A bispecific recombinant cytotoxin (DTEGF13) targeting human interleukin-13 and epidermal growth factor receptors in a mouse xenograft model of prostate cancer

Recent Advances in IL-13Rα2-Directed Cancer Immunotherapy

Interleukin-13 receptor subunit alpha-2 (IL-13Rα2, CD213A), a high-affinity membrane receptor of the anti-inflammatory Th2 cytokine IL-13, is overexpressed in a variety of solid tumors and is correlated with poor prognosis in glioblastoma, colorectal cancer, adrenocortical carcinoma, pancreatic cancer, and breast cancer. While initially hypothesized as a decoy receptor for IL-13-mediated signaling, recent evidence demonstrates IL-13 can signal through IL-13Rα2 in human cells. In addition, expression of IL-13Rα2 and IL-13Rα2-mediated signaling has been shown to promote tumor proliferation, cell survival, tumor progression, invasion, and metastasis. Given its differential expression in tumor versus normal tissue, IL-13Rα2 is an attractive immunotherapy target, as both a targetable receptor and an immunogenic antigen. Multiple promising strategies, including immunotoxins, cancer vaccines, and chimeric antigen receptor (CAR) T cells, have been developed to target IL-13Rα2. In this mini-review, we discuss recent developments surrounding IL-13Rα2-targeted therapies in pre-clinical and clinical study, including potential strategies to improve IL-13Rα2-directed cancer treatment efficacy.

Antibody-Based Immunotoxins for Colorectal Cancer Therapy

Monoclonal antibodies (mAbs) are included among the treatment options for advanced colorectal cancer (CRC). However, while these mAbs effectively target cancer cells, they may have limited clinical activity. A strategy to improve their therapeutic potential is arming them with a toxic payload. Immunotoxins (ITX) combining the cell-killing ability of a toxin with the specificity of a mAb constitute a promising strategy for CRC therapy. However, several important challenges in optimizing ITX remain, including suboptimal pharmacokinetics and especially the immunogenicity of the toxin moiety. Nonetheless, ongoing research is working to solve these limitations and expand CRC patients' therapeutic armory. In this review, we provide a comprehensive overview of targets and toxins employed in the design of ITX for CRC and highlight a wide selection of ITX tested in CRC patients as well as preclinical candidates.

A bispecific immunotoxin (IHPP) with a long half-life targeting HER2 and PDGFRβ exhibited improved efficacy against HER2-positive tumors in a mouse xenograft model

Multiple signaling pathways are usually involved in the development of tumors. Compared with monospecific antibodies, bispecific antibodies can recognize two different antigens at the same time, so they are more suitable for treating tumor diseases with complex etiology. Immunotoxins have good antitumor activity, however, single targeting limits their effectiveness. Herein, we designed a Pseudomonas exotoxin A (PE)-based bispecific immunotoxin IgBD-HER2-PDGFRβ-PE38 which could distinguish HER2 and PDGFRβ target in tumor. Meanwhile, IgG-affinity could extend the serum retention of immunotoxins after in vivo injection. In this work, we first detected the selective binding of the immunotoxins and antitumor effect in vitro. Compared with control group, IgBD-HER2-PDGFRβ-PE38 exhibited improved efficacy against HER2-positive tumors in an NCI-N87 subcutaneous xenograft model. Then, transcriptome sequencing was performed on tumor tissue originating from different treatment groups of mice bearing NCI-N87 tumors. Seven significantly differentially expressed genes were screened based on human genes, and the differential mouse genes were enriched based on the Reactome Pathway Database. At last, the RNA sequencing results were verified by real-time PCR and ELISA. Therefore, the new construct bispecific immunotoxin represents a potentially attractive therapeutic modality, and the proposed strategy make them promising for use in the development of anti-HER2 cancer therapeutics.

Targeting Receptors on Cancer Cells with Protein Toxins

Cancer cells frequently upregulate surface receptors that promote growth and survival. These receptors constitute valid targets for intervention. One strategy involves the delivery of toxic payloads with the goal of killing those cancer cells with high receptor levels. Delivery can be accomplished by attaching a toxic payload to either a receptor-binding antibody or a receptor-binding ligand. Generally, the cell-binding domain of the toxin is replaced with a ligand or antibody that dictates a new binding specificity. The advantage of this “immunotoxin” approach lies in the potency of these chimeric molecules for killing cancer cells. However, receptor expression on normal tissue represents a significant obstacle to therapeutic intervention.

Smart Targeting To Improve Cancer Therapeutics

Cancer is the second largest cause of death worldwide with the number of new cancer cases predicted to grow significantly in the next decades. Biotechnology and medicine can and should work hand-in-hand to improve cancer diagnosis and treatment efficacy. However, success has been frequently limited, in particular when treating late-stage solid tumors. There still is the need to develop smart and synergistic therapeutic approaches to achieve the synthesis of strong and effective drugs and delivery systems. Much interest has been paid to the development of smart drug delivery systems (drug-loaded particles) that utilize passive targeting, active targeting, and/or stimulus responsiveness strategies. This review will summarize some main ideas about the effect of each strategy and how the combination of some or all of them has shown to be effective. After a brief introduction of current cancer therapies and their limitations, we describe the biological barriers that nanoparticles need to overcome, followed by presenting different types of drug delivery systems to improve drug accumulation in tumors. Then, we describe cancer cell membrane targets that increase cellular drug uptake through active targeting mechanisms. Stimulus-responsive targeting is also discussed by looking at the intra- and extracellular conditions for specific drug release. We include a significant amount of information summarized in tables and figures on nanoparticle-based therapeutics, PEGylated drugs, different ligands for the design of active-targeted systems, and targeting of different organs. We also discuss some still prevailing fundamental limitations of these approaches, eg, by occlusion of targeting ligands.

Targeted Diphtheria Toxin-Based Therapy: A Review Article

Cancer remains one of the leading causes of death worldwide. Conventional therapeutic strategies usually offer limited specificity, resulting in severe side effects and toxicity to normal tissues. Targeted cancer therapy, on the other hand, can improve the therapeutic potential of anti-cancer agents and decrease unwanted side effects. Targeted applications of cytolethal bacterial toxins have been found to be especially useful for the specific eradication of cancer cells. Targeting is either mediated by peptides or by protein-targeting moieties, such as antibodies, antibody fragments, cell-penetrating peptides (CPPs), growth factors, or cytokines. Together with a toxin domain, these molecules are more commonly referred to as immunotoxins. Targeting can also be achieved through gene delivery and cell-specific expression of a toxin. Of the available cytolethal toxins, diphtheria toxin (DT) is one of the most frequently used for these strategies. Of the many DT-based therapeutic strategies investigated to date, two immunotoxins, Ontak^TM and Tagraxofusp^TM, have gained FDA approval for clinical application. Despite some success with immunotoxins, suicide-gene therapy strategies, whereby controlled tumor-specific expression of DT is used for the eradication of malignant cells, are gaining prominence. The first part of this review focuses on DT-based immunotoxins, and it then discusses recent developments in tumor-specific expression of DT.

A bispecific enediyne-energized fusion protein targeting both epidermal growth factor receptor and insulin-like growth factor 1 receptor showing enhanced antitumor efficacy against non-small cell lung cancer

Epidermal growth factor receptor (EGFR) and insulin-like growth factor 1 receptor (IGF-1R) both overexpressed on non-small cell lung cancer (NSCLC) and are known cooperatively to promote tumor progression and drug resistance. This study was to construct a novel bispecific fusion protein EGF-IGF-LDP-AE consisting of EGFR and IGF-IR specific ligands (EGF and IGF-1) and lidamycin, an enediyne antibiotic with potent antitumor activity, and investigate its antitumor efficacy against NSCLC. Binding and internalization assays showed that EGF-IGF-LDP protein could bind to NSCLC cells with high affinity and then internalized into cells with higher efficiency than that of monospecific proteins. In vitro, the enediyne-energized analogue of bispecific fusion protein (EGF-IGF-LDP-AE) displayed extremely potent cytotoxicity to NSCLC cell lines with IC₅₀<10⁻¹¹ mol/L. Moreover, the bispecific protein EGF-IGF-LDP-AE was more cytotoxic than monospecific proteins (EGF-LDP-AE and LDP-IGF-AE) and lidamycin. In vivo, EGF-IGF-LDP-AE markedly inhibited the growth of A549 xenografts, and the efficacy was more potent than that of lidamycin and monospecific counterparts. EGF-IGF-LDP-AE caused significant cell cycle arrest and it also induced cell apoptosis in a dosage-dependent manner. Pretreatment with EGF-IGF-LDP-AE inhibited EGF-, IGF-stimulated EGFR and IGF-1R phosphorylation, and blocked two main downstream signaling molecules AKT and ERK activation. These data suggested that EGF-LDP-IGF-AE protein would be a promising targeted agent for NSCLC patients with EGFR and/or IGF-1R overexpression.

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.

A novel bispecific immunotoxin delivered by human bone marrow-derived mesenchymal stem cells to target blood vessels and vasculogenic mimicry of malignant gliomas

Background

In previous years, immunotoxins have been shown to be a greatly promising therapeutic tool for brain malignancies, such as gliomas. Human mesenchymal stem cells (hMSCs) exhibit tropism to tumor tissue. However, the effect of bispecific immunotoxins in malignant gliomas is still unknown. The aim of this study was to investigate the function of bispecific immunotoxins in human malignant gliomas.

Materials and methods

In the present study, the bispecific immunotoxin VEGF₁₆₅-ephrin A1-PE38KDEL was established using deoxyribonucleic acid shuffling and cloning techniques. The VEGF₁₆₅-ephrin A1-PE38KDEL was delivered by hMSCs to mouse malignant gliomas. The effects of the bispecific immunotoxins on glioma-derived blood vessels and vasculogenic mimicry to elucidate the molecular mechanisms underlying the antitumorigenic effects of immunotoxins were examined in vivo.

Results

In vitro, transfected hMSCs significantly inhibited the cell viability of gliomas cell lines U87 and U251 in a dose-dependent manner compared with untransfected hMSCs (P<0.01). In vivo, the intratumoral injection of engineered hMSCs was effective at inhibiting tumor growth in a malignant glioma tumor model.

Conclusion

The bispecific immunotoxin secreted from hMSCs acts as a novel strategy for improving treatment options for malignant gliomas in the clinic.

A dual-targeting triplebody mediates preferential redirected lysis of antigen double-positive over single-positive leukemic cells

The single-chain triplebody HLA-ds16-hu19 consists of three single-chain Fv (scFv) antibody fragments connected in a single polypeptide chain. This protein with dual-targeting capacity mediated preferential lysis of antigen double positive(dp) over single-positive (sp) leukemic cells by recruitment of natural killer (NK) cells as effectors. The two distal scFv modules were specific for the histocompatibility protein HLA-DR and the lymphoid antigen CD19, the central one for the Fc gamma receptor CD16. In antibody-dependent cellular cytotoxicity (ADCC) experiments with a mixture of leukemic target cells comprising both HLA-DR sp HuT-78 or Kasumi-1 cells and (HLA-DR plus CD19) dp SEM cells, the triplebody mediated preferential lysis of the dp cells even when the sp cells were present in ≤ 20-fold numerical excess.The triplebody promoted equal lysis of SEM cells at 2.5-fold and 19.5-fold lower concentrations than the parental antibodies specific for HLA-DR and CD19, respectively. Finally, the triplebody also eliminated primary leukemic cells at lower concentrations than an equimolar mixture of bispecific single-chain Fv fragments (bsscFvs) separately addressing each target antigen (hu19-ds16 and HLA-ds16). The increased selectivity of targeting and the preferential lysis of dp over sp cells achieved by dual-targeting open attractive new perspectives for the use of dual-targeting agents in cancer therapy.

The next generation of antibody drug conjugates

Antibody-drug conjugates (ADCs) represent a promising therapeutic modality for the clinical management of cancer. The recent approvals of brentuximab vedotin and ado-trastuzumab emtansine plus emerging data for many molecules in clinical trials highlight the potential for ADCs to offer new therapeutic options for patients. Currently, more than 30 ADCs are being evaluated in early- or late-stage clinical trials. Accordingly, much has been done to refine and transform the early-generation ADCs to the highly effective products that we now have in clinical development. These changes include a better understanding of optimal target selection, advances in antibody engineering, improvements in linker/payload conjugation strategies, and the generation of highly potent ADC payloads. In this review, we detail the current status of ADCs in both preclinical and clinical development, highlight technological advancements in ADC development, and speculate towards the future of this targeted therapeutic platform.

An EGFR/CD13 bispecific fusion protein and its enediyne-energized analog show potent antitumor activity

Targeting to two or more objectives simultaneously has been pursued as a strategy to potentially increase the efficiency and selectivity of targeted drugs to certain cancers. In this study, an epidermal growth factor receptor (EGFR)/CD13-targeting, bispecific fusion protein ER(Fv)-LDP-NGR consisting of an anti-EGFR single-chain variable fragment (scFv), an apoprotein (LDP) of lidamycin (LDM), and a tri-CNGRC (Cys-Asn-Gly-Arg-Cys) peptide against CD13 was constructed, and then an enediyne-energized analog ER(Fv)-LDP-NGR-AE was generated by integration with an enediyne chomophore (AE) derived from LDM. The apoprotein LDP was used as a 'scaffold' to connect the scFv fragment and the tri-CNGRC peptide and also served as a specific 'carrier' for the extremely potent cytotoxic enediyne chromophore of LDM. Compared with its monospecific counterparts, ER(Fv)-LDP and LDP-NGR, the bispecific fusion protein ER(Fv)-LDP-NGR showed higher affinity to EGFR/CD13-overexpressed tumor cells. Determined by the MTT assay, the bispecific, enediyne-energized ER(Fv)-LDP-NGR-AE showed highly potent cytotoxicity to EGFR/CD13-overexpressed MCF-7 cells, with an IC50 value of 3.4×10 mol/l, whereas for the EGFR-overexpressed A431 cells, the IC50 value was 2.2×10 mol/l. For MCF-7 cells, the bispecific ER(Fv)-LDP-NGR-AE was more potent in cytotoxicity than the corresponding monospecific energized fusion proteins. In athymic mice models, the bispecific fusion protein ER(Fv)-LDP-NGR presented stronger inhibitory activity than the monospecific ER(Fv)-LDP and LDP-NGR. For the enediyne-energized fusion proteins, ER(Fv)-LDP-NGR-AE significantly inhibited the growth of EGFR/CD13-overexpressed MCF-7 xenograft and EGFR-overexpressed A431 xenograft by 86.3 and 81.4%, respectively. In addition, the bispecific ER(Fv)-LDP-NGR-AE showed much higher efficacy than its monospecific analogs ER(Fv)-LDP-AE and LDP-NGR-AE in both MCF-7 and A431 xenograft models. The results show that EGFR/CD13 bitargeting effectively improved the antitumor efficacy. Both the bispecific fusion protein and its enediyne-energized analog are highly effective in athymic mice bearing xenografts, and the latter exerts more marked efficacy. Generation of a pair of bispecific antibody-based therapeutics and its corresponding antibody-drug conjugate simultaneously may be a feasible strategy for the development of new targeted drugs for cancer therapy.

Prodrug applications for targeted cancer therapy

Prodrugs are widely used in the targeted delivery of cytotoxic compounds to cancer cells. To date, targeted prodrugs for cancer therapy have achieved great diversity in terms of target selection, activation chemistry, as well as size and physicochemical nature of the prodrug. Macromolecular prodrugs such as antibody-drug conjugates, targeted polymer-drug conjugates and other conjugates that self-assemble to form liposomal and micellar nanoparticles currently represent a major trend in prodrug development for cancer therapy. In this review, we explore a unified view of cancer-targeted prodrugs and highlight several examples from recombinant technology that exemplify the prodrug concept but are not identified as such. Recombinant "prodrugs" such as engineered anthrax toxin show promise in biological specificity through the conditionally targeting of multiple cellular markers. Conditional targeting is achieved by structural complementation, the spontaneous assembly of engineered inactive subunits or fragments to reconstitute functional activity. These complementing systems can be readily adapted to achieve conditionally bispecific targeting of enzymes that are used to activate low-molecular weight prodrugs. By leveraging strengths from medicinal chemistry, polymer science, and recombinant technology, prodrugs are poised to remain a core component of highly focused and tailored strategies aimed at conditionally attacking complex molecular phenotypes in clinically relevant cancer.

An EGFR/HER2-Bispecific and enediyne-energized fusion protein shows high efficacy against esophageal cancer

Esophageal cancer is one of the most common cancers, and the 5-year survival rate is less than 10% due to lack of effective therapeutic agents. This study was to evaluate antitumor activity of Ec-LDP-Hr-AE, a recently developed bispecific enediyne-energized fusion protein targeting both epidermal growth factor receptor (EGFR) and epidermal growth factor receptor 2 (HER2), on esophageal cancer. The fusion protein Ec-LDP-Hr-AE consists of two oligopeptide ligands and an enediyne antibiotic lidamycin (LDM) for receptor binding and cell killing, respectively. The current study demonstrated that Ec-LDP-Hr had high affinity to bind to esophageal squamous cell carcinoma (ESCC) cells, and enediyne-energized fusion protein Ec-LDP-Hr-AE showed potent cytotoxicity to ESCC cells with differential expression of EGFR and HER2. Ec-LDP-Hr-AE could cause significant G2-M arrest in EC9706 and KYSE150 cells, and it also induced apoptosis in ESCC cells in a dosage-dependent manner. Western blot assays showed that Ec-LDP-Hr-AE promoted caspase-3 and caspase-7 activities as well as PARP cleavage. Moreover, Ec-LDP-Hr-AE inhibited cell proliferation via decreasing phosphorylation of EGFR and HER2, and further exerted inhibition of the activation of their downstream signaling molecules. In vivo, at a tolerated dose, Ec-LDP-Hr-AE inhibited tumor growth by 88% when it was administered to nude mice bearing human ESCC cell KYSE150 xenografts. These results indicated that Ec-LDP-Hr-AE exhibited potent anti-caner efficacy on ESCC, suggesting it could be a promising candidate for targeted therapy of esophageal cancer.

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.

Antitumor efficacy of the scFv-based fusion protein and its enediyne-energized analogue directed against epidermal growth factor receptor

Epidermal growth factor receptor (EGFR), overexpressed in many epithelial tumors, plays important roles in the formation and the development of tumors, and thus it is regarded as a promising target for cancer therapy. Single-chain variable fragment (scFv), an engineered antibody fragment, is generally used for constructing antibody-targeted drugs, owing to its low immunogenicity and high penetration capability into solid tumors. A fusion protein ER(Fv-LDP), consisting of an anti-EGFR scFv and the apoprotein (LDP) of lidamycin (LDM), was prepared and then assembled with the active chomophore [active enediyne (AE)] of LDM to generate enediyne-energized analogue ER(Fv-LDP-AE). The fusion protein ER(Fv-LDP) bound specifically to EGFR-overexpressing cancer cells and internalized into the cytoplasm through receptor-mediated endocytosis. ER(Fv-LDP) possessed cytotoxicity against carcinoma cell lines, which was hundreds of times more potent than the separate moiety of ER(Fv) and LDP. The enediyne-energized fusion protein ER(Fv-LDP-AE) also showed stronger cytotoxicity to target-relevant cancer cells than LDM in vitro. In human epidermoid carcinoma A431 xenografts, ER(Fv-LDP) presented higher antitumor efficacy than that of ER(Fv), LDP, and their mixture, with tumor growth inhibition rates of 63.6, 46.7, 48.5, and 49.9%, respectively. The enediyne-energized fusion protein ER(Fv-LDP-AE) at a dose of 0.4 mg/kg inhibited tumor growth by 89.2%, while no significant body weight loss was seen in treated animals. The results show that an anti-EGFR scFv-based fusion protein and its enediyne-energized analogue can be prepared by DNA recombination and molecular reconstitution. Both ER(Fv-LDP) and ER(Fv-LDP-AE) are effective against EGFR-overexpressing cancer xenograft in athymic mice. An integrated technical platform for scFv-based enediyne-energized fusion proteins has been established.

Dual targeting strategies with bispecific antibodies

Monoclonal antibodies are widely used for the treatment of cancer, inflammatory and infectious diseases and other disorders. Most of the marketed antibodies are monospecific and therefore capable of interacting and interfering with a single target. However, complex diseases are often multifactorial in nature, and involve redundant or synergistic action of disease mediators or upregulation of different receptors, including crosstalk between their signaling networks. Consequently, blockade of multiple, different pathological factors and pathways may result in improved therapeutic efficacy. This result can be achieved by combining different drugs, or use of the dual targeting strategies applying bispecific antibodies that have emerged as an alternative to combination therapy. This review discusses the various dual targeting strategies for which bispecific antibodies have been developed and provides an overview of the established bispecific antibody formats.

Molecular targeting of malignant glioma cells with an EphA2-specific immunotoxin delivered by human bone marrow-derived mesenchymal stem cells

Immunotoxins have shown great promise as an alternative treatment for brain malignancies such as gliomas, but their failure to penetrate into the tumor mass remains a major problem. Mesenchymal stem cells exhibit tropism to tumor tissue and may serve as a cellular vehicle for the delivery and local production of antitumor agents. In this study, we used human bone marrow-derived mesenchymal stem cells (hMSCs) as a vehicle for the targeted delivery of EphrinA1-PE38, a very specific immunotoxin against the EphA2 receptor that is overexpressed in gliomas. hMSCs were transduced with adenovirus to express secretable EphrinA1-PE38. Our invitro assays confirmed the expression, release and selective killing effect of the immunotoxin produced by hMSCs. Furthermore, the intratumoral injection of engineered hMSCs was effective at inhibiting tumor growth in a malignant glioma tumor model. These results indicate that gene therapy utilizing EphrinA1-PE38-secreting hMSCs may provide a novel approach for the local treatment of malignant gliomas.

A novel bispecific ligand-directed toxin designed to simultaneously target EGFR on human glioblastoma cells and uPAR on tumor neovasculature

A bispecific ligand-directed toxin (BLT), called EGFATFKDEL, consisting of human epidermal growth factor, a fragment of urokinase, and truncated pseudomonas exotoxin (PE38) was assembled in order to target human glioblastoma. Immunogenicity was reduced by mutating seven immunodominant B-cell epitopes on the PE38 molecule to create a new agent, EGFATFKDEL 7mut. In vitro, the drug selectively killed several human glioblastoma cell lines. EGFATFKDEL is our first BLT designed to simultaneously target EGFR on solid tumors and uPAR on the tumor neovasculature. In vitro assays revealed that the agent is effective against glioblastoma cell lines as well as human umbilical vein endothelial cells (HUVEC). Additionally, the bispecific drug displayed enhanced binding to overexpressed epidermal growth factor receptor and urokinase receptor when compared to similar monospecific drugs, EGFKDEL and ATFKDEL. In vivo, an aggressive human glioblastoma cell line was genetically marked with a firefly luciferase reporter gene and administered to the flanks of nude mice. Treatment with intratumoral injections of EGFATFKDEL 7mut eradicated small tumors in over half of the treated mice, which survived with tumor free status at least 100 days post tumor inoculation. ATFKDEL, which primarily targets the tumor neovasculature, prevented tumor growth but did not result in tumor-free mice in most cases. Specificity was shown by treating with an irrelevant BLT control which did not protect mice. Finally, immunization experiments in immunocompetent mice revealed significantly reduced anti-toxin production in EGFATFKDEL 7mut treated groups. Thus, EGFATFKDEL 7mut is an effective drug for glioblastoma therapy in this murine model and warrants further study.

A new drug delivery method of bispecific ligand-directed toxins, which reduces toxicity and promotes efficacy in a model of orthotopic pancreatic cancer

OBJECTIVE

Biologicals targeting epidermal growth factor (EGF) and interleukin 13 receptors not only react with overexpressed markers on cancer cells but also react with receptors on normal cells. Because we developed novel bispecific ligand-directed toxins synthesized by cloning EGF and interleukin 13 on the same molecule with toxin, our objective was to determine whether we could block normal receptors while still targeting receptors overexpressed on cancer cells, thereby decreasing toxicity while maintaining efficacy.

METHODS

A method, toxicity blocking (ToxBloc), was developed in which a bolus intraperitoneal dose of recombinant EGF13 (without toxin) was given to mice approximately 15 to 20 minutes before DTEGF13. Experiments were then performed to determine whether the maximal tolerated dose (MTD) was reduced and whether we were still able to eliminate progression of aggressive human, metastatic, pancreatic cancer induced by orthotopic injection (OT) in nude mice.

RESULTS

ToxBloc permitted us to safely exceed the DTEGF13 maximal tolerated dose by 15-fold. This approach permitted repetitive high dosing with the bispecific ligand-directed toxin resulting in tumor regression (P < 0.01). Tumor effects were documented using a tumor imaging model in which OT tumor growth was monitored noninvasively in real time. ToxBloc was selective because other bispecific peptides did not block.

CONCLUSIONS

ToxBloc represents a new method of drug delivery and a potential solution to the problem of toxicity.

Bioengineering a unique deimmunized bispecific targeted toxin that simultaneously recognizes human CD22 and CD19 receptors in a mouse model of B-cell metastases

A drug of high potency and reduced immunogenicity is needed to develop a targeted biological drug that when injected systemically can penetrate to malignant B cells. Therefore, a novel deimmunized bispecific ligand-directed toxin targeted by dual high-affinity single-chain Fvs (scFv) spliced to PE38 with a KDEL COOH-terminus was genetically engineered. The aims were to reduce toxin immunogenicity using mutagenesis, measure the ability of mutated drug to elicit antitoxin antibody responses, and show that mutated drug was effective against systemic B-cell lymphoma in vivo. Both human anti-CD22 scFv and anti-CD19 scFv were cloned onto the same single-chain molecule with truncated pseudomonas exotoxin (PE38) to create the drug. Site-specific mutagenesis was used to mutate amino acids in seven key epitopic toxin regions that dictate B-cell generation of neutralizing antitoxin antibodies. Bioassays were used to determine whether mutation reduced potency, and ELISAs were done to determine whether antitoxin antibodies were reduced. Finally, a powerful genetically altered luciferase xenograft model was used that could be imaged in real time to determine the effect on systemic malignant human B-cell lymphoma, Raji-luc. Patient B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B lymphoma were high in CD22 and CD19 expression. 2219KDEL7mut was significantly effective against systemic Raji-luc in mice and prevented metastatic spread. Mutagenesis reduced neutralizing antitoxin antibodies by approximately 80% with no apparent loss in in vitro or in vivo activity. Because 2219KDEL7mut immunogenicity was significantly reduced and the drug was highly effective in vivo, we can now give multiple drug treatments with targeted toxins in future clinical trials.

A bispecific enediyne-energized fusion protein containing ligand-based and antibody-based oligopeptides against epidermal growth factor receptor and human epidermal growth factor receptor 2 shows potent antitumor activity

PURPOSE

The cooverexpression of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) observed in many human tumors and their synergistic interaction in the transformation of cells make these receptors important targets for the development of new targeted therapeutics. Targeting of EGFR and HER2 simultaneously has been pursued as a strategy with which to potentially increase efficiency and selectivity in therapy of certain cancers. This study was set to construct a bispecific energized fusion protein (Ec-LDP-Hr-AE) consisting of two oligopeptides against EGFR and HER2, and lidamycin, and investigate its antitumor efficacy.

EXPERIMENTAL DESIGN

In vitro experiments measured the binding and internalization of bispecific Ec-LDP-Hr fusion protein. The potency of energized fusion proteins was also done in which the bispecific Ec-LDP-Hr-AE was compared with lidamycin (LDM) and its monospecific counterparts, Ec-LDP-AE and LDP-Hr-AE. In vivo, Ec-LDP-Hr-AE was given i.v. to nude mice bearing human ovarian carcinoma SK-OV-3 xenografts.

RESULTS

Binding and internalization studies showed that bispecific fusion protein Ec-LDP-Hr bound to carcinoma cells specifically and then were internalized into the cytoplasm. Bispecific Ec-LDP-Hr-AE was more potent and selective in its cytotoxicity against different carcinoma cell lines than corresponding momospecific agents and LDM in vitro. In addition, Ec-LDP-Hr-AE significantly inhibited the growth of SK-OV-3 xenografts in nude mouse model. In vivo imaging study showed that FITC-labeled Ec-LDP-Hr was targeted and accumulated in the tumors.

CONCLUSION

A ligand-based and an antibody-based oligopeptide fused to the enediyne antibiotic LDM created a new bispecific fusion protein with low molecular weight and more potent in vitro and in vivo antitumor activity (than momospecific fusion proteins).

Design and modification of EGF4KDEL 7Mut, a novel bispecific ligand-directed toxin, with decreased immunogenicity and potent anti-mesothelioma activity

BACKGROUND

Potency, immunogenicity, and toxicity are three problems that limit the use of targeted toxins in solid tumour therapy.

METHODS

To address potency, we used genetic engineering to develop a novel bispecific ligand-directed toxin (BLT) called EGF4KDEL, a novel recombinant anti-mesothelioma agent created by linking human epidermal growth factor (EGF) and interleukin-4 (IL-4) to truncated pseudomonas exotoxin (PE38) on the same single-chain molecule. Immunogenicity was reduced by mutating seven immunodominant B-cell epitopes on the PE38 molecule to create a new agent, EGF4KDEL 7Mut.

RESULTS

In vitro, bispecific EGF4KDEL showed superior anti-mesothelioma activity compared with its monospecific counterparts. Toxicity in mice was diminished by having both ligands on the same molecule, allowing administration of a 10-fold greater dose of BLT than a mixture of monomeric IL4KDEL and EGFKDEL. EGF4KDEL 7Mut, retained all of its functional activity and induced about 87% fewer anti-toxin antibodies than mice given the parental, non-mutated form. In vivo, intraperitoneal (IP) injection of the BLT showed significant (P<0.01) and impressive effects against two aggressive, malignant IP mesothelioma models when treatment was begun 14-16 days post tumour innoculation.

CONCLUSION

These data show that EGF4KDEL 7Mut is a promising new anti-mesothelioma agent that was developed to specifically address the obstacles facing clinical utility of targeted toxins.

A novel reduced immunogenicity bispecific targeted toxin simultaneously recognizing human epidermal growth factor and interleukin-4 receptors in a mouse model of metastatic breast carcinoma

PURPOSE

To develop a targeted biological drug that when systemically injected can penetrate to metastatic breast cancer tumors, one needs a drug of high potency and reduced immunogenicity. Thus, we bioengineered a novel bispecific ligand-directed toxin (BLT) targeted by dual high-affinity cytokines with a PE(38)KDEL COOH terminus. Our purpose was to reduce toxin immunogenicity using mutagenesis, measure the ability of mutated drug to elicit B-cell antitoxin antibody responses, and show that mutated drug was effective against systemic breast cancer in vivo.

EXPERIMENTAL DESIGN

A new BLT was created in which both human epidermal growth factor (EGF) and interleukin 4 cytokines were cloned onto the same single-chain molecule with truncated Pseudomonas exotoxin (PE(38)). Site-specific mutagenesis was used to mutate amino acids in seven key epitopic toxin regions that dictate B-cell generation of neutralizing antitoxin antibodies. Bioassays were used to determine whether mutation reduced potency, and ELISA studies were done to determine whether antitoxin antibodies were reduced. Finally, a genetically altered luciferase xenograft model was used; this model could be imaged in real time to determine the effect on the systemic malignant human breast cancer MDA-MB-231.

RESULTS

EGF4KDEL 7mut was significantly effective against established systemic human breast cancer and prevented metastatic spread. Mutagenesis reduced immunogenicity by approximately 90% with no apparent loss in in vitro or in vivo activity.

CONCLUSIONS

Because EGF4KDEL 7mut was highly effective even when we waited 26 days to begin therapy and because immunogenicity was significantly reduced, we can now give multiple drug treatments for chemotherapy-refractory breast cancer in clinical trials.

Intracranial elimination of human glioblastoma brain tumors in nude rats using the bispecific ligand-directed toxin, DTEGF13 and convection enhanced delivery

A bispecific ligand-directed toxin (BLT) consisting of human interleukin-13, epithelial growth factor, and the first 389 amino acids of diphtheria toxin was assembled in order to target human glioblastoma. In vitro, DTEGF13 selectively killed the human glioblastoma cell line U87-luc as well as other human glioblastomas. DTEGF13 fulfilled the requirement of a successful BLT by having greater activity than either of its monospecific counterparts or their mixture proving it necessary to have both ligands on the same single chain molecule. Aggressive brain tumors established intracranially (IC) in nude rats with U87 glioma genetically marked with a firefly luciferase reporter gene were treated with two injections of DTEGF13 using convection enhanced delivery resulting in tumor eradication in 50% of the rats which survived with tumor free status at least 110 days post tumor inoculation. An irrelevant BLT control did not protect establishing specificity. The bispecific DTEGF13 MTD dose was measured at 2 microg/injection or 0.5 microg/kg and toxicity studies indicated safety in this dose. Combination of monospecific DTEGF and DTIL13 did not inhibit tumor growth. ELISA assay indicated that anti-DT antibodies were not generated in normal immunocompetent rats given identical intracranial DTEGF13 therapy. Thus, DTEGF13 is safe and efficacious as an alternative drug for glioblastoma therapy and warrants further study.

Genetic alteration of a bispecific ligand-directed toxin targeting human CD19 and CD22 receptors resulting in improved efficacy against systemic B cell malignancy

A bispecific ligand-directed toxin (BLT) called DT2219ARL consisting of two scFv ligands recognizing CD19 and CD22 and catalytic DT390 was genetically enhanced for superior in vivo anti-leukemia activity. Genetic alterations included reverse orienting VH-VL domains and adding aggregation reducing/stabilizing linkers. In vivo, these improvements resulted in previously unseen long-term tumor-free survivors measured in a bioluminescent xenograft imaging model in which the progression of human Raji Burkitt's lymphoma could be tracked in real time and in a Daudi model as well. Studies showed DT2219ARL was potent (IC50s 0.06-0.2 nM range) and selectively blockable. Imaging studies indicated the highly invasive nature of this B cell malignancy model and showed it likely induced pre-terminal hind limb paralysis because of metastasis to spinal regions prevented by DT2219ARL. DT2219ARL represents a new class of bispecific biological that can be continually improved by genetic mutation.

Anti-glioblastoma effect of a recombinant bispecific cytotoxin cotargeting human IL-13 and EGF receptors in a mouse xenograft model

To improve activity of a recombinant IL-13 cytotoxin (CT) comprised of IL-13 spliced to truncated diphtheria toxin (DT(390)), epidermal growth factor (EGF) was added to the same single chain protein. This new recombinant bispecific CT, called DTEGF13, enhanced the killing potency against the human glioblastoma lines, U87MG (0.015 nM) and U118MG (0.02 nM). A similar enhancement was observed against the lung carcinoma cell line, Calu-3 (0.0018 nM). Enhanced activity could not be explained by an increased number of cytokines available for binding since a combination of monospecific DTEGF and DTIL13 did not cause the same enhanced activity. Enhanced activity was dependent on the presence of both cytokines on the same single chain molecule and killing was receptor specific since target receptor negative leukemia cells were unaffected by the highly selective DTEGF13 and cytotoxicity could be blocked with anti-EGFR and anti-IL-13 antibodies. In a xenograft flank tumor model, intratumoral injection of DTEGF13, but not monospecific DTEGF or DTIL13, significantly inhibited the growth of established U87 tumors in nude mice (P < 0.04). In this model, the human EGF and IL-13 components of DTEGF13 are reactive with mouse EGFR and IL-13R, respectively. These studies show that a new co-targeting agent that simultaneously recognizes EGFR and IL-13R is more effective than its monospecific counterparts and that DTEGF13 has therapeutic advantages for glioblastoma.