Differential scanning fluorimetry as secondary screening platform for small molecule inhibitors of Bcl-XL

• Published in: Cell cycle (Georgetown, Tex.) Vol. 8; no. 23; pp. 3943 - 3952
• Main Authors: Wan, Kah Fei, Wang, Sifang, Brown, Christopher J., Yu, Victor C., Entzeroth, Michael, Lane, David P., Lee, May Ann
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 01.12.2009
• Subjects: Amino Acid Sequence; bcl-X Protein - antagonists & inhibitors; bcl-X Protein - metabolism; Binding; Biology; Bioscience; Calcium; Cancer; Cell; Cycle; Drug Design; Fluorescence Polarization - methods; Glutathione Transferase - chemistry; Glutathione Transferase - metabolism; High-Throughput Screening Assays; Landes; Molecular Sequence Data; Organogenesis; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Proteins; Proto-Oncogene Proteins - chemistry; Proto-Oncogene Proteins - metabolism; Small Molecule Libraries; Temperature
• ISSN: 1538-4101; 1551-4005
• DOI: 10.4161/cc.8.23.10114

Since apoptosis is impaired in malignant cells overexpressing prosurvival Bcl-2 proteins, drugs mimicking their natural antagonists, BH3-only proteins, might overcome chemoresistance. Small molecule inhibitors of Bcl-X L function have been discovered from diverse structure classes using rational drug design as well as high-throughput screening (HTS) approaches. However, most of the BH3 mimetics that have been identified via screening based on fluorescence polarization displayed an affinity for their presumed protein targets that is far lower than that of BH3-only proteins.  Therefore, it is important to establish a simple and inexpensive secondary platform for hit validation which is pertinent to current efforts for developing compounds that mimic the action of BH3-only proteins as novel anticancer agents. These considerations prompted us to explore the differential scanning fluorimetry (DSF) method that is based on energetic coupling between ligand binding and protein unfolding. We have systematically tested known Bcl-X L /Bcl-2 inhibitors using DSF and have revealed distinct subsets of inhibitors. More importantly, we report that some of these inhibitors interacted selectively with glutathione S-transferase tagged Bcl-X L , whereas certain inhibitors exhibited marked selectivity towards native untagged Bcl-X L . Therefore, we propose that the affinity tag may cause a significant conformational switch in the Bcl-X L , which results in the selectivity for certain subsets of small molecule inhibitors. This finding also implies that the previous screens involving tagged proteins need to be carefully reexamined while further investigations must ensure that the right conformation of protein is used in future screens.