Four and a half LIM protein 1: a partner for KCNA5 in human atrium.

AIMS: Protein-protein interactions are critical for the normal membrane trafficking, localization, and function of voltage-gated ion channels. In human heart, the Shaker-related voltage-gated K(+) channel KCNA5 alpha-subunit forms the major basis of an atrial-specific, ultra-rapid delayed rectifier K(+) current, I(Kur). We sought to identify proteins that interact with KCNA5 in human atrium and investigate their role in the I(Kur) complex. METHODS AND RESULTS: Using a glutathione-S-transferase (GST)-KCNA5 C-terminal fusion protein and mass spectrometry-based methods, the scaffolding protein four and a half LIM (for Lin-11, Isl-1, and Mec3) protein 1 (FHL1) was identified as a potential protein partner for KCNA5. Immunoprecipitation experiments confirmed a physical interaction of FHL1 with the K(+) channel complex in human atrium, as well as in Chinese hamster ovary (CHO) cells transfected with both KCNA5 and FHL1. In cotransfected cells, confocal microscopy demonstrated areas of colocalization after immunolabelling both proteins. To investigate the functional effects of this interaction, K(+) currents were recorded in CHO cells transfected with KCNA5 in the absence and presence of FHL1 coexpression. With coexpression of FHL1, K(+) current density was markedly increased, compared with cells expressing KCNA5 alone. This effect was associated with a shift in the voltage dependence of K(+) channel activation to more positive potentials, consistent with findings of I(Kur) in atrial myocytes. FHL1 also increased the extent and speed of K(+) current slow inactivation, with additional effects on the voltage dependence and recovery of this process. CONCLUSION: These results support a role of FHL1 as a key molecular component in the I(Kur) complex in human atrium, where it likely regulates functional expression of KCNA5.

Discovery of Quinazolines That Activate SOS1-Mediated Nucleotide Exchange on RAS.

Proteins in the RAS family are important regulators of cellular signaling and, when mutated, can drive cancer pathogenesis. Despite considerable effort over the last 30 years, RAS proteins have proven to be recalcitrant therapeutic targets. One approach for modulating RAS signaling is to target proteins that interact with RAS, such as the guanine nucleotide exchange factor (GEF) son of sevenless homologue 1 (SOS1). Here, we report hit-to-lead studies on quinazoline-containing compounds that bind to SOS1 and activate nucleotide exchange on RAS. Using structure-based design, we refined the substituents attached to the quinazoline nucleus and built in additional interactions not present in the initial HTS hit. Optimized compounds activate nucleotide exchange at single-digit micromolar concentrations in vitro. In HeLa cells, these quinazolines increase the levels of RAS-GTP and cause signaling changes in the mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway.

Discovery and biological characterization of potent myeloid cell leukemia-1 inhibitors.

Myeloid cell leukemia 1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family of proteins that when overexpressed is associated with high tumor grade, poor survival, and resistance to chemotherapy. Mcl-1 is amplified in many human cancers, and knockdown of Mcl-1 using RNAi can lead to apoptosis. Thus, Mcl-1 is a promising cancer target. Here, we describe the discovery of picomolar Mcl-1 inhibitors that cause caspase activation, mitochondrial depolarization, and selective growth inhibition. These compounds represent valuable tools to study the role of Mcl-1 in cancer and serve as useful starting points for the discovery of clinically useful Mcl-1 inhibitors. PDB ID CODES: Comp. 2: 5IEZ; Comp. 5: 5IF4.

Identification and Optimization of Anthranilic Acid Based Inhibitors of Replication Protein†A.

Replication protein A (RPA) is an essential single-stranded DNA (ssDNA)-binding protein that initiates the DNA damage response pathway through protein-protein interactions (PPIs) mediated by its 70N domain. The identification and use of chemical probes that can specifically disrupt these interactions is important for validating RPA as a cancer target. A high-throughput screen (HTS) to identify new chemical entities was conducted, and 90 hit compounds were identified. From these initial hits, an anthranilic acid based series was optimized by using a structure-guided iterative medicinal chemistry approach to yield a cell-penetrant compound that binds to RPA70N with an affinity of 812 nm. This compound, 2-(3- (N-(3,4-dichlorophenyl)sulfamoyl)-4-methylbenzamido)benzoic acid (20 c), is capable of inhibiting PPIs mediated by this domain.

Discovery of tricyclic indoles that potently inhibit Mcl-1 using fragment-based methods and structure-based design.

Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family of proteins that is overexpressed and amplified in many cancers. Overexpression of Mcl-1 allows cancer cells to evade apoptosis and contributes to the resistance of cancer cells to be effectively treated with various chemotherapies. From an NMR-based screen of a large fragment library, several distinct chemical scaffolds that bind to Mcl-1 were discovered. Here, we describe the discovery of potent tricyclic 2-indole carboxylic acid inhibitors that exhibit single digit nanomolar binding affinity to Mcl-1 and greater than 1700-fold selectivity over Bcl-xL and greater than 100-fold selectivity over Bcl-2. X-ray structures of these compounds when complexed to Mcl-1 provide detailed information on how these small-molecules bind to the target, which was used to guide compound optimization.