Obatoclax is a direct and potent antagonist of membrane-restricted Mcl-1 and is synthetic lethal with treatment that induces Bim

Abstract

BackgroundObatoclax is a clinical stage drug candidate that has been proposed to target and inhibit prosurvival members of the Bcl-2 family, and thereby contribute to cancer cell lethality. The insolubility of this compound, however, has precluded the use of many classical drug-target interaction assays for its study. Thus, a direct demonstration of the proposed mechanism of action, and preferences for individual Bcl-2 family members, remain to be established.MethodsEmploying modified proteins and lipids, we recapitulated the constitutive association and topology of mitochondrial outer membrane Mcl-1 and Bak in synthetic large unilamellar liposomes, and measured bakdependent bilayer permeability. Additionally, cellular and tumor models, dependent on Mcl-1 for survival, were employed.ResultsWe show that regulation of bilayer permeabilization by the tBid – Mcl-1 - Bak axis closely resemblesthe tBid - Bcl-XL - Bax model. Obatoclax rapidly and completely partitioned into liposomal lipid but also rapidly exchanged between liposome particles. In this system, obatoclax was found to be a direct and potent antagonist of liposome-bound Mcl-1 but not of liposome-bound Bcl-XL, and did not directly influence Bak. A 2.5 molar excess of obatoclax relative to Mcl-1 overcame Mcl-1-mediated inhibition of tBid-Bak activation. Similar results were found for induction of Bak oligomers by Bim. Obatoclax exhibited potent lethality in a cellmodel dependent on Mcl-1 for viability but not in cells dependent on Bcl-XL. Molecular modeling predicts that the 3-methoxy moiety of obatoclax penetrates into the P2 pocket of the BH3 binding site of Mcl-1. A desmethoxy derivative of obatoclax failed to inhibit Mcl-1 in proteoliposomes and did not kill cells whose survival depends on Mcl-1. Systemic treatment of mice bearing Tsc2+/- Em-myc lymphomas (whose cells depend on Mcl-1 for survival) with obatoclax conferred a survival advantage compared to vehicle alone (median 31 days vs 22 days, respectively; p=0.003). In an Akt-lymphoma mouse model, the anti-tumor effects of obatoclax synergized with doxorubicin. Finally, treatment of the multiple myeloma KMS11 cell model (dependent on Mcl-1 for survival) with dexamethasone induced Bim and Bim-dependent lethality. As predicted for an Mcl-1 antagonist, obatoclax and dexamethasone were synergistic in this model.ConclusionsTaken together, these findings indicate that obatoclax is a potent antagonist of membranerestricted Mcl-1. Obatoclax represents an attractive chemical series to generate second generation Mcl-1 inhibitors.

Insights into Novel Drugs Targeting Bcl-2 protein as Potential Anti-cancer Agents

“…This inhibition stimulate apoptosis in cells of cancer, inhibiting tumor growth. Solubility has been a matter in the improvement of the drug (Nguyen et al, 2015).…”

Programmed Cell Death Deregulation in BCR-ABL1-Negative Myeloproliferative Neoplasms

“…Obatoclax (GX15-070) is a BH3-mimetic designed to target and counteract antiapoptotic BCL-2 proteins. Obatoclax is an MCL-1 antagonist [123] and downregulates p53, and it has a dual mechanism of action, being capable to induce apoptosis or autophagy [124]. On the other side, obatoclax accumulates in lysosomes inducing their alkalinization and inhibiting their function [125].…”

Identification of synthetic lethality based on a functional network by using machine learning algorithms

“…66,67 Genes that can be clustered into the Bcl-2 family, which also participates in catabolic processes of carbohydrate derivatives, have synthetic lethal potentials in cancer cells. 67 The molecular function, cysteine protease activity, and thiol protease activity of GO: 0008234 play a role in oncogene addiction of cancer cells, and this trait is necessary to maintain the viability of cancer cells and show potential synthetic lethality. 68 GO: 1903772 participates in the regulation of viral budding via the host endosomal sorting complex required for transport complex, thereby modulating the frequency, rate, or extent of viral budding.…”