In vitro and in vivo cytotoxic activities of recombinant immunotoxin 8H9(Fv)-PE38 against breast cancer, osteosarcoma, and neuroblastoma

Advancing therapy for neuroblastoma

Neuroblastomas are tumours of sympathetic origin, with a heterogeneous clinical course ranging from localized or spontaneously regressing to widely metastatic disease. Neuroblastomas recapitulate many of the features of sympathoadrenal development, which have been directly targeted to improve the survival outcomes in patients with high-risk disease. Over the past few decades, improvements in the 5-year survival of patients with metastatic neuroblastomas, from <20% to >50%, have resulted from clinical trials incorporating high-dose chemotherapy with autologous stem cell transplantation, differentiating agents and immunotherapy with anti-GD2 monoclonal antibodies. The next generation of trials are designed to improve the initial response rates in patients with high-risk neuroblastomas via the addition of immunotherapies, targeted therapies (such as ALK inhibitors) and radiopharmaceuticals to standard induction regimens. Other trials are focused on testing precision medicine strategies for patients with relapsed and/or refractory disease, enhancing the antitumour immune response and improving the effectiveness of maintenance regimens, in order to prolong disease remission. In this Review, we describe advances in delineating the pathogenesis of neuroblastoma and in identifying the drivers of high-risk disease. We then discuss how this knowledge has informed improvements in risk stratification, risk-adapted therapy and the development of novel therapies.

Chimeric Antigen Receptor T-Cell Therapy: The Light of Day for Osteosarcoma

Simple Summary

As a novel immunotherapy, chimeric antigen receptor (CAR) T-cell therapy has achieved encouraging results in leukemia and lymphoma. Furthermore, CAR-T cells have been explored in the treatment of osteosarcoma (OS). However, there is no strong comprehensive evidence to support their efficacy. Therefore, we reviewed the current evidence on CAR-T cells for OS to demonstrate their feasibility and provide new options for the treatment of OS.

Abstract

Osteosarcoma (OS) is the most common malignant bone tumor, arising mainly in children and adolescents. With the introduction of multiagent chemotherapy, the treatments of OS have remarkably improved, but the prognosis for patients with metastases is still poor, with a five-year survival rate of 20%. In addition, adverse effects brought by traditional treatments, including radical surgery and systemic chemotherapy, may seriously affect the survival quality of patients. Therefore, new treatments for OS await exploitation. As a novel immunotherapy, chimeric antigen receptor (CAR) T-cell therapy has achieved encouraging results in treating cancer in recent years, especially in leukemia and lymphoma. Furthermore, researchers have recently focused on CAR-T therapy in solid tumors, including OS. In this review, we summarize the safety, specificity, and clinical transformation of the targets in treating OS and point out the direction for further research.

Antibody Conjugates for Sarcoma Therapy: How Far along Are We?

Sarcomas are one of the most difficult type of cancer to manage and treat because of their extremely heterogeneous molecular and morphological features. Despite the progress made over the years in the establishment of standard protocols for high and low grading/staging sarcoma patients, mostly with chemotherapy and/or radiotherapy, 50% of treated patients experience relapse episodes. Because of this, in the last 20 years, new therapeutic approaches for sarcoma treatment have been evaluated in preclinical and clinical studies. Among them, antibody-based therapies have been the most studied. Immunoconjugates consist of a carrier portion, frequently represented by an antibody, linked to a toxic moiety, i.e., a drug, toxin, or radionuclide. While the efficacy of immunoconjugates is well demonstrated in the therapy of hematological tumors and more recently also of epithelial ones, their potential as therapeutic agents against sarcomas is still not completely explored. In this paper, we summarize the results obtained with immunoconjugates targeting sarcoma surface antigens, considering both preclinical and clinical studies. To date, the encouraging results obtained in preclinical studies allowed nine immunoconjugates to enter clinical trials, demonstrating the validity of immunotherapy as a promising pharmacological tool also for sarcoma therapy.

Advancing therapy for osteosarcoma

Improving the survival of patients with osteosarcoma has long proved challenging, although the treatment of this disease is on the precipice of advancement. The increasing feasibility of molecular profiling together with the creation of both robust model systems and large, well-annotated tissue banks has led to an increased understanding of osteosarcoma biology. The historical invariability of survival outcomes and the limited number of agents known to be active in the treatment of this disease facilitate clinical trials designed to identify efficacious novel therapies using small cohorts of patients. In addition, trial designs will increasingly consider the genetic background of the tumour through biomarker-based patient selection, thereby enriching for clinical activity. Indeed, osteosarcoma cells are known to express a number of surface proteins that might be of therapeutic relevance, including B7-H3, GD2 and HER2, which can be targeted using antibody-drug conjugates and/or adoptive cell therapies. In addition, immune-checkpoint inhibition might augment the latter approach by helping to overcome the immunosuppressive tumour microenvironment. In this Review, we provide a brief overview of current osteosarcoma therapy before focusing on the biological insights from the molecular profiling and preclinical modelling studies that have opened new therapeutic opportunities in this disease.

Recent development and optimization of pseudomonas aeruginosa exotoxin immunotoxins in cancer therapeutic applications

Recombinant immunotoxins are fusion proteins composed of a peptide toxin and a specific targeting domain through genetic recombination. They are engineered to recognize disease-specific target receptors and kill the cell upon internalization. Full-sized monoclonal antibodies, smaller antibody fragments and ligands, such as a cytokine or a growth factor, have been commonly used as the targeting domain, while bacterial Pseudomonas aeruginosa exotoxin (PE) is the usual toxin fusion partner, due to its natural cytotoxicity and other unique advantages. PE-based recombinant immunotoxins have shown remarkable efficacy in the treatment of tumors and autoimmune diseases. At the same time, efforts are underway to address major challenges, including immunogenicity, nonspecific cytotoxicity and poor penetration, which limit their clinical applications. Recent strategies for structural optimization of PE-based immunotoxins, combined with mutagenesis approaches, have reduced the immunogenicity and non-specific cytotoxicity, thus increasing both their safety and efficacy. This review highlights novel insights and design concepts that were used to advance immunotoxins for the treatment of hematological and solid tumors and also presents future development prospect of PE-based recombinant immunotoxins that are expected to play an important role in cancer therapy.

Preclinical Development of MGC018, a Duocarmycin-based Antibody-drug Conjugate Targeting B7-H3 for Solid Cancer

B7-H3, also referred to as CD276, is a member of the B7 family of immune regulatory proteins. B7-H3 is overexpressed on many solid cancers, including prostate cancer, renal cell carcinoma, melanoma, squamous cell carcinoma of the head and neck, non-small cell lung cancer, and breast cancer. Overexpression of B7-H3 is associated with disease severity, risk of recurrence and reduced survival. In this article, we report the preclinical development of MGC018, an antibody-drug conjugate targeted against B7-H3. MGC018 is comprised of the cleavable linker-duocarmycin payload, valine-citrulline-seco duocarmycin hydroxybenzamide azaindole (vc-seco-DUBA), conjugated to an anti-B7-H3 humanized IgG1/kappa mAb through reduced interchain disulfides, with an average drug-to-antibody ratio of approximately 2.7. MGC018 exhibited cytotoxicity toward B7-H3-positive human tumor cell lines, and exhibited bystander killing of target-negative tumor cells when cocultured with B7-H3-positive tumor cells. MGC018 displayed potent antitumor activity in preclinical tumor models of breast, ovarian, and lung cancer, as well as melanoma. In addition, antitumor activity was observed toward patient-derived xenograft models of breast, prostate, and head and neck cancer displaying heterogeneous expression of B7-H3. Importantly, MGC018 exhibited a favorable pharmacokinetic and safety profile in cynomolgus monkeys following repeat-dose administration. The antitumor activity observed preclinically with MGC018, together with the positive safety profile, provides evidence of a potentially favorable therapeutic index and supports the continued development of MGC018 for the treatment of solid cancers. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/11/2235/F1.large.jpg.

Immune-Based Approaches for the Treatment of Pediatric Malignancies

Immune-based therapies have now been credentialed for pediatric cancers with the robust efficacy of chimeric antigen receptor (CAR) T cells for pediatric B cell acute lymphocytic leukemia (ALL), offering a chance of a cure for children with previously lethal disease and a potentially more targeted therapy to limit treatment-related morbidities. The developmental origins of most pediatric cancers make them ideal targets for immune-based therapies that capitalize on the differential expression of lineage-specific cell surface molecules such as antibodies, antibody-drug conjugates, or CAR T cells, while the efficacy of other therapies that depend on tumor immunogenicity such as immune checkpoint inhibitors has been limited to date. Here we review the current status of immune-based therapies for childhood cancers, discuss challenges to developing immunotherapeutics for these diseases, and outline future directions of pediatric immunotherapy discovery and development.

A new scfv-based recombinant immunotoxin against EPHA2-overexpressing breast cancer cells; High in vitro anti-cancer potency

Immunotoxin therapy is one of the immunotherapy strategies providing a new, effective and high potency treatment against various cancers. Breast cancer is the most common cancer among women in many countries. The EPH receptors are a large part of tyrosine kinase receptors family and play an effective role in tumor development and angiogenesis. Among EPH receptors, EPHA2 is more commonly well-known and widely expressed in many cancers like breast cancer. In this study, we evaluated the specification of a designed immunotoxin formed by EPHA2-specific scfv linked with PE38KDEL on EPHA2-overexpressing breast cancer cell line. This new scfv-based recombinant immunotoxin was studied in terms of features such as binding potency, cytotoxicity effects, apoptosis induction ability, and internalization. The flow cytometry results showed that the immunotoxin can significantly (approximately 99%) bind to EPHA2-overexpressing breast cancer cell line (MDA-MB-231) in a low concentration (2.5 ng/ul) while cannot significantly bind to the normal cell line (HEK-293) or even EPHA2-very low expressing cell line (MCF-7). Using the MTT assay and Annexin V/Propidium iodide (PI) double staining method by flow cytometry, we observed significant killing and apoptosis induction of the MDA-MB-231 cells at different concentrations. Immunotoxin tracking by confocal microscopy at 2 h and 6 h revealed a massive presence of immunotoxin in the cytoplasm. Finally, given the in vitro results, it seems that this immunotoxin is competent enough to serve as a good candidate for in vivo studies to further explore the possibility of breast cancer treatment.

Recombinant Immunotoxin Therapy of Glioblastoma: Smart Design, Key Findings, and Specific Challenges

Recombinant immunotoxins (RITs) refer to a group of recombinant protein-based therapeutics, which consists of two components: an antibody variable fragment or a specific ligand that allows RITs to bind specifically to target cells and an engineered toxin fragment that kills the target cells upon internalization. To date, over 1,000 RITs have been generated and significant success has been achieved in the therapy of hematological malignancies. However, the immunogenicity and off-target toxicities of RITs remain as significant barriers for their application to solid tumor therapy. A group of RITs have also been generated for the treatment of glioblastoma multiforme, and some have demonstrated evidence of tumor response and an acceptable profile of toxicity and safety in early clinical trials. Different from other solid tumors, how to efficiently deliver the RITs to intracranial tumors is more critical and needs to be solved urgently. In this article, we first review the design and expression of RITs, then summarize the key findings in the preclinical and clinical development of RIT therapy of glioblastoma multiforme, and lastly discuss the specific issues that still remain to forward RIT therapy to clinical practice.

Humanized Affinity-matured Monoclonal Antibody 8H9 Has Potent Antitumor Activity and Binds to FG Loop of Tumor Antigen B7-H3

B7-H3 (CD276) is both an inhibitory ligand for natural killer cells and T cells and a tumor antigen that is widely expressed among human solid tumors. Anti-B7-H3 mouse monoclonal antibody 8H9 has been successfully used for radioimmunotherapy for patients with B7-H3(+) tumors. We present the humanization, affinity maturation, and epitope mapping of 8H9 based on structure determination, modeling, and yeast display methods. The crystal structure of ch8H9 Fab fragment was solved to 2.5-Å resolution and used as a template for humanization. By displaying the humanized 8H9 single chain Fv (scFv) on the surface of yeast, the affinity was matured by sequential random mutagenesis and fluorescence-activated cell sorting. Six mutations (three in the complementarity-determining region and three in the framework regions) were identified and incorporated into an affinity-matured humanized 8H9 construct (hu8H9-6m) and an affinity-matured chimeric 8H9 construct (ch8H9-6m). The hu8H9-6m scFv had a 160-fold improvement in affinity (0.9 nm KD) compared with parental hu8H9 scFv (144 nm KD). The IgG formats of ch8H9-6m and hu8H9-6m (nanomolar to subnanomolar KD) had 2-9-fold enhancements in affinity compared with their parental forms, potent in vitro antibody-dependent cell-mediated cytotoxicity (0.1-0.3 μg/ml EC50), and high tumor uptake in mouse xenografts. Based on in silico docking studies and experimental validation, the molecular epitope of 8H9 was determined to be dependent on the FG loop of B7-H3, a region critical to its function in immunologic blockade and unique among anti-B7-H3 antibodies published to date.

Development of a novel treatment for leukemia directed at tumor-associated mRNA splicing

This report describes a novel approach to cancer therapy that targets genes that are preferentially alternatively spliced and expressed in leukemia. We developed CD44v6 and CD44v8 splicing constructs fused with GFP or a humanized fragment of Pseudomonas aeruginosa exotoxin A (hPE24). Transfection of K562 leukemia cells with the GFP-linked splicing constructs led to subsequent production of detectable levels of GFP. Transfection of K562 cells with the hPE24-linked splicing constructs led to significant reduction of cell viability and an increase in the induction of apoptosis. Normal human PBMCs were unaffected by following transfection with these constructs.

B7-H3, a potential therapeutic target, is expressed in diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is a brain cancer with a median survival of only 1 year. Lack of molecular characterization of this tumor impedes the development of novel therapies. Membrane protein B7-H3, aka CD276, involved in interactions with host defenses in certain cancers, has been shown to be over-expressed in the majority of malignant neuroectodermal tumors including adult high-grade glioma. Targeting B7-H3 with a monoclonal antibody has demonstrated safety and efficacy in the salvage treatment of stage IV childhood neuroblastoma, another neuroectodermal tumor. It thus stands to reason that B7-H3 might serve as a therapeutic target in DIPG. B7-H3 immunoreactivity was determined in DIPG and non-diffuse brainstem glioma specimens with immunohistochemistry. In addition, B7-H3 mRNA expression was evaluated with microarrays in another set of specimens. All of the nine (100 %) DIPG specimens were shown to be B7-H3 immunoreactive. In the non-diffuse brainstem glioma group, none of the eight WHO grade I specimens showed B7-H3 immunoreactivity and nine of the 24 WHO grade II specimens (37.5 %) showed B7-H3 immunoreactivity. The association between histological grade and B7-H3 immunoreactivity was statistically highly significant. B7-H3 mRNA expression was also significantly higher in DIPG samples than in normal brain and juvenile pilocytic astrocytoma (WHO grade I) specimens. In summary, B7-H3 is over-expressed in DIPG. Given the need for novel treatment in this disease, antibody-based immunotherapy against B7-H3 in DIPG warrants further investigation.

Specific killing of CCR9 high-expressing acute T lymphocytic leukemia cells by CCL25 fused with PE38 toxin

We have previously demonstrated that CCR9 plays a pivotal role in drug resistance and invasion in human acute T-lymphocytic leukemia (T-ALL). In this study, we investigated whether the MOLT4 cells, which naturally express CCR9 at high levels, can be successfully killed by the specific ligand, CCL25 fused to Pseudomonas exotoxin 38 (PE38) toxin. Our results demonstrated that CCL25-PE38 was able to specifically kill MOLT4 cells via apoptosis induction, and suppress the growth of CCR9(+) tumors. This work shows that CCR9 high-expressing human T-ALL cells can be successfully killed by delivering PE38 toxin fused to the ligand CCL25.

Preparation and Cytotoxicity Effect of Anti-Hepatocellular Carcinoma Scfv Immunoliposome on Hepatocarcinoma Cell in Vitro

The use of PE38 for cancer therapy has attracted considerable attention for a long time. However, the extensive use of PE38 is prohibited by its severe side effects. Even though immunotoxin PE38 has been researched for cancer therapy, it has displayed low antitumor activity. The aim of this study is to compare the killing efficacy on Hepatocellular carcinoma (HCC) SMMC-7721 cell of immunoliposome PE38, immunotoxin PE38 and liposome PE38. In this study, the sterically stabilized liposomal PE38 was prepared using soybean phosphatidylcholine, cholesterol, and Cholesterol-PEG-COOH. The humanized anti-hepatoma disulfide-stabilized Fv (hdsFv25) was coupled to sterically stabilized liposomes using the N-hydroxysuccinimide ester method. The immunoliposome PE38 was prepared in our lab using the above-mentioned single-chain antibody. The hdsFv25-immunoliposomes were immunoreactive as determined by ELISA assay. Immunoliposome PE38 can kill SMMC-7721 cells in vitro with higher efficiency than non-targeted liposomes. These results indicate that immunoliposome PE38 may be potential in the treatment of hepatocarcinoma.

Interstitial infusion of glioma-targeted recombinant immunotoxin 8H9scFv-PE38

Monoclonal antibodies have the potential to target therapy for high-grade gliomas. Monoclonal antibody 8H9 is specific for membrane protein B7H3 and is reactive with most human high-grade gliomas. We tested the 8H9scFv-PE38 recombinant Pseudomonas immunotoxin in a preclinical model of high-grade glioma. The half maximal inhibitory concentration (IC(50)) of 8H9scFv-PE38 in vitro was determined using glioblastoma cell lines U87 and U251. Maximum tolerated infusion dose of 8H9scFv-PE38 following interstitial infusion to the striatum and pons was defined using athymic rats. Maximum tolerated infusion dose of 8H9scFv-PE38 or PBS control were interstitially delivered to athymic rats xenografted with U87 in the striatum or brain stem. Radiographic response and survivals were measured and compared between treatment groups. The in vitro IC(50) of 8H9scFv-PE38 for U87 was 1,265 ng/mL and, for U251, 91 ng/mL. The maximum tolerated infusion doses of interstitially infused 8H9scFv-PE38 to the striatum and brain stem were 0.75 and 1.8 mug, respectively. For rats harboring intracranial U87 xenografts, infusion of 8H9scFv-PE38 increased mean survival (striatum, 43.4 versus 24.6 days; brain stem, 80.6 versus 45.5 days; n = 28 total) and produced three long-term survivors past 120 days. None of the 14 placebo-treated animals survived >54 days. Tumors also showed volumetric response to infusion of 8H9scFv-PE38 by magnetic resonance imaging. Interstitial infusion of 8H9scFv-PE38 shows potential for the treatment of hemispherical and brain stem glioma. Mol Cancer Ther; 9(4); 1039-46. (c)2010 AACR.

Whole neuraxis irradiation to address central nervous system relapse in high-risk neuroblastoma

BACKGROUND

As systemic control of high-risk neuroblastoma (NB) has improved, relapse in the central nervous system (CNS) is an increasingly recognized entity that carries a grim prognosis. This study describes the use of craniospinal irradiation (CSI) for CNS relapse and compares outcomes to patients who received focal radiotherapy (RT).

METHODS

A retrospective query identified 29 children with NB treated at Memorial Sloan-Kettering Cancer Center since 1987 who received RT for CNS relapse. At CNS relapse, 16 patients received CSI (median dose, 2160cGy), and 13 received focal RT. Of those who underwent CSI, 14 (88%) received intra-Ommaya (IO) radioimmunotherapy (RIT); one patient in the non-CSI cohort received IO-RIT.

RESULTS

Patient characteristics were similar between the groups. Time to CNS relapse was 20 and 17 months for the CSI and non-CSI cohorts, respectively. At a median follow-up of 28 months, 12 patients (75%) in the CSI group are alive without CNS disease, including two patients with isolated skeletal relapse. Another patient is alive without disease after a brain relapse was retreated with RT. Three patients died-one with no NB at autopsy, one of CNS disease, and one of systemic disease. The two patients who died of NB did not receive IO-RIT. All 13 patients in the non-CSI cohort died at a median of 8.8 months.

CONCLUSIONS

Low-dose CSI together with IO-RIT provides durable CNS remissions and improved survival compared with focal RT and conventional therapies. Further evaluation of long-term NB survivors after CSI is warranted to determine the treatment consequences for this cohort.

Affitoxin--a novel recombinant, HER2-specific, anticancer agent for targeted therapy of HER2-positive tumors

Expression of the human epidermal growth factor receptor 2 (HER2) is amplified in 25% to 30% of breast cancers and has been associated with an unfavorable prognosis. Here we report the construction, purification, and characterization of Affitoxin-a novel class of HER2-specific cytotoxic molecules combining HER2-specific Affibody molecule as a targeting moiety and PE38KDEL, which is a truncated version of Pseudomonas exotoxin A, as a cell killing agent. It is highly soluble and does not require additional refolding, oxidation, or reduction steps during its purification. Using surface plasmon resonance technology and competitive binding assays, we have shown that Affitoxin binds specifically to HER2 with nanomolar affinity. We have also observed a high correlation between HER2 expression and retention of Affitoxin bound to the cell surface. Affitoxin binding and internalization is followed by Pseudomonas exotoxin A activity domain-mediated ADP-ribosylation of translation elongation factor 2 and, consequently, inhibition of protein synthesis as shown by protein expression analysis of HER2-positive cells treated with Affitoxin. Measured IC50 value for HER2-negative cells MDA-MB468 (65+/-2.63 pM) was more than 20 times higher than the value for low HER2 level-expressing MCF7 cells (2.56+/-0.1 pM), and almost 3 orders of magnitude higher for its HER2-overexpressing derivative MCF7/HER2 (62.7+/-5.9 fM). These studies suggest that Affitoxin is an attractive PE38-based candidate for treatment of HER2-positive tumors.

Pseudomonas exotoxin A: from virulence factor to anti-cancer agent

The pathogenic bacterium Pseudomonas aeruginosa has the ability to cause severe acute and chronic infections in humans. Pseudomonas exotoxin A (PE) is the most toxic virulence factor of this bacterium. It has ADP-ribosylation activity and decisively affects the protein synthesis of the host cells. The cytotoxic pathways of PE have been elucidated, and it could be shown that PE uses several molecular strategies developed under evolutionary pressure for effective killing. Interestingly, a medical benefit from this molecule has also been ascertained in recent years and several PE-based immunotoxins have been constructed and tested in preclinical and clinical trials against different cancers. In these molecules, the enzymatic active domain of PE is specifically targeted to tumor-related antigens. This review describes the current knowledge about the cytotoxic pathways of PE. Additionally, it summarizes preclinical and clinical trials of PE-based immunotoxins and furthermore discusses current problems and answers with these agents.

Chimeric receptor mRNA transfection as a tool to generate antineoplastic lymphocytes

mRNA transfection is a useful approach for temporal cell reprogramming with minimal risk of transgene-mediated mutagenesis. We applied this to redirect lymphocyte cytotoxicity toward malignant cells. Using the chimeric immune receptor (CIR) constructs anti-CD19 CIR and 8H9 CIR, we achieved uniform expression of CIRs on virtually the entire population of lymphocytes. We reprogrammed CD3+ CD8+, CD3+ CD4+, and natural killer (NK ) cells toward autologous and allogeneic targets such as B cells, Daudi lymphoma, primary melanoma, breast ductal carcinoma, breast adenocarcinoma, and rhabdomyosarcoma. The reprogramming procedure is fast. Although most of the experiments were performed on lymphocytes obtained after 7-day activation, only 1-day activation of T cells with anti-CD3, anti-CD28 antibodies, and interleukin-2 is sufficient to develop both lymphocyte cytotoxicity and competence for mRNA transfer. The entire procedure, which includes lymphocyte activation and reprogramming, can be completed in 2 days. The efficiency of mRNA-modified human T cells was tested in a murine xenograft model. Human CD3+CD8+ lymphocytes expressing anti-CD19 CIR mRNA inhibited Daudi lymphoma growth in NOD=SCID mice. These results demonstrate that a mixed population of cytotoxic lymphocytes, including T cells together with NK cells, can be quickly and simultaneously reprogrammed by mRNA against autologous malignancies. With relatively minor modifications the described method of lymphocyte reprogramming can be scaled up for cancer therapy.

WT1 expression distinguishes astrocytic tumor cells from normal and reactive astrocytes

Particularly in small brain biopsies, it might be difficult to distinguish reactive astrogliosis from low-grade or infiltration zones of high-grade astrocytomas. So far no immunohistochemical marker allows a reliable distinction. Recently, the over-expression of Wilms' tumor gene product WT1 was reported in astrocytic tumor cells. However, no sufficient data on WT1 expression in normal or reactive astrocytes are available. Therefore, we investigated WT1 expression in paraffin-embedded brain sections from 28 controls, 48 cases with astrogliosis of various etiology and 219 astrocytomas [World Health Organization (WHO) grades I-IV] by immunohistochemistry. In normal brains and in astrogliosis, expression of WT1 was restricted to endothelial cells. In astrocytomas, WT1-positive tumor cells were found in pilocytic astrocytomas (66.7% of cases), diffuse astrocytomas (52.7%) WHO grade II (52.7%), anaplastic astrocytomas (83.4%) and glioblastomas (98.1%). Overall, the majority of all astrocytic neoplasms (84.5%) expressed WT1. Establishing a cut-off value of 0% immunoreactive tumor cells served to recognize neoplastic astrocytes with 100% specificity and 68% sensitivity and was associated with positive and negative predictive values of 1 and 0.68, respectively. Therefore, WT1 expression in astrocytes indicates a neoplastic origin and might represent an important diagnostic tool to differentiate reactive from neoplastic astrocytes by immunohistochemistry.

Anti-PSMA immunotoxin as novel treatment for prostate cancer? High and specific antitumor activity on human prostate xenograft tumors in SCID mice

BACKGROUND

Expression of the prostate specific membrane antigen (PSMA) is highly restricted to prostate epithelial cells. Therefore, toxin-based immunotherapy against this antigen may represent an alternative therapeutic option for prostate cancer. For these purposes, the effects of the recombinant anti-PSMA immunotoxin A5-PE40 on prostate tumor growth were investigated in vitro and in vivo.

METHODS

The in vitro binding and cytotoxicity of A5-PE40 were tested on the PSMA-expressing prostate cancer cell line C4-2 and on the PSMA-negative cell line DU145 by flow cytometry and WST assays. The binding of the immunotoxin to SCID mouse xenografts and to various mouse organs was examined by Western blot analysis. In vivo, the antitumor activity of the immunotoxin was tested by injecting A5-PE40 in mice bearing C4-2 or DU145 xenografts.

RESULTS

In vitro, a specific binding of A5-PE40 to C4-2 cells could be shown with a concentration-dependent cytotoxicity (IC(50) value=220 pM). In the next step, a specific binding of the immunotoxin to C4-2 xenografts could be demonstrated. In contrast, no binding on mouse organs expressing high homologous mouse PSMA was found. The treatment of mice with C4-2 tumors caused a significant inhibition of tumor growth in vivo, whereas DU145 xenografts remained totally unaffected.

CONCLUSIONS

A5-PE40 represents a recombinant anti-PSMA immunotoxin with potent antitumor activity in mice bearing human prostate cancer xenograft tumors. Therefore, A5-PE40 could be a promising candidate for therapeutic applications in patients with prostate cancer.

CCR4-expressing T cell tumors can be specifically controlled via delivery of toxins to chemokine receptors

Expression of chemokine receptors by tumors, specifically CCR4 on cutaneous T cell lymphomas, is often associated with a poor disease outcome. To test the hypothesis that chemokine receptor-expressing tumors can be successfully controlled by delivering toxins through their chemokine receptors, we have generated fusion proteins designated chemotoxins: chemokines fused with toxic moieties that are nontoxic unless delivered into the cell cytosol. We demonstrate that chemokines fused with human RNase eosinophil-derived neurotoxin or with a truncated fragment of Pseudomonas exotoxin 38 are able to specifically kill tumors in vitro upon internalization through their respective chemokine receptors. Moreover, treatment with the thymus and activation-regulated chemokine (CCL17)-expressing chemotoxin efficiently eradicated CCR4-expressing cutaneous T cell lymphoma/leukemia established in NOD-SCID mice. Taken together, this work represents a novel concept that may allow control of growth and dissemination of tumors that use chemokine receptors to metastasize and circumvent immunosurveillance.

EGFRvIII-targeted immunotoxin induces antitumor immunity that is inhibited in the absence of CD4+ and CD8+ T cells

PURPOSE

Immunotoxins as anti-cancer therapeutics have several potential advantages over conventional agents including a high specificity, extraordinary potency, and a lack of an identified mechanism for resistance. It has been clearly demonstrated that Pseudomonas-based immunotoxins have a direct cytotoxic effect. However, delayed and often dramatic antitumor responses seen in human studies with targeted toxins led us to hypothesize that immunologic responses may be a secondary mechanism that enhances the therapeutic efficacy of these novel drugs.

EXPERIMENTAL DESIGN

This hypothesis was tested in a murine system using an immunotoxin, MR1-1 [MR1-1(dsFv)-PE38KDEL], that targets a syngeneic murine homologue of the tumor-specific human epidermal growth factor mutation, EGFRvIII, expressed on a murine cell line.

RESULTS

Intratumoral treatment with MR1-1 eliminated EGFRvIII-expressing tumors (P < 0.0001). The antitumor activity of MR1-1 was dependent on the expression of EGFRvIII on some, but not all tumors cells, and was significantly inhibited in the absence of CD4+ (P = 0.0193) and CD8+ (P = 0.0193) T cells. MR1-1 induced EGFRvIII-specific immunity (P < 0.0005) and produced long lasting immunity against tumors expressing EGFRvIII as well as EGFRvIII-negative tumors.

CONCLUSIONS

These data suggest that immunotoxins may not be strictly dependent on direct cytotoxicity for their efficacy, but may also be potent inducers of antitumor immunity active even against cells that do not express the targeted antigen.

Human peripheral blood T regulatory cells (Tregs), functionally primed CCR4+ Tregs and unprimed CCR4- Tregs, regulate effector T cells using FasL

Regulatory CD25(+)CD4(+) T cells (Tregs) play an important role in the control of peripheral tolerance. In this study we demonstrate that human peripheral blood Tregs can be divided into two distinct populations based on the expression of CCR4. The majority ( approximately 75%) of freshly isolated Tregs express CCR4 and presumably represent memory-type Tregs. Interestingly, CCR4(-) Tregs require anti-CD3 Ab-mediated activation to acquire a regulatory activity, while CCR4(+) Tregs appear to be already primed to suppress the proliferation of CD8(+) T cells. CCR4 is also expressed on CD25(low)CD4(+) T cells (CCR4(+) non-Tregs) that mostly suppress Th1-type polarization without affecting T cell proliferation, presumably via the production of immunomodulatory cytokines like IL-10. In contrast, CCR4(+) Tregs express FasL to primarily regulate T cell proliferation via a contact-mediated process involving FasL/Fas signaling, a major regulatory pathway of T cell homeostasis. Finally, we also demonstrate that the depletion of CCR4(+) T cells leads to Th1-type polarization of CD4(+) T cells and augmentation of CD8(+) T cell responses to tumor Ags.

A cleavable molecular adapter reduces side effects and concomitantly enhances efficacy in tumor treatment by targeted toxins in mice

Two of the main problems associated with administration of receptor-targeted toxins in tumor therapy are severe systemic side effects and low transfer of the toxins into the cytosol after binding to the tumor cell surface. To improve chimeric toxins in this respect we have developed a molecular adapter that links the toxic moiety and ligand. The adapter is designed to improve cytosolic uptake, retain the toxin inside the cytosol and detoxify the drug after cell death. The plant toxin saporin linked either directly or via the adapter to epidermal growth factor (EGF) served to evaluate efficacy to inhibit tumor growth and reduce side effects in vivo. The lethal dose for BALB/c mice was three times less for the adapter-containing toxin (SA2E) than for the adapter-free construct (SE). Furthermore, SE only reduced the average weight of induced tumors by 33% whereas SA2E-treated mice exhibited 71% reduction with an almost complete suppression in 60% of the cases. Additionally, severe side effects like hyperalgesia, alopecia and death were drastically reduced in SA2E-treated animals. Tumors without target receptor were only slightly affected by SA2E and the reduction in side effects less pronounced indicating specific depletion from the blood by target receptor expressing cells.

Immunotoxins: a review of their use in cancer treatment

Abstract

Antibody therapies have become an important component in the management of malignant disease. Antibodies can block tumour growth factors or their receptors, activate immunological attack on the tumour, and are used to deliver payloads such as radioisotopes, cytotoxic drugs or toxins. Immunotoxins are a new class of antitumour agents consisting of tumour- selective ligands (generally monoclonal antibodies [MoAbs]) linked to highly toxic protein molecules and take the advantage of the exquisite specificity of antibodies to selectively target drug delivery and the potency of toxins to kill the target cells. Toxins are modified to remove their normal tissue-binding domains by genetic engineering. Analysis of the aminoacid sequence of the region specific for immunogenecity and the signal transduction mechanisms involved in the interaction of immunotoxins with tumour cells will give the clue for the development of most efficient immunotoxins.

In vitro and in vivo efficacy of a recombinant immunotoxin against folate receptor beta on the activation and proliferation of rheumatoid arthritis synovial cells

OBJECTIVE

To investigate the effects of the recombinant immunotoxin dsFv anti-FRbeta-PE38, which consists of the disulfide-stabilized Fv fragment (dsFv) of the anti-folate receptor beta (anti-FRbeta) antibody and the 38-kd portion of Pseudomonas exotoxin A (PE38), on the activation and proliferation of cells that function in inflammatory and degradative processes in rheumatoid arthritis (RA) synovial tissue.

METHODS

The Ig VH-PE38 fusion protein and the Ig VL protein were produced in Escherichia coli, and then joined with a disulfide bond by engineering cysteine residues in the framework regions of these proteins. The effects of dsFv anti-FRbeta-PE38 on the activation and proliferation of cells in RA synovial tissue were investigated by immunohistochemistry; the numbers of cells expressing CD68, vascular cell adhesion molecule 1, angiopoietin 1, CD34, proliferating cell nuclear antigen, and interleukin-6 and the numbers of apoptotic cells were counted in RA synovial tissue engrafted into SCID mice treated or not treated with dsFv anti-FRbeta-PE38. The effects of dsFv anti-FRbeta-PE38 on the generation of osteoclasts from RA adherent synovial mononuclear cells in vitro was investigated by counting the number of resorption pits on dentin slices treated or not treated with dsFv anti-FRbeta-PE38.

RESULTS

Administration of dsFv anti-FRbeta-PE38 reduced the numbers of macrophages, activated fibroblast-like cells, endothelial cells, and proliferating cells and increased the numbers of apoptotic cells in RA synovial tissue engrafted into SCID mice. In vitro, the generation of osteoclasts from RA adherent synovial mononuclear cells was largely suppressed by treatment with dsFv anti-FRbeta-PE38.

CONCLUSION

Our findings show that dsFv anti-FRbeta-PE38 immunotoxin would be a promising tool for the treatment of RA synovitis, especially when administered intraarticularly.

Immunotoxins for targeted cancer therapy

Immunotoxins are proteins that contain a toxin along with an antibody or growth factor that binds specifically to target cells. Nearly all protein toxins work by enzymatically inhibiting protein synthesis. For the immunotoxin to work, it must bind to and be internalized by the target cells, and the enzymatic fragment of the toxin must translocate to the cytosol. Once in the cytosol, 1 molecule is capable of killing a cell, making immunotoxins some of the most potent killing agents. Various plant and bacterial toxins have been genetically fused or chemically conjugated to ligands that bind to cancer cells. Among the most active clinically are those that bind to hematologic tumors. At present, only 1 agent, which contains human interleukin-2 and truncated diphtheria toxin, is approved for use in cutaneous T-cell lymphoma. Another, containing an anti-CD22 Fv and truncated Pseudomonas exotoxin, has induced complete remissions in a high proportion of cases of hairy-cell leukemia. Refinement of existing immunotoxins and development of new immunotoxins are underway to improve the treatment of cancer.

Adenovirus-mediated p53 tumor suppressor gene therapy of osteosarcoma

The clinical outcome for osteosarcoma (OS) remains discouraging despite efforts to optimize treatment using conventional modalities including surgery, radiotherapy and chemotherapy. Novel therapeutic approaches based on our expanding understanding of the mechanisms of tumor cell killing have the potential to alter this situation. Tumor suppressor gene therapy aims to restore the function of a tumor suppressor gene lost or functionally inactivated in cancer cells. One such molecule, the p53 tumor suppressor gene plays a critical role in safeguarding the integrity of the genome and preventing tumorigenesis. Introduction of wild-type (wt) p53 into transformed cells has been shown to be lethal for most cancer cells in vitro, but clinical trials of p53 gene replacement have had limited success. Analysis of these clinical trials highlighted the insufficient efficacy of current vectors and low proapoptotic activity of wt p53 as a single agent in vivo. In this review, a contemporary summarization of the current status of adenovirus-mediated p53 gene therapy of OS is presented. Advancement in our understanding of p53 tumor suppressor activity, the molecular biology of chemoresistant OS, and recent advances in tumor targeting with adenoviral vectors are also addressed. Based on these parameters, prospects for future investigations are proposed.

Radioimmunotargeting of human rhabdomyosarcoma using monoclonal antibody 8H9

Although metastatic rhabdomyosarcoma (RMS) is chemotherapy and radiotherapy responsive, few patients are cured. 8H9, a murine IgG(1) monoclonal antibody, recognizes a unique cell surface tumor antigen broadly distributed on neuroectodermal, epithelial, and mesenchymal tumors, including RMS. We now report on the in vitro characterization of radiolabeled 8H9 and its in vivo immunotargeting potential in mice with subcutaneous human RMS. Saturation-binding studies carried out to determine (125)I-8H9 affinity to the RMS cell line HTB82 demonstrated that (125)I-8H9 had a K(d) of 10.3nM with an estimated 115,000 binding sites on every HTB82 cell. (125)I-8H9 was retained on the cell surface without significant internalization. Biodistribution of (125)I-8H9 was studied in athymic mice bearing HTB82 xenografts. Following intravenous injection of 4.44MBq of (125)I-8H9, selective tumor uptake was evident 4 to 172 hours after injection. Average tumor uptake was 7.0 +/- 1.8, 11.5 +/- 3.9, 15.1 +/- 3.7, and 5.4 +/- 1.2% injected dose per gram at 4, 24, 48, and 172 hours, respectively. Mean tumor: tissue ratios were maximal at 172 hours (for lung, 4, kidney, 6, liver, 7, spleen, 11, femur, 14, muscle, 18, and brain, 48). Established RMS xenografts treated with a single injection of 18.5 MBq (131)I-8H9 were significantly suppressed compared to controls. Radiolabeled 8H9 effectively targeted RMS xenografts and may have a potential clinical role in radioimmunotherapy.

Rhabdomyosarcoma lysis by T cells expressing a human autoantibody-based chimeric receptor targeting the fetal acetylcholine receptor

Rhabdomyosarcomas are the most frequent malignant soft tissue tumors of childhood; however, because current multimodality treatments fail to improve the poor survival rate of children with metastatic rhabdomyosarcoma, new treatments are required. We previously identified the gamma-subunit of the fetal acetylcholine receptor (fAChR) as a specific cell surface target in rhabdomyosarcoma. Here, we engineered human T lymphocytes to express chimeric receptors composed of the antigen-binding domain of a human anti-fAChR antibody joined to the signaling domain of the human T-cell receptor zeta-chain. The interaction of fAChRzeta-transduced T cells with fAChR-positive rhabdomyosarcoma cell lines, but not with fAChR-negative control cells, induced T-cell activation characterized by strong secretion of IFN-gamma and delayed lysis of tumor cells. Importantly, we found that in six of six rhabdomyosarcoma patients, chemotherapy increased fAChR expression on residual tumor cells in vivo. Our observations suggest that these fully human chimeric fAChRzeta-transduced T cells, which should be well tolerated by the patient, have potential use in vivo both as a primary treatment for rhabdomyosarcoma and as a complementary approach to eradicate residual tumor cells after chemotherapy.

Recent advances in tumor-targeting anticancer drug conjugates

Traditional cancer chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be a killed by cytotoxic agent. In reality, however, cytotoxic agents have very little or no specificity, which leads to systemic toxicity, causing severe undesirable side effects. Therefore, various drug delivery protocols and systems have been explored in the last three decades. Tumor cells overexpress many receptors and biomarkers, which can be used as targets to deliver cytotoxic agents into tumors. In general, a tumor-targeting drug delivery system consists of a tumor recognition moiety and a cytotoxic warhead connected directly or through a suitable linker to form a conjugate. The conjugate, which can be regarded as 'prodrug', should be systemically non-toxic. This means that the linker must be stable in circulation. Upon internalization into the cancer cell the conjugate should be readily cleaved to regenerate the active cytotoxic agent. Tumor-targeting conjugates bearing cytotoxic agents can be classified into several groups based on the type of cancer recognition moieties. This review describes recent advances in tumor-targeting drug conjugates including monoclonal antibodies, polyunsaturated fatty acids, folic acid, hyaluronic acid, and oligopeptides as tumor-targeting moieties.

Antibody–cytotoxic agent conjugates for cancer therapy

Antibody-based delivery of cytotoxic agents, including toxins, to tumours can dramatically reduce systemic toxicity and increase therapeutic efficacy. The advantage of a monoclonal antibody (mAb) is superior selectivity towards antigens expressed on the surface of cancer cells. Recent advances in biotechnology accelerated progress in the pharmaceutical applications of mAbs. A cytotoxic warhead is attached to a mAb in an immunoconjugate via a linker, which is stable in circulation but efficiently cleaved in the tumour tissue. The warhead, mAb and linker play important roles in the successful design of potent and efficient immunoconjugates. To date, one mAb-cytotoxic agent conjugate has been approved by the FDA and several other candidates are in various stages of clinical trials. This review describes the recent progress in the design and development of mAb-based immunoconjugates of cytotoxic agents, and summarises the criteria for the critical choices of a suitable mAb, linker and cytotoxic agent to design an efficacious immunoconjugate.

Effectiveness of anti-folate receptor beta antibody conjugated with truncated Pseudomonas exotoxin in the targeting of rheumatoid arthritis synovial macrophages

OBJECTIVE

To define the distribution of folate receptor beta (FRbeta)-expressing cells in various tissues, including rheumatoid arthritis (RA) synovial tissues, and to verify the effects of an immunotoxin composed of an anti-FRbeta monoclonal antibody (mAb) and truncated Pseudomonas exotoxin A (PEA) on apoptosis and tumor necrosis factor alpha (TNFalpha) production by adherent synovial mononuclear cells from RA patients.

METHODS

Anti-FRbeta mAb were produced by immunizing mice with FRbeta-transfected murine pre-B cells. The distribution of the FRbeta antigen was examined by immunohistochemical analysis using anti-FRbeta mAb and macrophage-specific anti-CD163 mAb. Anti-FRbeta mAb was chemically crosslinked with truncated PEA. FRbeta-expressing macrophages were produced by the transfection of adenovirus vector containing the FRbeta gene. Apoptotic cells were detected by staining with propidium iodide. TNFalpha was measured by enzyme-linked immunosorbent assay.

RESULTS

FRbeta-expressing cells were not present in peripheral blood leukocytes and their activated cells. In all of the tissues examined, most FRbeta-expressing cells were CD163+. The immunotoxin significantly induced the apoptosis of FRbeta-transfected macrophages and adherent RA synovial mononuclear cells and inhibited TNFalpha production by adherent RA synovial mononuclear cells.

CONCLUSION

We demonstrated the limited distribution of FRbeta-expressing cells in various tissues. The immunotoxin targeting FRbeta-expressing cells will provide a therapeutic tool for rheumatoid synovitis.

Isolation and characterization of a scFv antibody specific for tumor endothelial marker 1 (TEM1), a new reagent for targeted tumor therapy

Tumor endothelial marker 1 (TEM1) is a protein predominantly expressed on the cell surface of endothelial cells in newly developing blood vessels and on tumor cells. It is therefore ideally suited as a target for anti-angiogenic tumor therapy. Using phage display technology a single chain antibody fragment (scFv-CM6) was isolated that specifically binds to the extracellular part of TEM1. Antibody specificity was determined in ELISA, by Western analysis, fluorescence microscopy and flow cytometry performed with TEM1-expressing cells. ScFv-CM6 was further functionalized and coupled to liposomes. Such immunoliposomes loaded with the cytotoxic drug N4-octadecyl-1-beta-D-arabinofuranosylcytosine-(5'-5')-3'-C-ethinylcytidine showed increased binding affinity and up to 80% higher cytotoxic activity towards TEM1-expressing IMR-32 tumor cells compared with control liposomes.

Monoclonal antibodies for brain tumour treatment

Conventional treatment of brain tumours includes surgical, radiotherapeutic and chemotherapeutic modalities. Nonetheless, the outcome of patients with brain tumours, in particular glioblastoma, remains poor. Immunotherapy with armed or unarmed monoclonal antibodies targeting tumour-specific antigens has emerged in the last two decades as a novel potential adjuvant treatment for all types of neoplasia. Many challenges to its implementation as a safe and viable therapy for brain tumours still need to be addressed; nevertheless, results from ongoing Phase I/II clinical trials are encouraging, as disease stabilisation and patient survival prolongation have been observed. Advances in preclinical and clinical research indicate that treatment of brain tumours with monoclonal antibodies can be increasingly adjusted to the characteristics of the targeted tumour and its environment. This aspect relies on the careful selection of the target antigen and corresponding specific monoclonal antibody, and antibody format (size, class, affinity), conjugation to the appropriate toxin or radioactive isotope (half-life, range), and proper compartmental administration.

TP-3 immunotoxins improve antitumor activity in mice with osteosarcoma

We measured the antitumor activity of two types of TP-3 immunotoxins that target an antigen expressed in tumors associated with osteosarcoma. Development of novel agents for treatment of patients with osteosarcoma is important. We previously described a monovalent-disulfide-stabilized recombinant immunotoxin made from the TP-3 antibody. This agent is called TP-3(dsFv)-PE38 and is cytotoxic to human osteosarcoma cells in vitro. To improve antigen binding, we designed and produced a bivalent immunotoxin, TP-3(dsFv)2-PE38. We evaluated the activity of both molecules in vitro and in vivo using tumor-bearing mice. Compared with the monovalent TP-3 immunotoxin, the bivalent TP-3 immunotoxin showed an approximately sevenfold increase in cytotoxic activity against three osteosarcoma cell lines which react with the TP-3 monoclonal antibody. The apparent affinity of the bivalent TP-3 immunotoxin was 12-fold greater than that of the monovalent TP-3 immunotoxin. The antitumor activities of both TP-3 immunotoxins were measured using severe combined immunodeficient mice bearing osteosarcoma cell line OHS-M1 tumors. The dose at which the bivalent TP-3 immunotoxin produces complete regressions of tumors is (1/2) that of the monovalent TP-3 immunotoxin. Increasing the avidity of TP-3(dsFv)-PE38 significantly improves its cytotoxic activity in vitro and results in a twofold increase in antitumor activity in vivo. Because TP-3-based immunotoxins have good antitumor activity in mice, these molecules merit additional development for possible treatment of osteosarcoma in humans.

Transfected Cell Microarrays for the Expression of Membrane-Displayed Single-Chain Antibodies

The expression of recombinant antibody fragments on the surface of mammalian cells has recently emerged as a therapeutic strategy, particularly in the treatment of a number of cancers. Screening technologies that allow for the facile characterization of fragments expressed on the cell surface would hasten the identification and isolation of reagents to be used as therapeutics. In this report, we describe a cellular microarray-based platform for the comparative functional analysis of single-chain antibodies (scFvs) expressed on the plasma membrane of mammalian cells. Using the anti-fluorescein monoclonal antibody 4-4-20 as a model system, the native binding site and three mutants were expressed as scFvs on the membrane of HEK 293T/17 cells in a microarray format. Collectively, the equilibrium dissociation constants of the soluble forms of the wild-type scFv and the three mutants spanned nearly 3 orders of magnitude. Expression of the scFvs on the surface of mammalian cells was achieved by the deposition of plasmid DNAs in micrometer-sized spots onto the surface of a glass microscope slide. The addition of cells to the printed array resulted in the expression of the scFvs in clusters of cells in spatially discrete locations. Ligand binding assays performed with a fluorescein-bovine serum albumin conjugate demonstrated the ability of the transfected cell microarray to differentiate the relative binding affinities of the expressed scFvs. Further, the apparent affinities of the membrane-displayed scFvs were within 10-fold of those reported for the soluble forms of the scFvs. The assays described herein demonstrate the potential for cellular microarrays to be used for the high-throughput screening of potential therapeutic reagents. More generally, our work details the utility of transfected cell microarrays in mediating the functional characterization of expressed membrane receptor proteins.