Enhancement of the antitumor activity of interleukin-12 by targeted delivery to neovasculature

Engineering a Single-Agent Cytokine/Antibody Fusion That Selectively Expands Regulatory T Cells for Autoimmune Disease Therapy

IL-2 has been used to treat diseases ranging from cancer to autoimmune disorders, but its concurrent immunostimulatory and immunosuppressive effects hinder efficacy. IL-2 orchestrates immune cell function through activation of a high-affinity heterotrimeric receptor (composed of IL-2Rα, IL-2Rβ, and common γ [γ_c]). IL-2Rα, which is highly expressed on regulatory T (T_Reg) cells, regulates IL-2 sensitivity. Previous studies have shown that complexation of IL-2 with the JES6-1 Ab preferentially biases cytokine activity toward T_Reg cells through a unique mechanism whereby IL-2 is exchanged from the Ab to IL-2Rα. However, clinical adoption of a mixed Ab/cytokine complex regimen is limited by stoichiometry and stability concerns. In this study, through structure-guided design, we engineered a single agent fusion of the IL-2 cytokine and JES6-1 Ab that, despite being covalently linked, preserves IL-2 exchange, selectively stimulating T_Reg expansion and exhibiting superior disease control to the mixed IL-2/JES6-1 complex in a mouse colitis model. These studies provide an engineering blueprint for resolving a major barrier to the implementation of functionally similar IL-2/Ab complexes for treatment of human disease.

Potentiation of PD-L1 blockade with a potency-matched dual cytokine-antibody fusion protein leads to cancer eradication in BALB/c-derived tumors but not in other mouse strains

We have recently described a novel therapeutic antibody product (IL2-F8-TNF^mut), featuring the simultaneous fusion of murine IL2 and of a TNF mutant with scFv(F8), an antibody specific to the alternatively-spliced extra domain A of fibronectin (EDA). Here, we report on the in vivo characterization of the anti-cancer activity of IL2-F8-TNF^mut in four immunocompetent murine models of cancer, CT26, WEHI-164, F9 teratocarcinoma and Lewis lung carcinoma (LLC), using the product alone or in combination with a monoclonal antibody specific to murine PD-L1. All four models exhibited a strong expression of EDA-fibronectin, which was confined to vascular structures for F9 tumors, while the other three malignancies exhibited a more stromal pattern of staining. A complete and long-lasting tumor eradication of CT26 and WEHI-164 tumors was observed in BALB/c mice when IL2-F8-TNF^mut was used in combination with PD-L1 blockade. The combination treatment led to improved tumor growth inhibition in 129/SvEv mice bearing murine teratocarcinoma or in C57BL/6 mice bearing murine LLC, but those cancer cures were difficult to achieve in those models. A microscopic analysis of tumor sections, obtained 24 h after pharmacological treatment, revealed that the PD-L1 antibody had homogenously reached tumor cells in vivo and that the combination of PD-L1 blockade with IL2-F8-TNF^mut stimulated an influx of NK cells and of T cells into the neoplastic mass. These data indicate that potency-matched dual-cytokine fusion proteins may be ideally suited to potentiate the therapeutic activity of immune check-point inhibitors.

Heterodimeric Fc-fused IL12 shows potent antitumor activity by generating memory CD8+ T cells

Interleukin-12 (IL12) (p35/p40 complex) is a heterodimeric cytokine with potent anti-tumor activity. However, its short serum half-life and high dose-related toxicities limit its clinical efficacy. Here, we constructed heterodimeric immunoglobulin Fc-fused mouse IL12 (mIL12) in a monovalent binding format (mono-mIL12-Fc) to generate long-acting mIL12 in the naturally occurring heterodimeric form. Mono-mIL12-Fc exhibited a much longer plasma half-life than recombinant mIL12, enabling twice-weekly systemic injections to remove established tumors in syngeneic mouse models. Mono-mIL12-Fc was more potent than wild-type Fc-based bivalent-binding IL12-Fc (bi-mIL12-Fc) for eradicating large established immunogenic tumors without noticeable toxicities by enhancing interferon-γ production and the proliferation of immune effector cells in tumors. More importantly, mono-mIL12-Fc triggered weaker IL12 signaling than bi-mIL12-Fc, favoring the generation of functional and protective memory CD8⁺ T cells. Our results demonstrate that heterodimeric-Fc-fused IL12 is a suitable format for augmenting adaptive CD8⁺ T cell immune responses, providing a practical alternative to the systemic administration of IL12 for antitumor therapy.

Current progress in innovative engineered antibodies

As of May 1, 2017, 74 antibody-based molecules have been approved by a regulatory authority in a major market. Additionally, there are 70 and 575 antibody-based molecules in phase III and phase I/II clinical trials, respectively. These total 719 antibody-based clinical stage molecules include 493 naked IgGs, 87 antibody-drug conjugates, 61 bispecific antibodies, 37 total Fc fusion proteins, 17 radioimmunoglobulins, 13 antibody fragments, and 11 immunocytokines. New uses for these antibodies are being discovered each year. For oncology, many of the exciting new approaches involve antibody modulation of T-cells. There are over 80 antibodies in clinical trials targeting T cell checkpoints, 26 T-cell-redirected bispecific antibodies, and 145 chimeric antigen receptor (CAR) cell-based candidates (all currently in phase I or II clinical trials), totaling more than 250 T cell interacting clinical stage antibody-based candidates. Finally, significant progress has been made recently on routes of delivery, including delivery of proteins across the blood-brain barrier, oral delivery to the gut, delivery to the cellular cytosol, and gene- and viral-based delivery of antibodies. Thus, there are currently at least 864 antibody-based clinical stage molecules or cells, with incredible diversity in how they are constructed and what activities they impart. These are followed by a next wave of novel molecules, approaches, and new methods and routes of delivery, demonstrating that the field of antibody-based biologics is very innovative and diverse in its approaches to fulfill their promise to treat unmet medical needs.

Evolution of the magic bullet: Single chain antibody fragments for the targeted delivery of immunomodulatory proteins

Immunocytokines are fusion proteins that combine the specific antigen binding capacities of an antibody or derivative thereof and the potent bioactivity of a cytokine partner. These novel biopharmaceuticals have been directed to various targets of oncological as well as non-oncological origin and a handful of promising constructs are currently advancing in the clinical trial pipeline. Several factors such as the choice of a disease specific antigen, the antibody format and the modulatory nature of the payload are crucial, not only for therapeutic efficacy and safety but also for the commercial success of such a product. In this review, we provide an overview of the basic principles and obstacles in immunocytokine design with a specific focus on single chain antibody fragment-based constructs that employ interleukins as the immunoactive component. Impact statement Selective activation of the immune system in a variety of malignancies represents an attractive approach when existing strategies have failed to provide adequate treatment options. Immunocytokines as a novel class of bifunctional protein therapeutics have emerged recently and generated promising results in preclinical and clinical studies. In order to harness their full potential, multiple different aspects have to be taken into consideration. Several key points of these fusion constructs are discussed here and should provide an outline for the development of novel products based on an overview of selected formats.

EDB Fibronectin-Specific SPECT Probe 99mTc-HYNIC-ZD2 for Breast Cancer Detection

Extradomain-B fibronectin (EDB-FN), an oncofetal isoform of FN, is a promising diagnostic and therapeutic target of tumors, including breast cancer. Many EDB-FN-targeted drugs have been developed and have shown therapeutic effects in clinical trials. Molecular imaging to visualize EDB-FN-positive cancers may help select the right patients who will be benefit from EDB-FN-targeted therapy. Although a few EDB-FN-targeted imaging probes have been developed, the complicated manufacturing procedure and expensive material and equipment required limit their application for large-scale screening of EDB-FN-positive cancer patients. Thus, more simple and economic EDB-FN-targeted imaging probes are still urgently needed. Previously, we have identified a breast cancer-targeted peptide, CTVRTSADC. Coincidently, it was later identified as an EDB-FN-targeted peptide and named ZD2. In this study, we found a positive correlation between the binding activity of the ZD2 phage and the expression level of EDB-FN in breast cancer cells. Moreover, we observed the colocalization of the ZD2 peptide with EDB-FN in breast cancer cells. Furthermore, in vivo tumor targeting of the ZD2 phage, near-infrared fluorescence imaging, and flow cytometry showed tumor-specific homing of the ZD2 peptide in mice bearing EDB-FN-positive breast cancers. Importantly, on the basis of this EDB-FN-targeted ZD2 peptide, we developed a kit-formulated probe, ^99mTc-HYNIC-ZD2, for single-photon-emission computed tomography (SPECT) imaging of breast cancer. The high tumor uptake of ^99mTc-HYNIC-ZD2 demonstrated its feasibility for use in visualizing EDB-FN-positive breast cancers in vivo. This kit-formulated EDB-FN-targeted SPECT probe has potential clinical applications for precision screening of EDB-FN-positive cancer patients who may benefit from EDB-FN-targeted therapy.

Addressing the Immunogenicity of the Cargo and of the Targeting Antibodies with a Focus on Demmunized Bacterial Toxins and on Antibody-Targeted Human Effector Proteins

Third-generation immunotoxins are composed of a human, or humanized, targeting moiety, usually a monoclonal antibody or an antibody fragment, and a non-human effector molecule. Due to the non-human origin of the cytotoxic domain, these molecules stimulate potent anti-drug immune responses, which limit treatment options. Efforts are made to deimmunize such immunotoxins or to combine treatment with immunosuppression. An alternative approach is using the so-called “human cytotoxic fusion proteins”, in which antibodies are used to target human effector proteins. Here, we present three relevant approaches for reducing the immunogenicity of antibody-targeted protein therapeutics: (1) reducing the immunogenicity of the bacterial toxin, (2) fusing human cytokines to antibodies to generate immunocytokines and (3) addressing the immunogenicity of the targeting antibodies.

Tumor rim cells: From resistance to vascular targeting agents to complete tumor ablation

Current vascular targeting strategies pursue two main goals: anti-angiogenesis agents aim to halt sprouting and the formation of new blood vessels, while vascular disrupting agents along with coaguligands seek to compromise blood circulation in the vessels. The ultimate goal of such therapies is to deprive tumor cells out of oxygen and nutrients long enough to succumb cancer cells to death. Most of vascular targeting agents presented promising therapeutic potential, but the final goal which is cure is rarely achieved. Nevertheless, in both preclinical and clinical settings, tumors tend to grow back, featuring a highly invasive, metastatic, and extremely resistant form. This review highlights the critical significance of tumor rim cells as the main factor, determining therapy success with vascular targeting agents. We present an overview of different single and combination treatments with vascular targeting agents that enable efficient targeting of tumor rim cells and long-lasting tumor cure. Understanding the nature of tumor rim cells, how they establish, how they manage to survive of vascular targeting agents, and how they contribute in tumor refractoriness, may open new avenues to the development of beneficial strategies, capable to eliminate residual rim cells, and enable tumor ablation once and forever.

Targeting Fibronectin for Cancer Imaging and Therapy

During cancer progression, the extracellular matrix (ECM) undergoes dramatic changes, which promote cancer cell migration and invasion. In the remodeled tumor ECM, fibronectin (FN) level is upregulated to assist tumor growth, progression, and invasion. FN serves as a central organizer of ECM molecules and mediates the crosstalk between the tumor microenvironment and cancer cells. Its upregulation is correlated with angiogenesis, cancer progression, metastasis, and drug resistance. A number of FN-targeting ligands have been developed for cancer imaging and therapy. Thus far, FN-targeting imaging agents have been tested for nuclear imaging, MRI, and fluorescence imaging, for tumor detection and localization. FN-targeting therapeutics, including nuclear medicine, chemotherapy drugs, cytokines, and photothermal moieties, were also developed in cancer therapy. Because of the prevalence of FN overexpression in cancer, FN targeting imaging agents and therapeutics have the promise of broad applications in the diagnosis, treatment, and image-guided interventions of many types of cancers. This review will summarize current understanding on the role of FN in cancer, discuss the design and development of FN-targeting agents, and highlight the applications of these FN-targeting agents in cancer imaging and therapy.

Targeted Reconstitution of Cytokine Activity upon Antigen Binding using Split Cytokine Antibody Fusion Proteins

The targeted assembly of antibody products upon antigen binding represents a novel strategy for the reconstitution of potent therapeutic activity at the site of disease, sparing healthy tissues. We demonstrate that interleukin-12, a heterodimeric pro-inflammatory cytokine consisting of the disulfide-linked p40 and p35 subunits, can be reconstituted by sequential reassembly of fusion proteins based on antibody fragments and interleukin-12 subunit mutants. Analysis of the immunostimulatory properties of interleukin-12 and its derivatives surprisingly revealed that the mutated p35 subunit partially retained the activity of the parental cytokine, whereas the p40 subunit alone was not able to stimulate T cells or natural killer cells. The concept of stepwise antibody-based reassembly of split cytokines could be useful for the development of other anticancer therapeutics with improved safety and tolerability.

Immunoscintigraphy of patients with head and neck carcinomas, with an anti-angiogenetic antibody fragment

Objective

In a phase I/II clinical study, we investigated tumor targeting in patients with head and neck squamous cell carcinomas (SCC), using an antibody directed against the extra-domain-B of fibronectin (EDB), a marker of angiogenesis and tissue remodeling.

Study Design And Setting

Five patients with SCC were injected with the 123-iodine-radiolabeled L19(scFv)2 antibody and underwent scintigraphic detection with single photon emission tomography with computerized tomography (SPECT/CT). In addition, 18 F-fluorodeoxyglucose ( 18 FDG) positron emission tomography with computerized tomography (PET/CT) was performed.

Results

Successful targeting of the primary tumor could be achieved in 4 of 5 patients and was comparable to PET imaging. No side effects were observed.

Conclusions

Tumor targeting with the L19(scFv)2 antibody is also feasible for head and neck SCC.

Significance

These results may serve as a base for future therapeutical applications in human beings, with modified versions of the L19(scFv)2 antibody, designed to selectively deliver bioactive molecules into malignant tumors.

Immunocytokines for cancer treatment: past, present and future

Immunocytokines are antibody-cytokine fusion proteins, with the potential to preferentially localize on tumor lesions and to activate anticancer immunity at the site of disease. Various tumor targets (e.g., cell membrane antigens and extracellular matrix components) and antibody formats (e.g., intact IgG and antibody fragments) have been considered for immunocytokine development and some products have advanced to clinical trials. In this review, we present relevant concepts and strategies for the design and use of anticancer immunocytokine products. In addition, we discuss emerging strategies for the pharmaceutical development and clinical application of this promising class of biopharmaceuticals.

Genetically Engineered Multivalent Proteins for Targeted Immunotherapy

mAbs initiated the unprecedented breakthroughs in cancer immunotherapy and are rapidly evolving with multiple therapeutic platforms. One next-generation strategy engineers multivalent proteins that ligate single-chain variable fragments targeting cellular effectors, tumor-associated antigens, and cytokines. These developing therapeutics target and regulate cellular effector bioactivity and significantly improve clinical outcomes. Clin Cancer Res; 22(14); 3419-21. ©2016 AACRSee related article by Vallera et al., p. 3440.

Immunocytokines and bispecific antibodies: two complementary strategies for the selective activation of immune cells at the tumor site

The activation of the immune system for a selective removal of tumor cells represents an attractive strategy for the treatment of metastatic malignancies, which cannot be cured by existing methodologies. In this review, we examine the design and therapeutic potential of immunocytokines and bispecific antibodies, two classes of bifunctional products which can selectively activate the immune system at the tumor site. Certain protein engineering aspects, such as the choice of the antibody format, are common to both classes of therapeutic agents and can have a profound impact on tumor homing performance in vivo of individual products. However, immunocytokines and bispecific antibodies display different mechanisms of action. Future research activities will reveal whether an additive of even synergistic benefit can be obtained from the judicious combination of these two types of biopharmaceutical agents.

Fibronectin-targeted drug delivery in cancer

Fibronectin is an extracellular matrix protein with pivotal physiological and pathological functions in development and adulthood. Alternative splicing of the precursor mRNA, produced from the single copy fibronectin gene, occurs at three sites coding for the EDA, EDB and IIICS domains. Fibronectin isoforms comprising the EDA or EDB domains are known as oncofetal forms due to their developmental importance and their re-expression in tumors, contrasting with restricted presence in normal adult tissues. These isoforms are also recognized as important markers of angiogenesis, a crucial physiological process in development and required by tumor cells in cancer progression. Attributed to this feature, EDA and EDB domains have been extensively used for the targeted delivery of cytokines, cytotoxic agents, chemotherapy drugs and radioisotopes to fibronectin-expressing tumors to exert therapeutic effects on primary cancers and metastatic lesions. In addition to drug delivery, the EDA and EDB domains of fibronectin have also been utilized to develop imaging strategies for tumor tissues. Furthermore, EDA and EDB based vaccines seem to be promising for the treatment and prevention of certain cancer types. In this review, we will summarize recent advances in fibronectin EDA and EDB-based therapeutic strategies developed to treat cancer.

Immunocytokines: a novel class of products for the treatment of chronic inflammation and autoimmune conditions

Antibody-cytokine fusion proteins, often referred to as immunocytokines, represent a novel class of biopharmaceutical agents that combine the disease-homing activity of certain antibodies with the immunomodulatory properties of cytokine payloads. Originally, immunocytokines were mainly developed for cancer therapy applications. More recently, however, the use of anti-inflammatory cytokines for the treatment of chronic inflammatory conditions and to treat autoimmune diseases has been considered. This review analyzes basic principles in the design of immunocytokines and describes the most advanced products in preclinical and clinical development.

Fibronectin Mechanobiology Regulates Tumorigenesis

Fibronectin (Fn) is an essential extracellular matrix (ECM) glycoprotein involved in both physiological and pathological processes. The structure–function relationship of Fn has been and is still being studied, as changes in its molecular structure are integral in regulating (or dysregulating) its biological activities via its cell, matrix component, and growth factor binding sites. Fn comprises three types of repeating modules; among them, FnIII modules are mechanically unstable domains that may be extended/unfolded upon cell traction and either uncover cryptic binding sites or disrupt otherwise exposed binding sites. Cells assemble Fn into a fibrillar network; its conformational flexibility implicates Fn as a critical mechanoregulator of the ECM. Fn has been shown to contribute to altered stroma remodeling during tumorigenesis. This review will discuss (i) the significance of the structure–function relationship of Fn at both the molecular and the matrix scales, (ii) the role of Fn mechanobiology in the regulation of tumorigenesis, and (iii) Fn-related advances in cancer therapy development.

The antibody-mediated targeted delivery of interleukin-13 to syngeneic murine tumors mediates a potent anticancer activity

We describe the expression and in vivo characterization of an antibody-cytokine fusion protein, based on murine Interleukin-13 (IL13) and the monoclonal antibody F8, specific to the alternatively spliced extra domain A of fibronectin, a marker of neo-angiogenesis. The IL13 moiety was fused at the C-terminal extremity of the F8 antibody in diabody format. The resulting F8-IL13 immunocytokine retained the full binding properties of the parental antibody and cytokine bioactivity. The fusion protein could be expressed in mammalian cells, purified to homogeneity and showed a preferential accumulation at the tumor site. When used as single agent at doses of 200 μg, F8-IL13 exhibited a strong inhibition of tumor growth rate in two models of cancer (F9 teratocarcinoma and Wehi-164), promoting an infiltration of various types of leukocytes into the neoplastic mass. This anticancer activity could be potentiated by combination with an immunocytokine based on the F8 antibody and murine IL12, leading to complete and long-lasting tumor eradications. Mice cured from Wehi-164 sarcomas acquired a durable protective antitumor immunity, and selective depletion of immune cells revealed that the antitumor activity was mainly mediated by cluster of differentiation 4-positive T cells. This study indicates that IL13 can be efficiently delivered to the tumor neo-vasculature and that it mediates a potent anticancer activity in the two models of cancer investigated in this study. The observed mechanism of action for F8-IL13 was surprising, since immunocytokines based on other payloads (e.g., IL2, IL4, IL12 and TNF) eradicate cancer by the combined contribution of natural killer cells and cluster of differentiation 8-positive T cells.

Antigen specificity can be irrelevant to immunocytokine efficacy and biodistribution

Cytokine therapy can activate potent, sustained antitumor responses, but collateral toxicity often limits dosages. Although antibody-cytokine fusions (immunocytokines) have been designed with the intent to localize cytokine activity, systemic dose-limiting side effects are not fully ameliorated by attempted tumor targeting. Using the s.c. B16F10 melanoma model, we found that a nontoxic dose of IL-2 immunocytokine synergized with tumor-specific antibody to significantly enhance therapeutic outcomes compared with immunocytokine monotherapy, concomitant with increased tumor saturation and intratumoral cytokine responses. Examination of cell subset biodistribution showed that the immunocytokine associated mainly with IL-2R-expressing innate immune cells, with more bound immunocytokine present in systemic organs than the tumor microenvironment. More surprisingly, immunocytokine antigen specificity and Fcγ receptor interactions did not seem necessary for therapeutic efficacy or biodistribution patterns because immunocytokines with irrelevant specificity and/or inactive mutant Fc domains behaved similarly to tumor-specific immunocytokine. IL-2-IL-2R interactions, rather than antibody-antigen targeting, dictated immunocytokine localization; however, the lack of tumor targeting did not preclude successful antibody combination therapy. Mathematical modeling revealed immunocytokine size as another driver of antigen targeting efficiency. This work presents a safe, straightforward strategy for augmenting immunocytokine efficacy by supplementary antibody dosing and explores underappreciated factors that can subvert efforts to purposefully alter cytokine biodistribution.

Beyond peptides and mAbs--current status and future perspectives for biotherapeutics with novel constructs

Biotherapeutics are attractive anti-cancer agents due to their high specificity and limited toxicity compared to conventional small molecules. Antibodies are widely used in cancer therapy, either directly or conjugated to a cytotoxic payload. Peptide therapies, though not as prevalent, have been utilized in hormonal therapy and imaging. The limitations associated with unmodified forms of both types of biotherapeutics have led to the design and development of novel structures, which incorporate key features and structures that have improved the molecules' abilities to bind to tumor targets, avoid degradation, and exhibit favorable pharmacokinetics. In this review, we highlight the current status of monoclonal antibodies and peptides, and provide a perspective on the future of biotherapeutics using novel constructs.

Armed antibodies for cancer treatment: a promising tool in a changing era

Advances in the understanding of tumor immunology and molecular biology of melanoma cells have favored a larger application of immunotherapy and targeted therapies in the clinic. Several selective mutant gene inhibitors and immunomodulating antibodies have been reported to improve overall survival or progression-free survival in metastatic melanoma patients. However, despite impressive initial responses, patients treated with selective inhibitors relapse quickly, and toxicities associated to the use of immunomodulating antibodies are not easily manageable. In this sense, the concept of using antibodies as delivery vehicles for the preferential in vivo localization of the drug at the site of disease with reduction of side effects has raised particular interest. Antibody-cytokine fusion proteins (termed immunocytokines) represent a new simple and effective way to deliver the immunomodulatory payload at the tumor site, with the aim of inducing both local and systemic antitumoral immune responses and limiting systemic toxicities. Several clinical trials have been conducted and are actually ongoing with different immunocytokines, in several tumor histotypes. In metastatic melanoma patients, different drug delivery modalities such as systemic, loco-regional and intratumoral are under investigation. In this review, the rationale for the use of L19-IL2 and L19-TNF, two clinical stage immunocytokines produced by the Philogen group, as well as opportunities for their future development will be discussed.

Interleukin-7 and interleukin-15 for cancer

Interleukin 7 and 15 are considered powerful pro-inflammatory cytokines, they have the ability to destabilize chromosomes and induce tumorigenesis. Additionally, they can control malignancy proliferation by influencing the tumor microenvironment and immune system. Immunotherapy has been proposed as a treatment modality for malignancy for over a decade; the exact mechanisms of action and pathways are still under investigation. Interleukin 7 and 15 have been extensively investigated in hematological malignancies since their mode of action influences the stimulation of the immune system in a more direct way than other malignancies such as lung, melanoma, and breast, renal and colorectal cancer.

The development of immunoconjugates for targeted cancer therapy

Immunoconjugates are specific, highly effective, minimally toxic anticancer therapies that are beginning to show promise in the clinic. Immunoconjugates consist of three separate components: an antibody that binds to a cancer cell antigen with high specificity, an effector molecule that has a high capacity to kill the cancer cell, and a linker that will ensure the effector does not separate from the antibody during transit and will reliably release the effector to the cancer cell or tumour stroma. The high affinity antibody-antigen interaction allows specific and selective delivery of a range of effectors, including pharmacologic agents, radioisotopes, and toxins, to cancer cells. Some anticancer molecules are not well tolerated when administered systemically owing to unacceptable toxicity to the host. However, this limitation can be overcome through the linking of such cytotoxins to specific antibodies, which mask the toxic effects of the drug until it reaches its target. Conversely, many unconjugated antibodies are highly specific for a cancer target, but have low therapeutic potential and can be repurposed as delivery vehicles for highly potent effectors. In this Review, we summarize the successes and shortcomings of immunoconjugates, and discuss the future potential for the development of these therapies.

New insights into IL-12-mediated tumor suppression

During the past two decades, interleukin-12 (IL-12) has emerged as one of the most potent cytokines in mediating antitumor activity in a variety of preclinical models. Through pleiotropic effects on different immune cells that form the tumor microenvironment, IL-12 establishes a link between innate and adaptive immunity that involves different immune effector cells and cytokines depending on the type of tumor or the affected tissue. The robust antitumor response exerted by IL-12, however, has not yet been successfully translated into the clinics. The majority of clinical trials involving treatment with IL-12 failed to show sustained antitumor responses and were associated to toxic side effects. Here we discuss the therapeutic effects of IL-12 from preclinical to clinical studies, and will highlight promising strategies to take advantage of the antitumor activity of IL-12 while limiting adverse effects.

Preclinical evaluation of IL2-based immunocytokines supports their use in combination with dacarbazine, paclitaxel and TNF-based immunotherapy

Antibody-cytokine fusion proteins ("immunocytokines") represent a promising class of armed antibody products, which allow the selective delivery of potent pro-inflammatory payloads at the tumor site. The antibody-based selective delivery of interleukin-2 (IL2) is particularly attractive for the treatment of metastatic melanoma, an indication for which this cytokine received marketing approval from the US Food and drug administration. We used the K1735M2 immunocompetent syngeneic model of murine melanoma to study the therapeutic activity of F8-IL2, an immunocytokine based on the F8 antibody in diabody format, fused to human IL2. F8-IL2 was shown to selectively localize at the tumor site in vivo, following intravenous administration, and to mediate tumor growth retardation, which was potentiated by the combination with paclitaxel or dacarbazine. Combination treatment led to a substantially more effective tumor growth inhibition, compared to the cytotoxic drugs used as single agents, without additional toxicity. Analysis of the immune infiltrate revealed a significant accumulation of CD4(+) T cells 24 h after the administration of the combination. The fusion proteins F8-IL2 and L19-IL2, specific to the alternatively spliced extra domain A and extra domain B of fibronectin respectively, were also studied in combination with tumor necrosis factor (TNF)-based immunocytokines. The combination treatment was superior to the action of the individual immunocytokines and was able to eradicate neoplastic lesions after a single intratumoral injection, a procedure that is being clinically used for the treatment of Stage IIIC melanoma. Collectively, these data reinforce the rationale for the use of IL2-based immunocytokines in combination with cytotoxic agents or TNF-based immunotherapy for the treatment of melanoma patients.

Tumor-targeting properties of novel immunocytokines based on murine IL1β and IL6

There is an increasing biotechnological interest in 'arming' therapeutic antibodies with bioactive payloads. Many antibody-cytokine fusion proteins (immunocytokines) have been described and some of these biopharmaceuticals have progressed to clinical studies. Here, we describe for the first time the expression and in vivo characterization of immunocytokines based on murine IL1β and IL6. These potent pro-inflammatory cytokines were fused at the N-terminus or at the C-terminus of the monoclonal antibodies F8 (specific to the alternatively-spliced extra-domain A domain of fibronectin, a marker of tumor angiogenesis). All immunocytokines retained the binding properties of the parental antibody and were homogenous, when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography, except for the N-terminal fusion of IL1β which revealed the presence of glycosylated species. When analyzed by quantitative biodistribution analysis using radioiodinated protein preparations, F8 fusions with IL6 revealed a preferential accumulation at the tumor site for both cytokine orientations, whereas IL1β fusions exhibited lower tumor to organ ratios and a slower blood clearance profile. The fusion proteins with the cytokine payload at the C-terminus were studied in therapy experiments in immunocompetent mice bearing F9 tumors. Immunocytokines based on IL1β resulted in 10% body weight loss at a 5-µg dose, whereas IL6-based products caused a 5% body weight loss at a 225-µg dose. Both F8-IL1β and F8-IL6 exhibited a <50% inhibition of tumor growth rate, which was substantially lower than the one previously reported for F8-TNF, a closely related pro-inflammatory immunocytokine. This study indicates that IL6 can be efficiently delivered to the tumor neo-vasculature by fusion with the F8 antibody. While F8-IL6 was not as potent as other F8-based immunocytokines that exhibit similar biodistribution profiles, the fusion protein sheds light on the different roles of pro-inflammatory cytokines in boosting immunity against the tumor.

Antibody-based delivery of interleukin-2 to neovasculature has potent activity against acute myeloid leukemia

Acute myeloid leukemia (AML) is a rapidly progressing disease that is accompanied by a strong increase in microvessel density in the bone marrow. This observation prompted us to stain biopsies of AML and acute lymphoid leukemia (ALL) patients with the clinical-stage human monoclonal antibodies F8, L19, and F16 directed against markers of tumor angiogenesis. The analysis revealed that the F8 and F16 antibodies strongly stained 70% of AML and 75% of ALL bone marrow specimens, whereas chloroma biopsies were stained with all three antibodies. Therapy experiments performed in immunocompromised mice bearing human NB4 leukemia with the immunocytokine F8-IL2 [consisting of the F8 antibody fused to human interleukin-2 (IL-2)] mediated a strong inhibition of AML progression. This effect was potentiated by the addition of cytarabine, promoting complete responses in 40% of treated animals. Experiments performed in immunocompetent mice bearing C1498 murine leukemia revealed long-lasting complete tumor eradication in all treated mice. The therapeutic effect of F8-IL2 was mediated by both natural killer cells and CD8(+) T cells, whereas CD4(+) T cells appeared to be dispensable, as determined in immunodepletion experiments. The treatment of an AML patient with disseminated extramedullary AML manifestations with F16-IL2 (consisting of the F16 antibody fused to human IL-2, currently being tested in phase 2 clinical trials in patients with solid tumors) and low-dose cytarabine showed significant reduction of AML lesions and underlines the translational potential of vascular tumor-targeting antibody-cytokine fusions for the treatment of patients with leukemia.

Immunocytokines: a review of molecules in clinical development for cancer therapy

The concept of therapeutically enhancing the immune system’s responsiveness to tumors is long standing. Several cytokines have been investigated in clinical trials for their therapeutic activity in cancer patients. However, substantial side effects and unfavorable pharmacokinetic properties have been a major drawback hampering the administration of therapeutically relevant doses. The use of recombinant antibody–cytokine fusion proteins promises to significantly enhance the therapeutic index of cytokines by targeting them to the site of disease. This review aims to provide a concise and complete overview of the preclinical data and clinical results currently available for all immunocytokines having reached clinical development.

Combination therapy of immunocytokines with ipilimumab: a cure for melanoma?

Although biological therapy has shown promising clinical responses in many cancers including metastatic melanoma, only a subset of patients has shown marked regression of lesions. In most patients, systemic administration of biological therapies with cytokines is associated with severe toxicities. Schwager et al., in this issue of Journal of Investigative Dermatology, have examined the role of immunocytokines L19-IL2 and L19-TNF to minimize toxicities, and in combination with Ipilimumab they report complete regression of tumors using syngeneic mouse models. The results, if confirmed in clinical trials, will have major implications for the treatment of human cancers, including melanomas.

Molecular MRI of liver fibrosis by a peptide-targeted contrast agent in an experimental mouse model

OBJECTIVES

Cyclic decapeptide CGLIIQKNEC (CLT1) has been demonstrated to target fibronectin-fibrin complexes in the extracellular matrix of different tumors and tissue lesions. Although liver fibrosis is characterized by an increased amount of extracellular matrix consisting of fibril-forming collagens and matrix glycoconjugates such as fibronectin, we aimed to investigate the feasibility of detecting and characterizing liver fibrosis using CLT1 peptide-targeted nanoglobular contrast agent (Gd-P) with dynamic contrast-enhanced magnetic resonance imaging in an experimental mouse model of liver fibrosis at 7 T.

MATERIALS AND METHODS

Gd-P, control peptide KAREC conjugated nanoglobular contrast agent (Gd-CP), and control nontargeting nanoglobular contrast agent (Gd-C) were synthesized. Male adult C57BL/6N mice (22-25 g; N = 54) were prepared and were divided into fibrosis (n = 36) and normal (n = 18) groups. Liver fibrosis was induced in the fibrosis group through subcutaneous injection of 1:3 mixture of carbon tetrachloride (CCl(4)) in olive oil at a dose of 4 μL/g of body weight twice a week for 8 weeks. Dynamic contrast-enhanced MRI was performed in all animals. Dynamic contrast-enhanced magnetic resonance imaging was analyzed to yield postinjection ΔR(1)(t) maps for quantitative measurements. Histological analysis was also performed.

RESULTS

Differential enhancements were observed and characterized between the normal and fibrotic livers using Gd-P at 0.03 mmol/kg, when compared with nontargeted controls (Gd-CP and Gd-C). For Gd-P injection, both the peak and steady-state ΔR(1) of the normal livers were significantly lower than those after 4 and 8 weeks of CCl(4) dosing. Liver fibrogenesis with increased amount of fibronectin in the extracellular space in insulted livers were confirmed by histological observations.

CONCLUSIONS

These results indicated that dynamic contrast-enhanced magnetic resonance imaging with CLT1 peptide-targeted nanoglobular contrast agent can detect and stage liver fibrosis by probing the accumulation of fibronectin in fibrotic livers.

A novel model for evaluating therapies targeting human tumor vasculature and human cancer stem-like cells

Human tumor vessels express tumor vascular markers (TVM), proteins that are not expressed in normal blood vessels. Antibodies targeting TVMs could act as potent therapeutics. Unfortunately, preclinical in vivo studies testing anti-human TVM therapies have been difficult to do due to a lack of in vivo models with confirmed expression of human TVMs. We therefore evaluated TVM expression in a human embryonic stem cell-derived teratoma (hESCT) tumor model previously shown to have human vessels. We now report that in the presence of tumor cells, hESCT tumor vessels express human TVMs. The addition of mouse embryonic fibroblasts and human tumor endothelial cells significantly increases the number of human tumor vessels. TVM induction is mostly tumor-type-specific with ovarian cancer cells inducing primarily ovarian TVMs, whereas breast cancer cells induce breast cancer specific TVMs. We show the use of this model to test an anti-human specific TVM immunotherapeutics; anti-human Thy1 TVM immunotherapy results in central tumor necrosis and a three-fold reduction in human tumor vascular density. Finally, we tested the ability of the hESCT model, with human tumor vascular niche, to enhance the engraftment rate of primary human ovarian cancer stem-like cells (CSC). ALDH(+) CSC from patients (n = 6) engrafted in hESCT within 4 to 12 weeks whereas none engrafted in the flank. ALDH(-) ovarian cancer cells showed no engraftment in the hESCT or flank (n = 3). Thus, this model represents a useful tool to test anti-human TVM therapy and evaluate in vivo human CSC tumor biology.

Tumor targeting of the IL-15 superagonist RLI by an anti-GD2 antibody strongly enhances its antitumor potency

Immunocytokines (ICKs) targeting cytokines to the tumor environment using antibodies directed against a tumor-associated antigen often have a higher therapeutic index than the corresponding unconjugated cytokines. Various ICKs displaying significant antitumoral effects in several murine tumor models have already been developed, and some of them, in particular interleukin (IL)-2-based ICKs, are in Phase II clinical trials. Although sharing common biological activities with IL-2 in vitro, IL-15 is now considered as having a better potential in antitumor immunotherapeutical strategies and has been shown to be less toxic than IL-2 in preclinical studies. We previously developed the fusion protein RLI, linking a soluble form of human IL-15Rα-sushi+ domain to human IL-15. RLI showed better biological activities than IL-15 in vitro as well as higher antitumoral effects in vivo in murine and human cancer models. Here, we investigated, in the context of an ICK, the effect of associating RLI with an antibody targeting the GD2 ganglioside, a validated tumoral target expressed on many neurectodermal tumors. Anti-GD2-RLI fully retained the cytokine potential of RLI and the antibody effector functions (antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity). It displayed strong antitumor activities in two syngeneic cancer models in immunocompetent mice (subcutaneous EL4 and metastatic NXS2). Its therapeutic potency was higher than those of RLI and anti-GD2 alone or in combination. We suggest that this is related to its bifunctional (cytokine and antibody) nature.

A critical evaluation of the tumor-targeting properties of bispecific antibodies based on quantitative biodistribution data

Bispecific and bifunctional antibodies are attracting considerable interest as innovative anti-cancer therapeutics, but their ability to selectively localize at the tumor site has rarely been studied by quantitative biodistribution studies in immunocompetent animal models or in patients. Here, we describe the production of a novel bifunctional antibody, consisting of the F8 antibody (specific to the alternatively spliced EDA domain of fibronectin) fused to the extracellular portion of CD86 (co-stimulatory molecule B7.2). However, the fusion molecule was unable to target tumors in vivo. These data suggest that bispecific antibodies do not always localize on tumors and should therefore be characterized by imaging or biodistribution studies.

The antibody-based delivery of interleukin-12 to the tumor neovasculature eradicates murine models of cancer in combination with paclitaxel

PURPOSE

Interleukin-12 (IL12) is a potent proinflammatory cytokine with antitumor activity. Its heterodimeric nature makes it compatible with a large variety of different immunocytokine formats. Here we report the design, production, and characterization of a novel immunocytokine, based on the fusion of the F8 antibody (specific to the alternatively spliced EDA domain of fibronectin, a marker of tumor neovasculature) with IL12 (termed IL12-F8-F8).

EXPERIMENTAL DESIGN

We developed a novel immunocytokine based on the sequential fusion of interleukin-12 as a single polypeptide with two F8 antibodies in single-chain Fv (scFv) format. The fusion protein was characterized in vitro, and its targeting performance was assessed in vivo. The immunocytokine antitumor activity was studied as monotherapy as well as in combination therapies in three different murine tumor models. Moreover, depletion experiments and tumor analysis revealed a dominant role of natural killer cells for the mechanism of action.

RESULTS

IL12-F8-F8 can be produced in mammalian cells, yielding a product of good pharmaceutical quality, capable of selective localization on the tumor neovasculature in vivo, as judged by quantitative biodistribution analysis with radioiodinated protein preparations. The protein potently inhibited tumor growth in three different immunocompetent syngeneic models of cancer. The treatment was generally well tolerated. Moreover, the IL12-F8-F8 fusion protein could be produced both with murine IL12 (mIL12) and with human IL12 (hIL12).

CONCLUSIONS

The potent antitumor activity of mIL12-F8-F8, studied alone or in combination with paclitaxel in different tumor models, paves the way to the clinical development of the fully human immunocytokine.

Local delivery of recombinant adenovirus expressing hepatitis B virus X protein and interleukin-12 results in antitumor effects via inhibition of hepatoma cell growth and intervention of tumor microenvironment

Hepatocellular carcinoma (HCC) is a typical hypervascular tumor. Our previous studies have demonstrated that hepatitis B virus X protein (HBx) was able to inhibit the growth of HCC cells via inducing apoptosis and inhibiting tumor angiogenesis. Interleukin-12 (IL-12) is a disulfide-linked heterodimeric cytokine with potent immunostimulatory activity and anti-angiogenic properties. In this study, to further investigate the regulatory effect of IL-12 on HBx-mediated intervention of hepatoma microenvironment especially on intervention of neovessels and immune microenvironment, we constructed the recombinant adenovirus expressing HBx and mouse IL-12 named Ad-HBx-mIL-12. HBx-mIL-12 could effectively suppress tumor growth and induce apoptosis in vivo. Moreover, treatment with Ad-HBx-mIL-12 not only induced a massive accumulation of immune cells (CD8(+) T leukocytes, macrophages and dendritic cells) in tumors in situ, also apparently reduced the number of angiogenic blood vessels within tumor tissues. These results suggest that HBx-mIL-12 can not only induce cell cycle arrest and apoptosis in HCC cells, but also effectively shift the tumor microenvironment from pro-oncogenic to antitumor through recruitment of immune cells and inhibiting stromal cell growth, such as vascular endothelial cells.

Angiogenic activity of classical hematopoietic cytokines

Hematopoiesis is regulated by several cytokines with pleiotropic activity. Several evidences have clearly demonstrated that these molecules, formerly regarded as specific for the hematopoietic system, also affect certain endothelial cell functions and that hematopoietic factors clearly influence angiogenesis. This review article summarizes the most important literature data concerning this inconvertible relationship.

Local delivery of interleukin-12 using T cells targeting VEGF receptor-2 eradicates multiple vascularized tumors in mice

PURPOSE

We investigated the feasibility of delivering the proinflammatory cytokine interleukin (IL)-12 into tumor using T cells genetically engineered to express a chimeric antigen receptor (CAR) against the VEGF receptor-2 (VEGFR-2).

EXPERIMENTAL DESIGN

Two different strains of mice bearing five different established subcutaneous tumors were treated with syngeneic T cells cotransduced with an anti-VEGFR-2 CAR and a constitutively expressed single-chain murine IL-12 or an inducible IL-12 gene after host lymphodepletion. Tumor regression, survival of mice, and persistence of the transferred cells were evaluated.

RESULTS

Adoptive transfer of syngeneic T cells cotransduced with an anti-VEGFR-2 CAR and a constitutively expressing single-chain IL-12 resulted in the regression of five different established tumors of different histologies without the need for IL-2 administration. T cells transduced with either anti-VEGFR-2 CAR or single-chain IL-12 alone did not alter the tumor growth indicating that both of them had to be expressed in the same cell to mediate tumor regression. Anti-VEGFR-2 CAR and IL-12-cotransduced T cells infiltrated the tumors, expanded, and persisted for prolonged periods. The antitumor effect did not require the presence of host T and B cells but was dependent on host IL-12R-expressing cells. The anti-VEGFR-2 CAR changed the immunosuppressive tumor environment by altering/reducing both the systemic and the intratumoral CD11b(+)Gr1(+) myeloid suppressor cell subsets that expressed VEGFR-2.

CONCLUSIONS

These results suggest that targeted delivery of IL-12 into the tumor environment with T cells redirected against VEGFR-2 is a promising approach for treating patients with a variety of solid tumor types.

Immunocytokines: a novel class of potent armed antibodies

Several cytokines have been investigated in clinical trials, based on their potent therapeutic activity observed in animal models of cancer and other diseases. However, substantial toxicities are often reported at low doses, thus preventing escalation to therapeutically active regimens. The use of recombinant antibodies or antibody fragments as delivery vehicles promises to enhance greatly the therapeutic index of pro-inflammatory and anti-inflammatory cytokines. This review surveys preclinical and clinical data published in the field of antibody-cytokine fusions (immunocytokines). Molecular determinants (such as molecular format, valence, target antigen), which crucially contribute to immunocytokine performance in vivo, are discussed in the article, as well as recent trends for the combined use of this novel class of biopharmaceuticals with other therapeutic agents.

The targeted delivery of IL17 to the mouse tumor neo-vasculature enhances angiogenesis but does not reduce tumor growth rate

There has been a long controversy as to whether interleukin-17 (IL17) has an impact on tumor growth. In order to assess whether IL17 may affect tumor growth, it would be convenient to achieve high levels of this pro-inflammatory cytokine at the tumor neo-vasculature, since IL17 is known to promote angiogenesis. Here, we have generated and tested in vivo a fusion protein, consisting of the F8 antibody (specific to the alternatively spliced EDA domain of fibronectin, a marker of angiogenesis) and of murine IL17 (mIL17). The resulting immunocytokine (termed F8-mIL17) was shown to selectively localize at the tumor neo-vasculature and to vigorously promote tumor angiogenesis, without however reducing or enhancing tumor growth rate both in immunocompetent and in immunodeficient mice.

Novel insights into the role of interleukin-27 and interleukin-23 in human malignant and normal plasma cells

Multiple myeloma is a monoclonal postgerminal center tumor that has phenotypic features of plasmablasts and/or plasma cells and usually localizes at multiple sites in the bone marrow. The pathogenesis of multiple myeloma is complex and dependent on the interactions between tumor cells and their microenvironment. Different cytokines, chemokines, and proangiogenic factors released in the tumor microenvironment are known to promote multiple myeloma cell growth. Here, we report recent advances on the role of 2 strictly related immunomodulatory cytokines, interleukin-27 (IL-27) and IL-23, in human normal and neoplastic plasma cells, highlighting their ability to (i) act directly against multiple myeloma cells, (ii) influence the multiple myeloma microenvironment by targeting osteoclast and osteoblast cells, and (iii) modulate normal plasma cell function. Finally, the therapeutic implication of these studies is discussed.

Absence of IL-12Rβ2 in CD33(+)CD38(+) pediatric acute myeloid leukemia cells favours progression in NOD/SCID/IL2RγC-deficient mice

Childhood acute myeloid leukemia (AML) is a hematological malignancy in which tumor burden is continuously replenished by leukemic-initiating cells (ICs), which proliferate slowly and are refractory to chemotherapeutic agents. We investigated whether interleukin (IL)-12, an immuno-modulatory cytokine with anti-tumor activity, may target AML blasts (CD45(+)CD33(+)) and populations known to contain leukemia ICs (that is, CD34(+)CD38(-), CD33(+)CD38(+) and CD44(+)CD38(-) cells). We demonstrate for the first time that: i) AML blasts and their CD34(+)CD38(-), CD33(+)CD38(+), CD44(+)CD38(-) subsets express the heterodimeric IL-12 receptor (IL-12R), ii) AML cells injected subcutaneously into NOD/SCID/Il2rg(-/-) (NSG) mice developed a localized tumor mass containing leukemic ICs and blasts that were virtually eliminated by IL-12 treatment, iii) AML cells injected intravenously into NSG mice engrafted within the first month in the spleen, but not in bone marrow or peripheral blood. At this time, IL-12 dramatically dampened AML CD45(+)CD33(+), CD34(+)CD38(-), CD33(+)CD38(+) and CD44(+)CD38(-) populations, only sparing residual CD33(+)CD38(+) cells that did not express IL-12Rβ2. From 30 to 60 days after the initial inoculum, these IL-12-unresponsive cells expanded and metastasized in both control and IL-12-treated NSG mice. Our data indicate that the absence of IL-12Rβ2 in pediatric AML cells favours leukemia progression in NOD/SCID/IL2Rγc-deficient mice.

Regulation of angiostatic chemokines driven by IL-12 and IL-27 in human tumors

Chemokines have pleiotropic effects in regulating immunity, angiogenesis, and tumor growth. CXC and CC chemokine families members and their receptors are able to exert a proangiogenic or an antiangiogenic effect in experimental models and in human tumors. In this review article, we have summarized literature data and our studies concerning the angiostatic activity of chemokines. Their angiostatic activity may be a result of a direct effect on the biological functions of endothelial cells and/or an effect on tumor cells inhibiting their capability to stimulate new blood vessel formation. Moreover, chemokines have a pro- and antitumor effect within the tumor microenvironment by regulating immune cell infiltration and its antitumor activities. We have focused our interest on the role of IL-12 and IL-27 in solid and hematological tumors, and we have suggested and discussed their potential use as antiangiogenic agents in the treatment of such tumors.