A novel approach to attenuate proliferative vitreoretinopathy using ultrasound-targeted microbubble destruction and recombinant adeno-associated virus-mediated RNA interference targeting transforming growth factor-β2 and platelet-derived growth factor-B

External stimuli-responsive drug delivery to the posterior segment of the eye

Posterior segment eye diseases represent the leading causes of vision impairment and blindness globally. Current therapies still have notable drawbacks, including the need for frequent invasive injections and the associated risks of severe ocular complications. Recently, the utility of external stimuli, such as light, ultrasound, magnetic field, and electric field, has been noted as a promising strategy to enhance drug delivery to the posterior segment of the eye. In this review, we briefly summarize the main physiological barriers against ocular drug delivery, focusing primarily on the recent advancements that utilize external stimuli to improve treatment outcomes for posterior segment eye diseases. The advantages of these external stimuli-responsive drug delivery strategies are discussed, with illustrative examples highlighting improved tissue penetration, enhanced control over drug release, and targeted drug delivery to ocular lesions through minimally invasive routes. Finally, we discuss the challenges and future perspectives in the translational research of external stimuli-responsive drug delivery platforms, aiming to bridge existing gaps toward clinical use.

Experimental Models to Study Epithelial-Mesenchymal Transition in Proliferative Vitreoretinopathy

Proliferative vitreoretinal diseases (PVDs) encompass proliferative vitreoretinopathy (PVR), epiretinal membranes, and proliferative diabetic retinopathy. These vision-threatening diseases are characterized by the development of proliferative membranes above, within and/or below the retina following epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) and/or endothelial-mesenchymal transition of endothelial cells. As surgical peeling of PVD membranes remains the sole therapeutic option for patients, development of in vitro and in vivo models has become essential to better understand PVD pathogenesis and identify potential therapeutic targets. The in vitro models range from immortalized cell lines to human pluripotent stem-cell-derived RPE and primary cells subjected to various treatments to induce EMT and mimic PVD. In vivo PVR animal models using rabbit, mouse, rat, and swine have mainly been obtained through surgical means to mimic ocular trauma and retinal detachment, and through intravitreal injection of cells or enzymes to induce EMT and investigate cell proliferation and invasion. This review offers a comprehensive overview of the usefulness, advantages, and limitations of the current models available to investigate EMT in PVD.

Vitreous humor proteome: unraveling the molecular mechanisms underlying proliferative and neovascular vitreoretinal diseases

Proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and neovascular age-related macular degeneration (nAMD) are among the leading causes of blindness. Due to the multifactorial nature of these vitreoretinal diseases, omics approaches are essential for a deeper understanding of the pathophysiologic processes underlying the evolution to a proliferative or neovascular etiology, in which patients suffer from an abrupt loss of vision. For many years, it was thought that the function of the vitreous was merely structural, supporting and protecting the surrounding ocular tissues. Proteomics studies proved that vitreous is more complex and biologically active than initially thought, and its changes reflect the physiological and pathological state of the eye. The vitreous is the scenario of a complex interplay between inflammation, fibrosis, oxidative stress, neurodegeneration, and extracellular matrix remodeling. Vitreous proteome not only reflects the pathological events that occur in the retina, but the changes in the vitreous itself play a central role in the onset and progression of vitreoretinal diseases. Therefore, this review offers an overview of the studies on the vitreous proteome that could help to elucidate some of the pathological mechanisms underlying proliferative and/or neovascular vitreoretinal diseases and to find new potential pharmaceutical targets.

Ultrasound and Microbubbles for the Treatment of Ocular Diseases: From Preclinical Research towards Clinical Application

The unique anatomy of the eye and the presence of various biological barriers make efficacious ocular drug delivery challenging, particularly in the treatment of posterior eye diseases. This review focuses on the combination of ultrasound and microbubbles (USMB) as a minimally invasive method to improve the efficacy and targeting of ocular drug delivery. An extensive overview is given of the in vitro and in vivo studies investigating the mechanical effects of ultrasound-driven microbubbles aiming to: (i) temporarily disrupt the blood–retina barrier in order to enhance the delivery of systemically administered drugs into the eye, (ii) induce intracellular uptake of anticancer drugs and macromolecules and (iii) achieve targeted delivery of genes, for the treatment of ocular malignancies and degenerative diseases. Finally, the safety and tolerability aspects of USMB, essential for the translation of USMB to the clinic, are discussed.

Inflammatory mediators of proliferative vitreoretinopathy: hypothesis and review

Purpose

To review the role of inflammatory mediators in proliferative vitreoretinopathy (PVR) development and the current treatment for PVR prevention.

Methods

A PubMed search was carried out using these keywords “PVR,” “inflammatory mediators,” “growth factors,” “cytokines” and “treatment.” Studies regarding inflammatory mediators and PVR therapy were included and published up to December 2019.

Results

Inflammatory mediators, namely growth factors and cytokines, have been implicated in the occurrence and development of PVR. Among various inflammatory mediators, transforming growth factor-β, platelet-derived growth factor, interleukin-6, interleukin-8 and tumor necrosis factor-α are considered to be particularly important. In this review, we focus on the hypothesis that growth factors and cytokines are involved in the development of PVR, and current treatment for the prevention of PVR.

Conclusion

We support the hypothesis that growth factors and cytokines may participate in the complex process of PVR development. More importantly, the identification of inflammatory mediators provides novel and efficacious therapeutic targets for the treatment of PVR.

Enhanced delivery of biodegradable mPEG-PLGA-PLL nanoparticles loading Cy3-labelled PDGF-BB siRNA by UTMD to rat retina

We investigated the efficacy and safety of ultrasound (US)-targeted microbubble (MB) destruction (UTMD)-enhanced delivery of monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly-L-lysine (mPEG-PLGA-PLL) nanoparticles (NPs) loading Cy3-labelled platelet-derived growth factor BB (PDGF-BB) siRNA to rat retina in vivo. Eighty Wistar rats were divided into five groups (G). The right eyes, respectively, received an intravitreal injection as follows: normal saline (NS) (G1), NPs and NS (G2), NPs and MBs (G3), NPs and NS (G4) and NPs and MBs (G5). In G4 and G5, the eyes were exposed to US for 5 mins. Twenty-four hours after transfection, the uptake and distribution of Cy3-labelled siRNA in rat retina were observed by fluorescent microscope. The percentage of Cy3- labelled siRNA-positive cells was evaluated by flow cytometer. The levels of PDGF-BB mRNA in retinal pigment epithelium (RPE) cells and secreted PDGF-BB proteins were also measured. Hematoxylin and eosin staining and frozen sections were used to observe tissue damage. Our results showed that the number of Cy3-labelled siRNApositive cells in G5 was significantly higher than those of the other groups (P less than 0.05 for all comparisons). The maximum efficiency of siRNA uptake in neural retina was 18.22 +/_ 1.67%. In G4 and G5, a small number of Cy3- labelled siRNA-positive cells were also detected in the pigmented cell layer of the retina. NPs loading siRNA delivered with UTMD could more effectively down-regulate the mRNA and protein expression of PDGF-BB than NPs plus US (P=0.014 and P=0.007, respectively). Histology showed no evident tissue damage after UTMDmediated NPs loading siRNA transfection. UTMD could be used safely to enhance the delivery of mPEG-PLGAPLL NPs loading siRNA into rat retina.

TGF-β1 and TIMP1 double directional rAAV targeted by UTMD in atherosclerotic vulnerable plaque

In the present study, we determined whether ultrasound-targeted microbubble destruction (UTMD) combined with dual targeting of transforming growth factor (TGF)-β1 and tissue inhibitors of metalloproteinase (TIMP) 1 recombinant adeno-associated virus (rAAV) can stabilize atherosclerotic vulnerable plaques. First, we used rabbit model to detect the TGF-β1/TIMP1 virus therapy result. H&E staining was used to evaluate the tissues. The protein levels of TGF-β1 and TIMP1 were detected in rabbit models. The THP-1 cells were induced into macrophages, and transfected with TGF-β1 and TIMP1 rAAV under optimized UTMD. The expression of TGF-β1 and TIMP1 was measured by RT-PCR and western blotting. We found that the apoptotic rates were induced when compared to the control group. The rAAV virus group showed a significant decrease in the p-ERT and p-AKT expression. These data support the hypothesis that TGF-β1 and TIMP1 are crucial in the regulation of atherosclerotic plaques.

Gene therapy for ocular diseases meditated by ultrasound and microbubbles (Review)

The eye is an ideal target organ for gene therapy as it is easily accessible and immune‑privileged. With the increasing insight into the underlying molecular mechanisms of ocular diseases, gene therapy has been proposed as an effective approach. Successful gene therapy depends on efficient gene transfer to targeted cells to prove stable and prolonged gene expression with minimal toxicity. At present, the main hindrance regarding the clinical application of gene therapy is not the lack of an ideal gene, but rather the lack of a safe and efficient method to selectively deliver genes to target cells and tissues. Ultrasound‑targeted microbubble destruction (UTMD), with the advantages of high safety, repetitive applicability and tissue targeting, has become a potential strategy for gene‑ and drug delivery. When gene‑loaded microbubbles are injected, UTMD is able to enhance the transport of the gene to the targeted cells. High‑amplitude oscillations of microbubbles act as cavitation nuclei which can effectively focus ultrasound energy, produce oscillations and disruptions that increase the permeability of the cell membrane and create transient pores in the cell membrane. Thereby, the efficiency of gene therapy can be significantly improved. The UTMD‑mediated gene delivery system has been widely used in pre‑clinical studies to enhance gene expression in a site‑specific manner in a variety of organs. With reasonable application, the effects of sonoporation can be spatially and temporally controlled to improve localized tissue deposition of gene complexes for ocular gene therapy applications. In addition, appropriately powered, focused ultrasound combined with microbubbles can induce a reversible disruption of the blood‑retinal barrier with no significant side effects. The present review discusses the current status of gene therapy of ocular diseases as well as studies on gene therapy of ocular diseases meditated by UTMD.

Diagnostic and therapeutic research on ultrasound microbubble/nanobubble contrast agents (Review)

The contrast enhanced imaging function of ultrasound contrast agents (UCAs) has been extensively investigated using physical acoustic signatures. It has a number of novel applications, including tissue‑specific molecular imaging and multi‑modal imaging. In addition there are numerous other therapeutic applications of UCAs, for example as vehicles for drug or gene delivery. These uses are discussed, as well as the acoustically‑induced biological effects, including ultrasound targeted microbubble destruction (UTMD). This review also explores the considerations for the safe use of UCA from an acoustic standpoint. The scope of the application of UCA has markedly expanded in recent years, and it is a rapidly growing field of medical research. The current article reviews recent advances in the diagnostic and therapeutic applications of ultrasound microbubble/nanobubble contrast agents.

The dual effect of ultrasound-targeted microbubble destruction in mediating recombinant adeno-associated virus delivery in renal cell carcinoma: transfection enhancement and tumor inhibition

BACKGROUND

Recombinant adeno-associated virus (rAAV) is recognized as a promising vector for cancer gene therapy, although its low transfer efficiency in less permissive cells limits extensive application. Our previous studies reported that ultrasound-targeted microbubble (MB) destruction (UTMD) enhanced rAAV transfer in its permissive retinal cells. In the present study, we investigated whether UTMD increased rAAV transfer in less permissive human renal cell carcinoma (hRCC) cells and tumors.

METHODS

hRCC cells were treated with rAAV2 under different conditions of UTMD, and the viral transfer efficiency and cell viability were analyzed. Fifty-two male nude mice (BALB/c) implanted with hRCC cells were randomly assigned to four groups consisting of rAAV, rAAV + ultrasound and rAAV + UTMD (20 µl and 40 µl of MBs). UTMD was initiated immediately after intratumoral viral injection, and viral transfer efficiency and tumor volumes were analyzed at 12 weeks after infection.

RESULTS

The efficiency of non-augmented transfer of rAAV2 into hRCC cells was low (17.28 ± 2.44%). The use of UTMD enhanced viral transfer efficiency by two- to three-fold, and enhanced viral genomic DNA by more than nine-fold, without decreasing cell viability. In vivo studies also showed that UTMD increased rAAV2 transfer in tumor. The enhancements were maintained for a period of 12 weeks. Tumor growth in mice was inhibited by UTMD treatment, and UTMD treatment augmented by MBs (40 µl) produced an even stronger effect.

CONCLUSIONS

UTMD enhanced rAAV2 transfer into less permissive RCC cells and tumors, resulting in inhibition of tumor growth, which suggests that UTMD may be a useful delivery tool for cancer gene therapy.

Ultrasound‑targeted microbubble destruction enhances gene transduction of adeno-associated virus in a less-permissive cell type, NIH/3T3

Adeno‑associated virus (AAV) is a common vector utilized in gene therapy. The NIH/3T3 cell line, which is a potential induced pluripotent stem (iPS) cell type, was identified to be a less-permissive cell type to AAV due to its defective endosomal processing. Ultrasound‑targeted microbubble destruction (UTMD) enhanced the gene transduction of AAV in permissive cells. However, there are no data concerning UTMD enhancement in less-permissive cells, and the exact mechanism of UTMD enhancement in cellular uptake is unclear. Greater knowledge concerning the rate-limiting steps in NIH/3T3 cells would aid in the elucidation of the mechanism of UTMD enhancement in the gene transduction of AAV. In the present study, UTMD enhanced the gene transduction of AAV in NIH/3T3 cells, suggesting that UTMD‑enhanced AAV‑mediated gene transduction may be beneficial for gene therapy in iPS cells. The dose dependence of UTMD enhancement indicated that mechanisms other than sonoporation were involved in the cellular uptake of AAV. However, UTMD did not greatly increase the gene transduction of AAV in NIH/3T3 cells. Additionally, the similar degree of enhancement in the two cell types resulted in no correlation between UTMD and endosomal processing. Future studies on UTMD‑mediated AAV transduction in other non- or less‑permissive cell types may aid in elucidating the exact mechanism of UTMD enhancement in cellular uptake.

Ultrasound targeted microbubble destruction stimulates cellular endocytosis in facilitation of adeno-associated virus delivery

The generally accepted mechanism for ultrasound targeted microbubble destruction (UTMD) to enhance drug and gene delivery is through sonoporation. However, passive uptake of adeno-associated virus (AAV) into cells following sonoporation does not adequately explain observations of enhanced transduction by UTMD. This study investigated alternative mechanisms of UTMD enhancement in AAV delivery. UTMD significantly enhanced transduction efficiency of AAV in a dose-dependent manner. UTMD stimulated a persistent uptake of AAV into the cytoplasm and nucleus. This phenomenon occurred over several hours, suggesting that some viral particles are endocytosed by cells rather than exclusively passing through pores created by sonoporation. Additionally, UTMD enhanced clathrin expression and accumulation at the plasma membrane suggesting greater clathrin-mediated endocytosis following UTMD. Transmission electron microscopy (TEM) revealed that UTMD stimulated formation of clathrin-coated pits (CPs) and uncoated pits (nCPs). Furthermore, inhibition of clathrin-mediated endocytosis partially blocked the enhancement of AAV uptake following UTMD. The results of this study implicate endocytosis as a mechanism that contributes to UTMD-enhanced AAV delivery.