Nano Delivery

The great potential of using nanodevices as delivery systems to specific targets in living organisms was first explored for medical uses. In plants, the same principles can be applied for a broad range of uses, in particular to tackle infections. Nanoparticles tagged to agrochemicals or other substances could reduce the damage to other plant tissues and the amount of chemicals released into the environment. To explore the benefits of applying nanotechnology to agriculture, the first stage is to work out the correct penetration and transport of the nanoparticles into plants................. The nanoparticles can be charged with different substances, introduced within the plants and, if necessary, concentrated into localized areas by using magnets. Also simple or more complex microscopical techniques can be used in localization studies.

Annals of Botany 101: 187–195, 2008, Oxford Journals; Nanoparticles as Smart Treatment-delivery Systems in Plants: Assessment of Different Techniques of Microscopy for their Visualization in Plant Tissues



The role of water ingress in tablet dissolution, and subsequent drug release, is usually inferred from the drug release profile and by models that make various assumptions concerning the geometry, water diffusion and the physical changes that occur.....There are numerous examples of the use of Magnetic Resonance Imaging (MRI) for pharmaceutical applications1 and, especially, hydration studies. Since the technique is non-invasive and non-destructive, it is possible to study the dissolution of one tablet without disturbing the process. However, its use is frequently constrained by the availability of MRI systems for long experiments, the high running costs (i.e. helium and nitrogen for superconducting magnets) and a requirement for expert users.

MRI provides information on the water, and lipid (where present), proton* density (M0) and mobility (by the spin-lattice and spin-spin relaxation times, T1, and T2) in up to three spatial dimensions. ‘Diagnostic’ or weighted images primarily use T1/T2
contrast to augment the signal intensity of various features, in addition to the usual proton density contrast, i.e. the variation of signal intensity according to water concentration. This enables segmentation of those features for quantifying thicknesses (1D), areas (2D) and volumes (3D), for example. For example, ‘T1 contrast’ can be altered by varying the repetition time (TR) of a spin echo imaging protocol3. T1 is the time constant for recovery of the magnetization, or signal, after a radio frequency pulse, therefore the inherent signal-to-noise of the image is increased by increasing TR. Unfortunately this proportionally lengthens the image scan time. However, different materials, or parts thereof, with different water-content and/or - mobility have different T1 recoveries so TR can be reduced to enhance the contrast between various features, which also serves to reduce the image scan time.

PharmaSense; Measurement of Water Ingress and Gel Layer Formation during Tablet Dissolution in a US Pharmacopeia 4 Flow Cell; www.oxford-instruments.com

Hydrogels represent an ideal class of polymeric material for various biomedical applications, including drug delivery, cell encapsulation and tissue engineering [1]. Thermosensitive hydrogels can be used as in situ forming implants.These biodegradable delivery systems are generally liquid formulations that form a semisolid or solid depot after injection into the desired tissue or organ. General advantages are localized or systemic prolonged drug delivery periods, drug dosage reduction along with reduction of undesirable side effects and reduced frequency of application.
Source: Non-invasive in vitro characterization of chitosan based in situ gelling O/W emulsions by 1H-NMR Relaxometry; www.oxford-instruments.com



A single oral dose of the formulation to mice could maintain sustained drug levels for 5–8 days in the plasma and for 9 days in the brain. There was a significant improvement in the pharmacokinetic parameters such as mean residence time and relative bioavailability as compared with free drugs. The pharmacodynamic parameters such as the ratio of area under the curve to minimum inhibitory concentration (AUC/MIC) and the time up to which MIC levels were maintained in plasma (TMIC) were also improved. In Mycobacterium tuberculosis H37Rv infected mice, five oral doses of the nanoparticle formulation administered every 10th day resulted in undetectable bacilli in the meninges, as assessed on the basis of cfu and histopathology.

Oral nanoparticle-based antituberculosis drug delivery to the brain in an experimental model; Journal of Antimicrobial Chemotherapy 2006 57
www.oxfordjournals.org



Drug delivery and penetration into neoplastic cells distant from tumor vessels is critical for the effectiveness of solid tumor chemotherapy. We hypothesized that 10- to 20-nm nanoassemblies of phospholipids containing doxorubicin would improve the drug's penetration, accumulation, and antitumor activity.

We have developed a novel PEG-PE–based nanocarrier of doxorubicin that increased cytotoxicity in vitro and enhanced antitumor activity in vivo with low systemic toxicity. This drug packaging technology may provide a new strategy for design of cancer therapies.

Encapsulation of doxorubicin in PEG-PE micelles increased its internalization by A549 cells into lysosomes and enhanced cytotoxicity. Drug-encapsulated doxorubicin was more effective in inhibiting tumor growth in the subcutaneous LLC tumor model (mean tumor volumes in mice treated with 5 mg/kg M-Dox = 1126 mm3 and in control mice = 3693 mm3, difference = 2567 mm3, 95% confidence interval [CI] = 2190 to 2943 mm3, P<.001) than free doxorubicin (mean tumor volumes in doxorubicin-treated mice = 3021 mm3 and in control mice = 3693 mm3, difference = 672 mm3, 95% CI = 296 to 1049 mm3, P = .0332, Wilcoxon signed rank test). M-Dox treatment prolonged survival in both mouse models and reduced metastases in the pulmonary model; it also reduced toxicity.

Improving Penetration in Tumors With Nanoassemblies of Phospholipids and Doxorubicin;http://jnci.oxfordjournals.org/cgi/content/abstract/99/13/1004


the treatment of solid tumors may be improved by controlling the pharmacologic properties of anticancer therapeutics. In 1906, Paul Ehrlich established the concept of drug delivery (2) by proposing a carrier that would "bring therapeutically active groups to the organ in question." The objective of drug delivery in the treatment of solid tumors is to increase the concentration of a therapeutic agent in the tumor while limiting systemic exposure (3–5). Increasing the concentration of drugs in the tumor relative to normal tissues results in improved tumor control and reduced toxic side effects. Numerous drug delivery technologies have been developed to accomplish this objective, including liposomes (6), micelles (7), antibody-directed enzyme–prodrug therapy (8), photodynamic therapy (9), affinity targeting (10), and macromolecular drug carriers (11,12).

Many of these drug delivery technologies, including the one described by Tang et al., take advantage of the unique pathophysiology of tumor vasculature. As early as the 1920s, researchers using a transparent chamber and injectable dye techniques found that, in contrast to normal tissue, tumors contain a high density of abnormal blood vessels that are dilated and poorly differentiated, with chaotic architecture and aberrant branching (13–16). Subsequently, various parameters of tumor vasculature were found to be impaired: for example, tumor blood vessels were observed to have a higher permeability than normal ones. These impaired functions contribute to the higher concentration of plasma proteins detected in tumor tissues than in normal tissues (17–26). This phenomenon was elucidated by Maeda and colleagues (27–29) and reviewed by Seymour (30), who described it as the enhanced permeability and retention effect, which is a combination of the increased permeability of tumor blood vessels and the decreased rate of clearance. The enhanced permeability of tumor vessels is due in part to larger pores in the tumor vasculature (~100–2000 nm) (31–33) compared with those of normal healthy continuous vasculature (2–6 nm) (34). The decreased rate of clearance is due to the lack of functional lymphatic vessels within a tumor, although there are indications that lymphatic vessels may exist in the periphery of a tumor (35–37). Even though retention and cellular uptake in a tumor may be improved with a targeting moiety specific for tumor receptors, all macromolecules, including targeted ones, preferentially accumulate in solid tumors after intravenous administration because their longer plasma half-life compared with small molecules provides a sustained driving force for their migration across the leaky tumor vasculature into the tumor mass.

Despite the constant development of new drug delivery vehicles that focus on increasing the overall accumulation of anticancer drugs within a tumor, the penetration of these drug carriers––a factor that is equally important in determining efficacy––has received much less attention. The penetration of drugs and/or drug carriers in a tumor can be operationally defined at different length scales as 1) penetration from the surface of the tumor boundary into the tumor center (i.e., whole tissue scale), 2) penetration across the tumor blood vessel (i.e., vascular permeability), 3) penetration away from the blood vessels through the extracellular matrix (analogous to the effective diffusion coefficient), and 4) penetration into the tumor cell itself (cellular uptake). Optimizing penetration in a tumor is important at length scales that are relevant to the mode of action of the drug. Hence, for chemotherapeutic drugs such as doxorubicin that normally have an intranuclear mode of action, optimization of penetration from the macroscale down to the intracellular site of action is critical, whereas for radionuclides, homogeneous penetration through the tumor mass without substantial tumor cell uptake may suffice to elicit a therapeutic effect. In terms of the determinants of penetration, properties of the drug or drug carrier, such as molecular size and binding affinity, as well as properties of the tissue, including extracellular matrix constituents and pore interconnectedness, are important factors that will affect penetration at all length scales (38–44). Increasing molecular size limits penetration across the blood vessel (40) and through the tumor tissue (41). Although Tang et al. (1) used doxorubicin encapsulated in a polyethylene glycol-phosphatidylethanolamine (PEG-PE) micelle with a diameter of 10–20 nm, which is larger than doxorubicin alone, they achieved sufficient tumor accumulation to elicit a therapeutic response that they claimed could be attributed to the improved penetration of doxorubicin within the tumor.

Tang et al. (1) used a multitude of analytic, in vitro, and in vivo techniques to raise many interesting questions and present some promising results. Most notably, cellular uptake of doxorubicin was improved when delivered with PEG-PE, and this increased uptake may have contributed to the lower IC50 observed for doxorubicin PEG-PE micelles. Furthermore, the doxorubicin encapsulated within PEG-PE micelles demonstrated a different intracellular distribution than the free drug, and, in the light of the lower IC50 compared with free doxorubicin, these data suggest that the encapsulated doxorubicin may well have a different mechanism of cytotoxicity (45,46), though the precise mechanism of both cellular uptake and cytotoxicity of doxorubicin PEG-PE micelles remains a mystery. These results are also intriguing because they are in stark contrast to other drug delivery systems, in which encapsulated or conjugate drugs are often less cytotoxic than free drug. Many drug delivery systems demonstrate impressive tumor targeting in vivo but fail to elicit tumor regression because the drug is less bioavailable than free drug once it is localized to the tumor due to the encapsulation or conjugation process.

.....In our view, several aspects of this study are puzzling and deserve further scrutiny: first, it is surprising that the ability of PEG-PE to form micelles that can encapsulate doxorubicin has not been previously explored, as claimed by the authors, and, if this claim is correct, the authors deserve credit for examining the interaction of an old drug with a well-known formulation agent to create a potent drug delivery system.


Toward a Systems Engineering Approach to Cancer Drug Delivery; http://jnci.oxfordjournals.org/cgi/content/full/99/13/983