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Positron emission tomography (PET) is a non-invasive imaging technique that is emerging as a useful tool in the field of cancer medicine particularly in drug development. The purpose of this thesis has been to perform clinical studies using two different radiotracers, 5-[^V]fIuorouracil (5-['^F]FU) and 2-[''C]thymidine, to assess pharmacokinetic and pharmacodynamic parameters respectively, which were derived from PET imaging and to establish the contribution that PET can add to drug development, in vivo, in man. Aims: 1) Quantify the pharmacodynamic effects of cytotoxic agents in tumour and normal tissue using 2-["C]thymidine 2) Measure changes in tumour and normal tissue pharmacokinetics of 5-Fluorouracil in response to the modulating agents carbogen and nicotinamide or interferon 3) Assessment of blood flow change in tumour and normal tissue to carbogen and nicotinamide or interferon 4) Interpretation of PET data using novel analysis methods with modified Patlak and spectral analysis Methods: In the 5-['^]FU study, patients with metastatic gastrointestinal cancer underwent PET scanning at the start of 2 separate chemotherapy cycles. The 2nd scan was performed after the administration of carbogen and nicotinamide or interferon. In the 2-["C]thymidine study patients receiving chemotherapy were scanned before commencing chemotherapy, and 1 week after the 3''' cycle of chemotherapy. Patients also had conventional imaging before the start of and after 3 cycles of treatment. Findings: After carbogen and nicotinamide administration, 5-['^]FU uptake was increased in tumour, but not in normal tissue. Regional perfusion was elevated in tumours but decreased in kidneys after carbogen and nicotinamide. After interferon administration, there was an increase in 5-['^]FU retention in tumours, but no increase in uptake. Regional perfusion in tumour and normal tissue was unaltered by interferon. Retention of 2-["C]thymidine decreased in tumour in keeping with the results of conventional radiology, suggesting a pathological response, assessed in vivo, to chemotherapy.

In recent years, there has been a growing interest towards the use of transdermal drug delivery systems (TDDS). However, a great challenge in this arena is the formidable barrier posed by the skin that can limit permeation of therapeutic agents. Therefore, there is a need for novel strategies or enhancement techniques to deliver the drug across the skin. The use of hot melt extrusion technology (HME) to prepare these TDDS is also generating considerable interest in the pharmaceutical field. This work combines these interests through preparation of several hot melt extruded formulations screened for their potential for transdermal development. A substantial database has been generated on physicochemical characteristics of these formulations with a prime focus on their in vitro drug release and permeation properties. Processing parameters (temperature, heating duration and mixing speed) for preparing hot melt extruded compositions comprising ibuprofen (model drug) and various carrier excipients were established with minimal thermal degradation. Ibuprofen displayed a plasticizing effect enough to perform extrusion. HME processing facilitated the formation of solid solutions and dispersions. The feasibility of delivering ibuprofen from Eudragit RS PO-based extruded patches was investigated. The formation of solid solutions with high drug loading (35% w/w) was achieved in relatively stable extruded Eudragit RS PO matrices under dry conditions. However, these systems were associated with limited drug release. This has given the way to explore the effect of addition of release modifiers (sucrose, methylcellulose, Xantural®75, Pluronic® F127, Gelucire 44/14) and hydration influence. Gelucire 44/14 containing formulations emerged as the most satisfactory systems which improved in vitro drug permeation profiles significantly by means of hydration. Intriguing structural changes upon hydration are believed to facilitate drug release as observed from the medicated and non-medicated formulations. These include consistency changes, softening of the extruded films and surface imperfections. Similar changes were detected in vivo using non-medicated Eudragit RS PO/Gelucire 44/14 carrier extruded systems after human skin occlusion. This employed strategy holds the promise for potential of a novel transdermal drug delivery activated by hydration.

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Activation of extracellular signal-regulated kinases 1 and 2 (ERK 1 and 2) is a key signalling event in the modulation of presynaptic function. This study looks at the upstream regulation of ERK 1 and 2 signalling in rat cerebrocortical synaptosomes. Kinase activation assays based on phospho-state specific antibodies revealed two major inputs for the activation of ERK 1 and 2: i) a neurotrophin-mediated signalling to ERK 1 and 2 which is dependent on the activation of small GTP-binding protein Ras and the presence of Ca ii) a Ca -dependent activation of ERK 1 and 2, stimulated by depolarisation or by the Ca ionophore ionomycin. Treatment of synaptosomes with Ca2+ chelators showed that basal ERK 1 and 2 activation was partly supported by Ca2+ from intracellular sources, whilst depolarisation-dependent activation of ERK 1 and 2 was entirely attributable to extracellular Ca influx. Like the BDNF-mediated activation, this Ca -dependent signalling to ERK was contingent on Ras, as evinced by the use of Ras inhibitor lovastatin. Using inhibitors of Ca /CaM-dependent protein kinase II (CaMKII) and phosphatidylinositol-3-kinase (PI3K), we next showed that both kinases are involved in mediating the Ca -dependent ERK 1&2 pathway. Furthermore, the Src family kinase (SFK) inhibitor, PP2, strongly reduced Ca -dependent ERK 1 and 2 activation, suggesting a role for non-receptor tyrosine kinases (nRTKs) in upstream signalling. Finally, using okadaic acid, roscovitine and baclofen respectively, we showed that the duration and efficacy of ERK 1 and 2 activation are determined by the function of protein phosphatase 2A (PP2A), cyclin- dependent kinase 5 (cdk5) and the presynaptic Gj/0-coupled GABAb receptors. Interestingly, our data demonstrate that baclofen-mediated inhibition of ERK 1&2 can be overridden by BDNF stimulation, revealing a potential feedback and cross-talk mechanism between the excitatory ERK and inhibitory GABA cascades. Together, these studies elucidate the role of ERK 1 and 2 as a hub for signalling in the nerve terminal.