S DORSAZ¹, Q FAVRE-GODAL², E FERREIRA QUEIROZ², K GINDRO³, H RIEZMAN⁴, J-L WOLFENDER², D SANGLARD<sup>1

1</sup>Institute of Microbiology, University Hospital of Lausanne, Lausanne, Switzerland, ²School of pharmaceutical sciences, University of Geneva, University of Lausanne, Switzerland, ³Swiss Federal Research Station, Agroscope Changins Wädenswil ACW, Switzerland, ⁴Department of Biochemistry, University of Geneva, Switzerland

Candida infections is a major cause of fungal diseases in humans and their increasing resistance against available drugs is of major concern. There is an urgent need for the development of new antifungals and plant natural products may represent a potential reservoir for new discoveries.

We initiated a small scale screening of a library of natural compounds (NPs) extracted from plants(1). We submitted the selected compounds to diverse in vitro profiling experiments including antimicrobial susceptibility test (MIC), activity spectrum against different Candida and bacterial species as well as toxicity assays with mammalian HeLa cells. Over 240 compounds that were screened so far, 41 exhibited in vitro activities against C. albicans (MIC50 ≤ 32 µg/ml). Among these NPs, we identified one promising substance, the sterol alkaloid tomatidine from Solanum lycopersicum (tomato). It showed high activity against Candida spp. such as Candida albicans (MIC50 = 1 µg/ml) and the azole-resistant Candida krusei (MIC50 = 0.5 µg/ml), but no activity on E. coli species (MIC50 > 100 µg/ml) and low toxicity against mammalian cell culture (lethal dose 50 (LD50) > 100 µg/ml).

It has been earlier reported than tomatidine has an antifungal activity against Saccharomyces cerevisiae in vitro and it may interfere with the ergosterol biosynthetic pathway (2). Sterol profile analysis of tomatidine-treated Candida cells showed that two enzymes involved in ergosterol synthesis, ERG6 (24-C methyl transferase) and ERG4, were inhibited.

RNA-seq analysis of cell treated with tomatidine revealed that the drug induced several ERG genes, ERG6 being the most upregulated gene (9.5 times). Several other genes were upregulated, especially those belonging to the TAC1 regulon.

In vivo efficacy of the drug is under investigation in two different Candida infection models, the mini host wax moth Galleria mellonella model and the murine systemic infection model.

(1) Favre-Godal, Q., Dorsaz, S, et al. (2014). Phytochemistry 105: 68-78.

(2) Simmons, V, et al (2006). AAC. 50 :2732.