Second generation tetrahydroquinoline-based protein farnesyltransferase inhibitors as antimalarials.
ABSTRACT: Substituted tetrahydroquinolines (THQs) have been previously identified as inhibitors of mammalian protein farnesyltransferase (PFT). Previously we showed that blocking PFT in the malaria parasite led to cell death and that THQ-based inhibitors are the most potent among several structural classes of PFT inhibitors (PFTIs). We have prepared 266 THQ-based PFTIs and discovered several compounds that inhibit the malarial enzyme in the sub- to low-nanomolar range and that block the growth of the parasite (P. falciparum) in the low-nanomolar range. This body of structure-activity data can be rationalized in most cases by consideration of the X-ray structure of one of the THQs bound to mammalian PFT together with a homology structural model of the malarial enzyme. The results of this study provide the basis for selection of antimalarial PFTIs for further evaluation in preclinical drug discovery assays.
Project description:New antimalarials are urgently needed. We have shown that tetrahydroquinoline (THQ) protein farnesyltransferase (PFT) inhibitors (PFTIs) are effective against the Plasmodium falciparum PFT and are effective at killing P. falciparum in vitro. Previously described THQ PFTIs had limitations of poor oral bioavailability and rapid clearance from the circulation of rodents. In this paper, we validate both the Caco-2 cell permeability model for predicting THQ intestinal absorption and the in vitro liver microsome model for predicting THQ clearance in vivo. Incremental improvements in efficacy, oral absorption, and clearance rate were monitored by in vitro tests; and these tests were followed up with in vivo absorption, distribution, metabolism, and excretion studies. One compound, PB-93, achieved cure when it was given orally to P. berghei-infected rats every 8 h for a total of 72 h. However, PB-93 was rapidly cleared, and dosing every 12 h failed to cure the rats. Thus, the in vivo results corroborate the in vitro pharmacodynamics and demonstrate that 72 h of continuous high-level exposure to PFTIs is necessary to kill plasmodia. The metabolism of PB-93 was demonstrated by a novel technique that relied on double labeling with a radiolabel and heavy isotopes combined with radiometric liquid chromatography and mass spectrometry. The major liver microsome metabolite of PB-93 has the PFT Zn-binding N-methyl-imidazole removed; this metabolite is inactive in blocking PFT function. By solving the X-ray crystal structure of PB-93 bound to rat PFT, a model of PB-93 bound to malarial PFT was constructed. This model suggests areas of the THQ PFTIs that can be modified to retain efficacy and protect the Zn-binding N-methyl-imidazole from dealkylation.
Project description:A new synthetic protocol provides a simple and direct method to generate functionalized ?-hydroxy-tetrahydroquinolines (THQs). Hydroboration of quinolines using chloroboranes followed by oxidation with NaBO3 ?H2 O led to the formation of functionalized ?-hydroxy THQs. High regio- and diastereoselectivities were observed in ? and ? substituted quinolines and the trans diastereomer of the ?-hydroxy-THQ was the major isostere. This new protocol was utilized to build the novel antibody-targeted lupus peptidomimetic, FISLE-412.
Project description:The post-translational farnesylation of proteins serves to anchor a subset of intracellular proteins to membranes in eukaryotic organisms and also promotes protein-protein interactions. This enzymatic reaction is carried out by protein farnesyltransferase (PFT), which catalyzes the transfer of a 15-carbon isoprenoid lipid unit, a farnesyl group, from farnesyl pyrophosphate to the C-termini of proteins containing a CaaX motif. Inhibition of PFT is lethal to the pathogenic protozoa Plasmodium falciparum. Previously, we have shown that parasites resistant to a tetrahydroquinoline (THQ)-based PFT inhibitor BMS-388891 have mutations leading to amino acid substitutions in PFT that map to the peptide substrate binding domain. We now report the selection of parasites resistant to another THQ PFT inhibitor BMS-339941. In whole cell assays sensitivity to BMS-339941 was reduced by 33-fold in a resistant clone, and biochemical analysis demonstrated a corresponding 33-fold increase in the BMS-339941 K(i) for the mutant PFT enzyme. More detailed kinetic analysis revealed that the mutant enzyme required higher concentration of peptide and farnesyl pyrophosphate substrates for optimum catalysis. Unlike previously characterized parasites resistant to BMS-388891, the resistant parasites have a mutation which is predicted to be in a distinct location of the enzymatic pocket, near the farnesyl pyrophosphate binding pocket. This is the first description of a mutation from any species affecting the farnesyl pyrophosphate binding pocket with reduced efficacy of PFT inhibitors. These data provide further support that PFT is the target of THQ inhibitors in P. falciparum and suggest that PFT inhibitors should be combined with other antimalarial agents to minimize the development of resistant parasites.
Project description:A 2328-membered library of 2,3,4-trisubstituted tetrahydroquinolines was produced using a combination of solution- and solid-phase synthesis techniques. A tetrahydroquinoline (THQ) scaffold was prepared via an asymmetric Povarov reaction using cooperative catalysis to generate three contiguous stereogenic centers. A matrix of 4 stereoisomers of the THQ scaffold was prepared to enable the development of stereo/structure-activity relationships (SSAR) upon biological testing. A sparse matrix design strategy was employed to select library members to be synthesized with the goal of generating a diverse collection of tetrahydroquinolines with physicochemical properties suitable for downstream discovery.
Project description:New chemotherapeutics are urgently needed to combat malaria. We previously reported on a novel series of antimalarial, ethylenediamine-based inhibitors of protein farnesyltransferase (PFT). In the current study, we designed and synthesized a series of second generation inhibitors, wherein the core ethylenediamine scaffold was varied in order to examine both the homology model of Plasmodium falciparum PFT (PfPFT) and our predicted inhibitor binding mode. We identified several PfPFT inhibitors (PfPFTIs) that are selective for PfPFT versus the mammalian isoform of the enzyme (up to 136-fold selectivity), that inhibit the malarial enzyme with IC50 values down to 1 nM, and that block the growth of P. falciparum in infected whole cells (erythrocytes) with ED50 values down to 55 nM. The structure-activity data for these second generation, ethylenediamine-inspired PFT inhibitors were rationalized by consideration of the X-ray crystal structure of mammalian PFT and the homology model of the malarial enzyme.
Project description:A series of 44 hybrid compounds that included in their structure tetrahydroquinoline (THQ) and isoxazole/isoxazoline moieties were synthesized through the 1,3-dipolar cycloaddition reaction (1,3-DC) from the corresponding N-allyl/propargyl THQs, previously obtained via cationic Povarov reaction. In vitro cholinergic enzymes inhibition potential of all compounds was tested. Enzyme inhibition assays showed that some hybrids exhibited significant potency to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Especially, the hybrid compound 5n presented the more effective inhibition against AChE (4.24 µM) with an acceptable selectivity index versus BChE (SI: 5.19), while compound 6aa exhibited the greatest inhibition activity on BChE (3.97 µM) and a significant selectivity index against AChE (SI: 0.04). Kinetic studies were carried out for compounds with greater inhibitory activity of cholinesterases. Structure-activity relationships of the molecular hybrids were analyzed, through computational models using a molecular cross-docking algorithm and Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) binding free energy approach, which indicated a good correlation between the experimental inhibition values and the predicted free binding energy.
Project description:1,2,3,4-Tetrahydroquinolines have been identified as the most potent inhibitors of LPS-induced NF-?B transcriptional activity. To discover new molecules of this class with excellent activities, we designed and synthesized a series of novel derivatives of 1,2,3,4-tetrahydroquinolines (4a-g, 5a-h, 6a-h, and 7a-h) and bioevaluated their in vitro activity against human cancer cell lines (NCI-H23, ACHN, MDA-MB-231, PC-3, NUGC-3, and HCT 15). Among all synthesized scaffolds, 6g exhibited the most potent inhibition (53 times that of a reference compound) of LPS-induced NF-?B transcriptional activity and the most potent cytotoxicity against all evaluated human cancer cell lines.
Project description:The synthesis of novel tetrahydroquinolines (THQ) and dihydroquinolines (DHQ) are reported using three practical, scalable synthetic approaches to access highly lipophilic analogues bearing a 6-iodo substituent, each with a different means of cyclisation. A versatile and stable quinolin-2-one intermediate was identified, which could be reduced to the corresponding THQ with borane reagents, or to the DHQ with diisobutylaluminium hydride via a novel elimination that is more favourable at higher temperatures. Coupling these strongly electron-donating scaffolds to electron-accepting moieties caused the resulting structures to exhibit strong fluorescence.
Project description:The Bromodomain and Extra-Terminal domain (BET) family of proteins are involved in the regulation of gene transcription, and their dysregulation is implicated in several diseases including cancer. BET proteins contain two tandem bromodomains (BD1 and BD2) that independently recognize acetylated-lysine residues and appear to have distinct biological roles. We compared several published co-crystal structures and found five positions near the substrate binding pocket that vary between BET bromodomains. One position located in the ZA loop has unique properties. In BRD2-4, this residue is glutamine in BD1 and lysine in BD2; in BRDT, this residue is arginine in BD1 and asparagine in BD2. Using molecular modeling, we identified differences in the water-mediated network at this position between bromodomains. Molecular dynamics simulations helped rationalize the observed bromodomain selectivity for exemplar BET inhibitors and a congeneric series of tetrahydroquinolines (THQ) that differed by a single heteroatom near the ZA channel. The 2-furan SJ830599, the most BD2-selective THQ analog, did not disrupt the water-mediated networks in either domain, but was electrostatically-repulsed by the specific arrangement of the W5 water dipole in BD1. Our work underscores the value of exploring water-mediated interactions to study ligand binding, and highlights the difficulty of optimizing polar interactions due to high desolvation penalties. Finally, we suggest further modifications to THQ-based BET inhibitors that would increase BD2-selectivity in BRD2-4, while minimizing affinity for one or both bromodomains of BRDT.
Project description: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.