Rebastinib (DCC-2036) Bcr-Abl inhibitor

A conformational control inhibitor of Abl1 and T315I Abl1.

Rebastinib (DCC-2036) shows potent inhibitory activities against purified native Abl1 in unphosphorylated (u-Abl1^native) and phosphorylated (p-Abl1^native) forms, unphosphorylated and phosphorylated gatekeeper mutant Abl1^T315I, and the activation loop mutant Abl1^H396P in a non-ATP-competitive manner with IC50 values of 0.8 nM, 2 nM, 1.4 nM, 5 nM, and 4 nM, respectively. Moreover, it also inhibits the Src family kinases Src, LYN, FGR, and HCK, and the receptor TKs KDR, FLT3, and TIE2 with IC50 values of 34 nM, 29 nM, 38 nM, 40 nM, 4 nM, 2 nM and 6 nM, respectively. [1] This compound shows anti-proliferative activities against Ba/F3 cells expressing native or mutant Bcr-Abl1 with IC50 ranging from 2 nM to 150 nM. In addition, it also inhibits proliferation of the Ph⁺ cell line K562 (IC50 5.5 nM), and induces apoptosis in both Bcr-Abl1-expressing Ba/F3 and K562 cells potently. [1] A recent study shows that it exhibits selectivity for growth inhibition of Bcr-Abl-positive cells by its marked inhibition of CML cell lines compared to non-CML leukemia lines. [2]

Assay of Abl1 kinase isoforms and determination of inhibitor potency

Activity of u-Abl1native is determined by following the production of ADP from the kinase reaction through coupling with the pyruvate kinase/lactate dehydrogenase system. In this assay, the oxidation of NADH (measured as a decreased A340nm) is continuously monitored spectrophotometrically. The final reaction mixture (100 μL, in a 384-well Corning plate) is prepared as follows: An Abl1 kinase/coupled assay components mixture is prepared containing u-Abl1 kinase (1 nM), Abltide (EAIYAAPFAKKK, 0.2 mM), MgCl₂ (9 mM), pyruvate kinase (~ 4 units), lactate dehydrogenase (~ 0.7 units), phosphoenol pyruvate (1 mM), and NADH (0.28 mM) in 90 mM Tris containing 0.1 % octyl-glucoside and 1 % DMSO, pH 7.5. Separately, an inhibitor mixture is prepared containing Rebastinib (DCC-2036) serially diluted 3-fold in DMSO followed by dilution into buffer composed of 180 mM Tris, pH 7.5, containing MgCl₂ (18 mM) and 0.2 % octyl-glucoside. Fifty μL of the inhibitor mixture is mixed with 50 μL of the above Abl1 kinase/coupled assay components mixture, which is then incubated at 30 °C for 2 hours before 2 μL of 25 mM ATP (500 μM, final) is added to start the reaction. The reaction is recorded every 2 minutes for 2.5 hours at 30 °C on a Polarstar Optima or Synergy2 plate reader. Reaction rate (slope) is calculated using the 1 to 2 hour time frame with reader's software. Percent inhibition is obtained by comparison of reaction rate with that of a DMSO control. IC50 values are calculated from a series of percent inhibition values determined at a range of inhibitor concentrations using GraphPad Prism. The kinase assay for Abl1T315I, p-Abl1native or Abl1H396P is assayed the same as above except that 2.2 nM Abl1T315I, 1 nM p-Abl1 native or 1.3 nM Abl1H396P is used. The above assay format is also used for kinases other than Abl1 with the exception of TIE2, for which a fluorescence polarization/Transcreener format is used. The assay conditions are the same as described above except that PolyE4Y (final 1 mg/mL) is used as the substrate and one hour preincubation is used.

In a mouse allograft model bearing Ba/F3-Bcr-Abl1T315I leukemia cells, treatment with Rebastinib (DCC-2036) by oral gavage at 100 mg/kg once daily effectively inhibits Bcr-Abl1 signaling and significantly prolongs mouse survival. [1]