Harendra S. Parekh

A new dawn for the use of traditional Chinese medicine in cancer therapy

Although traditional Chinese medicine has benefitted one fifth of the worlds population in treating a plethora of diseases, its acceptance as a real therapeutic option by the West is only now emerging. In light of a new wave of recognition being given to traditional Chinese medicine by health professionals and regulatory bodies in the West, an understanding of their molecular basis and highlighting potential future applications of a proven group of traditional Chinese medicine in the treatment of a variety of cancers is crucial – this is where their calling holds much hope and promise in both animal and human trials. Furthermore, the rationale for combining conventional agents and modern biotechnological approaches to the delivery of traditional Chinese medicine is an avenue set to revolutionize the future practice of cancer medicine – and this may well bring on a new dawn of therapeutic strategies where East truly meets West.

Dendrimer nanocarriers as versatile vectors in gene delivery

UNLABELLED The successful delivery of nucleic acids to particular target sites is the challenge that is being addressed using a variety of viral and nonviral delivery systems, both of which have distinct advantages and disadvantages. Nonviral vectors offer the advantage of safety and flexibility over viral vectors, although they lack efficiency. Dendrimers are novel, three-dimensional polymers that have the ability to interact with various forms of nucleic acids such as plasmid DNA, antisense oligonucleotides, and RNA to form complexes that protect the nucleic acid from degradation. The interaction between the dendrimers and the nucleic acids is purely electrostatic where the cationic dendrimer condenses the anionic nucleic acids. Because cell membranes are negatively charged, the net positive charge of the dendrimer nucleic acid complex determines the transfection efficiency, although highly cationic systems are also cytotoxic. The nature of the dendrimer nucleic acid complex depends on various factors like stoichiometry, concentration of dendrimer-amines and nucleic acid-phosphates, as well as bulk solvent properties like pH, salt concentration, buffer strength, and dynamics of mixing. This article aims to review the role of dendrimers as novel gene delivery vectors both in vitro and in vivo. Dendrimer-based transfection reagents have become routine tools for in vitro transfection, but in vivo delivery of therapeutic nucleic acids remains a challenge. FROM THE CLINICAL EDITOR This review discusses the role of dendrimers as novel gene delivery vectors both in vitro and in vivo. Dendrimer based transfection reagents have become routine tools for in vitro transfection but in vivo delivery of therapeutic nucleic acids remains a challenge.

The advance of dendrimers : A versatile targeting platform for gene/drug delivery

The quest towards achieving a better understanding of underlying mechanisms by which genetic factors contribute to human disease has gathered considerable momentum, most notably due to the drafting of the complete human genome sequence. This has in turn accelerated research into identifying genes responsible for a plethora of genetic, infectious and metabolic diseases with the vision that therapies can then be developed. Although achieving a therapeutic intervention by gene delivery is perfectly feasible, the practical approach to achieving such a goal, at least in vivo, has proved far more challenging. Employing viruses as gene vectors has to-date proven to be the most effective method of delivery however concerns have emerged about both the short and long-term risks they pose. These fears being confirmed by incidents which led to the tragic deaths of subjects believed to have been triggered by adeno- & retroviral vectors used in clinical trials. This prompted many in the field to turn their research focus towards developing non-viral vectors deemed not only to be safer (non-immunogenic) than their viral counterparts but with a greater gene loading capacity. Polycationic dendrimers (PCDs) as vectors for this purpose have attracted significant interest due to their ease of synthesis, versatility and tolerability. This review will explore the physicochemical parameters crucial to PCD-mediated gene delivery and highlight some innovative strategies designed to maximise transfection efficacy and facilitate tissue-targeting of these elaborate macromolecules.

RETRACTED: Dendrimer nanocarriers as versatile vectors in gene delivery

UNLABELLED The successful delivery of nucleic acids to particular target sites is the challenge that is being addressed using a variety of viral and nonviral delivery systems, both of which have distinct advantages and disadvantages. Nonviral vectors offer the advantage of safety and flexibility over viral vectors, although they lack efficiency. Dendrimers are novel, three-dimensional polymers that have the ability to interact with various forms of nucleic acids such as plasmid DNA, antisense oligonucleotides, and RNA to form complexes that protect the nucleic acid from degradation. The interaction between the dendrimers and the nucleic acids is purely electrostatic where the cationic dendrimer condenses the anionic nucleic acids. Because cell membranes are negatively charged, the net positive charge of the dendrimer nucleic acid complex determines the transfection efficiency, although highly cationic systems are also cytotoxic. The nature of the dendrimer nucleic acid complex depends on various factors like stoichiometry, concentration of dendrimer-amines and nucleic acid-phosphates, as well as bulk solvent properties like pH, salt concentration, buffer strength, and dynamics of mixing. This article aims to review the role of dendrimers as novel gene delivery vectors both in vitro and in vivo. Dendrimer-based transfection reagents have become routine tools for in vitro transfection, but in vivo delivery of therapeutic nucleic acids remains a challenge. FROM THE CLINICAL EDITOR This review discusses the role of dendrimers as novel gene delivery vectors both in vitro and in vivo. Dendrimer based transfection reagents have become routine tools for in vitro transfection but in vivo delivery of therapeutic nucleic acids remains a challenge.

Structure, dynamics, and energetics of siRNA-cationic vector complexation:a molecular dynamics study

The design and synthesis of safe and efficient nonviral vectors for gene delivery has attracted significant attention in recent years. Previous experiments have revealed that the charge density of a polycation (the carrier) plays a crucial role in complexation and the release of the gene from the complex in the cytosol. In this work, we adopt an atomistic molecular dynamics simulation approach to study the complexation of short strand duplex RNA with six cationic carrier systems of varying charge and surface topology. The simulations reveal detailed molecular-level pictures of the structures and dynamics of the RNA-polycation complexes. Estimates for the binding free energy indicate that electrostatic contributions are dominant followed by van der Waals interactions. The binding free energy between the 8(+)polymers and the RNA is found to be larger than that of the 4(+)polymers, in general agreement with previously published data. Because reliable binding free energies provide an effective index of the ability of the polycationic carrier to bind the nucleic acid and also carry implications for the process of gene release within the cytosol, these novel simulations have the potential to provide us with a much better understanding of key mechanistic aspects of gene-polycation complexation and thereby advance the rational design of nonviral gene delivery systems.

Native and β-cyclodextrin-enclosed curcumin: entrapment within liposomes and their in vitro cytotoxicity in lung and colon cancer.

With a view to improving the solubility and delivery characteristics of poorly water-soluble drugs, we prepared β-cyclodextrin-curcumin (βCD-C) inclusion complexes (hydrophilic curcumin) and entrapped both native curcumin (hydrophobic) and the complexes separately into liposomes; these were then assessed for in vitro cytotoxicity in lung and colon cancer cell lines. Optimization of curcumin entrapment within βCD was achieved, with the resultant βCD-C complexes prepared by methanol reflux. Inclusion complexes were confirmed using UV spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction. The water solubility of βCD-C complexes improved markedly (c.f. native curcumin) and successful entrapment of complexes into liposomes, prepared using a thin-film hydration approach, was also achieved. All the liposomal formulations were characterized for curcumin and βCD-C complex entrapment efficiency, particle size, polydispersity and stability at 2–8°C. Curcumin, βCD-C complex and their optimized liposomal formulations were evaluated for anticancer activity in lung (A-459) and colon (SW-620) cancer cell lines. All curcumin-containing formulations tested were effective in inhibiting cell proliferation, as determined via an MTT assay. The median effective dose (EC50) for all curcumin formulations was found to be in the low µM range for both lung and colon cancer cell lines tested. Our results confirm that βCD inclusion complexes of poorly water soluble drugs, such as curcumin can be entrapped within biocompatible vesicles such as liposomes, and this does not preclude their anticancer activity.

A combined approach of chemical enhancers and sonophoresis for the transdermal delivery of tizanidine hydrochloride

The effects of chemical enhancers and sonophoresis on the transdermal permeation of tizanidine hydrochloride (TIZ) across mouse skin were investigated. Parameters including drug solubility, apparent partition coefficient (APC), drug permeation, and degradation in skin were determined. Low frequency ultrasound was also applied in the presence and absence of chemical enhancers to assess whether drug permeation improved. APC values indicated that TIZ preferentially partitions into intercellular spaces and does not form a reservoir, with the drug also exhibiting good enzymatic stability in skin. Most of the enhancers studied significantly increased the permeation rate of TIZ through full thickness mouse skin in comparison with TIZ formulated in phosphate buffer. Maximum enhancement was observed for TIZ formulated as a suspension in 50% v/v aqueous ethanol containing 5% v/v citral. Sonophoresis significantly (p < 0.05) increased the cumulative amount of TIZ permeating through the skin at 15 and 30 min in comparison to passive diffusion. A synergistic effect was noted when sonophoresis was applied in the presence of chemical enhancers. The results suggest that the formulation of TIZ with an appropriate penetration enhancer may be useful in the development of a therapeutic system to deliver TIZ across the skin for a prolonged period, i.e. 24 hr. The application of ultrasound in association with chemical enhancers, such as the combination of 5% v/v citral in 50% v/v aqueous ethanol, could further serve as a non-oral and non-invasive drug delivery modality for the immediate therapeutic effect of muscle relaxants such as TIZ.

Structure and Dynamics of Multiple Cationic Vectors−siRNA Complexation by All-Atomic Molecular Dynamics Simulations

Understanding the molecular mechanism of gene condensation is a key component to rationalizing gene delivery phenomena, including functional properties such as the stability of the gene-vector complex and the intracellular release of the gene. In this work, we adopt an atomistic molecular dynamics simulation approach to study the complexation of short strand duplex RNA with four cationic carrier systems of varying charge and surface topology at different charge ratios. At lower charge ratios, polymers bind quite effectively to siRNA, while at high charge ratios, the complexes are saturated and there are free polymers that are unable to associate with RNA. We also observed reduced fluctuations in RNA structures when complexed with multiple polymers in solution as compared to both free siRNA in water and the single polymer complexes. These novel simulations provide a much better understanding of key mechanistic aspects of gene-polycation complexation and thereby advance progress toward rational design of nonviral gene delivery systems.

Low-generation asymmetric dendrimers exhibit minimal toxicity and effectively complex DNA

Conventional dendrimers are spherical symmetrically branched polymers ending with active surface functional groups. Polyamidoamine (PAMAM) dendrimers have been widely studied as gene delivery vectors and have proven effective at delivering DNA to cells in vitro. However, higher‐generation (G4‐G8) PAMAM dendrimers exhibit toxicity due to their high cationic charge density and this has limited their application in vitro and in vivo. Another limitation arises when attempts are made to functionalize spherical dendrimers as targeting moieties cannot be site‐specifically attached. Therefore, we propose that lower‐generation asymmetric dendrimers, which are likely devoid of toxicity and to which site‐specific attachment of targeting ligands can be achieved, would be a viable alternative to currently available dendrimers. We synthesized and characterized a series of peptide‐based asymmetric dendrimers and compared their toxicity profile and ability to condense DNA to spherical PAMAM G1 dendrimers. We show that asymmetric dendrimers are minimally toxic and condense DNA into stable toroids which have been reported necessary for efficient cell transfection. This paves the way for these systems to be conjugated with targeting ligands for gene delivery in vitro and in vivo. Copyright

Dendrosome-based delivery of siRNA against E6 and E7 oncogenes in cervical cancer.

UNLABELLED Although small interfering RNA (siRNA) treatment holds great promise for the treatment of cancers, the field has been held back by the availability of suitable delivery vehicles. For cervical cancer the E6 and E7 oncogenes are ideal siRNA targets for treatment. The purpose of the present study was to explore the potential of dendrosomes for the delivery of siRNA targeting E6 and E7 proteins of cervical cancer cells in vitro. Optimization of dendrimer generation and nitrogen-to-phosphate (N/P) ratio was carried out using dendrimer-fluorescein isothiocyanate oligo complexes. The optimized N/P ratios were used in formulating complexes between dendrimers and siRNA targeting green fluorescence protein (siGFP). Although formulation 4D100 (dendrimer-siRNA complex) displayed the highest GFP knockdown, it was also found to be highly toxic to cells. In the final formulation 4D100 was encapsulated into dendrosomes so as to mask these toxic effects. The optimized dendrosomal formulation (DF), DF3 was found to possess a siGFP-entrapment efficiency of 49.76% +/- 1.62%, vesicle size of 154 +/- 1.73 nm, and zeta potential of +3.21 +/- 0.07 mV. The GFP knockdown efficiency of DF3 (dendrosome) was found to be almost identical to that of 4D100, but the former was completely nontoxic to the cells. DF3 containing siRNA against E6 and E7 was found to knock down the target genes considerably, as compared with the other formulations tested. Our results imply that dendrosomes hold potential for the delivery of siRNA and that a suitable targeting strategy could be useful for applications in vivo. FROM THE CLINICAL EDITOR siRNA treatment holds great promise for the treatment of cancers, but overall, the availability of suitable delivery vehicles remains a major issue. The purpose of this study was to explore the potential of dendrosomes for the delivery of siRNA targeting specific proteins in cervical cancer cells in vitro. The results suggest that dendrosomes hold potential for the delivery of siRNA and a suitable targeting strategy could be useful for applications in vivo.