In vitro activity: Using Tipifarnib 5 μM for 72 hours, the percentage of apoptotic cells is significantly higher in drug-treated compared to DMSO-treated LGL T-cells. Using T-cells from healthy donors, Tipifarnib reduces the percentage of IFNγ-positive cells in a time-dependent manner. Tipifarnib reduces the amount of activated Ras in precipitates compared to DMSO. Tipifarnib exerts selective in vitro toxicity against clonal MDS hematopoiesis at concentrations less than 10 nM the effect being more prominent in white cell progenitors. This action is not due to apoptosis induction as both normal and MDS progenitors displays equivalent DiOC3 and annexin V expression up to 72 hours after exposure to Tipifarnib. Combining Tipifarnib with 10 nM 4-OH-tamoxifen in the presence of E2 reduces the IC50 8-fold from 400 to 50 nM. Tipifarnib induces apoptosis in U937 cells. In addition, Tipifarnib inhibits isolated human farnesyltransferase for a lamin B peptide and for the K-RasB peptide with IC50 of 0.86 nM and 7.9 nM, respectively.

Kinase Assay: Tipifarnib binds to and inhibits farnesyltransferase (FTase) with IC50 of 0.6 nM.

Cell Assay: MACS-selected CD34+ cells are seeded in Methocult 4435 'complete' 1% bovine serum albumin, 3 U/mL recombinant human (rh) erythropoietin, 0.1 mM 2-mercaptoethanol, 2 mM L-glutamine and the following cytokines: 50 ng/mL rh stem cell factor, 20 ng/mL rh GM-CSF, 20 ng/mL rh IL-3, 20 ng/mL rh IL-6 and 20 ng/mL h G-CSF. DMSO or Tipifarnib is added at the concentrations of 2.5, 10, 25 and 50 nM at day 1. All cultures are performed in duplicates and the numbers of colonies are scored after 14 days of incubation at 37 °C in a humidified incubator containing 5% CO2.