Recombinant immunotoxins for the treatment of chemoresistant hematologic malignancies

Molecular and functional insight into anti-EGFR nanobody: Theranostic implications for malignancies

Targeted therapy and imaging are the most popular techniques for the intervention and diagnosis of cancer. A potential therapeutic target for the treatment of cancer is the epidermal growth factor receptor (EGFR), primarily for glioblastoma, lung, and breast cancer. Over-production of ligand, transcriptional up-regulation due to autocrine/paracrine signalling, or point mutations at the genomic locus may contribute to the malfunction of EGFR in malignancies. This exploit makes use of EGFR, an established biomarker for cancer diagnostics and treatment. Despite considerable development in the last several decades in making EGFR inhibitors, they are still not free from limitations like toxicity and a short serum half-life. Nanobodies and antibodies share similar binding properties, but nanobodies have the additional advantage that they can bind to antigenic epitopes deep inside the target that conventional antibodies are unable to access. For targeted therapy, anti-EGFR nanobodies can be conjugated to various molecules such as drugs, peptides, toxins and photosensitizers. These nanobodies can be designed as novel immunoconjugates using the universal modular antibody-based platform technology (UniCAR). Furthermore, Anti-EGFR nanobodies can be expressed in neural stem cells and visualised by effective fluorescent and radioisotope labelling.

Targeted Delivery of Endosomal Escape Peptides to Enhance Immunotoxin Potency and Anti-cancer Efficacy

This work describes use of anti-carcinoembryonic antigen antibodies (10H6, T84.66) for targeted delivery of an endosomal escape peptide (H6CM18) and gelonin, a type I ribosome inactivating protein. The viability of colorectal cancer cells (LS174T, LoVo) was assessed following treatment with gelonin or gelonin immunotoxins, with or without co-treatment with T84.66-H6CM18. Fluorescent microscopy was used to visualize the escape of immunoconjugates from endosomes of treated cells, and efficacy and toxicity were assessed in vivo in xenograft tumor-bearing mice following single- and multiple-dose regimens. Application of 25 pM T84.66-H6CM18 combined with T84.66-gelonin increased gelonin potency by ~ 1,000-fold and by ~ 6,000-fold in LS174T and LoVo cells. Intravenous 10H6-gelonin at 1.0 mg/kg was well tolerated by LS174T tumor-bearing mice, while 10 and 25 mg/kg doses led to signs of toxicity. Single-dose administration of PBS, gelonin conjugated to T84.66 or 10H6, T84.66-H6CM18, or gelonin immunotoxins co-administered with T84.66-H6CM18 were evaluated. The combinations of T84.66-gelonin + 1.0 mg/kg T84.66-H6CM18 and 10H6-gelonin + 0.1 mg/kg T84.66-H6CM18 led to significant delays in LS174T growth. Use of a multiple-dose regimen allowed further anti-tumor effects, significantly extending median survival time by 33% and by 69%, for mice receiving 1 mg/kg 10H6-gelonin + 0.1 mg/kg T84.66-H6CM18 (p = 0.0072) and 1 mg/kg 10H6-gelonin + 1 mg/kg T84.66-H6CM18 (p = 0.0017). Combined administration of gelonin immunoconjugates with antibody-targeted endosomal escape peptides increased the delivery of gelonin to the cytoplasm of targeted cells, increased gelonin cell killing in vitro by 1,000-6,000 fold, and significantly increased in vivo efficacy.

Bacterial-based cancer therapy: An emerging toolbox for targeted drug/gene delivery

Precise targeting and high therapeutic efficiency are the major requisites of personalized cancer treatment. However, some unique features of the tumor microenvironment (TME) such as hypoxia, low pH and elevated interstitial fluid pressure cause cancer cells resistant to most therapies. Bacteria are increasingly being considered for targeted tumor therapy owing to their intrinsic tumor tropism, high motility as well as the ability to rapidly colonize in the favorable TME. Compared to other nano-strategies using peptides, aptamers, and other biomolecules, tumor-targeting bacteria are largely unaffected by the tumor cells and microenvironment. On the contrary, the hypoxic TME is highly conducive to the growth of facultative anaerobes and obligate anaerobes. Live bacteria can be further integrated with anti-cancer drugs and nanomaterials to increase the latter's targeted delivery and accumulation in the tumors. Furthermore, anaerobic and facultatively anaerobic bacteria have also been combined with other anti-cancer therapies to enhance therapeutic effects. In this review, we have summarized the applications and advantages of using bacteria for targeted tumor therapy (Scheme 1) in order to aid in the design of novel intelligent drug delivery systems. The current challenges and future prospects of tumor-targeting bacterial nanocarriers have also been discussed.

Tumor-Specific T-Cells Engineered to Overcome Tumor Immune Evasion Induce Clinical Responses in Patients With Relapsed Hodgkin Lymphoma

Purpose Transforming growth factor-β (TGF-β) production in the tumor microenvironment is a potent and ubiquitous tumor immune evasion mechanism that inhibits the expansion and function of tumor-directed responses; therefore, we conducted a clinical study to discover the effects of the forced expression of a dominant-negative TGF-β receptor type 2 (DNRII) on the safety, survival, and activity of infused tumor-directed T cells. Materials and Methods In a dose escalation study, eight patients with Epstein Barr virus-positive Hodgkin lymphoma received two to 12 doses of between 2 × 107 and 1.5 × 108 cells/m2 of DNRII-expressing T cells with specificity for the Epstein Barr virus-derived tumor antigens, latent membrane protein (LMP)-1 and LMP-2 (DNRII-LSTs). Lymphodepleting chemotherapy was not used before infusion. Results DNRII-LSTs were resistant to otherwise inhibitory concentrations of TGF-β in vitro and retained their tumor antigen-specific activity. After infusion, the signal from transgenic T cells in peripheral blood increased up to 100-fold as measured by quantitative polymerase chain reaction for the transgene, with a corresponding increase in the frequency of functional LMP-specific T cells. Expansion was not associated with any acute or long-term toxicity. DNRII-LSTs persisted for up to ≥ 4 years. Four of the seven evaluable patients with active disease achieved clinical responses that were complete and ongoing in two patients at > 4 years, including in one patient who achieved only a partial response to unmodified tumor-directed T cells. Conclusion TGF-β-resistant tumor-specific T cells safely expand and persist in patients with Hodgkin lymphoma without lymphodepleting chemotherapy before infusion. DNRII-LSTs can induce complete responses even in patients with resistant disease. Expression of DNRII may be useful for the many other tumors that exploit this potent immune evasion mechanism.

Tolerogenic nanoparticles restore the antitumor activity of recombinant immunotoxins by mitigating immunogenicity

Protein-based drugs are very active in treating cancer, but their efficacy can be limited by the formation of neutralizing antidrug antibodies (ADAs). Recombinant immunotoxins are proteins that are very effective in patients with leukemia, where immunity is suppressed, but induce ADAs, which compromise their activity, in patients with intact immunity. Here we induced a specific, durable, and transferable immune tolerance to recombinant immunotoxins by combining them with nanoparticles containing rapamycin (SVP-R). SVP-R mitigated the formation of inhibitory ADAs in naïve and sensitized mice, resulting in restoration of antitumor activity. The immune tolerance is mediated by colocalization of the SVP-R and immunotoxin to dendritic cells and macrophages in the spleen and is abrogated by depletion of regulatory T cells. Tolerance induced by SVPs was not blocked by checkpoint inhibitors or costimulatory agonist monoclonal antibodies that by themselves enhance ADA formation.

Development of a Deimmunized Bispecific Immunotoxin dDT2219 against B-Cell Malignancies

Diphtheria toxin (DT) related targeted toxins are effective in cancer treatment, but efficacy diminishes in time because of their immunogenic potential and/or former vaccinations. In order to overcome this limitation for DT2219, a promising bispecific targeted toxin which targets CD19 and CD22, we deimmunized the DT moiety, and thereby developed an exciting improved drug (dDT2219) which still has the potential to sufficiently target B-cell malignancies but also limits clearance because of its reduced immunogenicity. The DT moiety was modified by inducing point mutations in prominent positions on the molecular surface. The new engineered dDT2219 was tested for activity, efficacy, and specificity using functional assays, proliferation assays, and flow cytometry. Furthermore, 12 samples of Chronic Lymphatic Leukemia (CLL) patients were used to assess binding. Immunogenicity was determined using a BALB/c mouse model. dDT2219 was efficient and specific against B-cell malignancies such as Bukitt-Lymphoma cell lines Daudi and Raji. dDT2219 showed specific binding on targets and on CLL samples. Intraperitoneal vaccination of immune competent mice showed that even after multiple administrations with increasing doses, induction of neutralizing antibodies was significantly lower in the dDT2219 treated animal group. The new dDT2219 combines potent anti-tumor cell activity with a reduced immunogenicity. With regard to the frequent development of neutralizing antibodies after multiple administrations with immunotoxins, dDT2219 shows promise to overcome this limitation and thus might maintain effectiveness even after multiple treatment cycles.

Rational design of low immunogenic anti CD25 recombinant immunotoxin for T cell malignancies by elimination of T cell epitopes in PE38

LMB-2, is a potent recombinant immunotoxin (RIT) that is composed of scFv antibody that targets CD25 (Tac) and a toxin fragment (PE38). It is used to treat T cell leukemias and lymphomas. To make LMB-2 less immunogenic, we introduced a large deletion in domain II and six point mutations in domain III that were previously shown to reduce T cell activation in other RITs. We found that unlike other RITs, deletion of domain II from LMB-2 severely compromised its activity. Rather than deletion, we identified T cell epitopes in domain II and used alanine substitutions to identify point mutations that diminished those epitopes. The novel RIT, LMB-142 contains a 38kDa toxin and nine point mutations that diminished T cell response to the corresponding peptides by an average of 75%. LMB-142 has good cytotoxic activity and has lower nonspecific toxicity in mice. LMB-142 should be more efficient in cancer therapy because more treatment cycles can be given.

Epidermal growth factor receptor is overexpressed in neuroblastoma tissues and cells

Neuroblastoma is the most common abdominal malignant tumor in childhood. Immunotoxin (IT) that targets the tumor cell surface receptor is a new supplementary therapeutic treatment approach. The purpose of this study is to detect the expression of epidermal growth factor receptor (EGFR) in neuroblastoma cell lines and tissues, and to explore if IT therapy can be used to treat refractory neuroblastoma. The EGFR expression in human neuroblastoma tissue samples was detected by immunohistochemistry staining. The positive rate of EGFR expression was 81.0% in neuroblastoma tissue and 50.0% in gangliocytoma, respectively, but without statistical significance between them (P > 0.05). The positive rate of EGFR expression in favorable type and unfavorable type was 62.5% and 92.3%, respectively, but they were not statistically different (P > 0.05). Results from pre-chemotherapy and post-chemotherapy samples showed that there was no significant statistical difference (P > 0.05) between them in the EGFR expression. Furthermore, the EGFR expression levels in five neuroblastoma cell lines were measured using cell-based ELISA assay and western blot analysis. The results showed that the expression of EGFR was higher in KP-N-NS and BE(2)-C than those in other cell lines. Our results revealed that there are consistent and widespread expressions of EGFR in neuroblastoma tissues as well as in neuroblastoma cell lines, suggesting that it is possible to develop future treatment strategies of neuroblastoma by targeting at the EGFR.

Immunogenicity of therapeutic recombinant immunotoxins

Recombinant immunotoxins (RITs) are chimeric proteins designed to treat cancer. They are made up of an Fv or Fab that targets an antigen on a cancer cell fused to a 38-kDa portion of Pseudomonas exotoxin A (PE38). Because PE38 is a bacterial protein, it is highly immunogenic in patients with solid tumors that have normal immune systems, but much less immunogenic in patients with hematologic malignancies where the immune system is suppressed. RITs have shown efficacy in refractory hairy cell leukemia and in some children with acute lymphoblastic leukemia, but have been much less effective in solid tumors, because neutralizing antibodies develop and prevent additional treatment cycles. In this paper we will (i) review data from clinical trials describing the immunogenicity of PE38 in different patient populations; (ii) review results from clinical trials using different immunosuppressive drugs; and (iii) describe our efforts to make new less-immunogenic RITs by identifying and removing T- and B-cell epitopes to hide the RIT from the immune system.

Mutagenic Deimmunization of Diphtheria Toxin for Use in Biologic Drug Development

BACKGROUND

Targeted toxins require multiple treatments and therefore must be deimmunized. We report a method of protein deimmunization based on the point mutation of highly hydrophilic R, K, D, E, and Q amino acids on the molecular surface of truncated diphtheria-toxin (DT390).

METHODS

Based on their surface position derived from an X-ray-crystallographic model, residues were chosen for point mutation that were located in prominent positions on the molecular surface and away from the catalytic site. Mice were immunized with a targeted toxin containing either a mutated DT390 containing seven critical point mutations or the non-mutated parental toxin form.

RESULTS

Serum analysis revealed a significant 90% reduction in anti-toxin antibodies in mice immunized with the mutant, but not the parental drug form despite multiple immunizations. The experiment was repeated in a second strain of mice with a different MHC-haplotype to address whether point mutation removed T or B cell epitopes. Findings were identical indicating that B cell epitopes were eliminated from DT. The mutant drug form lost only minimal activity in vitro as well as in vivo.

CONCLUSION

These findings indicate that this method may be effective for deimmunizing of other proteins and that discovery of a deimmunized form of DT may lead to the development of more effective targeted toxin.

Pseudomonas aeruginosa exotoxin T induces potent cytotoxicity against a variety of murine and human cancer cell lines

In patients with malignancy, the major barrier to achieving complete response is emergence of resistance to current chemotherapeutic agents. One of the major mechanisms by which tumour cells become resistant to therapies is by altering cellular drug targets through mutations and/or deletions. Resistance by this mechanism is achieved more easily if the drug has limited cellular targets and/or processes. We hypothesized that as Pseudomonas aeruginosa exotoxin T (ExoT) targets six proteins that are required for cancer cell survival and proliferation, it is highly unlikely for cancer cells to develop resistance to this toxin. We assessed ExoT's cytotoxicity against multiple invasive and highly resistant tumour cell lines in order to evaluate its potential as a chemotherapeutic agent. Our data demonstrated that ExoT induced potent cytotoxicity in all tumour cell lines that we examined. Collectively, our data highlighted the potential of ExoT as a possible chemotherapeutic candidate for the treatment of cancer.

Development and scale-up of a commercial fed batch refolding process for an anti-CD22 two chain immunotoxin

We describe the development and scale-up of a novel two chain immunotoxin refolding process. This work provides a case study comparing a clinical manufacturing process and the commercial process developed to replace it. While the clinical process produced high quality material, it suffered from low yield and high yield variability. A systematic approach to process development and understanding led to a number of improvements that were implemented in the commercial process. These include a shorter inclusion body recovery process, limiting the formation of an undesired deamidated species and the implementation of fed batch dilution refolding for increased refold titers. The use of a combination of urea, arginine and DTT for capture column cleaning restored the binding capacity of the capture step column and resulted in consistent capture step yields compared to the clinical process. Scalability is shown with data from 250 L and 950 L scale refolding processes. Compared to the clinical process it replaces, the commercial process demonstrated a greater than fivefold improvement in volumetric productivity at the 950 L refolding scale. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1380–1389, 2014

Cytotoxicity of purified listeriolysin O on mouse and human leukocytes and leukaemia cells

Background

Listeriolysin O (LLO) is the main virulence factor of Listeria monocytogenes and facilitates the intracellular survival of the pathogen. Some of its characteristics endorse the growing popularity of LLO for use in biotechnology, particularly in the development of novel vaccines. Here, we evaluate the use of LLO to eradicate leukaemia cells.

Results

A purified LLO preparation was obtained by affinity chromatography. The LLO preparation procedure was optimized and purified LLO was tested for optimal conditions of storage including temperature, application of proteinase inhibitors and serum components. We demonstrated the possibility of regulating LLO activity by adjusting cell membrane cholesterol content. The LLO preparation had haemolytic activity and had a cytotoxic effect on the human T-leukaemia Jurkat cell line as well as mouse and human peripheral blood mononuclear cells.

Conclusions

LLO has a very potent cytotoxic activity towards human leukocytes. Importantly, the cytotoxic activity was easily regulated in vitro and could be restricted to areas containing malignant cells, raising the possibility of future clinical application of LLO for leukaemia treatment.

Hairy cell leukemia-new genes, new targets

Hairy cell leukemia (HCL), a B cell malignancy comprising 2 % of all leukemias, has become quite exciting recently with regard to the development of new targets for therapy. This review will focus on advancements made within the past 1-2 years in targeted therapy for this disease. These advances may be grouped into two very difference categories, namely targeting of CD22 with the recombinant immunotoxin moxetumomab pasudotox, and targeting of the mutated BRAF component of the MAP kinase pathway. Moxetumomab pasudotox in phase I testing was recently reported to be associated with an overall response rate of 86 % and a complete remission (CR) rate of 46 % in 28 patients with relapsed and refractory HCL. Many of the CRs are without minimal residual disease (MRD). Severe or dose limiting toxicity was not observed on this trial, but a completely reversible and largely asymptomatic form of grade 2 hemolytic uremic syndrome occurred in two patients during retreatment. This agent has commenced phase III multicenter testing to validate its phase I results. An extensive number of studies have documented the V600E mutation in nearly all HCL patients, but not in similar hematologic malignancies. The thymidine kinase inhibitor vemurafenib, which inhibits the V600E mutant of BRAF, was reported to induce a CR in multiply relapsed and refractory HCL, with nearly complete clearing of MRD. One additional partial and one additional complete remission were subsequently reported.

Lipid requirements for entry of protein toxins into cells

The plant toxin ricin and the bacterial toxin Shiga toxin both belong to a group of protein toxins having one moiety that binds to the cell surface, and another, enzymatically active moiety, that enters the cytosol and inhibits protein synthesis by inactivating ribosomes. Both toxins travel all the way from the cell surface to endosomes, the Golgi apparatus and the ER before the ribosome-inactivating moiety enters the cytosol. Shiga toxin binds to the neutral glycosphingolipid Gb3 at the cell surface and is therefore dependent on this lipid for transport into the cells, whereas ricin binds both glycoproteins and glycolipids with terminal galactose. The different steps of transport used by these toxins have specific requirements for lipid species, and with the recent developments in mass spectrometry analysis of lipids and microscopical and biochemical dissection of transport in cells, we are starting to see the complexity of endocytosis and intracellular transport. In this article we describe lipid requirements and the consequences of lipid changes for the entry and intoxication with ricin and Shiga toxin. These toxins can be a threat to human health, but can also be exploited for diagnosis and therapy, and have proven valuable as tools to study intracellular transport.

Targeting CD133 in an in vivo ovarian cancer model reduces ovarian cancer progression

OBJECTIVES

While most women with ovarian cancer will achieve complete remission after treatment, the majority will relapse within two years, highlighting the need for novel therapies. Cancer stem cells (CSC) have been identified in ovarian cancer and most other carcinomas as a small population of cells that can self-renew. CSC are more chemoresistant and radio-resistant than the bulk tumor cells; it is likely that CSC are responsible for relapse, the major problem in cancer treatment. CD133 has emerged as one of the most promising markers for CSC in ovarian cancer. The hypothesis driving this study is that despite their low numbers in ovarian cancer tumors, CSC can be eradicated using CD133 targeted therapy and tumor growth can be inhibited.

METHODS

Ovarian cancer cell lines were evaluated using flow cytometry for expression of CD133. In vitro viability studies with an anti-CD133 targeted toxin were performed on one of the cell lines, NIH:OVCAR5. The drug was tested in vivo using a stably transfected luciferase-expressing NIH:OVCAR5 subline in nude mice, so that tumor growth could be monitored by digital imaging in real time.

RESULTS

Ovarian cancer cell lines showed 5.6% to 16.0% CD133 expression. dCD133KDEL inhibited the in vitro growth of NIH:OVCAR5 cells. Despite low numbers of CD133-expressing cells in the tumor population, intraperitoneal drug therapy caused a selective decrease in tumor progression in intraperitoneal NIH:OVCAR5-luc tumors.

CONCLUSIONS

Directly targeting CSC that are a major cause of drug resistant tumor relapse with an anti-CD133 targeted toxin shows promise for ovarian cancer therapy.

Immunoconjugates and new molecular targets in hairy cell leukemia

Hairy cell leukemia (HCL) is a B-cell malignancy that in its classic form is exquisitely sensitive to single-agent purine analog therapy, but that is associated in many patients with late relapse and eventual purine analog resistance. Minimal residual disease, which is present in most patients achieving complete remission with purine analogs, retains Ags that are ideal for targeted therapy. Rituximab, which targets CD20, is active as a single agent, particularly if combined with purine analogs. Recombinant immunotoxins targeting either CD25 or CD22 and containing truncated Pseudomonas exotoxin have achieved major responses in relapsed/refractory HCL. Moxetumomab pasudotox in phase 1 testing achieved responses in 86% of such patients (complete in 46%) without dose limiting toxicity and often without MRD. Soluble CD22 has been used for improved detection and monitoring of HCL, particularly the poor-prognosis variant that lacks CD25. Ig rearrangements unique for each HCL patient have been cloned, sequenced, and followed by real-time quantitative PCR using sequence-specific reagents. Analysis of these rearrangements has identified an unmutated IGVH4-34–expressing poor-prognosis variant with immunophenotypic characteristics of either classic or variant HCL. The BRAF V600E mutation, reported in 50% of melanomas, is present in > 85% of HCL cases that are both classic and express rearrangements other than IGVH4-34, making HCL a potential target for specific inhibitors of BRAF V600E. Additional targets are being defined in both classic and variant HCL, which should improve both detection and therapy.

Risks and untoward toxicities of antibody-based immunoconjugates

Antibody-based immunoconjugates are specifically targeted monoclonal antibodies that deliver a cytotoxic payload to their target. The cytotoxic agents can be highly potent drugs, radionuclides or toxins. Such molecules, referred to as antibody-drug conjugates, radioimmunoconjugates and immunotoxins, respectively, represent a promising approach for enhancing the efficacy of unconjugated (naked) antibodies for improved therapeutic results. Though tremendous progress has been achieved over the last few decades, the safety of these molecules still remains a matter of concern and a careful design is required for achieving a relatively safe toxicity profile along with therapeutic effectiveness. This review focuses on the toxicities arising from the use of these potent agents.

Process scale separation of an anti-CD22 immunotoxin charge variant

We describe the analytical characterization and process scale separation of a deamidated variant of an immunotoxin. The different charge variants of the immunotoxin were separated using analytical ion-exchange HPLC. These charge variants were analyzed by peptide mapping and LC-MS/MS to identify the site of modification, which was determined to reside in the toxin portion of the molecule. Using a cell-based bioassay it was also determined that deamidation led to reduced biological activity, requiring it be controlled during manufacturing. This was accomplished using process scale anion-exchange chromatography. The process was capable of reducing the deamidated form to a level low enough for the resulting product to maintain acceptable biological activity. Keys to the successful control of this impurity at process scale were a good understanding of structure-function relationship and the availability of an analytical HPLC assay to provide a surrogate for the cell-based bioassay.

Macrophage-targeted therapy: CD64-based immunotoxins for treatment of chronic inflammatory diseases

Diseases caused by chronic inflammation (e.g., arthritis, multiple sclerosis and diabetic ulcers) are multicausal, thus making treatment difficult and inefficient. Due to the age-associated nature of most of these disorders and the demographic transition towards an overall older population, efficient therapeutic intervention strategies will need to be developed in the near future. Over the past decades, elimination of activated macrophages using CD64-targeting immunotoxins has proven to be a promising way of resolving inflammation in animal models. More recent data have shown that the M1-polarized population of activated macrophages in particular is critically involved in the chronic phase. We recapitulate the latest progress in the development of IT. These have advanced from full-length antibodies, chemically coupled to bacterial toxins, into single chain variants of antibodies, genetically fused with fully human enzymes. These improvements have increased the range of possible target diseases, which now include chronic inflammatory diseases. At present there are no therapeutic strategies focusing on macrophages to treat chronic disorders. In this review, we focus on the role of different polarized macrophages and the potential of CD64-based IT to intervene in the process of chronic inflammation.

Purification of clinical-grade disulfide stabilized antibody fragment variable--Pseudomonas exotoxin conjugate (dsFv-PE38) expressed in Escherichia coli

Immunotoxins are rationally designed cancer targeting and killing agents. Disulfide stabilized antibody Fv portion-toxin conjugates (dsFv-toxin) are third generation immunotoxins containing only the antibody fragment variable portions and a toxin fused to the V(H) or V(L). Pseudomonas exotoxin fragment (PE-38) is a commonly used toxin in immunotoxin clinical trials. dsFv-toxin purification was previously published, but the recovery was not satisfactory. This report describes the development of a cGMP production process of the dsFv-toxin that incorporated a novel purification method. The method has been successfully applied to the clinical manufacturing of two dsFv-PE38 immunotoxins, MR1-1 targeting EGFRvIII and HA22 targeting CD22. The two subunits, V(L) and V(H) PE-38 were expressed separately in Escherichia coli using recombinant technology. Following cell lysis, inclusion bodies were isolated from the biomass harvested from fermentation in animal source component-free media. The dsFv-toxin was formed after denaturation and refolding, and subsequently purified to homogeneity through ammonium sulfate precipitation, hydrophobic interaction and ion-exchange chromatography steps. It was shown, in a direct comparison experiment using MR1-1 as model protein, that the recovery from the new purification method was improved three times over that from previously published method. The improved recovery was also demonstrated during the clinical production of two dsFv-PE38 immunotoxins-MR1-1 and HA22.

In vitro and in vivo antitumor effects of the recombinant immunotoxin IL6(T23)-PE38KDEL in multiple myeloma

IL6(T23)-PE38KDEL is a chimeric molecule composed of interleukin 6 (IL6), missing the N-terminal 23 amino acids, and fused to a truncated mutant form of Pseudomonas exotoxin (PE38KDEL). The aim of this study was to evaluate this recombinant immunotoxin in terms of its specific cytotoxicity to IL6R-overexpressing multiple myeloma (MM) cells in vitro, as well as its antitumor effects and side effects in vivo. IL6(T23)-PE38KDEL was expressed in Escherichia coli, refolded and purified from inclusion bodies. The purified IL6(T23)-PE38KDEL was found to be selectively cytotoxic to IL6 receptor-positive tumor cells in vitro. IC(50) values of IL6(T23)-PE38KDEL were evaluated by MTS assay. Toxicity and maximum-tolerated dose of IL6(T23)-PE38KDEL were determined in mice. The antitumor activity of IL6(T23)-PE38KDEL was evaluated in mice with MM through intravenous injection and interventional therapy. Intravenous administration of IL6(T23)-PE38KDEL caused a significantly increased survival time in treated mice, and exhibited dose- and time-dependent antitumor effects against MM mice. Moreover, complete tumor regression was observed in 30 and 80% of mice treated intravenously and intraperitoneally, respectively, with 0.4 mg/kg/day for 10 days. These results demonstrated that the recombinant immunotoxin IL6(T23)-PE38KDEL kills IL6R-overexpressing cancer cells, and causes significant tumor regression.

Cell-targeting fusion constructs containing recombinant gelonin

Therapeutic agents capable of targeting tumor cells present as established tumors and micrometastases have already demonstrated their potential in clinical trials. Immunotoxins targeting hematological malignancies and solid tumors have additionally demonstrated excellent clinical activity. This review focuses on our design and characterization studies of constructs composed of recombinant gelonin toxin fused to either growth factors or single-chain antibodies targeting solid tumor cells, tumor vasculature or hematological malignancies. These agents demonstrate cytotoxicity at nanomolar or sub-nanomolar levels. All of these constructs display impressive selectivity and specificity for antigen-bearing target cells in vitro and in vivo and are excellent clinical trial candidates.

Immunoconjugates and new molecular targets in hairy cell leukemia

Hairy cell leukemia (HCL) is a B-cell malignancy that in its classic form is exquisitely sensitive to single-agent purine analog therapy, but that is associated in many patients with late relapse and eventual purine analog resistance. Minimal residual disease, which is present in most patients achieving complete remission with purine analogs, retains Ags that are ideal for targeted therapy. Rituximab, which targets CD20, is active as a single agent, particularly if combined with purine analogs. Recombinant immunotoxins targeting either CD25 or CD22 and containing truncated Pseudomonas exotoxin have achieved major responses in relapsed/refractory HCL. Moxetumomab pasudotox in phase 1 testing achieved responses in 86% of such patients (complete in 46%) without dose limiting toxicity and often without MRD. Soluble CD22 has been used for improved detection and monitoring of HCL, particularly the poor-prognosis variant that lacks CD25. Ig rearrangements unique for each HCL patient have been cloned, sequenced, and followed by real-time quantitative PCR using sequence-specific reagents. Analysis of these rearrangements has identified an unmutated IGVH4-34-expressing poor-prognosis variant with immunophenotypic characteristics of either classic or variant HCL. The BRAF V600E mutation, reported in 50% of melanomas, is present in > 85% of HCL cases that are both classic and express rearrangements other than IGVH4-34, making HCL a potential target for specific inhibitors of BRAF V600E. Additional targets are being defined in both classic and variant HCL, which should improve both detection and therapy.

A guide to taming a toxin--recombinant immunotoxins constructed from Pseudomonas exotoxin A for the treatment of cancer

Pseudomonas exotoxin A (PE) is a highly toxic protein secreted by the opportunistic pathogen Pseudomonas aeruginosa. The modular structure and corresponding mechanism of action of PE make it amenable to extensive modifications that can redirect its potent cytotoxicity from disease to a therapeutic function. In combination with a variety of artificial targeting elements, such as receptor ligands and antibody fragments, PE becomes a selective agent for the elimination of specific cell populations. This review summarizes our current understanding of PE, its intoxication pathway, and the ongoing efforts to convert this toxin into a treatment for cancer.

Phase I studies of AVE9633, an anti-CD33 antibody-maytansinoid conjugate, in adult patients with relapsed/refractory acute myeloid leukemia

The efficacy of anti-CD33 immunoconjugates had been previously demonstrated for gemtuzumab-ozogamicin. AVE9633 is an anti-CD33-maytansine conjugate created by ImmunoGen Inc. Phase I trials of AVE9633 were performed in patients with AML to evaluate tolerability, pharmacokinetics and pharmacodynamics. Three phase I studies of AVE9633 were performed in 54 patients with refractory/relapsed AML, evaluating drug infusion on day 1 of a 21-day cycle (Day 1 study), day 1 and 8 (Day 1/8 study) and day 1, 4 and 7 (Day 1/4/7 study) of a 28-day cycle. Toxicity was mainly allergic reaction during infusion (3 grade 3 bronchospasms). DLT was reached for the D1-D7 schedule at 150 mg/sqm (1 keratitis, 1 liver toxicity), and the MTD was set at 130 mg/sqm for this schedule. In the two other phases I, the DLT was not reached. In the Day 1/8 study, CD33 on peripheral blasts was saturated and down-modulated for doses of 75 mg/m(2) × 2 or higher, which was correlated with WBC kinetics and plasma levels of AVE9633. Decrease of DM4/CD33 ratio on the blasts surface between day 1 and 8 was the rational for evaluating day 1/4/7 schedule. This induced relatively constant DM4/CD33 levels over the first 8 days, however no activity was noted. One CRp, one PR and biological activity in five other patients were observed in this study. The Day 1 and Day 1/4/7 studies were early discontinued because of drug inactivity at doses significantly higher than CD33 -saturating doses. No myelossuppression was observed at any trial of AVE9633. The pharmacokinetics/pharmacodynamics data obtained in these studies will provide very useful information for the design of the next generation of immunoconjugates.

Insight into the behavior of hairy cell leukemia by immunogenetic analysis

The B cell receptor (BCR) is the functional distinguishing unit that defines any B cell. Immunoglobulin gene (IG) status is preserved in the neoplastic B cell clone and can provide an indicator of the maturation stage reached by the B cell prior to transformation. In hairy cell leukemia (HCL), several data from IG analysis provide clear hints regarding the cell of origin and the ongoing selective interactions of the tumor BCR with environmental stimuli: HCLs (i) have variable levels of IG somatic mutations, (ii) continue somatic mutations at low levels, (iii) have active processes of IG class switching after transformation, and (iv) have a relatively high frequency of selective events in the light chain of the BCR. It has recently emerged that an unmutated status of the HCL-derived IG can be associated with failure to respond to cladribine, genetic abnormalities indicative of poor outcome, and aggressive disease. These observations suggest that IG gene analysis may have biological and prognostic relevance in HCL and merits further characterization.

Modern strategies for hairy cell leukemia

Enormous progress in the treatment of hairy cell leukemia over the last five decades has emerged as a result of organized clinical investigations. Although interferon represented one of the initial major therapeutic advances in the management of this disease in 1984, the subsequent introduction of purine nucleoside analogs (pentostatin and cladribine) changed the natural history of this rare disease by achieving a high rate of complete and durable remissions. The disease-free survival after effective therapy has not reached a plateau, suggesting control but not cure of the disease. Identification of minimal residual disease in patients achieving a complete hematologic remission provides insight into the potential source for predicting eventual relapse. Modern strategies of targeted therapies directed against immunophenotypic markers on the leukemic cells provide hope that improved long-term control of the disease is possible. Combined chemoimmunotherapy may hold the highest promise for disease eradication, but the optimal strategy for using this approach is under active investigation. Despite the perception by hematologists that this disease has already been conquered, there are critically important unanswered questions that remain. Investigation of the bone marrow microenvironment and its impact on minimal residual disease may ultimately prevent relapse. Consideration of the median age of patients at diagnosis combined with a substantial relapse rate mandates continued pursuit of improved therapy. The ultimate goal will be to achieve cure rather than simple control of the disease.

Molecular insight into the biology and clinical course of hairy cell leukemia utilizing immunoglobulin gene analysis

The B cell receptor (BCR) is the functional distinguishing unit that defines any B cell. Immunoglobulin gene (IG) status is preserved in the neoplastic B cell clone and can provide an indicator of the maturation stage reached by the B cell prior to transformation. In hairy cell leukemia (HCL), several pieces of data from IG analysis provide clear hints regarding the cell of origin and the ongoing selective interactions of the tumor BCR with environmental stimuli. HCLs have variable levels of IG somatic mutations, and continue somatic mutations at low levels as well as IG class switching after transformation. More recent data also show the occurrence of selective events in the light chain of the BCR, suggesting a dominant role for IG status in the pathogenesis of HCL. Moreover, it has recently emerged that an unmutated status of the HCL IG can be associated with failure to respond to cladribine, genetic abnormalities indicative of poor outcome, and aggressive disease. These observations suggest that IG analysis may have biological and prognostic relevance in HCL and merits further characterization.

HER-2/neu as a target for cancer vaccines

A novel modality toward the treatment of HER-2/neu-positive malignancies, mostly including breast and, more recently prostate carcinomas, has been the use of vaccines targeting HER-2/neu extracellular and intracellular domains. HER-2/neu-specific vaccines have been demonstrated to generate durable T-cell anti-HER-2/neu immunity when tested in Phase I and II clinical trials with no significant toxicity or autoimmunity directed against normal tissues. Targeting of HER-2/neu in active immunotherapy may involve peptide and DNA vaccines. Moreover, active anti-HER-2/neu immunization could facilitate the ex vivo expansion of HER-2/neu-specific T cells for use in adoptive immunotherapy for the treatment of established metastatic disease. In addition, early data from trials examining the potential use of HER-2/neu-based vaccines in the adjuvant setting to prevent the relapse of breast cancer in high-risk patients have shown promising results. Future approaches include multiepitope preventive vaccines and combinatorial treatments for generating the most efficient protective anti-tumor immunity.

Toxin-based therapeutic approaches

Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.

Immunologic mechanisms in RCC and allogeneic renal transplant rejection

The tolerance state that exists between renal cell carcinoma (RCC) and the host's immune system would be an ideal situation in the setting of human kidney transplantation, in which graft tolerance is the ultimate goal of immunosuppressive therapy. On the other hand, acute rejection, as it appears in renal allografts, would be the optimal immunologic situation in patients with RCC. Analysis of the underlying mechanisms of acute allograft rejection and local pro-tumor immunosuppression could help to identify potential therapeutic targets for inducing immune tolerance in allograft recipients and immune rejection in RCC patients. Experimental kidney transplantation might be a suitable model in which to analyze these processes. Macrophages are a prominent and vital cell type in the cellular infiltrate seen in both RCC and renal allografts. Depending on their polarization, they can initiate and promote either proinflammatory or pro-tumor responses, which lead to tissue rejection or acceptance, respectively. Improved understanding of macrophage biology could lead to therapeutic modification of their function in order to promote a desirable immunologic response in either RCC or transplant tissue.