CEP-26401 (irdabisant), a potent and selective histamine H3 receptor antagonist/inverse agonist with cognition-enhancing and wake-promoting activities.

CEP-26401 [irdabisant; 6-{4-[3-((R)-2-methyl-pyrrolidin-1-yl)-propoxy]-phenyl}-2H-pyridazin-3-one HCl] is a novel, potent histamine H3 receptor (H3R) antagonist/inverse agonist with drug-like properties. High affinity of CEP-26401 for H3R was demonstrated in radioligand binding displacement assays in rat brain membranes (K(i) = 2.7 ± 0.3 nM) and recombinant rat and human H3R-expressing systems (K(i) = 7.2 ± 0.4 and 2.0 ± 1.0 nM, respectively). CEP-26401 displayed potent antagonist and inverse agonist activities in [³5S]guanosine 5'-O-(γ-thio)triphosphate binding assays. After oral dosing of CEP-26401, occupancy of H3R was estimated by the inhibition of ex vivo binding in rat cortical slices (OCC50 = 0.1 ± 0.003 mg/kg), and antagonism of the H3R agonist R-α-methylhistamine- induced drinking response in the rat dipsogenia model was demonstrated in a similar dose range (ED50 = 0.06 mg/kg). CEP-26401 improved performance in the rat social recognition model of short-term memory at doses of 0.01 to 0.1 mg/kg p.o. and was wake-promoting at 3 to 30 mg/kg p.o. In DBA/2NCrl mice, CEP-26401 at 10 and 30 mg/kg i.p. increased prepulse inhibition (PPI), whereas the antipsychotic risperidone was effective at 0.3 and 1 mg/kg i.p. Coadministration of CEP-26401 and risperidone at subefficacious doses (3 and 0.1 mg/kg i.p., respectively) increased PPI. These results demonstrate potent behavioral effects of CEP-26401 in rodent models and suggest that this novel H3R antagonist may have therapeutic utility in the treatment of cognitive and attentional disorders. CEP-26401 may also have therapeutic utility in treating schizophrenia or as adjunctive therapy to approved antipsychotics.

Discovery of a potent, selective, and orally active proteasome inhibitor for the treatment of cancer.

The ubiquitin-proteasome pathway plays a central role in regulation of the production and destruction of cellular proteins. These pathways mediate proliferation and cell survival, particularly in malignant cells. The successful development of the 20S human proteasome inhibitor bortezomib for the treatment of relapsed and refractory multiple myeloma has established this targeted intervention as an effective therapeutic strategy. Herein, the potent, selective, and orally bioavailable threonine-derived 20S human proteasome inhibitor that has been advanced to preclinical development, [(1R)-1-[[(2 S,3 R)-3-hydroxy-2-[(6-phenylpyridine-2-carbonyl)amino]-1-oxobutyl]amino]-3-methylbutyl]boronic acid 20 (CEP-18770), is disclosed.

TrkA kinase inhibitors from a library of modified and isosteric Staurosporine aglycone.

An immobilized Staurosporine aglycone isostere where one of the indole nitrogen atoms was replaced by carbon has been sequentially functionalized to generate compounds inhibiting TrkA kinase. In the first phase, initial screening of a library of C13-hydroxymethyl-7-oxo-indenopyrrolocarbazoles resulted in several potent compounds, one of which was further optimized to generate the corresponding carbamates on solid phase. Some of the major carbamate diastereomers were found to be several-fold more potent than their alcohol parents. Synthesis, SAR analysis, kinase selectivity, and anti-tumor properties of a TrkA inhibitor (12a) are discussed.

Synthesis and mixed lineage kinase activity of pyrrolocarbazole and isoindolone analogs of (+)K-252a.

Structural modification of the indolecarbazole natural product (+)K-252a identified structural requirements for MLK activity and a novel series of potent fused pyrrolocarbazole MLK1/3 inhibitors. The SAR revealed that the lactam regiochemistry, the shape of the heterocycle, and aryl rings B and F are important to MLK activity. Heteroatom and alkyl replacement of the N-12 and/or N-13 indole nitrogen atoms identified the nonplanar dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-7-one (8) and corresponding 5,7-dione (7) as potent cell-permeable MLK1/3 family-selective leads with in vitro activity comparable to that of (+)K-252a and determined them to be 2- to 3-fold more potent than the aglycone natural product K-252c.

Knowledge-based chemoinformatic approaches to drug discovery.

The modern drug discovery process is steadily becoming more information driven. Structural, physicochemical and ADME-Tox property profiles of reference (successful) ligands, along with structural information of their target proteins, have been extremely useful for early-stage drug discovery. Recently, databases of known biologically active ligands (knowledge bases) have become more focused toward different protein-target classes. The number of new chemoinformatics tools used to analyze structures and properties of successful molecules has also increased enormously. Scientists in this area are exploring new physicochemical properties and appropriate drug sets to understand druglike properties. In this review, the various uses of the ligand knowledge bases in the drug discovery process have been critically reviewed.

A new class of potent vascular endothelial growth factor receptor tyrosine kinase inhibitors: structure-activity relationships for a series of 9-alkoxymethyl-12-(3-hydroxypropyl)indeno[2,1-a]pyrrolo[3,4-c]carbazole-5-ones and the identification of CEP-5214 and its dimethylglycine ester prodrug clinical candidate CEP-7055.

A series of potent vascular endothelial growth factor R2 (VEGF-R2) tyrosine kinase inhibitors from a new indenopyrrolocarbazole template is reported. The structure-activity relationships for a series of 9-alkoxymethyl-12-(3-hydroxypropyl)indeno[2,1-a]pyrrolo[3,4-c]carbazole-5-ones revealed an optimal R9 substitution with ethoxymethyl 19 (VEGF-R2 IC(50) = 4 nM) and isopropoxymethyl 21 (VEGF-R2 IC(50) = 8 nM) being the most potent inhibitors in the series. The VEGF-R2 activity was reduced appreciably by increasing the size of the R9 alkoxy group or by alpha-methyl branching adjacent to the ring. The combined R9 alkoxymethyl and N12 hydroxypropyl substitutions were required for potent VEGF-R2 activity, and the corresponding thioether analogues were weaker than their ether counterparts. Compound 21 (R9 isopropoxymethyl, CEP-5214) was identified as a potent, low-nanomolar pan inhibitor of human VEGF-R tyrosine kinases, displaying IC(50) values of 16, 8, and 4 nM for VEGF-R1/FLT-1, VEGF-R2/KDR, and VEGF-R3/FLT-4, respectively, with cellular activity equivalent to the isolated enzyme activity. Compound 21 exhibited good selectivity against numerous tyrosine and serine/threonine kinases including PKC, Tie2, TrkA, CDK1, p38, JNK, and IRK. To increase water solubility and oral bioavailability, the N,N-dimethylglycine ester 40 was prepared. In pharmacokinetic studies in mice and rats, increased plasma levels of 21 were observed after oral administration of 40. Compound 21 demonstrated significant in vivo antitumor activity in numerous tumor models and was advanced into phase I clinical trials as the water-soluble N,N-dimethylglycine ester prodrug 40 (CEP-7055).

Knowledge-Based, Central Nervous System (CNS) Lead Selection and Lead Optimization for CNS Drug Discovery.

The central nervous system (CNS) is the major area that is affected by aging. Alzheimer's disease (AD), Parkinson's disease (PD), brain cancer, and stroke are the CNS diseases that will cost trillions of dollars for their treatment. Achievement of appropriate blood-brain barrier (BBB) penetration is often considered a significant hurdle in the CNS drug discovery process. On the other hand, BBB penetration may be a liability for many of the non-CNS drug targets, and a clear understanding of the physicochemical and structural differences between CNS and non-CNS drugs may assist both research areas. Because of the numerous and challenging issues in CNS drug discovery and the low success rates, pharmaceutical companies are beginning to deprioritize their drug discovery efforts in the CNS arena. Prompted by these challenges and to aid in the design of high-quality, efficacious CNS compounds, we analyzed the physicochemical property and the chemical structural profiles of 317 CNS and 626 non-CNS oral drugs. The conclusions derived provide an ideal property profile for lead selection and the property modification strategy during the lead optimization process. A list of substructural units that may be useful for CNS drug design was also provided here. A classification tree was also developed to differentiate between CNS drugs and non-CNS oral drugs. The combined analysis provided the following guidelines for designing high-quality CNS drugs: (i) topological molecular polar surface area of <76 Å(2) (25-60 Å(2)), (ii) at least one (one or two, including one aliphatic amine) nitrogen, (iii) fewer than seven (two to four) linear chains outside of rings, (iv) fewer than three (zero or one) polar hydrogen atoms, (v) volume of 740-970 Å(3), (vi) solvent accessible surface area of 460-580 Å(2), and (vii) positive QikProp parameter CNS. The ranges within parentheses may be used during lead optimization. One violation to this proposed profile may be acceptable. The chemoinformatics approaches for graphically analyzing multiple properties efficiently are presented.

Synthesis and biological profile of the pan-vascular endothelial growth factor receptor/tyrosine kinase with immunoglobulin and epidermal growth factor-like homology domains 2 (VEGF-R/TIE-2) inhibitor 11-(2-methylpropyl)-12,13-dihydro-2-methyl-8-(pyrimidin-2-ylamino)-4H-indazolo[5,4-a]pyrrolo[3,4-c]carbazol-4-one (CEP-11981): a novel oncology therapeutic agent.

A substantial body of evidence supports the utility of antiangiogenesis inhibitors as a strategy to block or attenuate tumor-induced angiogenesis and inhibition of primary and metastatic tumor growth in a variety of solid and hematopoietic tumors. Given the requirement of tumors for different cytokine and growth factors at distinct stages of their growth and dissemination, optimal antiangiogenic therapy necessitates inhibition of multiple, complementary, and nonredundant angiogenic targets. 11-(2-Methylpropyl)-12,13-dihydro-2-methyl-8-(pyrimidin-2-ylamino)-4H-indazolo[5,4-a]pyrrolo[3,4-c]carbazol-4-one (11b, CEP-11981) is a potent orally active inhibitor of multiple targets (TIE-2, VEGF-R1, 2, and 3, and FGF-R1) having essential and nonredundant roles in tumor angiogenesis and vascular maintenance. Outlined in this article are the design strategy, synthesis, and biochemical and pharmacological profile for 11b, which completed Phase I clinical assessing safety and pharmacokinetics allowing for the initiation of proof of concept studies.

Discovery and characterization of 6-{4-[3-(R)-2-methylpyrrolidin-1-yl)propoxy]phenyl}-2H-pyridazin-3-one (CEP-26401, irdabisant): a potent, selective histamine H3 receptor inverse agonist.

Optimization of a novel series of pyridazin-3-one histamine H(3) receptor (H(3)R) antagonists/inverse agonists identified 6-{4-[3-(R)-2-methylpyrrolidin-1-yl)propoxy]phenyl}-2H-pyridazin-3-one (8a, CEP-26401; irdabisant) as a lead candidate for potential use in the treatment of attentional and cognitive disorders. 8a had high affinity for both human (K(i) = 2.0 nM) and rat (K(i) = 7.2 nM) H(3)Rs with greater than 1000-fold selectivity over the hH(1)R, hH(2)R, and hH(4)R histamine receptor subtypes and against an in vitro panel of 418 G-protein-coupled receptors, ion channels, transporters, and enzymes. 8a demonstrated ideal pharmaceutical properties for a CNS drug in regard to water solubility, permeability and lipophilicity and had low binding to human plasma proteins. It weakly inhibited recombinant cytochrome P450 isoforms and human ether-a-go-go-related gene. 8a metabolism was minimal in rat, mouse, dog, and human liver microsomes, and it had good interspecies pharmacokinetic properties. 8a dose-dependently inhibited H(3)R agonist-induced dipsogenia in the rat (ED(50) = 0.06 mg/kg po). On the basis of its pharmacological, pharmaceutical, and safety profiles, 8a was selected for preclinical development. The clinical portions of the single and multiple ascending dose studies assessing safety and pharmacokinetics have been completed allowing for the initiation of a phase IIa for proof of concept.

Mixed-lineage kinase 1 and mixed-lineage kinase 3 subtype-selective dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-ones: optimization, mixed-lineage kinase 1 crystallography, and oral in vivo activity in 1-methyl-4-phenyltetrahydropyridine models.

The optimization of the dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-one R(2) and R(12) positions led to the identification of the first MLK1 and MLK3 subtype-selective inhibitors within the MLK family. Compounds 14 (CEP-5104) and 16 (CEP-6331) displayed good potency for MLK1 and MLK3 inhibition with a greater than 30- to 100-fold selectivity for related family members MLK2 and DLK. Compounds 14 and 16 were orally active in vivo in a mouse MPTP biochemical efficacy model that was comparable to the first-generation pan-MLK inhibitor 1 (CEP-1347). The MLK1 structure-activity relationships were supported by the first-reported X-ray crystal structure of MLK1 bound with 16.

1,2,3-Thiadiazole substituted pyrazolones as potent KDR/VEGFR-2 kinase inhibitors.

KDR kinase inhibition is considered to play an important role in regulating angiogenesis, which is vital for the survival and proliferation of tumor cells. Recently we disclosed a structure-based kinase inhibitor design strategy which led to the identification of a new class of VEGFR-2/KDR kinase inhibitors bearing heterocyclic substituted pyrazolones as the core template. Instability in a rat S9 preparation and poor iv PK profiles for most of these inhibitors necessitated exploration of new pyrazolones to identify new analogs with improved metabolic stability. Optimization of the heterocyclic moiety led to the identification of the thiadiazole series of pyrazolones (D) as potent VEGFR-2/KDR kinase inhibitors. SAR modifications, kinase selectivity profiling, and structural elements for improved PK properties were explored. Oral bioavailability up to 29% was achieved in the rat. Modeling results based on the Glide XP docking approach supported our postulation regarding the interaction of the lactam segment of the pyrazolones with the hinge region of the KDR kinase.

Overview of drug discovery and development.

This overview unit describes the core activities involved in the drug discovery and development process, from target identification - including preclinical biology, medicinal and process chemistry - to pharmacokinetics and metabolism (ADME), and also activities related to the to the drug approval process. The latter include the activities related to the filing of an IND (Investigational New Drug) application and also Phases I - III of clinical trials that form the basis of an NDA (New Drug Application) submission, as well as post-marketing Phase IV activities as required by the U.S. Food and Drug Administration (FDA) and the European and Japanese counterparts.

Structure-guided identification of novel VEGFR-2 kinase inhibitors via solution phase parallel synthesis.

Structural analysis of the essential binding elements of the oxindole-based kinase inhibitor (1) led to the identification of a novel class of heterocyclic-substituted pyrazolones. Knoevenagel condensation of a variety of activated methylene nucleophiles with indole or pyrrole carboxaldehydes provided a focused library of molecules, each containing elements of kinase pharmacophore probe. Initial screening for VEGFR-2 kinase inhibition eliminated several of the probes. Identification of an active pyrazolone motif and further optimization resulted in several highly potent VEGFR-2 inhibitors with cellular efficacy, anti-angiogenic activity ex vivo in rat aortic ring explant cultures, and oral anti-tumor efficacy in nude mice.

Syntheses of C12,N13 heterocyclic bridged fused indenopyrrolocarbazoles.

Tandem alkylation/cyclization of indenopyrrolocarbazole 4a, a C12 carbon analogue of indolocarbazole K252c, was carried out by general solid-phase and solution-phase methods. Alkylation of fused pyrroloindenylcarbazole 4a derivatives with appropriate monoacetals of diketones afforded the corresponding C12-substituted acetal alcohols. Acid-catalyzed cyclization of these adducts yielded C12,N13-bridged tetrahydrofuran, pyran, and dioxane compounds 10-13.

1,2-Benzothiazine 1,1-dioxide alpha-ketoamide analogues as potent calpain I inhibitors.

A series of potent 1,2-benzothiazine 1,1-dioxide alpha-ketoamide inhibitors of calpain I is described.