Obatoclax Mesylate (GX15-070)

Obatoclax completely inhibits Bak recovery of Mcl-1 at 5 μM 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. ^[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]

Obatoclax also exhibits high antitumor activity in SCID mice bearing human C33A cerivical carcinoma tumors at a dose of 0.5 mg/kg. ^[1]

• Bcl-2 Binding affinity calculation

  A predicted binding affinity for Obatoclax binding to BCL-2 is calculated using the SIE scoring function. ^[4] As a control in determining the reliability of the calculation, predicted binding affinities K_i) are calculated for a set of 12 small molecules with experimentally measured binding affinities to BCL-2.

• Cell lines

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

• Concentrations

  ~10 μM

• Incubation Time

  48-72 hours

• Method

  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 5~10 × 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.

• Animal Models

  Female BALB/c or CB17 SCID/SCID mice bearing SW480, C33A, PC3, and 4T1 cells are used.

• Dosages

  0.0313, 0.25, 0.5 and 2 mg/kg

• Administration

  Administered intravenously (tail vein) once a day