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Photoresponsive multifunctional DNA block copolymer nanocarriers for drug delivery and vaccine development

Final Report Summary - PHOMULDNAPOL (Photoresponsive multifunctional DNA block copolymer nanocarriers for drug delivery and vaccine development)

The development of effective drug delivery systems and vaccines for cancer treatment is still nowadays a scientific challenge that requires further exploration and development. The design of such systems involves the consideration of different aspects crucial for their performance such as composition, functionalization, morphology and release mechanism. The present project explores the development of innovative nanocarriers based on degradable (DNA) block copolymers which disassemble under specific stimuli such as reducing environment and light. The use of DNA block copolymers provides the possibility of incorporating multifunctionality by hybridization of complementary DNA sequences linked to specific molecules resulting in systems that combine both a controlled release of the encapsulants and multifunctionality.
Over the past years different delivery systems have been developed with the aim of making the most of their combined features. The use of biodegradable block copolymers which yield to harmless byproducts easy to eliminate from the organism is a fundamental pre-requisite for in vivo applications. Other features such as the morphology, functionality or release mechanism can be tuned as advanced attributes. It has been for example demonstrated that worm-like micelles remain in circulation for longer time than their spherical counterparts due to their ability to avoid uptake by macrophages.1 On the other hand moieties responsive to specific stimuli have been incorporated into nanoparticle-based systems providing a higher degree of control over the release of encapsulated molecules.2 The vast majority of the stimuli-sensitive delivery systems developed until the moment have been however limited to spherical aggregates. Thus combining the advantages of shape and controlled disassembly, the creation of novel and advanced delivery systems can be envisioned.
The work performed during the outgoing phase of the project focused in the development of two different stimuli-sensitive worm-like micelles which disassemble under reducing conditions or under irradiation. In the last stage of the project also micellar systems from redox-sensitive DNA block copolymers were developed in order to provide the possibility of incorporating multifunctionality. During this period block copolymers from poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) containing either a disulfide bond or a photocleavable linker between the two polymer groups were synthesized, purified and characterized. These copolymers were assembled into worm-like micelles and their triggered disassembly was studied in vitro. The redox-sensitive micelles containing the anti-cancer drug paclitaxel were also tested in vivo. Tumor-bearing mice injected with the formulation showed a systematic reduction in the tumor size during the treatment proving this system as an effective tool in drug delivery for cancer treatment. These results are currently being written in a manuscript for submission to a high impact peer-reviewed journal.
Parallel to this work DNA block copolymers containing a disulfide bond were also synthesized, purified, characterized and assembled into micelles. Their disassembly in vitro in a reducing environment was proven.
The return phase of the project focused in applying the acquired knowledge in the development of redox-sensitive DNA block copolymers for the creation of innovative vaccines. The development of nanoparticle-based vaccines involves the delivery of immunostimulatory and co-stimulatory molecules, antigen and adjuvant respectively, to antigen presenting cells (APCs) to trigger subsequent events that lead to immune responses.
Among the antigens and adjuvants used in the field of vaccines the work was focused on two of them, namely ovalbumin (OVA) or a derived peptide from OVA (SIINFEKL) as the antigen and CpG B as the adjuvant. CpG B is a short single-stranded DNA molecule that acts as immunostimulant. Different CpG B- polymer conjugates containing disulfide bonds were synthesized and purified successfully. CpG B-S-S-PEG conjugates were used in the formation of polyionic complex (PIC) micelles which are formed by the combination of the conjugate with a polycation such as branched polyethylenimine (B-PEI). Although such kind of micelles has been reported before, their application as vaccines is still missing and that is what is being at the moment explored in our group. PIC micelles from CpG-B in combination with OVA were studied in vivo on tumor-bearing mice. Although the results are still inconclusive the micelles showed some effect and resulted in tumor shrinkage. These results represent the first step in the development of PIC micelle-based vaccines and further experimentation is taking place at the moment combining the peptide SIINFEKL.
The results obtained during the three year project represent an advancement in the fields of drug delivery and vaccine development since the combination of different relevant features have been further explored, i.e. morphology, functionality and triggered release, and novel effective systems have been developed. Although their social impact is still far from being patent, these results are a step further in the elaboration of effective systems in both fields and represent a very useful tool for the progress towards that end.
1 Y. Geng, P. Dalhaimer, S. Cai, R. Tsai, M. Tewari, T. Minko, D. E. Discher, Nature Nanotechnol. 2007, 2, 249
2 S. Mura, J. Nicolas, P. Couvreur, Nature Mat. 2013, 12, 991