Cotinine-conjugated aptamer/anti-cotinine antibody complexes as a novel affinity unit for use in biological assays

Specific ablation of PDGFRβ-overexpressing pericytes with antibody-drug conjugate potently inhibits pathologic ocular neovascularization in mouse models

BACKGROUND

Crosstalk between pericytes and endothelial cells is critical for ocular neovascularization. Endothelial cells secrete platelet-derived growth factor (PDGF)-BB and recruit PDGF receptor β (PDGFRβ)-overexpressing pericytes, which in turn cover and stabilize neovessels, independent of vascular endothelial growth factor (VEGF). Therapeutic agents inhibiting PDGF-BB/PDGFRβ signaling were tested in clinical trials but failed to provide additional benefits over anti-VEGF agents. We tested whether an antibody-drug conjugate (ADC) - an engineered monoclonal antibody linked to a cytotoxic agent - could selectively ablate pericytes and suppress retinal and choroidal neovascularization.

METHODS

Immunoblotting, flow cytometry, cell viability test, and confocal microscopy were conducted to assess the internalization and cytotoxic effect of ADC targeting mPDGFRβ in an in vitro setting. Immunofluorescence staining of whole-mount retinas and retinal pigment epithelium-choroid-scleral complexes, electroretinography, and OptoMotry test were used to evaluate the effect and safety of ADC targeting mPDGFRβ in the mouse models of pathologic ocular neovascularization.

RESULTS

ADC targeting mPDGFRβ is effectively internalized into mouse brain vascular pericytes and showed significant cytotoxicity compared with the control ADC. We also show that specific ablation of PDGFRβ-overexpressing pericytes using an ADC potently inhibits pathologic ocular neovascularization in mouse models of oxygen-induced retinopathy and laser-induced choroidal neovascularization, while not provoking generalized retinal toxicity.

CONCLUSION

Our results suggest that removing PDGFRβ-expressing pericytes by an ADC targeting PDGFRβ could be a potential therapeutic strategy for pathologic ocular neovascularization.

Biomedical Applications of a Novel Class of High-Affinity Peptides

Most therapeutic peptides available on the market today are naturally occurring hormones or protein fragments that were serendipitously discovered to possess therapeutic effects. However, the limited repertoire of available natural resources presents difficulties for the development of new peptide drug candidates. Traditional peptides possess several shortcomings that must be addressed for biomedical applications, including relatively low affinity or specificity toward biological targets compared to antibody- and protein scaffold-based affinity molecules, poor in vivo stability owing to rapid enzymatic degradation, and rapid clearance from circulation owing to their small size. Going forward, it will be increasingly important for scientists to develop novel classes of high-affinity and -specificity peptides against desired targets that mitigate these limitations while remaining compatible with pharmaceutical manufacturing processes. Recently, several highly constrained, artificial cyclic peptides have emerged as platforms capable of generating high-affinity peptide binders against various disease-associated protein targets by combining with phage or mRNA display method, some of which have entered clinical trials. In contrast, although linear peptides are relatively easy to synthesize cost-effectively and modify site-specifically at either N- or C-termini compared to cyclic peptides, there have been few linear peptide-based platforms that can provide high-affinity and -specificity peptide binders.In this Account, we describe the creation and development of a novel class of high-affinity peptides, termed "aptide"-from the Latin word "aptus" meaning "to fit" and "peptide"-and summarize their biomedical applications. In the first part, we consider the design and creation of aptides, with a focus on their unique structural features and binding mode, and address screening and identification of target protein-specific aptides. We also discuss advantages of the aptide platform over ordinary linear peptides lacking preorganized structures in terms of the affinity and specificity of identified peptide binders against target molecules. In the second part, we describe the potential biomedical applications of various target-specific aptides, ranging from imaging and therapy to theranostics, according to the types of aptides and diseases. We show that certain aptides can not only bind to a target protein but also inhibit its biological function, thereby showing potential as therapeutics per se. Further, aptides specific for cancer-associated protein antigens can be used as escort molecules or targeting ligands for delivery of chemotherapeutics, cytokine proteins, and nanomedicines, such as liposomes and magnetic particles, to tumors, thereby substantially improving therapeutic effects. Finally, we present a strategy capable of overcoming the critical issue of short blood circulation time associated with most peptides by constructing a hybrid system between an aptide and a hapten cotinine-specific antibody.

Therapeutic Application of Drug-Conjugated HER2 Oligobody (HER2-DOligobody)

Antibody drug conjugates (ADCs), consisting of a cancer-specific antibody and cytotoxic payload, are shown to be a potent class of anticancer therapeutics, with enhanced therapeutic efficacy and reduced “off-target” side effects. However, the therapeutic window of ADCs is narrowed by problems such as difficulty in site-specific conjugation of payload, changes in antibody stability due to payload conjugation, and difficulty in tissue penetration. In this respect, aptamers have advantages in drug-delivery, as they can be easily and stably conjugated with cytotoxic drugs. We previously reported that oligobody, an aptamer-antibody complex, is a novel delivery method for aptamer-based therapeutics. In the current study, we describe DOligobody, a drug-conjugated oligobody comprising an aptamer-drug conjugate and an antibody. A cotinine-conjugated anti-HER2 aptamer (cot-HER2apt) was specifically bound to HER2-positive NCI-N87 cells, and underwent receptor-mediated endocytosis. Further, HER2-DOligobody, a cot-HER2apt-conjugated monomethyl auristatin E (cot-HER2apt-MMAE) oligobody, inhibited the growth of HER2-positive NCI-N87 cells. Finally, systemic administration of HER2-DOligobody significantly reduced tumor growth in a xenograft mouse model. Taken together, these results suggest that our DOligobody strategy may be a powerful platform for rapid, low-cost and effective cancer therapy.

Potent anti-angiogenesis and anti-tumour activity of pegaptanib-loaded tetrahedral DNA nanostructure

OBJECTIVES

Pegaptanib might be a promising anti-tumour drug targeting VEGF to inhibit tumour vascular endothelial cell proliferation. However, the poor biostability limited its application. In this study, we took tetrahedron DNA nanostructures (TDNs) as drug nanocarrier for pegaptanib to explore the potent anti-angiogenesis and anti-tumour activity of this drug delivery system.

MATERIALS AND METHODS

The successful synthesis of TDNs and pegaptanib-TDNs was determined by 8% polyacrylamide gel electrophoresis (PAGE), capillary electrophoresis and dynamic light scattering (DLS). The cytotoxicity of pegaptanib alone and pegaptanib-TDNs on HUVECs and Cal27 was evaluated by the cell count kit-8 (CCK-8) assay. The effect of pegaptanib and pegaptanib-TDNs on proliferation, migration and tube formation of HUVECs induced by VEGF was examined by CCK-8 assay, wound healing assay and tubule formation experiment. The cell binding capacity and serum stability were detected by flow cytometry and PAGE, respectively.

RESULTS

Pegaptanib-TDNs had stronger killing ability than pegaptanib alone, and the inhibiting effect was in a concentration-dependent manner. What's more, pegaptanib-loaded TDNs could effectively enhance the ability of pegaptanib to inhibit proliferation, migration and tube formation of HUVECs induced by VEGF. These might attribute to the stronger binding affinity to the cell membrane and greater serum stability of pegaptanib-TDNs.

CONCLUSIONS

These results suggested that pegaptanib-TDNs might be a novel strategy to improve anti-angiogenesis and anti-tumour ability of pegaptanib.

Antibody-Assisted Delivery of a Peptide-Drug Conjugate for Targeted Cancer Therapy

A number of cancer-targeting peptide-drug conjugates (PDCs) have been explored as alternatives to antibody-drug conjugates (ADCs) for targeted cancer therapy. However, the much shorter circulation half-life of PDCs compared with ADCs in vivo has limited their therapeutic value and thus their translation into the clinic, highlighting the need to develop new approaches for extending the half-life of PDCs. Here, we report a new strategy for targeted cancer therapy of a PDC based on a molecular hybrid between an antihapten antibody and a hapten-labeled PDC. An anticotinine antibody (Ab^cot) was used as a model antihapten antibody. The anticancer drug SN38 was linked to a cotinine-labeled aptide specific to extra domain B of fibronectin (cot-APT_EDB), yielding the model PDC, cot-APT_EDB-SN38. The cotinine-labeled PDC showed specific binding to and cytotoxicity toward an EDB-overexpressing human glioblastoma cell line (U87MG) and also formed a hybrid complex (HC) with Ab^cot in situ, designated HC[cot-APT_EDB-SN38/Ab^cot]. In glioblastoma-bearing mice, in situ HC[cot-APT_EDB-SN38/Ab^cot] significantly extended the circulation half-life of cot-APT_EDB-SN38 in blood, and it enhanced accumulation and penetration within the tumor and, ultimately, inhibition of tumor growth. These findings suggest that the present platform holds promise as a new, targeted delivery strategy for PDCs in anticancer therapy.

Bispecific anti-mPDGFRβ x cotinine scFv-Cκ-scFv fusion protein and cotinine-duocarmycin can form antibody-drug conjugate-like complexes that exert cytotoxicity against mPDGFRβ expressing cells

Antibody selection for antibody-drug conjugates (ADCs) has traditionally depended on its internalization into the target cell, although ADC efficacy also relies on recycling of the receptor-ADC complex, endo-lysosomal trafficking, and subsequent linker/antibody proteolysis. In this study, we observed that a bispecific anti-murine platelet-derived growth factor receptor beta (mPDGFRβ) x cotinine single-chain variable fragment (scFv)-kappa constant region (C_κ)-scFv fusion protein and cotinine-duocarmycin can form an ADC-like complex to induce cytotoxicity against mPDGFRβ expressing cells. Multiple anti-mPDGFRβ antibody candidates can be produced in this bispecific scFv-C_κ-scFv fusion protein format and tested for their ability to deliver cotinine-conjugated cytotoxic drugs, thus providing an improved approach for antibody selection in ADC development.

An anti-EGFR × cotinine bispecific antibody complexed with cotinine-conjugated duocarmycin inhibits growth of EGFR-positive cancer cells with KRAS mutations

Antibody-drug conjugates (ADCs) can selectively deliver cytotoxic agents to tumor cells and are frequently more potent than naked antibodies. However, optimization of the conjugation process between antibodies and cytotoxic agents and characterization of ADCs are laborious and time-consuming processes. Here, we describe a novel ADC platform using a tetravalent bispecific antibody that simultaneously binds to the tumor-associated antigen and a hapten conjugated to a cytotoxic agent. We selected cotinine as the hapten because it is not present in biological systems and is inert and nontoxic. We prepared an anti-epidermal growth factor receptor (EGFR) × cotinine bispecific antibody and mixed it with an equimolar amount of cotinine-conjugated duocarmycin to form the ADC. This ADC showed significant in vitro and in vivo antitumor activity against EGFR-positive, cetuximab-refractory lung adenocarcinoma cells with KRAS mutations.

A new method for producing antibody-drug conjugates (ADCs), pairing anti-cancer drugs with antibodies that deliver them specifically to cancer cells, may help to develop therapies for hard-to-treat cancers. ADCs show promise for treating several cancers, but are difficult to produce. Junho Chung at the Seoul National University College of Medicine in South Korea and co-workers tested a new way of forming the conjugates, using cotinine, a non-toxic molecule related to nicotine, as a link. They bound cotinine to the anti-cancer drug duocarmycin, then formulated an antibody with two binding sites, one for cotinine, one for tumor cells. Combining the drug−cotinine complex with the antibody resulted in a drug–cotinine-antibody ADC that delivered duocarmycin exclusively to cancer cells and inhibited tumor growth in mice. This simplified method may help develop treatments for other drug-resistant cancers.

G-quartet oligonucleotide mediated delivery of proteins into photoreceptors and retinal pigment epithelium via intravitreal injection

There is currently no available method to efficiently deliver proteins across the plasma membrane of photoreceptor or retinal pigment epithelium (RPE) cells in vivo. Thus, current clinical application of recombinant proteins in ophthalmology is limited to the use of proteins that perform their biological function extracellularly. The ability to traverse biological membranes would enable the mobilization of a significantly larger number of proteins with previously well characterized properties. Nucleolin is abundantly present on the surface of rapidly dividing cells including cancer cells. Surprisingly, nucleolin is also present on the surface of photoreceptor cell bodies. Here we investigated whether nucleolin can be utilized as a gateway for the delivery of proteins into retinal cells following intravitreal injection. AS1411 is a G-quartet aptamer capable of targeting nucleolin. Subsequent to intravitreal injection, fluorescently labeled AS1411 localized to various retinal cell types including the photoreceptors and RPE. AS1411 linked to streptavidin (a ∼50 kDa protein) via a biotin bridge enabled the uptake of Streptavidin into photoreceptors and RPE. AS1411-Streptavidin conjugate applied topically to the cornea allowed for uptake of the conjugate into the nucleus and cytoplasm of corneal endothelial cells. Clinical relevance of AS1411 as a delivery vehicle was strongly indicated by demonstration of the presence of cell surface nucleolin on the photoreceptors, inner neurons and ganglion cells of human retina. These data support exploration of AS1411 as a means of delivering therapeutic proteins to diseased retina.

An aptamer-antibody complex (oligobody) as a novel delivery platform for targeted cancer therapies

Aptamers have recently emerged as reliable and promising targeting agents in the field of biology. However, their therapeutic potential has yet to be completely assessed due to their poor pharmacokinetics for systemic administration. Here, we describe a novel aptamer-antibody complex, designated an "oligobody" (oligomer+antibody) that may overcome the therapeutic limitations of aptamers. To provide proof-of-principle study, we investigated the druggability of oligobody in vivo using cotinine conjugated t44-OMe aptamer, which is specific for the sequence of pegaptanib, and an anti-cotinine antibody. The antibody part of oligobody resulted in extended in vivo pharmacokinetics of the aptamer without influencing its binding affinity. Moreover, the aptamer of oligobody penetrated deeply into the tumor tissues whereas the anti-VEGF antibody did not. Finally, the systemic administration of this oligobody reduced the tumor burden in a xenograft mouse model. Together, these results suggested that our oligobody strategy may represent a novel platform for rapid, low-cost and high-throughput cancer therapy.

In vitro and in vivo application of anti-cotinine antibody and cotinine-conjugated compounds

The combination of a high-affinity antibody to a hapten, and hapten-conjugated compounds, can provide an alternative to the direct chemical cross-linking of the antibody and compounds. An optimal hapten for in vitro use is one that is absent in biological systems. For in vivo applications, additional characteristics such as pharmacological safety and physiological inertness would be beneficial. Additionally, methods for cross-linking the hapten to various chemical compounds should be available. Cotinine, a major metabolite of nicotine, is considered advantageous in these aspects. A high-affinity anti-cotinine recombinant antibody has recently become available, and can be converted into various formats, including a bispecific antibody. The bispecific anti-cotinine antibody was successfully applied to immunoblot, enzyme immunoassay, immunoaffinity purification, and pre-targeted in vivo radioimmunoimaging. The anti-cotinine IgG molecule could be complexed with aptamers to form a novel affinity unit, and extended the in vivo half-life of aptamers, opening up the possibility of applying the same strategy to therapeutic peptides and chemical compounds. [BMB Reports 2014; 47(3): 130-134]

Bispecific Her2 × cotinine antibody in combination with cotinine-(histidine)2-iodine for the pre-targeting of Her2-positive breast cancer xenografts

PURPOSE

Cotinine has optimal characteristics as a hapten for pre-targeted radioimmunotherapy (PRIT). This study was performed to evaluate the applicability of cotinine/anti-cotinine antibody to PRIT.

METHODS

We developed and prepared a tandem, single-chain, variable fragment Fc fusion protein [tandem single-chain variable fragment (scFv) Fc fusion protein] that is reactive to both human epidermal growth factor receptor 2 (Her2) and cotinine. Its simultaneous reactivity to Her2 and cotinine was tested in an enzyme-linked immunosorbent assay (ELISA) and two radioimmunoassays (RIA) employing Her2-coated RIA tubes and a Her2-overexpressing cell line. For in vivo imaging, mice bearing Her2-positive tumors were injected with a mixture of tandem scFv Fc fusion and (125)I-cotinine-conjugated histidine dipeptide ((125)I-cotinine peptide). After a delay, (125)I-cotinine peptide was injected again.

RESULTS

ELISA and RIA results showed that tandem scFv Fc fusion protein successfully bound to both Her2 and cotinine. In single-photon emission computed tomography (SPECT), the complex of tandem scFv Fc fusion protein and (125)I-cotinine peptide was localized to Her2-positive tumor xenografts in mice 4 h after the first injection. Enhanced radioactivity at the site of the Her2-positive tumor lesion was monitored 1 h after the second injection.

CONCLUSIONS

With these findings, we conclude that the tandem scFv Fc fusion protein and cotinine hapten system have the potential to be applied in PRIT.

Application of bispecific antibody against antigen and hapten for immunodetection and immunopurification

We present a bispecific antibody that recognizes an antigen and a hapten and can be applied to various biological assays, including immunoblotting and immunoprecipitation. In immunoblot analysis of serum, an anti-C5 × anti-cotinine bispecific tandem single-chain variable fragment (scFv)-Fc fusion protein and cotinine-conjugated horseradish peroxidase (HRP) generated a clean signal without the high background that was observed in a parallel experiment using HRP-conjugated goat anti-rabbit immunoglobulin G (Fc-specific) antibody. In immunoprecipitation analysis of serum, use of the bispecific tandem scFv-Fc fusion protein and cotinine-crosslinked magnetic beads significantly reduced the amount of protein contaminants compared with a parallel experiment done with protein A agarose beads. In subsequent immunoblot analysis, use of cotinine–HRP as the secondary probe instead of HRP-conjugated goat anti-rabbit IgG (Fc-specific) antibody successfully eliminated the band corresponding to the bispecific tandem scFv-Fc fusion protein.