This cell-permeable antiapoptotic agent (FWfree-base = 317.39 g/mol; FWmesylate-salt = 413.49 g/mol; CAS 803712-79-0; Solubility: 83 mg/mL DMSO, also known as GX15-070 and (Z)-2-(5-((3,5-dimethyl-1H-pyrrol-2- yl)methylene)-4-methoxy-5H-pyrrol-2-yl)-1H-indole mesylate, is a pan- Bcl-2 antagonist (Ki = 0.22 μM), binding to the BH3-binding groove of the B-cell lymphoma-2 (i.e., Bcl) family of proteins. Bcl-2 proteins confer a protective effect on malignant cells against death signals of apoptosis, and cancer cells that are resistant to various anti-cancer drugs and treatment regimen are often found to overexpress these Bcl-2, Bcl-XL, Mcl-1, Bcl-w, and A1/Bfl1. Obatoclax inhibits the binding of Bak to Mcl-1, up-regulating Bim, inducing cytochrome c release, and activating capase-3 in human myeloma cell lines. Acting as a single agent, it also induces potent cytotoxic responses against diverse patient-derived neoplasias, including multiple myeloma. Obatoclax retains its efficacy in cells overexpressing the P-glycoprotein multidrug-resistance transporter (P-gp), multidrug resistance-associated protein 2 (MRP2), or breast cancer resistance protein (BCRP) and might also act as a perpetrator drug in interactions with drugs, for example being substrates of CYP1A2 or BCRP. In human pharmacokinetic experiments, Obatoclax has Cmax of 10 to 80 ng/mL, below the level needed for effective in vitro activity against most tumor targets, a finding that is consistent with its failure to reach levels in a mouse xenograft tumor model sufficient to disrupt Mcl-1/Bax protein-protein interaction.
