Preparation and characterization of nano- and micro- particles for targeted drug delivery in cancer therapy

Abstract

It is well established that cancer is one of the most common and debilitating diseases with high mortality rates, and yet the most commonly used therapy method for cancer is intravenous chemotherapy and/or radiotherapy, which causes unwanted and serious side effects and can affect healthy tissues or organs. Seek for new therapy methods with higher efficiency and fewer side effects still continues to be popular amongst researchers. One of the most promising methods to optimize cancer treatment is targeted drug delivery of already available antitumor drugs, which aims to minimize systemic concentration while increasing drug concentration at the target site. Hence, reducing the side effects while increasing the therapeutic effect of the antitumor drugs. Particle-based targeted drug delivery systems have various advantages over conventional drugs and can significantly improve cancer therapy in various ways. These drug carrier particles can provide many advantages such as; high drug capasities, protection of loaded drugs, sustained and/or controlled drug release, possible variable routes of administration, ease of surface modification, precise targeting to tumor sites, etc. Although particle-based drug delivery is a popular research subject, there are still several limitations to particle-based drug delivery applications such as; possible toxicity of particles in their unmodified form, possibility, insufficient accumulation at the target site, immunogenicity, unstable particles, aggregation, etc. If these disadvantages could be eliminated and/or significantly reduced targeted drug delivery applications could be highly efficient and effective in cancer therapy. In the scope of this thesis particulate-based targeted drug delivery vehicles were produced via several techniques and characterized in order to achieve effective and efficient cancer treatment. To ensure our objective, nano- and micro-sized drug delivery particles were prepared, which depending on the size will have different physical properties, targeting strategies, working mechanisms, and administration routes. Clay minerals (montmorillonite) and iron oxide particles were used separately to produce both nano- and micro-particles for drug delivery applications. Lures of using magnetic particles such as iron oxide particles are that they are magnetically targetable, heatable under applied alternating magnetic fields, imageable, etc. And clay minerals also possess attractive properties such as; good biocompatibility, the ability to adsorb large amounts of drugs and improve drug stability, controlled and/or sustained release behavior, etc. Four different targeted drug delivery particles were produced during this thesis for different types of targeting strategies and administration routes. Iron oxide-based and clay-based microparticles were produced for direct targeting such as transarterial chemoembolization and Iron oxide-based and clay-based nanoparticles were produced for magnetic, active, and/or passive targeting. The most suitable form of each particle for the desired targeted drug delivery application was obtained via conventional, rheological, and in vitro characterization, tuning colloidal behavior, surface modification, etc. Different types of targeted drug delivery particles that were produced for this thesis comprise of montmorillonite-based microparticles, montmorillonite-based nanoparticles, iron oxide-based microparticles, and iron oxide-based nanoparticles, which were explained in chapters 2,3,4 and 5-7, respectively. Each particle is briefly summarized in the following 5 paragraphs. Drug-delivering montmorillonite-based microparticles that are also imageable were produced and characterized and the results indicated that these microparticles can be utilized for imaging or targeted drug delivery applications such as transcatheter arterial chemoembolization. Furthermore, the adsorption of antitumor drugs and/or radio-opaque contrast material onto montmorillonite influenced particle size and could be modified to the desired size for specific applications. So, these particles were suitable for embolization and can occlude tumor vasculature. The traceability of particles via CT was successful and precise. Moreover, the drug release behaviors of montmorillonite-based microparticles were sustained over a long period of time and were able to exhibit antitumor activity as the pure drug against cancerous cells. The adsorbed antitumor drug on the particles caused both devascularization and simultaneous release of the drug around the tumor site which was predicted to cause progressive shrinkage and/or necrosis of the tumor while the shrinkage of the tumor can be monitored by the imageable particles. Targeted drug delivery particles from raw and purified montmorillonite were produced and their potential to be delivery vehicles and effects of purification on the final product were analyzed. The results showed that the chemical composition, interlayer spaces, surface, and adsorption properties of raw montmorillonite were altered during purification. Both purified and raw montmorillonite Were able to load significant amounts of antitumor drugs and perform similarly to pure antitumor drugs against cancerous cells. However, In vitro drug release profiles indicated that purified and raw montmorillonite drug release behavior was different over 20 days which indicates that purification had an effect on desorption. In addition, cytotoxicity tests using normal cells revealed that raw and purified montmorillonite did not significantly affect cell viability at low concentrations, but at high concentrations, both treatments significantly decreased cell viability. Both drug loaded forms of raw and purified montmorillonite were effective as the pure antitumor drug, but it is important to take their release behavior into account before deciding which formulation is most suitable for the specific application. Iron oxide based microparticles suitable for transcatheter chemoembolization and magnetic hyperthermia were produced via utilizing both micro- and nano-iron oxide particles. Particles were linked together with a polymer and later enveloped using another polymer to obtain particle sizes suitable for embolization. Embolization particles produced from both micro- and nano-iron oxide particles exhibited different drug loading capacities and dimensional variance. Regardless of these differences, they both demonstrated favorable drug releasing behaviors, the ability to induce magnetic hyperthermia, could achieve arterial occlusion, etc. Both chemoembolic particles showed that they might be successfully utilized in chemoembolization and hyperthermia procedures. Furthermore, magnetic nanoparticles suitable for targeted drug delivery were produced using iron oxide nanoparticles, several different biopolymers, and an antitumor drug. Nanoparticles were coated with different polymers and drugs were loaded onto polymer-coated surfaces. The effect of coating and each polymer's effect on the final product was analyzed. Polymers that were chosen were each either anionic, cationic or nonionic in nature and results indicated that there were several differences in the final product properties depending on the polymer type. Although almost all polymers except anionic ones, completely covered particle surfaces, our studies indicated that cationic polymers may be more suitable for targeted delivery applications. The cationic polymer was able to completely cover particle surfaces and reduce particle toxicity to normal cells more than anionic and nonionic polymers. Furthermore, cationic polymer also allowed antitumor drug loading on the particles and drug-loaded particles were effective enough similar to pure antitumor drugs. Additionally, the magnetism of the particles was not considerably diminished by the cationic polymer coatings, allowing the particles to be guided to the appropriate location by applied magnetic fields and induction of hy hyperthermia if desired. Finally, actively targeted forms of magnetic iron oxide nanoparticles were produced using several different biopolymers (PVP and PVA), targeting agents (Folic acid or - Estradiol) and an antitumor drug in order to target folate or estrogen receptors that are highly expressed on certain breast cancers and achieve ligand-receptor binding at the target site. Results indicated that incorporation of targeting ligands onto particle surfaces stabilized the dispersions and also increased antitumor activity compared to particles without targeting ligands. Which suggests that incorporation of Folic acid or - Estradiol enhanced antitumor drug activity while stabilizing state of the dispersions. Studies carried out in this thesis indicated that the production of targeted drug delivery particles suitable for almost all desired targeting strategies (active, passive, direct, and/or magnetic) and preferred modes of drug administration can be successfully produced by exploiting the unique properties of clay minerals and/or magnetic particles. In sum, micro- and nano-particles suitable for various strategies of targeted drug delivery applications were successfully produced within the scope of this thesis. All particles produced for this study exhibited an advantageous combination of properties to be utilized as drug delivery vehicles to the target site.