The design and analysis of sugar-based carrier systems for the protection of nucleic acids

The overall aim of the work detailed in this thesis was to design and analyse sugar-based (trehalose, raffinose and sucrose) carrier systems for the protection of naked plasmid DNA formulations generated by spray drying. Trehalose exists in multiple crystalline anhydrous and hydrated forms and is thought to exist in two different amorphous forms. Reported thermal transitions of trehalose dihydrate vary with environmental conditions and particle size. The first area of this thesis focused on investigating the inter-conversion properties of trehalose dihydrate to observe if an in-depth understanding of its physical properties will provide an insight into its bio-protective properties. Within this area, two standardised forms of α,α-trehalose dihydrate were generated and characterised by performing a series of thermal, spectroscopic and X-ray diffraction techniques. This resulted in the identification of an intermediary anhydrous form. Within the second area of this thesis the use of the fragility parameter m and the strength parameter D as predictors of amorphous stability of generated co-spray dried sucrose-raffinose and sucrose-trehalose samples was investigated. Results showed addition of both raffinose and trehalose improved predicted amorphous stability, with the greatest effect seen at highest additive concentrations. The third area of the thesis was to evaluate the degree of degradation of plasmid DNA spray dried in the presence of amorphous sugars. Spray-drying can be used to develop biopharmaceutical particles for the pulmonary delivery. However, it runs the risk of loss of biological activity, sample instability as well as thermal degradation of the biopharmaceutical. Results showed that plasmid DNA degradation was reduced when co-spray dried in the presence of raffinose and to a greater extent with trehalose. Co-spray drying of plasmid DNA in the presence of sucrose, sucrose-raffinose and sucrose-trehalose formulations offered less protection than trehalose and raffinose. Overall, two key messages are concluded from the work detailed in this thesis. Firstly, the thermal transitions of trehalose dihydrate can be influenced by environmental factors as well as inter-batch variability. This can affect authenticity of polymorphous and amorphous forms identified. Secondly, addition of raffinose and trehalose to amorphous sucrose formulations improved the predicted amorphous stability of the formulations however; these co-spray dried samples offered less protection compared to plasmid DNA co-spray dried in the presence of trehalose and raffinose alone

Microfibrous Solid Dispersions of Poorly Water-Soluble Drugs Produced via Centrifugal Spinning: Unexpected Dissolution Behavior on Recrystallization

Temperature-controlled, solvent-free centrifugal spinning may be used as a means of rapid production of amorphous solid dispersions in the form of drug-loaded sucrose microfibers. However, due to the high content of amorphous sucrose in the formulations, such microfibers may be highly hygroscopic and unstable on storage. In this study, we explore both the effects of water uptake of the microfibers and the consequences of deliberate recrystallization for the associated dissolution profiles. The stability of sucrose microfibers loaded with three selected BCS class II model drugs (itraconazole (ITZ), olanzapine (OLZ), and piroxicam (PRX)) was investigated under four different relative humidity conditions (11, 33, 53, and 75% RH) at 25 °C for 8 months, particularly focusing on the effect of the highest level of moisture (75% RH) on the morphology, size, drug distribution, physical state, and dissolution performance of microfibers. While all samples were stable at 11% RH, at 33% RH the ITZ-sucrose system showed greater resistance against devitrification compared to the OLZ- and PRX-sucrose systems. For all three samples, the freshly prepared microfibers showed enhanced dissolution and supersaturation compared to the drug alone and physical mixes; surprisingly, the dissolution advantage was largely maintained or even enhanced (in the case of ITZ) following the moisture-induced recrystallization under 75% RH. Therefore, this study suggests that the moisture-induced recrystallization process may result in considerable dissolution enhancement compared to the drug alone, while overcoming the physical stability risks associated with the amorphous state