In vitro activity: KX2-391 is a Src inhibitor that is directed to the Src substrate pocket. KX2-391 shows steep dose-response curves against Huh7 (GI 50 = 9 nM), PLC/PRF/5 (GI 50 = 13 nM), Hep3B (GI 50 = 26 nM), and HepG2 (GI 50 = 60 nM), four hepatic cell cancer (HCC) cell lines. KX2-391 is found to inhibit certain leukemia cells that are resistant to current commercially available drugs, such as those derived from chronic leukemia cells with the T3151 mutation. KX2-391 is evaluated in engineered Src driven cell growth assays inNIH3T3/c-Src527F and SYF/c-Src527F cells and exhibits GI50 with 23 nM and 39 nM, respectively.

Kinase Assay: Tirbanibulin (KX2-391) is a Src inhibitor that is directed to the Src substrate pocket. Tirbanibulin (KX2-391) shows steep dose-response curves against Huh7 (GI50=9 nM), PLC/PRF/5 (GI50=13 nM), Hep3B (GI50=26 nM), and HepG2 (GI50=60 nM), four hepatic cell cancer (HCC) cell lines.

Cell Assay: Liver cell lines including Huh7, PLC/PRF/5, Hep3B, and HepG2 (NutriCyte, Buffalo, NY) are routinely cultured and maintained in basal medium containing 2% fetal bovine serum (FBS) at 37 °C and 5% CO2. Cells are seeded at 4.0 × 103/190 μL and 8.0 × 103/190 μL per well of 96-well plate in basal medium containing 1.5% FBS. These are cultured overnight at 37 °C and 5% CO2 prior to the addition of KX2-391, at concentrations ranging from 6,564 to 0.012 nM in triplicates. Treated cells are incubated for 3 days. Ten microliters of 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution (5 mg/mL) is then added to each well on day 3 and cells incubated for 4 hours. The formazan product is dissolved with 10% SDS in dilute HCl. Optical density at 570 nm is measured by using BioTek Synergy HT multiplatform microplate reader. For comparison of activity and potency, parallel experiments are performed using KX2-391. Growth inhibition curves, 50% inhibition concentration (GI50), and 80% inhibition concentration (GI80) are determined using GraphPad Prism 5 statistical software. Data are normalized to represent percentage of maximum response as well as reported in optical density at wavelength of 570 nm (OD570) signal format.