Discovery of novel antifungal agents targeting the synthesis of Glucosyl Ceramide

According to recent statistics, more than 300 million people are affected by serious fungal infections globally. Current drugs have a variety of drawbacks including drug-drug interactions, toxicity and narrow spectrum of activity. With the emergence of fungal infections resistant to current drugs, there is an urgent need for the development of new antifungal agents with novel mechanisms of action. In this context, fungal sphingolipids that are essential for their virulence in alkaline environment is a potential target for the development of new antifungal agents. Glucosyl Ceramide (GlcCer), is one such sphingolipid that can be potentially targeted.

Figure 1: Structure of fungal and mammalian GlcCer

Structurally, there is adequate differences between mammalian and fungal GlcCer, to specifically target fungal GlcCer (Figure 1). In an effort to identify compounds that inhibit the synthesis of fungal GlcCer, a library of compounds was purchased from ChmeBridge and tested against C. neoformans, that resulted in the identification of two hits (Figure 2).Figure 1: Structure of fungal and mammalian GlcCer

Figure 2: ChemBridge library screening, and structures BHBM and D0.

Both BHBM and D0 selectively inhibited the synthesis of fungal GlcCer (Cn) and not mammalian (J774) GlcCer (Figure 3), thus showing they are not cytotoxic.

Figure 3: Inhibition of synthesis of fungal GlcCer by BHBM and D0.

Based on these results, a new library of ~200 aromatic acylhydrazones were designed, and synthesized for SAR studies (Scheme 1).

Scheme 1: Synthesis of library of aromatic acylhydrazones.

Out of the 200 compounds, 42 compounds displayed MIC₈₀ £ 1 µg/mL against C. neoformans. Of the 42 active compounds, 20 of them are completely new and have never been reported before. Most of the newly synthesized compounds are fungicidal. One of the compounds P3G8, killed C. neoformans cells at a concentration as low as 0.25 µg/mL as fast as 24 hours (Figure 3). P3G8 was also not cytotoxic against mammalian cell lines.

Figure 3: In vitro killing activity of P3G8 against C. neoformans cells.

Currently in vivo studies on the lead compounds from the library that was synthesized, is being carried out. In a continued effort towards SAR, several heteroaromatic acyl hydrazones are being synthesized as well.