Apicidin: a novel antiprotozoal agent that inhibits parasite histone deacetylase

Abstract

A novel fungal metabolite, apicidin [cyclo(N-O-methyl-L-tryptophanyl-L -isoleucinyl-D-pipecolinyl-L-2-amino-8-oxodecanoyl)], that exhibits potent, broad spectrum antiprotozoal activity in vitro against Apicomplexan parasites has been identified. It is also orally and parenterally active in vivo against Plasmodium berghei malaria in mice. Many Apicomplexan parasites cause serious, life-threatening human and animal diseases, such as malaria, cryptosporidiosis, toxoplasmosis, and coccidiosis, and new therapeutic agents are urgently needed. Apicidin's antiparasitic activity appears to be due to low nanomolar inhibition of Apicomplexan histone deacetylase (HDA), which induces hyperacetylation of histones in treated parasites. The acetylation-deacetylation of histones is a thought to play a central role in transcriptional control in eukaryotic cells. Other known HDA inhibitors were also evaluated and found to possess antiparasitic activity, suggesting that HDA is an attractive target for the development of novel antiparasitic agents.

Figure 1

(A and B) The structures of apicidin and trichostatin (A), and structurally related tetrapeptides (B). Pip, Pipecolic acid; Aib, aminoisobutyric acid.

Figure 2

Evaluation of apicidin and HC-toxin against acute P. berghei malaria. BALB/C mice were injected i.p. with 10⁶ P. berghei-infected erythrocytes and then treated twice a day for 3 days with HC-toxin or apicidin at various doses starting at 2 hr p.i. Results are expressed as the percent of parasitized erythrocytes at 6 days p.i. (A) Parenteral (i.p.) treatment with HC-toxin (50 mg/kg), apicidin, or chloroquine (10 mg/kg). (B) Oral treatment with apicidin. Error bars represent SEM. Each group consisted of five mice.

Figure 3

The effect of apicidin and other compounds on histone acetylation in P. falciparum. Treatment of P. falciparum-parasitized erythrocytes with vehicle only, control: 1.6–400 ng/ml apicidin (A), or vehicle only, control; 100 ng/ml of apicidin, HC-toxin, or trichostatin, or 500 ng/ml β-hydroxy-HC-toxin or chloroquine (B). Histones were extracted from parasites and visualized by AUT gel electrophoresis and autoradiography. Labeled species on the AUT gels are identified as histones as (i) they comigrate with HeLa cell histones on SDS/polyacrylamide gels, (ii) they bind antisera raised against acetylated histones (28) (a generous gift from B. Turner, University of Birmingham Medical School, Birmingham, AL), (iii) [¹⁴C]acetate incorporation increases as a result of treatment with diverse inhibitors of HDA, and (iv) acetylated histone species show slower rates of migration than nonacetylated histones (28). Uninfected erythrocytes processed under similar conditions did not show any labeled bands on AUT gels (data not shown).