, a related nucleotide analog with the potential to induce renal tubular dysfunction.

Cell Assay: Cells are plated into 48-well tissue culture plates (39,000 cells/mL) and allowed to grow for 48 h followed by treatment with vehicle or Tenofovir. Following the treatment period, cell viability is assessed using the MTT assay. The MTT assay relies on the conversion of tetrazolium dye 3-(4,5-dimethlthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to formazan by NAD(P)H-dependent oxidoreductases.