Investigation of the role of pharmacokinetics and the development of novel anti-obesity agents

Abstract

Oxyntomodulin is a gut hormone that promotes satiety by exhibiting an anorectic effect through the action at the GLP-1 receptor while at the same time it has been suggested that it is able to increase energy expenditure through the glucagon receptor, albeit with a less potency than native peptides. This dual mode of action makes it an ideal candidate for an anti-obesity medication. However, oxyntomodulin possesses an inadequate pharmacokinetic profile with a very short half-life and duration of action. These observations promoted the idea that oxyntomodulin could be used as the starting point for developing an anti-obesity drug agent through modifications of its primary amino acid structure. The exact knowledge of the pharmacokinetic properties of peptides (half-life, metabolic clearance rate, volume of distribution) is crucial in drug development as it allows investigating the effect of amino acid changes in the presence of the peptide in the plasma and correlates this with the exerted biological effect. The first aim of this thesis was to develop a reliable in vivo animal model that could be used to measure the pharmacokinetic properties of anti-obesity drug candidates based on oxyntomodulin. Results have shown that the proposed model is robust enough to be used for this scope. The second aim was to develop an analogue, based on oxyntomodulin, with a higher anorectic effect and a prolonged duration of action with the aim of developing an anti-obesity medication that could be used as a therapeutic agent in humans given once-weekly. Point substitutions in the primary amino acid structure of oxyntomodulin (positions 16, 23, 24, 29 and 30) were done in order to enhance the anorectic effect of oxyntomodulin and 26 analogues were developed and tested in order to investigate the effect of these substitutions. The pharmacokinetic properties of these analogues were measured with the help of the in vivo animal model. Other substitutions in the C terminal of the analogues were made in order to allow the formation of a subcutaneous depot when given in a zinc-containing slow-release formulation with the aim to prolong the presence of the peptide in the circulation. Data presented in this thesis have identified OXM analogue X26 presents a 8.3– and 45-fold higher potency at the GLP-1R and GCGR respectively when compared to native OXM. When administered in a zinc containing formula, X26 is present in the circulation 7 days post-injection. Furthermore, it has demonstrated a significantly longer half-life than OXM (21.3 vs. 12 min). Its ability to inhibit food intake and reduce body weight has been shown in rodent species; mice and rats. Analogue X26 is a novel and valuable pharmaceutical approach for the treatment of obesity.