A strategy for mapping and neutralizing conformational immunogenic sites on protein therapeutics

Glucarpidase (carboxypeptidase G2): Biotechnological production, clinical application as a methotrexate antidote, and placement in targeted cancer therapy

Patients receiving high-dose methotrexate (HDMTX) for malignancies are exposed to diverse complications, including nephrotoxicity, hepatotoxicity, mucositis, myelotoxicity, neurological symptoms, and death. Glucarpidase is a recombinant carboxypeptidase G2 (CPG2) that converts MTX into nontoxic metabolites. In this study, the role of vector type, gene optimization, orientation, and host on the expression of CPG2 is investigated. The effectiveness of various therapeutic regimens containing glucarpidase is classified and perspectives on the dose adjustment based on precision medicine are provided. Conjugation with cell-penetrating peptides, human serum albumin, and polymers such as PEG and dextran for delivery, higher stability, and production of the biobetter variants of CPG2 is highlighted. Conjugation of CPG2 to F(ab՜)2 or scFv antibody fragments against tumor-specific antigens and the corresponding prodrugs for tumor-targeted drug delivery using the antibody-directed enzyme prodrug therapy (ADEPT) is communicated. Trials to reduce the off-target effects and the possibility of repeated ADEPT cycles by adding pro-domains sensitive to tumor-overexpressed proteases, antiCPG2 antibodies, CPG2 mutants with immune-system-unrecognizable epitopes, and protective polymers are reported. Intracellular cpg2 gene expression by gene-directed enzyme prodrug therapy (GDEPT) and the concerns regarding the safety and transfection efficacy of the GDEPT vectors are described. A novel bifunctional platform using engineered CAR-T cell micropharmacies, known as Synthetic Enzyme-Armed KillER (SEAKER) cells, expressing CPG2 to activate prodrugs at the tumor niche is introduced. Taken together, integrated data in this review and recruiting combinatorial strategies in novel drug delivery systems define the future directions of ADEPT, GDEPT, and SEAKER cell therapy and the placement of CPG2 therein.

Antibody Directed Enzyme Prodrug Therapy (ADEPT): Trials and tribulations

Antibody directed enzyme prodrug therapy has the potential to be an effective therapy for most common solid cancers. Clinical studies with CPG2 system have shown the feasibility of this approach. The key limitation has been immunogenicity of the enzyme. Technologies now exist to eliminate this problem. Non-immunogenic enzymes in combination with prodrugs that generate potent cytotoxic drugs can provide a powerful approach to cancer therapy. ADEPT has the potential to be non -toxic to normal tissue and can therefore be combined with other modalities including immunotherapy for greater clinical benefit.

Principles and properties of ion flow in P2X receptors

P2X receptors are a family of trimeric ion channels that are gated by extracellular adenosine 5′-triphosphate (ATP). These receptors have long been a subject of intense research interest by virtue of their vital role in mediating the rapid and direct effects of extracellular ATP on membrane potential and cytosolic Ca²⁺ concentration, which in turn underpin the ability of ATP to regulate a diverse range of clinically significant physiological functions, including those associated with the cardiovascular, sensory, and immune systems. An important aspect of an ion channel's function is, of course, the means by which it transports ions across the biological membrane. A concerted effort by investigators over the last two decades has culminated in significant advances in our understanding of how P2X receptors conduct the inward flux of Na⁺ and Ca²⁺ in response to binding by ATP. However, this work has relied heavily on results from current recordings of P2X receptors altered by site-directed mutagenesis. In the absence of a 3-dimensional channel structure, this prior work provided only a vague and indirect appreciation of the relationship between structure, ion selectivity and flux. The recent publication of the crystal structures for both the closed and open channel conformations of the zebrafish P2X4 receptor has thus proved a significant boon, and has provided an important opportunity to overview the amassed functional data in the context of a working 3-dimensional model of a P2X receptor. In this paper, we will attempt to reconcile the existing functional data regarding ion permeation through P2X receptors with the available crystal structure data, highlighting areas of concordance and discordance as appropriate.

Exploiting bias in a non-immune human antibody library to predict antigenicity

Non-immune human antibody fragment libraries have generated antigen-binding proteins useful as prospective research, imaging, diagnostic and therapeutic agents. However, because the generation of such libraries relies on cloning antibody sequences from the circulating immune repertoire rather than truly naïve, germline sequences, their composition may reflect the deletion of autoreactive sequences, making them less suited for isolating binding clones to human antigens, but perhaps useful in applications where an in vitro handle on representative circulating antibody diversity is desired. Here we demonstrate that a large non-immune human scFv library is relatively depleted of sequences capable of recognizing human antigens as compared with orthologs antigens. Additionally, because this non-naïve, non-immune library may capture a representative section of antibody diversity, we explore its possible utility in conducting early pre-screens to predict the antigenicity of prospective therapeutics and find a correlation between the clinical immunogenicity of a small panel of protein therapeutics with their propensity for interacting with the library.

Antibody-enzyme fusion proteins for cancer therapy

Advances in biomolecular technology have allowed the development of genetically fused antibody-enzymes. Antibody-enzyme fusion proteins have been used to target tumors for cancer therapy in two ways. In one system, an antibody-enzyme is pretargeted to the tumor followed by administration of an inactive prodrug that is converted to its active form by the pretargeted enzyme. This system has been described as antibody-directed enzyme prodrug therapy. The other system uses antibody-enzyme fusion proteins as direct therapeutics, where the enzyme is toxic in its own right. The key feature in this approach is that the antibody is used to internalize the toxic enzyme into the tumor cell, which activates cell-death processes. This antibody-enzyme system has been largely applied to deliver ribonucleases. This article addresses these two antibody-enzyme targeting strategies for cancer therapy from concept to (pre)clinical trials.

Directed evolution of a lysosomal enzyme with enhanced activity at neutral pH by mammalian cell-surface display

Human beta-glucuronidase, due to low intrinsic immunogenicity in humans, is an attractive enzyme for tumor-specific prodrug activation, but its utility is hindered by low activity at physiological pH. Here we describe the development of a high-throughput screening procedure for enzymatic activity based on the stable retention of fluorescent reaction product in mammalian cells expressing properly folded glycoproteins on their surface. We utilized this procedure on error-prone PCR and saturation mutagenesis libraries to isolate beta-glucuronidase tetramers that were up to 60-fold more active (k(cat)/K(m)) at pH 7.0 and were up to an order of magnitude more effective at catalyzing the conversion of two structurally disparate glucuronide prodrugs to anticancer agents. The screening procedure described here can facilitate investigation of eukaryotic enzymes requiring posttranslational modifications for biological activity.

An immunotoxin with greatly reduced immunogenicity by identification and removal of B cell epitopes

Recombinant immunotoxins are hybrid proteins composed of an Fv that binds to a tumor antigen fused to a bacterial or plant toxin. Immunotoxin BL22 targets CD22 positive malignancies and is composed of an anti-CD22 Fv fused to a 38-kDa fragment of Pseudomonas exotoxin A (PE38). BL22 has produced many complete remissions in drug-resistant Hairy cell leukemia, where many treatment cycles can be given, because neutralizing antibodies do not form. In marked contrast, only minor responses have been observed in trials with immunotoxins targeting solid tumors, because only a single treatment cycle can be given before antibodies develop. To allow more treatment cycles and increase efficacy, we have produced a less immunogenic immunotoxin by identifying and eliminating most of the B cell epitopes on PE38. This was accomplished by mutation of specific large hydrophilic amino acids (Arg, Gln, Glu, Lys) to Ala, Ser, or Gly. The new immunotoxin (HA22-8X) is significantly less immunogenic in three strains of mice, yet retains full cytotoxic and anti-tumor activities. Elimination of B-cell epitopes is a promising approach to the production of less immunogenic proteins for therapeutic purposes.

Detection and significance of serum protein marker of Hirschsprung disease

OBJECTIVE

The objective of this study was to identify a specific fingerprint chromatogram model of serum proteins for early screening and diagnosis of Hirschsprung disease.

METHODS

To detect the protein mass spectrograms of 78 serum specimens (42 specimens of Hirschsprung disease, 16 specimens of adhesive ileus including appendicitis and Meckel diverticulum after operation and inflammatory bowel disease, and 20 specimens of normal control subjects), we used surface-enhanced laser desorption/ionization time of flight mass spectrometry technology, combined with bioinformatics methods (support vector machine) to develop and compare protein mass spectrograms from serum samples.

RESULTS

We identified 3 protein markers, the mass-to-charge ratio of which is positioned at 3221.7, 5639.2, and 6884.2 from the fingerprint chromatogram model of serum protein for early screening and diagnosis of Hirschsprung disease. The markers had 100% sensitivity and specificity.

CONCLUSION

The fingerprint chromatogram model of serum protein using surface-enhanced laser desorption/ionization time of flight mass spectrometry technology combining support vector machine is a new method of early screening and diagnosis of Hirschsprung disease that is worthy of additional research and application.

A phase I study of single administration of antibody-directed enzyme prodrug therapy with the recombinant anti-carcinoembryonic antigen antibody-enzyme fusion protein MFECP1 and a bis-iodo phenol mustard prodrug

PURPOSE

Antibody-directed enzyme prodrug therapy is a two-stage treatment whereby a tumor-targeted antibody-enzyme complex localizes in tumor for selective conversion of prodrug. The purpose of this study was to establish optimal variables for single administration of MFECP1, a recombinant antibody-enzyme fusion protein of an anti-carcinoembryonic antigen single-chain Fv antibody and the bacterial enzyme carboxypeptidase G2 followed by a bis-iodo phenol mustard prodrug. MFECP1 is manufactured in mannosylated form to facilitate normal tissue elimination.

EXPERIMENTAL DESIGN

Pharmacokinetic, biodistribution, and tumor localization studies were used to test the hypothesis that MFECP1 localizes in tumor and clears from normal tissue via the liver. Firstly, safety of MFECP1 and a blood concentration of MFECP1 that would avoid systemic prodrug activation were tested. Secondly, dose escalation of prodrug was done. Thirdly, the dose of MFECP1 and timing of prodrug administration were optimized.

RESULTS

MFECP1 was safe and well tolerated, cleared rapidly via the liver, and was less immunogenic than previously used products. Eighty-fold dose escalation from the starting dose of prodrug was carried out before dose-limiting toxicity occurred. Confirmation of the presence of enzyme in tumor and DNA interstrand cross-links indicating prodrug activation were obtained for the optimal dose and time point. A total of 28 of 31 patients was evaluable for response, the best response being a 10% reduction of tumor diameter, and 11 of 28 patients had stable disease.

CONCLUSIONS

Optimal conditions for effective therapy were established. A study testing repeat treatment is currently being undertaken.

Development of antibodies for cancer therapy

Antibody therapies have become an important component in the management of malignant disease. Recombinant technology offers enormous opportunities to tailor antibodies to meet clinical requirements. This includes the reduction of immunogenicity and the development of smaller antibody fragments that can be incorporated into fusion proteins. Antibodies can block tumour growth factors or their receptors, activate immunological attack on the tumour, or be used to deliver payloads such as radioisotopes, cytotoxic drugs or toxins. Pretargeting includes streptavidin/biotin systems and antibody-directed enzyme prodrug therapy (ADEPT). ADEPT uses an antibody-enzyme complex to deliver a prodrug-activating enzyme to tumours for selective prodrug conversion at the tumour site. New antibody targets, refined antibodies, antibody fusion proteins, combination therapies and the use of antibodies as adjuvant therapy are important topics in the development of antibody therapy against cancer.

Antibody-directed enzyme prodrug therapy (ADEPT) for cancer

Antibody-directed enzyme prodrug therapy (ADEPT) aims to restrict the cytotoxic action to tumour sites. The obstacles to achieve this were recognised at the outset, but time and experience have given these better definition. The development of fusion proteins has provided the means of making consistent antibody-enzyme constructs on an adequate scale, and glycosylation has provided the means to control the clearance of enzyme from non-tumour sites. Human enzymes have yet to be tested in a clinical setting, and there are pointers indicating that the immunological response to foreign enzymes can be overcome. The relatively small number of purpose-designed prodrugs tested so far leaves this an area ripe for further development. The ongoing iterative process between preclinical and clinical studies is critical to achieving the objective.

Proteomic identification of Ku70/Ku80 autoantigen recognized by monoclonal antibody against hepatocellular carcinoma

A murine monoclonal antibody (mAb), CLD3 (IgG(1),kappa), was generated against hepatocellular carcinoma (HCC). Both immunofluorescence and immunohistochemical assays indicated the reactivity of CLD3 mAb localized at the nucleus and/or cytoplasm of tumorigenic HCC cell lines as well as in liver cancer tissues. By immunoprecipitation and using the matrix-assisted laser desorption/ionization-time of flight mass spectrometry approach, the antigenic specificity of CLD3 was determined to be heterodimeric Ku70 and Ku80 autoantigen, which was confirmed by Western blotting.

Sustained Tumor Regression of Human Colorectal Cancer Xenografts Using a Multifunctional Mannosylated Fusion Protein in Antibody-Directed Enzyme Prodrug Therapy

Purpose: Antibody-directed enzyme prodrug therapy (ADEPT) requires highly selective antibody-mediated delivery of enzyme to tumor. MFE-CP, a multifunctional genetic fusion protein of antibody and enzyme, was designed to achieve this by two mechanisms. First by using a high affinity and high specificity single chain Fv antibody directed to carcinoembryonic antigen. Second by rapid removal of antibody-enzyme from normal tissues by virtue of post-translational mannosylation. The purpose of this paper is to investigate these dual functions in an animal model of pharmacokinetics, pharmacodynamics, toxicity, and efficacy.

Experimental Design: MFE-CP was expressed in the yeast Pichia pastoris and purified via an engineered hexahistidine tag. Biodistribution and therapeutic effect of a single ADEPT cycle (1,000 units/kg MFE-CP followed by 70 mg/kg ZD2767P prodrug at 6, 7, and 8 hours) and multiple ADEPT cycles (9-10 cycles within 21-24 days) was studied in established human colon carcinoma xenografts, LS174T, and SW1222.

Results: Selective localization of functional enzyme in tumors and rapid clearance from plasma was observed within 6 hours, resulting in tumor to plasma ratios of 1,400:1 and 339:1, respectively for the LS174T and SW1222 models. A single ADEPT cycle produced reproducible tumor growth delay in both models. Multiple ADEPT cycles significantly enhanced the therapeutic effect of a single cycle in the LS174T xenografts (P = 0.001) and produced regressions in the SW1222 xenografts (P = 0.0001), with minimal toxicity.

Conclusions: MFE-CP fusion protein, in combination with ZD2767P, provides a new and successful ADEPT system, which offers the potential for multiple cycles and antitumor efficacy. These results provide a basis for the next stage in clinical development of ADEPT.

Synthesis, conformation, receptor binding and biological activities of monobiotinylated human insulin-like peptide 3

Biotin-avidin immobilization has been routinely used as a tool to study peptide-receptor and peptide-antibody interactions. Biotinylated peptides can also be employed to localize cells that express the peptides' receptor, and to analyse ligand-receptor binding. Insulin-like peptide 3 (INSL3) is a peptide hormone which contains A- and B-chains connected by two disulphide bonds and plays a role in testicular descent during sexual development. In order to study the interaction of INSL3 with its receptor LGR8, a G protein-coupled receptor, we chemically synthesized Nalpha-mono-biotinylated human INSL3 (B-hINSL3) and compared it structurally and biologically with hINSL3. Both peptides exhibited similar, but high, receptor binding affinities on human foetal kidney fibroblast 293T cells transfected human LGR8 based on a competition radioreceptor assay with 33P-labelled relaxin H2 (B33). The modified B-hINSL3 showed full biological activity as determined by the stimulation of gubernacular cell proliferation. The labelled B-hINSL3 contains a higher alpha-helix content, and this increased helical structure is accompanied by an increase in ability to stimulate cAMP accumulation in 293T cells expressing LGR8. Our results suggest that the N-terminal region of the A-chain is not involved in the interaction of INSL3 with its receptor. However, the introduction of biotin onto the N-terminus of the A-chain promoted conformational stability which, in turn, permitted better receptor activation.

Demystified...recombinant antibodies

Recombinant antibodies are important tools for biomedical research and are increasingly being used as clinical diagnostic/therapeutic reagents. In this article, a background to humanized antibodies is given, together with details of the generation of antibody fragments--for example, single chain Fv fragments. Phage antibody fragments are fast becoming popular and can be generated by simple established methods of affinity enrichment from libraries derived from immune cells. Phage display methodology can also be used for the affinity enrichment of existing antibody fragments to provide a reagent with a higher affinity. Here, phage antibodies are demystified to provide a greater understanding of the potential of these reagents and to engage clinicians and biomedical scientists alike to think about potential applications in pathology and clinical settings.

Modifying an immunogenic epitope on a therapeutic protein: a step towards an improved system for antibody-directed enzyme prodrug therapy (ADEPT)

Carboxypeptidase G2 (CP) is a bacterial enzyme, which is targeted to tumours by an antitumour antibody for local prodrug activation in antibody-directed enzyme prodrug therapy (ADEPT). Repeated cycles of ADEPT are desirable but are hampered by human antibody response to CP (HACA). To address this, we aimed to identify and modify clinically important immunogenic sites on MFECP, a recombinant fusion protein of CP with MFE-23, a single chain Fv (scFv) antibody. A discontinuous conformational epitope at the C-terminus of the CP previously identified by the CM79 scFv antibody (CM79-identified epitope) was chosen for study. Modification of MFECP was achieved by mutations of the CM79-identified epitope or by addition of a hexahistidine tag (His-tag) to the C-terminus of MFECP, which forms part of the epitope. Murine immunisation experiments with modified MFECP showed no significant antibody response to the CM79-identified epitope compared to A5CP, an unmodified version of CP chemically conjugated to an F(ab)(2) antibody. Success of modification was also demonstrated in humans because patients treated with His-tagged MFECP had a significantly reduced antibody response to the CM79-identified epitope, compared to patients given A5CP. Moreover, the polyclonal antibody response to CP was delayed in both mice and patients given modified MFECP. This increases the prospect of repeated treatment with ADEPT for effective cancer treatment.

Clostridia in cancer therapy

During the past decade, the search for an effective system for the selective delivery of high therapeutic doses of anti-cancer agents to tumours has explored a variety of ingenious and increasingly complex biological systems. These systems are most often based on gene therapy and use viral vectors as the delivery vehicle. Invariably, such systems have been found wanting with respect to a lack of tumour specificity, poor levels of transgene expression and inefficient distribution of the vector throughout the tumour mass. By contrast, the ability of intravenously injected clostridial spores to infiltrate, then selectively germinate in, the hypoxic regions of solid tumours seems to be a totally natural phenomenon, which requires no fundamental alterations and is exquisitely specific.

Minimizing the immunogenicity of protein therapeutics

As is cautioned in many package inserts, 'with all therapeutic proteins, there is a potential for immunogenicity'. Immunogenicity problems in humans, which currently can be detected only in clinical trials or after product launch, pose a significant barrier to the development and acceptance of protein drugs. Recent and ongoing research, presented in this review, seeks to address the challenge of protein therapeutic immunogenicity by elucidating the mechanisms underlying immune recognition of protein therapeutics, establishing preclinical methods for assessing immunogenicity and developing strategies for minimizing immune responses.

Essential roles of zinc ligation and enzyme dimerization for catalysis in the aminoacylase-1/M20 family

Members of the aminoacylase-1 (Acy1)/M20 family of aminoacylases and exopeptidases exist as either monomers or homodimers. They contain a zinc-binding domain and a second domain mediating dimerization in the latter case. The roles that both domains play in catalysis have been investigated for human Acy1 (hAcy1) by x-ray crystallography and by site-directed mutagenesis. Structure comparison of the dinuclear zinc center in a mutant of hAcy1 reported here with dizinc centers in related enzymes points to a difference in zinc ligation in the Acy1/M20 family. Mutational analysis supports catalytic roles of zinc ions, a vicinal glutamate, and a histidine from the dimerization domain. By complementing different active site mutants of hAcy1, we show that catalysis occurs at the dimer interface. Reinterpretation of the structure of a monomeric homolog, peptidase V, reveals that a domain insertion mimics dimerization. We conclude that monomeric and dimeric Acy1/M20 family members share a unique active site architecture involving both enzyme domains. The study may provide means to improve homologous carboxypeptidase G2 toward application in antibody-directed enzyme prodrug therapy.

Rapid discovery and identification of a tissue-specific tumor biomarker from 39 human cancer cell lines using the SELDI ProteinChip platform

Useful biomarkers are needed for early detection of cancers. To demonstrate the potential diagnostic usefulness of a new proteomic technology, we performed Expression Difference Mapping analysis on 39 cancer cell lines from 9 different tissues using ProteinChip technology. A protein biomarker candidate of 12kDa was found in colon cancer cells. We then optimized the purification conditions for this biomarker by utilizing Retentate Chromatography mass spectrometry (RC-MS). The optimized purification conditions developed "on-chip" were directly transferred to conventional chromatography to purify the biomarker, which was identified as prothymosin-alpha by ProteinChip time-of-flight mass spectrometry (TOF MS) and ProteinChip-Tandem MS systems. The relative expression level of prothymosin-alpha between colon cancer cells and normal colon mucosal cells was evaluated on the same ProteinChip platform. Prothymosin-alpha expression in colon cancer cells was clearly higher than in normal colon cells. These results indicate that prothymosin-alpha could be a potential biomarker for colon cancer, and that the ProteinChip platform could perform the whole process of biomarker discovery from screening to evaluation of the identified marker.

Proteomics in biomarker discovery and drug development

Proteomics is a research field aiming to characterize molecular and cellular dynamics in protein expression and function on a global level. The introduction of proteomics has been greatly broadening our view and accelerating our path in various medical researches. The most significant advantage of proteomics is its ability to examine a whole proteome or sub-proteome in a single experiment so that the protein alterations corresponding to a pathological or biochemical condition at a given time can be considered in an integrated way. Proteomic technology has been extensively used to tackle a wide variety of medical subjects including biomarker discovery and drug development. By complement with other new technique advances in genomics and bioinformatics, proteomics has a great potential to make considerable contribution to biomarker identification and to revolutionize drug development process. This article provides a brief overview of the proteomic technologies and their application in biomarker discovery and drug development.