In vitro activity: Poziotinib specifically inhibits the cell growth in HER2 amplified gastric cancer cells, and inhibits the phosphorylation of EGFR and key components of downstream signaling cascades such as STAT3, AKT and ERK. Poziotinib also induces apoptosis and G1 cell cycle arrest by activating the mitochondrial pathway in HER2 amplified gastric cancer cells. Furthermore, Poziotinib also exerts synergistic effects with chemotherapeutic agents in both HER2 amplified and HER2 non-amplified gastric cancer cells.

Kinase Assay: To determine the IC50 values of HM781-36B for kinase inhibition, enzymes of EGFR, HER2, and HER4 are expressed as recombinant proteins in Sf9 insect cells. Enzyme selectivity screening is then performed using a tyrosine kinase assay kit. Briefly, the reactions are performed in 96 well polystyrene round-bottomed plates containing kinase buffer composed of 100 mM HEPES (pH 7.4), 25 mM MgCl2, 10 mM MnCl2 and 250 μM Na3VO4. The reactions are initiated by the addition of 100 ng/assay enzyme, 100 μM ATP, and 10 ng/mL poly(Glu, Tyr). After 1 h of incubation at room temperature, the reactions are terminated by adding 6 mM EDTA solution and then anti-phosphotyrosine antibody, PTK Green Tracer, and FP dilution buffer mixtures. The fluorescence polarization values are then measured after 30 min at room temperature using a Victor3 microplate reader. Finally, the IC50 values were calculated using the following equation: Y = bottom + (top–bottom)/(1 + 10(X-logIC50)).

Cell Assay: Viable cell growth is determined by an MTT reduction assay. Briefly, all cell lines (SNU-1, 5, 16, 216, 484, 601, 620, 638, 668, 719, N87 and AGS) are seeded at a density of 3 × 103 per well in 96-well culture plates and then incubated at 37 °C for 24 h. The cells are then treated with 0.001, 0.01, 0.1, or 10 μM of HM781-36B. Three days later, 50 μg of MTT are added to each well and the samples are then incubated for 4 h to reduce the dye. Next, the samples are treated with DMSO, after which the absorbance of the converted dye in the living cells is measured at a wavelength of 540 nm. Six replicate wells are used for each analysis, and at least three independent experiments are conducted. Data points shown represent the mean while bars represent the SE.

Cancer Lett. 2011 Mar 28;302(2):155-65; Int J Cancer. 2012 May 15;130(10):2445-54.