Targeted Degradation of Protein Kinase A via a Stapled Peptide PROTAC.

Proteolysis-targeting chimeras (PROTACs) are bifunctional molecules that bind and recruit an E3 ubiquitin ligase to a targeted protein of interest, often through the utilization of a small molecule inhibitor. To expand the possible range of kinase targets that can be degraded by PROTACs, we sought to develop a PROTAC utilizing a hydrocarbon-stapled peptide as the targeting agent to bind the surface of a target protein of interest. In this study, we describe the development of a proteolysis-targeting chimera, dubbed Stapled Inhibitor Peptide - PROTAC or StIP-TAC, linking a hydrocarbon-stapled peptide with an E3 ligase ligand for targeted degradation of Protein Kinase A (PKA). This StIP-TAC molecule stimulated E3-mediated protein degradation of PKA, and this effect could be reversed by the addition of the proteasomal inhibitor MG-132. Further, StIP-TAC treatment led to a significant reduction in PKA substrate phosphorylation. Since many protein targets of interest lack structural features that make them amenable to small molecule targeting, development of StIP-TACs may broaden the potential range of protein targets using a PROTAC-mediated proteasomal degradation approach.

Targeting the WASF3 complex to suppress metastasis.

Wiskott-Aldrich syndrome protein family members (WASF) regulate the dynamics of the actin cytoskeleton, which plays an instrumental role in cancer metastasis and invasion. WASF1/2/3 forms a hetero-pentameric complex with CYFIP1/2, NCKAP1/1 L, Abi1/2/3 and BRK1 called the WASF Regulatory Complex (WRC), which cooperatively regulates actin nucleation by WASF1/2/3. Activation of the WRC enables actin networking and provides the mechanical force required for the formation of lamellipodia and invadopodia. Although the WRC drives cell motility essential for several routine physiological functions, its aberrant deployment is observed in cancer metastasis and invasion. WASF3 expression is correlated with metastatic potential in several cancers and inversely correlates with overall progression-free survival. Therefore, disruption of the WRC may serve as a novel strategy for targeting metastasis. Given the complexity involved in the formation of the WRC which is largely comprised of large protein-protein interfaces, there are currently no inhibitors for WASF3. However, several constrained peptide mimics of the various protein-protein interaction interfaces within the WRC were found to successfully disrupt WASF3-mediated migration and invasion. This review explores the role of the WASF3 WRC in driving metastasis and how it may be selectively targeted for suppression of metastasis.

In Silico Optimized Stapled Peptides Targeting WASF3 in Breast Cancer.

Wiskott-Aldrich Syndrome Protein Family (WASF) members regulate actin cytoskeletal dynamics, and WASF3 is directly associated with breast cancer metastasis and invasion. WASF3 forms a heteropentameric complex with CYFIP, NCKAP, ABI, and BRK1, called the WASF Regulatory Complex (WRC), which cooperatively regulates actin nucleation by WASF3. Since aberrant deployment of the WRC is observed in cancer metastasis and invasion, its disruption provides a novel avenue for targeting motility in breast cancer cells. Here, we report the development of a second generation WASF3 mimetic peptide, WAHMIS-2, which was designed using a combination of structure-guided design, homology modeling, and in silico optimization to disrupt binding of WASF3 to the WRC. WAHMIS-2 was found to permeate cells and inhibit cell motility, invasion, and MMP9 expression with greater potency than its predecessor, WAHM1. Targeted disruption of WASF3 from the WRC may serve as a useful strategy for suppression of breast cancer metastasis.