Research in the Paulusse Group

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Bionanoparticles for drug delivery & imaging

The Paulusse Group is involved in several diverse research topics, from organic synthesis to biology. Our main focus lies with the preparation of small, well-defined polymeric nanoparticles for medical applications, for example drug/gene delivery and imaging. These particles can have multiple functionalities, such as a biocompatible backbone, a degradable moiety for triggered release, a reporter agent for imaging and a biologically active group to achieve active targeting. Use the menu on the left for more details on the individual research projects and to find out what student projects are available. 

Single-Chain Nanoparticles

In order to widen the existing polymeric drug carrier systems to the sub-20 nm size regime, we are investigating single-chain polymer nanoparticles (SCNPs). SCNPs are prepared through intramolecular crosslinking of individual polymer chains into individual nanoparticles (Figure 1) and thus offer tremendous control over size and dispersity, without the requirement of complex synthetic strategies. Moreover, polymeric nanoparticles offer ample possibilities for pre- or post-synthesis modification, enabling functionalizations for targeted drug delivery.

Owing to the ease of preparation, the majority of currently developed SCNPs are soluble only in organic media, impeding their biomedical application. We therefore recently developed water-soluble SCNPs, and are currently investigating drug encapsulation.
 

Figure 1. Schematic of SCNP formation.

Size-controlled nanogels

The size of nanoparticles is known to dramatically affect biological processes such as cellular uptake, tissue/tumor penetration and immune response. However, preparation of sub-100 nm nanogels can be challenging. We prepare nanogels using reversible addition–fragmentation chain transfer (RAFT) polymerization as depicted in Figure 1. By quenching the reaction at appropriate timepoints, nanogels of different sizes are obtained. In prinicple, this approach is suitable for most vinyl monomers, and copolymerization of appropriate monomer easily yields functional nanogels. We are currently investigating the effect of nanogel-size on biological processes such as cell uptake, tissue diffusion and drug delivery.


Figure 1. Nano/macrogel formation over time via controlled radical polymerization.

Cyclic monomers

The development of new non-viral drug and gene delivery vehicles has made tremendous progress over the past decade. Cationic polymers such as polyethyleneimine (PEI) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) have proven very effective transfection agents, since they readily form stable polyplexes with for example siRNA and easily penetrate the cell wall to deliver their cargo.

A major drawback, however, to these polymers is their persistent nature. The main polymer chain of PDMAEMA consists of non-degradable carbon-carbon bonds. Our recently developed cyclic monomers for radical polymerization may provide a solution to this problem. These cyclic monomers may be added to an existing recipe for PDMAEMA polymers, and whichever functional group is present in the cyclic monomer, will be incorporated into the main polymer chain during the polymerization (Figure 1.). For example, PDMAEMA having disulfide moieties in its backbone can be prepared, to obtain bioreducible gene delivery agents.
 

Figure 1. Incorporation of degradable groups in polymer backbone using cyclic monomers.

PAAs for drug delivery

Water-soluble dispersed nano-sized crosslinked polymer networks, or nanogels, possess properties which are very interesting in drug delivery and imaging applications. Due to their swollen and dissolved state, nanogels may respond to changes in pH, temperature and ionic strength, which can trigger controlled release of therapeutic agents. Furthermore, zwitterionic materials have shown great potential as a biomaterial, due to low interaction with biological compounds and cells.
 
We prepare zwitterionic nanogels based on poly(amido amine)s (PAAs) by a surfactant-free inverse nanoprecipitation, as shown in Figure 1.. The formed nanogels have a diameter of around 100 nm and exhibit a low dispersity. The overall charge of these nanogels can be tuned to improve properties such as stability, cell toxicity and cell accumulation. These nanogels can be functionalized, for example using a Prostate-Specific Membrane Antigen (PSMA) targeting ligand, and used for drug encapsulation to achieve controlled drug release. 

Figure 1.. Preparation of PAAs followed by inverse nanoprecipitation to obtain zwitterionic nanogels.

PAAs for gene delivery

Gene therapy involves the intracellular delivery of nucleic acids for the treatment, detection and prevention of diseases, such as cancer, infections and hemophilia. Cationic polymers have been widely applied as gene carriers, among them poly(amido amine)s (PAAs) such as CBA-ABOL. The disulfide bonds in this polymer exploit the reducing intracellular environment (high glutathione, GSH, concentration, see Figure 1) and ensure intracellular release of the genetic payload. We design and evaluate many different PAAs in order to optimize gene delivery and the safety of these polymers. For example, PAAs bearing sterically hindering groups adjacent to the disulfide moiety were prepared; these groups prevent or slow GSH attack, thereby slowing the degradation rate of these polymers. In this way, polymer stability can be fine-tuned and optimized for specific gene therapy applications.

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Figure 1. Schematic of cationic PAA gene delivery (left) and example of GFP-transfected cells (right).

β-Receptor imaging

Cardiovascular diseases are among the three main causes of death, along with cancer and respiratory diseases. Early detection of heart failure could aid treatment and monitoring of these diseases. The β1-adrenergic receptor (β1-AR) is a promising marker for heart failure imaging, since reduced β1-AR levels on the cardiac muscle are often observed in cardiac patients. Therefore, a β1-AR selective binding ligand with high binding affinity is required. Our approach is to take advantage of the multivalency effect to increase both binding strength and specificity. We are working on the synthesis of dendrimers with tunable-valency, their functionalization using a β1-AR binding ligand and finally incorporating an 18F-compound for Positron Emission Tomography (PET), as depicted in Figure 1.
 

Figure 1. Dendrimer design, including β1-AR binding ligands and 18F PET reporter.


 

Optimization of size-controlled nanogels

The size of nanoparticles is known to dramatically affect biological processes such as cellular uptake, tissue/tumor penetration and immune response.1 For example, nanogels of 30 nm are frequently reported as optimally-sized nanogels for tumoral drug delivery.2 However, preparation of sub-100 nm nanogels can be challenging. In this project, nanogels will be prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization as depicted in Fig. 1. By quenching the reaction at appropriate timepoints, nanogels of different sizes should be obtained. A library of particles with sizes between 10-100 nm and several chemical compositions (styrene, DMAEMA, HEAA, NIPAM and SBMA) will by synthesized and characterized. Conditions such as concentration, monomer ratio and temperature will be optimized. Finally, cellular uptake will be investigated by copolymerizing a fluorescent tag and performing confocal microscopy.


Figure 1. Nano/macrogel formation over time via controlled radical polymerization.
 
 
References
(1)      Zhang, S.; Gao, H.; Bao, G. Physical Principles of Nanoparticle Cellular Endocytosis. ACS Nano 2015, 9,  8655–8671.
(2)      Cabral, H.; Matsumoto, Y.; Mizuno, K.; Chen, Q.; Murakami, M.; Kimura, M.; Terada, Y.; Kano, M. R.; Miyazono, K.; Uesaka, M.; et al. Accumulation of Sub-100 Nm Polymeric Micelles in Poorly Permeable Tumours Depends on Size. Nat. Nanotechnol. 2011, 6, 815–823.
 
 
Reducible vinyl polymers for drug and gene delivery

The development of new non-viral drug and gene delivery vehicles has made tremendous progress over the past decade. Cationic polymers such as polyethyleneimine (PEI) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) have proven very effective transfection agents, since they readily form stable polyplexes with for example siRNA and easily penetrate the cell wall to deliver their cargo.
 

A major drawback, however, to these polymers is their persistent nature. The main polymer chain, also called backbone, of PDMAEMA consists of carbon-carbon bonds. The recent development of cyclic monomers for radical polymerization may provide a solution to this problem. These cyclic monomers may be added to an existing recipe for PDMAEMA polymers, and whichever functional group is present in the cyclic monomer, will be incorporated into the main polymer chain during the polymerization.

AIM OF THE PROJECT
The monomer 2-dimethylaminoethyl methacrylate will be polymerized via controlled radical polymerization techniques, in the presence of a disulfide-functional cyclic monomer. Polymers of different lengths and containing different amounts of cyclic monomer will be prepared and fully characterized. Their degradation will be studied and, depending on available time and experience, their efficacy in DNA delivery will be studied.
 
APPROACH
Initially, we will prepare PDMAEMA polymers of different length, without the cyclic monomer. A disulfide-functional cyclic monomer will be prepared via a 3-step synthesis, and the products will be characterized with NMR and infra-red spectroscopy. PDMAEMA polymers with the cyclic monomer will be prepared, and these polymers will also be fully characterized. Finally, their degradation will be studied as well as their efficacy in DNA delivery.
 

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