Novel 5-HT3 antagonists. Isoquinolinones and 3-aryl-2-pyridones

Structure-based design of imidazole-containing peptidomimetic inhibitors of protein farnesyltransferase

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).

Design, synthesis, and evaluation of potent and selective benzoyleneurea-based inhibitors of protein geranylgeranyltransferase-I

A series of novel protein geranylgeranyltransferase-I (PGGTase-I) inhibitors based on a benzoyleneurea scaffold has been synthesized. Using a benzoyleneurea scaffold as a mimetic for the central dipeptide (AA), we have developed CAAX peptidomimetic inhibitors that selectively block the activity of PGGTase-I over the closely related enzyme protein farnesyltransferase. In this new class of PGGTase-I inhibitors, compound (6c) with X=L-phenylalanine, displayed the highest inhibition activity against PGGTase-I with an IC50 value of 170 nM. The inhibitors described in this study represent novel and promising leads for the development of potent and selective inhibitors of mammalian PGGTase-I for potential application as antitumor agents.

Design and Synthesis of Peptidomimetic Protein Farnesyltransferase Inhibitors as Anti-Trypanosoma brucei Agents

On the basis of the structure of the CVIM tetrapeptide substrate of mammalian protein farnesyltransferase, a series of imidazole-containing peptidomimetics was designed and synthesized, and their inhibition activity against Trypanosoma brucei protein farnesyltransferase (TbPFT) was evaluated. Peptidomimetics where the 5-position of the imidazole ring was linked to the hydrophobic scaffold showed over 70% inhibition activity at 50 nM in the enzyme assay, whereas the corresponding C-4 regioisomers were less potent. The ester prodrug 23 was found to be a potent inhibitor against cultured Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense cells with ED(50) values of 0.025 and 0.0026 microM, respectively. Furthermore, introducing a second imidazole group into 23 led to 31, which showed the highest inhibition activity against the parasite with an ED(50) of 0.0015 microM. The potency of the TbPFT inhibitors and the cytotoxicity of the corresponding esters to T. brucei cells were shown to be highly correlated. These studies validate TbPFT as a target for the development of novel therapeutics against African sleeping sickness.

2-nitroimidazol-5-ylmethyl as a potential bioreductively activated prodrug system: reductively triggered release of the PARP inhibitor 5-bromoisoquinolinone

5-Chloromethyl-1-methyl-2-nitroimidazole reacted efficiently with the anion derived from 5-bromoisoquinolin-1-one to give 5-bromo-2-((1-methyl-2-nitroimidazol-5-yl)methyl)isoquinolin -1-one. Biomimetic reduction effected release of the 5-bromoisoquinolin-1-one. The 2-nitroimidazol-5-ylmethyl unit thus has potential for development as a general prodrug system for selective drug delivery to hypoxic tissues.

GYKI-46 903, a non-competitive antagonist for 5-HT3 receptors

The effects of GYKI-46 903 ((+)endo-4-propionyloxy-6-(4-fluorophenyl)-1-azabicyclo [3.3.1]non-6-ene HCl), on 5-HT3 receptors have been studied and compared with ondansetron in peripheral organs in vitro and in vivo, and in a receptor binding assay in membranes prepared from rat cerebral cortex. GYKI-46 903 was found to be a non-competitive antagonist at 5-HT3 receptors present in non-stimulated longitudinal muscle strip of guinea-pig ileum (pD2' against serotonin = 5.54), and also in 5-methoxytryptamine-pretreated electrically stimulated ileal preparations (pD2' against serotonin = 5.26). On the contrary, ondansetron was found to be a competitive antagonist for 5-HT3 receptors; the pA2 value against serotonin was 7.40 in non-stimulated ileum, and it was 7.08 in electrically stimulated ileal preparation pretreated with 5-methoxytryptamine. In displacement studies, the pIC50 values of GYKI-46 903 and ondansetron against [3H]granisetron binding to rat cerebral cortex membranes were 6.91 and 8.58 respectively. GYKI-46 903, when administered by intravenous infusion, antagonized the decrease in heart rate evoked by serotonin (Bezold-Jarisch reflex) in anaesthetized rats, and the maximal reversal was less than 50%. This was in striking contrast with ondansetron, which, after intravenous injection, completely antagonized the serotonin-induced bradycardia with an ID50 value of 3.28 ug/kg. These data classify GYKI-46 903 as a non-competitive antagonist for 5-HT3 receptors.