Enhancing brain entry and therapeutic activity of chimeric antigen receptor T cells with intra-arterial NEO100 in a mouse model of CNS lymphoma

OBJECTIVE

Malignancies of the CNS are difficult to treat because the blood-brain barrier (BBB) prevents most therapeutics from reaching the intracranial lesions at sufficiently high concentrations. This also applies to chimeric antigen receptor (CAR) T cells, for which systemic delivery is inferior to direct intratumoral or intraventricular injection of the cells. The authors previously reported on a novel approach to safely and reversibly open the BBB of mice by applying intra-arterial (IA) injections of NEO100, a pharmaceutical-grade version of the natural monoterpene perillyl alcohol. The authors hypothesized that this method would enable enhanced brain entry and therapeutic activity of intravenously delivered CAR T cells, which the authors tested in a mouse model of CNS lymphoma.

METHODS

Human Raji lymphoma cells were implanted into the brains of immune-deficient mice. After tumor uptake was confirmed with bioluminescent imaging, 0.3% NEO100 was injected intra-arterially, which was followed by intravenous (IV) delivery of CD19-targeted CAR T cells. After this single intervention, tumor growth was monitored with imaging, long-term survival of mice was recorded, and select mice were euthanized to analyze the distribution of CAR T cells in brain tissue.

RESULTS

Intravenously injected CAR T cells could be readily detected in brain tumor areas after IA injection of NEO100 but not after IA injection of the vehicle (without NEO100). Although all untreated control animals died within 3 weeks, all mice that received IA NEO100 followed by IV CAR T cells survived and thrived for 200 days, when the experiment was terminated. Of the mice that received IV CAR T cells without prior IA NEO100, 3 died within 3 weeks and 2 survived long-term.

CONCLUSIONS

BBB opening by IA NEO100 facilitates brain entry of intravenously delivered CD19 CAR T cells. The long-term survival of all mice with CNS lymphoma, along with the disappearance of the tumor as determined with imaging, suggests that this one-time therapeutic intervention was curative. BBB opening by IA NEO100 may offer a novel option to increase brain access by CAR T cells.

Brain Disposition of Antibody-Based Therapeutics: Dogma, Approaches and Perspectives

Due to their high specificity, monoclonal antibodies have been widely investigated for their application in drug delivery to the central nervous system (CNS) for the treatment of neurological diseases such as stroke, Alzheimer’s, and Parkinson’s disease. Research in the past few decades has revealed that one of the biggest challenges in the development of antibodies for drug delivery to the CNS is the presence of blood–brain barrier (BBB), which acts to restrict drug delivery and contributes to the limited uptake (0.1–0.2% of injected dose) of circulating antibodies into the brain. This article reviews the various methods currently used for antibody delivery to the CNS at the preclinical stage of development and the underlying mechanisms of BBB penetration. It also describes efforts to improve or modulate the physicochemical and biochemical properties of antibodies (e.g., charge, Fc receptor binding affinity, and target affinity), to adapt their pharmacokinetics (PK), and to influence their distribution and disposition into the brain. Finally, a distinction is made between approaches that seek to modify BBB permeability and those that use a physiological approach or antibody engineering to increase uptake in the CNS. Although there are currently inherent difficulties in developing safe and efficacious antibodies that will cross the BBB, the future prospects of brain-targeted delivery of antibody-based agents are believed to be excellent.

Advances in Immuno-PET for the Detection of Cancer and Assessment of Response to Therapy

BACKGROUND

Monoclonal antibodies (mAbs) against tumor-associated antigens have been shown to target tumors with specificity and selectivity; therefore, it was hypothesized that cancer could be treated with mAbs without side effects. In the early 1980s, clinical studies demonstrated that tumors could be visualized using radiolabeled mAbs. However, with the introduction of positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), antibody-based imaging became less important because of its limited diagnostic accuracy. During the last two decades, a revival of imaging with radiolabeled mAbs has taken place, specifically PET with longer half-life isotopes. Development of immune checkpoints as targets for immunotherapy has opened opportunities for the development of a wide variety of antibodies, such as anti-CTLA-4, anti-PD-L1, and anti-PD1. Thus, imaging with these antibodies radiolabeled with 89Zr or another long-half-life PET isotope, known as immuno-PET, has become mainstream.

OBJECTIVE

This study aimed to review the rapid development of immuno-PET for the detection of cancer and assessment of therapeutic response combining surgery, radiation, chemotherapy, and/or immunotherapy. This review includes reports on the radiolabeling, imaging and clinical utility of ⁸⁹Zr-, ⁶⁴Cu- and ¹²⁴I-labeled mAbs.

RESULTS

More than 120 research and review articles on immuno-PET were reviewed.

CONCLUSION

Many mAbs have been developed and used for the treatment of cancer; however, a limited number of antibodies have been radiolabeled for immuno-PET. While much progress has been made with the therapeutic applications of mAbs, immuno-PET for diagnosis and treatment assessment needs more research. Improved chelating agents and extensive imaging studies are needed to refine immuno-PET for the diagnosis of cancers and assessment of response to therapy.

A Humanized Lym-1 CAR with Novel DAP10/DAP12 Signaling Domains Demonstrates Reduced Tonic Signaling and Increased Antitumor Activity in B-Cell Lymphoma Models

PURPOSE

The murine Lym-1 mAb targets a discontinuous epitope (Lym-1 epitope) on several subtypes of HLA-DR, which is upregulated in a majority of human B-cell lymphomas and leukemias. Unlike CD19, the Lym-1 epitope does not downregulate upon crosslinking, which may provide an advantage as a target for CAR T-cell therapy. Lym-1 CAR T cells with a conventional 4-1BB and CD3ζ (BB3z) signaling domain exhibited impaired ex vivo expansion. This study aimed to identify the underlying mechanisms and develop strategies to overcome this effect.

EXPERIMENTAL DESIGN

A functional humanized Lym-1 antibody (huLym-1-B) was identified and its scFv form was used for CAR design. To overcome observed impaired expansion in vitro, a huLym-1-B CAR using DAP10 and DAP12 (DAP) signaling domains was evaluated for ex vivo expansion and in vivo function.

RESULTS

Impaired expansion in huLym-1-B-BB3z CAR T cells was shown to be due to ligand-dependent suboptimal CAR signaling caused by interaction of the CAR binding domain and the surface of human T cells. Using the novel DAP signaling domain construct, the effects of suboptimal CAR signaling were overcome to produce huLym-1-B CAR T cells with improved expansion ex vivo and function in vivo. In addition, the Lym-1 epitope does not significantly downregulate in response to huLym-1-B-DAP CAR T cells both ex vivo and in vivo.

CONCLUSIONS

DAP intracellular domains can serve as signaling motifs for CAR, and this new construct enables nonimpaired production of huLym-1-B CAR T cells with potent in vivo antitumor efficacy.

Biodistribution and efficacy of an anti-TENB2 antibody-drug conjugate in a patient-derived model of prostate cancer

TENB2, a transmembrane proteoglycan protein, is a promising target for antibody drug conjugate (ADC) therapy due to overexpression in human prostate tumors and rapid internalization. We previously characterized how predosing with parental anti-TENB2 monoclonal antibody (mAb) at 1 mg/kg in a patient-derived LuCap77 explant model with high (3+) TENB2 expression could (i) block target-mediated intestinal uptake of tracer (& 0.1 mg/kg) levels of radiolabeled anti-TENB2-monomethyl auristatin E ADC while preserving tumor uptake, and (ii) maintain efficacy relative to ADC alone. Here, we systematically revisit this strategy to evaluate the effects of predosing on tumor uptake and efficacy in LuCap96.1, a low TENB2-expressing (1+) patient-derived model that is more responsive to ADC therapy than LuCap77. Importantly, rather than using tracer (& 0.1 mg/kg) levels, radiolabeled ADC tumor uptake was assessed at 1 mg/kg – one of the doses evaluated in the tumor growth inhibition study – in an effort to bridge tissue distribution (PK) with efficacy (PD). Predosing with mAb up to 1 mg/kg had no effect on efficacy. These findings warrant further investigations to determine whether predosing prior to ADC therapy might improve therapeutic index by preventing ADC disposition and possible toxicological liabilities in antigen-expressing healthy tissues.

Lym-1 Chimeric Antigen Receptor T Cells Exhibit Potent Anti-Tumor Effects against B-Cell Lymphoma

T cells expressing chimeric antigen receptors (CARs) recognizing CD19 epitopes have produced remarkable anti-tumor effects in patients with B-cell malignancies. However, cancer cells lacking recognized epitopes can emerge, leading to relapse and death. Thus, CAR T cells targeting different epitopes on different antigens could improve immunotherapy. The Lym-1 antibody targets a conformational epitope of Human Leukocyte Antigen-antigen D Related (HLA-DR) on the surface of human B-cell lymphomas. Lym-1 CAR T cells were thus generated for evaluation of cytotoxic activity towards lymphoma cells in vitro and in vivo. Human T cells from healthy donors were transduced to express a Lym-1 CAR, and assessed for epitope-driven function in culture and towards Raji xenografts in NOD-scidIL2Rgamma^null (NSG) mice. Lym-1 CAR T cells exhibited epitope-driven activation and lytic function against human B-cell lymphoma cell lines in culture and mediated complete regression of Raji/Luciferase-Green fluorescent protein (Raji/Luc-GFP) in NSG mice with similar or better reactivity than CD19 CAR T cells. Lym-1 CAR transduction of T cells is a promising immunotherapy for patients with Lym-1 epitope positive B-cell malignancies.

Systemic delivery of chTNT-3/CpG immunoconjugates for immunotherapy in murine solid tumor models

CpG oligodeoxynucleotides (CpG) potently activate the immune system by mimicking microbial DNA. Conjugation of CpG to chTNT-3, an antibody targeting the necrotic centers of tumors, enabled CpG to accumulate in tumors after systemic delivery, where it can activate the immune system in the presence of tumor antigens. CpG chemically conjugated to chTNT-3 (chTNT-3/CpG) were compared to free CpG in their ability to stimulate the immune system in vitro and reduce tumor burden in vivo. In subcutaneous Colon 26 adenocarcinoma and B16-F10 melanoma models in BALB/c and C57BL/6 mice, respectively, chTNT-3/CpG, free CpG, or several different control constructs were administered systemically. Intraperitoneal injections of chTNT-3/CpG delayed tumor growth and improved survival and were comparable to intratumorally administered CpG. Compared to saline-treated mice, chTNT-3/CpG-treated mice had smaller average tumor volumes by as much as 72% in Colon 26-bearing mice and 79% in B16-bearing mice. Systemically delivered free CpG and CpG conjugated to an isotype control antibody did not reduce tumor burden or improve survival. In this study, chTNT-3/CpG retained immunostimulatory activity of the CpG moiety and enabled delivery to tumors. Because systemically administered CpG rapidly clear the body and do not accumulate into tumors, chTNT-3/CpG provide a solution to the limitations observed in preclinical and clinical trials.

Key factors influencing ADME properties of therapeutic proteins: A need for ADME characterization in drug discovery and development

Protein therapeutics represent a diverse array of biologics including antibodies, fusion proteins, and therapeutic replacement enzymes. Since their inception, they have revolutionized the treatment of a wide range of diseases including respiratory, vascular, autoimmune, inflammatory, infectious, and neurodegenerative diseases, as well as cancer. While in vivo pharmacokinetic, pharmacodynamic, and efficacy studies are routinely carried out for protein therapeutics, studies that identify key factors governing their absorption, distribution, metabolism, and excretion (ADME) properties have not been fully investigated. Thorough characterization and in-depth study of their ADME properties are critical in order to support drug discovery and development processes for the production of safer and more effective biotherapeutics. In this review, we discuss the main factors affecting the ADME characteristics of these large macromolecular therapies. We also give an overview of the current tools, technologies, and approaches available to investigate key factors that influence the ADME of recombinant biotherapeutic drugs, and demonstrate how ADME studies will facilitate their future development.

Evaluating the Use of Antibody Variable Region (Fv) Charge as a Risk Assessment Tool for Predicting Typical Cynomolgus Monkey Pharmacokinetics

The pharmacokinetic (PK) behavior of monoclonal antibodies in cynomolgus monkeys (cynos) is generally translatable to that in humans. Unfortunately, about 39% of the antibodies evaluated for PKs in cynos have fast nonspecific (or non-target-mediated) clearance (in-house data). An empirical model relating variable region (Fv) charge and hydrophobicity to cyno nonspecific clearance was developed to gauge the risk an antibody would have for fast nonspecific clearance in the monkey. The purpose of this study was to evaluate the predictability of this empirical model on cyno nonspecific clearance with antibodies specifically engineered to have either high or low Fv charge. These amino acid changes were made in the Fv region of two test antibodies, humAb4D5-8 and anti-lymphotoxin α. The humAb4D5-8 has a typical nonspecific clearance in cynos, and by making it more positively charged, the antibody acquires fast nonspecific clearance, and making it less positively charged did not impact its clearance. Anti-lymphotoxin α has fast nonspecific clearance in cynos, and making it more positively charged caused it to clear even faster, whereas making it less positively charged caused it to clear slower and within the typical range. These trends in clearance were also observed in two other preclinical species, mice and rats. The effect of modifying Fv charge on subcutaneous bioavailability was also examined, and in general bioavailability was inversely related to the direction of the Fv charge change. Thus, modifying Fv charge appears to impact antibody PKs, and the changes tended to correlate with those predicted by the empirical model.

Quantitative cumulative biodistribution of antibodies in mice: effect of modulating binding affinity to the neonatal Fc receptor

The neonatal Fc receptor (FcRn) plays an important and well-known role in antibody recycling in endothelial and hematopoietic cells and thus it influences the systemic pharmacokinetics (PK) of immunoglobulin G (IgG). However, considerably less is known about FcRn's role in the metabolism of IgG within individual tissues after intravenous administration. To elucidate the organ distribution and gain insight into the metabolism of humanized IgG1 antibodies with different binding affinities FcRn, comparative biodistribution studies in normal CD-1 mice were conducted. Here, we generated variants of herpes simplex virus glycoprotein D-specific antibody (humanized anti-gD) with increased and decreased FcRn binding affinity by genetic engineering without affecting antigen specificity. These antibodies were expressed in Chinese hamster ovary cell lines, purified and paired radiolabeled with iodine-125 and indium-111. Equal amounts of I-125-labeled and In-111-labeled antibodies were mixed and intravenously administered into mice at 5 mg/kg. This approach allowed us to measure both the real-time IgG uptake (I-125) and cumulative uptake of IgG and catabolites (In-111) in individual tissues up to 1 week post-injection. The PK and distribution of the wild-type IgG and the variant with enhanced binding for FcRn were largely similar to each other, but vastly different for the rapidly cleared low-FcRn-binding variant. Uptake in individual tissues varied across time, FcRn binding affinity, and radiolabeling method. The liver and spleen emerged as the most concentrated sites of IgG catabolism in the absence of FcRn protection. These data provide an increased understanding of FcRn's role in antibody PK and catabolism at the tissue level.

Enhanced tumor retention of a radiohalogen label for site-specific modification of antibodies

A known limitation of iodine radionuclides for labeling and biological tracking of receptor targeted proteins is the tendency of iodotyrosine to rapidly diffuse from cells following endocytosis and lysosomal degradation. In contrast, radiometal-chelate complexes such as indium-111-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (In-111-DOTA) accumulate within target cells due to the residualizing properties of the polar, charged metal-chelate-amino acid adduct. Iodine radionuclides boast a diversity of nuclear properties and chemical means for incorporation, prompting efforts to covalently link radioiodine with residualizing molecules. Herein, we describe the Ugi-assisted synthesis of [I-125]HIP-DOTA, a 4-hydroxy-3-iodophenyl (HIP) derivative of DOTA, and demonstration of its residualizing properties in a murine xenograft model. Overall, this study displays the power of multicomponent synthesis to yield a versatile radioactive probe for antibodies across multiple therapeutic areas with potential applications in both preclinical biodistribution studies and clinical radioimmunotherapies.

Cytoreductive chemotherapy improves the biodistribution of antibodies directed against tumor necrosis in murine solid tumor models

Current strategies in cancer treatment employ combinations of different treatment modalities, which include chemotherapy, radiotherapy, immunotherapy, and surgery. Consistent with that approach, the present study demonstrates how chemotherapeutic agents can potentiate the delivery of radiolabeled, necrosis-targeting antibodies (chTNT-3, NHS76) to tumor. All chemotherapeutics in this study (5-fluorouracil, etoposide, vinblastine, paclitaxel, and doxorubicin) resulted in statistically significant increases in tumor uptake of radiolabeled antibodies and their F(ab')2 fragments compared to no pretreatment with chemotherapy. Labeled antibodies were administered at various time points following a single dose of chemotherapy in multiple tumor models, and the biodistribution of the antibodies was determined by measuring radioactivity in harvested tissues. MicroPET/CT was also done to demonstrate clinical relevancy of using chemotherapy pretreatment to increase antibody uptake. Results of biodistribution and imaging data reveal specific time frames following chemotherapy when necrosis-targeting antibodies are best delivered, either for imaging or radiotherapy. Thus, the present work offers the prospect of using cytoreductive chemotherapy to increase tumor accumulation of select therapeutic antibodies, especially when combined with other forms of immunotherapy, for the successful treatment of solid tumors.

An integrated approach to identify normal tissue expression of targets for antibody-drug conjugates: case study of TENB2

BACKGROUND AND PURPOSE

The success of antibody-drug conjugates (ADCs) depends on the therapeutic window rendered by the differential expression between normal and pathological tissues. The ability to identify and visualize target expression in normal tissues could reveal causes for target-mediated clearance observed in pharmacokinetic characterization. TENB2 is a prostate cancer target associated with the progression of poorly differentiated and androgen-independent tumour types, and ADCs specific for TENB2 are candidate therapeutics. The objective of this study was to locate antigen expression of TENB2 in normal tissues, thereby elucidating the underlying causes of target-mediated clearance.

EXPERIMENTAL APPROACH

A series of pharmacokinetics, tissue distribution and mass balance studies were conducted in mice using a radiolabelled anti-TENB2 ADC. These data were complemented by non-invasive single photon emission computed tomography - X-ray computed tomography imaging and immunohistochemistry.

KEY RESULTS

The intestines were identified as a saturable and specific antigen sink that contributes, at least in part, to the rapid target-mediated clearance of the anti-TENB2 antibody and its drug conjugate in rodents. As a proof of concept, we also demonstrated the selective disposition of the ADC in a tumoural environment in vivo using the LuCaP 77 transplant mouse model. High tumour uptake was observed despite the presence of the antigen sink, and antigen specificity was confirmed by antigen blockade.

CONCLUSIONS AND IMPLICATIONS

Our findings provide the anatomical location and biological interpretation of target-mediated clearance of anti-TENB2 antibodies and corresponding drug conjugates. Further investigations may be beneficial in addressing the relative contributions to ADC disposition from antigen expression in both normal and pathological tissues.

Vascular physiology and protein disposition in a preclinical model of neurodegeneration

The development of clinically relevant preclinical models that mimic the hallmarks of neurodegenerative disease is an ongoing pursuit in early drug development. In particular, robust physiological characterization of central nervous system (CNS) disease models is necessary to predict drug delivery to target tissues and to correctly interpret pharmacodynamic responses to disease-modifying therapeutic candidates. Efficient drug delivery across the blood-CNS barrier is a particularly daunting task, prompting our strategy to evaluate the biodistribution of five distinct molecular probes in a well-characterized mouse model of neurodegeneration. A transgenic mouse model of amyotrophic lateral sclerosis was selected based on a phenotype resembling clinical symptoms, including loss of motor neurons from the spinal cord and paralysis in one or more limbs, due to expression of a G93A mutant form of human superoxide dismutase (SOD1). The tissue distributions of two proteins, albumin and a representative immunoglobulin G antibody, as well as two blood flow markers, the lipophilic blood flow marker Ceretec (i.e., (99m)Tc-HMPAO) and the polar ionic tracer, rubidium-86 chloride ((86)RbCl), were measured following intravenous injection in SOD1(G93A) and age-matched control mice. The radiopharmaceutical TechneScan PYP was also used to measure the distribution of (99m)Tc-labeled red blood cells as a blood pool marker. Both the antibody and (86)Rb were able to cross the blood-spinal cord barrier in SOD1(G93A) mice to a greater extent than in control mice. Although the biodistribution patterns of antibody, albumin, and RBCs were largely similar, notable differences were detected in muscle and skin. Moreover, vastly different biodistribution patterns were observed for a lipophilic and polar perfusion agent, with SOD1(G93A) mutation resulting in reduced renal filtration rates for the former but not the latter. Overall, the multiprobe strategy provided an opportunity to efficiently collect an abundance of physiological information, including the degree and regional extent of blood-CNS barrier permeability, in a preclinical model of neurodegeneration.

Characterization of therapeutic monoclonal antibodies reveals differences between in vitro and in vivo time-course studies

PURPOSE

To examine and determine the sites and the kinetics of IgG1 mAb modifications from both in vitro (rat plasma and PBS) and in vivo (rat model) time-course studies.

METHODS

A comprehensive set of protein characterization methods, including RPLC/MS, LC-MS/MS, iCIEF, capSEC, and CE-SDS were performed in this report.

RESULTS

We demonstrate that plasma incubation and in vivo circulation increase the rate of C-terminal lysine removal, and the levels of deamidation, pyroglutamic acid (pyroE), and thioether-linked (lanthionine) heavy chain and light chain (HC-S-LC). In contrast, incubation in PBS shows no C-terminal lysine removal, and slower rates of deamidation, pyroE, and HC-S-LC formation. Other potential modifications such as oxidation, aggregation, and peptide bonds hydrolysis are not enhanced.

CONCLUSION

This study demonstrates that in vivo mAb modifications are not fully represented by in vitro PBS or plasma incubation. The differences in modifications and their rates reflect the dissimilarities of matrices and the impact of enzymes. These observations provide valuable evidence and knowledge in evaluating the criticality of modifications that occur naturally in vivo that might impact formulation design, therapeutic outcome, and critical quality attribute assessments for therapeutic mAb manufacturing and quality control.

Differential effects of predosing on tumor and tissue uptake of an 111In-labeled anti-TENB2 antibody-drug conjugate

TENB2, also known as tomoregulin or transmembrane protein with epidermal growth factor-like and 2 follistatin-like domains, is a transmembrane proteoglycan overexpressed in human prostate tumors. This protein is a promising target for antimitotic monomethyl auristatin E (MMAE)-based antibody-drug conjugate (ADC) therapy. Nonlinear pharmacokinetics in normal mice suggested that antigen expression in normal tissues may contribute to targeted mediated disposition. We evaluated a predosing strategy with unconjugated antibody to block ADC uptake in target-expressing tissues in a mouse model while striving to preserve tumor uptake and efficacy.

METHODS

Unconjugated, unlabeled antibody was preadministered to mice bearing the TENB2-expressing human prostate explant model, LuCaP 77, followed by a single administration of (111)In-labeled anti-TENB2-MMAE for biodistribution and SPECT/CT studies. A tumor-growth-inhibition study was conducted to determine the pharmacodynamic consequences of predosing.

RESULTS

Preadministration of anti-TENB2 at 1 mg/kg significantly increased blood exposure of the radiolabeled ADC and reduced intestinal, hepatic, and splenic uptake while not affecting tumor accretion. Similar tumor-to-heart ratios were measured by SPECT/CT at 24 h with and without the predose. Consistent with this, the preadministration of 0.75 mg/kg did not interfere with efficacy in a tumor-growth study dosed at 0.75 mg or 2.5 mg of ADC per kilogram.

CONCLUSION

Overall, the potential to mask peripheral, nontumor antigen uptake while preserving tumor uptake and efficacy could ameliorate toxicity and may significantly affect future dosing strategies for ADCs.

Maximizing tumour exposure to anti-neuropilin-1 antibody requires saturation of non-tumour tissue antigenic sinks in mice

BACKGROUND AND PURPOSE

Neuropilin-1 (NRP1) is a VEGF receptor that is widely expressed in normal tissues and is involved in tumour angiogenesis. MNRP1685A is a rodent and primate cross-binding human monoclonal antibody against NRP1 that exhibits inhibition of tumour growth in NPR1-expressing preclinical models. However, widespread NRP1 expression in normal tissues may affect MNRP1685A tumour uptake. The objective of this study was to assess MNRP1685A biodistribution in tumour-bearing mice to understand the relationships between dose, non-tumour tissue uptake and tumour uptake.

EXPERIMENTAL APPROACH

Non-tumour-bearing mice were given unlabelled MNRP1685A at 10 mg·kg(-1) . Tumour-bearing mice were given (111) In-labelled MNRP1685A along with increasing amounts of unlabelled antibody. Blood and tissues were collected from all animals to determine drug concentration (unlabelled) or radioactivity level (radiolabelled). Some animals were imaged using single photon emission computed tomography - X-ray computed tomography.

KEY RESULTS

MNRP1685A displayed faster serum clearance than pertuzumab, indicating that target binding affected MNRP1685A clearance. I.v. administration of (111) In-labelled MNRP1685A to tumour-bearing mice yielded minimal radioactivity in the plasma and tumour, but high levels in the lungs and liver. Co-administration of unlabelled MNRP1685A with the radiolabelled antibody was able to competitively block lungs and liver radioactivity uptake in a dose-dependent manner while augmenting plasma and tumour radioactivity levels.

CONCLUSIONS AND IMPLICATIONS

These results indicate that saturation of non-tumour tissue uptake is required in order to achieve tumour uptake and acceptable exposure to antibody. Utilization of a rodent and primate cross-binding antibody allows for translation of these results to clinical settings.

Compartmental tissue distribution of antibody therapeutics: experimental approaches and interpretations

Monoclonal antibodies have provided many validated and potential new therapeutic candidates for various diseases encompassing the realms of neurology, ophthalmology, immunology, and especially oncology. The mechanism of action for these biological molecules typically involves specific binding to a soluble ligand or cell surface protein in order to block or alter a molecular pathway, induce a desired cellular response, or deplete a target cell. Many antigens reside within the interstitial space, the fluid-filled compartment that lies between the outer endothelial vessel wall and the plasma membranes of cells. This mini-review examines the concepts relevant to the kinetics and behavior of antibodies within the interstitium with a special emphasis on radiometric measurement of quantitative pharmacology. Molecular probes are discussed to outline chemical techniques, selection criteria, data interpretation, and relevance to the study of antibody pharmacokinetics. The importance of studying the tissue uptake of antibodies at a compartmental level is highlighted, including a brief overview of receptor occupancy and its interpretation in radiotracer studies. Experimental methods for measuring the spatial composition of tissues are examined in terms of relative vascular, interstitial, and cellular volumes using solid tumors as a representative example. Experimental methods and physiologically based pharmacokinetic modeling are introduced as distinct approaches to distinguish between free and bound fractions of interstitial antibody. Overall, the review outlines the available methods for pharmacokinetic measurements of antibodies and physiological measurements of the compartments that they occupy, while emphasizing that such approaches may not fully capture the complexities of dynamic, heterogeneous tumors and other tissues.

Physiochemical and biochemical factors influencing the pharmacokinetics of antibody therapeutics

Monoclonal antibodies are increasingly being developed to treat multiple disease areas, including those related to oncology, immunology, neurology, and ophthalmology. There are multiple factors, such as charge, size, neonatal Fc receptor (FcRn) binding affinity, target affinity and biology, immunoglobulin G (IgG) subclass, degree and type of glycosylation, injection route, and injection site, that could affect the pharmacokinetics (PK) of these large macromolecular therapeutics, which in turn could have ramifications on their efficacy and safety. This minireview examines how characteristics of the antibodies could be altered to change their PK profiles. For example, it was observed that a net charge modification of at least a 1-unit shift in isoelectric point altered antibody clearance. Antibodies with enhanced affinity for FcRn at pH 6.0 display longer serum half-lives and slower clearances than wild type. Antibody fragments have different clearance rates and tissue distribution profiles than full length antibodies. Fc glycosylation is perceived to have a minimal effect on PK while that of terminal high mannose remains unclear. More investigation is warranted to determine if injection route and/or site impacts PK. Nonetheless, a better understanding of the effects of all these variations may allow for the better design of antibody therapeutics.

Pharmacokinetics and toxicology of therapeutic proteins: Advances and challenges

Significant progress has been made in understanding pharmacokinetics (PK), pharmacodynamics (PD), as well as toxicity profiles of therapeutic proteins in animals and humans, which have been in commercial development for more than three decades. However, in the PK arena, many fundamental questions remain to be resolved. Investigative and bioanalytical tools need to be established to improve the translation of PK data from animals to humans, and from in vitro assays to in vivo readouts, which would ultimately lead to a higher success rate in drug development. In toxicology, it is known, in general, what studies are needed to safely develop therapeutic proteins, and what studies do not provide relevant information. One of the major complicating factors in nonclinical and clinical programs for therapeutic proteins is the impact of immunogenicity. In this review, we will highlight the emerging science and technology, as well as the challenges around the pharmacokinetic- and safety-related issues in drug development of mAbs and other therapeutic proteins.

Minipig as a potential translatable model for monoclonal antibody pharmacokinetics after intravenous and subcutaneous administration

Subcutaneous (SC) delivery is a common route of administration for therapeutic monoclonal antibodies (mAbs) with pharmacokinetic (PK)/pharmacodynamic (PD) properties requiring long-term or frequent drug administration. An ideal in vivo preclinical model for predicting human PK following SC administration may be one in which the skin and overall physiological characteristics are similar to that of humans. In this study, the PK properties of a series of therapeutic mAbs following intravenous (IV) and SC administration in Göttingen minipigs were compared with data obtained previously from humans. The present studies demonstrated: (1) minipig is predictive of human linear clearance; (2) the SC bioavailabilities in minipigs are weakly correlated with those in human; (3) minipig mAb SC absorption rates are generally higher than those in human and (4) the SC bioavailability appears to correlate with systemic clearance in minipigs. Given the important role of the neonatal Fc-receptor (FcRn) in the PK of mAbs, the in vitro binding affinities of these IgGs against porcine, human and cynomolgus monkey FcRn were tested. The result showed comparable FcRn binding affinities across species. Further, mAbs with higher isoelectric point tended to have faster systemic clearance and lower SC bioavailability in both minipig and human. Taken together, these data lend increased support for the use of the minipig as an alternative predictive model for human IV and SC PK of mAbs.

Effects of anti-VEGF on pharmacokinetics, biodistribution, and tumor penetration of trastuzumab in a preclinical breast cancer model

Both human epidermal growth factor receptor 2 (HER-2/neu) and VEGF overexpression correlate with aggressive phenotypes and decreased survival among breast cancer patients. Concordantly, the combination of trastuzumab (anti-HER2) with bevacizumab (anti-VEGF) has shown promising results in preclinical xenograft studies and in clinical trials. However, despite the known antiangiogenic mechanism of anti-VEGF antibodies, relatively little is known about their effects on the pharmacokinetics and tissue distribution of other antibodies. This study aimed to measure the disposition properties, with a particular emphasis on tumor uptake, of trastuzumab in the presence or absence of anti-VEGF. Radiolabeled trastuzumab was administered alone or in combination with an anti-VEGF antibody to mice bearing HER2-expressing KPL-4 breast cancer xenografts. Biodistribution, autoradiography, and single-photon emission computed tomography-X-ray computed tomography imaging all showed that anti-VEGF administration reduced accumulation of trastuzumab in tumors despite comparable blood exposures and similar distributions in most other tissues. A similar trend was also observed for an isotype-matched IgG with no affinity for HER2, showing reduced vascular permeability to macromolecules. Reduced tumor blood flow (P < 0.05) was observed following anti-VEGF treatment, with no significant differences in the other physiologic parameters measured despite immunohistochemical evidence of reduced vascular density. In conclusion, anti-VEGF preadministration decreased tumor uptake of trastuzumab, and this phenomenon was mechanistically attributed to reduced vascular permeability and blood perfusion. These findings may ultimately help inform dosing strategies to achieve improved clinical outcomes.

Impact of drug conjugation on pharmacokinetics and tissue distribution of anti-STEAP1 antibody-drug conjugates in rats

Antibody-drug conjugates (ADCs) are designed to combine the exquisite specificity of antibodies to target tumor antigens with the cytotoxic potency of chemotherapeutic drugs. In addition to the general chemical stability of the linker, a thorough understanding of the relationship between ADC composition and biological disposition is necessary to ensure that the therapeutic window is not compromised by altered pharmacokinetics (PK), tissue distribution, and/or potential organ toxicity. The six-transmembrane epithelial antigen of prostate 1 (STEAP1) is being pursued as a tumor antigen target. To assess the role of ADC composition in PK, we evaluated plasma and tissue PK profiles in rats, following a single dose, of a humanized anti-STEAP1 IgG1 antibody, a thio-anti-STEAP1 (ThioMab) variant, and two corresponding thioether-linked monomethylauristatin E (MMAE) drug conjugates modified through interchain disulfide cysteine residues (ADC) and engineered cysteines (TDC), respectively. Plasma PK of total antibody measured by enzyme-linked immunosorbent assay (ELISA) revealed ∼45% faster clearance for the ADC relative to the parent antibody, but no apparent difference in clearance between the TDC and unconjugated parent ThioMab. Total antibody clearances of the two unconjugated antibodies were similar, suggesting minimal effects on PK from cysteine mutation. An ELISA specific for MMAE-conjugated antibody indicated that the ADC cleared more rapidly than the TDC, but total antibody ELISA showed comparable clearance for the two drug conjugates. Furthermore, consistent with relative drug load, the ADC had a greater magnitude of drug deconjugation than the TDC in terms of free plasma MMAE levels. Antibody conjugation had a noticeable, albeit minor, impact on tissue distribution with a general trend toward increased hepatic uptake and reduced levels in other highly vascularized organs. Liver uptakes of ADC and TDC at 5 days postinjection were 2-fold and 1.3-fold higher, respectively, relative to the unmodified antibodies. Taken together, these results indicate that the degree of overall structural modification in anti-STEAP1-MMAE conjugates has a corresponding level of impact on both PK and tissue distribution.

Abstract 4588: Tumor distribution of anti-neuropilin-1 is affected by antibody dose level in a tumor xenograft mouse model

Neuropilin-1 (NRP1) is a VEGF165 and semaphorin receptor widely expressed by vascular endothelial cells in normal tissues and on some tumor cells. Blocking NRP1 with human IgG1 against its b domain has been shown to inhibit tumor growth in several preclinical models. The objective of this study was to assess tumor distribution of anti-NRP1 at different dose levels with the aim of supporting the clinical development of this antibody. Nude mice bearing HM7 tumors were administered [111In]-DOTA labeled anti-NRP1 in the presence of increasing amounts of unlabeled anti-NRP1 via single IV injection. Following dosing, blood and tumors were collected at pre-selected time points. Tumor distribution was evaluated by measuring the radioactivity levels in the tumor and blood samples using a gamma counter. The mice that received only the radiolabeled antibody had relatively low plasma and tumor radioactivity levels at all time points. The plasma and tumor radioactivity levels for all other dose groups were higher than those of the group that received only radiolabeled antibody due to the saturation of the normal tissue sink previously identified. Comparing the tumor to blood radioactivity ratios demonstrated that the different dose groups maintained maximum exposure in the tumor for variable lengths of time, depending on the dose level. At 24 hours post-dose, all doses greater than the radiolabeled antibody alone were able to maintain maximum exposure. Conversely, at 48 hours post-dose, doses ≥ 10 mg/kg were able to maintain that level, while at 120 hours post-dose, only doses ≥ 20 mg/kg were able to maintain maximum exposure. Taken together, this suggests that tumor distribution is both dose and time dependent. This approach has been used to aid the clinical dose selection for anti-NRP1 and may be a valuable tool for the clinical development of other targeted therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4588. doi:10.1158/1538-7445.AM2011-4588

Effects of anti-VEGF on predicted antibody biodistribution: roles of vascular volume, interstitial volume, and blood flow

Background

The identification of clinically meaningful and predictive models of disposition kinetics for cancer therapeutics is an ongoing pursuit in drug development. In particular, the growing interest in preclinical evaluation of anti-angiogenic agents alone or in combination with other drugs requires a complete understanding of the associated physiological consequences.

Methodology/Principal Findings

Technescan™ PYP™, a clinically utilized radiopharmaceutical, was used to measure tissue vascular volumes in beige nude mice that were naïve or administered a single intravenous bolus dose of a murine anti-vascular endothelial growth factor (anti-VEGF) antibody (10 mg/kg) 24 h prior to assay. Anti-VEGF had no significant effect (p>0.05) on the fractional vascular volumes of any tissues studied; these findings were further supported by single photon emission computed tomographic imaging. In addition, apart from a borderline significant increase (p = 0.048) in mean hepatic blood flow, no significant anti-VEGF-induced differences were observed (p>0.05) in two additional physiological parameters, interstitial fluid volume and the organ blood flow rate, measured using indium-111-pentetate and rubidium-86 chloride, respectively. Areas under the concentration-time curves generated by a physiologically-based pharmacokinetic model changed substantially (>25%) in several tissues when model parameters describing compartmental volumes and blood flow rates were switched from literature to our experimentally derived values. However, negligible changes in predicted tissue exposure were observed when comparing simulations based on parameters measured in naïve versus anti-VEGF-administered mice.

Conclusions/Significance

These observations may foster an enhanced understanding of anti-VEGF effects in murine tissues and, in particular, may be useful in modeling antibody uptake alone or in combination with anti-VEGF.

Charge variants in IgG1: Isolation, characterization, in vitro binding properties and pharmacokinetics in rats

Antibody charge variants have gained considerable attention in the biotechnology industry due to their potential influence on stability and biological activity. Subtle differences in the relative proportions of charge variants are often observed during routine biomanufacture or process changes and pose a challenge to demonstrating product comparability. To gain further insights into the impact on biological activity and pharmacokinetics (PK) of monoclonal antibody (mAb) charge heterogeneity, we isolated the major charge forms of a recombinant humanized IgG1 and compared their in vitro properties and in vivo PK. The mAb starting material had a pI range of 8.7-9.1 and was composed of about 20% acidic variants, 12% basic variants, and 68% main peak. Cation exchange displacement chromatography was used to isolate the acidic, basic, and main peak fractions for animal studies. Detailed analyses were performed on the isolated fractions to identify specific chemical modification contributing to the charge differences, and were also characterized for purity and in vitro potency prior to being administered either subcutaneously (SC) or intravenously (IV) in rats. All isolated materials had similar potency and rat FcRn binding relative to the starting material. Following IV or SC administration (10 mg/kg) in rats, no difference in serum PK was observed, indicating that physiochemical modifications and pI differences among charge variants were not sufficient to result in PK changes. Thus, these results provided meaningful information for the comparative evaluation of charge-related heterogeneity of mAbs, and suggested that charge variants of IgGs do not affect the in vitro potency, FcRn binding affinity, or the PK properties in rats.

Development and evaluation of a novel method for preclinical measurement of tissue vascular volume

Identification of clinically predictive models of disposition kinetics for antibody therapeutics is an ongoing pursuit in drug development. To encourage translation of drug candidates from early research to clinical trials, clinical diagnostic agents may be used to characterize antibody disposition in physiologically relevant preclinical models. TechneScan PYP was employed to measure tissue vascular volumes (V(v)) in healthy mice. Two methods of red blood cell (RBC) labeling were compared: a direct in vivo method that is analogous to a clinical blood pool imaging protocol, and an indirect method in which radiolabeled blood was transfused from donor mice into recipient mice. The indirect method gave higher precision in RBC labeling yields, lower V(v) values in most tissues, and lower (99m)Tc uptake in kidneys and bladder by single photon emission computed tomographic (SPECT) imaging relative to the direct method. Furthermore, the relative influence of each method on the calculated area under the first 7 days of the concentration-time curve (AUC(0-7)) of an IgG in nude mice was assessed using a physiologically based pharmacokinetic model. The model was sensitive to the source of V(v) values, whether obtained from the literature or measured by either method, when used to predict experimental AUC(0-7) values for radiolabeled trastuzumab in healthy murine tissues. In summary, a novel indirect method for preclinical determination of V(v) offered higher precision in RBC labeling efficiency and lower renal uptake of (99m)Tc than the direct method. In addition, these observations emphasize the importance of obtaining accurate physiological parameter values for modeling antibody uptake.

Abstract 696: Anti-NRP1 tumor uptake is impacted by normal tissue sinks in a tumor bearing mouse model

Neuropilin-1 (NRP1) is a VEGF165 and semaphorin receptor widely expressed by vascular endothelial cells in normal tissues and on some tumor cells. Blocking NRP1 with a human IgG1 against the b domain of NRP1 has been shown to inhibit tumor growth in several preclinical models. However, due to the wide expression of NRP1 in normal tissues, the uptake of anti-NRP1 by tumor cells may be impacted by the uptake in normal tissues. The objective of this study was to determine the normal tissue uptake of anti-NRP1 and assess its impact on tumor tissue uptake in a tumor bearing mouse model. Nude mice bearing tumors with either low, HM7, or high, SKMES, NRP1 expression were dosed with [111In]-DOTA labeled anti-NRP1 with or without excess amounts of unlabeled anti-NRP1 via single IV injection. Following dosing, blood, tumor, and several normal tissues were collected at pre-selected time points for the determination of radioactivity levels using a gamma counter. In the absence of unlabeled anti-NRP1, 3% Injected Dose (ID)/ml of radioactivity was observed in the blood at 15 minutes post-dose and decreased quickly. There was minimal radioactivity seen in tumor tissue. In contrast, the majority of radioactivity was detected in the lungs and liver. With increasing amount of unlabeled anti-NRP1, the radioactivity in the lungs/liver dropped, while increasing in blood and tumor tissue. At ∼10 mg/kg unlabeled anti-NRP1, there was no additional decrease of radioactivity in these normal tissues whereas the tumor radioactivity appeared to reach its peak. Taken together, these data suggest that the lungs/liver are tissue sinks that sequester a majority of the anti-NRP1 when given at lower doses, thus hampering tumor uptake. It is important to optimize the dose and dose regimen in order to overcome this tissue sink binding and allow for a sufficient amount of antibody to be available for tumor uptake.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 696.

Construction and preclinical characterization of Fc-mGITRL for the immunotherapy of cancer

PURPOSE

To provide proper costimulation required for effective cancer T-cell immunity, Fc-GITRL fusion proteins were generated for use in immunotherapy protocols.

EXPERIMENTAL DESIGN

Soluble fusion proteins consisting of the Fc fragment of immunoglobulin and the murine glucocorticoid-induced tumor necrosis factor-related receptor ligand (mGITRL) connected with different linkers were genetically engineered and tested for their potency in two BALB/c solid tumor models.

RESULTS

In vivo, construct #178-14 (-5aa, -linker) showed the best activity (>90% tumor reduction) at doses ranging from 5 to 25 microg and was found to be intact by gel electrophoresis. Similar doses used with construct #175-2 (-linker) produced good but not as high tumor regression. Construct #5-1 (+linker), which was found to be relatively unstable by SDS gel electrophoresis, produced <60% tumor regression and required a higher dose (100 microg) to produce optimal results. Survival curves showed that Fc-mGITRL treatment extended the life of 80% of tumor-bearing mice to >3 months compared with controls that died by day 40. T-cell depletion studies showed that CD8(+) T cells play a major role in Fc-mGITRL immunotherapy, and tumors removed from Fc-mGITRL- and DTA-1-treated mice showed a significant influx of granzyme B(+) lymphocytes compared with controls. Finally, T regulatory (Treg) cell assays showed that, unlike other Fc fusion proteins, all three Fc-mGITRL constructs profoundly suppressed Treg activity.

CONCLUSIONS

These studies suggest that a stable, intact Fc-mGITRL fusion protein can provide missing costimulation for the immunotherapy of solid tumors. In addition, Fc-mGITRL may alter Treg activity to enhance its effectiveness for tumor immunotherapy.

Cytokine, chemokine, and co-stimulatory fusion proteins for the immunotherapy of solid tumors

This chapter describes the generation of novel reagents for the treatment of cancer using fusion proteins constructed with natural ligands of the immune system. Immunotherapy is a powerful therapeutic modality that has not been fully harnessed for the treatment of cancer. We and others have hypothesized that if the proper immunoregulatory ligands can be targeted to the tumor, an effective immune response can be mounted to treat both established primary tumors and distant metastatic lesions. Though it is generally believed that immunotherapy has the potential to treat only residual disease, we offer evidence that this approach can, by itself, destroy large tumor masses and produce lasting remissions of experimental solid tumors. From these studies, three major classes of immune activators, namely, cytokines, chemokines, and costimulatory molecules, have been shown to generate antitumor responses in animal models. In addition, the reversal of immune tolerance by the deletion of T regulatory (Treg) cells has been shown to be equally important for effective immunotherapy. In an attempt to identify reagents that can provide an enhanced immune stimulation and treatment of cancer, our laboratory has developed a novel monoclonal antibody targeting approach, designated Tumor Necrosis Therapy (TNT), which utilizes stable intracellular antigens present in all cell types but which are only accessible in dead and/or dying cells. Since tumors contain necrotic and degenerating regions that account for 30-80% of the tumor mass, this targeting approach can be used to deliver therapeutic reagents to the core of tumors, a site abundant in tumor antigens. In our first set of reagents, a panel of cytokine fusion proteins was genetically engineered using monoclonal antibody chimeric TNT-3 (chTNT-3) directed against necrotic regions of tumors (single-stranded DNA) fused with IL-2, or GM-CSF, or TNFalphaa, or IFNgamma. Tested against different solid tumors, these reagents were found to mount an effective although transient immune response to tumor especially when used in combination. To improve upon these results, additional chTNT-3 fusion proteins using the liver-expression chemokine (LEC) and the costimulatory molecule B7.1 were constructed. Both of these reagents were found to work significantly better than the above cytokine fusion proteins due to their ability to stimulate multiple arms of the immune system deemed useful for cancer immunotherapy. Finally, the Tumor Necrosis Factor Superfamily (TNFSF) gene DC137L was used to generate chTNT-3 antibody (targeted) and soluble Fc (untargeted) fusion proteins. When used alone, both forms of costimulatory fusion proteins were found to produce in a s dose-dependent manner, complete regression of murine solid tumors. Evidence is presented to show that Treg cells play an important role in suppressing antitumor immunity since the deletion of these cells, when used in combination with LEC or costimulatory fusion proteins, produced profound and effective treatment with sustained memory. It is hoped that these data will further the preclinical development of soluble Fc and antibody based fusion proteins fro the immunotherapy of cancer.

Lym-1-induced apoptosis of non-Hodgkin's lymphomas produces regression of transplanted tumors

Lym-1 was one of the first antibodies to be used successfully for the radioimmunotherapy of the human malignant lymphomas. This antibody, which recognizes the HLA-DR10 antigen preferentially expressed in B-cell lymphomas, was recently shown to induce apoptosis upon binding to lymphoma cells. In this study, Lym-1-induced apoptosis was studied to identify the potential molecular pathways of programmed cell death and to demonstrate the clinical potential of this antibody in the treatment of the human malignant lymphomas. Immunofluorescence microscopy revealed that Lym-1 stained focal areas of the cell surface, consistent with the fact that the HLA-DR10 antigen is associated with lipid rafts, a known prerequisite for apoptosis signaling. Likewise, Annexin V/propidium iodide staining and TUNEL assays demonstrated that both murine Lym-1 and chimeric Lym-1 induced both early and late apoptosis, respectively, unlike anti-CD20 rituximab. Furthermore, Lym-1 was found to produce a rapid loss of mitochondrial membrane potential and mitochondrial release of cytochrome C 14 hours post-Lym-1 treatment. Although it was found to activate caspase-3, inhibitors of caspase pathways showed that the Lym-1-induced apoptosis in lymphoma cell lines is independent of caspase induction. Finally, treatment studies in vivo demonstrated that, compared with murine anti-CD20 (2B8), Lym-1 was more effective in inducing the regression of human lymphoma xenografts. Based upon these results, chimeric Lym-1 should be especially effective in treating lymphoma patients, as, in addition to being able to elicit immune effector functions such as chimeric anti-CD20, it can also induce apoptosis directly upon cell binding.

RA8, a human anti-CD25 antibody against human Treg cells

Although anti-CD25 antibodies exist for clinical use in patients, there is a need for the development of a human Treg antibody that will abrogate the immunosuppressive function of this small but critical T cell subtype. Based upon mounting evidence that the level of Treg cells in the tumor microenvironment correlates with clinical prognosis and stage in man, it appears that Treg cells play an important role in the tumor's ability to overcome host immune responses. In mice, the rat anti-mouse CD25 antibody PC61 causes depletion of CD25-bearing Treg cells both peripherally in lymphatic tissues and in the tumor microenvironment, without inducing symptoms of autoimmunity. A similar antibody, though with the ability to delete Treg cells specifically, would be an important new tool for reversing tumor escape associated with Treg immunosuppression in man. To begin to generate such a reagent, we now describe the development of a human anti-CD25 antibody using a novel yeast display library. The target antigen CD25-Fc was constructed and used for five rounds of selection using a non-immune yeast display library that contained as many as 10(9) single chain variable fragments (scFv). Two unique clones with low K(D) values (RA4 and RA8) were then selected to construct fully human anti-CD25 antibodies (IgG1/kappa) for stable expression. One antibody, RA8, showed excellent binding to human CD25(+) cell lines and to human Treg cells and appears to be an excellent candidate for the generation of a human reagent that may be used in man for the immunotherapy of cancer.

Targeted and untargeted CD137L fusion proteins for the immunotherapy of experimental solid tumors

INTRODUCTION

CD137L is a member of the tumor necrosis factor superfamily that provides a costimulatory signal to T cells. In this study, two novel CD137L fusion proteins were produced and compared with the CD137 agonist antibody 2A.

MATERIALS AND METHODS

Murine CD137L was linked to the COOH terminus of either the Fc fragment of immunoglobulin (untargeted version) or TNT-3 (targeted version), an antibody that binds to necrotic regions of tumors. Groups of mice bearing established Colon 26 tumors were then treated daily x 5 with each fusion protein or 2A to determine their immunotherapeutic potential.

RESULTS

Both fusion proteins retained CD137L activity in vitro and TNT-3/CD137L showed tumor-binding activity by biodistribution analysis in tumor-bearing mice. The fusion proteins also produced similar responses in vivo at the 1 nmol per dose range and showed a 60% (TNT-3/CD137L) or 40% (Fc/CD137L) survival of treated mice at 150 days after tumor implantation, similar to the effects of 2A. Morphologic and immunohistochemical analyses showed massive central necrosis and infiltration of granzyme B-positive cells in necrotic areas and viable peripheral regions of treated tumors. Finally, cell depletion studies showed that CD137L-mediated tumor regression was CD8(+) T cell dependent.

CONCLUSIONS

From these studies, it was determined that both targeted and untargeted CD137L fusion proteins showed effective antitumor activity, but that the targeted version was more potent. Therefore, the use of the natural CD137 ligand is a promising approach to the treatment of solid tumors by virtue of its ability to produce physiologic costimulation within the tumor, limiting side effects often seen with agonist antibody therapies.

Soluble Fc fusion proteins for biomedical research

As a source of recombinant antigen, soluble constant fragment (Fc) fusion proteins have become valuable reagents for immunotherapy and laboratory investigations. Additional applications for these reagents include flow cytometry, immunohistochemistry, and in vitro activity assays. To aid investigators in the generation of these reagents, the materials and methods required for producing Fc fusion proteins are described. The investigator's protein moiety of interest is genetically linked to the N-terminus of murine Fc and subsequently expressed in large quantity using a mammalian cell expression system. The resulting Fc fusion proteins are purified on a protein A column and may be stored for at least one year at -20 degrees C. The availability of easily purified, soluble Fc fusion proteins in such quantity can facilitate research in multiple fields of medicine and biotechnology.

B7.1/NHS76: a new costimulator fusion protein for the immunotherapy of solid tumors

Tumor evasion from immune surveillance is due to the anergic status of tumor-infiltrating lymphocytes, especially T cells. Inappropriate or absent expression of costimulatory molecules such as B7.1 and B7.2 lead to anergy and apoptosis of tumor-infiltrating T cells. To reverse this situation, a tumor-targeted fusion protein, human B7.1/NHS76, was generated by molecular engineering, which retains both the costimulatory activity of B7.1 and the tumor-targeting ability of NHS76 antibody. NHS76 is a human tumor necrosis therapy monoclonal antibody derived from phage display, and is capable of binding intracellular antigens, which are accessible and abundant in necrotic regions of tumors. As human B7.1 can interact functionally with murine B7.1 counter-receptors, the immunotherapeutic potential of this fusion protein was tested in 3 mouse tumor models (Colon 26, RENCA, and MAD109), and animal studies showed a 35% to 55% reduction in tumor volume. To modulate the immune inhibitory microenvironment in tumors, naturally occurring CD4+ CD25+ Treg cells were depleted by cytotoxic CD4 or CD25 antibodies. Combination therapy with anti-Treg and B7.1/NHS76 produced complete regression of established tumors and was associated with increased effector T-cell infiltration in tumors. Rechallenge experiments performed 3 months after mice attained complete remission by combination therapy showed that immunologic memory was established by these treatments. These studies indicate that the targeting of B7.1 to necrotic areas of tumors, where both the release of tumor antigens and infiltrating lymphocytes are prevalent, may be a new approach for the immunotherapy of solid tumors. Our results also suggest that the manifestation of immune-inhibitory factors such as the presence of Treg cells at the tumor site and associated draining lymph nodes may be a major cause for immune system failure to eradicate solid tumors.

H60/TNT-3 fusion protein activates NK cells in vitro and improves immunotherapeutic outcome in murine syngeneic tumor models

H60 is a murine minor histocompatibility antigen that binds to NKG2D and activates an effector phenotype in NK and T cells. In the present study, H60 was genetically fused to the tumor-targeting murine MAb TNT-3. The resultant fusion protein, named H60/TNT-3, was produced in NS0 cells and determined by ELISA to possess an H60 epitope. The Ka of H60/TNT-3 (2.43 x 10(9) M(-1)) was nearly identical to that of the parental Ab (2.22 x 10(9) M(-1)), demonstrating that addition of the H60 moiety to the N-terminus of TNT-3 heavy chain did not affect antigen affinity. In vitro, H60/TNT-3 bound and activated murine NK cells, eliciting IFN-gamma production in a higher percentage of cells than the activating NKG2D Ab A10. In vivo, H60/TNT-3 possessed a half-life of approximately 12 hours and effectively targeted tumor tissue versus control organs, with nearly 2% injected dose per gram of tumor retained after 48 hours. Finally, H60/TNT-3 was tested for antitumor efficacy in BALB/c and C57BL/6 mice bearing subcutaneous syngeneic carcinomas. Tumor volume reduction was observed in both CT26 and Lewis Lung models (53% and 52%, respectively) relative to untreated control mice. Further, Lewis Lung carcinoma-bearing mice treated with H60/TNT-3 experienced a statistically significant survival advantage. Taken together, these data characterize a new immunotherapeutic MAb with antitumor efficacy that prolonged overall survival in a resistant solid tumor model.

131I-chTNT Radioimmunotherapy of 43 Patients with Advanced Lung Cancer

The treatment of advanced lung cancer remains a major challenge in clinical medicine, justifying an urgent need for new therapeutic approaches. In a rather unique international collaboration, 43 patients with advanced lung cancer were treated using iodine-131-labeled tumor necrosis therapy chimeric antibody (131I-chTNT).

METHODS

Patients were treated either with intravenous (i.v.) infusion (n = 22), intratumoral injection using a computer tomography (CT)-guided catheter (n = 16), or combination i.v. and intratumoral infusion (n = 5). All patients, regardless of route of administration, received 2 doses of 131I-chTNT on days 1 and 14.

RESULTS

The results showed that of those patients receiving i.v. injection alone, 2 achieved partial response (PR) (9%), 16 had stable disease (73%), and 4 progressed (18%). Of those patients receiving intratumoral injection only, 1 had a complete response (CR) (6%), 8 achieved PR (50%), 7 had stable disease (44%), and none (0%) progressed. Finally, of those patients receiving both i.v. and intratumoral administration, 1 had a CR (20%), 1 achieved PR (20%), 2 had stable disease (40%), and 1 (20%) showed progression.

CONCLUSIONS

These promising results demonstrate that sufficient doses of radiolabeled antibody can be safely delivered to tumors to cause significant therapeutic effects in advanced lung cancer.

Combination B7-Fc fusion protein treatment and Treg cell depletion therapy

PURPOSE

A B7.1 fusion protein consisting of the extracellular domains of human B7.1 and the Fc portion of human IgG1, called B7.1-Fc, was generated and evaluated for its antitumor potential when used alone or in combination with regulatory T (Treg) cell depletion.

METHODS

A human B7.1-Fc fusion protein was constructed, expressed, purified, and examined for its antitumor activity in experimental mouse tumor models.

RESULTS

Soluble B7.1-Fc showed costimulatory activity of T-cell proliferation in vitro, and when given in vivo, it induced complete regression of Colon 26 tumors after a 5-day treatment regimen. Parallel studies with human B7.2-Fc gave very similar results in the Colon 26 tumor model. Even in mice with established RENCA and Madison 109 tumors, which are poorly immunogenic, B7.1-Fc treatment slowed tumor growth dramatically. In these models, more potent antitumor activity was achieved when B7.1-Fc was used in combination with Treg depletion by i.p. administration of antibody PC61. Rechallenge experiments done with mice that had sustained complete tumor regressions showed that these mice had immunologic memory by their ability to reject subsequent implants. Histologically, B7.1-Fc treatment induced multiple areas of necrosis and infiltration of CD4+ and CD8+ T cells in tumors along with a concomitant dramatic increase in T-cell proliferation in tumor-draining lymph nodes.

CONCLUSIONS

The B7.1-Fc fusion protein seems to be an effective antitumor agent especially in combination with Treg depletion. Its potency in stimulating immune responses and its human origin suggest that clinical studies may be warranted in the future.

Generation of rituximab polymer may cause hyper-cross-linking-induced apoptosis in non-Hodgkin's lymphomas

PURPOSE

Although Rituximab has produced significant tumor regressions in lymphoma patients, only 50% respond. Clinically, it has been shown that the major mechanism of action of Rituximab is antibody-dependent cytotoxicity requiring presentation by Fc-bearing cells. To improve the clinical efficacy of Rituximab for the treatment of CD20+ lymphomas, we now describe a new formulation of Rituximab, which, on direct binding to target, can induce apoptosis.

METHODS

In this report, enhanced apoptosis was observed by treating CD20+ lymphoma cells with a new polymer formulation of Rituximab. The polymer was produced by formation of a peptide bond using the sugar moiety of dextran (MW 6,000) to generate a clinically relevant reagent for use in vivo.

RESULTS

Comparison of Rituximab with a previously described dimer and the newly generated polymer shows that the polymer induced apoptosis more effectively in CD20+ cells as shown by the terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling assay (Rituximab, 3%; dimer, 3%; polymer, 58%). Consistent with these results, the polymer produced marked regression in CD20+ lymphoma xenografts, whereas the dimer and monomer reagents showed little effect. In addition, we were able to show that the level of apoptosis induced in human lymphoma cell lines was in accordance with the extent of both surface CD20 clustering and caspase-3 activation.

CONCLUSIONS

These data suggest that hyper-cross-linking-induced apoptosis can be simulated by the use of a dextran polymer of Rituximab, which, when used in vivo, can directly kill CD20+ lymphoma cells and improve the clinical efficacy of this important therapeutic for human B-cell lymphomas.

NHS76/PEP2, a fully human vasopermeability-enhancing agent to increase the uptake and efficacy of cancer chemotherapy

PURPOSE

Previously, we have shown that the attachment of interleukin 2 (IL-2) to a tumor-targeting antibody can produce a 4-fold enhancement in the uptake of antibodies and drugs in tumors. More recently, we discovered that a 37-amino-acid linear sequence of IL-2 designated vasopermeability-enhancing peptide (PEP), contained the vasopermeability activity of IL-2, and could be used after linkage to tumor-targeting antibodies to produce the same enhancement of drugs and antibodies in tumors. We now describe the generation of a fully human antibody fusion protein, designated NHS76/PEP(2), which can be used in patients to enhance the therapeutic potential of chemotherapy.

METHODS

NHS76/PEP(2) was expressed in NS0 cells using the glutamine synthetase gene amplification system. To show its clinical potential as a pretreatment to chemotherapy, NHS76/PEP(2) was given i.v. 2 hours before the injection of suboptimal doses of etoposide, doxorubicin, Taxol, Taxotere, 5-fluorouracil, or vinblastine in mice bearing established solid tumors. Results were recorded by measuring tumor volumes thrice per week.

RESULTS

Compared with drug treatment alone, NHS76/PEP(2) pretreatment substantially improved the effectiveness of chemotherapeutic agents in solid tumor models. Tumor suppression was most pronounced in those groups of mice bearing tumors known to be sensitive to the specific drug under study. However, in certain instances, tumors previously known to be resistant to specific single chemotherapeutic agents were shown to respond by the addition of NHS76/PEP(2) pretreatment.

CONCLUSIONS

NHS76/PEP(2) seems an excellent candidate to improve the value of standard chemotherapy drug treatment by virtue of its ability to increase the uptake of drugs in solid tumors selectively.

Pivotal study of iodine-131-labeled chimeric tumor necrosis treatment radioimmunotherapy in patients with advanced lung cancer

PURPOSE

Tumor necrosis treatment (TNT) uses degenerating tumor cells and necrotic regions of tumors as targets for radioimmunotherapy. Previous studies in animal tumor models and clinical trials have demonstrated that when linked to the therapeutic radionuclide iodine-131, recombinant chimeric TNT antibody ((131)I-chTNT) can deliver therapeutic doses to tumors regardless of the location or type of malignancy. Therapeutic efficacy and toxicity of (131)I-chTNT in advanced lung cancer patients were studied in this pivotal registration trial.

PATIENTS AND METHODS

Patients with advanced lung cancer were treated with systemic or intratumoral injection of (131)I-chTNT in eight oncology centers in China. The objective response rate (ORR) was assessed as the primary end point.

RESULTS

All 107 patients who were entered onto the study and completed therapy had experienced treatment failure after prior radiotherapy or chemotherapy a mean of three times. The results showed an ORR of 34.6% (complete response, 3.7%; partial response, 30.8%; no change, 55.1%; and progressive disease, 10.3%) in all patients and 33% in 97 non-small-cell lung cancer patients. A biodistribution study demonstrated excellent localization of the radioactivity in tumors in both systemically and intratumorally injected patients. The most obvious adverse side effect was mild and reversible bone marrow suppression.

CONCLUSION

Radioimmunotherapy with (131)I-chTNT was well tolerated and can be used systemically or locally to treat refractory tumors of the lung.

Tumor targeting properties of indium-111 labeled genetically engineered Fab' and F(ab')2 constructs of chimeric tumor necrosis treatment (chTNT)-3 antibody

Genetic engineering techniques have allowed the construction of Fab' and F(ab')2 constructs of chimeric tumor necrosis treatment antibody (chTNT-3), a chimeric monoclonal antibody (MAb) that targets necrotic regions of solid tumors. The purpose of this study is to evaluate the in vitro and in vivo properties of Fab' and F(ab')2 constructs radiolabeled with indium-111 (111In) using diethylentriamine pentaacetic acid (DTPA) conjugation to develop a clinically useful imaging agent for the detection of necrosis in solid tumors. Optimization of the MAb-to-DTPA ratio showed that a 1:2 ratio gave the best immunoreactivity while providing good radiolabeling efficiency and high specific activity for all three DPTA conjugates. In addition, 111In-labeled Fab' and F(ab')2 conjugates were found to have faster whole body clearance times and better biodistribution profiles compared to parental 111In-labeled chTNT-3 in tumor-bearing mice. Although radiolabeled Fab' and F(ab')2 constructs showed lower tumor uptake than radiolabeled chTNT-3, biodistribution results showed that these constructs had significantly lower uptake in liver, spleen, and other normal organs (except the kidney), and therefore had higher tumor-to-organ ratios. In addition, a comparison of all derivatives showed that the F(ab')2 reagent gave the best results in tumor imaging studies. These results demonstrate that stable, a genetically engineered F(ab')2 construct can be successfully radiolabeled with 111In to produce potential imaging reagents for the imaging and monitoring of tumor necrosis.

chTNT-3/hu IL-12 fusion protein for the immunotherapy of experimental solid tumors

Fusion proteins are emerging as a promising approach for targeting cytokines to the tumor site in order to generate an effective anti-tumor response. In this study, a fusion protein, chTNT-3/huIL-12, consisting of the necrosis targeting antibody, chTNT-3, and human interleukin-12 (IL-12), was constructed and expressed using the glutamine synthetase gene amplification system in NS0 cells. For these studies, IL-12 was chosen since it has been shown to be a powerful anti-tumor cytokine. To generate the fusion protein, an expression vector was prepared by linking the huIL-12 p35 subunit cDNA to the 3' end of the chTNT-3 heavy chain cDNA and the p40 subunit was added to a separate vector. The activity of the expressed chTNT-3/huIL-12 was confirmed by standard IL-12 bioactivity assays which demonstrated that the fusion protein induced similar levels of peripheral blood lymphocyte (PBL) proliferation as free recombinant IL-12. In addition, the lytic activity of the fusion protein was demonstrated in both naive and IL-2-activated lymphocytes using cytotoxicity assays against three human pancreatic and prostatic cancer cell lines (CAPAN, DU145, and PC3-MA). Human PBL incubated with this fusion protein showed an increase in IFN-gamma production which was augmented dramatically by pre-incubation with IL-2. Finally, the immunotherapeutic potential of the fusion protein was demonstrated in the human PBL-SCID mouse model where a 44% reduction in DU145 prostatic tumor growth was obtained compared to control treated mice. These results demonstrate that tumor-targeted human IL-12 may be an effective immunotherapeutic reagent for the treatment of solid tumors in man.