Selective targeting of tumoral vasculature: comparison of different formats of an antibody (L19) to the ED-B domain of fibronectin

Targeting interleukin-2 to the bone marrow stroma for therapy of acute myeloid leukemia relapsing after allogeneic hematopoietic stem cell transplantation

The antibody-based delivery of IL2 to extracellular targets expressed in the easily accessible tumor-associated vasculature has shown potent antileukemic activity in xenograft and immunocompetent murine models of acute myelogenous leukemia (AML), especially in combination with cytarabine. Here, we report our experience with 4 patients with relapsed AML after allogeneic hematopoietic stem cell transplantation (allo-HSCT), who were treated with the immunocytokine F16-IL2, in combination with low-dose cytarabine. One patient with disseminated extramedullary AML lesions achieved a complete metabolic response identified by PET/CT, which lasted 3 months. Two of 3 patients with bone marrow relapse achieved a blast reduction with transient molecular negativity. One of the 2 patients enjoyed a short complete remission before AML relapse occurred 2 months after the first infusion of F16-IL2. In line with a site-directed delivery of the cytokine, F16-IL2 led to an extensive infiltration of immune effector cells in the bone marrow. Grade 2 fevers were the only nonhematologic side effects in 2 patients. Grade 3 cytokine-release syndrome developed in the other 2 patients but was manageable in both cases with glucocorticoids. The concept of specifically targeting IL2 to the leukemia-associated stroma deserves further evaluation in clinical trials, especially in patients who relapse after allo-HSCT.

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.

Targeted PDT agent eradicates TrkC expressing tumors via photodynamic therapy (PDT)

This contribution features a small molecule that binds TrkC (tropomyosin receptor kinase C) receptor that tends to be overexpressed in metastatic breast cancer cells but not in other breast cancer cells. A sensitizer for ¹O₂ production conjugated to this structure gives 1-PDT for photodynamic therapy. Isomeric 2-PDT does not bind TrkC and was used as a control throughout; similarly, TrkC– cancer cells were used to calibrate enhanced killing of TrkC+ cells. Ex vivo, 1- and 2-PDT where only cytotoxic when illuminated, and 1-PDT, gave higher cell death for TrkC+ breast cancer cells. A 1 h administration-to-illumination delay gave optimal TrkC+/TrkC–-photocytotoxicity, and distribution studies showed the same delay was appropriate in vivo. In Balb/c mice, a maximum tolerated dose of 20 mg/kg was determined for 1-PDT. 1- and 2-PDT (single, 2 or 10 mg/kg doses and one illumination, throughout) had similar effects on implanted TrkC– tumors, and like those of 2-PDT on TrkC+ tumors. In contrast, 1-PDT caused dramatic TrkC+ tumor volume reduction (96% from initial) relative to the TrkC– tumors or 2-PDT in TrkC+ models. Moreover, 71% of the mice treated with 10 mg/kg 1-PDT (n = 7) showed full tumor remission and survived until 90 days with no metastasis to key organs.

Phage antibody display libraries: a powerful antibody discovery platform for immunotherapy

Phage display technology (PDT), a combinatorial screening approach, provides a molecular diversity tool for creating libraries of peptides/proteins and discovery of new recombinant therapeutics. Expression of proteins such as monoclonal antibodies (mAbs) on the surface of filamentous phage can permit the selection of high affinity and specificity therapeutic mAbs against virtually any target antigen. Using a number of diverse selection platforms (e.g. solid phase, solution phase, whole cell and in vivo biopannings), phage antibody libraries (PALs) from the start point provides great potential for the isolation of functional mAb fragments with diagnostic and/or therapeutic purposes. Given the pivotal role of PDT in the discovery of novel therapeutic/diagnostic mAbs, in the current review, we provide an overview on PALs and discuss their impact in the advancement of engineered mAbs.

A human monoclonal antibody specific to placental alkaline phosphatase, a marker of ovarian cancer

Placental alkaline phosphatase (PLAP) is a promising ovarian cancer biomarker. Here, we describe the isolation, affinity-maturation and characterization of two fully human monoclonal antibodies (termed B10 and D9) able to bind to human PLAP with a dissociation constant (Kd) of 10 and 30 nM, respectively. The ability of B10 and D9 antibodies to recognize the native antigen was confirmed by Biacore analysis, FACS and immunofluorescence studies using ovarian cancer cell lines and freshly-frozen human tissues. A quantitative biodistribution study in nude mice revealed that the B10 antibody preferentially localizes to A431 tumors, following intravenous administration. Anti-PLAP antibodies may serve as a modular building blocks for the development of targeted therapeutic products, armed with cytotoxic drugs, radionuclides or cytokines as payloads.

New radiotracers for imaging of vascular targets in angiogenesis-related diseases

Tremendous advances over the last several decades in positron emission tomography (PET) and single photon emission computed tomography (SPECT) allow for targeted imaging of molecular and cellular events in the living systems. Angiogenesis, a multistep process regulated by the network of different angiogenic factors, has attracted world-wide interests, due to its pivotal role in the formation and progression of different diseases including cancer, cardiovascular diseases (CVD), and inflammation. In this review article, we will summarize the recent progress in PET or SPECT imaging of a wide variety of vascular targets in three major angiogenesis-related diseases: cancer, cardiovascular diseases, and inflammation. Faster drug development and patient stratification for a specific therapy will become possible with the facilitation of PET or SPECT imaging and it will be critical for the maximum benefit of patients.

A chemically defined trifunctional antibody-cytokine-drug conjugate with potent antitumor activity

The combination of immunostimulatory agents with cytotoxic drugs is emerging as a promising approach for potentially curative tumor therapy, but advances in this field are hindered by the requirement of testing individual combination partners as single agents in dedicated clinical studies, often with suboptimal efficacy. Here, we describe for the first time a novel multipayload class of targeted drugs, the immunocytokine-drug conjugates (IDC), which combine a tumor-homing antibody, a cytotoxic drug, and a proinflammatory cytokine in the same molecular entity. In particular, the IL2 cytokine and the disulfide-linked maytansinoid DM1 microtubular inhibitor could be coupled to the F8 antibody, directed against the alternatively spliced EDA domain of fibronectin, in a site-specific manner, yielding a chemically defined product with selective tumor-homing performance and potent anticancer activity in vivo, as tested in two different immunocompetent mouse models.

Antibody-mediated delivery of interleukin 4 to the neo-vasculature reduces chronic skin inflammation

BACKGROUND

The antibody-mediated delivery of cytokines ("immunocytokines") to sites of pathological angiogenesis represents an attractive strategy for the development of innovative biopharmaceuticals, capable of modulating the activity of the immune system in cancer and in chronic inflammatory conditions.

OBJECTIVE

Recombinant IL4 has previously been shown to be therapeutically active in patients with psoriasis. The antibody-mediated delivery of this cytokine to sites of chronic skin inflammatory conditions should lead to an improved potency and selectivity, compared to non-targeted IL4.

METHODS

The therapeutic activity of F8-IL4, a fusion protein of the F8 antibody (specific to the alternatively-spliced EDA domain of fibronectin) with murine IL4, was investigated in three immunocompetent mouse models of skin inflammation: two induced by the TLR7/8 ligand imiquimod (in Balb/c and C57BL/6) and one mediated by the over-expression of VEGF-A.

RESULTS

The EDA domain of fibronectin, a marker for angiogenesis, is expressed in the inflamed skin in all three models and F8-IL4 selectively localized to inflamed skin lesions following intravenous administration. The F8-IL4 fusion protein mediated a therapeutic benefit, which was superior to the one of a non-targeted version of IL4 and led to increased levels of key regulatory cytokines (including IL5, IL10, IL13, and IL27) in the inflamed skin, while IL2 levels were not affected in all treatment groups. A murine version of etanercept and a murine anti-IL17 antibody were used as positive control in the therapy experiments.

CONCLUSION

Skin inflammatory lesions can be selectively targeted using anti-EDA antibody-cytokine fusion proteins and the pharmacodelivery of IL4 confers a therapeutic benefit by shifting the cytokine balance.

Antibody-based delivery of IL4 to the neovasculature cures mice with arthritis

Antibody-cytokine fusion proteins (immunocytokines) are innovative biopharmaceutical agents, which are being considered for the therapy of cancer and chronic inflammatory conditions. Immunomodulatory fusion proteins capable of selective localization at the sites of rheumatoid arthritis (RA) are of particular interest, as they may increase the therapeutic index of the cytokine payload. The F8 antibody recognizes the alternatively spliced extra domain A of fibronectin, a marker of angiogenesis, which is strongly overexpressed at sites of arthritis. In this study, we investigated the targeting and therapeutic activity of the immunocytokine F8-IL4 in the mouse model of collagen-induced arthritis. Different combination regimes were tested and evaluated by the analysis of serum and tissue cytokine levels. We show that F8-IL4 selectively localizes to neovascular structures at sites of rheumatoid arthritis in the mouse, leading to high local concentrations of IL4. When used in combination with dexamethasone, F8-IL4 was able to cure mice with established collagen-induced arthritis. Response to treatment was associated with an elevation of IL13 levels and decreased IL6 plasma concentrations. A fully human version of F8-IL4 is currently being developed for clinical investigations.

A fibrin-specific monoclonal antibody from a designed phage display library inhibits clot formation and localizes to tumors in vivo

Fibrin formation from fibrinogen is a rare process in the healthy organism but is a pathological feature of thrombotic events, cancer and a wide range of inflammatory conditions. We have designed and constructed an antibody phage display library (containing 13 billion clones) for the selective recognition of the N-terminal peptide of fibrin alpha chain. The key structural feature for selective fibrin binding was a K94E mutation in the VH domain. From this library, an antibody was isolated (termed AP2), which recognizes the five N-terminal amino acids of fibrin with high affinity (Kd=44nM), but does not bind to fibrinogen. The AP2 antibody could be expressed in various formats (scFv, small immune protein and IgG) and inhibited fibrin clot formation in a concentration-dependent manner. Moreover, the AP2 antibody stained the fibrin-rich provisional stroma in solid tumors but did not exhibit any detectable staining toward normal tissues. Using a radioiodinated antibody preparation and quantitative biodistribution studies in tumor-bearing mice, AP2 was shown to selectively localize to fibrin-rich F9 murine teratocarcinomas, but not to SKRC-52 human kidney cancer xenografts. Collectively, the experiments indicate that the AP2 antibody recognizes fibrin in vitro and in vivo. The antibody may facilitate the development of fibrin-specific therapeutic agents.

A highly functional synthetic phage display library containing over 40 billion human antibody clones

Several synthetic antibody phage display libraries have been created and used for the isolation of human monoclonal antibodies. The performance of antibody libraries, which is usually measured in terms of their ability to yield high-affinity binding specificities against target proteins of interest, depends both on technical aspects (such as library size and quality of cloning) and on design features (which influence the percentage of functional clones in the library and their ability to be used for practical applications). Here, we describe the design, construction and characterization of a combinatorial phage display library, comprising over 40 billion human antibody clones in single-chain fragment variable (scFv) format. The library was designed with the aim to obtain highly stable antibody clones, which can be affinity-purified on protein A supports, even when used in scFv format. The library was found to be highly functional, as >90% of randomly selected clones expressed the corresponding antibody. When selected against more than 15 antigens from various sources, the library always yielded specific and potent binders, at a higher frequency compared to previous antibody libraries. To demonstrate library performance in practical biomedical research projects, we isolated the human antibody G5, which reacts both against human and murine forms of the alternatively spliced BCD segment of tenascin-C, an extracellular matrix component frequently over-expressed in cancer and in chronic inflammation. The new library represents a useful source of binding specificities, both for academic research and for the development of antibody-based therapeutics.

Monoclonal antibodies to murine thrombospondin-1 and thrombospondin-2 reveal differential expression patterns in cancer and low antigen expression in normal tissues

There is a considerable interest for the discovery and characterization of tumor-associated antigens, which may facilitate antibody-based pharmacodelivery strategies. Thrombospondin-1 and thrombospondin-2 are homologous secreted proteins, which have previously been reported to be overexpressed during remodeling typical for wound healing and tumor progression and to possibly play a functional role in cell proliferation, migration and apoptosis. To our knowledge, a complete immunohistochemical characterization of thrombospondins levels in normal rodent tissues has not been reported so far. Using antibody phage technology, we have generated and characterized monoclonal antibodies specific to murine thrombospondin-1 and thrombospondin-2, two antigens which share 62% aminoacid identity. An immunofluorescence analysis revealed that both antigens are virtually undetectable in normal mouse tissues, except for a weak staining of heart tissue by antibodies specific to thrombospondin-1. The analysis also showed that thrombospondin-1 was strongly expressed in 5/7 human tumors xenografted in nude mice, while it was only barely detectable in 3/8 murine tumors grafted in immunocompetent mice. By contrast, a high-affinity antibody to thrombospondin-2 revealed a much lower level of expression of this antigen in cancer specimens. Our analysis resolves ambiguities related to conflicting reports on thrombosponding expression in health and disease. Based on our findings, thrombospondin-1 (and not thrombospondin-2) may be considered as a target for antibody-based pharmacodelivery strategies, in consideration of its low expression in normal tissues and its upregulation in cancer.

Evaluation of antibody–chemokine fusion proteins for tumor-targeting applications

There is an increasing biotechnological interest in the ‘arming’ of therapeutic antibodies with bioactive payloads. While many antibody–cytokine fusion proteins have been extensively investigated in preclinical and clinical studies, there are only few reports related to antibody–chemokine fusion proteins (‘immunochemokines’). Here, we describe the cloning, expression, and characterization of 10 immunochemokines based on the monoclonal antibody F8, specific to the alternatively spliced extra domain A (EDA) of fibronectin, a marker of angiogenesis. Among the 10 murine chemokines tested in our study, only CCL19, CCL20, CCL21, and CXCL10 could be expressed and isolated at acceptable purity levels as F8-based fusion proteins. The immunochemokines retained the binding characteristics of the parental antibody, but could not be characterized by gel-filtration analysis, an analytical limitation which had previously been observed in our laboratory for the unconjugated chemokines. When radioiodinated preparations of CCL19-F8, CCL20-F8, CCL21-F8, and CXCL10-F8 were tested in quantitative biodistribution studies in tumor-bearing mice, the four fusion proteins failed to preferentially accumulate at the tumor site, while the unconjugated parental antibody displayed a tumor:blood ratio >20:1, 24 h after intravenous (i.v.) administration. The tumor-targeting ability of CCL19-F8 could be rescued only in part by preadministration of unlabeled CCL19-F8, indicating that a chemokine trapping mechanism may hinder pharmacodelivery strategies. While this article highlights expression, analytical, and biodistribution challenges associated with the antibody-based in vivo delivery of chemokines at sites of disease, it provides the first comprehensive report in this field and may facilitate future studies with immunochemokines.

Antibody-based delivery of IL2 and cytotoxics eradicates tumors in immunocompetent mice

Antibody-drug conjugates are increasingly being used for cancer therapy, but little is known about their ability to promote anticancer immunity, which may lead to long-lasting remissions. We investigated the therapeutic effect of antibody-based pharmacodelivery of cemadotin, a cytotoxic drug, and IL2, a strong proinflammatory cytokine. Using the F8 antibody, which selectively localizes to the tumor neovasculature, combination treatment led to tumor eradication, in a process dependent on CD8(+) T cells and natural killer cells in the C1498 syngeneic mouse model of acute myelogenous leukemia. The clinical combination of antibody-drug conjugates and antibody-cytokine proteins should be facilitated by their orthogonal toxicity profiles.

From target discovery to clinical trials with armed antibody products

Conventional chemotherapy of serious conditions (e.g., cancer and chronic inflammatory diseases) relies on the use of potent bioactive agents, which do not preferentially localize at the site of disease and which may harm healthy tissues. Intense pharmaceutical research efforts are being devoted to the development of targeted therapeutic agents, capable of selectively homing to diseased tissues, while sparing normal body structures. Biological mass spectrometry and chemical proteomics have revolutionized the way targets for ligand-based pharmacodelivery applications are discovered. In this article, we present a personal account on research activities in the field for the last decade, outlining our experience in the discovery of accessible biomarkers and in the development of potent targeted therapeutic agents.

BIOLOGICAL SIGNIFICANCE

The present review discusses evolution of proteomic methodologies applied to the discovery of new targets for therapeutic intervention in cancer and inflammatory diseases. Chemical proteomics-driven target discovery allowed the development of new classes of antibody-based targeting biologics, which are having an impact in the oncological and chronic inflammation clinical research. This article is part of a Special Issue entitled: 20years of Proteomics in memory of Viatliano Pallini. Guest Editors: Luca Bini, Juan J. Calvete, Natacha Turck, Denis Hochstrasser and Jean-Charles Sanchez.

Novel ubiquitin-derived high affinity binding proteins with tumor targeting properties

Targeting effector molecules to tumor cells is a promising mode of action for cancer therapy and diagnostics. Binding proteins with high affinity and specificity for a tumor target that carry effector molecules such as toxins, cytokines, or radiolabels to their intended site of action are required for these applications. In order to yield high tumor accumulation while maintaining low levels in healthy tissues and blood, the half-life of such conjugates needs to be in an optimal range. Scaffold-based binding molecules are small proteins with high affinity and short systemic circulation. Due to their low molecular complexity, they are well suited for combination with effector molecules as well as half-life extension technologies yielding therapeutics with half-lives adapted to the specific therapy. We have identified ubiquitin as an ideal scaffold protein due to its outstanding biophysical and biochemical properties. Based on a dimeric ubiquitin library, high affinity and specific binding molecules, so-called Affilin® molecules, have been selected against the extradomain B of fibronectin, a target almost exclusively expressed in tumor tissues. Extradomain B-binding molecules feature high thermal and serum stability as well as strong in vitro target binding and in vivo tumor accumulation. Application of several half-life extension technologies results in molecules of largely unaffected affinity but significantly prolonged in vivo half-life and tumor retention. Our results demonstrate the utility of ubiquitin as a scaffold for the generation of high affinity binders in a modular fashion, which can be combined with effector molecules and half-life extension technologies.

Reformatting of scFv antibodies into the scFv-Fc format and their downstream purification

The scFv-Fc format allows for rapid characterization of candidate scFvs isolated from phage display libraries before conversion into a full-length IgG. This format offers several advantages over the phage display-derived scFv, including bivalent binding, longer half-life, and Fc-mediated effector functions. Here, a detailed method is presented, which describes the cloning, expression, and purification of an scFv-Fc fragment, starting from scFv fragments obtained from a phage display library. This method facilitates the rapid screening of candidate antibodies, prior to a more time-consuming conversion into a full IgG format. Alternatively, the scFv-Fc format may be used in the clinic for therapeutic applications.

Tumor targeting properties of antibody fusion proteins based on different members of the murine tumor necrosis superfamily

The tumor necrosis factor superfamily (TNFSF) consists of more than 20 members that can modulate cellular and immunological functions, including cell survival and the stimulation of an inflammatory response. Many TNF superfamily members display potent anticancer activity when used as recombinant proteins in vitro and in vivo. While TNF, TRAIL and FasL have already been used as payloads in antibody-based pharmacodelivery strategies, most TNF superfamily members have not yet been investigated as antibody payloads. Here, we report the cloning, production and characterization of eight novel antibody fusion proteins based on CD40L, FasL, TRAIL, LiGHT, VEGI, lymphotoxin alpha, lymphotoxin beta and lymphotoxin alpha1/beta2. The monoclonal antibody F8 was chosen as fusion partner of proven tumor targeting performance, which recognizes the alternatively-spliced EDA domain of fibronectin, a marker of angiogenesis. A quantitative biodistribution analysis performed with radioiodinated protein preparations in tumor-bearing mice revealed that TRAIL and lymphotoxin alpha1/beta2 were able to selectively accumulate at the tumor site, while all other members of the TNF superfamily abrogated the selective tumor targeting performance of the parental antibody or accumulated also in healthy tissues. The study indicates that even cytokines, which are closely related in terms of structure and function, may have a substantially different impact on the biodistribution and functional properties of the corresponding fusions with disease-homing antibodies.

Use of the uteroglobin platform for the expression of a bivalent antibody against oncofetal fibronectin in Escherichia coli

Escherichia coli is a robust, economic and rapid expression system for the production of recombinant therapeutic proteins. However, the expression in bacterial systems of complex molecules such as antibodies and fusion proteins is still affected by several drawbacks. We have previously described a procedure based on uteroglobin (UG) for the engineering of very soluble and stable polyvalent and polyspecific fusion proteins in mammalian cells (Ventura et al. 2009. J. Biol. Chem. 284∶26646–26654.) Here, we applied the UG platform to achieve the expression in E. coli of a bivalent human recombinant antibody (L19) toward the oncofetal fibronectin (B-FN), a pan-tumor target. Purified bacterial L19-UG was highly soluble, stable, and, in all molecules, the L19 moiety maintained its immunoreactivity. About 50–70% of the molecules were covalent homodimer, however after refolding with the redox couple reduced-glutathione/oxidized-glutathione (GSH/GSSG), 100% of molecules were covalent dimers. Mass spectrometry studies showed that the proteins produced by E. coli and mammalian cells have an identical molecular mass and that both proteins are not glycosylated. L19-UG from bacteria can be freeze-dried without any loss of protein and immunoreactivity. In vivo, in tumor-bearing mice, radio-iodinated L19-UG selectively accumulated in neoplastic tissues showing the same performance of L19-UG from mammalian cells. The UG-platform may represent a general procedure for production of various biological therapeutics in E. coli.

Latent cytokines for targeted therapy of inflammatory disorders

INTRODUCTION

The use of cytokines as therapeutic agents is important, given their potent biological effects. However, this very potency, coupled with the pleiotropic nature and short half-life of these molecules, has limited their therapeutic use. Strategies to increase the half-life and to decrease toxicity are necessary to allow effective treatment with these molecules.

AREAS COVERED

A number of strategies are used to overcome the natural limitations of cytokines, including PEGylation, encapsulation in liposomes, fusion to targeting peptides or antibodies and latent cytokines. Latent cytokines are engineered using the latency-associated peptide of transforming growth factor-β to produce therapeutic cytokines/peptides that are released only at the site of disease by cleavage with disease-induced matrix metalloproteinases. The principles underlying the latent cytokine technology are described and are compared to other methods of cytokine delivery. The potential of this technology for developing novel therapeutic strategies for the treatment of diseases with an inflammatory-mediated component is discussed.

EXPERT OPINION

Methods of therapeutic cytokine delivery are addressed. The latent cytokine technology holds significant advantages over other methods of drug delivery by providing simultaneously increased half-life and localised drug delivery without systemic effects. Cytokines that failed clinical trials should be reassessed using this delivery system.

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.

Mapping biological behaviors by application of longer-lived positron emitting radionuclides

With the technological development of positron emission tomography (PET) and the advent of novel antibody-directed drug delivery systems, longer-lived positron-emitting radionuclides are moving to the forefront to take important roles in tracking the distribution of biotherapeutics such as antibodies, and for monitoring biological processes and responses. Longer half-life radionuclides possess advantages of convenient on-site preparation procedures for both clinical and non-clinical applications. The suitability of the long half-life radionuclides for imaging intact monoclonal antibodies (mAbs) and their respective fragments, which have inherently long biological half-lives, has attracted increased interest in recent years. In this review, we provide a survey of the recent literature as it applies to the development of nine-selected longer-lived positron emitters with half-lives of 9-140h (e.g., (124)I, (64)Cu, (86)Y and (89)Zr), and describe the biological behaviors of radionuclide-labeled mAbs with respect to distribution and targeting characteristics, potential toxicities, biological applications, and clinical translation potentials.

Pharmacotherapy of metastatic melanoma: emerging trends and opportunities for a cure

Metastatic melanoma is one of the most deadly forms of cancer and is poorly responsive to standard chemotherapeutics, such as Dacarbazine and Paclitaxel. Recently, the advent of Vemurafenib and Ipilimumab has broadened the spectrum of therapeutic options for advanced melanoma patients but the occurrence of resistance and of high-grade toxicities call for better and more effective treatments. This review focuses on approved and experimental therapies for metastatic melanoma. The mechanism of action and the reported efficacy data for small molecule drugs and biologics are discussed, outlining directions for future pharmaceutical research in this field.

Radretumab radioimmunotherapy in patients with brain metastasis: a 124I-L19SIP dosimetric PET study

Radioimmunotherapy (RIT) with (131)I-labeled L19SIP (radretumab; a small immunoprotein format antibody directed against the ED-B domain of fibronectin; ∼ 80 kDa molecular weight) has been investigated in several clinical trials. Here, we describe the use of immuno-PET imaging with iodine-124 ((124)I)-labeled L19SIP to predict doses delivered to tumor lesions and healthy organs by a subsequent radretumab RIT in patients with brain metastases from solid cancer. Bone marrow doses were evaluated both during the diagnostic phase and posttherapy, measuring activities in blood (germanium detector) and whole body (lanthanum bromide detector). Expected doses for radretumab administration (4,107 MBq/m(2)) were calculated from data obtained after administration of an average of 167 MBq (124)I-L19SIP to 6 patients. To assess lesion average doses, the positron emission tomography (PET) scanner was calibrated for the use of (124)I with an International Electrotechnical Commission (IEC) Body Phantom and recovery coefficients were calculated. The average dose to bone red marrow was 0.21 Gy/GBq, with high correlation between provisional and actual posttherapy doses. Although the fraction of injected activity in normal organs was similar in different patients, the antibody uptake in the neoplastic lesions varied by as much as a factor of 60. Immuno-PET with (124)I-labeled L19SIP offers significant advantages over conventional (131)I imaging, in particular accuracy of dosimetric results. Furthermore, the study indicates that antibody uptake can be highly variable even in different lesions of the same patient and that immuno-PET procedures may guide product development with armed antibodies.

Phase 0 microdosing PET study using the human mini antibody F16SIP in head and neck cancer patients

The aim of this microdosing phase 0 clinical study was to obtain initial information about pharmacokinetics, biodistribution, and specific tumor targeting of the antitenascin-C mini antibody F16SIP.

METHODS

Two milligrams of F16SIP, labeled with 74 MBq of (124)I, were intravenously administered to patients with head and neck cancer (n = 4) scheduled for surgery 5-7 d later. Immuno-PET scans were acquired at 30 min and 24 h after injection. For pharmacokinetic analysis, blood samples were taken at different time points after infusion. Tissue uptake was extracted from whole-body PET scans. In addition, ex vivo radioactivity measurements of blood and of biopsies from the surgical specimens were performed.

RESULTS

(124)I-F16SIP was well tolerated. Uptake was visible mainly in the liver, spleen, kidneys, and bone marrow and diminished over time. Tumor uptake increased over time, with all 4 tumors visible on 24-h PET images. The tumor-to-blood ratio was 7.7 ± 1.7 at the time of surgery. Pharmacokinetic analysis revealed good bioavailability of (124)I-F16SIP.

CONCLUSION

Performing a microdosing immuno-PET study appeared feasible and demonstrated adequate bioavailability and selective tumor targeting of (124)I-F16SIP.The results of this study justify further clinical exploration of (124)I-F16SIP-based therapies.

Advances in immuno-positron emission tomography: antibodies for molecular imaging in oncology

Identification of cancer cell-surface biomarkers and advances in antibody engineering have led to a sharp increase in the development of therapeutic antibodies. These same advances have led to a new generation of radiolabeled antibodies and antibody fragments that can be used as cancer-specific imaging agents, allowing quantitative imaging of cell-surface protein expression in vivo. Immuno-positron emission tomography (immunoPET) imaging with intact antibodies has shown success clinically in diagnosing and staging cancer. Engineered antibody fragments, such as diabodies, minibodies, and single-chain Fv (scFv) -Fc, have been successfully employed for immunoPET imaging of cancer cell-surface biomarkers in preclinical models and are poised to bring same-day imaging into clinical development. ImmunoPET can potentially provide a noninvasive approach for obtaining target-specific information useful for titrating doses for radioimmunotherapy, for patient risk stratification and selection of targeted therapies, for evaluating response to therapy, and for predicting adverse effects, thus contributing to the ongoing development of personalized cancer treatment.

The immunocytokine L19-IL2 eradicates cancer when used in combination with CTLA-4 blockade or with L19-TNF

Systemic high-dose IL2 promotes long-term survival in a subset of metastatic melanoma patients, but this treatment is accompanied by severe toxicities. The immunocytokine L19-IL2, in which IL2 is fused to the human L19 antibody capable of selective accumulation on tumor neovasculature, has recently shown encouraging clinical activity in patients with metastatic melanoma. In this study, we have investigated the therapeutic performance of L19-IL2, administered systemically in combination with a murine anti-CTLA-4 antibody or with a second clinical-stage immunocytokine (L19-TNF) in two syngeneic immunocompetent mouse models of cancer. We observed complete tumor eradications when L19-IL2 was used in combination with CTLA-4 blockade. Interestingly, mice cured from F9 tumors developed new lesions when rechallenged with tumor cells after therapy, whereas mice cured from CT26 tumors were resistant to tumor rechallenge. Similarly, L19-IL2 induced complete remissions when administered in a single intratumoral injection in combination with L19-TNF, whereas the two components did not lead to cures when administered as single agents. These findings provide a rationale for combination trials in melanoma, as the individual therapeutic agents have been extensively studied in clinical trials, and the antigen recognized by the L19 antibody has an identical sequence in mouse and man.

Biodistribution studies with tumor-targeting bispecific antibodies reveal selective accumulation at the tumor site

Bispecific antibodies are proteins that bind two different antigens and may retarget immune cells with a binding moiety specific for a leukocyte marker. A binding event in blood could in principle prevent antibody extravasation and accumulation at the site of disease. In this study, we produced and characterized two tetravalent bispecific antibodies that bind with high affinity to the alternatively-spliced EDB domain of fibronectin, a tumor-associated antigen. The bispecific antibodies simultaneously engaged the cognate antigens (murine T cell co-receptor CD3 and hen egg lysozyme) and selectively accumulated on murine tumors in vivo. The results, which were in agreement with predictions based on pharmacokinetic modeling and antibody binding characteristics, confirmed that bispecific antibodies can reach abluminal targets without being blocked by peripheral blood leukocytes.

The IgM CH2 domain as covalently linked homodimerization module for the generation of fusion proteins with dual specificity

Dimeric assembly of antibody fragments and other therapeutic molecules can result in increased binding and improved bioactivity. Here, we investigated the use of the IgM heavy chain domain 2 (MHD2) as covalently linked homodimerization module. Fusion of single-chain fragment variable (scFv) molecules directed against epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 to the N- and/or C-terminus of the MHD2, respectively, resulted in molecules with single or dual specificity for tumor cells. Bispecific tetravalent molecules were further generated by fusing a bispecific single-chain diabody directed against EGFR and epithelial cell adhesion molecule to the N-terminus of the MHD2. By combining an anti-EGFR scFv with a single-chain derivative of tumor necrosis factor, a tetravalent bifunctional fusion protein was produced. This fusion protein exhibited improved TNF activity, also mimicking the membrane-bound form of TNF, as shown by the activation of TNFR2-mediated cell killing. Furthermore, the scFv moiety allowed for an antigen-dependent delivery of TNF to EGFR-positive cells and an improved stimulatory TNF action on these cells. Thus, we established the MHD2 as a versatile module for the generation of bispecific and bifunctional fusion proteins.

Drug targeting to tumors: principles, pitfalls and (pre-) clinical progress

Many different systems and strategies have been evaluated for drug targeting to tumors over the years. Routinely used systems include liposomes, polymers, micelles, nanoparticles and antibodies, and examples of strategies are passive drug targeting, active drug targeting to cancer cells, active drug targeting to endothelial cells and triggered drug delivery. Significant progress has been made in this area of research both at the preclinical and at the clinical level, and a number of (primarily passively tumor-targeted) nanomedicine formulations have been approved for clinical use. Significant progress has also been made with regard to better understanding the (patho-) physiological principles of drug targeting to tumors. This has led to the identification of several important pitfalls in tumor-targeted drug delivery, including I) overinterpretation of the EPR effect; II) poor tumor and tissue penetration of nanomedicines; III) misunderstanding of the potential usefulness of active drug targeting; IV) irrational formulation design, based on materials which are too complex and not broadly applicable; V) insufficient incorporation of nanomedicine formulations in clinically relevant combination regimens; VI) negligence of the notion that the highest medical need relates to metastasis, and not to solid tumor treatment; VII) insufficient integration of non-invasive imaging techniques and theranostics, which could be used to personalize nanomedicine-based therapeutic interventions; and VIII) lack of (efficacy analyses in) proper animal models, which are physiologically more relevant and more predictive for the clinical situation. These insights strongly suggest that besides making ever more nanomedicine formulations, future efforts should also address some of the conceptual drawbacks of drug targeting to tumors, and that strategies should be developed to overcome these shortcomings.

Isolated limb perfusion with the tumor-targeting human monoclonal antibody-cytokine fusion protein L19-TNF plus melphalan and mild hyperthermia in patients with locally advanced extremity melanoma

BACKGROUND

L19-TNF is a tumor-targeting immunocytokine composed of the human L19 antibody binding to extra domain B (ED-B) of fibronectin of newly formed blood vessels, and of human TNF. This exploratory trial evaluates safety and clinical activity of L19-TNF plus melphalan-containing isolated limb perfusion (ILP) in extremity melanoma patients.

METHODS

Seven and 10 patients received 325 µg and 650 µg of L19-TNF, respectively, during the ILP. Patients were studied for safety, tolerability, and clinical activity of this experimental L19-TNF ILP procedure.

RESULTS

Non-hematologic toxicity of L19-TNF ILP was very low, but severe myelosuppression was seen in four patients. Although L19-TNF was administered at a TNF-equivalent dose of only 3.13 and 6.25% of the approved TNF (Beromun®) dose of 4 mg, L19-TNF ILP induced objective responses in 86 and 89% of patients, respectively, including a complete response (CR) in 5/10 patients treated with L19-TNF ILP at 650 µg that was durable at 12 months in four patients. No CR was seen at 325 µg of L19-TNF.

CONCLUSIONS

ILP with L19-TNF had a favorable safety and a promising activity profile at a dose of 650 µg of L19-TNF, supporting the exploration of higher L19-TNF doses and a Phase II trial comparing L19-TNF ILP with standard melphalan-containing ILP.

Site-specific traceless coupling of potent cytotoxic drugs to recombinant antibodies for pharmacodelivery

Aldehyde drugs are gaining increasing research interest, considering that aldehyde dehydrogenases overexpression is characteristic of cancer stem cells. Here, we describe the traceless site-specific coupling of a novel potent drug, containing an aldehyde moiety, to recombinant antibodies, which were engineered to display a cysteine residue at their N-terminus, or a 1,2-aminothiol at their C-terminus. The resulting chemically defined antibody-drug conjugates represent the first example in which a thiazolidine linkage is used for the targeted delivery and release of cytotoxic agents.

Anti-angiogenesis therapy in cancer: current challenges and future perspectives

It has been nearly 9years since the FDA (Food and Drug Administration) approved the first anti-angiogenic drug (bevacizumab) for treatment of metastatic colorectal cancer. Other angiogenic inhibitors have since been approved or are in different stages of clinical trials. However, continued clinical and preclinical investigations have identified major drawbacks associated with the application of this class of agents, including inherent/acquired resistance and induction of tumor invasiveness. In addition, lack of thoroughly validated predictive biomarkers has been one of the major hurdles to stratify cancer patients and to monitor tumor progression and response to the therapy. Investigations in clinic and preclinical models have provided some molecular and cellular mechanisms for the above challenges. This review aims to provide a concise update from recent findings.