A microsphere-liposome (microplex) vector for targeted gene therapy of cancer. II. In vivo biodistribution study in a solid tumor model

Recent Advances in Anti-Atherosclerosis and Potential Therapeutic Targets for Nanomaterial-Derived Drug Formulations

Atherosclerosis, the leading cause of death worldwide, is responsible for ≈17.6 million deaths globally each year. Most therapeutic drugs for atherosclerosis have low delivery efficiencies and significant side effects, and this has hampered the development of effective treatment strategies. Diversified nanomaterials can improve drug properties and are considered to be key for the development of improved treatment strategies for atherosclerosis. The pathological mechanisms underlying atherosclerosis is summarized, rationally designed nanoparticle-mediated therapeutic strategies, and potential future therapeutic targets for nanodelivery. The content of this study reveals the potential and challenges of nanoparticle use for the treatment of atherosclerosis and highlights new effective design ideas.

The sustained and targeted treatment of hemangiomas by propranolol-loaded CD133 aptamers conjugated liposomes-in-microspheres

We previously developed propranolol-encapsulated liposomes-in-microspheres (PLIM) to realize the sustained propranolol release for the treatment of hemangiomas. However, the liposomes released from the microspheres still lacked specificity for CD133-positive hemangioma-derived stem cells (HemSCs) which are considered to be the seeds of hemangiomas. Therefore, we hereby encapsulated propranolol-loaded CD133 aptamers conjugated liposomes in poly(lactic-co-glycolic acid (PLGA) microspheres to develop propranolol-loaded CD133 aptamers conjugated liposomes-in-microspheres (PCLIM), to realize the aim of the sustained and targeted therapy of hemangiomas. The evaluation of the release of propranolol from PCLIM was carried out, and the cytotoxic effect and angiogenic growth factor expression inhibitory ability of PCLIM were performed in HemSCs. The in vivo hemangioma inhibitory ability of PCLIM was also investigated in nude mice with subcutaneous human hemangiomas. PCLIM possessed a desired size of 29.2 μm, drug encapsulation efficiency (25.3%), and a prolonged drug release for 40 days. Importantly, PCLIM could inhibit HemSCs proliferation and the protein expression of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor-A (VEGF) in HemSCs to a greater extent compared with PLIM. In nude mice bearing hemangioma xenograft, PCLIM showed the best therapeutic efficacy towards hemangiomas, as reflected by remarkably decreased hemangioma volume, weight and microvessel density (MVD). Thus, our results demonstrated that PCLIM realized the sustained and targeted treatment of hemangiomas, resulting in remarkable inhibition of hemangiomas.

Significant inhibition of infantile hemangioma growth by sustained delivery of urea from liposomes-in-microspheres

Infantile hemangioma (IH) is a benign pediatric tumor, and rapid growth of IH can result in serious morbidity and even mortality. Only one drug Hemangeol™ (propranolol hydrochloride oral solution) has been approved for the treatment of IH, whereas patients suffer from its adverse effects and high frequency of administration. We have used urea, an organic compound and a normal body metabolite, in the treatment of IH for 20 years, and demonstrated that urea is an effective and well-tolerated treatment for IH. To reduce the daily administration of urea, we firstly utilized urea-loaded liposomes-in-microspheres (ULIM) as a novel topical controlled release system to realize the sustained release of urea. ULIM were fabricated from the encapsulation of urea-loaded liposomes in poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) microspheres. The characteristics, activity and mechanism against IH of ULIM were examined in vitro and in vivo. ULIM were of a desired particle size (~62.4 µm), drug encapsulation efficiency (~51.5%) and sustained drug release for 40 days. ULIM inhibited the proliferation of hemangioma endothelia cells (HemECs) and expression of vascular endothelial growth factor-A in HemECs. The therapeutic effect of ULIM in IH was better than propranolol, urea, urea-loaded liposomes and urea-loaded microspheres in vivo, as reflected by markedly decreased hemangioma weight, volume and microvessel density. None of the treated mice showed behavioral changes, severe side-effects and weight loss. Our results suggest that use of ULIM is a potential and safe approach with which to locally and efficiently deliver urea to hemangioma, and is a promising alternative to propranolol in the treatment of IH.

Continuous delivery of propranolol from liposomes-in-microspheres significantly inhibits infantile hemangioma growth

Purpose

To reduce the adverse effects and high frequency of administration of propranolol to treat infantile hemangioma, we first utilized propranolol-loaded liposomes-in-microsphere (PLIM) as a novel topical release system to realize sustained release of propranolol.

Methods

PLIM was developed from encapsulating propranolol-loaded liposomes (PLs) in microspheres made of poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) copolymers (PLGA-PEG-PLGA). The release profile of propranolol from PLIM was evaluated, and its biological activity was investigated in vitro using proliferation assays on hemangioma stem cells (HemSCs). Tumor inhibition was studied in nude mice bearing human subcutaneous infantile hemangioma.

Results

The microspheres were of desired particle size (~77.8 μm) and drug encapsulation efficiency (~23.9%) and achieved sustained drug release for 40 days. PLIM exerted efficient inhibition of the proliferation of HemSCs and significantly reduced the expression of two angiogenesis factors (vascular endothelial growth factor-A [VEGF-A] and basic fibroblast growth factor [bFGF]) in HemSCs. Notably, the therapeutic effect of PLIM in hemangioma was superior to that of propranolol and PL in vivo, as reflected by significantly reduced hemangioma volume, weight, and microvessel density. The mean hemangioma weight of the PLIM-treated group was significantly lower than that of other groups (saline =0.28 g, propranolol =0.21 g, PL =0.13 g, PLIM =0.03 g; PLIM vs saline: P<0.001, PLIM vs propranolol: P<0.001, PLIM vs PL: P<0.001). The mean microvessel density of the PLIM-treated group was significantly lower than that of other groups (saline =40 vessels/mm², propranolol =31 vessels/mm², PL =25 vessels/mm², PLIM =11 vessels/mm²; PLIM vs saline: P<0.001, PLIM vs propranolol: P<0.01, PLIM vs PL: P<0.05).

Conclusion

Our findings show that PLIM is a very promising approach to locally and efficiently deliver propranolol to the hemangioma site leading to a significant inhibition of infantile hemangioma.

Nucleotropic doxorubicin nanoparticles decrease cancer cell viability, destroy mitochondria, induce autophagy and enhance tumour necrosis

Objective

Doxorubicin (Dox) is used clinically against various neoplasias, but suffers from serious side effects, and for the past three decades, this shortcoming has spurred research towards finding better drug delivery systems (DDSs) for this frontline drug.

Methods

A non-targeted nucleotropic Dox-loaded nanoparticle (DNP) DDS is described, which has a simple chemical design, is easy to formulate and administer, is inexpensive, non-biohazardous and may prove to be useful clinically.

Key findings

The DNP formulated via vortex-assisted complex coarcevation enhanced (300-fold) cell-inhibitory activity of the drug in a panel of human cancer cells (osteosarcoma, breast, prostate and colorectal cancer) and enhanced (10-fold) efficacy against osteosarcoma (OS) in vivo. The slow-release DNPs localised to the endoplasmic reticulum disrupted the mitochondria and entered the nucleus. Prominent cytosolic vacuolisation, budding off of portions of the cytoplasm, both suggestive of autophagy, were observed. Mice that were administered with DNPs intratumorally had the smallest tumours at the end of the study, with more necrotic hotspots.

Conclusion

This promising nucleotropic DDS enhances the cell delivery and activity of Dox against a variety of human cancer cell lines and in OS tumours in mice.

Review: doxorubicin delivery systems based on chitosan for cancer therapy

Objectives

This review sheds insight into an increasingly popular polymer that has been widely explored as a potential drug delivery system. The abundant, biodegradable and biocompatible polysaccharide chitosan, with many other favourable properties, has been favoured as a drug delivery system for the purposes of encapsulating and delivery of doxorubicin with reduced side-effects.

Key findings

Doxorubicin is frequently used as a frontline chemotherapeutic agent against a variety of cancers. It has largely been able to demonstrate anti-tumour effects, though there are major shortfalls of doxorubicin, which include serious side-effects such as cardiomyopathy and myelosuppression, and also an ever-present danger of extravasation during drug administration. In view of this, drug delivery systems are currently being explored as alternative methods of drug delivery in a bid to more effectively direct doxorubicin to the specific lesion site and reduce its systemic side-effects. Liposomes and dendrimers have been tested as potential carriers for doxorubicin; however they are not the focus of this review.

Summary

Recent advancements in doxorubicin and chitosan technology have shown some preliminary though promising results for cancer therapy.

The use of chitosan formulations in cancer therapy

With the advent of the theranostics era in biomedical research, gene therapy is poised to offer more, provided that more efficient delivery vehicles are discovered and developed. Chitosan is a biomatrix that is abundant, biocompatible, biodegradable, versatile, inexpensive and safe. These features have paved the way for its use in gene therapy, mainly for delivery of therapeutic plasmids and more recently for siRNA. Recent studies show that chitosan per se exhibits anticancer properties both in vitro and in animal models, most probably through the p21/Cip and p27/Kip pathways. This review looks at the in vivo studies using chitosan technology towards cancer gene therapy, drawing some support from non-cancer studies. The future of this promising technology lies in the evolution of new ideas for enhanced nucleic acid drug pharmacokinetics and, consequently, pharmacodynamics for cancer patients.

RECK--a newly discovered inhibitor of metastasis with prognostic significance in multiple forms of cancer

The RECK (reversion-inducing cysteine rich protein with Kazal motifs) protein was initially discovered by its ability to induce reversion in ras-activated fibroblasts. The key action of RECK is to inhibit matrix metalloproteinases (MMPs) involved in breakdown of the extracellular matrix (ECM), and angiogenesis-namely MMP-2, MMP-9 and MTP-1. To this effect, it plays important physiological roles in embryogenesis and vasculogenesis. Additionally, it has a significant effect on tumorigenesis by limiting angiogenesis and invasion of tumours through the ECM. RECK has been studied in the context of a number of human tumours including colorectal, breast, pancreas, gastric, hepatocellular, prostate, and non-small cell lung carcinoma. In many of these tumours, RECK is down-regulated most likely as a result of inhibition at the Sp1 promoter site. MMP-2 and MMP-9 generally show an inverse association with RECK expression, but there are exceptions to this rule. Likewise, a reduction in tumour microvascular density (MVD) and VEGF have also been correlated with increased RECK levels, although more studies are required to define this effect. The predominant finding across all human tumour studies is a significantly improved prognosis (due to decreased invasion and metastasis) in tumours with preserved RECK expression. Although further research is required, RECK is a promising prognostic marker and potential therapeutic agent in multiple cancers.

A novel orthotopic murine model provides insights into cellular and molecular characteristics contributing to human osteosarcoma

As a reliable model for osteosarcoma is lacking, three human cell lines (SaOS-2, U2OS and 143B) were evaluated in cell-based assays for proliferation, adhesion, migration, invasion, anchorage-independent growth, angiogenesis, mineralised nodule formation, plasmid transfection and oligonucleotide transfection. Tumor take and metastasis after orthotopic injection of the three cell lines into mice was monitored. The levels of expression of typical bone markers were determined with semi-quantitative RT-PCR in cultured cells, primary tumors, and for the SaOS-2 cell line, the metastases. Tumors grew and spread to the lungs within 3 and 5 weeks respectively, mimicking the clinical progression of the disease as analysed by x-ray. Expression of molecular markers in SaOS-2 indicated a mostly differentiated cell type at the primary and secondary sites. The ability of osteosarcoma cells to interact with collagen-1 and to form mineralised deposits correlated positively with tumor aggression in vivo. Expression of alkaline phosphatase was a common theme in both tumor models at the primary site. The newly established SaOS-2 model should allow the testing of candidate anti-osteosarcoma agents as well as dissection of more intricate mechanisms involved in human osteosarcoma.

Carrier-mediated delivery of peptidic drugs for cancer therapy

Protein and peptide drugs are used for treatment of a variety of ailments. However, their wider use has been hindered by issues such as poor bioavailability in vivo and the cost involved in producing these drugs. This review discusses the various carrier-mediated methods used for delivery of peptide and protein drugs, with emphasis on liposomal and microspherical drug delivery systems. A brief look at the types of peptidic drugs currently in use clinically, and a brief discourse on several novel ideas for better protein delivery systems for cancer therapy is included.

Targeting of small molecule anticancer drugs to the tumour and its vasculature using cationic liposomes: lessons from gene therapy

Cationic (positively charged) liposomes have been tested in various gene therapy clinical trials for neoplastic and other diseases. They have demonstrated selectivity for tumour vascular endothelial cells raising hopes for both antiangiogenic and antivascular therapies. They are also capable of being selectively delivered to the lungs and liver when administered intravenously. These vesicles are being targeted to the tumour in various parts of the body by using advanced liposomal systems such as ligand-receptor and antibody-antigen combinations. At present, the transferrin receptor is commonly used for cancer-targeted drug delivery systems including cationic liposomes. This review looks at the growing utility of these vesicles for delivery of small molecule anticancer drugs.

Selective gene delivery for cancer therapy using cationic liposomes: in vivo proof of applicability

Targeted gene therapy is essential if cancer treatment is to become a reality with this form of therapy. In the past few years, cationic liposomes, discovered 2 decades ago, and at present, the most commonly used class of transfection reagents, have been tested in various clinical trials for diseases not restricted to cancer. They have been shown to be selective for tumour vascular endothelial cells raising hopes for antiangiogenic and antivascular therapies. They are also capable of being selectively delivered to the lungs and liver when administered intravenously. These vesicles are also being targeted to the tumour in various parts of the body by using advanced liposomal systems such as antibody-antigen and ligand-receptor combinations. This review looks at the state of play in this rapidly growing field.

Improving anti-angiogenic therapy via selective delivery of cationic liposomes to tumour vasculature

In the past three decades, two very important findings regarding tumour vasculature have been made. Firstly, it has been known a solid tumour has to establish an adequate blood supply to grow beyond a critical mass. Secondly, it has been proven that the tumour vasculature is relatively more aberrant, dynamic and permeable than healthy host tissue. This review discusses the potential of delivering therapeutic nucleic acids to tumour vasculature using cationic liposomes, vehicles recently demonstrated to be selectively delivered to tumour vasculature.

In-vitro evaluation of ion-exchange microspheres for the sustained release of liposomal–adenoviral conjugates

This study looks at the development of a novel combination vector consisting of adenovirus conjugated to liposomes (AL complexes) bound to cation-exchanging microspheres (MAL complexes). With adenovirus having a net negative charge and the liposomes a net positive charge it was possible to modify the net charge of the AL complexes by varying the concentrations of adenovirus to liposomes. The modification of the net charge resulted in altered binding and release characteristics. Of the complexes tested, the 5:1 and 2:1 ratio AL complexes were able to be efficiently bound by the microspheres and exhibited sustained release over 24 h. The 1:1 and 1:2 AL complexes, however, bound poorly to the microspheres and were rapidly released. In addition the MAL complexes also were able to reduce the toxicity of the AL complexes, which was seen with the 10:1 ratio. The AL complexes showed considerably more toxicity alone than in combination with microspheres, highlighting a potential benefit of this vector.

Modified microplex vector enhances transfection of cells in culture while maintaining tumour-selective gene delivery in-vivo

A non-commercial liposome (dimethyl dioctadecyl ammonium bromide:dioleoyl phosphatidylethanolamine) was compared with a commercial variety (Lipofectamine) for transfection of cultured rat adenocarcinoma cells and in an in-vivo kidney tumour model. Transfection of the cells in culture and in tumours in-vivo was variable with both types of liposomes. A high-dose microplex (lipoplex-microsphere) vector enhanced liposome-mediated transfection of cells in culture. When these high-dose microplexes were tested in-vivo, they were better than both microspherical and liposomal delivery modes in terms of transgene expression levels and the tumour-to-normal tissue ratio of gene delivery. Microplexes have been demonstrated to be capable of not only selective delivery of plasmids to solid tumours, but also of increasing transfection in cell culture, a finding that may be used in ex-vivo transfection studies. It is hypothesized that microspheres anchored the combination vector closer to the cultured cells, allowing attached liposomes to gain easier access into cells. In-vivo, microspheres permitted the microplexes to selectively deliver their genetic payload within the tumour tissue, from where the action of cationic liposomes on cellular membranes facilitated increased access of plasmids into the cytosol of target cells.

A model for evaluating selective delivery of plasmid DNA to tumours via the vasculature

A comparative study of plasmid DNA delivery in a newly established rat renal solid tumour model was undertaken. Free plasmid, plasmids bound to microspheres, and plasmids complexed with liposomes were selectively delivered to tumours via arterial catheterisation. Forty-eight hours post delivery, tumour to normal kidney tissue chloramphenicol acetyltransferase expression ratios were as follows: free (1.8:1), microspherical (3.9:1), and liposomal (1.2:1). Microspheres were able to selectively deliver the plasmids to tumours, whereas cationic liposomes distributed the plasmids to both kidney parenchymal and tumour cells. This tumour model has the potential of screening delivery vehicles as well as therapeutic agents for the capacity of selective delivery to tumours via the vasculature.

Biochemical and biophysical characteristics of lipoplexes pertinent to solid tumour gene therapy

Cationic liposomes have become the reagent of choice for transfer of nucleic acids such as plasmids and oligodeoxynucleotides to cells in culture and in vivo. Whilst these reagents have several advantages over other forms of nucleic acid transfer methods, toxicity remains a significant problem, especially in vivo. Recent studies have also highlighted the immunostimulatory nature of these cationic vesicles when complexed to plasmid DNA, a phenomenon that may be harnessed for efficacious usage against tumours. Current research in this dynamic technological field is aimed at the development of cationic lipids that have negligible toxic effects and enhanced transfection capabilities.

Cytotoxicity issues pertinent to lipoplex-mediated gene therapy in-vivo

Cationic liposomes bind with nucleic acids such as plasmids and oligodeoxynucleotides to form complexes known as lipoplexes. Although these lipoplexes have several advantages over other forms of nucleic acid transfer methods in cell culture and in-vivo, toxicity remains a problem, especially in-vivo. Nevertheless, these carriers have been used in clinical trials against cystic fibrosis and cancer and their usage is attributed mainly to their versatility, especially when it comes to the range of routes available for administration of nucleic-acid-based drugs in-vivo.

Vehicles for oligonucleotide delivery to tumours

The vasculature of a tumour provides the most effective route by which neoplastic cells may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue should enable selective delivery of drugs to tumour tissue. Such delivery is relevant to carrier-mediated delivery of genetic medicine to tumours. This review discusses the potential of delivering therapeutic oligonucleotides (ONs) to tumours using cationic liposomes and cyclodextrins (CyDs), and the major hindrances posed by the tumour itself on such delivery. Cationic liposomes are generally 100-200 nm in diameter, whereas CyDs typically span 1.5 nm across. Cationic liposomes have been used for the introduction of nucleic acids into mammalian cells for more than a decade. CyD molecules are routinely used as agents that engender cholesterol efflux from lipid-laden cells, thus having an efficacious potential in the management of atherosclerosis. A recent trend is to employ these oligosaccharide molecules for delivering nucleic acids in cells both in-vitro and in-vivo. Comparisons are made with other ON delivery agents, such as porphyrin derivatives (< 1 nm), branched chain dendrimers (approximately 10 nm), polyethylenimine polymers (approximately 10 nm), nanoparticles (20-1,000 nm) and microspheres (> 1 microm), in the context of delivery to solid tumours. A discourse on how the chemical and physical properties of these carriers may affect the uptake of ONs into cells, particularly in-vivo, forms a major basis of this review.

Aquaporin gene delivery to kidney

BACKGROUND

Several aquaporin- (AQP) type water channels are expressed in kidney tubules and microvessels, including AQP1 in proximal tubule, thin descending limb of Henle and vasa recta, AQP2 in collecting duct apical membrane, and AQP3 and AQP4 in collecting duct basolateral membrane. Mice deficient in these aquaporins have distinct phenotypic abnormalities. AQP1 null mice are polyuria and unable to generate a concentrated urine after water deprivation. AQP2-T126M mutant mice and AQP3 null mice manifest nephrogenic diabetes insipidus (NDI) with severe polyuria, whereas AQP4 null mice have only a mild defect in maximal urinary concentrating ability. We reasoned that these mice could serve as useful models for gene replacement because of their predictable and unambiguous phenotypes.

METHODS

In an initial feasibility study, an adenovirus directing the expression of AQP1 was introduced into AQP1 null mice by intravenous infusion.

RESULTS

At 1 week after adenovirus infusion, AQP1 was seen in many proximal tubules and microvessels. Compared with untreated null mice, the treated mice were able to partially concentrate their urine and lost less weight after water deprivation. However, AQP1 transgene expression and functional correction were lost over 3-5 weeks.

CONCLUSION

Although there remain many technical problems to overcome, aquaporin gene replacement has potential applications in hereditary and acquired NDI, and in the transient modulation of renal fluid conservation.

Plasmid gene delivery to human keratinocytes through a fibrin-mediated transfection system

We have developed a matrix-mediated transfection system to deliver plasmids to human keratinocytes. The matrix is a soluble, self-hardening fibrin matrix (Tissucol), Baxter) that has been used clinically. Recently it has been shown that full thickness burn wounds can be successfully treated with a keratinocyte fibrin glue suspension. Further, it has been demonstrated that hEGF transfected cells accelerate wound healing. In this study, we inoculated the matrix with the hEGF expression plasmid and resuspended the matrix with either cultured or noncultured human keratinocytes. We obtained successful transfection rates of these cells (up to a 100-fold increase compared to controls containing no EGF expression plasmid) in vitro. After transplantation to full thickness wounds on athymic mice we were able to show a 180-fold increase in EGF concentration compared to controls, which persisted over the entire 7-day monitored period, decreasing from 180 to 20 pg/mL at day seven. This unique approach indicates the possible utility to combine a matrix for cell transplantation with a transfection system to release therapeutic proteins in vitro and in vivo.

Delivery of lipoplexes for genotherapy of solid tumours: role of vascular endothelial cells

The cells constituting a solid tumour may vary considerably due to biological disparities, but for a solid tumour to pose as a threat to its host, an adequate blood supply has to be established. Although neovascularisation may have dire consequences for the host, it provides a common route by which tumours in general may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue means that selective delivery of drugs may be achieved. A closer examination of the role played by the cells making up the tumour vascular bed, vascular endothelial cells (VECs), is required to facilitate design of ways for enhancing drug delivery to solid tumours via the vascular route. VECs have two major roles in the body, barrier and transport, both of which are highly pertinent to drug delivery. This review discusses the factors regulating VEC function, and how these cells may be manipulated in-vivo to improve the selective delivery of lipoplexes, carriers for gene therapy constructs, to solid tumours. It also discusses how genotherapeutic drugs may be targeted against tumour VECs on the premise that by killing these cells, the tumour itself will perish.

Apolipoprotein A-I, cyclodextrins and liposomes as potential drugs for the reversal of atherosclerosis. A review

Several studies have revealed that high-density lipoprotein (HDL) is the most reliable predictor for susceptibility to cardiovascular disease. Since apolipoprotein A-I (apoA-I) is the major protein of HDL, it is worthwhile evaluating the potential of this protein to reduce the lipid burden of lesions observed in the clinic. Indeed, apoA-I is used extensively in cell culture to induce cholesterol efflux. However, while there is a large body of data emanating from in-vitro and cell-culture studies with apoA-I, little animal data and scant clinical trials examining the potential of this apolipoprotein to induce cholesterol (and other lipid) efflux exists. Importantly, the effects of oxysterols, such as 7-ketocholesterol (7KC), on cholesterol and other lipid efflux by apoA-I needs to be investigated in any attempt to utilise apoA-I as an agent to stimulate efflux of lipids. Lessons may be learnt from studies with other lipid acceptors such as cyclodextrins and phospholipid vesicles (PLVs, liposomes), by combination with other effluxing agents, by remodelling the protein structure of the apolipoprotein, or by altering the composition of the lipoprotein intended for administration in-vivo. Akin to any other drug, the usage of this apolipoprotein in a therapeutic context has to follow the traditional sequence of events, namely an evaluation of the biodistribution, safety and dose-response of the protein in animal trials in advance of clinical trials. Mass production of the apolipoprotein is now a simple process due to the advent of recombinant DNA technology. This review also considers the potential of cyclodextrins and PLVs for use in inducing reverse cholesterol transport in-vivo. Finally, the potential of cyclodextrins as delivery agents for nucleic acid-based constructs such as oligonucleotides and plasmids is discussed.