Selective targeting of adenovirus to alphavbeta3 integrins, VEGFR2 and Tie2 endothelial receptors by angio-adenobodies

Oncolytic Adenoviruses: Strategies for Improved Targeting and Specificity

Cancer is a major health problem. Most of the treatments exhibit systemic toxicity, as they are not targeted or specific to cancerous cells and tumors. Adenoviruses are very promising gene delivery vectors and have immense potential to deliver targeted therapy. Here, we review a wide range of strategies that have been tried, tested, and demonstrated to enhance the specificity of oncolytic viruses towards specific cancer cells. A combination of these strategies and other conventional therapies may be more effective than any of those strategies alone.

CRISPR/Cas9: a powerful tool for identification of new targets for cancer treatment

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated nuclease 9 (Cas9), as a powerful genome-editing tool, has revolutionized genetic engineering. It is widely used to investigate the molecular basis of different cancer types. In this review, we present an overview of recent studies in which CRISPR/Cas9 has been used for the identification of potential molecular targets. Based on the collected data, we suggest here that CRISPR/Cas9 is an effective system to distinguish between mutant and wild-type alleles in cancer. We show that several new potential therapeutic targets, such as CD38, CXCR2, MASTL, and RBX2, as well as several noncoding (nc)RNAs have been identified using CRISPR/Cas9 technology. We also discuss the obstacles and challenges that we face for using CRISPR/Cas9 as a therapeutic.

Targeting the Tie2-αvβ3 integrin axis with bi-specific reagents for the inhibition of angiogenesis

BACKGROUND

Increased activity of the receptor tyrosine kinase Tie2 has been implicated in the promotion of pathological angiogenesis. This activity is mainly mediated through angiopoietin (Ang)1- and Ang2-dependent activation of integrins by Tie2, rendering the Ang/Tie2/integrin axis an attractive putative target for cancer therapeutics.

RESULTS

To target this axis, we developed single domain, non-immunoglobulin high-affinity bi-specific protein inhibitors against both Tie2 and αvβ3 integrin. We have previously engineered the Ang2-binding domain of Tie2 (Ang2-BD) as a Tie2 inhibitor. Here, we engineered an exposed loop in Ang2-BD to generate variants that include an integrin-binding Arg-Gly-Asp (RGD) motif and used flow cytometry screening of a yeast-displayed Ang2-BD RGD loop library to identify the integrin antagonists. The bi-specific antagonists targeting both Tie2 and αvβ3 integrin inhibited adhesion and proliferation of endothelial cells cultured together with the αvβ3 integrin ligand vitronectin, as well as endothelial cell invasion and tube formation. The bi-specific reagents inhibited downstream signaling by Tie2 intracellularly in response to its agonist Ang1 more effectively than the wild-type Ang2 BD that binds Tie2 alone.

CONCLUSIONS

Collectively, this study-the first to describe inhibitors targeting all the known functions resulting from Tie2/integrin αvβ3 cross-talk-has created new tools for studying Tie2- and integrin αvβ3-dependent molecular pathways and provides the basis for the rational and combinatorial engineering of ligand-Tie2 and ligand-integrin αvβ3 receptor interactions. Given the roles of these pathways in cancer angiogenesis and metastasis, this proof of principle study paves the route to create novel Tie2/integrin αvβ3-targeting proteins for clinical use as imaging and therapeutic agents.

Design, synthesis, and evaluation of VEGFR-targeted macromolecular MRI contrast agent based on biotin-avidin-specific binding

Developing magnetic resonance imaging (MRI) contrast agents with high relaxivity and specificity was essential to increase MRI diagnostic sensitivity and accuracy. In this study, the MRI contrast agent, vascular endothelial growth factor receptor (VEGFR)-targeted poly (l-lysine) (PLL)-diethylene triamine pentacetate acid (DTPA)-gadolinium (Gd) (VEGFR-targeted PLL-DTPA-Gd, VPDG), was designed and prepared to enhance the MRI diagnosis capacity of tumor. Biotin-PLL-DTPA-Gd was synthesized first, then, VEGFR antibody was linked to biotin-PLL-DTPA-Gd using biotin-avidin reaction. In vitro cytotoxicity study results showed that VPDG had low toxicity to MCF-7 cells and HepG2 cells at experimental concentrations. In cell uptake experiments, VPDG could significantly increase the internalization rates (61.75%±5.22%) in VEGFR-positive HepG2 cells compared to PLL-DTPA-Gd (PDG) (25.16%±4.71%, P<0.05). In MRI studies in vitro, significantly higher T1 relaxivity (14.184 mM^-1 s^-1) was observed compared to Magnevist^® (4.9 mM^-1 s^-1; P<0.01). Furthermore, in vivo MRI study results showed that VPDG could significantly enhance the tumor signal intensity and prolong the diagnostic time (from <1 h to 2.5 h). These results indicated that macromolecular VPDG was a promising MRI contrast agent and held great potential for molecular diagnosis of tumor.

Ponicidin induces apoptosis via JAK2 and STAT3 signaling pathways in gastric carcinoma

Ponicidin has a variety of biological effects such as immunoregulatory and anti-inflammatory functions as well as anti-viral functions especially in the upper respiratory tract infection. This study was aimed to elucidate the antitumor effect of ponicidin in gastric carcinoma MKN28 cells and the possible molecular mechanism involved. Cell viability was measured by the Cell Count Kit-8 (CCK8). Cell apoptosis was assessed by flow cytometry as well as cell cycle and reactive oxygen species (ROS) analysis. Western blot analysis was used to detect the active form of caspase-3 as well as Bax and B-cell lymphoma-2 (Bcl-2) expressions after cells were treated with different concentrations of ponicidin. The results revealed that ponicidin could inhibit the growth of MKN28 cells significantly in both a time- and dose-dependent manner. The cell cycle was blocked and ROS generation was increased after the cells were treated with ponicidin. Bcl-2 expression was down-regulated remarkably while Bax expression and the active form of caspase-3 were increased after apoptosis occurred. We therefore conclude that ponicidin exhibited significant growth inhibition of gastric carcinoma cell line MKN28 and induced apoptosis of MKN28 cells via the signaling pathway regulated by Janus kinase 2 (JAK2) and signal transducers and activators of transcription 3 (STAT3). Ponicidin may serve as a potential therapeutic agent for gastric carcinoma.

The myeloid-binding peptide adenoviral vector enables multi-organ vascular endothelial gene targeting

Vascular endothelial cells (ECs) are ideal gene therapy targets as they provide widespread tissue access and are the first contact surfaces following intravenous vector administration. Human recombinant adenovirus serotype 5 (Ad5) is the most frequently used gene transfer system because of its appreciable transgene payload capacity and lack of somatic mutation risk. However, standard Ad5 vectors predominantly transduce liver but not the vasculature following intravenous administration. We recently developed an Ad5 vector with a myeloid cell-binding peptide (MBP) incorporated into the knob-deleted, T4 fibritin chimeric fiber (Ad.MBP). This vector was shown to transduce pulmonary ECs presumably via a vector handoff mechanism. Here we tested the body-wide tropism of the Ad.MBP vector, its myeloid cell necessity, and vector-EC expression dose response. Using comprehensive multi-organ co-immunofluorescence analysis, we discovered that Ad.MBP produced widespread EC transduction in the lung, heart, kidney, skeletal muscle, pancreas, small bowel, and brain. Surprisingly, Ad.MBP retained hepatocyte tropism albeit at a reduced frequency compared with the standard Ad5. While binding specifically to myeloid cells ex vivo, multi-organ Ad.MBP expression was not dependent on circulating monocytes or macrophages. Ad.MBP dose de-escalation maintained full lung-targeting capacity but drastically reduced transgene expression in other organs. Swapping the EC-specific ROBO4 for the CMV promoter/enhancer abrogated hepatocyte expression but also reduced gene expression in other organs. Collectively, our multilevel targeting strategy could enable therapeutic biological production in previously inaccessible organs that pertain to the most debilitating or lethal human diseases.

Adenoviral overexpression of Lhx2 attenuates cell viability but does not preserve the stem cell like phenotype of hepatic stellate cells

Hepatic stellate cells (HSC) are well known initiators of hepatic fibrosis. After liver cell damage, HSC transdifferentiate into proliferative myofibroblasts, representing the major source of extracellular matrix in the fibrotic organ. Recent studies also demonstrate a role of HSC as progenitor or stem cell like cells in liver regeneration. Lhx2 is described as stem cell maintaining factor in different organs and as an inhibitory transcription factor in HSC activation. Here we examined whether a continuous expression of Lhx2 in HSC could attenuate their activation and whether Lhx2 could serve as a potential target for antifibrotic gene therapy. Therefore, we evaluated an adenoviral mediated overexpression of Lhx2 in primary HSC and investigated mRNA expression patterns by qRT-PCR as well as the activation status by different in vitro assays. HSC revealed a marked increase in activation markers like smooth muscle actin alpha (αSMA) and collagen 1α independent from adenoviral transduction. Lhx2 overexpression resulted in attenuated cell viability as shown by a slightly hampered migratory and contractile phenotype of HSC. Expression of stem cell factors or signaling components was also unaffected by Lhx2. Summarizing these results, we found no antifibrotic or stem cell maintaining effect of Lhx2 overexpression in primary HSC.

Peptide-based technologies to alter adenoviral vector tropism: ways and means for systemic treatment of cancer

Due to the fundamental progress in elucidating the molecular mechanisms of human diseases and the arrival of the post-genomic era, increasing numbers of therapeutic genes and cellular targets are available for gene therapy. Meanwhile, the most important challenge is to develop gene delivery vectors with high efficiency through target cell selectivity, in particular under in situ conditions. The most widely used vector system to transduce cells is based on adenovirus (Ad). Recent endeavors in the development of selective Ad vectors that target cells or tissues of interest and spare the alteration of all others have focused on the modification of the virus broad natural tropism. A popular way of Ad targeting is achieved by directing the vector towards distinct cellular receptors. Redirecting can be accomplished by linking custom-made peptides with specific affinity to cellular surface proteins via genetic integration, chemical coupling or bridging with dual-specific adapter molecules. Ideally, targeted vectors are incapable of entering cells via their native receptors. Such altered vectors offer new opportunities to delineate functional genomics in a natural environment and may enable efficient systemic therapeutic approaches. This review provides a summary of current state-of-the-art techniques to specifically target adenovirus-based gene delivery vectors.

Transcriptional targeting of primary and metastatic tumor neovasculature by an adenoviral type 5 roundabout4 vector in mice

New approaches targeting metastatic neovasculature are needed. Payload capacity, cellular transduction efficiency, and first-pass cellular uptake following systemic vector administration, motivates persistent interest in tumor vascular endothelial cell (EC) adenoviral (Ad) vector targeting. While EC transductional and transcriptional targeting has been accomplished, vector administration approaches of limited clinical utility, lack of tumor-wide EC expression quantification, and failure to address avid liver sequestration, challenged prior work. Here, we intravenously injected an Ad vector containing 3 kb of the human roundabout4 (ROBO4) enhancer/promoter transcriptionally regulating an enhanced green fluorescent protein (EGFP) reporter into immunodeficient mice bearing 786-O renal cell carcinoma subcutaneous (SC) xenografts and kidney orthotopic (KO) tumors. Initial experiments performed in human coxsackie virus and adenovirus receptor (hCAR) transgenic:Rag2 knockout mice revealed multiple ECs with high-level Ad5ROBO4-EGFP expression throughout KO and SC tumors. In contrast, Ad5CMV-EGFP was sporadically expressed in a few tumor vascular ECs and stromal cells. As the hCAR transgene also facilitated Ad5ROBO4 and control Ad5CMV vector EC expression in multiple host organs, follow-on experiments engaged warfarin-mediated liver vector detargeting in hCAR non-transgenic mice. Ad5ROBO4-mediated EC expression was undetectable in most host organs, while the frequencies of vector expressing intratumoral vessels and whole tumor EGFP protein levels remained elevated. In contrast, AdCMV vector expression was only detectable in one or two stromal cells throughout the whole tumor. The Ad5ROBO4 vector, in conjunction with liver detargeting, provides tractable genetic access for in-vivo EC genetic engineering in malignancies.

Development of Adenoviral Delivery Systems to Target Hepatic Stellate Cells In Vivo

Hepatic stellate cells (HSCs) are known as initiator cells that induce liver fibrosis upon intoxication or other noxes. Deactivation of this ongoing remodeling process of liver parenchyma into fibrotic tissue induced by HSCs is an interesting goal to be achieved by targeted genetic modification of HSCs. The most widely applied approach in gene therapy is the utilization of specifically targeted vectors based on Adenovirus (Ad) serotype 5. To narrow down the otherwise ubiquitous tropism of parental Ad, two modifications are required: a) ablating the native tropism and b) redirecting the vector particles towards a specific entity solely present on the cells of interest. Therefore, we designed a peptide of the nerve growth factor (NGF_p) with specific affinity for the p75 neurotrophin receptor (p75NTR) present on HSCs. Coupling of this NGF_p to vector particles was done either via chemical conjugation using bifunctional polyethylene glycol (PEG) or, alternatively, by molecular bridging with a fusion protein specific for viral fiber knob and p75NTR. Both Ad vectors transmit the gene for the green fluorescent protein (GFP). GFP expression was monitored in vitro on primary murine HSCs as well as after systemic administration in mice with healthy and fibrotic livers using intravital fluorescence microscopy. Coupling of NGF_p to Ad via S11 and/or PEGylation resulted in markedly reduced liver tropism and an enhanced adenoviral-mediated gene transfer to HSCs. Transduction efficiency of both specific Ads was uniformly higher in fibrotic livers, whereas Ad.GFP-S11-NGF_p transduce activated HSCs better than Ad.GFP-PEG-NGF_p. These experiments contribute to the development of a targeted gene transfer system to specifically deliver antifibrotic compounds into activated HSCs by systemically applied adenoviral vector modified with NGF_p.

Chapter two--Adenovirus strategies for tissue-specific targeting

Cancer gene therapy approaches have benefited greatly from the utilization of molecular-based therapeutics. Of these, adenovirus-based interventions hold much promise as a platform for targeted therapeutic delivery to tumors. However, a barrier to this progression is the lack of native adenovirus receptor expression on a variety of cancer types. As such, any adenovirus-based cancer therapy must take into consideration retargeting the vector to nonnative cellular surface receptors. Predicated upon the knowledge gained in native adenovirus biology, several strategies to transductionally retarget adenovirus have emerged. Herein, we describe the biological hurdles as well as strategies utilized in adenovirus transductional targeting, covering the progress of both adapter-based and genetic manipulation-based targeting. Additionally, we discuss recent translation of these targeting strategies into a clinical setting.

Development of a generic adenovirus delivery system based on structure-guided design of bispecific trimeric DARPin adapters

Adenoviruses (Ads) have shown promise as vectors for gene delivery in clinical trials. Efficient viral targeting to a tissue of choice requires both ablation of the virus' original tropism and engineering of an efficient receptor-mediated uptake by a specific cell population. We have developed a series of adapters binding to the virus with such high affinity that they remain fully bound for >10 d, block its natural receptor binding site and mediate interaction with a surface receptor of choice. The adapter contains two fused modules, both consisting of designed ankyrin repeat proteins (DARPins), one binding to the fiber knob of adenovirus serotype 5 and the other binding to various tumor markers. By solving the crystal structure of the complex of the trimeric knob with three bound DARPins at 1.95-Å resolution, we could use computer modeling to design a link to a trimeric protein of extraordinary kinetic stability, the capsid protein SHP from the lambdoid phage 21. We arrived at a module which binds the knob like a trimeric clamp. When this clamp was fused with DARPins of varying specificities, it enabled adenovirus serotype 5-mediated delivery of a transgene in a human epidermal growth factor receptor 2-, epidermal growth factor receptor-, or epithelial cell adhesion molecule-dependent manner with transduction efficiencies comparable to or even exceeding those of Ad itself. With these adapters, efficiently produced in Escherichia coli, Ad can be converted rapidly to new receptor specificities using any ligand as the receptor-binding moiety. Prefabricated Ads with different payloads thus can be retargeted readily to many cell types of choice.

Retargeting of viruses to generate oncolytic agents

Oncolytic virus therapy is based on the ability of viruses to effectively infect and kill tumor cells without destroying the normal tissues. While some viruses seem to have a natural preference for tumor cells, most viruses require the modification of their tropism to specifically enter and replicate in such cells. This review aims to describe the transductional targeting strategies currently employed to specifically redirect viruses towards surface receptors on tumor cells. Three major strategies can be distinguished; they involve (i) the incorporation of new targeting specificity into a viral surface protein, (ii) the incorporation of a scaffold into a viral surface protein to allow the attachment of targeting moieties, and (iii) the use of bispecific adapters to mediate targeting of a virus to a specified moiety on a tumor cell. Of each strategy key features, advantages and limitations are discussed and examples are given. Because of their potential to cause sustained, multiround infection—a desirable characteristic for eradicating tumors—particular attention is given to viruses engineered to become self-targeted by the genomic expression of a bispecific adapter protein.

Microvascular modifications in diabetic retinopathy

Patients struggling with diabetes are at elevated risks for several sight-threatening diseases, including proliferative diabetic retinopathy (DR). DR manifests in two stages: first, the retinal microvasculature is compromised and capillary degeneration occurs; subsequently, an over-compensatory angiogenic response is initiated. Early changes in the retinal microcirculation include disruptions in blood flow, thickening of basement membrane, eventual loss of mural cells, and the genesis of acellular capillaries. Endothelial apoptosis and capillary dropout lead to a hypoxic inner retina, alterations in growth factors, and upregulation of inflammatory mediators. With disease progression, pathologic angiogenesis generates abnormal preretinal microvessels. Current therapies, which include panretinal photocoagulation and vitrectomy, have remained unaltered for several decades. With several exciting preclinical advances, emergent technologies and innovative cellular targets may offer newfound hope for developing "next-generation" interventional or preventive clinical approaches that will significantly advance current standards of care and clinical outcomes.

Pharmacological interventions for improving adenovirus usage in gene therapy

Gene therapy may be an innovative and promising new treatment strategy for cancer but is limited due to a low efficiency and specificity of gene delivery to the target cells. Adenovirus is the preferred gene therapy vector for systemic delivery because of its unparalleled in vivo transduction efficiency. Intravenous administration of low doses of adenovirus results in adenovirus sequestration in the liver due to binding to the scavenger receptor present on Kupffer cells. When the amount of adenovirus surpasses the binding capacity of Kupffer cells, hepatocytes absorb adenovirus particles in a blood factor-dependent manner. Increasing the Ad dose even more will saturate both the Kupffer cells and hepatocytes. Then sinusoid endothelial cells bind adenovirus particles in an RGD motif-dependent manner. Strategies to eradicate the binding to liver cells include drugs to interfere or eliminate binding to specific cell types, adenovirus capsid protein mutations and chemical modifications of adenovirus to shield the capsid proteins from cellular receptors. The combined use of these approaches should ultimately lead to successful systemic application of adenovirus in humans.

Her2-specific multivalent adapters confer designed tropism to adenovirus for gene targeting

Adenoviruses (Ads) hold great promise as gene vectors for diagnostic or therapeutic applications. The native tropism of Ads must be modified to achieve disease site-specific gene delivery by Ad vectors and this should be done in a programmable way and with technology that can realistically be scaled up. To this end, we applied the technologies of designed ankyrin repeat proteins (DARPins) and ribosome display to develop a DARPin that binds the knob domain of the Ad fiber protein with low nanomolar affinity (K(D) 1.35 nM) and fused this protein with a DARPin specific for Her2, an established cell-surface biomarker of human cancers. The stability of the complex formed by this bispecific targeting adapter and the Ad virion resulted in insufficient gene transfer and was subsequently improved by increasing the valency of adapter-virus binding. In particular, we designed adapters that chelated the knob in a bivalent or trivalent fashion and showed that the efficacy of gene transfer by the adapter-Ad complex increased with the functional affinity of these molecules. This enabled efficient transduction at low stoichiometric adapter-to-fiber ratios. We confirmed the Her2 specificity of this transduction and its dependence on the Her2-binding DARPin component of the adapters. Even the adapter molecules with four fused DARPins could be produced and purified from Escherichia coli at very high levels. In principle, DARPins can be generated against any target and this adapter approach provides a versatile strategy for developing a broad range of disease-specific gene vectors.