Queensland Natural Products
The Nature Bank at Eskitis Institute, Queensland, Australia, represents a truly unique chemical resource with unparalleled geographic and taxonomic diversity that has never before been screened against targets relevant to malaria. State of- the-art platform technology has opened the door for new approaches to identify new drugs by probing the biology of cells, subsequent identification of new targets, and discovery of previously unknown modes of action.
There is a continuing need for new lead compounds to feed the drug development pipeline in the search for new and effective drugs to fight malaria. This project combines the chemical diversity and biological relevance of natural products with the power of high content screening (HCS) to image cells, and will expedite the search for biologically-active compounds that will form the basis for the next generation of antimalarials.
The project utilizes Australian-based expertise in malaria biology and drug discovery to provide naturally-occurring compounds with potent and selective activity against malaria parasites and well-characterized physicochemical properties optimized for drug development.
The Eskitis Institute’s Nature Bank in Queensland is a screening set derived from a collection of plants and marine invertebrates from diverse areas in Australia (Queensland), China, Papua New Guinea and Tasmania. The collection includes representatives of 60 per cent of global plant families; and 9,500 marine invertebrates, including 10 per cent of the world’s sponges and ascidians (commonly known as sea squirts).
The screening set has been developed using proprietary technology to enrich extracts in lead-like and drug-like components prior to pre-fractionation. 18,453 extracts of plants and marine invertebrates have been pre-fractionated via a proprietary two-stage process to produce 202,983 individual fractions, each of which contain up to four compounds.
The resulting Lead- Like Peak (LLP) library of natural product fractions increases the concentration of drug- and leadlike molecules and thus the chances of detecting a ‘hit’. Using this method increases the likelihood of detecting a biologically-active compound compared with screening a complex natural product extract, thus maximizing the possibility of a successful screening outcome.
The Nature Bank therefore represents a unique chemical resource with unparalleled geographic and taxonomic diversity that has never before been screened against targets relevant to malaria.
The original proposal envisaged undertaking high throughput screening (HTS) of the Nature Bank, utilizing the 3Hhypoxanthine assay as the primary screening campaign. Although this HTS assay is widely used and reliable, it is expensive, complex, and generates radioactive waste. This and other automation issues led the project team to investigate alternative options for screening assays against whole parasites.
An HCS platform based on automated imaging and analysis of live cells was chosen, and the first high throughput whole cell antimalarial HCS assay developed. In addition, haemolysis artefact and mammalian cytotoxicity assays were established.
The HCS assay has significant advantages over the 3H-hypoxanthine assay as it is non-radioactive, requires less automation and is more cost–effective, while providing more information-rich data.
The primary screening of 121,800 fractions against both parasite strains (3D7 and Dd2) was completed during 2007. Active fractions have been screened against a panel of four mammalian cell lines to identify fractions which are selective against the parasites.
The remaining fractions will be screened in 2008 and all hit fractions will undergo Mass Spectometry directed isolation to identify their active components.
The exploratory approach illustrated the potential power of HCS technology in efficiently identifying fractions from the Nature Bank that exhibit antimalarial properties. This state-of-the-art platform technology has opened the door for new approaches to identify new drugs by probing the biology of cells, subsequent identification of new targets, and discovery of previously unknown modes of action.
The project team
The project has built on the specialized natural product screening and isolation skills in the laboratories of Professors Ronald J Quinn and Vicky M Avery (Eskitis Institute), and has put in place a team that can develop drug candidates. It is expected that during 2008, identified leads will be ready for preliminary in vitro studies at the Queensland Institute for Medical Research (QIMR) in Brisbane (Dr. Katherine T Andrews, Professor Michael Good), and the most promising will be investigated in wellestablished animal models at the Australian Army Medical Institute ( AMI ) to assess potency (Professor Dennis Shanks, Dr. Mike Edstein). In-depth understanding of the metabolism and pharmacokinetic properties will be provided by the Centre for Drug Candidate Optimisation (CDCO) at Monash University in Melbourne (Professor Bill Charman). The information will be used to allow the team to select compounds for lead optimization and drug development.