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The immune checkpoint protein B7-H4 plays an important role in the positive as well as the negative regulation of immune T-cell responses. When expressed on cancer cells, B7-H4 inhibits T-cell activity, and numerous types of cancer cells use upregulation of B7-H4 as a survival strategy. Thus, B7-H4 is a potential target for anticancer drug therapy. Unfortunately, the cell biology of this molecule has yet to be fully elucidated. Even basic properties, such as the nature of B7-H4 interactors, are controversial. In particular, the cis-inter-actors of B7-H4 on cancer cell plasma membranes have not been investigated to date. The present study used a proteomic proximity-labelling assay to investigate the molecular neighbours of B7-H4 on the surface of the human breast cancer cells SK-BR-3. By comparison to a comprehensive proteome analysis of SK-BR-3 cells, the proximity method detected a relatively small number of low abundance plasma membrane proteins highly enriched for proteins known to modulate cell adhesion and immune recognition. It may be inferred that these molecules contribute to the immunosuppressive behaviour that is characteristic of B7-H4 on cancer cells.

Infections of humans and livestock with African trypanosomes are treated with drugs introduced decades ago that are not always fully effective and often have severe side effects. Here, the trypanosome haptoglobin-haemoglobin receptor (HpHbR) has been exploited as a route of uptake for an antibody-drug conjugate (ADC) that is completely effective against Trypanosoma brucei in the standard mouse model of infection. Recombinant human anti-HpHbR monoclonal antibodies were isolated and shown to be internalised in a receptor-dependent manner. Antibodies were conjugated to a pyrrolobenzodiazepine (PBD) toxin and killed T. brucei in vitro at picomolar concentrations. A single therapeutic dose (0.25 mg/kg) of a HpHbR antibody-PBD conjugate completely cured a T. brucei mouse infection within 2 days with no re-emergence of infection over a subsequent time course of 77 days. These experiments provide a demonstration of how ADCs can be exploited to treat protozoal diseases that desperately require new therapeutics., Author summary Here we show that antibody-drug conjugates (ADCs) can be re-purposed from cancer immunotherapeutics to anti-protozoals by changing the specificity of the immunoglobulin to target a trypanosome cell surface receptor. Trypanosomes were used as a model system due to the availability of receptor null cell lines that allowed the unambiguous demonstration that ADCs targeted to a parasite surface receptor could be specifically internalised via receptor-mediated endocytosis. A single low dose of the resulting ADC was able to cure a stage 1 mouse model of trypanosome infection. We have used toxins and conjugation chemistry that are identical to anti-cancer ADCs demonstrating the ability to piggy-back onto the huge research efforts and resources that are being invested in the development of such ADCs. The potential for development of ADCs against a wide range of human pathogens is vast, where only epitope binding sites need vary in order to provide selectivity. This provides a far-reaching opportunity for the rapid development of novel anti-protozoals for the targeted killing of a wide range of pathogens that cause disease worldwide, especially in developing countries.

Antibodies that target cell-surface molecules on T cells can enhance anti-tumor immune responses, resulting in sustained immune-mediated control of cancer. We set out to find new cancer immunotherapy targets by phenotypic screening on human regulatory T (Treg) cells and report the discovery of novel activators of tumor necrosis factor receptor 2 (TNFR2) and a potential role for this target in immunotherapy. A diverse phage display library was screened to find antibody mimetics with preferential binding to Treg cells, the most Treg-selective of which were all, without exception, found to bind specifically to TNFR2. A subset of these TNFR2 binders were found to agonise the receptor, inducing iκ-B degradation and NF-κB pathway signalling in vitro. TNFR2 was found to be expressed by tumor-infiltrating Treg cells, and to a lesser extent Teff cells, from three lung cancer patients, and a similar pattern was also observed in mice implanted with CT26 syngeneic tumors. In such animals, TNFR2-specific agonists inhibited tumor growth, enhanced tumor infiltration by CD8+ T cells and increased CD8+ T cell IFN-γ synthesis. Together, these data indicate a novel mechanism for TNF-α-independent TNFR2 agonism in cancer immunotherapy, and demonstrate the utility of target-agnostic screening in highlighting important targets during drug discovery., GW, BM, SG, JC-U, AS, AG-M, CB, JJ, RL, AJL, SR, RS, LJ, VV-A, RM and RWW were funded by MedImmune; JP and VB were funded by AstraZeneca PLC; JW, RSA-L and JB were funded by NIHR Cambridge Biomedical Research Centre and Kidney Research UK; JS and JF were funded by Retrogenix Ltd.

The majority of antibody therapeutics have been isolated from target-led drug discovery, where many years of target research preceded drug program initiation. However, as the search for validated targets becomes more challenging and target space becomes increasingly competitive, alternative strategies, such as phenotypic drug discovery, are gaining favour. This review highlights successful examples of antibody phenotypic screens that have led to clinical drug candidates. We also review the requirements for performing an effective antibody phenotypic screen, including antibody enrichment and target identification strategies. Finally, the future impact of phenotypic drug discovery on antibody drug pipelines will be discussed.

Cancer stem cells (CSCs) represent an important clinical entity given their role in tumor initiation, metastasis and patient relapse. Phenotypic selection allows for identification of novel antigens important in biological processes. Therefore, we undertook a phenotypic selection campaign using a designed ankyrin-repeat (DARPin) library to identify new cancer stem cell (CSC) targets. CSCs generated from late-stage pancreatic cancer patient-derived xenograft (PDX) models were used to pan a designed Ankyrin repeat (DARPin) library. The most prevalent target identified in this screen was Annexin A2 (ANXA2). ANXA2 is a member of the Annexin family that has diverse roles in cancer including proliferation and invasion and is widely expressed in cancer. Furthermore, expression of ANXA2 is linked to poor prognosis in pancreatic cancer. Targeting of Annexin A2 on the surface of pancreatic cancer cells using DARPins resulted in decreased frequency of CSCs both in vitro and in vivo in several pancreatic patient-derived xenografts. ANXA2 DARPins also reduced proliferation and tumor growth of HPAC cells both in vitro and in vivo. Mechanistically, we found that blocking ANXA2 resulted in decreased IL6 and IL8 secretion, two cytokines that have been linked to CSC expansion and survival. Additionally, we found that pharmacological blockade of ANXA2 resulted in decreased plasmin activation, a pathway that has been linked to dissemination of cancer cells. Together our data suggests that targeting of cell surface ANXA2 is effective at reducing CSCs and could be a novel target for the treatment of pancreatic cancer. Citation Format: Elaine M. Hurt, Matt Flynn, Paul Hynes, M. Carla Cabrera, Suneetha B. Thomas, Lilian van Vlerken-Ysla, Louise Slater, Alan Sandercock, Steven Rust, Ralph Minter, Ronald Herbst. Phenotypic selection screening reveals Annexin A2 as a pancreatic cancer stem cell target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 151.

Huwentoxin-IV (HwTx-IV) is a 35-residue neurotoxin peptide with potential application as a novel analgesic. It is a member of the inhibitory cystine knot (ICK) peptide family, characterised by a compact globular structure maintained by three intramolecular disulfide bonds. Here we describe a novel strategy for producing non-tagged, fully folded ICK-toxin in a bacterial system. HwTx-IV was expressed as a cleavable fusion to small ubiquitin-related modifier (SUMO) in the cytoplasm of the SHuffle T7 Express lysY Escherichia coli strain, which allows cytosolic disulfide bond formation. Purification by IMAC with selective elution of monomeric SUMO fusion followed by proteolytic cleavage and polishing chromatographic steps yielded pure homogeneous toxin. Recombinant HwTx-IV is produced with a C-terminal acid, whereas the native peptide is C-terminally amidated. HwTx-IV(acid) inhibited Nav1.7 in a dose dependent manner (IC50 = 463-727 nM). In comparison to HwTx-IV(amide) (IC50 = 11 ± 3 nM), the carboxylate was ~50 fold less potent on Nav1.7, which highlights the impact of the C-terminus. As the amide bond of an additional amino acid may mimic the carboxamide, we expressed the glycine-extended analogue HwTx-IV(G36)(acid) in the SUMO/SHuffle system. The peptide was approximately three fold more potent on Nav1.7 in comparison to HwTx-IV(acid) (IC50 = 190 nM). In conclusion, we have established a novel system for expression and purification of fully folded and active HwTx-IV(acid) in bacteria, which could be applicable to other structurally complex and cysteine rich peptides. Furthermore, we discovered that glycine extension of HwTx-IV(acid) restores some of the potency of the native carboxamide. This finding may also apply to other C-terminally amidated peptides produced recombinantly.

Cancer stem cells (CSCs) represent an important subpopulation of tumor cells that are untouched and perhaps even expanded after chemotherapy and radiation. This population has been shown in murine models of cancer to be solely responsible for the regrowth of tumors following chemotherapy, underscoring the importance of therapeutically targeting this population. Therefore, we sought to find novel targets against CSCs using a phenotypic selection screen. Using a designed ankyrin repeat (DARpin) library, we panned cells disaggregated from tumor spheres from three patient-derived xenograft models of late stage pancreatic cancer to enrich for DARPins that bind CSCs. Once released from the cells, the DARPins were further analyzed for binding to both normal, pancreatic cancer total tumor cells and pancreatic CSCs in order to choose targets that showed either pancreatic cancer-specific or pancreatic CSC-specific binding. These DARPins were then tested in a sphere formation assay, an EZH2-based high content imaging screen, and a standard proliferation assay. Those DARPins showing good cancer-specific binding profiles were also tested for internalization and killing using a saporin-conjugated secondary antibody. Using this approach, we identified 30 DARPins of interest for either direct inhibitory antibody approaches or for potential antibody drug conjugate or nanoparticle delivery approaches. Identification of the proteins bound by each of the DARPins was done using either immunopreciptation followed by liquid chromatography tandem-mass spectrometry or through Retrogenix's cell expression microarray technology. Identified targets included known CSC antigens such as integrin alpha6 (CD49f) as well as other potentially novel targets. These results highlight the possibilities of finding therapeutic targets for CSCs and opens up an exciting possibility for novel therapies. Citation Format: Elaine M. Hurt, Matt Flynn, Suneetha Thomas, Lilian van Vlerken-Ysla, Alan Sandercock, Steven Rust, Minter Ralph, Robert Hollingsworth. Phenotypic selection screening reveals cancer stem cell therapeutic targets. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4218. doi:10.1158/1538-7445.AM2015-4218

Regulatory T cells (Treg cells) are observed within multiple tumor types and contribute to immune evasion. Effective and specific targeting of Treg cells by antibodies is hampered by the lack of a unique surface marker. With the aim of identifying such a marker, human Treg cells were isolated from peripheral blood, expanded in vitro and used as a source of antigen in phage display selections with a diverse library of designed ankyrin repeat proteins (DARPins). The resulting DARPins were screened for binding to multiple cell-types, and approximately thirty with preferential binding to Treg cells were identified. All of these DARPins were determined to bind to the third and/or fourth cysteine-rich extracellular domains of tumor necrosis factor receptor II (TNFRII, also known as TNFRSF1B or CD120b). Expression of TNFRII has previously been demonstrated on Treg cells, and TNFRII is shown here also to be expressed on CD8+ T cells following exposure to cognate antigen and on the surface of tumor-infiltrating T cells in the 4T1 mouse tumor model. Furthermore, TNFRII mRNA was detected at increased levels in tumor-infiltrating leukocytes isolated from cancer patients. Functional characterisation of the anti-TNFRII DARPins and mAbs revealed an ability to enhance T-cell activation in response to polyclonal and antigen specific stimuli, and in Treg cell suppression assays. These studies demonstrate the utility of DARPins for phenotypic selections to identify drug targets using primary human lymphocytes and highlight TNFRII as a potential therapeutic target enriched on Treg cells. Citation Format: Geoff Williams, Judith Anderton, Vahe Bedian, Jane Coates Ulrichsen, Andrea Gonzalez-Munoz, Sandrine Guillard, Olivia Harris, James Hair, Andrew Leishman, Arthur Lewis, Jacques Moissan, Ralph Minter, Bina Mistry, Julie Parmentier, Edmund Poon, Amy Popple, Steve Rust, Alan Sandercock, Ross Stewart, Viia Valge-Archer, Robert W. Wilkinson. Identification of tumor necrosis factor receptor II as a regulatory T cell target for cancer immunotherapy using designed ankyrin repeat protein phenotypic selections. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4613. doi:10.1158/1538-7445.AM2014-4613

Lung cancer is the most common type of cancer, with approximately 222,000 new cases expected each year in the United States. Approximately 72% of the individuals diagnosed with lung cancer will fall victim to the disease. Non-small cell lung cancer (NSCLC) is the most common type of lung cancer, but current treatments will not cure the disease for most patients. In an effort to identify novel therapeutics to address this unmet need, a phenotypic screening campaign was initiated. This type of target identification approach allows the discovery of novel drug targets by selection of antibodies based on their ability to elicit a specific desired phenotype. Once antibodies with the desired function are isolated, the targets to which the “hit” antibodies bind can be identified using a variety of approaches including IP-mass spec. Although phenotypic screens have been performed previously, the current effort has important advantages over those described previously. Specifically, this included the use of several unique screening assays run in parallel to allow the evaluation of multiple phenotypes simultaneously. Also unique was the use of primary material from NSCLC patients for both selection and functional screening. Specifically, we demonstrate the use of primary tumor cells in high throughput screening assays. We show the utility of incorporating novel screening assays including anoikis and spheroids with multiple endpoint readouts. Finally we provide data describing a series of “hit” antibodies isolated in the screen which had a variety of activities across the screening assays. These studies show the utility of function-first screening in the identification of unique potential therapeutic targets for oncology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 974. doi:1538-7445.AM2012-974

Background Monolayer cultures of immortalised cell lines are a popular screening tool for novel anti-cancer therapeutics, but these methods can be a poor surrogate for disease states, and there is a need for drug screening platforms which are more predictive of clinical outcome. In this study, we describe a phenotypic antibody screen using three-dimensional cultures of primary cells, and image-based multi-parametric profiling in PC-3 cells, to identify anti-cancer biologics against new therapeutic targets. Methods ScFv Antibodies and designed ankyrin repeat proteins (DARPins) were isolated using phage display selections against primary non-small cell lung carcinoma cells. The selected molecules were screened for anti-proliferative and pro-apoptotic activity against primary cells grown in three-dimensional culture, and in an ultra-high content screen on a 3-D cultured cell line using multi-parametric profiling to detect treatment-induced phenotypic changes. The targets of molecules of interest were identified using a cell-surface membrane protein array. An anti-CUB domain containing protein 1 (CDCP1) antibody was tested for tumour growth inhibition in a patient-derived xenograft model, generated from a stage-IV non-small cell lung carcinoma, with and without cisplatin. Results Two primary non-small cell lung carcinoma cell models were established for antibody isolation and primary screening in anti-proliferative and apoptosis assays. These assays identified multiple antibodies demonstrating activity in specific culture formats. A subset of the DARPins was profiled in an ultra-high content multi-parametric screen, where 300 morphological features were measured per sample. Machine learning was used to select features to classify treatment responses, then antibodies were characterised based on the phenotypes that they induced. This method co-classified several DARPins that targeted CDCP1 into two sets with different phenotypes. Finally, an anti-CDCP1 antibody significantly enhanced the efficacy of cisplatin in a patient-derived NSCLC xenograft model. Conclusions Phenotypic profiling using complex 3-D cell cultures steers hit selection towards more relevant in vivo phenotypes, and may shed light on subtle mechanistic variations in drug candidates, enabling data-driven decisions for oncology target validation. CDCP1 was identified as a potential target for cisplatin combination therapy. Electronic supplementary material The online version of this article (doi:10.1186/s12943-015-0415-0) contains supplementary material, which is available to authorized users.