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Bioprospecting in Cyanobacteria: Discovery of Novel Antifungals Through High-Throughput Yeast Halo Assays

Applicant Gademann Karl
Number 124716
Funding scheme Interdisciplinary projects
Research institution Organische Chemie Departement Chemie Universität Basel
Institution of higher education University of Basel - BS
Main discipline Organic Chemistry
Start/End 01.07.2009 - 30.06.2010
Approved amount 103'150.00
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Keywords (10)

antifungals; high throughput compound screen; target of rapamycin; kinase inhibitor; natural products; cyanobacteria; medicine; chemistry; biology; yeast

Lay Summary (English)

Lead
Lay summary
Natural products have been a rich source of novel bioactive agents in the past, and the availability of improved and sophisticated assays increases the chance of successfully finding potent compounds. We are screening extracts from cyanobacteria for antifungal activity in high-throughput assays, which will result in new chemical structures potentially useful in the clinic.Natural products have been used since decades as successful compounds for a variety of applications regarding human health. In medicine, powerful antibiotics or anticancer agents have improved the quality of life and longevity of humans, and our society would certainly look different today without these chemical compounds. Over the last decades, resistance to commonly used antibiotics has increased and reports of multi-resistant microorganisms are wide spread in the public media. At the same time, the rate of newly introduced antibiotic agents dropped significantly. This holds also true for fungal infections, which are a significant threat in hospitals in Switzerland.In collaboration with the group of Prof. Dr. Robbie Loewith at the University of Geneva, who is the co-applicant of this project, we will screen extracts from blue-green algae, so called cyanobacteria, for their antifungal properties. This is based on a newly developed high-throughput assay that allows for rapid identification of antifungal fractions. In addition, yeast allows for easy genetic modification which can allow for facile target identification.Cyanobacteria are a relatively unexplored resource of novel compounds, and bioprospecting this resource using sophisticated assays is an powerful strategy for the identification of potent antifungal compounds. In addition, as target identification can be carried out in yeast, compounds that can modulate certain pathways in yeast can be obtained, and new chemotypes for certain pathways might be obtained. Successful compounds that have been isolated will then be further evaluated with the pharmaceutical industry in Switzerland and might thus one day be used in the clinic to aid humans.
Direct link to Lay Summary Last update: 21.02.2013

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Abstract

Resistance to clinically used antimicrobials is rising at an alarming pace. Fungal infections caused by opportunistic pathogens are a serious threat to patients in hospitals. In particular, infections in immunocompromised patients are the main concern, and treatment with known antifungals such as amphotericin leads to serious side effects. Contrasting to this clinical evidence, several pharmaceutical companies have stopped their anti-infective research programs. The search for new antifungal agents through innovative strategies in an academic setting is thus warranted.In this project, we propose to screen natural products isolated from cyanobacteria in high-throughput yeast halo assays to identify new antifungal agents.The natural products library is based on two sources: the cyanobacteria culture collection at EPFL and derivatives of antifungal agents generated through precursor-directed biosynthesis. The culture collection consists of over 250 strains of cyanobacteria isolated from all over the world, the former EAWAG collection as well as strains collected by EPFL researchers in Switzerland. Extracts of these strains were microfractionated into 96-well plates that form the majority of the natural product library. The second part is consisting of derivatives of the fischerindole class of cyanobacterial natural products. These derivatives will be generated through precursor directed biosynthesis from simple precursors through feeding experiments. As the chemodiversity of the producing Fischerella and Hapalosiphon species is rather large (up to 20 members of this natural product class are observed), precursor directed biosynthesis will thus enable the generation of dozens of derivatives in a couple of feeding experiments. The compounds will then be screened in a high-throughout yeast halo assay.The yeast halo assay itself is robust and technically very simple - critically important parameters for a successful high-throughput assay. Specifically, sub-microliter aliquots of compounds are robotically transferred to a lawn of yeast. After a short incubation period, antifungal activities are identified by the ‘halo’ they create in the background of growing cells. Importantly, this assay can be very easily adapted to identify specific inhibitors of many, if not all, essential activities in yeast. Such a universal screen will greatly accelerate drug discovery.Successful hits will then be validated, and the resulting compounds characterized both on a chemical level (to elucidate the structure) and on a biological level (to profile the antifungal activity). Successful hits emerging out of this project have the potential to be transformed into leads for novel antifungals or anticancer agents. In addition to the clinical promise, these compounds will be exceptional tools for chemical genetic, cell biology, molecular biology and biochemical studies.In summary, the proposed project combines the complementary knowledge of two leading junior research groups in Switzerland to provide novel molecular strategies addressing clinical challenges in our society.
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