A human recombinant autoantibody-based immunotoxin specific for the fetal acetylcholine receptor inhibits rhabdomyosarcoma growth in vitro and in a murine transplantation model

Targeted immunotherapy and nanomedicine for rhabdomyosarcoma: The way of the future

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. Histology separates two main subtypes: embryonal RMS (eRMS; 60%-70%) and alveolar RMS (aRMS; 20%-30%). The aggressive aRMS carry one of two characteristic chromosomal translocations that result in the expression of a PAX3::FOXO1 or PAX7::FOXO1 fusion transcription factor; therefore, aRMS are now classified as fusion-positive (FP) RMS. Embryonal RMS have a better prognosis and are clinically indistinguishable from fusion-negative (FN) RMS. Next to histology and molecular characteristics, RMS risk groupings are now available defining low risk tumors with excellent outcomes and advanced stage disease with poor prognosis, with an overall survival of about only 20% despite intensified multimodal treatment. Therefore, development of novel effective targeted strategies to increase survival and to decrease long-term side effects is urgently needed. Recently, immunotherapies and nanomedicine have been emerging for potent and effective tumor treatments with minimal side effects, raising hopes for effective and safe cures for RMS patients. This review aims to describe the most relevant preclinical and clinical studies in immunotherapy and targeted nanomedicine performed so far in RMS and to provide an insight in future developments.

Single-Chain Fragment Variable: Recent Progress in Cancer Diagnosis and Therapy

Simple Summary

Recombinant antibody fragments have shown remarkable potential as diagnostic and therapeutic tools in the fight against cancer. The single-chain fragment variable (scFv) that contains the complete antigen-binding domains of a whole antibody, has several advantages such as a high specificity and affinity for antigens, a low immunogenicity, and the proven ability to penetrate tumor tissues and diffuse. This review provides an overview of the current studies on the principle, generation, and applications of scFvs, particularly in the diagnosis and therapy of cancer, and underscores their potential use in clinical trials.

Abstract

Cancer remains a public health problem worldwide. Although conventional therapies have led to some excellent outcomes, some patients fail to respond to treatment, they have few therapeutic alternatives and a poor survival prognosis. Several strategies have been proposed to overcome this issue. The most recent approach is immunotherapy, particularly the use of recombinant antibodies and their derivatives, such as the single-chain fragment variable (scFv) containing the complete antigen-binding domains of a whole antibody that successfully targets tumor cells. This review describes the recent progress made with scFvs as a cancer diagnostic and therapeutic tool, with an emphasis on preclinical approaches and their potential use in clinical trials.

Construction and preliminary identification of a prokaryotic expression single-chain antibody fragments library against Streptococcus pneumoniae from antibody-producing cells in human tonsil

Tonsillitis is the inflammation of the tonsils due to infection, many patients ultimately have to undergo tonsillectomy. In order to improve the accuracy of diagnosis and even create a new treatment for tonsillitis, we constructed a prokaryotic expression single-chain antibody fragment library against Streptococcus pneumoniae with immunoglobulin heavy chain variable region (VH), κ light chain (Vκ), and λ light chain (Vλ) genes by using human tonsil tissue. Plasmid DNA sequencing showed that single-chain antibodies were complete and constructed correctly. The binding activity of recombinant clones was detected by enzyme-linked immunosorbent assay (ELISA), results showed that the binding activity and specificity of anti-S. pneumoniae single-chain fragment variable (scfv) is proved to be successful. The single-chain antibody may be an attractive strategy for tonsillitis etiologic diagnosis and therapy.

Characterization of an anti-fetal AChR monoclonal antibody isolated from a myasthenia gravis patient

We report here the sequence and functional characterization of a recombinantly expressed autoantibody (mAb 131) previously isolated from a myasthenia gravis patient by immortalization of thymic B cells using Epstein-Barr virus and TLR9 activation. The antibody is characterized by a high degree of somatic mutations as well as a 6 amino acid insertion within the VHCDR2. The recombinant mAb 131 is specific for the γ-subunit of the fetal AChR to which it bound with sub-nanomolar apparent affinity, and detected the presence of fetal AChR on a number of rhabdomyosarcoma cell lines. Mab 131 blocked one of the two α-bungarotoxin binding sites on the fetal AChR, and partially blocked the binding of an antibody (mAb 637) to the α-subunit of the AChR, suggesting that both antibodies bind at or near one ACh binding site at the α/γ subunit interface. However, mAb 131 did not reduce fetal AChR ion channel currents in electrophysiological experiments. These results indicate that mAb 131, although generated from an MG patient, is unlikely to be pathogenic and may make it a potentially useful reagent for studies of myasthenia gravis, rhabdomyosarcoma and arthrogryposis multiplex congenita which can be caused by fetal-specific AChR-blocking autoantibodies.

A novel fully-human cytolytic fusion protein based on granzyme B shows in vitro cytotoxicity and ex vivo binding to solid tumors overexpressing the epidermal growth factor receptor

Human cytolytic fusion proteins (hCFPs) offer a promising immunotherapeutic approach for the treatment of solid tumors, avoiding the immunogenicity and undesirable side-effects caused by immunotoxins derived from plants or bacteria. The well-characterized human serine protease granzyme B has already been used as a therapeutic pro-apoptotic effector domain. We therefore developed a novel recombinant hCFP (GbR201K-scFv1711) consisting of an epidermal growth factor receptor-specific human antibody fragment and a granzyme B point mutant (R201K) that is insensitive to serpin B9 (PI9), a natural inhibitor of wild-type granzyme B that is often expressed in solid tumors. We found that GbR201K-scFv1711 selectively bound to epidermoid cancer and rhabdomyosarcoma cells and was rapidly internalized by them. Nanomolar concentrations of GbR201K-scFv1711 achieved the specific killing of epidermoid cancer cells by inducing apoptosis, and similar effects were observed in rhabdomyosarcoma cells when GbR201K-scFv1711 was combined with the endosomolytic substance chloroquine. The novel hCFP was stable in serum and bound to human rhabdomyosarcoma tissue ex vivo. These data confirm that GbR201K-scFv1711 is a promising therapeutic candidate suitable for further clinical investigation.

Targeted killing of rhabdomyosarcoma cells by a MAP-based human cytolytic fusion protein

The treatment of rhabdomyosarcoma (RMS) is challenging, and the prognosis remains especially poor for high-grade RMS with metastasis. The conventional treatment of RMS is based on multi-agent chemotherapy combined with resection and radiotherapy, which are often marked by low success rate. Alternative therapeutic options include the combination of standard treatments with immunotherapy. We generated a microtubule-associated protein (MAP)-based fully human cytolytic fusion protein (hCFP) targeting the fetal acetylcholine receptor, which is expressed on RMS cells. We were able to express and purify functional scFv35-MAP from Escherichia coli cells. Moreover, we found that scFv35-MAP is rapidly internalized by target cells after binding its receptor, and exhibits specific cytotoxicity toward FL-OH1 and RD cells in vitro. We also confirmed that scFv35-MAP induces apoptosis in FL-OH1 and RD cells. The in vivo potential of scFv35-MAP will need to be considered in further studies.

In vitro effects and ex vivo binding of an EGFR-specific immunotoxin on rhabdomyosarcoma cells

PURPOSE

Rhabdomyosarcoma (RMS) is a rare and aggressive soft tissue sarcoma with limited treatment options and a high failure rate during standard therapy. New therapeutic strategies based on targeted immunotherapy are therefore much in demand. The epidermal growth factor receptor (EGFR) has all the characteristics of an ideal target. It is overexpressed in up to 80 % of embryonal RMS and up to 50 % of alveolar RMS tumors. We therefore tested the activity of the EGFR-specific recombinant immunotoxin (IT) 425(scFv)-ETA' against EGFR(+) RMS cells in vitro and ex vivo.

METHODS

We tested the specific binding and internalization behavior of 425(scFv)-ETA' in RMS cell lines in vitro by flow cytometry, compared to the corresponding imaging probe 425(scFv)-SNAP monitored by live cell imaging. The cytotoxic activity of 425(scFv)-ETA' was tested using cell viability and apoptosis assays. Specific binding of the IT was confirmed on formalin-fixed paraffin-embedded tissue samples from two RMS patients.

RESULTS

We confirmed the specific binding of 425(scFv)-ETA' to RMS cells in vitro and ex vivo. Both the IT and the corresponding imaging probe were rapidly internalized. The IT killed EGFR(+) RMS cells in a dose-dependent manner, while showing no effect against control cells. It showed specific apoptotic activity against one selected RMS cell line.

CONCLUSIONS

This is the first study showing the promising therapeutic potential of a recombinant, EGFR-targeting, ETA'-based IT on RMS cells. We confirmed the selective killing with IC50 values of up to 50 pM, and immunohistochemical staining confirmed the specific ex vivo binding to primary RMS material.

A CSPG4-specific immunotoxin kills rhabdomyosarcoma cells and binds to primary tumor tissues

The treatment of rhabdomyosarcoma (RMS) remains challenging, with metastatic and alveolar RMS offering a particularly poor prognosis. Therefore, the identification and evaluation of novel antigens, which are suitable targets for immunotherapy, is one attractive possibility to improve the treatment of this disease. Here we show that chondroitin sulfate proteoglycan 4 (CSPG4) is expressed on RMS cell lines and RMS patient material. We evaluated the immunotoxin (IT) αMCSP-ETA', which specifically recognizes CSPG4 on the RMS cell lines RD, FL-OH1, TE-671 and Rh30. It is internalized rapidly, induces apoptosis and thus kills RMS cells selectively. We also demonstrate the specific binding of this IT to RMS primary tumor material from three different patients.

Technical and ethical limitations in making human monoclonal antibodies (an overview)

In the broadest sense there are no longer any technical limitations to making human mAbs. Biological issues involving the type and nature of either a synthetic or a natural antibody, advantages of various B cell immunological compartments, and various assays needed to qualitate and quantitate mAbs have essentially been solved. If the target antigen is known then procedures to optimize antibody development can be readily planned out and implemented. When the antigen or target is unknown and specificity is the driving force in generating a human mAb then considerations about the nature and location of the B cell making the sought after antibody become important. And, therefore, the person the B cell is obtained from can be an ethical challenge and a limitation. For the sources of B cells special considerations must be taken to insure the anonymity and privacy of the patient. In many cases informed consent is adequate for antibody development as well as using discarded tissues. After the antibody has been generated then manufacturing technical issues become important that greatly depend upon the amounts of mAb required. For kilogram quantities then special considerations for manufacturing that include FDA guidelines will be necessary.

Survivin blockade sensitizes rhabdomyosarcoma cells for lysis by fetal acetylcholine receptor-redirected T cells

Cellular immunotherapy may provide a strategy to overcome the poor prognosis of metastatic and recurrent rhabdomyosarcoma (RMS) under the current regimen of polychemotherapy. Because little is known about resistance mechanisms of RMS to cytotoxic T cells, we investigated RMS cell lines and biopsy specimens for expression and function of immune costimulatory receptors and anti-apoptotic molecules by RT-PCR, Western blot analysis, IHC, and cytotoxicity assays using siRNA or transfection-modified RMS cell lines, together with engineered RMS-directed cytotoxic T cells specific for the fetal acetylcholine receptor. We found that costimulatory CD80 and CD86 were consistently absent from all RMSs tested, whereas inducible T-cell co-stimulator ligand (ICOS-L; alias B7H2) was expressed by a subset of RMSs and was inducible by tumor necrosis factor α in two of five RMS cell lines. Anti-apoptotic survivin, along with other inhibitor of apoptosis (IAP) family members (cIAP1, cIAP2, and X-linked inhibitor of apoptosis protein), was overexpressed by RMS cell lines and biopsy specimens. Down-regulation of survivin by siRNA or pharmacologically in RMS cells increased their susceptibility toward a T-cell attack, whereas induction of ICOS-L did not. Treatment of RMS-bearing Rag(-/-) mice with fetal acetylcholine receptor-specific chimeric T cells delayed xenograft growth; however, this happened without definitive tumor eradication. Combined blockade of survivin and application of chimeric T cells in vivo suppressed tumor proliferation during survivin inhibition. In conclusion, survivin blockade provides a strategy to sensitize RMS cells for T-cell-based therapy.

Targeting the fetal acetylcholine receptor in rhabdomyosarcoma

INTRODUCTION

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Recent efforts to enhance overall survival of patients with clinically advanced RMS have failed and there is a demand for conceptually novel treatments. Immune therapeutic options targeting the fetal nicotinic acetylcholine receptor (fnAChR), which is broadly expressed on RMS, are novel approaches to overcome the therapeutic resistance of RMS. Expression of the fnAChR is restricted to developing fetal muscles, some apparently dispensable ocular muscle fibers and thymic myoid cells. Therefore, after-birth fnAChR is a tumor-associated and almost tumor-specific antigen on RMS cells.

AREAS COVERED

This review gives an overview on nAChR function and expression pattern in RMS tumor cells, and deals with the immunological significance of fnAChR-expressing cells, including the risk of anti-nAChR autoimmunity as a potential side effect of fnAChR-directed immunotherapies. The article also addresses the advantages and disadvantages of vaccination strategies, immunotoxins and chimeric T cells targeting the fnAChR.

EXPERT OPINION

Finally, we suggest technical and biological strategies to improve the available immunotherapeutic tools including increasing the in vivo expression of the target fnAChR on RMS cells.

scFv antibody: principles and clinical application

To date, generation of single-chain fragment variable (scFv) has become an established technique used to produce a completely functional antigen-binding fragment in bacterial systems. The advances in antibody engineering have now facilitated a more efficient and generally applicable method to produce Fv fragments. Basically, scFv antibodies produced from phage display can be genetically fused to the marker proteins, such as fluorescent proteins or alkaline phosphatase. These bifunctional proteins having both antigen-binding capacity and marker activity can be obtained from transformed bacteria and used for one-step immunodetection of biological agents. Alternatively, antibody fragments could also be applied in the construction of immunotoxins, therapeutic gene delivery, and anticancer intrabodies for therapeutic purposes. This paper provides an overview of the current studies on the principle, generation, and application of scFv. The potential of scFv in breast cancer research is also discussed in this paper.

A human Fab-based immunoconjugate specific for the LMP1 extracellular domain inhibits nasopharyngeal carcinoma growth in vitro and in vivo

Nasopharyngeal carcinoma (NPC) is a major cause of cancer-related death in Southeast Asia and China. Metastasis and relapse are the primary cause of morbidity and mortality in NPC. Recent evidence suggests that the Epstein-Barr virus latent membrane protein 1 (LMP1) is exclusively expressed in most NPC and is a potential target for biotherapy. In this study, we successfully prepared a novel human antibody Fab (HLEAFab) against LMP1 extracellular domain, which was subsequently conjugated with mitomycin C (MMC), thus forming an immunoconjugate (HLEAFab-MMC). The effects of HLEAFab-MMC on proliferation and apoptosis in NPC cell lines HNE2/LMP1 and the inhibition rate of growth of NPC xenografts in nude mice were examined. The inhibition rate of HNE2/LMP1 cell proliferation was the highest for HLEAFab-MMC (76%) compared with MMC (31%) and HLEAFab (22%) at a concentration of 200 nmol/L and showed dose-dependent fashion. The apoptosis rate of HNE2/LMP1 cell lines was 13.88% in HLEAFab-MMC group, 3.04% in MMC group, 2.78% in HLEAFab group, and 2.10% in negative control group at the same concentration, respectively. In vivo, the inhibition rate of growth of NPC xenografts in nude mice was 55.1% in HLEAFab-MMC group, 26.5% in MMC group, and 5.64% in HLEAFab group. In summary, our findings show that HLEAFab-MMC is a unique immunoconjugate with the potential as a novel therapeutic agent in the treatment of LMP1-expressing NPC.

Advances in targeted therapeutic agents

IMPORTANCE OF THE FIELD

The number of disease-associated protein targets has significantly increased over the past decade due to advances in molecular and cellular biology technologies, human genetic mapping efforts and information gathered from the human genome project. The identification of gene products that appear to be involved in supporting the underlying cause of disease has offered the biopharmaceutical industry an opportunity to develop compounds that can specifically target these molecules to improve therapeutic responses and lower the risk of unwanted side effects that are commonly seen in traditional small chemical-based medicines.

AREAS COVERED IN THIS REVIEW

An overview of targeted drug therapies is presented in this review. We include a review of the various classes of targeted therapeutic agents, the types of disease-associated molecules being targeted by these agents and the challenges currently being encountered for the successful development of these various platforms for the treatment of disease.

WHAT THE READER WILL GAIN

An understanding of the current targeted therapy landscape, the discovery and selection of disease-specific gene products that are being targeted, and an overview of targeted therapies in preclinical and clinical studies. A description of the various targeted therapeutic platforms, target selection criteria and examples of each are discussed in order to provide the reader with the current status of the field and emerging areas of targeted therapy discovery and development.

TAKE HOME MESSAGE

Novel medications are in demand for the treatment of serious medical conditions including cancer, autoimmune, infectious and metabolic diseases. Targeted therapies offer a way to develop very specific treatments for serious medical conditions while concomitantly resulting in little to no off-target toxicity. Targeted therapies provide an opportunity to develop personalized medicines with superior treatment modalities for the patient and a better quality of life.