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

Production of a Ribosome-Displayed Mouse scFv Antibody Against CD133, Analysis of Its Molecular Docking, and Molecular Dynamic Simulations of Their Interactions

The pentaspan transmembrane glycoprotein CD133, prominin-1, is expressed in cancer stem cells in many tumors and is promising as a novel target for the delivery of cytotoxic drugs to cancer-initiating cells. In this study, we prepared a mouse library of single-chain variable fragment (scFv) antibodies using mRNAs isolated from mice immunized with the third extracellular domain of a recombinant CD133 (D-EC3). First, the scFvs were directly exposed to D-EC3 to select a new specific scFv with high affinity against CD133 using the ribosome display method. Then, the selected scFv was characterized by the indirect enzyme-linked immunosorbent assay (ELISA), immunocytochemistry (ICC), and in silico analyses included molecular docking and molecular dynamics simulations. Based on ELISA results, scFv 2 had a higher affinity for recombinant CD133, and it was considered for further analysis. Next, the immunocytochemistry and flow cytometry experiments confirmed that the obtained scFv could bind to the CD133 expressing HT-29 cells. Furthermore, the results of in silico analysis verified the ability of the scFv 2 antibody to bind and detect the D-EC3 antigen through key residues employed in antigen-antibody interactions. Our results suggest that ribosome display could be applied as a rapid and valid method for isolation of scFv with high affinity and specificity. Also, studying the mechanism of interaction between CD133's scFv and D-EC3 with two approaches of experimental and in silico analysis has potential importance for the design and development of antibody with improved properties.

Site-specific antibody masking enables conditional activation with different stimuli

Antibody therapeutics show great potential to treat a variety of diseases. Often, the dose that can be safely administered is limited by side effects that arise from the interaction with the target outside the diseased tissue. Conditionally-active antibodies provide an additional layer of selectivity to improve safety. Distinct external stimuli or internal cues enable different control strategies and applications. However, current antibody masking strategies have low transferability across stimuli. Here we propose a versatile approach to conditionally mask antibody derivatives and its application to a single chain variable fragment (scFv) against a receptor expressed on cancer stem cells in several tumours. Our strategy relies on the site-specific conjugation of a polymer to an engineered cysteine residue through a chemically-synthesised linker that can be cleaved in response to the target stimulus. We show that the masking efficiency depends on the conjugation site and the size of the mask. An optimised mask decreases antigen binding by up to 20-fold and affinity can be fully recovered upon activation by exposure to light at 365 nm or by incubation with matrix metalloproteinases overexpressed in solid tumours. This approach opens up the possibility to rapidly engineer antibodies activatable with any internal or external stimulus.

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.

Engineering Biomimetic Trogocytosis with Farnesylated Chemically Self-Assembled Nanorings

Inspired by the natural intercellular material-transfer process of trans-endocytosis or trogocytosis, we proposed that targeted farnesylated chemically self-assembled nanorings (f-CSANs) could serve as a biomimetic trogocytosis vehicle for engineering directional cargo transfer between cells, thus allowing cell-cell interactions to be monitored and facilitating cell-cell communications. The membranes of sender cells were stably modified by hydrophobic insertion with the targeted f-CSANs, which were efficiently transferred to receiver cells expressing the appropriate receptors by endocytosis. CSAN-assisted cell-cell cargo transfer (C4T) was demonstrated to be receptor specific and dependent on direct cell-cell interactions, the rate of receptor internalization, and the level of receptor expression. In addition, C4T was shown to facilitate cell-to-cell delivery of an apoptosis inducing drug, as wells as antisense oligonucleotides. Taken together, the C4T approach is a potentially versatile biomimetic trogocytosis platform that can be deployed as a macro-chemical biological tool for monitoring cell-cell interactions and engineering cell-cell communications.

Intracavity generation of glioma stem cell-specific CAR macrophages primes locoregional immunity for postoperative glioblastoma therapy

Glioblastoma multiforme (GBM) remains incurable despite aggressive implementation of multimodal treatments after surgical debulking. Almost all patients with GBM relapse within a narrow margin around the initial resected lesion due to postsurgery residual glioma stem cells (GSCs). Tracking and eradicating postsurgery residual GSCs is critical for preventing postoperative relapse of this devastating disease, yet effective strategies remain elusive. Here, we report a cavity-injectable nanoporter-hydrogel superstructure that creates GSC-specific chimeric antigen receptor (CAR) macrophages/microglia (MΦs) surrounding the cavity to prevent GBM relapse. Specifically, we demonstrate that the CAR gene-laden nanoporter in the hydrogel can introduce GSC-targeted CAR genes into MΦ nuclei after intracavity delivery to generate CAR-MΦs in mouse models of GBM. These CAR-MΦs were able to seek and engulf GSCs and clear residual GSCs by stimulating an adaptive antitumor immune response in the tumor microenvironment and prevented postoperative glioma relapse by inducing long-term antitumor immunity in mice. In an orthotopic patient-derived glioblastoma humanized mouse model, the combined treatment with nanoporter-hydrogel superstructure and CD47 antibody increased the frequency of positive immune responding cells and suppressed the negative immune regulating cells, conferring a robust tumoricidal immunity surrounding the postsurgical cavity and inhibiting postoperative glioblastoma relapse. Therefore, our work establishes a locoregional treatment strategy for priming cancer stem cell-specific tumoricidal immunity with broad application in patients suffering from recurrent malignancies.

Cancer stem cells and strategies for targeted drug delivery

Cancer stem cells (CSCs) are a small proportion of cancer cells with high tumorigenic activity, self-renewal ability, and multilineage differentiation potential. Standard anti-tumor therapies including conventional chemotherapy, radiation therapy, and molecularly targeted therapies are not effective against CSCs, and often lead to enrichment of CSCs that can result in tumor relapse. Therefore, it is hypothesized that targeting CSCs is key to increasing the efficacy of cancer therapies. In this review, CSC properties including CSC markers, their role in tumor growth, invasiveness, metastasis, and drug resistance, as well as CSC microenvironment are discussed. Further, CSC-targeted strategies including the use of targeted drug delivery systems are examined.

Development of therapeutic antibodies for the treatment of diseases

It has been more than three decades since the first monoclonal antibody was approved by the United States Food and Drug Administration (US FDA) in 1986, and during this time, antibody engineering has dramatically evolved. Current antibody drugs have increasingly fewer adverse effects due to their high specificity. As a result, therapeutic antibodies have become the predominant class of new drugs developed in recent years. Over the past five years, antibodies have become the best-selling drugs in the pharmaceutical market, and in 2018, eight of the top ten bestselling drugs worldwide were biologics. The global therapeutic monoclonal antibody market was valued at approximately US$115.2 billion in 2018 and is expected to generate revenue of $150 billion by the end of 2019 and $300 billion by 2025. Thus, the market for therapeutic antibody drugs has experienced explosive growth as new drugs have been approved for treating various human diseases, including many cancers, autoimmune, metabolic and infectious diseases. As of December 2019, 79 therapeutic mAbs have been approved by the US FDA, but there is still significant growth potential. This review summarizes the latest market trends and outlines the preeminent antibody engineering technologies used in the development of therapeutic antibody drugs, such as humanization of monoclonal antibodies, phage display, the human antibody mouse, single B cell antibody technology, and affinity maturation. Finally, future applications and perspectives are also discussed.

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.

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.

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.

CD133, Selectively Targeting the Root of Cancer

Cancer stem cells (CSC) are capable of promoting tumor initiation and self-renewal, two important hallmarks of carcinoma formation. This population comprises a small percentage of the tumor mass and is highly resistant to chemotherapy, causing the most difficult problem in the field of cancer research, drug refractory relapse. Many CSC markers have been reported. One of the most promising and perhaps least ubiquitous is CD133, a membrane-bound pentaspan glycoprotein that is frequently expressed on CSC. There is evidence that directly targeting CD133 with biological drugs might be the most effective way to eliminate CSC. We have investigated two entirely unrelated, but highly effective approaches for selectively targeting CD133. The first involves using a special anti-CD133 single chain variable fragment (scFv) to deliver a catalytic toxin. The second utilizes this same scFv to deliver components of the immune system. In this review, we discuss the development and current status of these CD133 associated biological agents. Together, they show exceptional promise by specific and efficient CSC elimination.

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.

CD133-targeted paclitaxel delivery inhibits local tumor recurrence in a mouse model of breast cancer

Expression of the membrane protein CD133 marks a subset of cancer cells with drug resistant phenotype and enhanced tumor initiating ability in xenotransplantation assays. Because drug resistance and tumor relapse are significant problems, approaches to eliminate these cells are urgently needed. As a step towards achieving this goal, we developed polymeric nanoparticles targeting CD133 by conjugating an anti-CD133 monoclonal antibody to nanoparticles formulated using poly(D,L lactide-co-glycolide) polymer. Nanoparticles were loaded with paclitaxel, a microtubule-stabilizing anticancer agent, as well as with 6-coumarin, a fluorescent probe. CD133-targeted nanoparticles (CD133NPs) were efficiently internalized by Caco-2 cells, which abundantly express CD133 (>9-fold higher uptake than non-targeted control nanoparticles). The effectiveness of CD133NPs in reducing tumor initiating cell (TIC) fraction was investigated using mammosphere formation and soft-agar colony formation assays. Free paclitaxel treatment was not effective in decreasing the TIC population relative to untreated control, whereas CD133NPs effectively decreased the number of mammospheres and colonies formed. In vivo studies in the MDA-MB-231 xenograft model showed that free paclitaxel was initially effective in inhibiting tumor growth but the tumors rebounded rapidly once the treatment was stopped. Tumor regrowth was significantly lower when paclitaxel was delivered through CD133NPs (tumor volume was 518.6±228 vs. 1370.9±295mm(3) for free paclitaxel at 63days; P<0.05). Our studies thus show that encapsulation of paclitaxel in CD133NPs results in a significant decrease in the TIC population and improved therapeutic efficacy compared to that with free paclitaxel treatment. These results indicate the potential of targeting anticancer therapeutics to CD133+ cells for reducing tumor recurrence.

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.