ABSTRACT
Protein farnesyltransferase (FTase) catalyzes an essential posttranslational lipid modification of more than 60 proteins involved in intracellular signal transduction networks. FTase inhibitors have emerged as a significant target for development of anticancer therapeutics and, more recently, for the treatment of parasitic diseases caused by protozoan pathogens, including malaria (Plasmodium falciparum). We present the X-ray crystallographic structures of complexes of mammalian FTase with five inhibitors based on an ethylenediamine scaffold, two of which exhibit over 1000-fold selective inhibition of P. falciparum FTase. These structures reveal the dominant determinants in both the inhibitor and enzyme that control binding and selectivity. Comparison to a homology model constructed for the P. falciparum FTase suggests opportunities for further improving selectivity of a new generation of antimalarial inhibitors.
Subject(s)
Antimalarials/chemistry , Antineoplastic Agents/chemistry , Enzyme Inhibitors/chemistry , Farnesyltranstransferase/antagonists & inhibitors , Farnesyltranstransferase/chemistry , Animals , Antimalarials/metabolism , Antineoplastic Agents/metabolism , Cell Line, Tumor , Crystallography, X-Ray , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/metabolism , Ethylenediamines/chemistry , Farnesyltranstransferase/metabolism , Humans , Plasmodium falciparum/enzymology , Protein Binding , Protein Conformation , Protozoan Proteins/antagonists & inhibitors , Protozoan Proteins/chemistry , Protozoan Proteins/metabolism , Rats , Structural Homology, Protein , Structure-Activity Relationship , Substrate SpecificityABSTRACT
Third world nations require immediate access to inexpensive therapeutics to counter the high mortality inflicted by malaria. Here, we report a new class of antimalarial protein farnesyltransferase (PFT) inhibitors, designed with specific emphasis on simple molecular architecture, to facilitate easy access to therapies based on this recently validated antimalarial target. This novel series of compounds represents the first Plasmodium falciparum selective PFT inhibitors reported (up to 145-fold selectivity), with lead inhibitors displaying excellent in vitro activity (IC(50) < 1 nM) and toxicity to cultured parasites at low concentrations (ED(50) < 100 nM). Initial studies of absorption, metabolism, and oral bioavailability are reported.
Subject(s)
Aniline Compounds/chemical synthesis , Antimalarials/chemical synthesis , Farnesyltranstransferase/antagonists & inhibitors , Imidazoles/chemical synthesis , Plasmodium falciparum/drug effects , Plasmodium falciparum/enzymology , Administration, Oral , Aniline Compounds/chemistry , Aniline Compounds/pharmacology , Animals , Antimalarials/chemistry , Antimalarials/pharmacology , Binding Sites , Biological Availability , Caco-2 Cells , Cell Membrane Permeability , Humans , Imidazoles/chemistry , Imidazoles/pharmacology , In Vitro Techniques , Male , Mice , Microsomes, Liver/metabolism , Models, Molecular , Nitriles/chemical synthesis , Nitriles/chemistry , Nitriles/pharmacology , Rats , Structure-Activity Relationship , Sulfonamides/chemical synthesis , Sulfonamides/chemistry , Sulfonamides/pharmacologyABSTRACT
A series of compounds based on the carboxyl-terminal CAAL sequence of PGGTase-I substrates was designed and synthesized. Using piperazin-2-one as a semi-rigid scaffold, we have introduced critical pharmacophores in a well-defined arrangement to mimic the CAAL sequence. High potency and exceptional selectivity were obtained for inhibition of PGGTase-I with structures such as 45 and 70. Potency of this series of GGTIs was dependent on the presence of an L-leucine residue with a free carboxyl terminus, as well as an S configuration of the 3-aryl group. The selectivity was significantly enhanced by 5-methyl substitution on the imidazole ring and fluorine substitution on the 3-aryl group. Modification of the 6-position of the piperazinone scaffold was found to be unfavorable. Compounds 44 and 69, the corresponding methyl esters of 45 and 70, were found to selectively block processing of Rap1A by PGGTase-I in whole cells with IC(50) values of 0.4 microM and 0.7 microM respectively.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Enzyme Inhibitors/chemical synthesis , Piperazines/chemical synthesis , Amino Acid Sequence , Animals , Enzyme Inhibitors/pharmacology , Humans , Ketones/chemical synthesis , Ketones/pharmacology , Molecular Mimicry , Piperazines/pharmacology , Structure-Activity RelationshipABSTRACT
A series of imidazole-containing peptidomimetic PFTase inhibitors and their co-crystal structures bound to PFTase and FPP are reported. The structures reveal that the peptidomimetics adopt a similar conformation to that of the extended CVIM tetrapeptide, with the imidazole group coordinating to the catalytic zinc ion. Both mono- and bis-imidazole-containing derivatives, 13 and 16, showed remarkably high enzyme inhibition activity against PFTase in vitro with IC50 values of 0.86 and 1.7 nM, respectively. The peptidomimetics were also highly selective for PFTase over PGGTase-I both in vitro and in intact cells. In addition, peptidomimetics and were found to suppress tumor growth in nude mouse xenograft models with no gross toxicity at a daily dose of 25 mg kg(-1).
