Quinoline derivative MC1626, a putative GCN5 histone acetyltransferase (HAT) inhibitor, exhibits HAT-independent activity against Toxoplasma gondii

Abstract

We report that quinoline derivative MC1626, first described as an inhibitor of the histone acetyltransferase (HAT) GCN5, is active against the protozoan parasite Toxoplasma gondii in vitro. However, MC1626 does not inhibit Toxoplasma GCN5 HATs or reduce HAT-mediated activity; rather, this quinoline may target the plastid organelle called the apicoplast.

FIG. 1.

Effects of MC1626 on HAT activities. HAT assays were performed with recombinant TgGCN5-A (A) or TgGCN5-B (B) in the presence of increasing concentrations of MC1626 or a DMSO vehicle control (DC). (C) HAT assays with 0.5 μg of tachyzoite lysate as the enzyme source in the presence of increasing concentrations of MC1626. (D) Histone acetylation levels in lysates of parasites treated with MC1626. Tachyzoites were incubated in the presence of various concentrations of MC1626 or with DMSO for 3 days. After treatment, lysates were made to assess by Western blotting if acetylation of H3 or H4 was diminished relative to that of the untreated or vehicle-treated control. Tubulin (TUB) was used as a loading control. Note that the final two lanes are overloaded, which likely explains the apparent increase in histone acetylation seen in these samples. (E) MC1626 does not inhibit recombinant yeast GCN5 in vitro. Recombinant S. cerevisiae GCN5 (1.0 μg) was used as the enzyme source in HAT assays containing no drug or designated concentrations of MC1626. (F) Control experiment demonstrating that S. cerevisiae GCN5 (1.0 μg) is inhibited by anacardic acid (AA). AcH3 and AcH4, acetylated H3 and H4, respectively.

FIG. 2.

Effects of quinolines on the parasite apicoplast organelle. Toxoplasma tachyzoites were cultured in the presence of DMSO (control), 200 μM MC1626, or 200 μM quinoline prior to processing for DAPI staining. DAPI stains DNA, including the extrachromosomal DNA of the apicoplast. An example apicoplast is indicated by the arrow as a distinct dot anterior to the parasite nucleus.