ABSTRACT
Because of the promise of BCL-2 antagonists in combating chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphoma (NHL), interest in additional selective antagonists of antiapoptotic proteins has grown. Beginning with a series of selective, potent BCL-XL antagonists containing an undesirable hydrazone functionality, in silico design and X-ray crystallography were utilized to develop alternative scaffolds that retained the selectivity and potency of the starting compounds.
ABSTRACT
Developing potent molecules that inhibit Bcl-2 family mediated apoptosis affords opportunities to treat cancers via reactivation of the cell death machinery. We describe the hit-to-lead development of selective Bcl-XL inhibitors originating from a high-throughput screening campaign. Small structural changes to the hit compound increased binding affinity more than 300-fold (to IC50 < 20 nM). This molecular series exhibits drug-like characteristics, low molecular weights (Mw < 450), and unprecedented selectivity for Bcl-XL. Surface plasmon resonance experiments afford strong evidence of binding affinity within the hydrophobic groove of Bcl-XL. Biological experiments using engineered Mcl-1 deficient mouse embryonic fibroblasts (MEFs, reliant only on Bcl-XL for survival) and Bax/Bak deficient MEFs (insensitive to selective activation of Bcl-2-driven apoptosis) support a mechanism-based induction of apoptosis. This manuscript describes the first series of selective small-molecule inhibitors of Bcl-XL and provides promising leads for the development of efficacious therapeutics against solid tumors and chemoresistant cancer cell lines.
Subject(s)
Apoptosis/drug effects , Benzothiazoles/pharmacology , Hydrazones/pharmacology , bcl-X Protein/antagonists & inhibitors , Animals , Benzothiazoles/chemical synthesis , Benzothiazoles/metabolism , Binding, Competitive , Cell Line, Tumor , Cells, Cultured , Drug Discovery , Embryo, Mammalian/cytology , Fibroblasts/cytology , Fibroblasts/drug effects , Fibroblasts/metabolism , Hydrazones/chemical synthesis , Hydrazones/metabolism , Kinetics , Mice , Mice, Knockout , Models, Chemical , Molecular Structure , Myeloid Cell Leukemia Sequence 1 Protein/deficiency , Myeloid Cell Leukemia Sequence 1 Protein/genetics , Surface Plasmon Resonance , bcl-2 Homologous Antagonist-Killer Protein/deficiency , bcl-2 Homologous Antagonist-Killer Protein/genetics , bcl-2-Associated X Protein/deficiency , bcl-2-Associated X Protein/genetics , bcl-X Protein/chemistry , bcl-X Protein/metabolismABSTRACT
The prosurvival BCL-2 family protein BCL-X(L) is often overexpressed in solid tumors and renders malignant tumor cells resistant to anticancer therapeutics. Enhancing apoptotic responses by inhibiting BCL-X(L) will most likely have widespread utility in cancer treatment and, instead of inhibiting multiple prosurvival BCL-2 family members, a BCL-X(L)-selective inhibitor would be expected to minimize the toxicity to normal tissues. We describe the use of a high-throughput screen to discover a new series of small molecules targeting BCL-X(L) and their structure-guided development by medicinal chemistry. The optimized compound, WEHI-539 (7), has high affinity (subnanomolar) and selectivity for BCL-X(L) and potently kills cells by selectively antagonizing its prosurvival activity. WEHI-539 will be an invaluable tool for distinguishing the roles of BCL-X(L) from those of its prosurvival relatives, both in normal cells and notably in malignant tumor cells, many of which may prove to rely upon BCL-X(L) for their sustained growth.
