Topical gene silencing by iontophoretic delivery of an antisense oligonucleotide-dendrimer nanocomplex: the proof of concept in a skin cancer mouse model.

The study was aimed at investigating the feasibility of using a poly (amidoamine) (PAMAM) dendrimer as a carrier for topical iontophoretic delivery of an antisense oligonucleotide (ASO). Bcl-2, an anti-apoptotic protein implicated in skin cancer, was used as the model target protein to demonstrate the topical gene silencing approach. Confocal laser scanning microscopy studies demonstrated that the iontophoretically delivered ASO-dendrimer complex can reach the viable epidermis in porcine skin. In contrast, passively delivered free or dendrimer complexed ASO was mainly localized to the stratum corneum. The cell uptake of ASO was significantly enhanced by the dendrimer complex and the complex suppressed Bcl-2 levels in the cell. In the skin cancer mouse model, the iontophoretically delivered ASO-dendrimer complex reduced the tumor volume by 45% and was consistent with the reduction in Bcl-2 protein levels. The iontophoretically delivered ASO-dendrimer complex caused significant apoptosis in skin tumor. Overall, the findings from this study demonstrate that dendrimers are promising nanocarriers for developing topical gene silencing approaches for skin diseases.

Poly(amidoamine) dendrimers as skin penetration enhancers: Influence of charge, generation, and concentration.

The study investigates the influence of surface charge, generation and concentration of poly(amidoamine) (PAMAM) dendrimers on skin permeation of a model hydrophilic drug, 5-fluorouracil (5FU). Permeation studies were performed using excised porcine skin in a Franz diffusion cell. Saturated concentration of 5FU in isopropyl myristate was applied on the skin after pretreatment with dendrimers and (14)C labeled 5FU was analyzed using a liquid scintillation counter. The influence of dendrimer surface charge (G4-NH(2), G3.5-COOH, and G4-OH), generations (G2-G6-NH(2)) and concentration (0.1-10 mM of G4-NH(2)) on skin permeation of 5FU were studied. The enhancement in drug permeability coefficient (K(p)) was in the following decreasing order G4-NH(2) > G4-OH > G3.5-COOH. Dendrimer increased the skin permeation by increasing the skin partitioning of 5FU. Transepidermal water loss, skin resistance measurements and ATR-FTIR studies revealed that cationic dendrimers act by interacting with the skin lipid bilayers. Increase in G4-NH(2) concentration did not proportionally increase the skin permeation of 5FU. The 5FU K(p) was inversely related to the molecular weight of the dendrimer. G2-NH(2) dendrimer reduced skin resistance to a greater extent than higher generation dendrimers. Overall, the study showed that lower generation cationic dendrimer is more effective in enhancing the skin permeation of hydrophilic drugs.

Effect of poly(amidoamine) (PAMAM) dendrimer on skin permeation of 5-fluorouracil.

The aim of present study is to investigate the effect of poly(amidoamine) (PAMAM) dendrimer on skin permeation of 5-fluorouracil (5FU). Permeation studies were performed using excised porcine skin in a Franz diffusion cell and (14)C labeled 5FU samples were analyzed using liquid scintillation counter. Three different vehicles were used, including phosphate buffer (PB), mineral oil (MO) and isopropyl myristate (IPM). The studies were carried out by simultaneously applying the drug and dendrimer together or by pre-treating the skin with dendrimer before drug application. Simultaneous application of drug and dendrimer increased the flux of 5FU in IPM and MO, while there was no change in PB. The increased skin partitioning of dendrimer from lipophilic vehicles increased the drug solubility in skin. Pre-treatment with dendrimer increased permeability coefficient of 5FU by 4-fold in MO and 2.5-fold in IPM, while it decreased by half in PB. Skin partitioning of 5FU increased after dendrimer treatment from lipophilic vehicles. The flux increased linearly with increase in pre-treatment time. Dendrimer pre-treatment increased transepidermal water loss and decreased skin resistance. The decrease in skin resistance directly correlated to the enhancement in skin permeation of 5FU (r(2)=0.99). Overall, the study showed that dendrimer increases the skin permeation of 5FU from lipophilic vehicles mainly by altering the skin barrier.

The effect of surface functionality on cellular trafficking of dendrimers.

Dendrimers are an emerging group of nanostructured, polymeric biomaterials that have potential as non-viral vehicles for delivering drugs and genetic material to intracellular targets. They have a high charge density with tunable surface functional groups, which can alter the local environment and influence cellular interactions. This can have a significant impact on the intracellular trafficking of dendrimer-based nanodevices. With the help of flow cytometry, fluorescence microscopy, and by using specific inhibitors, the influence of surface functionality on their uptake in A549 lung epithelial cells, and subsequent intracellular distribution was investigated. In this paper, we have shown that even though all the dendrimers are taken up by fluid-phase endocytosis, significant differences in uptake mechanisms exist. Anionic dendrimers appear to be mainly taken up by caveolae mediated endocytosis in A549 lung epithelial cells, while cationic and neutral dendrimers appear to be taken in by a non-clathrin, non-caveolae mediated mechanism that may be by electrostatic interactions or other non-specific fluid-phase endocytosis. These findings open up new possibilities of targeting therapeutic agents to specific cell organelles based on surface charge.

Functional role of P-glycoprotein in limiting peroral drug absorption: optimizing drug delivery.

P-glycoprotein (P-gp) associated multi-drug resistance is one of the major challenges in the chemotherapy of various cancers. On the other hand, it is now widely recognized that P-gp influences drug transport across various biological membranes. To this end, there is an increasing trend to optimize pharmacokinetics and drug delivery right from the initial stages of drug discovery by exploring all the possible mechanisms involved in 'deliverability'. Recent advances in molecular biology techniques and biochemical characterization methodologies have helped in identification of various transporters involved in absorption or secretion of drugs. P-gp, an efflux pump expressed along the gastrointestinal tract, limits the permeability of many drugs and thus affects their peroral absorption and bioavailability. A fundamental insight and thorough understanding of P-gp and its functional role in limiting drug absorption is critical to improve predictability of dynamic absorption models and aid in selection of new candidates for development, and also widen the scope of peroral delivery for 'challenging' molecules.