Project

Discipline

Nanomedicine; Chemotherapy; Drug targeting; Surface functionalization; Water-insoluble drugs

Lead
Lay summary
Nanoparticulate drug delivery systems are currently used to overcome critical challenges associated with classic dosage forms. In particular, this approach is often used for hydrophobic anticancer drugs which are poorly water soluble and for which it is difficult to achieve accumulation at the site of disease and/or adequate pharmacokinetic profiles in humans. Miniaturization of the drug in a nanoparticulate form offers the possibility of altering these parameters. In the research proposed herein, we will use stabilized drug nanocrystals as a model platform for specifically and systematically evaluating the effect of size, circulation time, and surface functionality on biodistribution and efficacy of nanoparticulate drug delivery systems. More specifically, nanoparticles of paclitaxel (model anticancer agent) with target sizes of about 100 nm will be prepared by wet milling and stabilized by a tailored copolymeric surfactant composed of poly(ethylene glycol)-b-poly(caprolactone) (PEG-b-PCL) bearing pendant functional groups incorporated in the hydrophobic PCL block which can serve to stabilize the nanoparticles by subsequent crosslinking. This polymer may not only allow for adjusting the dissolution rate of the nanoparticles by means of chemical crosslinking, but will also permit grafting of targeting moieties,  thereby altering the surface functionality of the nanoparticles. We have selected a designed ankyrin repeat protein (DARPin) specific for the epithelial cell adhesion molecule (EpCAM) on cancer cells as model targeting ligand. In vitro tests on cells will be used to evaluate the cellular uptake and cytotoxicity of the drug nanoparticles. The pharmacokinetics, biodistribution and antitumoral activity of the nanoparticles will be evaluated in vivo on suitable models. Through this research we hope to develop and to correlate the intrinsic design parameters of drug nanocrystals with their biodistribution and efficacy in order to gain a better understanding of nanomedicines.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

Nanoparticulate drug delivery systems are currently used to overcome critical challenges associated with classic dosage forms. In particular, they are often investigated to reformulate hydrophobic anticancer drugs which are poorly water soluble and for which intravenous (i.v.) administration is complicated by potential aggregation in the bloodstream (leading to embolism). In addition, specific drug distribution to tumoral tissues is difficult to achieve. There is an increasing number of nanosized anticancer formulations under clinical trials and some have reached the market. For example, liposomal doxorubicin has now been used for more than 10 years in the treatment of myeloma, breast cancer, ovarian cancer, and AIDS-related Kaposi's sarcoma, while albumin-coated paclitaxel nanoparticles (Abraxane®) have received market approval in Europe in 2008, and are indicated for the treatment of metastatic breast cancer. In comparison to conventional solutions of drugs, a nanoparticulate formulation offers the possibility of limiting the use of excipients, which are often another source of side effects (e.g., hypersensitivity reactions for paclitaxel solution), or to encapsulate a drug and reduce its distribution in healthy tissues (e.g., cardiotoxicity in the case of doxorubicin). Drug nanocrystals are particularly interesting because they allow injecting i.v. poorly soluble drugs with minimal use of stabilizing excipients and potentially alter their pharmacokinetic and biodistribution profiles. Although this concept is appealing, it has been rarely implemented due partly to the lack of control on nanocrystal dissolution once in the bloodstream. Most polymeric coatings employed so far to stabilize drug nanocrystals are physically adsorbed onto the particle surface and exert no control on the dissolution rate. Moreover, they are prone to rapid dissociation and therefore not ideally suited for imparting the particles with targeting ligands. In the research proposed herein, we will evaluate the possibility of increasing the circulation time and targetability of paclitaxel nanocrystals. Paclitaxel is a potent anticancer drug that is practically insoluble in water. It therefore represents a suitable candidate for nanosizing. The proposed strategy is aimed at developing stabilizing polymers which will be adsorbed to the surface of the nanocrystals and then cross-linked. This cross-linking step should provide some control over the dissolution rate and enhance the circulation time of paclitaxel. Moreover, the presence of a stable coating at the surface of the particles will allow the surface functionalization of the latter with targeting ligands, providing means to not only change the pharmacokinetic and biodistribution patterns, but also the drug internalization/retention at the target site. More specifically, nanoparticles of paclitaxel with target sizes of about 150 nm will be prepared by wet milling and stabilized by a tailored polymeric surfactant composed of poly(ethylene glycol)-b-poly(e-caprolactone)-ran-poly(e-propargyl-delta-valerolactone) (PEG-b-PCL/VL), which bears pendant functional groups incorporated in the hydrophobic polyester block. These can serve to stabilize the nanoparticles by subsequent cross-linking. This polymer will not only allow for adjusting the dissolution rate of the nanoparticles by means of chemical cross-linking, but will also permit grafting of targeting moieties such as antibody fragments or designed ankyrin repeat proteins (DARPins), thereby altering the surface functionality of the nanoparticles. As model targeting ligands, we have selected an antibody which targets the fibronectin isoform containing the alternatively-spliced domain A (EDA) expressed in vascular structures in tumoral tissues, and a DARPin specific to the epithelial cell adhesion molecule (EpCAM) on adenocarcinoma cells. After demonstrating enhanced stability of the nanocrystals, in vitro tests on cells will be performed to evaluate their cellular uptake and cytotoxicity. In vivo experiments will be carried out in tumor-bearing mice to characterize the pharmacokinetics and biodistribution of the nanoparticles. Finally, the toxicity and antitumoral efficacy of the newly developed paclitaxel formulations will be assessed and compared to the Abraxane dosage form. Through this research we hope to better understand the role of key parameters in the design of more efficient drug nanocrystals in cancer chemotherapy.