Obatoclax Mesylate (GX15-070)

2 years -80 in solvent

Administered intravenously (tail vein) once a day

Human MM cells (HMCLs), peripheral blood lymphocytes (PBLs), bone marrow stromal cells (BMSCs)

ca.10 uM

Obatoclax (tartrate salt) is formulated in 9.6% polyethylene glycol 300, 0.4% polysorbate 20, and 5% dextrose, while for the 4T1 tumor model, Obatoclax is formulated at a concentration of 0.6 mg/mL in 9.48% polyethylene glycol, 0.38% polysorbate 20, 1.2 mg/mL mannitol, and 5% dextrose.

Obatoclax completely inhibits Bak recovery of Mcl-1 at 5 uM in SK-Mel5 cells and overcomes resistance to ABT-373-induced apoptosis conferred by Mcl-1 in KB/Bcl-2 cells. [1] Obatoclax is a BH3 mimetic which binds to a broad spectrum of Bcl-2 family members, including Bcl-2, Bcl-xL, and Mcl-1. Obatoclax uniquely displaces BH3 domains by activation of the pocket of Mcl-1 followed by a triggering of apoptosis mediated by oligomerization of Bak and release of cytochrome c. Obatoclax is sensitive to Bcl-xL in cell lines lacking it or showing low expression. It shows low cytotoxicity to Mcl-1, Bcl-2, and Bcl-xL in all the strongly-expressed cell lines. Obatoclax inhibits multiple myeloma (MM) cell lines (KMS12PE, KMS18, MY5, etc.) with IC50 values ranging from 52 to 1100 nM and the inhibition is umimpaired even in the presence of IL-6 or IGF-1, which are resistance to cytotoxic agents, at a concentration of 150 nM. Obatoclax enhances the antimyeloma activity induced by melphalan, dexamethasone, or bortezomib. [2] Obatoclax potentiates TRAIL (tumor necrosis factor-related apoptosis-inducing ligand)-mediated apoptosis by unsequestering Bak and Bim from Bcl-2/Bcl-xL or Mcl-1 proteins in PANC-1 and BxPC-3 cells. [3]

48-72 hours

Obatoclax is dissolved in DMSO at a stock concentration of 5 mM. Cell viability is assayed by MTT. Human MM cells (HMCLs), peripheral blood lymphocytes (PBLs), bone marrow stromal cells (BMSCs) are seeded in 96-well plates at a density of 2, 104 per well for HMCLs or 5ca.10, 103 for PBLs. Various concentrations of Obatoclax are added to the cells, with or without IGF-1 (50 ng/mL) or IL-6 (10 ng/mL). Cells are incubated for 48-72 hours and cell viability is determined.

Obatoclax Mesylate (GX15-070) is an antagonist of Bcl-2 with Ki of 0.22 μM in a cell-free assay, can assist in overcoming MCL-1 mediated resistance to apoptosis.

Obatoclax is a potential first-in-class small molecule antagonist of Bcl-2 designed to inhibit all relevant members of the Bcl-2 family of proteins, including the dominant member, Mcl-1.