dc.description.abstract
This work aims to develop novel systems for the transport of active pharmaceutical ingredient (API) especially small molecules to specific target in biological entities by tackling the main three challenges that this domain faces. The challenges of solubilizing hydrophobic drugs, the elimination of drugs from the blood stream and specific targeting to a defined site. The system is based on biodegradable polyglycerol copolymers by integrating biodegradable moieties into the polyglycerol backbone via the copolymerization of the glycidol monomer with 7-membered lactone rings containing an ester functional group or an ester and disulfide bond functional group, and a linear diacid that contains a disulfide bond. In the first two projects where the comonomer chosen was caprolactone, two host molecules were encapsulated in the DDS, sunitinib for cancer therapy and tofacitinib for skin inflammation therapy. The structure of the project can be divided into the following packages: (i) bulk straightforward-synthesis of the copolymer, (ii) chemical and physical characterization, (iii) encapsulation and release of the chosen API (iv) in vitro biological assays, and (v) in vivo or ex vivo tests. In both cases the system was proven to increase the solubilization of the guest drug significantly and improve its performance in comparison to the drug alone. The introduction of the sulfate end groups into the system led to its accumulation into the specific site in vivo.
In the first project, the copolymers were synthesized on a large scale (20 g) through a simple two-step process. In vivo fluorescence imaging revealed significant accumulation of the DDS in tumor environments. Sunitinib, an anticancer drug, was loaded into the DDS, and its toxicity was assessed both in vitro and in vivo. Results showed similar toxicities between the drug encapsulated in dPGS-PCL and the free drug in A431 and HT-29 cells, with comparable cellular uptake. In the second project, the chosen API was tofacitinib. Inflammatory skin disorders, such as psoriasis and alopecia areata, stem from dysregulation in the innate immune system, triggering the Janus kinase-signal transducer and activator of transcription (JAK-STAT) inflammatory pathway by cytokines like interleukin 6 (IL-6). JAK inhibitors, notably tofacitinib, disrupt this pathway by binding to JAK enzymes. However, topical applications of these inhibitors show limited efficacy, particularly for alopecia areata. This study introduces a novel carrier, sulfated dendritic polyglycerol with caprolactone segments (dPGS-PCL), to improve tofacitinib delivery. Testing on ex-vivo human skin models demonstrates enhanced skin penetration of tofacitinib when loaded into dPGS-PCL compared to free tofacitinib. Anti-inflammatory efficacy was evaluated through IL-6 and IL-8 release, and STAT3 and STAT5 activation assays in inflamed skin models, indicating reduced activation of inflammatory markers with increased tofacitinib penetration.
The second system and third project, glycidol was copolymerized with the comonomer containing an ester and a disulfide bond, were investigated thoroughly in terms of structure and physical characteristics. The purpose was to understand the effect of the disulfide bond, whether on the initial stages like synthesis or later stages like the chemical and physical characteristics of the copolymer. Its copolymerization with glycidol was compared to the copolymerization of caprolactone with glycidol under the same conditions via two different copolymerization mechanisms. Interestingly, the structure obtained when using the comonomer containing the disulfide bond was unique: an ideal random copolymer. This was not the case when the comonomer used was caprolactone. Moreover, three different copolymers of the same molecular weight with different disulfide ratios were tested for degradation and behavior in aqueous solution. The project also focused on the biocompatibility of the copolymer for future employment in biological entities.
Third system and fourth project, glycidol was copolymerized with a diacid that contains a disulfide bond in a simple manner, without another catalyst or solvent. The diacid acted as the proton donor to initiate the polymerization and was integrated in the polyglycerol backbone. Redox-degradable hydrogels loaded with an antibacterial peptide (vancomycin) were formed using the reducible polyglycerol as a building block, cross-linked by 4-arm polyethylene glycol-thiol (4-arm PEG-SH). The hydrogel degrades under reductive conditions triggered by glutathione, leading to the controlled release of the antibacterial peptide. Rheological analysis was conducted to assess the mechanical properties, including stiffness, softness, and self-healing capability, for various ratios and concentrations of both components. Hydrogel degradation was confirmed through rheological measurements and weight loss analysis. FITC-albumin and vancomycin were successfully loaded into the hydrogel, and the release kinetics were evaluated for both sustained and on-demand release profiles. Furthermore, in vitro, and in vivo experiments demonstrated that the vancomycin-loaded hydrogel acts as an effective antibacterial barrier for wound dressing and accelerates the healing of infectious wounds in a mouse model.
In conclusion, the design of straightforward, scalable, and solvent free drug delivery systems is crucial for an adequate translation of the system from research to application stage. However, the knowledge around the system should be complete and the performance should be maximized. Moving forward from the first system into the second, and third the expectation of the improvement of the system is suggested by introducing a second degradable moiety that will in retrospect enhance the drug release. Therefore, the future steps should focus on the encapsulation of a guest molecule and its release and testing the disulfide containing system in vivo, to be able to compare the performance to the caprolactone containing system, keeping in mind that challenges might also arise along the way due to the sensitive nature of the disulfide bond.
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