In vitro activity: Pelitinib displays much higher inhibitory activity against EGFR, compared with the closely related c-erbB-2, as well as other kinases such as Src, Cdk4, c-Met, Raf, and MEK/ERK, with IC50 ranging from 282 nM for Src to>20 μM for Cdk4. Consistently, Pelitinib treatment significantly inhibits the autophosphorylation of EGFR but not c-Met in A431 cells. Pelitinib potently inhibits the proliferation of normal human keratinocytes (NHEK), as well as A431 and MDA-468 tumor cells with IC50 of 61 nM, 125 nM, and 260 nM, respectively, while displaying little activity against MCF-7 cells with IC50 of 3.6 μM. Pelitinib inhibits EGF-induced phosphorylation of EGFR in A431 and NHEK cells with IC50 of 20-80 nM, as well as the phosphorylation of STAT3 with IC50 of 30-70 nM. Pelitinib at 75-500 nM also specifically inhibits the activation of AKT and ERK1/2, without affecting NF-κB pathway. In NHEK cells, Pelitinib also potently inhibits TGF-α mediated EGFR activation with IC50 of 56 nM, as well as activation of STAT3 and ERK1/2 with IC50 of 60 nM and 62 nM, respectively.

Kinase Assay: For experiments using cells in culture, A431 cells are treated with various concentrations of Pelitinib for 2.75 hours before co-incubation with 100 ng/mL EGF for 0.25 hour. Cells are washed twice with cold phosphate-buffered saline (PBS) before adding to lysis buffer (10 mM Tris, pH 7.5, 5 mM ethylenediamine tetra-acetic acid (EDTA), 150 mM NaCl, 1% Triton X-100, 1% Sodium deoxycholate, 0.1 % SDS, 1 mM PMSF, 10 mg/mL pepstatin A, 10 mg/mL leupeptin, 20 KIU/mL aprotinin, 2 mM sodium orthovanadate, and 100 mM sodium fluoride) for 20 minutes on ice, before immunoprecipitation and SDS-PAGE-immunoblotting. For immunoprecipitation, cultured cells are placed in cold lysis buffer and immediately homogenized on ice with a polytron with several pulses. The homogenate is first centrifuged at 2500 rpm (20 minutes, 4 °C) and then again at 14,000 rpm in a microcentrifuge (10 minutes, 4 °C). Supernatants (1000 μg protein) are incubated for 2 hours at 4 °C with 15 mL of EGFR polyclonal antibody. After 2 hours, 50 μL of protein G plus/protein A agarose beads is added and incubated with constant rotation for 2 hours at 4 °C. After washing with lysis buffer, beads are boiled for 2 minutes in Laemmli sample buffer. Proteins are then resolved by SDS-PAGE, transferred to immobilon membrane and probed overnight with an anti-phosphotyrosine antibody conjugated with horseradish peroxidase (HRP). Membranes are developed using the ECL reagent. Total EGFR protein is determined by stripping membranes and re-probing with receptor-specific antibodies. Quantitation of bands is done by densitometry, using ImageQuant software with a Molecular Dynamics laser transmittance scanner.

Cell Assay: Cells (NHEK, A431, MCF-7, and MDA-468) are seeded in 96-well dishes, and after 2 hours, Pelitinib is added and incubated for 5 days. After incubation, the medium is removed from each well and fresh medium (150 μL) + 1 mg/mL MTT solution (50 μL) is added. After incubation for 2 hours at 37 °C, the medium is replaced with 150 μL DMSO, and absorbance at 540 nm in each well is determined. The IC50 is calculated by linear regression of the data.

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