Synthesis of 4-Thiazolidinone Small Molecules as Potential Inhibitors of the Arp2/3 Complex

Life-essential cellular processes such as endocytosis, motility, and division rely on a cell’s ability to precisely regulate construction of actin filaments in response to external factors and signals. Intrinsically involved in this process is the Actin Related Protein 2/3 (Arp2/3) Complex, a seven-subunit ATPase that functions by nucleating a daughter branch of actin from the side of a pre-existing microfilament. Active Arp2/3 complex is necessary for the proliferation of certain metastatic cancers, and inhibition of Arp2/3 complex is emerging as a potentially useful treatment strategy for such cancers. We describe synthesis and in vitro assays of 4-thiazolidinones predicted by computational methods to inhibit of Arp2/3 Complex strongly, and therefore serve as potential lead compounds for drug development. Known Arp2/3 inhibitor CK-869 serves as the starting point for derivative synthesis. We discuss the efforts towards the synthesis of new compounds and the biochemical data collected about their potency

Synthesis of Small Molecule Derivatives of CK-666 as Potential Inhibitors of the Arp2/3 Complex

The Actin-Related Protein (Arp) 2/3 Complex is an actin nucleating factor intrinsically involved in cellular regulation of actin networks during life-essential processes such as motility. Overexpression of the Arp2/3 complex has indicated as a factor allowing the proliferation of certain metastatic cancers. This work describes the synthesis and in vitro biochemical testing of several molecules predicted by computational docking to be inhibitors of Arp2/3 Complex, and therefore of potential interest in clinical applications. The molecules are designed based off of the structure of known Arp2/3 inhibitor CK-666, which was discovered via high-throughput screening. Details of the synthesis of the tryptamine derivatives are discussed, and the bulk actin polymerization assay used to determine potency of the new compounds is discussed

\u3cem\u3eIn Vitro\u3c/em\u3e Determination of Potency of Small Molecule Inhibitors of Arp2/3 Complex

Actin is a key protein building block of actin microfilaments, which are constructed and deconstructed in response to cellular signaling pathways to regulate cellular processes such as motility, division, and endocytosis. Arp2/3 Complex is a 7-subunit protein complex that is in involved in cellular construction of branched actin networks, functioning by attaching to the side of a pre-existing actin filament and nucleating a daughter branch. Overexpression of Arp2/3 complex has been linked to the ability of certain metastatic cancers to proliferate. This work describes the synthesis and in vitro biochemical testing of several molecules predicted by computational docking to be inhibitors of Arp2/3 Complex, and therefore of potential interest in clinical applications. A bulk actin polymerization assay is used as the key method to determine the potency of inhibitor candidates. Structure-activity relationships derived from these results are also discussed

Small Molecules CK-666 and CK-869 Inhibit Actin-Related Protein 2/3 Complex by Blocking an Activating Conformational Change

SummaryActin-related protein 2/3 (Arp2/3) complex is a seven-subunit assembly that nucleates branched actin filaments. Small molecule inhibitors CK-666 and CK-869 bind to Arp2/3 complex and inhibit nucleation, but their modes of action are unknown. Here, we use biochemical and structural methods to determine the mechanism of each inhibitor. Our data indicate that CK-666 stabilizes the inactive state of the complex, blocking movement of the Arp2 and Arp3 subunits into the activated filament-like (short pitch) conformation, while CK-869 binds to a serendipitous pocket on Arp3 and allosterically destabilizes the short pitch Arp3-Arp2 interface. These results provide key insights into the relationship between conformation and activity in Arp2/3 complex and will be critical for interpreting the influence of the inhibitors on actin filament networks in vivo

The intrinsically disordered cytoplasmic tail of a dendrite branching receptor uses two distinct mechanisms to regulate the actin cytoskeleton

Dendrite morphogenesis is essential for neural circuit formation, yet the molecular mechanisms underlying complex dendrite branching remain elusive. Previous studies on the highly branched Caenorhabditis elegans PVD sensory neuron identified a membrane co-receptor complex that links extracellular signals to intracellular actin remodeling machinery, promoting high-order dendrite branching. In this complex, the claudin-like transmembrane protein HPO-30 recruits the WAVE regulatory complex (WRC) to dendrite branching sites, stimulating the Arp2/3 complex to polymerize actin. We report here our biochemical and structural analysis of this interaction, revealing that the intracellular domain (ICD) of HPO-30 is intrinsically disordered and employs two distinct mechanisms to regulate the actin cytoskeleton. First, HPO-30 ICD binding to the WRC requires dimerization and involves the entire ICD sequence, rather than a short linear peptide motif. This interaction enhances WRC activation by the GTPase Rac1. Second, HPO-30 ICD directly binds to the sides and barbed end of actin filaments. Binding to the barbed end requires ICD dimerization and inhibits both actin polymerization and depolymerization, resembling the actin capping protein CapZ. These dual functions provide an intriguing model of how membrane proteins can integrate distinct mechanisms to fine-tune local actin dynamics