Structure-function studies of kinetoplastid myristoylCoA : protein N-myristoyltransferase and two substrates, the 'Leishmania' vaccine antigen candidates, HASPA and HASPB

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Naturally occurring, tumor-specific, therapeutic proteins

The emerging approach to cancer treatment known as targeted therapies offers hope in improving the treatment of therapy-resistant cancers. Recent understanding of the molecular pathogenesis of cancer has led to the development of targeted novel drugs such as monoclonal antibodies, small molecule inhibitors, mimetics, antisense and small interference RNA-based strategies, among others. These compounds act on specific targets that are believed to contribute to the development and progression of cancers and resistance of tumors to conventional therapies. Delivered individually or combined with chemo‐ and/or radiotherapy, such novel drugs have produced significant responses in certain types of cancer. Among the most successful novel compounds are those which target tyrosine kinases (imatinib, trastuzumab, sinutinib, cetuximab). However, these compounds can cause severe side-effects as they inhibit pathways such as epidermal growth factor receptor (EGFR) or platelet-derived growth factor receptor, which are also important for normal functions in non-transformed cells. Recently, a number of proteins have been identified which show a remarkable tumor-specific cytotoxic activity. This toxicity is independent of tumor type or specific genetic changes such as p53, pRB or EGFR aberrations. These tumor-specific killer proteins are either derived from common human and animal viruses such as E1A, E4ORF4 and VP3 (apoptin) or of cellular origin, such as TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) and MDA-7 (melanoma differentiation associated-7). This review aims to present a current overview of a selection of these proteins with preferential toxicity among cancer cells and will provide an insight into the possible mechanism of action, tumor specificity and their potential as novel tumor-specific cancer therapeutics. </jats:p

Characterization and selective inhibition of myristoyl-CoA:protein N-myristoyltransferase from Trypanosoma brucei and Leishmania major

The eukaryotic enzyme NMT (myristoyl-CoA:protein N-myristoyltransferase) has been characterized in a range of species from Saccharomyces cerevisiae to Homo sapiens. NMT is essential for viability in a number of human pathogens, including the fungi Candida albicans and Cryptococcus neoformans, and the parasitic protozoa Leishmania major and Trypanosoma brucei. We have purified the Leishmania and T. brucei NMTs as active recombinant proteins and carried out kinetic analyses with their essential fatty acid donor, myristoyl-CoA and specific peptide substrates. A number of inhibitory compounds that target NMT in fungal species have been tested against the parasite enzymes in vitro and against live parasites in vivo. Two of these compounds inhibit TbNMT with IC(50) values of <1 μM and are also active against mammalian parasite stages, with ED(50) (the effective dose that allows 50% cell growth) values of 16–66 μM and low toxicity to murine macrophages. These results suggest that targeting NMT could be a valid approach for the development of chemotherapeutic agents against infectious diseases including African sleeping sickness and Nagana