Manipulating PTPRD function with ectodomain antibodies.

Protein tyrosine phosphatases (PTPs) are critical regulators of signal transduction but have yet to be exploited fully for drug development. Receptor protein tyrosine phosphatase δ (RPTPδ/PTPRD) has been shown to elicit tumor-promoting functions, including elevating SRC activity and promoting metastasis in certain cell contexts. Dimerization has been implicated in the inhibition of receptor protein tyrosine phosphatases (RPTPs). We have generated antibodies targeting PTPRD ectodomains with the goal of manipulating their dimerization status ectopically, thereby regulating intracellular signaling. We have validated antibody binding to endogenous PTPRD in a metastatic breast cancer cell line, CAL51, and demonstrated that a monoclonal antibody, RD-43, inhibited phosphatase activity and induced the degradation of PTPRD. Similar effects were observed following chemically induced dimerization of its phosphatase domain. Mechanistically, RD-43 triggered the formation of PTPRD dimers in which the phosphatase activity was impaired. Subsequently, the mAb-PTPRD dimer complex was degraded through lysosomal and proteasomal pathways, independently of secretase cleavage. Consequently, treatment with RD-43 inhibited SRC signaling and suppressed PTPRD-dependent cell invasion. Together, these findings demonstrate that manipulating RPTP function via antibodies to the extracellular segments has therapeutic potential.

A synthetic KLHL20 ligand to validate CUL3KLHL20 as a potent E3 ligase for targeted protein degradation.

Targeted protein degradation (TPD) has risen as a promising therapeutic modality. Leveraging the catalytic nature of the ubiquitin-proteasome enzymatic machinery, TPD exhibits higher potency to eliminate disease-causing target proteins such as oncogenic transcription factors that may otherwise be difficult to abrogate by conventional inhibitors. However, there are challenges that remain. Currently, nearly all degraders engage CUL4CRBN or CUL2VHL as the E3 ligase for target ubiquitination. While their immediate efficacies are evident, the narrowed E3 ligase options make TPD vulnerable to potential drug resistance. In addition, E3 ligases show differential tissue expression and have intrinsic limitations in accessing varying types of disease-relevant targets. As the success of TPD is closely associated with the ability of E3 ligases to efficiently polyubiquitinate the target of interest, the long-term outlook of TPD drug development will depend on whether E3 ligases such as CUL4CRBN and CUL2VHL are accessible to the targets of interest. To overcome these potential caveats, a broad collection of actionable E3 ligases is required. Here, we designed a macrocyclic degrader engaging CUL3KLHL20 for targeting BET proteins and validated CUL3KLHL20 as an E3 ligase system suitable for TPD. This work thus contributes to the expansion of usable E3 ligases for potential drug development.

Inhibition of oncogenic Wnt signaling through direct targeting of ß-catenin.

Aberrant activation of signaling by the Wnt pathway is strongly implicated in the onset and progression of numerous types of cancer. Owing to the persistent dependence of these tumors on Wnt signaling for growth and survival, inhibition of this pathway is considered an attractive mechanism-based therapeutic approach. Oncogenic activation of Wnt signaling can ensue from a variety of distinct aberrations in the signaling pathway, but most share the common feature of causing increased cellular levels of ß-catenin by interfering with its constitutive degradation. ß-Catenin serves as a central hub in Wnt signaling by engaging in crucial protein-protein interactions with both negative and positive effectors of the pathway. Direct interference with these protein-protein interactions is a biologically compelling approach toward suppression of ß-catenin hyperactivity, but such interactions have proven intransigent with respect to small-molecule targeting. Hence ß-catenin remains an elusive target for translational cancer therapy. Here we report the discovery of a hydrocarbon-stapled peptide that directly targets ß-catenin and interferes with its ability to serve as a transcriptional coactivator for T-cell factor (TCF) proteins, the downstream transcriptional regulators of the Wnt pathway.

Protein-templated peptide ligation.

Molecular templates bind particular reactants, thereby increasing their effective concentrations and accelerating the corresponding reaction. This concept has been successfully applied to a number of chemical problems with a strong focus on nucleic acid templated reactions. We present the first protein-templated reaction that allows N-terminal linkage of two peptides. In the presence of a protein template, ligation reactions were accelerated by more than three orders of magnitude. The templated reaction is highly selective and proved its robustness in a protein-labeling reaction that was performed in crude cell lysate.

Plasma cells in human pancreatic ductal adenocarcinoma secrete antibodies against self-antigens.

Intratumoral B cell responses are associated with more favorable clinical outcomes in human pancreatic ductal adenocarcinoma (PDAC). However, the antigens driving these B cell responses are largely unknown. We sought to discover these antigens by using single-cell RNA sequencing (scRNA-Seq) and immunoglobulin (Ig) sequencing of tumor-infiltrating immune cells from 7 primary PDAC samples. We identified activated T and B cell responses and evidence of germinal center reactions. Ig sequencing identified plasma cell (PC) clones expressing isotype-switched and hypermutated Igs, suggesting the occurrence of T cell-dependent B cell responses. We assessed the reactivity of 41 recombinant antibodies that represented the products of 235 PCs and 12 B cells toward multiple cell lines and PDAC tissues and observed frequent staining of intracellular self-antigens. Three of these antigens were identified: the filamentous actin (F-actin), the nucleic protein RuvB like AAA ATPase 2 (RUVBL2), and the mitochondrial protein heat shock protein family D (Hsp60) member 1 (HSPD1). Antibody titers against F-actin and HSPD1 were substantially elevated in the plasma of patients with PDAC compared with healthy donors. Thus, PCs in PDAC produce autoantibodies reacting with intracellular self-antigens, which may result from promotion of preexisting, autoreactive B cell responses. These observations indicate the chronic inflammatory microenvironment of PDAC can support the adaptive immune response.

Amino-Acid-Catalyzed Direct Aldol Bioconjugation.

A site-specific bioconjugation was developed based on direct aldol coupling using amino-acid-derived organocatalysts. The functionalization exhibits fast kinetics and occurs under mild, biocompatible conditions (viz., aqueous media, moderate temperature, and neutral pH). The resulting bioconjugates were found to be stable toward abundant aldolase enzymes, as well as acidic and basic pH. The methodology was demonstrated through conjugation of a variety of small molecules, dyes, and peptides to proteins, including a single-domain antibody, which was then used for cellular imaging.

Neutrophil extracellular traps produced during inflammation awaken dormant cancer cells in mice.

Cancer cells from a primary tumor can disseminate to other tissues, remaining dormant and clinically undetectable for many years. Little is known about the cues that cause these dormant cells to awaken, resume proliferating, and develop into metastases. Studying mouse models, we found that sustained lung inflammation caused by tobacco smoke exposure or nasal instillation of lipopolysaccharide converted disseminated, dormant cancer cells to aggressively growing metastases. Sustained inflammation induced the formation of neutrophil extracellular traps (NETs), and these were required for awakening dormant cancer. Mechanistic analysis revealed that two NET-associated proteases, neutrophil elastase and matrix metalloproteinase 9, sequentially cleaved laminin. The proteolytically remodeled laminin induced proliferation of dormant cancer cells by activating integrin α3ß1 signaling. Antibodies against NET-remodeled laminin prevented awakening of dormant cells. Therapies aimed at preventing dormant cell awakening could potentially prolong the survival of cancer patients.

eUnaG: a new ligand-inducible fluorescent reporter to detect drug transporter activity in live cells.

The absorption, distribution, metabolism and excretion (ADME) of metabolites and toxic organic solutes are orchestrated by the ATP-binding cassette (ABC) transporters and the organic solute carrier family (SLC) proteins. A large number of ABC and SLC transpoters exist; however, only a small number have been well characterized. To facilitate the analysis of these transporters, which is important for drug safety and physiological studies, we developed a sensitive genetically encoded bilirubin (BR)-inducible fluorescence sensor (eUnaG) to detect transporter-coupled influx/efflux of organic compounds. This sensor can be used in live cells to measure transporter activity, as excretion of BR depends on ABC and SLC transporters. Applying eUnaG in functional RNAi screens, we characterize l(2)03659 as a Drosophila multidrug resistant-associated ABC transporter.

Design and validation of a neutral protein scaffold for the presentation of peptide aptamers.

Peptide aptamers are peptides constrained and presented by a scaffold protein that are used to study protein function in cells. They are able to disrupt protein-protein interactions and to constitute recognition modules that allow the creation of a molecular toolkit for the intracellular analysis of protein function. The success of peptide aptamer technology is critically dependent on the performance of the scaffold. Here, we describe a rational approach to the design of a new peptide aptamer scaffold. We outline the qualities that an ideal scaffold would need to possess to be broadly useful for in vitro and in vivo studies and apply these criteria to the design of a new scaffold, called STM. Starting from the small, stable intracellular protease inhibitor stefin A, we have engineered a biologically neutral scaffold that retains the stable conformation of the parent protein. We show that STM is able to present peptides that bind to targets of interest, both in the context of known interactors and in library screens. Molecular tools based on our scaffold are likely to be used in a wide range of studies of biological pathways, and in the validation of drug targets.

PAPTi: a peptide aptamer interference toolkit for perturbation of protein-protein interaction networks.

Signaling proteins often form dynamic protein-protein interaction (PPI) complexes to achieve multi-functionality. Methods to abrogate a subset of PPI interfaces without depleting the full-length protein will be valuable for structure-function relationship annotations. Here, we describe the use of Peptide Aptamer Interference (PAPTi) approach for structure-function network studies. We identified peptide aptamers against Dishevelled (Dsh) and ß-catenin (ß-cat) to target the Wnt signaling pathway and demonstrate that these FN3-based MONOBODYs (FNDYs) can be used to perturb protein activities both in vitro and in vivo. Further, to investigate the crosstalk between the Wnt and Notch pathways, we isolated FNDYs against the Notch Ankyrin (ANK) region and demonstrate that perturbing the ANK domain of Notch increases the inhibitory activity of Notch towards Wnt signaling. Altogether, these studies demonstrate the power of the PAPTi approach to dissect specific PPI interactions within signaling networks.