Synthetic hydrogels as carriers in antisense therapy: preliminary evaluation of an oligodeoxynucleotide covalent conjugate with a copolymer of 1-vinyl-2-pyrrolidinone and 2-hydroxyethyl methacrylate

Antisense Oligonucleotide-Mediated Splice Switching: Potential Therapeutic Approach for Cancer Mitigation

Splicing is an essential process wherein precursor messenger RNA (pre-mRNA) is reshaped into mature mRNA. In alternative splicing, exons of any pre-mRNA get rearranged to form mRNA variants and subsequently protein isoforms, which are distinct both by structure and function. On the other hand, aberrant splicing is the cause of many disorders, including cancer. In the past few decades, developments in the understanding of the underlying biological basis for cancer progression and therapeutic resistance have identified many oncogenes as well as carcinogenic splice variants of essential genes. These transcripts are involved in various cellular processes, such as apoptosis, cell signaling and proliferation. Strategies to inhibit these carcinogenic isoforms at the mRNA level are promising. Antisense oligonucleotides (AOs) have been developed to inhibit the production of alternatively spliced carcinogenic isoforms through splice modulation or mRNA degradation. AOs can also be used to induce splice switching, where the expression of an oncogenic protein can be inhibited by the induction of a premature stop codon. In general, AOs are modified chemically to increase their stability and binding affinity. One of the major concerns with AOs is efficient delivery. Strategies for the delivery of AOs are constantly being evolved to facilitate the entry of AOs into cells. In this review, the different chemical modifications employed and delivery strategies applied are discussed. In addition to that various AOs in clinical trials and their efficacy are discussed herein with a focus on six distinct studies that use AO-mediated exon skipping as a therapeutic strategy to combat cancer.

[Artificial vitreous body: Strategies for vitreous body substitutes]

BACKGROUND

Although numerous advances have been made in technology and techniques of pars plana vitrectomy and tamponades, there are still unsolved issues, such as proliferative vitreoretinopathy (PVR), multiple retinal breaks and persistent hypotonia. All available internal tamponades (e.g, gases, oils and fluorocarbons) are hydrophobic, so they approximate the neurosensory retina to the retinal pigment epithelium due to buoyant force and surface tension. Even though these tamponade materials exhibit various beneficial attributes in the clinical application, the hydrophobic nature has clear disadvantages and compartmentalization and significant incidence of PVR development still occur.

RESULTS AND CONCLUSION

An ideal vitreous body substitute should mimic the native human vitreous body, in both form and function. Vitreous body substitutes, such as hydrogels fulfill the biophysical needs in a similar manner to the natural vitreous body by providing an internal tamponade effect through swelling pressure and viscosity. New approaches range from cross-linked semisynthetic to synthetic polymers. These hydrogels have a good biocompatibility, optical clarity, a refractive index and rheological properties that are similar to the natural human vitreous body and are able to act as anti-adhesive and anti-migrative agents and can therefore reduce PVR. Furthermore, hydrogels could also serve as controlled-release drug-delivery systems for anti-proliferative, neuroprotective or nutritive drugs.

Comparative study of the in vitro interaction of two fibroblast cell lines with a polyalkyl-imide hydrogel

The in vitro effects of polyalkyl-imide hydrogel (PAI) containing 96% pyrogen-free water on the viability, apoptosis, cell shape and metabolic activities of murine 3T3 and human Detroit 555 fibroblasts were investigated. Analysis of the viscous-elastic properties and the ultrastructure of PAI, performed by rheometer and AFM respectively, showed that the material has the typical characteristics of hydrogel, including a three-dimensional configuration of molecules arranged in a regular network with many discrete caveolae where most of the water is captured. Hydrogel biocompatibility was found to be high for both cell lines, with some differences. Cell viability decreased more in 3T3 cells than Detroit 550 fibroblasts when cultured in the presence of 100 mg/ml hydrogel but not at concentrations of 25 and 50 mg/ml hydrogel. The period of incubation with PAI (24 and 48 h) only partially affected cell viability. Apoptosis, most likely due to cells' inability to adhere to the polymer, was the only type of cell death observed. Fibroblasts grown in the presence of polymer were always metabolically active since they continued to synthesize collagen. In conclusion, PAI hydrogel, even at high concentrations, was biocompatible for both fibroblasts, but in particular for human cells, thus encouraging its use as a dermal filler.

A biodegradable copolymer for the slow release of growth hormone expedites scarring in diabetic rats

In many diseases wound healing is impaired. This study was designed to establish whether the healing process in diabetes could be improved using a site-specific polymer delivery system containing hGH. The system was first optimized in in vitro experiments performed on cultured fibroblasts taken from healthy and diabetic rats and then tested in an incisional wound model created in the diabetic Wistar rat. In the in vitro experiments using cultured fibroblasts, cell viability, growth, and proliferation were determined, along with polymer degradation, hormone release rates and the expression of TGFbeta1 in the culture medium. For the in vivo experiments, polymer discs with/without GH were inserted through 3 cm incisions made on the backs of the animals. Wound specimens were obtained 7 and 30 days after surgery to evaluate inflammatory/apoptotic cells, metalloprotease expression and neoangiogenesis using microscopy and immunohistochemical techniques. The local administration of GH using a polymer delivery system did not affect the normal wound healing process. Conversely, when used in diabetic animals, epidermal and dermal repair was expedited. Our findings indicate that GH induces cell proliferation, enhances CD4(+) infiltration; increases extracellular matrix protein deposition; stimulates angiogenesis; and diminishes apoptosis at the diabetic wound site. These effects give rise to a comparable wound healing process to that observed in healthy animals.

In vitro study of the interaction of polyalkilimide and polyvinyl alcohol hydrogels with cells

Hydrogels are a class of polymers that in the last decade have had a great development and application for soft tissue augmentation, due to their similarity to this tissue for their high water content. The in vitro effects of polyalkylmide hydrogel (pAI) and polyvinyl alcohol hydrogel (pVOH) on human lymphocytes and U937 cells viability, apoptosis and cell shape were investigated. Cell viability was always higher than 70%, thus showing the hydrogels were not cytotoxic for both cell lines. Some differences were, however, found. At short time, lymphocytes were very sensitive to the hydrogels incubation, while at long time, U937 cells were the most sensitive cells. Other differences on cell viability were related to the time of incubation, to the type of hydrogel and to the polymers concentration. Cell viability decreased only at the longest time of incubation and with the highest hydrogel concentration. Accordingly, cell death by apoptosis increased; necrosis was never observed in the cultures. Concentration- and hydrogel-dependent modifications of cell shape (bigger cell volume, elongations of cells) were observed in a few percentage of viable cells. In conclusion, the very high in vitro degree of biocompatibility shown by both hydrogels encourages their use as dermal fillers.

Selection of oligonucleotide aptamers with enhanced uptake and activation of human leukemia B cells

The clinical use of oligonucleotide (ODN) therapeutics has been hampered by their limited ability to penetrate intact cells. To identify ODN properties that would facilitate cellular uptake, we developed a repetitive selection procedure using an ODN library containing at least 10(14) different molecules and human B lymphoma cells as a target. Natural phosphodiester single-stranded DNA ODNs (R-aptamers) were obtained after 10 rounds of selection. A common feature in the R-aptamers was guanine-rich 3' terminal sequences, and many also contained potential immunostimulatory (ISS) CpG sequence motifs. Two R-aptamers (R10-60 and D-R15-8) with the predominant shared characteristics were selected for further study on primary human chronic lymphocytic leukemia (CLL) B cells, which are well known to be difficult to transfect and activate. Flow cytometry analysis of the CLL cells demonstrated that the fluorochrome-labeled R-aptamers were internalized much more efficiently than nonselected random sequence ODN. Studies on sequence modifications indicated that efficient uptake required ODN multimerization, that was promoted by guanine-rich sequences at the 3' terminus. In addition, CLL cells that were exposed to the aggregating R-aptamers containing CpG motifs were strongly activated, as indicated by upregulation of CD40 levels as compared to cells treated with nonaggregating CpG R-aptamers. Together, these findings suggest that the sequence compositions in R-aptamers that promote multimerization and contain optimal ISS CpG motifs facilitate the delivery of ISS-ODN to CLL cells and enhance the activation of these cells.

Advantages of antisense drugs for the treatment of oral diseases

For almost two decades, antisense oligonucleotides (AS-ON) have been used successfully to suppress and regulate gene expression in vitro and in vivo. They are, meanwhile, well established to serve as molecular tools for several biologic applications, from the study of single gene functions up to complex target gene validations. Based on an at least theoretically simple mode of action, the sequence-specific inhibition of mRNA functions after complex formation by Watson-Crick base pairing and presumably enzymatic degradation of the target mRNA, they obviously carry a high therapeutic potential for the treatment of human diseases. In recent years, a remarkable number of clinical trials have been initiated and performed to evaluate the therapeutic usefulness of antisense technology. However, after the successful development of the first antisense-based drug Vitravene (Isis Pharmaceutical Inc., Carlsbad, CA) in 1998, no second product has appeared on the market to date. Here, we describe substantial advantages for the development of antisense-based drugs against less severe oral diseases that represent novel but highly promising application fields of the technology.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

In vivo use of oligonucleotides to inhibit choroidal neovascularisation in the eye

BACKGROUND

We have previously demonstrated the in vivo uptake of oligonucleotides in the rat eye and have continued with experiments to look at the effectiveness of targeted oligonucleotide sequences. Vascular endothelial growth factor (VEGF) is correlated with new blood vessel formation and has been implicated in numerous eye diseases characterised by abnormal blood vessel proliferation. An oligonucleotide targeted to the VEGF sequence was examined for its effect on VEGF production in vitro and the development of choroidal neovascularisation in vivo in the eye.

METHODS

A series of sequences were assessed in an in vitro screening system using retinal pigment epithelial (RPE) cells to demonstrate a reduction in VEGF. A targeted sequence was further investigated using an animal model of choroidal neovascularisation where a krypton laser was used to produce a wound healing response in the choroid and retina. The oligonucleotide was injected into the vitreous and the development of choroidal neovascularisation assessed using fluorescein angiography.

RESULTS

The targeted sequence was shown in vitro to downregulate the VEGF produced by RPE cells grown under hypoxic conditions and when injected into laser treated eyes was shown to be preferentially taken up in the laser lesion. Fluorescein angiography demonstrated that the test oligonucleotide was successful in reducing laser-mediated choroidal neovascularisation.

CONCLUSIONS

A sequence corresponding to the 5'UTR of the VEGF gene has provided encouraging results for the treatment of neovascularisation.