A dual-targeting PDGFRbeta/VEGF-A molecule assembled from stable antibody fragments demonstrates anti-angiogenic activity in vitro and in vivo

Sorafenib-loaded nanostructured lipid carriers for topical ocular therapy of corneal neovascularization: development, in-vitro and in vivo study

Sorafenib (SRB), a multikinase inhibitor, is effective in reducing experimental corneal neovascularization (CNV) after oral administration; however, its therapeutic use in ocular surface disorders is restricted due to poor solubility and limited bioavailability. This study aimed to develop and optimize SRB-loaded nanostructured lipid carriers (SRB-NLCs) for topical ocular delivery by a central composite design response surface methodology (CCD-RSM). It was spherical and uniform in morphology with an average particle size of 111.87 ± 0.93 nm and a narrow size distribution. The in vitro drug release from the released SRB-NLC formulation was well fitted to Korsmeyer Peppas release kinetics. The cell counting kit-8 (CCK-8) cell viability assay demonstrated that SRB-NLC was not obviously cytotoxic to human corneal epithelial cells (HCECs). An in vivo ocular irritation test showed that SRB-NLC was well tolerated by rabbit eyes. Ocular pharmacokinetics revealed 6.79-fold and 1.24-fold increase in the area under concentration-time curves (AUC_0-12h) over 12 h in rabbit cornea and conjunctiva, respectively, treated with one dose of SRB-NLC compared with those treated with SRB suspension. Moreover, SRB-NLC (0.05% SRB) and dexamethasone (0.025%) similarly suppressed corneal neovascularization in mice. In conclusion, the optimized SRB-NLC formulation demonstrated excellent physicochemical properties and good tolerance, sustained release, and enhanced ocular bioavailability. It is safe and potentially effective for the treatment of corneal neovascularization.

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.

PDGF as an Important Initiator for Neurite Outgrowth Associated with Fibrovascular Membranes in Proliferative Diabetic Retinopathy

PURPOSE

The formation of fibrovascular membranes (FVMs) is a serious sight-threatening complication of proliferative diabetic retinopathy (PDR) that may result in retinal detachment and eventual blindness. During the formation of these membranes, neurite/process outgrowth occurs in retinal neurons and glial cells, which may both serve as a scaffold and have guiding or regulatory roles. To further understand this process, we investigated whether previously identified candidate proteins, from vitreous of PDR patients with FVMs, could induce neurite outgrowth in an experimental setting.

MATERIALS AND METHODS

Retinal explants of C57BL6/N mouse pups on postnatal day 3 (P3) were cultured in poly-L-lysine- and laminin-coated dishes. Outgrowth stimulation experiments were performed with the addition of potential inducers of neurite outgrowth. Automated analysis of neurite outgrowth was performed by measuring β-tubulin-immunopositive neurites using Image J. Expression of PDGF receptors was quantified by RT-PCR in FVMs of PDR patients.

RESULTS

Platelet-derived growth factor (PDGF) induced neurite outgrowth in a concentration-dependent manner, whilst neuregulin 1 (NRG1) and connective tissue growth factor (CTGF) did not. When comparing three different PDGF dimers, treatment with PDGF-AB resulted in the highest neurite induction, followed by PDGF-AA and -BB. In addition, incubation of retinal explants with vitreous from PDR patients resulted in a significant induction of neurite outgrowth as compared to non-diabetic control vitreous from patients with macular holes, which could be prevented by addition of CP673451, a potent PDGF receptor (PDGFR) inhibitor. Abundant expression of PDGF receptors was detected in FVMs.

CONCLUSION

Our findings suggest that PDGF may be involved in the retinal neurite outgrowth, which is associated with the formation of FVMs in PDR.

A small molecular multi-targeting tyrosine kinase inhibitor, anlotinib, inhibits pathological ocular neovascularization

Ocular neovascularization is a devastating pathology observed in numerous ocular diseases and is a major cause of blindness. However, all current treatments have their limitations. Hence, it is important to explore new therapeutic strategies. This study aimed to investigate the role of anlotinib, a small molecular multi-targeting tyrosine kinase inhibitor, in ocular neovascularization. Anlotinib administration did not induce any cytotoxicity and tissue toxicity at the tested concentrations. Cellular functional experiments demonstrated that anlotinib inhibited the viability, proliferation, migration, and tube formation ability of endothelial cells (ECs) and pericytes. Western blot analysis demonstrated that anlotinib significantly inhibited the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) and platelet-derived growth factor receptor β (PDGFR-β), as well as their downstream signaling pathways stimulated by VEGF or PDGF-BB, in a concentration-dependent manner in ECs and pericytes. Using an oxygen-induced retinopathy (OIR) model, our results demonstrated that injection of anlotinib reduced avascular areas and pathological neovascular tufts. Furthermore, using a laser-induced choroidal neovascularization (CNV) model, we observed that the combined treatment of anlotinib and Lucentis reduced the size and thickness of CNV lesions compared to Lucentis monotherapy alone. Taken together, our results suggest that anlotinib could be a promising drug candidate for ocular neovascularization.

Dual-acting therapeutic proteins for intraocular use

Intravitreally injected antibody-based medicines have revolutionised the treatment of retinal disease. Bispecific and dual-functional antibodies and therapeutic proteins have the potential to further increase the efficacy of intraocular medicines.

Blockade of Platelet-Derived Growth Factor Signaling Inhibits Choroidal Neovascularization and Subretinal Fibrosis in Mice

Neovascular age related macular degeneration (nAMD) leads to severe vision loss worldwide and is characterized by the formation of choroidal neovascularization (CNV) and fibrosis. In the current study, we aimed to investigate the effect of blockade for platelet derived growth factor receptor-β (PDGFR-β) on the formation of choroidal neovascularization and fibrosis in the laser-induced CNV model in mice. Firstly, the presence of PDGFR-β in CNV lesions were confirmed. Intravitreal injection of PDGFR-β neutralizing antibody significantly reduced the size of CNV and subretinal fibrosis. Additionally, subretinal hyperreflective material (SHRM), a landmark feature on OCT as a risk factor for subretinal fibrosis formation in nAMD patients was also suppressed by PDGFR-β blockade. Furthermore, pericytes were abundantly recruited to the CNV lesions during CNV formation, however, blockade of PDGFR-β significantly reduced pericyte recruitment. In addition, PDGF-BB stimulation increased the migration of the rat retinal pericyte cell line, R-rPCT1, which was abrogated by the neutralization of PDGFR-β. These results indicate that blockade of PDGFR-β attenuates laser-induced CNV and fibrosis through the inhibition of pericyte migration.

Novel multi-targeted inhibitors suppress ocular neovascularization by regulating unique gene sets

Neovascular diseases, such as many cancers and ocular disorders, are life threatening and devastating. Although anti-vascular endothelial growth factor A (VEGF-A) therapy is available, many patients are not responsive and drug resistance can develop. To try to overcome these problems, combination therapy targeting VEGF-A and platelet-derived growth factor B (PDGF-B) was tested. However, one obvious drawback was that the other VEGF and PDGF family members were not inhibited and therefore could compensate. Indeed, this was, at least to some extent, demonstrated by the disappointing outcomes. To this end, we designed novel multi-targeted inhibitors that can block most of the VEGF and PDGF family members simultaneously by making a fusion protein containing the ligand-binding domains of vascular endothelial growth factor receptor 1 (VEGFR1), vascular endothelial growth factor receptor 2 (VEGFR2) and platelet-derived growth factor receptor beta (PDGFRβ), which can therefore act as a decoy blocker for most of the VEGF and PDGF family members. Indeed, in cultured cells, the novel inhibitors suppressed the migration and proliferation of both vascular endothelial cells and smooth muscle cells, and abolished VEGFR2 and PDGFRβ activation. Importantly, in a choroidal neovascularization model in vivo, the novel inhibitor inhibited ocular neovascularization more efficiently than the mono-inhibitors against VEGFR or PDGFR alone respectively. Mechanistically, a genome-wide microarray analysis unveiled that the novel inhibitor regulated unique sets of genes that were not regulated by the mono-inhibitors, further demonstrating the functional uniqueness and superiority of the novel inhibitor. Together, we show that the multi-targeted inhibitors that can block VEGFR1, VEGFR2 and PDGFRβ simultaneously suppress pathological angiogenesis more efficiently than monotherapy, and may therefore have promising therapeutic value for the treatment of neovascular diseases.

Parallel Evolution of Antibody Affinity and Thermal Stability for Optimal Biotherapeutic Development

Naïve antibody libraries provide a rich resource for the identification of binding domains against targets of therapeutic interest. Being naïve in nature means a lack in antigen bias, resulting in a breadth of diversity with respect to epitopes that can be successfully targeted. In combination with display-based technology platforms, selection strategies allow for the generation of ortholog cross-reactive binding domains which enable critical preclinical proof-of-concept studies. However, naïve binding domains often suffer from low target affinity. In addition, construction of large naïve libraries results in non-native pairing of heavy and light v-domains which can present a challenge to molecular stability. Here we describe effective methods for the parallel evolution of antibody affinity and thermal stability which couple mutant antibody library phage display with carefully designed selection strategies.

Efficacy of Sunitinib, Sunitinib-Hesperetin, and Sunitinib-Doxycycline Combinations on Experimentally-Induced Corneal Neovascularization

Purpose: To investigate the preventive effects of topical sunitinib, sunitinib-hesperetin and sunitinib-doxycycline combinations on corneal neovascularization (CNV), apoptosis and fibrosis in a corneal alkali burn model. Materials and Methods: The corneas of 32 Wistar albino rats were cauterized with silver nitrate to induce CNV. Four groups were created receiving artificial tears (sham), sunitinib (0.5 mg/ml), sunitinib-hesperetin (0.5 mg/ml-0.2 mg/ml), and sunitinib-doxycycline (0.5 mg/ml-20 mg/ml) treatments. Corneal photographs were taken on days 0, 7 and 15‎. Photographs of the cornea were digitally analyzed to measure the size of the neovascularization area in comparison to the total corneal surface area. On the 15th day, the animals were euthanized, and the eyes were enucleated for immunohistochemical staining to investigate neovascularization, apoptosis, and fibrosis. Results: CNV areas on the 7th day in the sunitinib (4.8% ± 0.07%) and sunitinib-hesperetin (1.1% ± 0.03%) groups were smaller than those in the sham group (33.9% ± 0.12%) (p = 0.001 and, p < 0.001 respectively). On the 15th day, the CNV area in the sunitinib-hesperetin (20.8% ± 0.37%) group was significantly smaller than that of the sham group (74.6% ± 0.32%) (p = 0.039). The combination groups had lower levels of VEGF, TUNEL and α-SMA positivity than the sunitinib monotherapy group. TUNEL positivity was lowest in the sunitinib-hesperetin and sunitinib-doxycycline groups, and α-SMA positivity was lowest in the sunitinib-hesperetin group. Conclusion: Topical sunitinib-hesperetin was more effective than sunitinib alone and the sunitinib-doxycycline combination in the treatment of CNV. The combination of sunitinib and hesperetin seems to be a promising treatment for preventing corneal fibrosis and apoptosis.

Ocular delivery of proteins and peptides: Challenges and novel formulation approaches

The impact of proteins and peptides on the treatment of various conditions including ocular diseases over the past few decades has been advanced by substantial breakthroughs in structural biochemistry, genetic engineering, formulation and delivery approaches. Formulation and delivery of proteins and peptides, such as monoclonal antibodies, aptamers, recombinant proteins and peptides to ocular tissues poses significant challenges owing to their large size, poor permeation and susceptibility to degradation. A wide range of advanced drug delivery systems including polymeric controlled release systems, cell-based delivery and nanowafers are being exploited to overcome the challenges of frequent administration to ocular tissues. The next generation systems integrated with new delivery technologies are anticipated to generate improved efficacy and safety through the expansion of the therapeutic target space. This review will highlight recent advances in formulation and delivery strategies of protein and peptide based biopharmaceuticals. We will also describe the current state of proteins and peptides based ocular therapy and future therapeutic opportunities.

EGFR and Cortactin: Markers for potential double target therapy in oral squamous cell carcinoma

Survival periods of patients following surgical therapy of oral squamous cell carcinoma (OSCC) have previously been demonstrated to decrease over recent decades. Epidermal growth factor receptor (EGFR) and Cortactin are molecular markers that are important in tumour progression and development, and interact within the EGF pathway. Although EGFR antibody therapy exists, sufficient efforts for increased survival are still lacking due to the present limited response rates. The aim of the present study was to examine the association between EGFR and Cortactin expression on survival rates of OSCC patients and to determine whether EGFR and Cortactin expression levels are associated with advanced tumor sizes and lymphnode-metastases. In total, 222 OSCC patients were included in the study. EGFR and Cortactin expression in tumor tissue was evaluated by immunohistochemistry. Cox regression was used for survival analysis. Categories were tested for associations by using cross tabs (Chi-square test). Groups were compared by the non-parametric Mann Whitney U-test. Probabilities of less than 0.05 were considered significant and significant expression of Cortactin was observed in Advanced Union Internationale Contre le Cancer stage (P=0.032), including advanced tumour stage (P=0.021) and lymph node metastasis (P=0.049). High Cortactin expression was significantly associated with poorer survival rates (P=0.037). Further Cortactin expression was not associated with extracapsular spread, however EGFR exhibited a significant association (P=0.034). Neither EGFR nor Cortactin expression was correlated to grading. EGFR and Cortactin co-expression was demonstrated to be significantly associated with poorer survival rates in OSCC patients, suggesting that identification of predictive biomarkers for adjuvant therapies are of primary concern in OSCC. In particular, efficient dual-target therapy may act as an appropriate therapy to improve survival time for patients at advanced OSCC tumor stages.

Aptamers as targeted therapeutics: current potential and challenges

Nucleic acid aptamers, often termed 'chemical antibodies', are functionally comparable to traditional antibodies, but offer several advantages, including their relatively small physical size, flexible structure, quick chemical production, versatile chemical modification, high stability and lack of immunogenicity. In addition, many aptamers are internalized upon binding to cellular receptors, making them useful targeted delivery agents for small interfering RNAs (siRNAs), microRNAs and conventional drugs. However, several crucial factors have delayed the clinical translation of therapeutic aptamers, such as their inherent physicochemical characteristics and lack of safety data. This Review discusses these challenges, highlighting recent clinical developments and technological advances that have revived the impetus for this promising class of therapeutics.

Validation of Cross-Species Reactivity of the VEGF-A/PDGFRβ Bifunctional Antibody PF-06653157

PURPOSE

PF-06653157 is a bifunctional antagonist monoclonal antibody (mAb) that targets human VEGF-A ligand and PDGF-Rβ. With the advent of PF-06653157 as an angiogenesis inhibitor and potential treatment for angiogenesis deregulation diseases, a relevant toxicology species is needed for toxicity and efficacy studies. Investigative studies were conducted to validate the mAb dual antagonist properties in a human system and determine its cross-reactive pharmacology in nonhuman cells.

METHODS

Sequence alignment was used to determine percent sequence identity of VEGF and PDGF receptors and ligands; qualitative reverse transcription polymerase chain reaction (qRT-PCR) was used to determine the presence of PDGF-Rβ on cells of interest. The functional activity of PF-06653157 antibody was assessed in human, dog, porcine, rabbit, rat, mouse, and cynomolgus monkey cells treated with VEGF and PDGF ligands through cell proliferation assays and western blot analysis of AKT and p44/p42 (ERK1/2) protein phosphorylation and enzyme-linked immunosorbent assay.

RESULTS

PF-06653157 attenuated phosphorylation of AKT and p44/p42 proteins in human and cynomolgus monkey cells. The antibody did not attenuate AKT nor p44/p42 phosphorylation in any other species tested. PDGFR signaling could not be activated with human PDGF ligand in the porcine cells, so PF-06653157 activity in porcine remains inconclusive.

CONCLUSION

The PF-06653157 mAb cross-reacts with cynomolgus monkey cells in a similar manner to human cells. Therefore, cynomolgus monkeys are considered the appropriate species for efficacy and regulatory toxicology studies in PF-06653157 development.

A bi-functional antibody-receptor domain fusion protein simultaneously targeting IGF-IR and VEGF for degradation

Bi-specific antibodies (BsAbs), which can simultaneously block 2 tumor targets, have emerged as promising therapeutic alternatives to combinations of individual monoclonal antibodies. Here, we describe the engineering and development of a novel, human bi-functional antibody-receptor domain fusion molecule with ligand capture (bi-AbCap) through the fusion of the domain 2 of human vascular endothelial growth factor receptor 1 (VEGFR1) to an antibody directed against insulin-like growth factor - type I receptor (IGF-IR). The bi-AbCap possesses excellent stability and developability, and is the result of minimal engineering. Beyond potent neutralizing activities against IGF-IR and VEGF, the bi-AbCap is capable of cross-linking VEGF to IGF-IR, leading to co-internalization and degradation of both targets by tumor cells. In multiple mouse xenograft tumor models, the bi-AbCap improves anti-tumor activity over individual monotherapies. More importantly, it exhibits superior inhibition of tumor growth, compared with the combination of anti-IGF-IR and anti-VEGF therapies, via powerful blockade of both direct tumor cell growth and tumor angiogenesis. The unique "capture-for-degradation" mechanism of the bi-AbCap is informative for the design of next-generation bi-functional anti-cancer therapies directed against independent signaling pathways. The bi-AbCap design represents an alternative approach to the creation of dual-targeting antibody fusion molecules by taking advantage of natural receptor-ligand interactions.

Axitinib inhibits retinal and choroidal neovascularization in in vitro and in vivo models

Age-related Macular Degeneration (AMD) is the leading cause of visual impairment and blindness in the elderly in developed countries. Neovascular/exudative (wet) AMD is the aggressive form of AMD and can involve choroidal neovascularization and vascular leakage. Anti-vascular endothelial growth factor (anti-VEGF) medications have significantly improved treatment of wet-AMD. However, only approximately 40% of patients obtain full benefit from anti-VEGF therapy and the medications are given by intravitreal injection. Axitinib, a small molecule multi-receptor tyrosine kinase inhibitor used for the treatment of advanced renal cell carcinoma, is taken orally and inhibits VEGF activity by blocking VEGF receptors. Axitinib also has the advantage of blocking platelet derived growth factor (PDGF) receptors which play a role in neovascularization. Using in vitro human retinal microvascular endothelial cells (HRMVECs), human brain vascular pericytes (HBVRs), 3D co-culture vessel sprout assay, and in vivo laser induced rat choroidal neovascularization (CNV) models, the effect of axitinib on neovascularization was evaluated. Axitinib inhibited neovascularization better than anti-VEGF and/or anti-hPDGF-B mAb in the in vitro models demonstrating that combined inhibition of both VEGF and PDGF pathways may be synergistic in treating wet-AMD. Additionally, axitinib showed good efficacy at a low dose (0.875 mg/day) in laser-induced CNV model in rats. In conclusion our data shows that axitinib, an inhibitor of VEGF and PDGF-B pathways may be useful in ameliorating wet-AMD therapy.

Fit for the Eye: Aptamers in Ocular Disorders

For any new class of therapeutics, there are certain types of indications that represent a natural fit. For nucleic acid ligands in general, and aptamers in particular, the eye has historically been an attractive site for therapeutic intervention. In this review, we recount the discovery and early development of three aptamers designated for use in ophthalmology, one approved (Macugen), and two in late-stage development (Fovista and Zimura). Every one of these molecules was originally intended for other indications. Key improvements in technology, specifically with regard to libraries used for in vitro selection and subsequent chemical optimization of aptamers, have played an important role in allowing the identification of development candidates with suitable properties. The lessons learned from the selection of these molecules are valuable for informing us about the many remaining opportunities for aptamer-based therapeutics in ophthalmology as well as for identifying additional indications for which aptamers as a class of therapeutics have distinct advantages.

Clinical pharmacology of bispecific antibody constructs

The confluence of rapid scientific advancements especially in protein engineering and recombinant technology, unmet medical needs, and commercial incentives have led to the development of the next generation of therapeutic proteins. Bispecific antibody constructs are one of the novel strategies that is being pursued, combining the ability to bind simultaneously to two distinct targets and the advantages of purpose-designed and optimized antibody-based scaffolds. Their pharmacokinetic and pharmacodynamic properties, including their immunogenic potential, are closely related to their structural features and ability to interact with disposition mechanisms of immunoglobulin molecules. Catumaxomab and blinatumomab are bispecific constructs that are approved for clinical use and have provided clinical pharmacology data for this novel class of therapeutics. This knowledgebase on the clinical behavior of bispecific therapeutic proteins is poised to rapidly evolve over the next few years with many development programs having entered the clinical development stage.

A Combination of Structural and Empirical Analyses Delineates the Key Contacts Mediating Stability and Affinity Increases in an Optimized Biotherapeutic Single-chain Fv (scFv)

Fully-human single-chain Fv (scFv) proteins are key potential building blocks of bispecific therapeutic antibodies, but they often suffer from manufacturability and clinical development limitations such as instability and aggregation. The causes of these scFv instability problems, in proteins that should be theoretically stable, remains poorly understood. To inform the future development of such molecules, we carried out a comprehensive structural analysis of the highly stabilized anti-CXCL13 scFv E10. E10 was derived from the parental 3B4 using complementarity-determining region (CDR)-restricted mutagenesis and tailored selection and screening strategies, and carries four mutations in VL-CDR3. High-resolution crystal structures of parental 3B4 and optimized E10 scFvs were solved in the presence and absence of human CXCL13. In parallel, a series of scFv mutants was generated to interrogate the individual contribution of each of the four mutations to stability and affinity improvements. In combination, these analyses demonstrated that the optimization of E10 was primarily mediated by removing clashes between both the VL and the VH, and between the VL and CXCL13. Importantly, a single, germline-encoded VL-CDR3 residue mediated the key difference between the stable and unstable forms of the scFv. This work demonstrates that, aside from being the critical mediators of specificity and affinity, CDRs may also be the primary drivers of biotherapeutic developability.

Nanocell targeting using engineered bispecific antibodies

There are many design formats for bispecific antibodies (BsAbs), and the best design choice is highly dependent on the final application. Our aim was to engineer BsAbs to target a novel nanocell (EnGeneIC Delivery Vehicle or EDV^TMnanocell) to the epidermal growth factor receptor (EGFR). EDV^TMnanocells are coated with lipopolysaccharide (LPS), and BsAb designs incorporated single chain Fv (scFv) fragments derived from an anti-LPS antibody (1H10) and an anti-EGFR antibody, ABX-EGF. We engineered various BsAb formats with monovalent or bivalent binding arms and linked scFv fragments via either glycine-serine (G4S) or Fc-linkers. Binding analyses utilizing ELISA, surface plasmon resonance, bio-layer interferometry, flow cytometry and fluorescence microscopy showed that binding to LPS and to either soluble recombinant EGFR or MDA-MB-468 cells expressing EGFR, was conserved for all construct designs. However, the Fc-linked BsAbs led to nanocell clumping upon binding to EDV^TMnanocells. Clumping was eliminated when additional disulfide bonds were incorporated into the scFv components of the BsAbs, but this resulted in lower BsAb expression. The G4S-linked tandem scFv BsAb format was the optimal design with respect to EDV binding and expression yield. Doxorubicin-loaded EDV^TMnanocells actively targeted with tandem scFv BsAb in vivo to MDA-MB-468-derived tumors in mouse xenograft models enhanced tumor regression by 40% compared to passively targeted EDV^TMnanocells. BsAbs therefore provide a functional means to deliver EDV^TMnanocells to target cells.

Ovine carotid artery-derived cells as an optimized supportive cell layer in 2-D capillary network assays

BACKGROUND

Endothelial cell co-culture assays are differentiation assays which simulate the formation of capillary-like tubules with the aid of a supportive cell layer. Different cell types have been employed as a supportive cell layer, including human pulmonary artery smooth muscle cells (PASMCs) and human mammary fibroblasts. However, these sources of human tissue-derived cells are limited, and more readily accessible human or animal tissue-derived cell sources would simplify the endothelial cell co-culture assay. In the present study, we investigated the potential use of alternative, accessible supportive cells for endothelial cell co-culture assay, including human umbilical cord and ovine carotid artery.

METHODS AND RESULTS

Human umbilical artery SMCs (HUASMCs) and ovine carotid artery-derived cells were seeded into 96-well plates, followed by addition of human umbilical vein endothelial cells (HUVECs). Nine days after co-culture, cells were fixed, immunostained and analysed using an in vitro angiogenesis quantification tool. Capillary-like structures were detected on ovine carotid artery-derived supportive cell layers. The initial cell number, as well as pro- and anti-angiogenic factors (VEGF, PDGF-BB and Bevacizumab), had a positive or negative influence on the number of capillary-like structures. Furthermore, HUVECs from different donors showed distinct levels of VEGF receptor-2, which correlated with the amount of capillary-like structures. In the case of HUASMC supportive cell layers, HUVECs detached almost completely from the surface.

CONCLUSIONS

Cells of different origin have a varying applicability regarding the endothelial cell co-culture assay: under the conditions described here, ovine carotid artery-derived cells seem to be more suitable than HUASMCs for an endothelial co-culture assay. Furthermore, the ovine carotid artery-derived cells are easier to obtain and are in more abundant supply than the currently used dermal or breast tissue cells. The use of ovine carotid artery-derived cells simplifies the endothelial co-culture assay with respect to testing large amounts of pro- and anti-angiogenic factors.

Peptide-based targeting of the platelet-derived growth factor receptor beta

Purpose

The aim of this work is to identify new ligands targeting the platelet-derived growth factor receptor beta (PDGFRβ).

Procedures

Biopanning was carried out with a 12-amino-acid phage display library against the recombinant extracellular domain of PDGFRβ. The identified peptide PDGFR-P1 was chemically synthesized and labeled with ¹²⁵I or ¹³¹I. In vitro studies were performed on the PDGFRβ-expressing cell lines BxPC3 and MCF7 and on PDGFRβ-transfected HEK cells in comparison to negative control wtHEK293 and CaIX-transfected HEK cells. Biodistribution experiments were performed in Balb/c nude mice, carrying subcutaneously BxPC3 tumors.

Results

In vitro studies demonstrated a higher binding to BxPC3, MCF7, and PDGFRβ-tr-HEK cells in comparison to negative control cell lines. Binding was inhibited up to 90% by the unlabeled PDGFR-P1 peptide. Organ distribution studies revealed a higher accumulation in BxPC3 tumors than in most organs.

Conclusions

PDGFR-P1 is a promising candidate for targeting human PDGFRβ.

A tale of two specificities: bispecific antibodies for therapeutic and diagnostic applications

•

Recombinant DNA technologies are leading the rapid expansion of bispecific antibody formats.

•

The therapeutic potential of bispecific antibodies is being realized through creative design.

•

Bispecific antibodies are potentially underutilized reagents for diagnostics.

Artificial manipulation of antibody genes has facilitated the production of several unique recombinant antibody formats, which have highly important therapeutic and biotechnological applications. Although bispecific antibodies (bsAbs) are not new, they are coming to the forefront as our knowledge of the potential efficacy of antibody-based therapeutics expands. The next generation of bsAbs is developing due to significant improvements in recombinant antibody technologies. This review focuses on recent advances with a particular focus on improvements in format and design that are contributing to the resurgence of bsAbs, and in particular, on innovative structures applicable to next generation point-of-care (POC) devices with applicability to low resource environments.

CDR-restricted engineering of native human scFvs creates highly stable and soluble bifunctional antibodies for subcutaneous delivery

While myriad molecular formats for bispecific antibodies have been examined to date, the simplest structures are often based on the scFv. Issues with stability and manufacturability in scFv-based bispecific molecules, however, have been a significant hindrance to their development, particularly for high-concentration, stable formulations that allow subcutaneous delivery. Our aim was to generate a tetravalent bispecific molecule targeting two inflammatory mediators for synergistic immune modulation. We focused on an scFv-Fc-scFv format, with a flexible (A4T)3 linker coupling an additional scFv to the C-terminus of an scFv-Fc. While one of the lead scFvs isolated directly from a naïve library was well-behaved and sufficiently potent, the parental anti-CXCL13 scFv 3B4 required optimization for affinity, stability, and cynomolgus ortholog cross-reactivity. To achieve this, we eschewed framework-based stabilizing mutations in favor of complementarity-determining region (CDR) mutagenesis and re-selection for simultaneous improvements in both affinity and thermal stability. Phage-displayed 3B4 CDR-mutant libraries were used in an aggressive "hammer-hug" selection strategy that incorporated thermal challenge, functional, and biophysical screening. This approach identified leads with improved stability and>18-fold, and 4,100-fold higher affinity for both human and cynomolgus CXCL13, respectively. Improvements were exclusively mediated through only 4 mutations in VL-CDR3. Lead scFvs were reformatted into scFv-Fc-scFvs and their biophysical properties ranked. Our final candidate could be formulated in a standard biopharmaceutical platform buffer at 100 mg/ml with<2% high molecular weight species present after 7 weeks at 4 °C and viscosity<15 cP. This workflow has facilitated the identification of a truly manufacturable scFv-based bispecific therapeutic suitable for subcutaneous administration.

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.

Dual targeting strategies with bispecific antibodies

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

Phase II trial of imatinib mesylate in patients with recurrent platinum- and taxane-resistant low-grade serous carcinoma of the ovary, peritoneum, or fallopian tube

OBJECTIVE

To evaluate the efficacy and tolerability of imatinib mesylate in patients with recurrent low-grade serous carcinoma (LGSC) of the ovary, peritoneum, or fallopian tube.

METHODS

This open-label, single-institution phase II trial enrolled patients with platinum-resistant LGSC who had measurable disease, had received up to 4 platinum- and/or taxane-containing chemotherapy regimens, and had been previously screened for at least one imatinib targeted biomarker (c-kit, platelet-derived growth factor receptor [PDGFR]-β, or bcr-abl). Imatinib (600 mg) was administered daily for one 6-week course and continued in the absence of toxicity and disease progression.

RESULTS

Thirteen patients were enrolled; 12 were evaluable for toxicity, and 11 were evaluable for response. A total of 17 courses were administered (median, 1 course; range, 1-5 courses). Complete or partial responses were not observed. One patient had stable disease for 7.3 months. c-Kit, bcr-abl, or PDGFR-β were present in 48%, 77%, and 100% of patients, respectively. No correlation between best response (stable disease) and the presence of imatinib-targeted biomarkers was observed. Adverse events included grade 3 skin rash in one patient leading to discontinuation of the drug, and grade 3 febrile neutropenia and grade 2 weight gain in two patients leading to dose reductions. The most common grade 1 or 2 toxicities were fatigue (66%), nausea/vomiting (66%), and diarrhea (41%); grade 3 toxicities included skin rash and granulocytopenia events. No grade 4 or 5 toxicities were observed. The median progression-free survival time was 1.3 months (95% CI, 1.27, 1.40 months), and the median overall survival time was 14.9 months (95% CI, 11.0, 18.9 months).

CONCLUSION

Imatinib is well-tolerated but has no activity in patients with platinum- and taxane-resistant LGSC or the ovary, peritoneum, or fallopian tube.

PDGF: the nuts and bolts of signalling toolbox

PDGF is a growth factor and is extensively involved in multi-dimensional cellular dynamics. It switches on a plethora of molecules other than its classical pathway. It is engaged in various transitions of development; however, if the unleashed potentials lead astray, it brings forth tumourigenesis. Conventionally, it has been assumed that the components of this signalling pathway show fidelity and act with a high degree of autonomy. However, as illustrated by the PDGF signal transduction, reinterpretation of recent data suggests that machinery is often shared between multiple pathways, and other components crosstalk to each other through multiple mechanisms. It is important to note that metastatic cascade is an intricate process that we have only begun to understand in recent years. Many of the early steps of this PDGF cascade are not readily targetable in the clinic. In this review, we will unravel the paradoxes with reference to mitrons and cellular plasticity and discuss how disruption of signalling cascade triggers cellular proliferation phase transition and metastasis. We will also focus on the therapeutic interventions to counteract resultant molecular disorders.