PEI-g-PEG-RGD/small interference RNA polyplex-mediated silencing of vascular endothelial growth factor receptor and its potential as an anti-angiogenic tumor therapeutic strategy

Trends in the synthetic polymer delivery of RNA

Ribonucleic acid (RNA) has emerged as one of the most promising therapeutic payloads in the field of gene therapy. There are many unique types of RNA that allow for a range of applications including vaccination, protein replacement therapy, autoimmune disease treatment, gene knockdown and gene editing. However, RNA triggers the host immune system, is vulnerable to degradation and has a low proclivity to enter cells spontaneously. Therefore, a delivery vehicle is required to facilitate the protection and uptake of RNA therapeutics into the desired host cells. Lipid nanoparticles have emerged as one of the only clinically approved vehicles for genetic payloads, including in the COVID-19 messenger RNA vaccines. While lipid nanoparticles have distinct advantages, they also have drawbacks, including strong immune stimulation, complex manufacturing and formulation heterogeneity. In contrast, synthetic polymers are a widely studied group of gene delivery vehicles and boast distinct advantages, including biocompatibility, tunability, inexpensiveness, simple formulation and ease of modification. Some classes of polymers enhance efficient transfection efficiency, and lead to lower stimulation of the host immune system, making them more viable candidates for non-vaccine-related applications of RNA medicines. This review aims to identify the most promising classes of synthetic polymers, summarize recent research aimed at moving them into the clinic and postulate the future steps required for unlocking their full potential.

Nutraceutical-Based Nanoformulations for Breast and Ovarian Cancer Treatment

Different strategies have been investigated for a more satisfactory treatment of advanced breast cancer, including the adjuvant use of omega-3 polyunsaturated fatty acids (PUFAs). These nutritional compounds have been shown to possess potent anti-inflammatory and antiangiogenic activities, the capacity to affect transduction pathways/receptors involved in cell growth and to reprogram tumor microenvironment. Omega-3 PUFA-containing nanoformulations designed for drug delivery in breast cancer were shown to potentiate the effects of enclosed drugs, enhance drug delivery to target sites, and minimize drug-induced side effects. We have critically analyzed here the results of the most recent studies investigating the effects of omega-3 PUFA-containing nanoformulations in breast cancer. The anti-neoplastic efficacy of omega-3 PUFAs has also been convincingly demonstrated by using preclinical in vivo models of ovarian cancer. The results obtained are critically analyzed here and seem to provide a sufficient rationale to move to still lacking interventional clinical trials, as well as to evaluate possible advantages of enclosing omega-3 PUFAs to drug-delivery nanosystems for ovarian cancer. Future perspectives in this area are also provided.

Nanodrug Delivery Systems Modulate Tumor Vessels to Increase the Enhanced Permeability and Retention Effect

The use of nanomedicine for antitumor therapy has been extensively investigated for a long time. Enhanced permeability and retention (EPR) effect-mediated drug delivery is currently regarded as an effective way to bring drugs to tumors, especially macromolecular drugs and drug-loaded pharmaceutical nanocarriers. However, a disordered vessel network, and occluded or embolized tumor blood vessels seriously limit the EPR effect. To augment the EPR effect and improve curative effects, in this review, we focused on the perspective of tumor blood vessels, and analyzed the relationship among abnormal angiogenesis, abnormal vascular structure, irregular blood flow, extensive permeability of tumor vessels, and the EPR effect. In this commentary, nanoparticles including liposomes, micelles, and polymers extravasate through the tumor vasculature, which are based on modulating tumor vessels, to increase the EPR effect, thereby increasing their therapeutic effect.

Advances in Targeted Gene Delivery

Gene therapy has the potential to treat both acquired and inherited genetic diseases. Generally, two types of gene delivery vectors are used - viral vectors and non-viral vectors. Non-viral gene delivery systems have attracted significant interest (e.g. 115 gene therapies approved for clinical trials in 2018; clinicaltrials.gov) due to their lower toxicity, lack of immunogenicity and ease of production compared to viral vectors. To achieve the goal of maximal therapeutic efficacy with minimal adverse effects, the cell-specific targeting of non-viral gene delivery systems has attracted research interest. Targeting through cell surface receptors; the enhanced permeability and retention effect, or pH differences are potential means to target genes to specific organs, tissues, or cells. As for targeting moieties, receptorspecific ligand peptides, antibodies, aptamers and affibodies have been incorporated into synthetic nonviral gene delivery vectors to fulfill the requirement of active targeting. This review provides an overview of different potential targets and targeting moieties to target specific gene delivery systems.

New Aspects of Ultrasound-Mediated Targeted Delivery and Therapy for Cancer

Ultrasound-mediated targeted delivery (UMTD), a novel delivery modality of therapeutic materials based on ultrasound, shows great potential in biomedical applications. By coupling ultrasound contrast agents with therapeutic materials, UMTD combines the advantages of ultrasound imaging and carrier, which benefit deep tissue penetration and high concentration aggregation. In this paper we introduced recent advances in ultrasound contrast agents and applications in tumor therapy. Ultrasound contrast agents were categorized by their functions, mainly including thermosensitive, pH-sensitive and photosensitive ultrasound contrast agents. The various applications of UMTD in tumor treatment were summarized as follows: drug therapy, transfection of anti-oncogene, RNA interference, vaccine immunotherapy, monoclonal antibody immunotherapy, adoptive cellular immunotherapy, cytokine immunotherapy, and so on. In the end, we elaborated on the current challenges and provided perspectives of UMTD for clinical applications.

Integrin-Mediated Delivery of Drugs and Nucleic Acids for Anti-Angiogenic Cancer Therapy: Current Landscape and Remaining Challenges

Angiogenesis, sprouting of new blood vessels from pre-existing vasculatures, plays a critical role in regulating tumor growth. Binding interactions between integrin, a heterodimeric transmembrane glycoprotein receptor, and its extracellular matrix (ECM) protein ligands govern the angiogenic potential of tumor endothelial cells. Integrin receptors are attractive targets in cancer therapy due to their overexpression on tumor endothelial cells, but not on quiescent blood vessels. These receptors are finding increasing applications in anti-angiogenic therapy via targeted delivery of chemotherapeutic drugs and nucleic acids to tumor vasculatures. The current article attempts to provide a retrospective account of the past developments, highlight important contemporary contributions and unresolved set-backs of this emerging field.

Bioreducible Poly(Amino Ethers) Based mTOR siRNA Delivery for Lung Cancer

PURPOSE

Lung cancer is one of the leading causes of deaths in the United States, but currently available therapies for lung cancer are associated with reduced efficacy and adverse side effects. Small interfering RNA (siRNA) can knock down the expression of specific genes and result in therapeutic efficacy in lung cancer. Recently, mTOR siRNA has been shown to induce apoptosis in NSCLC cell lines but its use is limited due to poor stability in biological conditions.

METHODS

In this study, we modified an aminoglyocisde-derived cationic poly (amino-ether) by introducing a thiol group using Traut's reagent to generate a bio-reducible modified-poly (amino-ether) (mPAE). The mPAE polymer was used to encapsulate mTOR siRNA by nanoprecipitation method, resulting in the formation of stable and bio-reducible nanoparticles (NPs) which possessed an average diameter of 114 nm and a surface charge of approximately +27 mV.

RESULTS

The mTOR siRNA showed increased release from the mTS-mPAE NPs in the presence of 10 mM glutathione (GSH). The polymeric mTS-mPAE-NPs were also capable of efficient gene knockdown (60 and 64%) in A549 and H460 lung cancer cells, respectively without significant cytotoxicity at 30 μg/ml concentrations. The NPs also showed time-dependent cellular uptake for up to 24 h as determined using flow cytometry. Delivery of the siRNA using these NPs also resulted in significant inhibition of A549 and H460 cell proliferation in vitro, respectively.

CONCLUSIONS

The results demonstrate that the mPAE polymer based NPs show strong potential for siRNA delivery to lung cancer cells. It is anticipated that future modification can help improve the efficacy of nucleic acid delivery, leading to higher inhibition of lung cancer growth in vitro and in vivo.

Journey of siRNA: Clinical Developments and Targeted Delivery

Since the evolutionary discovery of RNA interference and its utilization for gene knockdown in mammalian cell, a remarkable progress has been achieved in small interfering RNA (siRNA) therapeutics. siRNA is a promising tool, utilized as therapeutic agent against various diseases. Despite its significant potential benefits, safe, efficient, and target oriented delivery of siRNA is one of the major challenges in siRNA therapeutics. This review covers major achievements in clinical trials and targeted delivery of siRNAs using various targeting ligand-receptor pair. Local and systemically administered siRNA drug candidates at various phases in clinical trials are described in this review. This review also provides a deep insight in development of targeted delivery of siRNA. Various targeting ligand-siRNA pair with complexation and conjugation approaches are discussed in this review. This will help to achieve further optimization and development in targeted delivery of siRNAs to achieve higher gene silencing efficiency with lowest siRNA dose availability.

Modulating angiogenesis with integrin-targeted nanomedicines

Targeting angiogenesis-related pathologies, which include tumorigenesis and metastatic processes, has become an attractive strategy for the development of efficient guided nanomedicines. In this respect, integrins are cell-adhesion molecules involved in angiogenesis signaling pathways and are overexpressed in many angiogenic processes. Therefore, they represent specific biomarkers not only to monitor disease progression but also to rationally design targeted nanomedicines. Arginine-glycine-aspartic (RGD) containing peptides that bind to specific integrins have been widely utilized to provide ligand-mediated targeting capabilities to small molecules, peptides, proteins, and antibodies, as well as to drug/imaging agent-containing nanomedicines, with the final aim of maximizing their therapeutic index. Within this review, we aim to cover recent and relevant examples of different integrin-assisted nanosystems including polymeric nanoconstructs, liposomes, and inorganic nanoparticles applied in drug/gene therapy as well as imaging and theranostics. We will also critically address the overall benefits of integrin-targeting.

Gene delivery nanoparticles to modulate angiogenesis

Angiogenesis is naturally balanced by many pro- and anti-angiogenic factors while an imbalance of these factors leads to aberrant angiogenesis, which is closely associated with many diseases. Gene therapy has become a promising strategy for the treatment of such a disordered state through the introduction of exogenous nucleic acids that express or silence the target agents, thereby engineering neovascularization in both directions. Numerous non-viral gene delivery nanoparticles have been investigated towards this goal, but their clinical translation has been hampered by issues associated with safety, delivery efficiency, and therapeutic effect. This review summarizes key factors targeted for therapeutic angiogenesis and anti-angiogenesis gene therapy, non-viral nanoparticle-mediated approaches to gene delivery, and recent gene therapy applications in pre-clinical and clinical trials for ischemia, tissue regeneration, cancer, and wet age-related macular degeneration. Enhanced nanoparticle design strategies are also proposed to further improve the efficacy of gene delivery nanoparticles to modulate angiogenesis.

Nanocomplexes from RGD-modified generation 1.0 polyamidoamine based copolymers used for intravascular gene release to prevent restenosis

Aim: To validate the efficacy of nanocomplexes from RGD-modified polyamidoamine (PAMAM G1) copolymer for prevention of restenosis. Materials & methods: Generation 1.0 polyamidoamine (PAMAM G1)-based copolymers (PGP) and RGD modified PGP (PGP-RGD) were synthesized and its properties were evaluated. Intravascular VEGF165 release tests were performed. Results: The PGP-RGD1 (2.6% grafting rate) exhibited lower cytotoxicity and larger combining ability with pDNA. The complexes had sizes of 80–160 nm and zeta potentials of 3–20 mV. Transfection efficiency of PGP-RGD1 complexes in human umbilical vein endothelial cells was larger than that of PGP complexes. Patency and expression level of artery in PGP-RGD1 group were higher than that in saline group. Conclusion: PGP-RGD1 will be a promising targeted gene vector.

Synthesis and evaluation of the targeted binding of RGD-containing PEGylated-PEI/DNA polyplex micelles as radiotracers for a tumor-targeting imaging probe

Polyplex micelles with pEGFP and RGD-modified poly(ethylene glycol)-grafted polyethylenimine (E[c(RGDyK)]₂-PEG-g-PEI) and were labeled with ^99mTc for the in vivo study as proficient probes for molecular imaging.

Targeted delivery of miRNA therapeutics for cardiovascular diseases: opportunities and challenges

Dysregulation of miRNA expression has been associated with many cardiovascular diseases in animal models, as well as in patients. In the present review, we summarize recent findings on the role of miRNAs in cardiovascular diseases and discuss the opportunities, possibilities and challenges of using miRNAs as future therapeutic targets. Furthermore, we focus on the different approaches that can be used to deliver these newly developed miRNA therapeutics to their sites of action. Since siRNAs are structurally homologous with the miRNA therapeutics, important lessons learned from siRNA delivery strategies are discussed that might be applicable to targeted delivery of miRNA therapeutics, thereby reducing costs and potential side effects, and improving efficacy.

Recent In Vivo Evidences of Particle-Based Delivery of Small-Interfering RNA (siRNA) into Solid Tumors

Small-interfering RNA (siRNA) is both a powerful tool in research and a promising therapeutic platform to modulate expression of disease-related genes. Malignant tumors are attractive disease targets for nucleic acid-based therapies. siRNA directed against oncogenes, and genes driving metastases or angiogenesis have been evaluated in animal models and in some cases, in humans. The outcomes of these studies indicate that drug delivery is a significant limiting factor. This review provides perspectives on in vivo validated nanoparticle-based siRNA delivery systems. Results of recent advances in liposomes and polymeric and inorganic formulations illustrate the need for mutually optimized attributes for performance in systemic circulation, tumor interstitial space, plasma membrane, and endosomes. Physiochemical properties conducive to efficient siRNA delivery are summarized and directions for future research are discussed.

Bioreducible polymers for therapeutic gene delivery

Most currently available cationic polymers have significant acute toxicity concerns such as cellular toxicity, aggregation of erythrocytes, and entrapment in the lung capillary bed, largely due to their poor biocompatibility and non-degradability under physiological conditions. To develop more intelligent polymers, disulfide bonds are introduced in the design of biodegradable polymers. Herein, the sustained innovations of biomimetic nano-sized constructs with bioreducible poly(disulfide amine)s demonstrate a viable clinical tool for the treatment of cardiovascular disease, anemia, diabetes, and cancer.

A review of RGD-functionalized nonviral gene delivery vectors for cancer therapy

The development of effective treatments that enable many patients suffering from cancer to be successfully cured is highly demanded. Angiogenesis, which is a process for the formation of new capillary blood vessels, has a crucial role in solid tumor progression and the development of metastasis. Antiangiogenic therapy designed to prevent tumor angiogenesis, thereby arresting the growth or spread of tumors, has emerged as a non-invasive and safe option for cancer treatment. Due to the fact that integrin receptors are overexpressed on the surface of angiogenic endothelial cells, various strategies have been made to develop targeted delivery systems for cancer gene therapy utilizing integrin-targeting peptides with an exposed arginine-glycine-aspartate (RGD) sequence. The aim of this review is to summarize the progress and prospect of RGD-functionalized nonviral vectors toward targeted delivery of genetic materials in order to achieve an efficient therapeutic outcome for cancer gene therapy, including antiangiogenic therapy.

A rapid and convenient method to enhance transgenic expression in target cells

Gene therapy provides a novel strategy and a new hope for patients with cancer. Unfortunately, the specifics of the delivery systems or the promoters have not achieved the specified efficacy so far, and the perfection of either system will be extremely difficult. In this study, we introduce a simple concept that a combination of a partially specific delivery system and a partially specific promoter activity may achieve a more specific effect on transgenic expression in target cells. The first section describes tumor-related transcription factors that were assayed in tumors or rapidly proliferating cells to determine their activities. The activities of nuclear factor (NF)-κB, CREB, and HIF-1 were higher, and three copies of each response element were used to construct a transcription factor-based synthetic promoter (TSP). The results showed that the expression of the TSP was active and partially specific to cell types. As described in the second section, the multifunctional peptide RGD-4C-HA was designed to absorb polyethyleneimine (PEI) molecules, and this complex was targeted to integrin αvβ3 on B16F10 cells. The results indicated that RGD-4C-HA could associate with PEI to mediate specific targeting in vitro. Finally, the combination of the PEI-peptide complex and TSP could enhance the specifically transgenic expression in B16F10 cells. This strategy has been proven to work in vitro and might potentially be used for specific gene therapy in vivo.

Cationic polymers and their therapeutic potential

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review.

Targeted polymeric micelles for siRNA treatment of experimental cancer by intravenous injection

Small interfering ribonucleic acid (siRNA) cancer therapies administered by intravenous injection require a delivery system for transport from the bloodstream into the cytoplasm of diseased cells to perform the function of gene silencing. Here we describe nanosized polymeric micelles that deliver siRNA to solid tumors and elicit a therapeutic effect. Stable multifunctional micelle structures on the order of 45 nm in size formed by spontaneous self-assembly of block copolymers with siRNA. Block copolymers used for micelle formation were designed and synthesized to contain three main features: a siRNA binding segment containing thiols, a hydrophilic nonbinding segment, and a cell-surface binding peptide. Specifically, poly(ethylene glycol)-block-poly(L-lysine) (PEG-b-PLL) comprising lysine amines modified with 2-iminothiolane (2IT) and the cyclo-Arg-Gly-Asp (cRGD) peptide on the PEG terminus was used. Modification of PEG-b-PLL with 2IT led to improved control of micelle formation and also increased stability in the blood compartment, while installation of the cRGD peptide improved biological activity. Incorporation of siRNA into stable micelle structures containing the cRGD peptide resulted in increased gene silencing ability, improved cell uptake, and broader subcellular distribution in vitro and also improved accumulation in both the tumor mass and tumor-associated blood vessels following intravenous injection into mice. Furthermore, stable and targeted micelles inhibited the growth of subcutaneous HeLa tumor models and demonstrated gene silencing in the tumor mass following treatment with antiangiogenic siRNAs. This new micellar nanomedicine could potentially expand the utility of siRNA-based therapies for cancer treatments that require intravenous injection.

Subcellular fate and off-target effects of siRNA, shRNA, and miRNA

RNA interference (RNAi) strategies include double-stranded RNA (dsRNA), small interfering RNA (siRNA), short hairpin RNA (shRNA), and microRNA (miRNA). As this is a highly specific technique, efforts have been made to utilize RNAi towards potential knock down of disease-causing genes in a targeted fashion. RNAi has the potential to selectively inhibit gene expression by degrading or blocking the translation of the target mRNA. However, delivering these RNAs to specific cells presents a significant challenge. Some of these challenges result from the necessity of traversing the circulatory system while avoiding kidney filtration, degradation by endonucleases, aggregation with serum proteins, and uptake by phagocytes. Further, non-specific delivery may result in side-effects, including the activation of immune response. We discuss the challenges in the systemic delivery to target cells, cellular uptake, endosomal release and intracellular transport of RNAi drugs and recent progress in overcoming these barriers. We also discuss approaches that increase the specificity and metabolic stability and reduce the off-target effects of RNAi strategy.

Suicide gene therapy using reducible poly (oligo-D-arginine) for the treatment of spinal cord tumors

Suicide gene therapy based on a combination of herpes simplex virus-thymidine kinase (HSV-tk) and ganciclovir (GCV) has obstacles to achieving a success in clinical use for the treatment of cancer due to inadequate thymidine kinase (TK) expression. The primary concern for improving anticancer efficacy of the suicide gene therapy is to develop an appropriate carrier that highly expresses TK in vivo. Despite great advances in the development of non-viral vectors, none has been used in cancer suicide gene therapy, not even in experimental challenge. Reducible poly (oligo-D-arginine) (rPOA), one of the effective non-viral carriers working in vivo, was chosen to deliver HSV-tk to spinal cord tumors which are appropriate targets for suicide gene therapy. Since the system exerts toxicity only in dividing cells, cells in the central nervous system, which are non-proliferative, are not sensitive to the toxic metabolites. In the present study, we demonstrated that the locomotor function of the model rat was maintained through the tumor suppression resulting from the tumor-selective suicide activity by co-administration of rPOA/HSV-tk and GCV. Thus, rPOA plays a crucial role in suicide gene therapy for cancer, and an rPOA/HSV-tk and GCV system could help promote in vivo trials of suicide gene therapy.