Species-Crossreactive scFv Against the Tumor Stroma Marker “Fibroblast Activation Protein” Selected by Phage Display From an Immunized FAP−/− Knock-Out Mouse

Mechanistic Characterization of Cancer-associated Fibroblast Depletion via an Antibody-Drug Conjugate Targeting Fibroblast Activation Protein

Cancer-associated fibroblasts (CAF) are a prominent cell type within the tumor microenvironment (TME) where they are known to promote cancer cell growth and survival, angiogenesis, drug resistance, and immunosuppression. The transmembrane prolyl protease fibroblast activation protein (FAP) is expressed on the surface of highly protumorigenic CAFs found in the stroma of nearly every cancer of epithelial origin. The widespread expression of FAP has made it an attractive therapeutic target based on the underlying hypothesis that eliminating protumorigenic CAFs will disrupt the cross-talk between components of TME resulting in cancer cell death and immune infiltration. This hypothesis, however, has never been directly proven. To eliminate FAP-expressing CAFs, we developed an antibody-drug conjugate using our anti-FAP antibody, huB12, coupled to a monomethyl auristatin E (huB12-MMAE) payload. After determining that huB12 was an effective targeting vector, we found that huB12-MMAE potently eliminated FAP-expressing cells as monocultures in vitro and significantly prolonged survival in vivo using a xenograft engineered to overexpress FAP. We investigated the effects of selectively eliminating CAFs using a layered, open microfluidic cell coculture platform, known as the Stacks. Analysis of mRNA and protein expression found that treatment with huB12-MMAE resulted in the increased secretion of the proinflammatory cytokines IL6 and IL8 by CAFs and an associated increase in expression of proinflammatory genes in cancer cells. We also detected increased secretion of CSF1, a cytokine involved in myeloid recruitment and differentiation. Our findings suggest that the mechanism of FAP-targeted therapies is through effects on the immune microenvironment and antitumor immune response.

SIGNIFICANCE

The direct elimination of FAP-expressing CAFs disrupts the cross-talk with cancer cells leading to a proinflammatory response and alterations in the immune microenvironment and antitumor immune response.

Nanobody-based trispecific T cell engager (Nb-TriTE) enhances therapeutic efficacy by overcoming tumor-mediated immunosuppression

BACKGROUND

T cell engagers (TCEs) have been established as an emerging modality for hematologic malignancies, but solid tumors remain refractory. However, the upregulation of programmed cell death 1 (PD-1) is correlated with T cell dysfunction that confer tumor-mediated immunosuppression. Developing a novel nanobody-based trispecific T cell engager (Nb-TriTE) would be a potential strategy to improve therapeutic efficacy.

METHODS

Given the therapeutic potential of nanobodies (Nbs), we first screened Nb targeting fibroblast activation protein (FAP) and successfully generated a Nb-based bispecific T cell engager (Nb-BiTE) targeting FAP. Then, we developed a Nb-TriTE by fusing an anti-PD-1 Nb to the Nb-BiTE. The biological activity and antitumor efficacy of the Nb-TriTE were evaluated in vitro and in both cell line-derived and patient-derived xenograft mouse models.

RESULTS

We had for the first time successfully selected a FAP Nb for the generation of novel Nb-BiTE and Nb-TriTE, which showed good binding ability to their targets. Nb-TriTE not only induced robust tumor antigen-specific killing, potent T cell activation and enhanced T cell function in vitro, but also suppressed tumor growth, improved survival and mediated more T cell infiltration than Nb-BiTE in mouse models of different solid tumors without toxicity.

CONCLUSIONS

This novel Nb-TriTE provides a promising and universal platform to overcome tumor-mediated immunosuppression and improve patient outcomes in the future.

Generation and in vivo validation of an IL-12 fusion protein based on a novel anti-human FAP monoclonal antibody

BACKGROUND

In this study, we describe the generation of a fully human monoclonal antibody (named '7NP2') targeting human fibroblast activation protein (FAP), an antigen expressed in the microenvironment of different types of solid neoplasms.

METHODS

7NP2 was isolated from a synthetic antibody phage display library and was improved by one round of mutagenesis-based affinity maturation. The tumor recognition properties of the antibody were validated by immunofluorescence procedures performed on cancer biopsies from human patients. A fusion protein consisting of the 7NP2 antibody linked to interleukin (IL)-12 was generated and the anticancer activity of the murine surrogate product (named mIL12-7NP2) was evaluated in mouse models. Furthermore, the safety of the fully human product (named IL12-7NP2) was evaluated in Cynomolgus monkeys.

RESULTS

Biodistribution analysis in tumor-bearing mice confirmed the ability of the product to selectively localize to solid tumors while sparing healthy organs. Encouraged by these results, therapy studies were conducted in vivo, showing a potent antitumor activity in immunocompetent and immunodeficient mouse models of cancer, both as single agent and in combination with immune checkpoint inhibitors. The fully human product was tolerated when administered to non-human primates.

CONCLUSIONS

The results obtained in this work provided a rationale for future clinical translation activities using IL12-7NP2.

Advances in CAR-T Cell Genetic Engineering Strategies to Overcome Hurdles in Solid Tumors Treatment

During this last decade, adoptive transfer of T lymphocytes genetically modified to express chimeric antigen receptors (CARs) emerged as a valuable therapeutic strategy in hematological cancers. However, this immunotherapy has demonstrated limited efficacy in solid tumors. The main obstacle encountered by CAR-T cells in solid malignancies is the immunosuppressive tumor microenvironment (TME). The TME impedes tumor trafficking and penetration of T lymphocytes and installs an immunosuppressive milieu by producing suppressive soluble factors and by overexpressing negative immune checkpoints. In order to overcome these hurdles, new CAR-T cells engineering strategies were designed, to potentiate tumor recognition and infiltration and anti-cancer activity in the hostile TME. In this review, we provide an overview of the major mechanisms used by tumor cells to evade immune defenses and we critically expose the most optimistic engineering strategies to make CAR-T cell therapy a solid option for solid tumors.

A novel anti-tumor/anti-tumor-associated fibroblast/anti-mPEG tri-specific antibody to maximize the efficacy of mPEGylated nanomedicines against fibroblast-rich solid tumor

The therapeutic efficacy of methoxypolyethylene glycol (mPEG)-coated nanomedicines in solid tumor treatment is hindered by tumor-associated fibroblasts (TAFs), which promote tumor progression and form physical barriers. We developed an anti-HER2/anti-FAP/anti-mPEG tri-specific antibody (TsAb) for one-step conversion of mPEG-coated liposomal doxorubicin (Lipo-Dox) to immunoliposomes, which simultaneously target HER2⁺ breast cancer cells and FAP⁺ TAFs. The non-covalent modification did not adversely alter the physical characteristics and stability of Lipo-Dox. The TsAb-Lipo-Dox exhibited specific targeting and enhanced cytotoxicity against mono- and co-cultured HER2⁺ breast cancer cells and FAP⁺ TAFs, compared to bi-specific antibody (BsAb) modified or unmodified Lipo-Dox. An in vivo model of human breast tumor containing TAFs also revealed the improved tumor accumulation and therapeutic efficacy of TsAb-modified mPEGylated liposomes without signs of toxicity. Our data indicate that arming clinical mPEGylated nanomedicines with the TsAb is a feasible and applicable approach for overcoming the difficulties caused by TAFs in solid tumor treatment.

Irinotecan/scFv co-loaded liposomes coaction on tumor cells and CAFs for enhanced colorectal cancer therapy

BACKGROUND

Cancer-associated fibroblasts (CAFs), as an important component of stroma, not only supply the "soils" to promote tumor invasion and metastasis, but also form a physical barrier to hinder the penetration of therapeutic agents. Based on this, the combinational strategy that action on both tumor cells and CAFs simultaneously would be a promising approach for improving the antitumor effect.

RESULTS

In this study, the novel multifunctional liposomes (IRI-RGD/R9-sLip) were designed, which integrated the advantages including IRI and scFv co-loading, different targets, RGD mediated active targeting, R9 promoting cell efficient permeation and lysosomal escape. As expected, IRI-RGD/R9-sLip showed enhanced cytotoxicity in different cell models, effectively increased the accumulation in tumor sites, as well as exhibited deep permeation ability both in vitro and in vivo. Notably, IRI-RGD/R9-sLip not only exhibited superior in vivo anti-tumor effect in both CAFs-free and CAFs-abundant bearing mice models, but also presented excellent anti-metastasis efficiency in lung metastasis model.

CONCLUSION

In a word, the novel combinational strategy by coaction on both "seeds" and "soils" of the tumor provides a new approach for cancer therapy, and the prepared liposomes could efficiently improve the antitumor effect with promising clinical application prospects.

Development of a Bispecific Antibody-Based Platform for Retargeting of Capsid Modified AAV Vectors

A major limiting factor for systemically delivered gene therapies is the lack of novel tissue specific AAV (Adeno-associated virus) derived vectors. Bispecific antibodies can be used to redirect AAVs to specific target receptors. Here, we demonstrate that the insertion of a short linear epitope “2E3” derived from human proprotein-convertase subtilisin/kexin type 9 (PCSK9) into different surface loops of the VP capsid proteins can be used for AAV de-targeting from its natural receptor(s), combined with a bispecific antibody-mediated retargeting. We chose to target a set of distinct disease relevant membrane proteins—fibroblast activation protein (FAP), which is upregulated on activated fibroblasts within the tumor stroma and in fibrotic tissues, as well as programmed death-ligand 1 (PD-L1), which is strongly upregulated in many cancers. Upon incubation with a bispecific antibody recognizing the 2E3 epitope and FAP or PD-L1, the bispecific antibody/rAAV complex was able to selectively transduce receptor positive cells. In summary, we developed a novel, rationally designed vector retargeting platform that can target AAVs to a new set of cellular receptors in a modular fashion. This versatile platform may serve as a valuable tool to investigate the role of disease relevant cell types and basis for novel gene therapy approaches.

FAP-Targeted Photodynamic Therapy Mediated by Ferritin Nanoparticles Elicits an Immune Response against Cancer Cells and Cancer Associated Fibroblasts

Cancer-associated fibroblasts (CAFs) are present in many types of tumors and play a pivotal role in tumor progression and immunosuppression. Fibroblast-activation protein (FAP), which is overexpressed on CAFs, has been indicated as a universal tumor target. However, FAP expression is not restricted to tumors, and systemic treatment against FAP often causes severe side effects. To solve this problem, a photodynamic therapy (PDT) approach was developed based on ZnF₁₆Pc (a photosensitizer)-loaded and FAP-specific single chain variable fragment (scFv)-conjugated apoferritin nanoparticles, or αFAP-Z@FRT. αFAP-Z@FRT PDT efficiently eradicates CAFs in tumors without inducing systemic toxicity. When tested in murine 4T1 models, the PDT treatment elicits anti-cancer immunity, causing suppression of both primary and distant tumors, i.e. abscopal effect. Treatment efficacy is enhanced when αFAP-Z@FRT PDT is used in combination with anti-PD1 antibodies. Interestingly, it is found that the PDT treatment not only elicits a cellular immunity against cancer cells, but also stimulates an anti-CAFs immunity. This is supported by an adoptive cell transfer study, where T cells taken from 4T1-tumor-bearing animals treated with αFAP PDT retard the growth of A549 tumors established on nude mice. Overall, our approach is unique for permitting site-specific eradication of CAFs and inducing a broad spectrum anti-cancer immunity.

Rapid Target Binding and Cargo Release of Activatable Liposomes Bearing HER2 and FAP Single-Chain Antibody Fragments Reveal Potentials for Image-Guided Delivery to Tumors

Liposomes represent suitable tools for the diagnosis and treatment of a variety of diseases, including cancers. To study the role of the human epidermal growth factor receptor 2 (HER2) as target in cancer imaging and image-guided deliveries, liposomes were encapsulated with an intrinsically quenched concentration of a near-infrared fluorescent dye in their aqueous interior. This resulted in quenched liposomes (termed LipQ), that were fluorescent exclusively upon degradation, dye release, and activation. The liposomes carried an always-on green fluorescent phospholipid in the lipid layer to enable tracking of intact liposomes. Additionally, they were functionalized with single-chain antibody fragments directed to fibroblast activation protein (FAP), a marker of stromal fibroblasts of most epithelial cancers, and to HER2, whose overexpression in 20–30% of all breast cancers and many other cancer types is associated with a poor treatment outcome and relapse. We show that both monospecific (HER2-IL) and bispecific (Bi-FAP/HER2-IL) formulations are quenched and undergo HER2-dependent rapid uptake and cargo release in cultured target cells and tumor models in mice. Thereby, tumor fluorescence was retained in whole-body NIRF imaging for 32–48 h post-injection. Opposed to cell culture studies, Bi-FAP/HER2-IL-based live confocal microscopy of a high HER2-expressing tumor revealed nuclear delivery of the encapsulated dye. Thus, the liposomes have potentials for image-guided nuclear delivery of therapeutics, and also for intraoperative delineation of tumors, metastasis, and tumor margins.

Targeting the Tumor Microenvironment with Fluorescence-Activatable Bispecific Endoglin/Fibroblast Activation Protein Targeting Liposomes

Liposomes are biocompatible nanocarriers with promising features for targeted delivery of contrast agents and drugs into the tumor microenvironment, for imaging and therapy purposes. Liposome-based simultaneous targeting of tumor associated fibroblast and the vasculature is promising, but the heterogeneity of tumors entails a thorough validation of suitable markers for targeted delivery. Thus, we elucidated the potential of bispecific liposomes targeting the fibroblast activation protein (FAP) on tumor stromal fibroblasts, together with endoglin which is overexpressed on tumor neovascular cells and some neoplastic cells. Fluorescence-quenched liposomes were prepared by hydrating a lipid film with a high concentration of the self-quenching near-infrared fluorescent dye, DY-676-COOH, to enable fluorescence detection exclusively upon liposomal degradation and subsequent activation. A non-quenched green fluorescent phospholipid was embedded in the liposomal surface to fluorescence-track intact liposomes. FAP- and murine endoglin-specific single chain antibody fragments were coupled to the liposomal surface, and the liposomal potentials validated in tumor cells and mice models. The bispecific liposomes revealed strong fluorescence quenching, activatability, and selectivity for target cells and delivered the encapsulated dye selectively into tumor vessels and tumor associated fibroblasts in xenografted mice models and enabled their fluorescence imaging. Furthermore, detection of swollen lymph nodes during intra-operative simulations was possible. Thus, the bispecific liposomes have potentials for targeted delivery into the tumor microenvironment and for image-guided surgery.

OMTX705, a Novel FAP-Targeting ADC Demonstrates Activity in Chemotherapy and Pembrolizumab-Resistant Solid Tumor Models

PURPOSE

The tumor microenvironment plays a key role in cancer development and progression and is involved in resistance to chemo- and immunotherapy. Cancer-associated fibroblast expressing fibroblast-activating protein α (FAPα) is one of the predominant stroma cell types and is involved in resistance to immunotherapy.

EXPERIMENTAL DESIGN

We generated OMTX705, a novel antibody-drug conjugate from a humanized anti-FAP antibody linked to a new cytolysin. Here, we studied its antineoplastic activity in vitro and in preclinical mouse models alone and in combination with chemotherapy as well as immunotherapy in PD-1-resistant tumors.

RESULTS

In Avatar models, OMTX705 showed a 100% tumor growth inhibition and prolonged tumor regressions as single agent and in combination with chemotherapy. Treatment rechallenge following treatment discontinuation induced additional tumor regression, suggesting lack of treatment resistance. In a mouse model with a humanized immune system resistant to PD-1 inhibition, OMTX705 increased tumor infiltration by CD8⁺ T cells, induced complete regressions, and delayed tumor recurrence.

CONCLUSIONS

These data suggest that FAP targeting with OMTX705 represents a novel and potent strategy for cancer treatment, including tumors resistant to immunotherapy, and support its clinical development.

IL15-Based Trifunctional Antibody-Fusion Proteins with Costimulatory TNF-Superfamily Ligands in the Single-Chain Format for Cancer Immunotherapy

IL15 and costimulatory receptors of the tumor necrosis superfamily (TNFRSF) have shown great potential to support and drive an antitumor immune response. However, their efficacy as monotherapy is limited. Here, we present the development of a novel format for a trifunctional antibody-fusion protein that combines and focuses the activity of IL15/TNFSF-ligand in a targeting-mediated manner to the tumor site. The previously reported format consisted of a tumor-directed antibody (scFv), IL15 linked to an IL15Rα-fragment (RD), and the extracellular domain of 4-1BBL, where noncovalent trimerization of 4-1BBL into its functional unit led to a homotrimeric molecule with 3 antibody and 3 IL15-RD units. To reduce the size and complexity of the molecule, we have now designed a second format, where 4-1BBL is introduced as single-chain (sc), that is 3 consecutively linked 4-1BBL ectodomains. Thus, a monomeric trifunctional fusion protein presenting only 1 functional unit of each component was generated. Interestingly, the in vitro activity on T-cell stimulation was conserved or even enhanced for the soluble and target-bound molecule, respectively. Also, in a lung tumor mouse model, comparable antitumor effects were observed. Furthermore, corroborating the concept, OX40L and GITRL were also successfully incorporated into the novel single-chain format and the advantage of target-bound trifunctional versus corresponding combined bifunctional fusion proteins demonstrated by measuring T-cell proliferation and cytotoxic potential in vitro and antitumor effects of RD_IL15_scFv_scGITRL in a lung tumor mouse model in vivo Thus, the trifunctional antibody-fusion protein single-chain format constitutes a promising innovative platform for further therapeutic developments.

Photosensitizer-Encapsulated Ferritins Mediate Photodynamic Therapy against Cancer-Associated Fibroblasts and Improve Tumor Accumulation of Nanoparticles

Nanoparticles have been widely tested as drug delivery carriers or imaging agents, largely because of their ability to selectively accumulate in tumors through the enhanced permeability and retention (EPR) effect. However, studies show that many tumors afford a less efficient EPR effect and that many nanoparticles are trapped in the perivascular region after extravasation and barely migrate into tumor centers. This is to a large degree attributed to the dense tumor extracellular matrix (ECM), which functions as a physical barrier to prevent efficient nanoparticle extravasation and diffusion. In this study, we report a photodynamic therapy (PDT) approach to enhance tumor uptake of nanoparticles. Briefly, we encapsulate ZnF16Pc, a photosensitizer, into ferritin nanocages, and then conjugate to the surface of the ferritin a single chain viable fragment (scFv) sequence specific to fibroblast activation protein (FAP). FAP is a plasma surface protein widely upregulated in cancer-associated fibroblasts (CAFs), which is a major source of the ECM fiber components. We found that the scFv-conjugated and ZnF16Pc-loaded ferritin nanoparticles (scFv-Z@FRT) can mediate efficient and selective PDT, leading to eradication of CAFs in tumors. When tested in bilateral 4T1 tumor models, we found that the tumor accumulation of serum albumin (BSA), 10 nm quantum dots (QDs), and 50 nm QDs was increased by 2-, 3.5-, and 18-fold after scFv-Z@FRT mediated PDT. Our studies suggest a novel and safe method to enhance the delivery of nanoparticles to tumors.

Glycosylation of MUC1 influences the binding of a therapeutic antibody by altering the conformational equilibrium of the antigen

In cancer cells, the glycoprotein Mucin 1 (MUC1) undergoes abnormal, truncated glycosylation. The truncated glycosylation exposes cryptic peptide epitopes that can be recognized by antibodies. Since these immunogenic regions are cancer specific, they represent ideal targets for therapeutic antibodies. We investigated the role of tumor-specific glycosylation on antigen recognition by the therapeutic antibody AR20.5. We explored the affinity of AR20.5 to a synthetic cancer-specific MUC1 glycopeptide and peptide. The antibody bound to the glycopeptide with an order of magnitude stronger affinity than the naked peptide. Given these results, we postulated that AR20.5 must specifically bind the carbohydrate as well as the peptide. Using X-ray crystallography, we examined this hypothesis by determining the structure of AR20.5 in complex with both peptide and glycopeptide. Surprisingly, the structure revealed that the carbohydrate did not form any specific polar contacts with the antibody. The high affinity of AR20.5 for the glycopeptide and the lack of specific binding contacts support a hypothesis that glycosylation of MUC1 stabilizes an extended bioactive conformation of the peptide recognized by the antibody. Since high affinity binding of AR20.5 to the MUC1 glycopeptide may not driven by specific antibody-antigen contacts, but rather evidence suggests that glycosylation alters the conformational equilibrium of the antigen, which allows the antibody to select the correct conformation. This study suggests a novel mechanism of antibody-antigen interaction and also suggests that glycosylation of MUC1 is important for the generation of high affinity therapeutic antibodies.

Development of a T-cell Receptor Mimic Antibody against Wild-Type p53 for Cancer Immunotherapy

The tumor suppressor p53 is widely dysregulated in cancer and represents an attractive target for immunotherapy. Because of its intracellular localization, p53 is inaccessible to classical therapeutic monoclonal antibodies, an increasingly successful class of anticancer drugs. However, peptides derived from intracellular antigens are presented on the cell surface in the context of MHC I and can be bound by T-cell receptors (TCR). Here, we report the development of a novel antibody, T1-116C, that acts as a TCR mimic to recognize an HLA-A*0201-presented wild-type p53 T-cell epitope, p5365-73(RMPEAAPPV). The antibody recognizes a wide range of cancers, does not bind normal peripheral blood mononuclear cells, and can activate immune effector functions to kill cancer cells in vitroIn vivo, the antibody targets p5365-73 peptide-expressing breast cancer xenografts, significantly inhibiting tumor growth. This represents a promising new agent for future cancer immunotherapy. Cancer Res; 77(10); 2699-711. ©2017 AACR.

Activatable bispecific liposomes bearing fibroblast activation protein directed single chain fragment/Trastuzumab deliver encapsulated cargo into the nuclei of tumor cells and the tumor microenvironment simultaneously

Molecular targeting plays a significant role in cancer diagnosis and therapy. However, the heterogeneity of tumors is a limiting obstacle for molecular targeting. Consequently, clinically approved drug delivery systems such as liposomes still rely on passive targeting to tumors, which does not address tumor heterogeneity. In this work, we therefore designed and elucidated the potentials of activatable bispecific targeted liposomes for simultaneous detection of fibroblast activation protein (FAP) and the human epidermal growth factor receptor 2 (HER2). The bispecific liposomes were encapsulated with fluorescence-quenched concentrations of the near-infrared fluorescent dye, DY-676-COOH, making them detectable solely post processing within target cells. The liposomes were endowed with a combination of single chain antibody fragments specific for FAP and HER2 respectively, or with the FAP single chain antibody fragment in combination with Trastuzumab, which is specific for HER2. The Trastuzumab based bispecific formulation, termed Bi-FAP/Tras-IL revealed delivery of the encapsulated dye into the nuclei of HER2 expressing cancer cells and caused cell death at significantly higher rates than the free Trastuzumab. Furthermore, fluorescence imaging and live microscopy of tumor models in mice substantiated the delivery of the encapsulated cargo into the nuclei of target tumor cells and tumor stromal fibroblasts. Hence, they convey potentials to address tumor plasticity, to improve targeted cancer therapy and reduce Trastuzumab resistance in the future.

STATEMENT OF SIGNIFICANCE

This work demonstrates the design of activatable bispecific liposomes aimed to target HER2, a poor prognosis tumor marker in many tumor types, and fibroblast activation protein (FAP), a universal tumor marker overexpressed on tumor fibroblasts and pericytes of almost all solid tumors. Encapsulating liposomes with a quenched concentration of a NIRF dye which only fluoresced after cellular degradation and activation enabled reliable visualization of the destination of the cargo in cells and animal studies. Conjugating single chain antibody fragments directed to FAP, together with Trastuzumab, a humanized monoclonal antibody for HER2 resulted in the activatable bispecific liposomes. In animal models of xenografted human breast tumors, the remarkable ability of the bispecific probes to simultaneously deliver the encapsulated dye into the nuclei of target tumor cells and tumor fibroblasts could be demonstrated. Hence, the bispecific probes represent model tools with high significance to address tumor heterogeneity and manage Trastuzumab resistance in the future.

Computational Identification of Antibody Epitopes on the Dengue Virus NS1 Protein

We have previously described a method to predict antigenic epitopes on proteins recognized by specific antibodies. Here we have applied this method to identify epitopes on the NS1 proteins of the four Dengue virus serotypes (DENV1-4) that are bound by a small panel of monoclonal antibodies 1H7.4, 1G5.3 and Gus2. Several epitope regions were predicted for these antibodies and these were found to reflect the experimentally observed reactivities. The known binding epitopes on DENV2 for the antibodies 1H7.4 and 1G5.3 were identified, revealing the reasons for the serotype specificity of 1H7.4 and 1G5.3, and the non-selectivity of Gus2. As DENV NS1 is critical for virus replication and a key vaccine candidate, epitope prediction will be valuable in designing appropriate vaccine control strategies. The ability to predict potential epitopes by computational methods significantly reduces the amount of experimental work required to screen peptide libraries for epitope mapping.

Protein Nanocage Mediated Fibroblast-Activation Protein Targeted Photoimmunotherapy To Enhance Cytotoxic T Cell Infiltration and Tumor Control

Carcinoma-associated fibroblasts (CAFs) are found in many types of cancer and play an important role in tumor growth and metastasis. Fibroblast-activation protein (FAP), which is overexpressed on the surface of CAFs, has been proposed as a universal tumor targeting antigen. However, recent studies show that FAP is also expressed on multipotent bone marrow stem cells. A systematic anti-FAP therapy may lead to severe side effects and even death. Hence, there is an urgent need of a therapy that can selectively kill CAFs without causing systemic toxicity. Herein we report a nanoparticle-based photoimmunotherapy (nano-PIT) approach that addresses the need. Specifically, we exploit ferritin, a compact nanoparticle protein cage, as a photosensitizer carrier, and we conjugate to the surface of ferritin a FAP-specific single chain variable fragment (scFv). With photoirradiation, the enabled nano-PIT efficiently eliminates CAFs in tumors but causes little damage to healthy tissues due to the localized nature of the treatment. Interestingly, while not directly killing cancer cells, the nano-PIT caused efficient tumor suppression in tumor-bearing immunocompetent mice. Further investigations found that the nano-PIT led to suppressed C-X-C motif chemokine ligand 12 (CXCL12) secretion and extracellular matrix (ECM) deposition, both of which are regulated by CAFs in untreated tumors and mediate T cell exclusion that prevents physical contact between T cells and cancer cells. By selective killing of CAFs, the nano-PIT reversed the effect, leading to significantly enhanced T cell infiltration, followed by efficient tumor suppression. Our study suggests a new and safe CAF-targeted therapy and a novel strategy to modulate tumor microenvironment (TME) for enhanced immunity against cancer.

A fast and effective determination of the biodistribution and subcellular localization of fluorescent immunoliposomes in freshly excised animal organs

Background

Preclinical research implementing fluorescence-based approaches is inevitable for drug discovery and technology. For example, a variety of contrast agents developed for biomedical imaging are usually evaluated in cell systems and animal models based on their conjugation to fluorescent dyes. Biodistribution studies of excised organs are often performed by macroscopic imaging, whereas the subcellular localization though vital, is often neglected or further validated by histological procedures. Available systems used to define the subcellular biodistribution of contrast agents such as intravital microscopes or ex vivo histological analysis are expensive and not affordable by the majority of researchers, or encompass tedious and time consuming steps that may modify the contrast agents and falsify the results. Thus, affordable and more reliable approaches to study the biodistribution of contrast agents are required. We developed fluorescent immunoliposomes specific for human fibroblast activation protein and murine endoglin, and used macroscopic fluorescence imaging and confocal microscopy to determine their biodistribution and subcellular localization in freshly excised mice organs at different time points post intravenous injection.

Results

Near infrared fluorescence macroscopic imaging revealed key differences in the biodistribution of the respective immunoliposomes at different time points post injection, which correlated to the first-pass effect as well as the binding of the probes to molecular targets within the mice organs. Thus, a higher accumulation and longer retention of the murine endoglin immunoliposomes was seen in the lungs, liver and kidneys than the FAP specific immunoliposomes. Confocal microscopy showed that tissue autofluorescence enables detection of organ morphology and cellular components within freshly excised, non-processed organs, and that fluorescent probes with absorption and emission maxima beyond the tissue autofluorescence range can be easily distinguished. Hence, the endoglin targeting immunoliposomes retained in some organs could be detected in the vascular endothelia cells of the organs.

Conclusions

The underlying work represents a quick, effective and more reliable setup to validate the macroscopic and subcellular biodistribution of contrast agents in freshly excised animal organs. The approach will be highly beneficial to many researchers involved in nanodrug design or in fluorescence-based studies on disease pathogenesis.

Advancing targeted co-stimulation with antibody-fusion proteins by introducing TNF superfamily members in a single-chain format

Co-stimulation via receptors of the tumor necrosis factor superfamily (TNFSF) emerges as promising strategy to support antitumor immune responses. Targeted strategies with antibody-fusion proteins composed of a tumor-directed antibody part and the extracellular domain of a co-stimulatory ligand of the TNFSF constitute an attractive option to focus the co-stimulatory activity to the tumor site. Since TNFSF members intrinsically form functional units of non-covalently linked homotrimers, the protein engineering of suitable antibody-fusion proteins is challenging. Aiming for molecules of simple and stable configuration, we used TNFSF ligands in a single-chain format (scTNFSF), i.e., three units of the ectodomain connected by polypeptide linkers, folding into an intramolecular trimer. By fusing tumor-directed scFv antibody fragments directed against EpCAM or FAP to co-stimulatory scTNFSF molecules (sc4-1BBL, scOX40L, scGITRL or scLIGHT), a set of monomeric scFv-scTNFSF fusion proteins was generated. In comparison to the scFv-TNFSF format, defined by intermolecular homotrimerization via the TNFSF part, scFv-scTNFSF showed equal or enhanced co-stimulatory activity despite reduced avidity in antibody binding. In addition, enhanced serum stability and improved bioavailability in mice were observed. We show that the scFv-scTNFSF format can be applied to various members of the TNFSF, presenting targeting-dependent co-stimulatory activity. Hence, this format exhibits favorable properties that make it a promising choice for further therapeutic fusion protein development.

A potent immunotoxin targeting fibroblast activation protein for treatment of breast cancer in mice

Fibroblast activation protein (FAP) is highly expressed in the tumor-associated fibroblasts (TAFs) of most human epithelial cancers. FAP plays a critical role in tumorigenesis and cancer progression, which makes it a promising target for novel anticancer therapy. However, mere abrogation of FAP enzymatic activity by small molecules is not very effective in inhibiting tumor growth. In this study, we have evaluated a novel immune-based approach to specifically deplete FAP-expressing TAFs in a mouse 4T1 metastatic breast cancer model. Depletion of FAP-positive stromal cells by FAP-targeting immunotoxin αFAP-PE38 altered levels of various growth factors, cytokines, chemokines and matrix metalloproteinases, decreased the recruitment of tumor-infiltrating immune cells in the tumor microenvironment and suppressed tumor growth. In addition, combined treatment with αFAP-PE38 and paclitaxel potently inhibited tumor growth in vivo. Our findings highlight the potential use of immunotoxin αFAP-PE38 to deplete FAP-expressing TAFs and thus provide a rationale for the use of this immunotoxin in cancer therapy.

Expression of anti-VEGF antibody together with anti-EGFR or anti-FAP enhances tumor regression as a result of vaccinia virotherapy

The tumor microenvironment plays an important role in tumor growth and progression. Here we demonstrate that vaccinia virus-mediated, constitutively expressed intratumoral antibodies against vascular endothelial growth factor (VEGF), epidermal growth factor receptor (EGFR), and fibroblast activation protein (FAP) significantly improved tumor regression and oncolytic virotherapy through suppression of angiogenesis, cell proliferation, and stromagenesis in virus-colonized tumors. In contrast to the tumor growth inhibition by the three tumor growth-inhibiting antibodies individually, when two of the three antibodies were expressed simultaneously by single vaccinia virus strains tumor regression was further enhanced. These findings strongly indicate that interference with the two tumor growth-stimulating mechanisms did in fact result in enhanced therapeutic efficacy in tumor xenograft models and may lead to an effective therapy in patients with cancer.

In vivo near-infrared fluorescence imaging of FAP-expressing tumors with activatable FAP-targeted, single-chain Fv-immunoliposomes

Molecular and cellular changes that precede the invasive growth of solid tumors include the release of proteolytic enzymes and peptides in the tumor stroma, the recruitment of phagocytic and lymphoid infiltrates and alteration of the extracellular matrix. The reactive tumor stroma consists of a large number of myofibroblasts, characterized by high expression of fibroblast activation protein alpha (FAP). FAP, a type-II transmembrane sialoglycoprotein is an attractive target in diagnosis and therapy of several pathologic disorders especially cancer. In the underlying work, a fluorescence-activatable liposome (fluorescence-quenched during circulation and fluorescence activation upon cellular uptake), bearing specific single-chain Fv fragments directed against FAP (scFv'FAP) was developed, and its potential for use in fluorescence diagnostic imaging of FAP-expressing tumor cells was evaluated by whole body fluorescence imaging. The liposomes termed anti-FAP-IL were prepared via post-insertion of ligand-phospholipid-conjugates into preformed DY-676-COOH-containing liposomes. The anti-FAP-IL revealed a homogeneous size distribution and showed specific interaction and binding with FAP-expressing cells in vitro. The high level of fluorescence quenching of the near-infrared fluorescent dye sequestered in the aqueous interior of the liposomes enables fluorescence imaging exclusively upon uptake and degradation by cells, which results in fluorescence activation. Only FAP-expressing cells were able to take up and activate fluorescence of anti-FAP-IL in vitro. Furthermore, anti-FAP-IL accumulated selectively in FAP-expressing xenograft models in vivo, as demonstrated by blocking experiments using free scFv'FAP. The local tumor fluorescence intensities were in agreement with the intrinsic degree of FAP-expression in different xenograft models. Thus, anti-FAP-IL can serve as a suitable in vivo diagnostic tool for pathological disorders accompanied by high FAP-expression.

Antitumor effects of chimeric receptor engineered human T cells directed to tumor stroma

Cancer-associated fibroblasts (CAFs), the principle component of the tumor-associated stroma, form a highly protumorigenic and immunosuppressive microenvironment that mediates therapeutic resistance. Co-targeting CAFs in addition to cancer cells may therefore augment the antitumor response. Fibroblast activation protein-α (FAP), a type 2 dipeptidyl peptidase, is expressed on CAFs in a majority of solid tumors making it an attractive immunotherapeutic target. To target FAP-positive CAFs in the tumor-associated stroma, we genetically modified T cells to express a FAP-specific chimeric antigen receptor (CAR). The resulting FAP-specific T cells recognized and killed FAP-positive target cells as determined by proinflammatory cytokine release and target cell lysis. In an established A549 lung cancer model, adoptive transfer of FAP-specific T cells significantly reduced FAP-positive stromal cells, with a concomitant decrease in tumor growth. Combining these FAP-specific T cells with T cells that targeted the EphA2 antigen on the A549 cancer cells themselves significantly enhanced overall antitumor activity and conferred a survival advantage compared to either alone. Our study underscores the value of co-targeting both CAFs and cancer cells to increase the benefits of T-cell immunotherapy for solid tumors.

An automated immunoassay for early specificity profiling of antibodies

Antibody-based therapeutics are of great value for the treatment of human diseases. In addition to functional activity, affinity or physico-chemical properties, antibody specificity is considered to be one of the most crucial attributes for safety and efficacy. Consequently, appropriate studies are required before entering clinical trials. High content protein arrays are widely applied to assess antibody specificity, but this commercial solution can only be applied to final therapeutic antibody candidates because such arrays are expensive and their throughput is limited. A flexible, high-throughput and economical assay that allows specificity testing of IgG or Fab molecules during early discovery is described here. The 384-well microtiter plate assay contains a comprehensive panel of 32 test proteins and uses electrochemiluminescence as readout. The Protein Panel Profiling ( 3P) was used to analyze marketed therapeutic antibodies that all showed highly specific binding profiles. Subsequently, 3P was applied to antibody candidates from early discovery and the results compared well with those obtained with a commercially available high content protein chip. Our results suggest that 3P can be applied as an additional filter for lead selection, allowing the identification of favorable antibody candidates in early discovery and thereby increasing the speed and possibility of success in drug development.

An antibody fusion protein for cancer immunotherapy mimicking IL-15 trans-presentation at the tumor site

Cytokines driving the immune response are powerful tools for cancer immunotherapy, but their application is generally limited by severe systemic toxicity. Targeted approaches by means of antibody-cytokine fusion proteins might enable focus on the cytokine activity to the tumor site, thereby reducing unwanted side effects. Here, we investigated the possibility to improve the efficiency of interleukin (IL)-15 presentation in a targeted approach by the incorporation of an IL-15Rα chain fragment, mimicking physiologic trans-presentation. Therefore, an antibody cytokine fusion protein (scFv_RD_IL-15) composed of an antibody moiety targeting the tumor stromal fibroblast activation protein (FAP), an extended IL-15Rαsushi domain (RD) and IL-15 was generated, exhibiting antibody-mediated specific binding and cytokine activity in soluble and targeted form. Comparative analysis with a corresponding antibody fusion protein devoid of RD (scFv_IL-15) showed for scFv_RD_IL-15 in solution enhanced stimulatory activity on Mo7e (IL-15Rβγ) cells and reduced proliferation response on CTLL-2 (IL-15Rαβγ) cells, while in FAP-targeted, that is, membrane-bound form, comparable proliferation of CTLL-2 (IL-15Rαβγ) cells was obtained. In addition, scFv_RD_IL-15 achieved in its soluble and target-bound form stronger proliferation and cytotoxicity on unstimulated and activated T cells, respectively. Furthermore, in vivo analysis in a lung metastasis tumor mouse model revealed a superior antitumor effect for scFv_RD_IL-15 in comparison with that obtained by an untargeted or RD missing version of IL-15 fusion protein. Thus, tumor-directed trans-presentation of IL-15 in association with RD in form of an antibody fusion protein seems to be a promising approach to further improve the antitumor effect of IL-15.

Improving TNF as a cancer therapeutic: tailor-made TNF fusion proteins with conserved antitumor activity and reduced systemic side effects

Tumor necrosis factor (TNF) is highly pleiotropic cytokine regulating diverse cellular processes such as proliferation, cell migration, angiogenesis, differentiation, apoptosis, necrosis, but also survival. Because of its name-giving tumor necrosis-inducing capabilities, TNF has attracted attention very early for antitumor therapy. Although TNF is in clinical use for treatment of soft tissue sarcoma in isolated limb perfusion, its broad use in tumor therapy is prevented so far by its strong systemic proinflammatory effects. Nevertheless, over the past decade, a variety of tailor-made TNF variants have been developed with the aim to reduce TNFs systemic activity without losing its antitumoral effects. Here, we review the progress made toward improving the efficacy of TNF by genetic engineering, tumor targeting, and introduction of prodrug concepts.

A novel antibody-4-1BBL fusion protein for targeted costimulation in cancer immunotherapy

Costimulation is an essential step in T-cell activation and hence, represents an important aspect in cancer immunotherapy. 4-1BB, a member of the tumor necrosis factor receptor family, has gained particular interest as a costimulatory molecule. Here, we investigated the potential of a targeted activation of 4-1BB-mediated costimulation at the tumor site by generating a recombinant antibody-cytokine fusion protein composed of a single-chain antibody fragment (scFv36) specific for the tumor stromal antigen fibroblast activation protein (FAP) and the extracellular domain of the 4-1BB ligand (4-1BBL). The scFv36-4-1BBL fusion protein is a homotrimeric molecule that binds specifically to FAP and the receptor 4-1BB. T-cell costimulation was demonstrated by interferon-gamma release of peripheral blood mononuclear cells cocultured with FAP-expressing HT1080 cells upon T-cell receptor triggering by monoclonal anti-CD3 antibody. Costimulatory activity of the scFv36-4-1BBL fusion protein was concentration dependent, ligand-specific, and substantially constrained to FAP-expressing target cell binding. Furthermore, scFv36-4-1BBL enhanced T-cell activation when the bispecific antibody scDb33CD3 (specific for FAP and CD3) was used as primary stimulus. Thus, target cell-dependent costimulation with scFv36-4-1BBL constitutes a new option to enhance T-cell activation by bispecific antibodies or antigen-dependent T-cell receptor triggering and should be useful to improve T cell-mediated antitumor responses.

Single-chain Fv immunoliposomes for the targeting of fibroblast activation protein-expressing tumor stromal cells

Tumor stromal cells have gained increasing attention as possible target for cancer therapy. Fibroblast activation protein (FAP) represents a cell surface antigen selectively expressed by reactive tumor stromal fibroblasts of various cancers. Here, we describe anti-FAP immunoliposomes as carrier systems for active targeting of FAP-expressing cells. As targeting ligand we used single-chain Fv (scFv) molecules cross-reacting with human and mouse FAP. These scFv molecules were genetically modified to express an additional cysteine residue at the C-terminus allowing a defined and site-directed conjugation. Coupling to Mal-PEG(2000)-DSPE containing liposomes resulted in sterically stabilized scFv immunoliposomes showing strong and specific binding to FAP-expressing cells. These immunoliposomes were highly stable when incubated under physiological conditions (human plasma, 37 degrees C). In addition, we could show that binding to FAP-expressing cells leads to internalization of intact liposomes into the endosomal compartment. Thus, these anti-FAP scFv immunoliposomes should be suitable for target cell-specific delivery and uptake of encapsulated drugs.

Activation of CD95L fusion protein prodrugs by tumor-associated proteases

To achieve tumor cell-restricted activation of CD95, we developed a CD95L fusion protein format, in which CD95L activity is only unmasked upon antibody-mediated binding to tumor cells and subsequent processing by tumor-associated proteases, such as matrix metalloproteases (MMPs) and urokinase plasminogen activator (uPA). On target-negative, but MMP- and uPA-expressing HT1080 tumor cells, the CD95L prodrugs were virtually inactive. On target antigen-expressing HT1080 cells, however, the CD95L prodrugs showed an apoptotic activity comparable to soluble CD95L artificially activated by crosslinking. CD95 activation by the CD95L prodrugs was preceded by prodrug processing. Apoptosis was blocked by inhibitors of MMPs or uPA and by neutralizing antibodies recognizing the targeted cell surface antigen or the CD95L moiety of the prodrugs. In a xenotransplantation tumor model, local application of the prodrug reduced the growth of target antigen-expressing, but not antigen-negative tumor cells, verifying targeted CD95L prodrug activation in vivo.

Restoration of membrane TNF-like activity by cell surface targeting and matrix metalloproteinase-mediated processing of a TNF prodrug

Tumor necrosis factor (TNF) prodrugs are fusion proteins comprised of an N-terminal single-chain antibody variable fragment (scFv) targeting a TNF effector and a C-terminal TNF receptor (TNFR)1-derived inhibitor module. Introduction of matrix metalloproteinase (MMP)-2 recognition motifs between TNF and the TNFR1 fragment allowed activation by recombinant MMP-2 and MMP-expressing HT1080 cells. Processing by endogeneous MMPs required specific membrane binding of the TNF prodrug via the targeting scFv, ensuring strictly antigen-dependent activation. Interestingly, TNF bioactivity of the processed prodrug was approximately 1000-fold higher upon scFv-mediated targeting, and signaled juxtatropic cell death also to antigen-negative cells. Microscopical analyses of TNFR2 clustering and TNF receptor-associated factor 2 recruitment at contact sites to adjacent cells revealed the formation of stable TNFR complexes by target-bound, processed prodrug, resembling the increased signal capacity of natural, membrane-expressed TNF. MMP-2-sensitive TNF prodrugs represent novel cytokine-based reagents for targeted cancer therapy, which should be exploitable for MMP-overexpressing tumors.

Antibody phage display technologies with special reference to angiogenesis

The presence of blood vessels is a prerequisite for normal development, tissue growth, and tissue repair. However, its abnormal occurrence or absence can also potentiate disease processes. Angiogenic therapies have been used to stimulate blood vessel growth in ischemic conditions such as severe end-stage peripheral vascular disease, ischemic heart disease and stroke and for inhibition of angiogenesis in tumors. The targeting and identification of novel endothelial cell (EC) markers that can ultimately be used in angiogenic strategies is an expanding field but is limited by the availability of reagents. For instance repeated injection of mouse monoclonal antibodies (Mabs) against angiogenic EC, can result in the production of autoantibodies. Therefore, these mouse Mabs cannot be used for therapeutic purposes. Phage display technology was employed in this context to select antibodies, proteins, and peptides against known or novel EC antigens. Furthermore, technologies have been developed that enable the specific targeting of epitopes on cells including the endothelium with high-affinity/avidity antibodies. The focus for these antibody targeting strategies are markers that are unique or up-regulated on angiogenic EC including the vascular endothelial growth factor receptor (VEGFR) KDR, endoglin (CD105), and the extracellular domain B (ED-B) domain of fibronectin (FN). These markers are reviewed herein.

The fibroblast: sentinel cell and local immune modulator in tumor tissue

Development and progression of epithelial malignancies are frequently accompanied by complex phenotypic alterations of resident tissue fibroblasts. Some of these changes, such as myofibroblastic differentiation and an oncofetal extracellular matrix (ECM) expression profile, are also implicated in inflammation and tissue repair. Studies over the past decade revealed the relevance of reciprocal interactions between tumor cells and tumor-associated host fibroblasts (TAF) in the malignant process. In many tumors, a considerable fraction of the inflammatory infiltrate is located within the fibroblast- and ECM-rich stromal compartment. However, while fibroblasts are known as "sentinel cells" in various nonneoplastic diseases, where they often regulate the composition and function of recruited leucocytes, they are hardly considered active participants in the inflammatory host response in tumors. This article focuses on the functional impact of TAF on immune cells. The complex network of immune-modulating effects transduced by TAF and TAF-derived factors is highlighted, and recent reports that support the hypothesis that TAF are involved in the inflammatory response and immune suppression in tumors are reviewed. The role of TAF-dependent ECM remodeling and TAF-derived peptide growth factors, cytokines, and chemokines in the immune modulation is stressed and the idea of TAF as an important therapeutic target is emphasized.

TNF-Selectokine: a novel prodrug generated for tumor targeting and site-specific activation of tumor necrosis factor

We describe a TNF fusion protein designated TNF-Selectokine, which is a homo-trimeric molecule comprised of a single chain antibody (scFv) targeting module, a trimerization domain and TNF. TNF-Selectokine exerts high bioactivity towards the targeted and adjacent, antigen negative cells. Membrane targeting dependent immobilization of the TNF-Selectokine induced cell death in TNFR1 and TNFR2 dependent manner, thus cell bound TNF-Selectokine mimicks membrane TNF. To restrict TNF activity to the tumor, a prototype of a TNF-Selectokine prodrug was constructed by insertion of a TNFR1 fragment, separated from TNF by a protease-sensitive linker. The prodrug exerts minimal TNF activity, but can be activated in vitro several thousand-fold by proteolytic digest, showing the principal feasibility of this approach. Choice of cleavage site(s) recognized by protease(s) typically associated with a given carcinoma should allow high dose systemic application of the respective TNF prodrug that unveils its specific bioactivity only in targeted tissues.