In vitro activity: Sorafenib inhibits both wild-type and V599E mutant B-Raf activity with IC50 of 22 nM and 38 nM, respectively. Sorafenib also potently inhibits mVEGFR2 (Flk-1), mVEGFR3, mPDGFRβ, Flt3, and c-Kit with IC50 of 15 nM, 20 nM, 57 nM, 58 nM, and 68 nM, respectively. Sorafenib weakly inhibits FGFR-1 with IC50 of 580 nM. Sorafenib tosylate is not active against ERK-1, MEK-1, EGFR, HER-2, IGFR-1, c-Met, PKB, PKA, cdk1/cyclinB, PKCα, PKCγ, and pim-1. Sorafenib markedly inhibits VEGFR2 phosphorylation in NIH 3T3 cells with IC50 of 30 nM, and Flt-3 phosphorylation in HEK-293 cells with IC50 of 20 nM. Sorafenib potently blocks MEK 1/2 and ERK 1/2 phosphorylation in most cell lines but not in A549 or H460 cells, while having no effect on inhibition of the PKB pathway. Sorafenib inhibits the proliferation of HAoSMC and MDA-MB-231 cells with IC50 of 0.28 μM and 2.6 μM, respectively. In addition to inhibition of the RAF/MEK/ERK signaling pathway, Sorafenib significantly inhibits the phosphorylation of eIF4E and down-regulates Mcl-1 levels in hepatocellular carcinoma (HCC) cells in a MEK/ERK-independent manner. Sorafenib inhibits the proliferation of PLC/PRF/5 and HepG2 cells with IC50 of 6.3 μM and 4.5 μM, respectively, and leads to the significant induction of apoptosis.

Kinase Assay: Recombinant baculoviruses expressing Raf-1 (residues 305–648) and B-Raf (residues 409–765) are purified as fusion proteins. Full-length human MEK-1 is generated by PCR and purified as a fusion protein from Escherichia coli lysates. Sorafenib tosylate is added to a mixture of Raf-1 (80 ng), or B-Raf (80 ng) with MEK-1 (1 μg) in assay buffer [20 mM Tris (pH 8.2), 100 mM NaCl, 5 mM MgCl2, and 0.15% β-mercaptoethanol] at a final concentration of 1% DMSO. The Raf kinase assay (final volume of 50 μL) is initiated by adding 25 μL of 10 μM γ[33P]ATP (400 Ci/mol) and incubated at 32 °C for 25 minutes. Phosphorylated MEK-1 is harvested by filtration onto a phosphocellulose mat, and 1% phosphoric acid is used to wash away unbound radioactivity. After drying by microwave heating, a β-plate counter is used to quantify filter-bound radioactivity. Human VEGFR2 (KDR) kinase domain is expressed and purified from Sf9 lysates. Time-resolved fluorescence energy transfer assays for VEGFR2 are performed in 96-well opaque plates in the time-resolved fluorescence energy transfer format. Final reaction conditions are as follows: 1 to 10 μM ATP, 25 nM poly GT-biotin, 2 nM Europium-labeled phospho (p)-Tyr antibody (PY20), 10 nM APC, 1 to 7 nM cytoplasmic kinase domain in final concentrations of 1% DMSO, 50 mM HEPES (pH 7.5), 10 mM MgCl2, 0.1 mM EDTA, 0.015% Brij-35, 0.1 mg/mL BSA, and 0.1% β-mercaptoethanol. Reaction volumes are 100 μL and are initiated by addition of enzyme. Plates are read at both 615 and 665 nM on a Perkin-Elmer VictorV Multilabel counter at ~1.5 to 2.0 hours after reaction initiation. Signal is calculated as a ratio: (665 nm/615 nM) × 10,000 for each well. For IC50 generation, Sorafenib tosylate is added before the enzyme initiation. A 50-fold stock plate is made with Sorafenib tosylate serially diluted 1:3 in a 50% DMSO/50% distilled water solution. Final Sorafenib tosylate concentrations range from 10 μM to 4.56 nM in 1% DMSO.

Cell Assay: Cells (MDA-MB-231, and HAoSMC) are exposed to increasing concentrations of Sorafenib tosylate for 72 hours. Cell number is quantitated using the Cell TiterGlo ATP Luminescent assay kit. This assay measures the number of viable cells per well by measurement of luminescent signal based on amount of cellular ATP.

Cancer Res. 2004 Oct 1;64(19):7099-109; Cancer Res. 2006 Dec 15;66(24):11851-8.