The protein farnesyltransferase inhibitor Tipifarnib as a new lead for the development of drugs against Chagas disease

Abstract

Tipifarnib (R115777), an inhibitor of human protein farnesyltransferase (PFT), is shown to be a highly potent inhibitor of Trypanosoma cruzi growth (ED(50) = 4 nM). Surprisingly, this is due to the inhibition of cytochrome P450 sterol 14-demethylase (CYP51, EC 1.14.13.70). Homology models of the T. cruzi CYP51 were used for the prediction of the binding modes of the substrate lanosterol and of Tipifarnib, providing a basis for the design of derivatives with selectivity for TcCYP51 over human PFT.

Figure 1

Structures of Tipifarnib and Fluconazole

Figure 2

Inhibition of sterol biosynthesis in T. cruzi cells treated with Tipifarnib at the level of sterol 14-demethylase activity. T. cruzi epimastigotes were grown for 24 h with 100 ∝Ci of ³H-mevalonolactone which is incorporated into endogenous sterol production. Neutral lipids were extracted and separated by thin layer chromatography. Lane 1, T. cruzi grown without drug. Lane 2, T. cruzi grown with Tipifarnib. Lane 3, T. cruzi grown with ketoconazole (a known inhibitor of T. cruzi CYP51). *In addition to ergosterol, T. cruzi produces other C4, C14-demethylated sterols

Figure 3

The predicted binding mode of lanosterol (green) in TcCYP51 as compared to estriol in MtCYP51 (yellow; 1X8V; stereo figure). TcCYP51 sidechains located within 4.0 Å of lanosterol are depicted, residues mentioned in the text are labeled. The hydrogen bond between the lanosterol hydroxyl group and the backbone of Met358 is indicated (dashed line). Estriol forms a H-bond with Met433 of MtCYP51, which corresponds to Met460 of TcCYP51. (The helix between residue 284 and 301 was omitted to allow this view, as were the sidechains of the residues Ala291 and His294.)

Figure 4

The predicted binding mode of Tipifarnib (green) in TcCYP51 as compared to fluconazole (yellow; 1EA1; stereo). TcCYP51 sidechains located within 4.5 Å of Tipifarnib are depicted. The inhibitor forms hydrogen bonds with Met123 and, via a water molecule, with a heme propionate (water oxygen atoms are indicated as red spheres, H-bonds as dashed yellow lines). The 4 water molecules in the upper right indicate the location of the hydrophilic pocket being utilized for the design of Tipifarnib derivatives with specificity for CYP51 over PFT. Pro99 and Ile105 replace Gln72 and Phe78 of MtCYP51, respectively. Due to clashes with these two residues, MtCYP51 is predicted to have low affinity for Tipifarnib.