Eradication of Heterogeneous Tumors by T Cells Targeted with Combination Bispecific Chemically Self-assembled Nanorings

Cancer stem-like cells (CSCs) are often the root cause of refractive relapse due to their inherent resistance to most therapies and ability to rapidly self-propagate. Recently, the antigen CD133 has been identified as a CSC marker on several cancer types and αCD133 therapies have shown selective targeting against CSCs with minimal off-target toxicity. Theoretically, by selectively eliminating CSCs, the sensitivity to bulk tumor-targeting therapies should be enhanced. Previously, our laboratory has developed bispecific chemically self-assembled nanorings (CSANs) that successfully induced T-cell eradication of EpCAM-positive (EpCAM+) tumors. We reasoned that targeting both CSCs [CD133-positive (CD133+)] and the bulk tumor (EpCAM+) simultaneously using our CSAN platform should produce a synergistic effect. We evaluated αCD133/αCD3 CSANs as both a single agent and in combination with αEpCAM/αCD3 CSANs to treat triple-negative breast cancer (TNBC) cells, which express a subpopulation of CD133+ cancer stem cells and EpCAM+ bulk tumor cells. Furthermore, an orthotopic breast cancer model validated the ability of αCD133 and αEpCAM targeting to combine synergistically in the elimination of TNBC MDA-MB-231 cells. Complete tumor eradication only occurred when EpCAM and CD133 were targeted simultaneously and lead to full remission in 80% of the test mice. Importantly, the depletion and enrichment of CD133 TNBCs highlighted the role of CD133+ cancer cells in regulating tumor growth and progression. Collectively, our results demonstrate that dual targeting with bispecific CSANs can be effective against heterogenous tumor cell populations and that elimination of primary and CD133+ CSCs may be necessary for eradication of at least a subset of TNBC.

A tri-specific killer engager against mesothelin targets NK cells towards lung cancer

New treatments are required to enhance current therapies for lung cancer. Mesothelin is a surface protein overexpressed in non-small cell lung cancer (NSCLC) that shows promise as an immunotherapeutic target in phase I clinical trials. However, the immunosuppressive environment in NSCLC may limit efficacy of these therapies. We applied time-of-flight mass cytometry to examine the state of circulating mononuclear cells in fourteen patients undergoing treatment for unresectable lung cancer. Six patients had earlier stage NSCLC (I-IVA) and eight had highly advanced NSCLC (IVB). The advanced NSCLC patients relapsed with greater frequency than the earlier stage patients. Before treatment, patients with very advanced NSCLC had a greater proportion of CD14- myeloid cells than patients with earlier NSCLC. These patients also had fewer circulating natural killer (NK) cells bearing an Fc receptor, CD16, which is crucial to antibody-dependent cellular cytotoxicity. We designed a high affinity tri-specific killer engager (TriKE®) to enhance NK cytotoxicity against mesothelin+ targets in this environment. The TriKE consisted of CD16 and mesothelin binding elements linked together by IL-15. TriKE enhanced proliferation of lung cancer patient NK cells in vitro. Lung cancer lines are refractory to NK cell killing, but the TriKE enhanced cytotoxicity and cytokine production by patient NK cells when challenged with tumor. Importantly, TriKE triggered NK cell responses from patients at all stages of disease and treatment, suggesting TriKE can enhance current therapies. These pre-clinical studies suggest mesothelin-targeted TriKE has the potential to overcome the immunosuppressive environment of NSCLC to treat disease.

A trispecific killer engager molecule against CLEC12A effectively induces NK-cell mediated killing of AML cells

The low five-year survival rate for patients with acute myeloid leukemia (AML), primarily caused due to disease relapse, emphasizes the need for better therapeutic strategies. Disease relapse is facilitated by leukemic stem cells (LSCs) that are resistant to standard chemotherapy and promote tumor growth. To target AML blasts and LSCs using Natural Killer (NK) cells, we have developed a trispecific killer engager (TriKE™) molecule containing a humanized anti-CD16 heavy chain camelid single domain antibody (sdAb) that activates NK cells, an IL-15 molecule that drives NK cell priming, expansion and survival, and a single-chain variable fragment (scFv) against human CLEC12A (CLEC12A TriKE). CLEC12A is a myeloid lineage antigen that is highly expressed by AML cells and LSCs, but not expressed by normal hematopoietic stem cells (HSCs), thus minimizing off-target toxicity. The CLEC12A TriKE induced robust NK cell specific proliferation, enhanced NK cell activation and killing of both AML cell lines and primary patient derived AML blasts in vitro while sparing healthy HSCs. Additionally, the CLEC12A TriKE was able to reduce tumor burden in pre-clinical mouse models. These findings highlight the clinical potential of the CLEC12A TriKE for the effective treatment of AML.

Abstract 4592: Early detection for strategic prevention of a terminal canine cancer: A model to reduce the impact of cancer in our society

Cancer mortality has surpassed all other causes of human death in parts of the developed world. Domestic dogs and cats are the only other species where cancer has an equivalent impact in overall mortality. Rapid gains in longevity over the past two centuries are sufficient to explain the increased incidence of cancer in all three species. Not only does longevity increase the probability of exposures to environmental mutagens, but it also allows for introduction of mutations in each somatic cell replication. In this context, an increase in the incidence of cancer becomes almost inevitable because the evolutionary, cancer protective adaptations of humans, dogs, and cats are insufficient to provide protection over the 2 to 6-fold extension in lifespan achieved by these species. We believe this problem is addressable by developing tests to detect malignancies at their earliest stages and pairing these tests with strategic interventions to eliminate tumors before they form. To test this premise, we have developed a blood test to detect the presence of hemangiosarcoma in dogs, a rapidly fatal malignancy. The shorter lifespan of dogs, compared to humans, and the similar shorter latency of disease provide an ideal opportunity to assess the feasibility of our approach. The test uses flow cytometry for detection of rare, non-leukocyte nucleated cells in blood, combining 42 parameters for analysis in a machine learning environment. Samples from 126 dogs with a confirmed diagnosis of hemangiosarcoma (n=28); other cancers (n=29); benign vascular pathology of the spleen (n=27); or apparently healthy and under 4 years of age (n=41) were used for training and 10-fold cross validation. The expected sensitivity and specificity for the diagnosis of hemangiosarcoma in this training set were approximately 90% and 95%, respectively. We then used our trained models to assign a risk category to apparently healthy dogs, 6 years of age or older, from three breeds with a predisposition for hemangiosarcoma (up to 20% lifetime risk): samples from 105 golden retrievers, 52 boxers and 52 Portuguese Water Dogs (N=209) were included in the study. Our results suggest that the probability of developing hemangiosarcoma or one of the other included pathological conditions within 6-18 months of testing was less than 2% in dogs with a negative result (low risk), but >90% in dogs with a positive result (high risk). We will follow the dogs in this study for the duration of their lifetime to assess the predictive value of the blood test over time. Dogs at high risk of hemangiosarcoma are eligible to receive eBAT, a drug capable of eliminating the cells that maintain and propagate the tumor, while making the environment inhospitable for tumor growth. This will provide means to explore the safety and efficacy of eBAT in the setting of prevention. This study serves as proof of concept for a new paradigm of early detection and strategic prevention to reduce the societal impact of canine and human cancers.

Citation Format: Jaime F. Modiano, Taylor A. DePauw, Ali Khammanivong, Ashley J. Schulte, Amber L. Winter, Jong Kim, Kathleen Stuebner, Andrea Fahrenkrug, Daniel A. Vallera, Antonella Borgatti, Erin B. Dickerson, Michael S. Henson. Early detection for strategic prevention of a terminal canine cancer: A model to reduce the impact of cancer in our society [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4592.

Potent Cytolytic Activity and Specific IL15 Delivery in a Second-Generation Trispecific Killer Engager

Natural killer (NK) cells are potent immune modulators that can quickly lyse tumor cells and elicit inflammatory responses. These characteristics make them ideal candidates for immunotherapy. However, unlike T cells, NK cells do not possess clonotypic receptors capable of specific antigen recognition and cannot expand via activating receptor signals alone. To enable NK cells with these capabilities, we created and have previously described a tri-specific killer engager (TriKE) platform capable of inducing antigen specificity and cytokine-mediated NK-cell expansion. TriKE molecules have three arms: (i) a single-chain variable fragment (scFv) against the activating receptor CD16 on NK cells to trigger NK-cell activation, (ii) an scFv against a tumor-associated antigen (CD33 here) to induce specific tumor target recognition, and (iii) an IL15 moiety to trigger NK-cell expansion and priming. Here, we demonstrate that by modifying the anti-CD16 scFv with a humanized single-domain antibody against CD16, we improved TriKE functionality. A CD33-targeting second-generation TriKE induced stronger and more specific NK-cell proliferation without T-cell stimulation, enhanced in vitro NK-cell activation and killing of CD33-expressing targets, and improved tumor control in preclinical mouse models. Given these improved functional characteristics, we propose rapid translation of second-generation TriKEs into the clinic.

Bispecific Targeting of EGFR and Urokinase Receptor (uPAR) Using Ligand-Targeted Toxins in Solid Tumors

Ligand-targeted toxins (LTTs) are bioengineered molecules which are composed of a targeting component linked to a toxin that induces cell death once the LTT binds its target. Bispecific targeting allows for the simultaneous targeting of two receptors. In this review, we mostly focus on the epidermal growth factor receptor (EGFR) as a target. We discuss the development and testing of a bispecific LTT targeting EGFR and urokinase-type plasminogen activator receptor (uPAR) as two attractive targets implicated in tumor growth and in the regulation of the tumor microvasculature in solid tumors. In vitro and mouse xenograft studies have shown that EGFR-targeted bispecific angiotoxin (eBAT) is effective against human solid tumors. Canine studies have shown that eBAT is both safe and effective against canine hemangiosarcoma, which is physiologically similar to human angiosarcoma. Finding the appropriate dosing strategy and sequencing of eBAT administration, in combination with other therapeutics, are among important factors for future directions. Together, the data indicate that eBAT targets cancer stem cells, it may have a role in inhibiting human tumor vasculature, and its bispecific conformation may have a role in reducing toxicity in comparative oncologic trials in dogs.

Impact of repeated cycles of EGF bispecific angiotoxin (eBAT) administered at a reduced interval from doxorubicin chemotherapy in dogs with splenic haemangiosarcoma

We previously reported that eBAT, an EGF-targeted angiotoxin, was safe and it improved the overall survival for dogs with splenic haemangiosarcoma when added to the standard of care in a single cycle of three administrations in the minimal residual disease setting. Our objective for the SRCBST-2 trial was to assess whether increased dosing through multiple cycles of eBAT would be well tolerated and would further enhance the benefits of eBAT. Eligibility was expanded to dogs with stage 3 haemangiosarcoma, provided that gross lesions could be surgically excised. The interval between eBAT and the start of chemotherapy was reduced, and the experimental therapy was expanded to three cycles, each administered at the biologically active dose (50 μg/kg) on a Monday/Wednesday/Friday schedule following splenectomy, and scheduled 1 week prior to the first, second and fifth doxorubicin chemotherapy. Twenty-five dogs were enrolled; six experienced acute hypotension with two requiring hospitalization. Self-limiting elevation of ALT was observed in one dog. A statistically significant survival benefit was not seen in this study in eBAT-treated dogs compared with a Contemporary comparison group of dogs with stages 1-3 haemangiosarcoma treated with standard of care alone. Our results indicate that repeated dosing cycles of eBAT starting 1 week prior to doxorubicin chemotherapy led to greater toxicity and reduced efficacy compared with a single cycle given between surgery and a delayed start of chemotherapy. Further work is needed to understand the precise mechanisms of action of eBAT in order to optimize its clinical benefits in the treatment of canine haemangiosarcoma and other tumours. IACUC Protocols 1110A06186 and 1507-32804A.

Design, Characterization, and Evaluation of scFvCD133/rGelonin: A CD133-Targeting Recombinant Immunotoxin for Use in Combination with Photochemical Internalization

The objective of this study was to develop and explore a novel CD133-targeting immunotoxin (IT) for use in combination with the endosomal escape method photochemical internalization (PCI). scFvCD133/rGelonin was recombinantly constructed by fusing a gene (scFvCD133) encoding the scFv that targets both non-glycosylated and glycosylated forms of both human and murine CD133/prominin-1 to a gene encoding the ribosome-inactivating protein (RIP) gelonin (rGelonin). RIP-activity was assessed in a cell-free translation assay. Selective binding and intracellular accumulation of scFvCD133/rGelonin was evaluated by flow cytometry and fluorescence microscopy. PCI of scFvCD133/rGelonin was explored in CD133^high and CD133^low cell lines and a CD133^neg cell line, where cytotoxicity was evaluated by the MTT assay. scFvCD133/rGelonin exhibited superior binding to and a higher accumulation in CD133^high cells compared to CD133^low cells. No cytotoxic responses were detected in either CD133^high or CD133^low cells after 72 h incubation with <100 nM scFvCD133/rGelonin. Despite a severe loss in RIP-activity of scFvCD133/rGelonin compared to free rGelonin, PCI of scFvCD133/rGelonin induced log-fold reduction of viability compared to PCI of rGelonin. Strikingly, PCI of scFvCD133/rGelonin exceeded the cytotoxicity of PCI of rGelonin also in CD133^low cells. In conclusion, PCI promotes strong cytotoxic activity of the per se non-toxic scFvCD133/rGelonin in both CD133^high and CD133^low cancer cells.

ImmunoPET, [64Cu]Cu-DOTA-Anti-CD33 PET-CT, Imaging of an AML Xenograft Model

PURPOSE

Acute myeloid leukemia (AML) is a highly aggressive form of leukemia, which results in poor survival outcomes. Currently, diagnosis and prognosis are based on invasive single-point bone marrow biopsies (iliac crest). There is currently no AML-specific noninvasive imaging method to detect disease, including in extramedullary organs, representing an unmet clinical need. About 85% to 90% of human myeloid leukemia cells express CD33 cell surface receptors, highlighting CD33 as an ideal candidate for AML immunoPET.

EXPERIMENTAL DESIGN

We evaluated whether [⁶⁴Cu]Cu-DOTA-anti-CD33 murine mAb can be used for immunoPET imaging of AML in a preclinical model. MicroCT was adjusted to detect spatial/anatomical details of PET activity. For translational purposes, a humanized anti-CD33 antibody was produced; we confirmed its ability to detect disease and its distribution. We reconfirmed/validated CD33 antibody-specific targeting with an antibody-drug conjugate (ADC) and radioimmunotherapy (RIT).

RESULTS

[⁶⁴Cu]Cu-DOTA-anti-CD33-based PET-CT imaging detected CD33⁺ AML in mice with high sensitivity (95.65%) and specificity (100%). The CD33⁺ PET activity was significantly higher in specific skeletal niches [femur (P < 0.00001), tibia (P = 0.0001), humerus (P = 0.0014), and lumber spine (P < 0.00001)] in AML-bearing mice (over nonleukemic control mice). Interestingly, the hybrid PET-CT imaging showed high disease activity in the epiphysis/metaphysis of the femur, indicating regional spatial heterogeneity. Anti-CD33 therapy using newly developed humanized anti-CD33 mAb as an ADC (P = 0.02) and [²²⁵Ac]Ac-anti-CD33-RIT (P < 0.00001) significantly reduced disease burden over that of respective controls.

CONCLUSIONS

We have successfully developed a novel anti-CD33 immunoPET-CT-based noninvasive modality for AML and its spatial distribution, indicating a preferential skeletal niche.

3D Bioprinted In Vitro Metastatic Models via Reconstruction of Tumor Microenvironments

The development of 3D in vitro models capable of recapitulating native tumor microenvironments could improve the translatability of potential anticancer drugs and treatments. Here, 3D bioprinting techniques are used to build tumor constructs via precise placement of living cells, functional biomaterials, and programmable release capsules. This enables the spatiotemporal control of signaling molecular gradients, thereby dynamically modulating cellular behaviors at a local level. Vascularized tumor models are created to mimic key steps of cancer dissemination (invasion, intravasation, and angiogenesis), based on guided migration of tumor cells and endothelial cells in the context of stromal cells and growth factors. The utility of the metastatic models for drug screening is demonstrated by evaluating the anticancer efficacy of immunotoxins. These 3D vascularized tumor tissues provide a proof-of-concept platform to i) fundamentally explore the molecular mechanisms of tumor progression and metastasis, and ii) preclinically identify therapeutic agents and screen anticancer drugs.

Immunotoxins Targeting B cell Malignancy-Progress and Problems With Immunogenicity

Few immunotoxins or targeted toxins have become mainline cancer therapies. Still immunotoxins continue to be of major interest and subject of research and development as alternative therapies for drug resistant cancer. A major matter of concern continues to be immunogenicity exemplified by the anti-toxin response of the treated patient. Since some of our most effective toxins are bacterial in nature and bacterial proteins are highly immunogenic, this review describes some efforts to address this pressing issue.

Targeting EGFR and uPAR on human rhabdomyosarcoma, osteosarcoma, and ovarian adenocarcinoma with a bispecific ligand-directed toxin

Purpose

Human sarcomas are rare and difficult to treat cancerous tumors typically arising from soft tissue or bone. Conversely, carcinomas are the most common cancer subtype in humans and the primary cause of mortality across all cancer patients. While conventional therapeutic modalities can prolong disease-free intervals and survival in some cases, treatment of refractory or recurrent solid tumors is challenging, and tumor-related mortality remains unacceptably high. The identification of overexpressed cell surface receptors on sarcoma and carcinoma cells has provided a valuable tool to develop targeted toxins as an alternative anticancer strategy. Recent investigation of recombinant protein-linked toxins that specifically target these cancer receptors has led to the development of highly specific, cytotoxic, and deimmunized drugs that can kill cancer cells.

Methods

This study investigated a recombinant protein called epidermal growth factor bispecific angiotoxin (eBAT), which is designed to target the epidermal growth factor receptor (EGFR) on cancer cells and the urokinase plasminogen activator receptor (uPAR) on cancer cells and associated tumor vasculature. Both receptors are expressed by a variety of human sarcomas and carcinomas. Flow cytometry techniques were used to determine binding affinity of eBAT to cancer cells, and proliferation assays were performed to calculate tumor killing ability based on half-maximal inhibitory concentrations.

Results

eBAT demonstrated cytotoxicity against a variety of sarcoma and carcinoma cells that overexpress EGFR and uPAR in vitro and showed greater cell killing ability and binding affinity to cancer cells compared with its monospecific counterparts.

Conclusion

The results of our study are promising, and further studies will be necessary to confirm the applicability of eBAT as a supplementary therapy for a variety of sarcomas, carcinomas, and possibly other refractory malignancies that express EGFR and uPAR.

Abstract 824: Targeting epidermal growth factor receptors and urokinase-type plasminogen activator receptors for sarcoma therapy

eBAT is a bispecific angiotoxin consisting of truncated, deimmunized Pseudomonas exotoxin fused to epidermal growth factor (EGF) and the amino terminal fragment of urokinase. This drug was designed to use epidermal growth factor receptors (EGFR) and urokinase-type plasminogen receptors (uPAR) as baits to deliver the lethal toxin into the cells, rather than as a means to interrupt signaling by the receptors. We previously showed that eBAT is remarkably safe, and that it reduced tumor burden in mice with established human rhabdomyosarcoma xenografts. It also was safe and showed a strong efficacy signal when used in the adjuvant setting in a clinical trial for dogs with splenic hemangiosarcoma. Nevertheless, the therapeutic mechanism of action of eBAT remains to be elucidated. Our goal is to identify patterns of uPAR expression in sarcomas that promote sarcoma growth and that mediate sensitivity for therapeutic activity by eBAT. We generated uPAR-knockout (KO) cells from MC1A-C1 mouse fibrosarcoma cell line using the CRISPR-Cas system to target exon 2 of the uPAR gene. The resulting cell lines D10 and H6 are clonal uPAR knockouts, whereas K02 and K06 represent mixtures where approximately 80% and 30% of the cells retain uPAR expression. uPAR expression in K02 and K06 has remained stable over numerous passages, indicating that loss of uPAR does not create selective pressure to enhance or inhibit cell growth in vitro. Furthermore, the growth kinetics of D10 and H6 are comparable to parental MC1A-C1 cells. eBAT treatment significantly inhibited proliferation of parental cells, but not of uPAR KO cells. In contrast, all of the cells were resistant to treatment with EGF- and uPA-monospecific toxins. The engraftment efficiency and tumor growth of uPAR KO cells in syngeneic hosts was substantially diminished when compared to K02 and K06 uPAR+ cells, suggesting that, even while uPAR-KO cells might be more resistant to eBAT therapy, uPAR expression appears to be necessary to create the tumor niche and/or to promote tumor growth in vivo. In our ongoing work, we are investigating how uPAR expression in stromal cells and in cells of the innate immune system influence sarcoma growth and the response to eBAT.

Citation Format: Ashley J. Graef, Jong-Hyuk Kim, Daniel A. Vallera, Jaime F. Modiano. Targeting epidermal growth factor receptors and urokinase-type plasminogen activator receptors for sarcoma therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 824.

Early Reconstitution of NK and γδ T Cells and Its Implication for the Design of Post-Transplant Immunotherapy

Relapse is the most frequent cause of treatment failure after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Natural killer (NK) cells and γδ T cells reconstitute early after allo-HSCT, contribute to tumor immunosurveillance via major histocompatibility complex-independent mechanisms and do not induce graft-versus-host disease. Here we performed a quantitative and qualitative analysis of the NK and γδ T cell repertoire in healthy individuals, recipients of HLA-matched sibling or unrelated donor allo-HSCT (MSD/MUD-HSCT) and umbilical cord blood-HSCT (UCB-HSCT). NK cells are present at high frequencies in all allo-HSCT recipients. Immune reconstitution (IR) of vδ2+ cells depended on stem cell source. In MSD/MUD-HSCT recipients, vδ2+ comprise up to 8% of the total lymphocyte pool, whereas vδ2+ T cells are barely detectable in UCB-HSCT recipients. Vδ1+ IR was driven by CMV reactivation and was comparable between MSD/MUD-HSCT and UCB-HSCT. Strategies to augment NK cell mediated tumor responses, similar to IL-15 and antibodies, also induced vδ2+ T cell responses against a variety of different tumor targets. Vδ1+ γδ T cells were induced less by these same stimuli. We also identified elevated expression of the checkpoint inhibitory molecule TIGIT (T cell Ig and ITIM domain), which is also observed on tumor-infiltrating lymphocytes and epidermal γδ T cells. Collectively, these data show multiple strategies that can result in a synergized NK and γδ T cell antitumor response. In the light of recent developments of low-toxicity allo-HSCT platforms, these interventions may contribute to the prevention of early relapse.

Tetraspecific scFv construct provides NK cell mediated ADCC and self-sustaining stimuli via insertion of IL-15 as a cross-linker

BACKGROUND

The design of a highly effective anti-cancer immune-engager would include targeting of highly drug refractory cancer stem cells (CSC). The design would promote effective antibody-dependent cell-mediated cytotoxicity (ADCC) and simultaneously promote costimulation to expand and self-sustain the effector NK cell population. Based on our bispecific NK cell engager platform we constructed a tetraspecific killer engager (TetraKE) comprising single-chain variable fragments (scFvs) binding FcγRIII (CD16) on NK cells, EpCAM on carcinoma cells and CD133 on cancer stem cells in order to promote ADCC. Furthermore, an Interleukin (IL)-15-crosslinker enhanced NK cell related proliferation resulting in a highly active drug termed 1615EpCAM133.

RESULTS

Proliferation assays showed TetraKE promoted proliferation and enhanced NK cell survival. Drug-target binding, NK cell related degranulation, and IFN-γ production was specific for both tumor related antigens in EpCAM and CD133 bearing cancer cell lines. The TetraKE showed higher killing activity and superior dose dependent degranulation. Cytokine profiling showed a moderately enhanced IFN-γ production, enhanced GM-CSF production, but no evidence of induction of excessive cytokine release.

METHODS

Assembly and synthesis of hybrid genes encoding the TetraKE were performed using DNA shuffling and ligation. The TetraKE was tested for efficacy, specificity, proliferation, survival, and cytokine production using carcinoma cell lines and functional assays measuring NK cell activity.

CONCLUSION

1615EpCAM133 combines improved induction of ADCC with enhanced proliferation, limited cytokine response, and prolonged survival and proliferation of NK cells. By linking scFv-related targeting of carcinoma and CSCs with a sustaining IL-15 signal, our new construct shows great promise to target cancer and CSCs.

Heterodimeric Bispecific Single Chain Variable Fragments (scFv) Killer Engagers (BiKEs) Enhance NK-cell Activity Against CD133+ Colorectal Cancer Cells

BACKGROUND

Natural killer (NK) cells are potent cytotoxic lymphocytes that play a critical role in tumor immunosurveillance and control. Cancer stem cells (CSC) initiate and sustain tumor cell growth, mediate drug refractory cancer relapse, and express the well-known surface marker CD133.

METHODS

DNA fragments from two fully humanized single chain fragment variable (scFv) antibodies recognizing CD16 on NK-cells and CD133 on CSC were genetically spliced forming a novel drug, 16 × 133 BiKE that simultaneously recognizes these antigens to facilitate an immunologic synapse. The anti-CD133 was created using a fusion protein prepared by fusing DNA fragments encoding the two extracellular domains of CD133. Immunization of mice with the resulting fusion protein generated a unique antibody that recognized the molecular framework and was species cross-reactive.

RESULTS

In vitro chromium-51 ((51)Cr) release cytotoxicity assays at both high and low effector:target ratios demonstrated the ability of the heterodimeric biological drug to greatly enhance NK-cell killing of human Caco-2 colorectal carcinoma cells known to overexpress CD133. The tumor associated antigen specificity of the drug for CD133 even enhanced NK-cell cytotoxicity against the NK-resistant human Burkitt's lymphoma Daudi cell line, which has less than 5 % CD133 surface expression. Flow cytometry analysis revealed increases in NK-cell degranulation and Interferon-γ production upon co-culture with Caco-2 targets in the presence of the drug.

CONCLUSION

These studies demonstrate that the innate immune system can be effectively recruited to kill CSC using bispecific antibodies targeting CD133 and that this anti-CD133 scFv may be useful in this bispecific platform or perhaps in the design of more complex trispecific molecules for carcinoma therapy.

Natural killer cells unleashed: Checkpoint receptor blockade and BiKE/TriKE utilization in NK-mediated anti-tumor immunotherapy

Natural killer (NK) cells have long been known to mediate anti-tumor responses without prior sensitization or recognition of specific tumor antigens. However, the tumor microenvironment can suppress NK cell function resulting in tumor escape and disease progression. Despite recent advances in cytokine therapy and NK cell adoptive transfer, tumor expression of ligands to NK - expressed checkpoint receptors can still suppress NK mediated tumor lysis. This review will explore many of the checkpoint receptors tumors utilize to manipulate the NK cell response as well as some of the current and upcoming pharmacological solutions to limit tumor suppression of NK cell function. Furthermore, we will discuss the potential to use these drugs in combinational therapies with novel antibody reagents such as bi- and tri-specific killer engagers (BiKEs and TriKEs) against tumor-specific antigens to enhance NK cell-mediated tumor rejection.

Safe and Effective Sarcoma Therapy through Bispecific Targeting of EGFR and uPAR

Sarcomas differ from carcinomas in their mesenchymal origin. Therapeutic advancements have come slowly, so alternative drugs and models are urgently needed. These studies report a new drug for sarcomas that simultaneously targets both tumor and tumor neovasculature. eBAT is a bispecific angiotoxin consisting of truncated, deimmunized Pseudomonas exotoxin fused to EGF and the amino terminal fragment of urokinase. Here, we study the drug in an in vivo "ontarget" companion dog trial as eBAT effectively kills canine hemangiosarcoma and human sarcoma cells in vitro We reasoned the model has value due to the common occurrence of spontaneous sarcomas in dogs and a limited lifespan allowing for rapid accrual and data collection. Splenectomized dogs with minimal residual disease were given one cycle of eBAT followed by adjuvant doxorubicin in an adaptive dose-finding, phase I-II study of 23 dogs with spontaneous, stage I-II, splenic hemangiosarcoma. eBAT improved 6-month survival from <40% in a comparison population to approximately 70% in dogs treated at a biologically active dose (50 μg/kg). Six dogs were long-term survivors, living >450 days. eBAT abated expected toxicity associated with EGFR targeting, a finding supported by mouse studies. Urokinase plasminogen activator receptor and EGFR are targets for human sarcomas, so thorough evaluation is crucial for validation of the dog model. Thus, we validated these markers for human sarcoma targeting in the study of 212 human and 97 canine sarcoma samples. Our results support further translation of eBAT for human patients with sarcomas and perhaps other EGFR-expressing malignancies. Mol Cancer Ther; 16(5); 956-65. ©2017 AACR.

Evaluation of 18-F-fluoro-2-deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) as a staging and monitoring tool for dogs with stage-2 splenic hemangiosarcoma - A pilot study

Positron Emission Tomography-Computed Tomography (PET-CT) is routinely used for staging and monitoring of human cancer patients and is becoming increasingly available in veterinary medicine. In this study, 18-fluorodeoxyglucose (18FDG)-PET-CT was used in dogs with naturally occurring splenic hemangiosarcoma (HSA) to assess its utility as a staging and monitoring modality as compared to standard radiography and ultrasonography. Nine dogs with stage-2 HSA underwent 18FDG-PET-CT following splenectomy and prior to commencement of chemotherapy. Routine staging (thoracic radiography and abdominal ultrasonography) was performed prior to 18FDG-PET-CT in all dogs. When abnormalities not identified on routine tests were noted on 18FDG-PET-CT, owners were given the option to repeat a PET-CT following treatment with eBAT. A PET-CT scan was repeated on Day 21 in three dogs. Abnormalities not observed on conventional staging tools, and most consistent with malignant disease based on location, appearance, and outcome, were detected in two dogs and included a right atrial mass and a hepatic nodule, respectively. These lesions were larger and had higher metabolic activity on the second scans. 18FDG-PET-CT has potential to provide important prognostic information and influence treatment recommendations for dogs with stage-2 HSA. Additional studies will be needed to precisely define the value of this imaging tool for staging and therapy monitoring in dogs with this and other cancers.

Engineering of Anti-CD133 Trispecific Molecule Capable of Inducing NK Expansion and Driving Antibody-Dependent Cell-Mediated Cytotoxicity

Purpose

The selective elimination of cancer stem cells (CSCs) in tumor patients is a crucial goal because CSCs cause drug refractory relapse. To improve the current conventional bispecific immune-engager platform, a 16133 bispecific natural killer (NK) cell engager (BiKE), consisting of scFvs binding FcγRIII (CD16) on NK cells and CD133 on carcinoma cells, was first synthesized and a modified interleukin (IL)-15 crosslinker capable of stimulating NK effector cells was introduced.

Materials and Methods

DNA shuffling and ligation techniques were used to assemble and synthesize the 1615133 trispecific NK cell engager (TriKE). The construct was tested for its specificity using flow cytometry, cytotoxic determinations using chromium release assays, and lytic degranulation. IL-15–mediated expansion was measured using flow-based proliferation assays. The level of interferon (IFN)-γ release was measured because of its importance in the anti-cancer response.

Results

1615133 TriKE induced NK cell–mediated cytotoxicity and NK expansion far greater than that achieved with BiKE devoid of IL-15. The drug binding and induction of cytotoxic degranulation was CD133⁺ specific and the anti-cancer activity was improved by integrating the IL-15 cross linker. The NK cell–related cytokine release measured by IFN-γ detection was higher than that of BiKE. NK cytokine release studies showed that although the IFN-γ levels were elevated, they did not approach the levels achieved with IL-12/IL-18, indicating that release was not at the supraphysiologic level.

Conclusion

1615133 TriKE enhances the NK cell anti-cancer activity and provides a self-sustaining mechanism via IL-15 signaling. By improving the NK cell performance, the new TriKE represents a highly active drug against drug refractory relapse mediated by CSCs.

Abstract 1493: Improvement of the bispecific antibody ADCC platform by genetic insertion of IL-15 as a cross-linker to create NK cell reactive TriKEs

Natural killer (NK)-cell related anti-tumor surveillance is limited by the ability of the tumor to escape killing. Previously, we constructed a bispecific NK-cell engager (BiKE) consisting of two scFV against CD16 (FcγRIII) on NK cells and EpCAM on tumor cells (EpCAM16). Epithelial cell adhesion molecule (EpCAM) is a transmembrane protein with prevalent expression on carcinomas making it a valuable marker for cancer targeting. This BiKE facilitated ADCC and tumor elimination, but did not account for the cellular expansion required for the success of T CARs. To improve this, we incorporated a modified interleukin (IL)-15 crosslinker to create a trispecific construct (TriKE) to enhance activation, proliferation, and to prolong survival of NK-cells. IL-15 was chosen since it is an established immunostimulatory cytokine with known effects on NK cells and is recognized as a promising cancer cure drug in NIH guided review. TriKE was assembled, expressed in E.coli, extracted, refolded, and purified to &gt;90% with a molecular weight of 68,860 daltons. To determine the functional activity of 1615EpCAM, its killing ability was measured in standard Cr-51 release assays with EpCAM+ HT-29 colorectal cancer cells. The 1615EpCAM TriKE induced the highest level of killing compared to BiKE and other controls. To determine if the effect of IL-15 in the drug correlated with NK-cell levels, donors were selected with different naturally occurring NK cell levels. Freshly isolated PBMCs were added to HT-29 cells at E:T ratios of 20:1, 6.6:1, and 2:1. Donors showed increasingly higher levels of Cr-51 kill with TriKE, but not with BiKE indicating that greater the presence of NK-cells, the greater the TriKE effect. In order to study lytic degranulation as a function of NK-cell activity, CD107a expression was measured. Cells treated with TriKE showed significantly elevated degranulation when co-cultivated with targets (p&lt;0.001) compared to BiKE. IL-15 alone did not enhance lytic degranulation. When PBMC were exposed to TriKE, only NK-cells, but not T-cells showed a proliferation specific pattern. Direct comparison of the BiKE and the TriKE showed that the TriKE had the ability to induce proliferation and expansion, the BiKE did not. Only with TriKE or IL-15 exposure was there a significantly enhanced expansion index. IFN-γ production from the same CD56+/CD3- NK-cell population was enhanced by 1615EpCAM, but levels did not approach levels seen with the IL12/IL18 combination that is known to stimulate cytokine production at supraphysiologic levels. We believe that this is a platform technology since anti-CD133 also can be substituted for anti-EpCAM to create functional anti-cancer stem cell TriKEs. These results indicate that we have successfully developed an immune engager that simultaneously mediates ADCC and also provides a self-sustaining costimulatory signal inducing NK effector cell expansion.

Citation Format: Daniel A. Vallera, Joerg U. Schmohl, Martin Felices, Jeffrey S. Miller. Improvement of the bispecific antibody ADCC platform by genetic insertion of IL-15 as a cross-linker to create NK cell reactive TriKEs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1493.

CD16-IL15-CD33 Trispecific Killer Engager (TriKE) induces NK cell expansion, persistence, and myeloid blast antigen specific killing

NK cell infusions induce complete remissions in 30–50% of patients with refractory AML when combined with lymphodepleting chemotherapy and IL-2. NK cell therapy is limited by lack of antigen specificity and by IL-2 mediated induction of Tregs. To overcome these limitations we developed a 161533 trispecific killer engager (TriKE) molecule containing an anti-CD16 scFv, to engage NK cells, an anti-CD33 scFv, to engage AML targets, and an IL-15 molecule. We have shown previously that a 1633 bispecific killer engager (BiKE) is capable of creating an immunologic synapse between NK cells and AML targets leading to target killing. These molecules generate higher affinity interactions than natural CD16 binding to Fc portions of therapeutic antibodies, resulting in increased NK cell functionality. Addition of IL-15 in the TriKE molecule is meant to enhance NK cell priming, proliferation, and maintenance without inducing Tregs. Cytotoxicity assays and cytokine secretion assessment of NK cells incubated with CD33+ HL-60 target cells indicated that the TriKE induced greater NK cell activation than the BiKE or no molecule control. The TriKE was able to induce potent NK cell proliferation and survival when compared to the BiKE. Interestingly, when compared to recombinant IL-15 the TriKE induced less proliferation of T cells while inducing similar proliferation of NK cells from healthy donors, indicating specificity. The TriKE was capable of rescuing NK cell function of post-transplant patients. In vivo functionality was tested in an NSG xenogeneic model engrafted with HL-60-luc targets and NK cells. TriKE treatment resulted in reduced tumor burden and NK cell maintenance at day 21, displaying the immunotherapeutic potential of the molecule.

IL15 Trispecific Killer Engagers (TriKE) Make Natural Killer Cells Specific to CD33+ Targets While Also Inducing Persistence, In Vivo Expansion, and Enhanced Function

PURPOSE

The effectiveness of NK cell infusions to induce leukemic remission is limited by lack of both antigen specificity and in vivo expansion. To address the first issue, we previously generated a bispecific killer engager (BiKE) containing single-chain scFv against CD16 and CD33 to create an immunologic synapse between NK cells and CD33(+) myeloid targets. We have now incorporated a novel modified human IL15 crosslinker, producing a 161533 trispecific killer engager (TriKE) to induce expansion, priming, and survival, which we hypothesize will enhance clinical efficacy.

EXPERIMENTAL DESIGN

Reagents were tested in proliferation and functional assays and in an in vivo xenograft model of AML.

RESULTS

When compared with the 1633 BiKE, the 161533 TriKE induced superior NK cell cytotoxicity, degranulation, and cytokine production against CD33(+) HL-60 targets and increased NK survival and proliferation. Specificity was shown by the ability of a 1615EpCAM TriKE to kill CD33-EpCAM(+) targets. Using NK cells from patients after allogeneic stem cell transplantation when NK cell function is defective, the 161533 TriKE restored potent NK function against primary AML targets and induced specific NK cell proliferation. These results were confirmed in an immunodeficient mouse HL-60-Luc tumor model where the 161533 TriKE exhibited superior antitumor activity and induced in vivo persistence and survival of human NK cells for at least 3 weeks.

CONCLUSIONS

Off-the-shelf 161533 TriKE imparts antigen specificity and promotes in vivo persistence, activation, and survival of NK cells. These qualities are ideal for NK cell therapy of myeloid malignancies or targeting antigens of solid tumors. Clin Cancer Res; 22(14); 3440-50. ©2016 AACRSee related commentary by Talmadge, p. 3419.

Phase I study of a bispecific ligand-directed toxin targeting CD22 and CD19 (DT2219) for refractory B-cell malignancies

PURPOSE

The novel bispecific ligand-directed toxin (BLT) DT2219 consists of a recombinant fusion between the catalytic and translocation enhancing domain of diphtheria toxin (DT) and bispecific single-chain variable fragments (scFV) of antibodies targeting human CD19 and CD22. We conducted a phase I dose-escalation study to assess the safety, maximum tolerated dose, and preliminary efficacy of DT2219 in patients with relapsed/refractory B-cell lymphoma or leukemia.

EXPERIMENTAL DESIGN

DT2219 was administered intravenously over 2 hours every other day for 4 total doses. Dose was escalated from 0.5 μg/kg/day to 80 μg/kg/day in nine dose cohorts until a dose-limiting toxicity (DLT) was observed.

RESULTS

Twenty-five patients with mature or precursor B-cell lymphoid malignancies expressing CD19 and/or CD22 enrolled to the study. Patients received median 3 prior lines of chemotherapy and 8 failed hematopoietic transplantation. All patients received a single course of DT2219; one patient was retreated. The most common adverse events, including weight gain, low albumin, transaminitis, and fever were transient grade 1-2 and occurred in patients in higher dose cohorts (≥40 μg/kg/day). Two subjects experienced DLT at dose levels 40 and 60 μg/kg. Durable objective responses occurred in 2 patients; one was complete remission after 2 cycles. Correlative studies showed a surprisingly low incidence of neutralizing antibody (30%).

CONCLUSIONS

We have determined the safety of a novel immunotoxin DT2219 and established its biologically active dose between 40 and 80 μg/kg/day ×4. A phase II study exploring repetitive courses of DT2219 is planned.

Generation of BiKEs and TriKEs to Improve NK Cell-Mediated Targeting of Tumor Cells

Cancer immunotherapies have gained significant momentum over the past decade, particularly with the advent of checkpoint inhibitors and CAR T-cells. While the latter personalized targeted immunotherapy has revolutionized the field, a need for off-the-shelf therapies remains. The ability of NK cells to quickly lyse antibody-coated tumors and potently secrete cytokines without prior priming has made NK cells ideal candidates for antigen-specific immunotherapy. NK cells have been targeted to tumors through two main strategies: mono-specific antibodies and bi/tri-specific antibodies. Mono-specific antibodies drive NK cell antibody-dependent cell-mediated cytotoxicity (ADCC) of tumor cells. Bi/tri-specific antibodies drive re-directed lysis of tumor cells through binding of a tumor antigen and direct binding and crosslinking of the CD16 receptor on NK cells, thus bypassing the need for binding of the Fc portion of mono-specific antibodies. This chapter focuses on the generation of bi- and tri-specific killer engagers (BiKEs and TriKEs) meant to target NK cells to tumors. BiKEs and TriKEs are smaller molecules composed of 2-3 variable portions of antibodies with different specificities, and represent a novel and more versatile strategy compared to traditional bi- and tri-specific antibody platforms.

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.

Immunotoxin targeting CD133(+) breast carcinoma cells

CD133 expression enriches for tumor-initiating cells and is a negative prognostic factor in numerous cancers. We previously developed an immunotoxin against CD133 by fusing a gene fragment encoding the scFv portion of an anti-CD133 antibody to a gene fragment encoding deimmunized PE38KDEL. The resulting fusion protein, dCD133KDEL, demonstrated potent antitumor activity following intratumoral delivery into head neck cell carcinoma xenografts. However, the efficacy against other tumors and the tolerability of systemic administration remained unclear. The purpose of this study was to evaluate the tolerability and efficacy of dCD133KDEL in a systemic human breast carcinoma model. Time course viability studies showed that dCD133KDEL selectively inhibited MDA-MB-231 ductal breast carcinoma cells that contained a minority CD133(+) subpopulation, implicating CD133(+) cells as a source for self-renewal within this cell line. Furthermore, systemic administration of dCD133KDEL caused regression or inhibition of tumor growth in mice bearing an intrasplenic MDA-MB-231 tumor challenge as a model for metastatic disease. In the same model, combined therapy with dCD133KDEL and another immunotoxin designed to target the bulk tumor mass was the most effective therapy, supporting the idea that such combination therapies might better address tumor heterogeneity. dCD133KDEL shows promise as a therapeutic agent and as a biologic tool to study cancer stem cells.

Identification and characterization of a novel scFv recognizing human and mouse CD133

CD133, also known as Prominin-1, is expressed on stem cells present in many tissues and tumors. In this work, we have identified and characterized a single-chain variable fragment (scFv) for the efficient and specific recognition of CD133. Phage display was used to develop the scFv from a previously reported anti-CD133 hybridoma clone 7, which was capable of recognizing both glycosylated and non-glycosylated forms of human CD133. The scFv immunostained CD133(+) Caco-2 cells, but not CD133(-/low) U87 cells. Significantly, it immunostained CD133(-) cells transiently transfected with the mouse CD133 gene as well as CD133(+) mouse cells. Co-immunostaining studies in mouse bone marrow cells, using anti-CD133 scFv-FITC and anti-mouse CD133-PE (clone 13A4) commercial antibody, indicated that the epitopes recognized by these reagents partially overlap. Taken together, these results suggest that the scFv can recognize mouse CD133 protein in addition to recognizing human CD133. This new scFv is expected to be valuable both as a molecular diagnostic reagent for identifying CD133(+) cells and as a ligand for targeting therapeutics to CD133(+) tumor-initiating cells.

A bispecific EpCAM/CD133-targeted toxin is effective against carcinoma

The discovery of chemoresistant cancer stem cells (CSCs) in carcinomas has created the need for therapies that specifically target these subpopulations of cells. Here, we characterized a bispecific targeted toxin that is composed of two antibody fragments and a catalytic protein toxin allowing it to bind two CSC markers on the same cell killing this resistant subpopulation. CD133 is a well-known CSC marker and has been successfully targeted and caused regression of head and neck squamous cell carcinoma (HNSCC) in vivo. To enable it to bind a broader range of CSCs, an anti-epithelial cell adhesion molecule (EpCAM) scFv was added to create dEpCAMCD133KDEL, a deimmunized bispecific targeted toxin on a single amino acid chain. This bispecific potently inhibited protein translation and proliferation in vitro in three different types of carcinoma. Furthermore, in a CSC spheroid model dEpCAMCD133KDEL eliminated Mary-X spheroids, an inflammatory breast carcinoma. Finally, this bispecific also caused tumor regression in an in vivo model of HNSCC. This represents the first bispecific CSC-targeted toxin and warrants further development as a possible therapy for carcinoma.

Diphtheria toxin-based targeted toxin therapy for brain tumors

Targeted toxins (TT) are molecules that bind cell surface antigens or receptors such as the transferrin or interleukin-13 receptor that are overexpressed in cancer. After internalization, the toxin component kills the cell. These recombinant proteins consist of an antibody or carrier ligand coupled to a modified plant or bacterial toxin such as diphtheria toxin (DT). These fusion proteins are very effective against brain cancer cells that are resistant to radiation therapy and chemotherapy. TT have shown an acceptable profile for toxicity and safety in animal studies and early clinical trials have demonstrated a therapeutic response. This review summarizes the characteristics of DT-based TT, the animal studies in malignant brain tumors and early clinical trial results. Obstacles to the successful treatment of brain tumors include poor penetration into tumor, the immune response to DT and cancer heterogeneity.

Targeting natural killer cells to acute myeloid leukemia in vitro with a CD16 x 33 bispecific killer cell engager and ADAM17 inhibition

PURPOSE

The graft versus leukemia effect by natural killer (NK) cells prevents relapse following hematopoietic stem cell transplantation. We determined whether a novel bispecific killer cell engager (BiKE) signaling through CD16 and targeting CD33 could activate NK cells at high potency against acute myelogenous leukemia (AML) targets.

EXPERIMENTAL DESIGN

We investigated the ability of our fully humanized CD16 × CD33 (CD16 × 33) BiKE to trigger in vitro NK cell activation against HL60 (CD33(+)), RAJI (CD33(-)), and primary AML targets (de novo and refractory) to determine whether treatment with CD16 × 33 BiKE in combination with an ADAM17 inhibitor could prevent CD16 shedding (a novel inhibitory mechanism induced by NK cell activation) and overcome inhibition of class I MHC recognizing inhibitory receptors.

RESULTS

NK cell cytotoxicity and cytokine release were specifically triggered by the CD16 × 33 BiKE when cells were cultured with HL60 targets, CD33(+) de novo and refractory AML targets. Combination treatment with CD16 × 33 BiKE and ADAM17 inhibitor resulted in inhibition of CD16 shedding in NK cells, and enhanced NK cell activation. Treatment of NK cells from double umbilical cord blood transplant (UCBT) recipients with the CD16 × 33 BiKE resulted in activation, especially in those recipients with cytomegalovirus reactivation.

CONCLUSION

CD16 × 33 BiKE can overcome self-inhibitory signals and effectively elicit NK cell effector activity against AML. These in vitro studies highlight the potential of CD16 × 33 BiKE ± ADAM17 inhibition to enhance NK cell activation and specificity against CD33(+) AML, which optimally could be applied in patients with relapsed AML or for adjuvant antileukemic therapy posttransplantation.

Hemangiosarcoma and its cancer stem cell subpopulation are effectively killed by a toxin targeted through epidermal growth factor and urokinase receptors

Targeted toxins have the potential to overcome intrinsic or acquired resistance of cancer cells to conventional cytotoxic agents. Here, we hypothesized that EGFuPA-toxin, a bispecific ligand-targeted toxin (BLT) consisting of a deimmunized Pseudomonas exotoxin (PE) conjugated to epidermal growth factor and urokinase, would efficiently target and kill cells derived from canine hemangiosarcoma (HSA), a highly chemotherapy resistant tumor, as well as cultured hemangiospheres, used as a surrogate for cancer stem cells (CSC). EGFuPA-toxin showed cytotoxicity in four HSA cell lines (Emma, Frog, DD-1 and SB) at a concentration of ≤100 nM, and the cytotoxicity was dependent on specific ligand-receptor interactions. Monospecific targeted toxins also killed these chemoresistant cells; in this case, a "threshold" level of EGFR expression appeared to be required to make cells sensitive to the monospecific EGF-toxin, but not to the monospecific uPA-toxin. The IC₅₀ of CSCs was higher by approximately two orders of magnitude as compared to non-CSCs, but these cells were still sensitive to EGFuPA-toxin at nanomolar (i.e., pharmacologically relevant) concentrations, and when targeted by EGFuPA-toxin, resulted in death of the entire cell population. Taken together, our results support the use of these toxins to treat chemoresistant tumors such as sarcomas, including those that conform to the CSC model. Our results also support the use of companion animals with cancer for further translational development of these cytotoxic molecules.

Heterodimeric bispecific single-chain variable-fragment antibodies against EpCAM and CD16 induce effective antibody-dependent cellular cytotoxicity against human carcinoma cells

A heterodimeric bispecific biological recombinant drug was synthesized by splicing DNA fragments from two fully humanized single-chain variable-fragment (scFV) antibody fragments forming a novel drug simultaneously recognizing the CD16 natural killer (NK) cell marker and the cancer marker epithelial cell adhesion molecule (EpCAM). The drug precipitously enhanced the killing of human carcinomas of the prostate, breast, colon, head, and neck even at very low effector:target ratios. The drug EpCAM16 rendered even nonactivated NK cell-proficient killers and activated them to kill via degranulation and cytokine production. Studies show that bispecific antibodies can be used to induce proficient killing of the carcinoma targets that ordinarily are resistant to NK-mediated killing. Apparently, the innate immune system can be effectively recruited to kill cancer cells using the bispecific antibody platform and EpCAM targeting.

Bispecific and trispecific killer cell engagers directly activate human NK cells through CD16 signaling and induce cytotoxicity and cytokine production

This study evaluates the mechanism by which bispecific and trispecific killer cell engagers (BiKEs and TriKEs) act to trigger human natural killer (NK) cell effector function and investigates their ability to induce NK cell cytokine and chemokine production against human B-cell leukemia. We examined the ability of BiKEs and TriKEs to trigger NK cell activation through direct CD16 signaling, measuring intracellular Ca²⁺ mobilization, secretion of lytic granules, induction of target cell apoptosis, and production of cytokine and chemokines in response to the Raji cell line and primary leukemia targets. Resting NK cells triggered by the recombinant reagents led to intracellular Ca²⁺ mobilization through direct CD16 signaling. Coculture of reagent-treated resting NK cells with Raji targets resulted in significant increases in NK cell degranulation and target cell death. BiKEs and TriKEs effectively mediated NK cytotoxicity of Raji targets at high and low effector-to-target ratios and maintained functional stability after 24 and 48 hours of culture in human serum. NK cell production of IFN-γ, TNF-α, granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-8, macrophage inflammatory protein (MIP)-1α, and regulated and normal T cell expressed and secreted (RANTES) was differentially induced in the presence of recombinant reagents and Raji targets. Moreover, significant increases in NK cell degranulation and enhancement of IFN-γ production against primary acute lymphoblastic leukemia and chronic lymphocytic leukemia targets were induced with reagent treatment of resting NK cells. In conclusion, BiKEs and TriKEs directly trigger NK cell activation through CD16, significantly increasing NK cell cytolytic activity and cytokine production against tumor targets, showing their therapeutic potential for enhancing NK cell immunotherapies for leukemias and lymphomas.

Bispecific targeting of EGFR and uPAR in a mouse model of head and neck squamous cell carcinoma

OBJECTIVES

To investigate the efficacy of the bispecific targeted toxin, dEGFATFKDEL, on head and neck carcinoma cell lines in vitro and in vivo.

MATERIALS AND METHODS

A deimmunized bispecific anti-cancer agent was constructed to simultaneously target both the overexpressed EGF receptor on carcinomas and the urokinase receptor (uPAR), that is found on the endothelial cells of the neovasculature within tumors. Flow cytometry assays were performed to determine the level of EGFR expressed on a variety of carcinoma lines. These lines were then tested in tritiated leucine incorporation assays to determine the efficacy of dEGFATFKDEL. Human vein endothelial primary cells were also tested to determine the effectiveness of the ATF portion of the molecule that binds uPAR. Furthermore, mouse studies were performed to determine whether dEGFATFKDEL was effective at inhibiting tumor growth in vivo.

RESULTS

UMSCC-11B and NA, two head and neck squamous cell carcinomas, highly expressed EGFR. Both the carcinoma lines and the human vein endothelial cells were inhibited at sub-nanomolar concentrations by dEGFATFKDEL. The tumor studies showed that the tumors treated with dEGFATFKDEL were significantly inhibited whereas the negative control and untreated tumors progressed. In a separate in vivo study involving another carcinoma line, MDA-MB-231, the effectiveness of dEGFATFKDEL was confirmed. No toxicity was seen at the doses used in either of these mouse studies.

CONCLUSIONS

This bispecific agent is effective in a mouse model of head and neck squamous cell carcinoma. Further study of this reagent for use in the treatment of carcinomas is warranted.

Intracerebral infusion of the bispecific targeted toxin DTATEGF in a mouse xenograft model of a human metastatic non-small cell lung cancer

The aim of this study is to investigate the anti-cancer effect of the bispecific diphtheria toxin (DT) based immunotoxin DTATEGF, which targets both the epidermal growth factor (EGF) receptor (EGFR) and the urokinase-type plasminogen activator (uPA) receptor (uPAR) in vitro and in vivo when delivered by convection-enhanced delivery (CED) via an osmotic minipump in a human metastatic non-small cell lung cancer (NSCLC) brain tumor mouse xenograft model. The effects of the bispecific immunotoxin DTATEGF, and monospecific DTAT, DTEGF and control DT at various concentrations were tested for their ability to inhibit the proliferation of human metastatic NSCLC PC9-BrM3 cells in vitro by MTT assay. A xenograft model of human metastatic NSCLC intracranial model was established in nude mice using the human NSCLC PC9-BrM3 cell line genetically marked with a firefly luciferase reporter gene. One microgram of DTATEGF in the treatment group or control DT in the control group was delivered intracranially by CED via an osmotic minipump. The bioluminescent imaging (BLI) was performed at day 7, 14, 1 month, 2 months, and 3 months. Kaplan-Meier survival curves for the two groups were generated. The brain tissue samples were stained by hematoxylin and eosin for histopathological assessment. In vitro, DTATEGF could selectively kill PC9-BrM3 cells and showed an IC(50) less than 0.001 nM, representing a more than 100- to 1000-fold increase in activity as compared to monospecific DTAT and DTEGF. In vivo, mice with tumors were treated intracranially with drug via CED where the results showed the treatment was successful in providing a survival benefit with the median survival of mice treated with DTATEGF being significantly prolonged relative to controls (87 vs. 63 days, P = 0.006). The results of these experiments indicate that DTATEGF kills the NSCLC PC9-BrM3 cell line in vitro, and when it is delivered via CED intracranially, it is highly efficacious against metastatic NSCLC brain tumors. DTATEGF is a safe and effective drug where further preclinical and clinical development is warranted for the management of metastatic brain tumors.

Targeting tumor-initiating cancer cells with dCD133KDEL shows impressive tumor reductions in a xenotransplant model of human head and neck cancer

A novel anticancer agent was constructed by fusing a gene encoding the scFV that targets both glycosylated and unglycosylated forms of CD133 to a gene fragment encoding deimmunized PE38KDEL. The resulting fusion protein, dCD133KDEL, was studied to determine its ability to bind and kill tumor-initiating cells in vitro and in vivo. The anti-CD133 scFV selectively bound HEK293 cells transfected with the CD133 receptor gene. Time course viability studies showed that dCD133KDEL selectively inhibited NA-SCC and UMSCC-11B, 2 head and neck squamous cell carcinomas that contain a CD133 expressing subpopulation. Importantly, the drug did not inhibit the viability of hematopoietic lineages measured by long-term culture-initiating cell and colony-forming assays from sorted human CD34+ progenitor cells. In addition to in vitro studies, in vivo tumor initiation experiments confirmed that CD133-sorted cells implanted into the flanks of nude mice grew faster and larger than unsorted cells. In contrast, cells that were pretreated with dCD133KDEL before implantation showed the slowest and lowest incidence of tumors. Furthermore, UMSCC-11B-luc tumors treated with multiple intratumoral injections of dCD133KDEL showed marked growth inhibition, leading to complete degradation of the tumors that was not observed with an irrelevant control-targeted toxin. Experiments in immunocompetent mice showed that toxin deimmunization resulted in a 90% reduction in circulating antitoxin levels. These studies show that dCD133KDEL is a novel anticancer agent effective at inhibiting cell proliferation, tumor initiation, and eliminating established tumors by targeting the CD133 subpopulation. This agent shows significant promise for potential development as a clinically useful therapy.

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.

Evaluation of a bispecific biological drug designed to simultaneously target glioblastoma and its neovasculature in the brain

OBJECT

The authors of this study aimed to genetically design a bispecific targeted toxin that would simultaneously target overexpressed markers on glioma as well as the tumor vasculature, to mutate certain amino acids to reduce the immunogenicity of this new drug, and to determine whether the drug was able to effectively reduce aggressive human brain tumors in a rat xenograft model via a novel hollow fiber (HF) catheter delivery system.

METHODS

A new bispecific ligand-directed toxin (BLT) was created in which 2 human cytokines-epidermal growth factor ([EGF], targeting overexpressed EGF receptor) and amino acid terminal fragment ([ATF], targeting urokinase plasminogen activator receptor)-were cloned onto the same single-chain molecule with truncated Pseudomonas exotoxin with a terminal lysyl-aspartyl-glutamyl-leucine (KDEL) sequence. Site-specific mutagenesis was used to mutate amino acids in 7 key epitopic toxin regions that dictate the B cell generation of neutralizing antitoxin antibodies to deimmunize the drug, now called "EGFATFKDEL 7mut." Bioassays were used to determine whether mutation reduced the drug's potency, and enzyme-linked immunosorbent assay studies were performed to determine whether antitoxin antibodies were decreased. Aggressive brain tumors were intracranially established in nude rats by using human U87 glioma genetically marked with a firefly luciferase reporter gene (U87-luc), and the rats were stereotactically treated with 2 intracranial injections of deimmunized EGFATFKDEL via convection-enhanced delivery (CED). Drug was administered through a novel HF catheter to reduce drug backflow upon delivery.

RESULTS

In vitro, EGFATFKDEL 7mut selectively killed the human glioblastoma cell line U87-luc as well as cultured human endothelial cells in the form of the human umbilical vein endothelial cells. Deimmunization did not reduce drug activity. In vivo, when rats with brain tumors were intracranially treated with drug via CED and a novel HF catheter to reduce backflow, there were significant tumor reductions in 2 experiments (p < 0.01). Some rats survived with a tumor-free status until 130 days post-tumor inoculation. An irrelevant BLT control did not protect establishing specificity. The maximal tolerated dose of EGFATFKDEL 7mut was established at 2 μg/injection or 8.0 μg/kg, and data indicated that this dose was nontoxic. Antitoxin antibodies were reduced by at least 90%.

CONCLUSIONS

First, data indicated that the BLT framework is effective for simultaneously targeting glioma and its neovasculature. Second, in the rodent CED studies, newly developed HF catheters that limit backflow are effective for drug delivery. Third, by mutating critical amino acids, the authors reduced the threat of the interference of neutralizing antibodies that are generated against the drug. The authors' experiments addressed some of the most urgent limitations in the targeted toxin field.

Chemically self-assembled antibody nanorings (CSANs): design and characterization of an anti-CD3 IgM biomimetic

A number of clever recombinant methodologies have been developed that recapitulate the valencies of IgG's (bivalent) and IgA's (tetravalent). Although higher synthetic valencies have been achieved by conjugation of either monoclonal antibodies or single-chain antibodies to nanoparticles and liposomes, a method for the preparation of recombinant antibodies with valencies similar to IgM's (decavalent) but considerably less than what is generally found after antibody particle conjugation has yet to be devised. Recently, we have developed a methodology for the design of bivalent Chemically Self-Assembled Antibody Nanorings (CSANs). We now report the crystal structure of the nanoring subunit composed of the E. coli DHFR dimer and a methotrexate dimerizer (MTX2-C9) containing a visible nine methylene linker and a protocol for the preparation of CSANs from this subunit with valencies similar to IgM's, ranging from 8-10 single chain antibodies (scFvs). The multivalent CSANs were reversibly assembled from a fusion protein dihydrofolate reductase (DHFR)-DHFR-antiCD3 scFv containing a single glycine linker between the two DHFR scaffolding proteins. We also demonstrate that, similar to the parental bivalent anti-CD3 monoclonal antibody (mAB), anti-CD3 CSANs selectively bind to CD3+ leukemia cells and undergo rapid internalization through a caveolin-independent pathway that requires cholesterol, actin polymerization, and protein tyrosine kinase activation. While treatment with the monoclonal antibody leads to T-cell activation and nearly complete loss (i.e., 90%) of the surface displayed T-cell receptor (TCR), only 25-30% of the TCR down regulate and no significant T-cell proliferation is observed after treatment of peripheral blood mononuclear cells (PBMCs) with anti-CD3 CSANs. Consistent with the proliferation findings, 15-25% less CD25 (IL-2 receptor) was found on the surface of PBMCs treated with either the polyvalent or bivalent anti-CD3 CSANs, respectively, than on PBMCs treated with the parental mAB. Comparative experiments with F(ab')2 derived from the mAB confirm that the activation of the T-cells by the mAB is dependent on the Fc domain, and thus interactions of the PBMC T-cells with accessory cells, such as macrophages. Taken together, our results demonstrate that anti-CD3 CSANs with valencies ranging from 2 to 8 could be employed for radionuclide, drug, or potentially oligonucleotide delivery to T-cells without, as has been observed for other antibody conjugated nanoparticles, the deleterious effects of activation observed for mAB. Further the CSAN construct may be adapted for the preparation of other multivalent scFvs.

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.

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.