A small molecule inhibitor of fungal histone acetyltransferase Rtt109

Abstract

The histone acetyltransferase Rtt109 is the sole enzyme responsible for acetylation of histone H3 lysine 56 (H3K56) in fungal organisms. Loss of Rtt109 renders fungal cells extremely sensitive to genotoxic agents, and prevents pathogenesis in several clinically important species. Here, via a high throughput chemical screen of >300,000 compounds, we discovered a chemical inhibitor of Rtt109 that does not inhibit other acetyltransferase enzymes. This compound inhibits Rtt109 regardless of which histone chaperone cofactor protein (Asf1 or Vps75) is present, and appears to inhibit Rtt109 via a tight-binding, uncompetitive mechanism.

Pneumocystis jirovecii Rtt109, a Novel Drug Target for Pneumocystis Pneumonia in Immunosuppressed Humans

“…Interestingly, the recently reported specific Rtt109 inhibitor compound 1 did not exhibit any suppression of Pneumocystis viability. Similar findings were noted when this compound was tested previously against C. albicans (43). There are several possible reasons for our observations, including possibly poor penetration of compound 1 into the fungal cytoplasm, the presence of active rapid export proteins that may limit internal accumulation of this agent, or compound instability under the testing conditions.…”

“…Pentamidine and ampicillin served as positive-and negative-control compounds, respectively. The lack of observed activity for compound 1 is consistent with its lack of activity against C. albicans in vivo (43). However, the activity of the reported HAT inhibitor garcinol to suppress Pneumocystis viability does support the further investigation of this class of agents, as well as novel small molecules with more drug-like characteristics, potency, and target specificity, as potential antifungal antimicrobials with activity against Pneumocystis species.…”

“…6A and B). Compound 1 has been recently reported as a low-nanomolar inhibitor of yeast Rtt109 in vitro and does not inhibit the HATs p300 and GCN5 in vitro (43). Like garcinol, compound 1 showed dosedependent inhibition of PjRtt109 HAT activity in vitro (IC 50 , 4.3 Ϯ 3.9 M) (Fig.…”

“…Garcinol, a natural product with reported anti-HAT activity in vitro, was purchased as a solid powder (Enzo Life Sciences) and was used without further purification. Compound 1 (PubChem compound identification 4785700), which has recently been reported to have selective activity against yeast Rtt109 in vitro, was also obtained commercially as a solid powder (Enamine) and was used after standard reverse-phase high-performance liquid chromatography (RP-HPLC) purification (43). All solids showed greater than 98% purity in ultra-performance liquid chromatography/mass spectrometry (UPLC/ MS) analyses, and their 1 H and 13 C NMR spectra were consistent with their reported chemical structures.…”

“…Additional evidence indicates that deletion of rtt109 in the opportunistic fungal pathogen Candida albicans reduces fungal infection burdens in mouse models (40,41). On this basis, we postulate that specific inhibitors of fungal Rtt109-catalyzed histone acetylation may be useful as novel antifungal agents, with minimal mammalian toxicities, and may have activity against recalcitrant organisms such as P. jirovecii (42,43). Pneumocystis is challenging to treat with standard antifun-gals, and the use of the available agents can be limited by drugrelated toxicities.…”