TOWARDS HIGH-EFFICIENCY ANTI-NEURODEGENERATIVE TREATMENTS EXPLOITING INHIBITORS DESIGNED FROM TRANSITION-STATE ANALOGUES DEFINED BY ISOTOPIC TECHNIQUES – ISOMODTS

1-Scientific background & objectives: The efficient exploitation of numerous medicaments is strongly dependent on their overall comportment within the human biosystem, described by their pharmacokinetic ADME (Absorption, Distribution, Metabolism, Excretion). Over the past few decades, the importance of understanding the metabolism of biologically active compounds in vivo in order to design improved therapeutic agents has become increasingly recognised. Degradative metabolism not only imposes higher dosages, but also leads to numerous metabolites, which may either interfere with the target receptors for the active agent or themselves have undesirable alternative effects. New drugs offering increased stability & resistance to metabolism are highly desirable to improve therapy through better targeting, decreased non-specific effects and, consequently, lower drug dosage. Within the biological context, transformation frequently involves Phase I reactions that modify the functionality of the molecule through oxidation, reduction, cleavage of small units, or ring opening following hydroxylation. The majority of these processes are catalysed by enzymes of the cytochrome P450 (CYP) mono-oxygenase class. Such transformations can not only destroy the active principle, they can also lead to metabolites having adverse side effects. It has been well demonstrated that overcoming such undesirable responses is facilitated by an understanding of the molecular mechanism(s) involved in their degradation. This knowledge leads directly to two approaches to improve the bioavailability of a given drug. Either the bio-active compound can be modified to reduce its degradation or it can be co-administered with an inhibitor of the enzymes responsible for in vivo de-activation. Rising human life expectancy is associated with an increasing occurrence of age-related diseases. New treatments for neurotoxic & neurodegenerative disorders have been developed but the drug's efficiency is often limited due to poor bio-disposition. This is commonly due to rapid metabolism & elimination by mechanisms as described above. Their pharmacological parameters may be optimized by increasing drug lifetime. Our objective is to develop better treatments for neurotoxic & neurodegenerative disorders by enhancing drug lifetime through preventing degradation. The approach adopted is novel but is based on sound & tested principles. 2-Description of the project & methodology: The project will involve the molecular design of analogues of transition-state structures within the reaction mechanism of the enzymes that degrade the target therapeutic agents. It opens the way to the synthesis of blockers of degradation that will give enhanced stability to therapeutic agents. This is achieved by a multi-disciplinary project to understand in detail the reaction mechanisms of degradation within an ambitious research plan that combines synthesis, biochemical experiments, & theoretical chemical methods for the analysis & the explanation of metabolism in human tissue in vivo & in vitro. Access to transition state structures is through the proven approach of determining kinetic isotope effects in vivo & using these to interpret the reaction mechanisms of degradation in silico. It requires the synthesis of target compounds site-specifically isotopically-labelled. It requires the determination of the kinetic isotope effects for their degradation. It requires molecular modelling to define the reaction centre & to parameterize the small-molecule-ligand geometries. It requires the calculation by QM/MM methods of the reaction parameters & the energetics of reaction pathways that match the experimental isotopic data. Finally, it will require the development of synthetic approaches to make the stable compounds that are analogues of the identified transition states. 3-Expected results: The project will lead to the description of molecular mechanisms that degrade alkaloid-based drugs active in the important areas of the fight against tobacco addiction, progressive toxicity & neurodegenerative diseases. The knowledge obtained will make possible the molecular design & synthesis of potential TS-analogue inhibitors of the degradation process(es) that eliminate beneficial drugs. It will provide knowledge valuable in assisting with the molecular design & synthesis of more stable analogues of bio-active compounds for this fight. This work will generate & preliminary metabolic & toxicological data for new active compounds. Such compounds can be directly patented as new chemical entities. The value of biochemical data available to the biochemical testing platform will be amplified, thus improving biological targeting & their dossiers as potent drugs. Furthermore, the exploitation of results can be done through collaborative studies or licence agreements with industrial partners.