Discovery and optimization of a highly efficacious class of 5-aryl-2-aminopyridines as FMS-like tyrosine kinase 3 (FLT3) inhibitors.

Based on a putative binding mode of quizartinib (AC220, 1), a potent FMS-like tyrosine kinase 3 (FLT3) inhibitor in Phase III clinical development, we have designed de novo a simpler aminopyridine-based hinge binding motif. Further optimization focusing on maximizing in vivo efficacy and minimizing CYP3A4 time-dependent inhibition resulted in a highly efficacious compound (6s) in tumor xenograft model for further preclinical development.

Discovery of highly potent and selective pan-Aurora kinase inhibitors with enhanced in vivo antitumor therapeutic index.

Serine/threonine protein kinases Aurora A, B, and C play essential roles in cell mitosis and cytokinesis. Currently a number of Aurora kinase inhibitors with different isoform selectivities are being evaluated in the clinic. Herein we report the discovery and characterization of 21c (AC014) and 21i (AC081), two structurally novel, potent, kinome-selective pan-Aurora inhibitors. In the human colon cancer cell line HCT-116, both compounds potently inhibit histone H3 phosphorylation and cell proliferation while inducing 8N polyploidy. Both compounds administered intravenously on intermittent schedules displayed potent and durable antitumor activity in a nude rat HCT-116 tumor xenograft model and exhibited good in vivo tolerability. Taken together, these data support further development of both 21c and 21i as potential therapeutic agents for the treatment of solid tumors and hematological malignancies.

CEP-32496: a novel orally active BRAF(V600E) inhibitor with selective cellular and in vivo antitumor activity.

Mutations in the BRAF gene have been identified in approximately 7% of cancers, including 60% to 70% of melanomas, 29% to 83% of papillary thyroid carcinomas, 4% to 16% colorectal cancers, and a lesser extent in serous ovarian and non-small cell lung cancers. The V600E mutation is found in the vast majority of cases and is an activating mutation, conferring transforming and immortalization potential to cells. CEP-32496 is a potent BRAF inhibitor in an in vitro binding assay for mutated BRAF(V600E) (K(d) BRAF(V600E) = 14 nmol/L) and in a mitogen-activated protein (MAP)/extracellular signal-regulated (ER) kinase (MEK) phosphorylation (pMEK) inhibition assay in human melanoma (A375) and colorectal cancer (Colo-205) cell lines (IC(50) = 78 and 60 nmol/L). In vitro, CEP-32496 has multikinase binding activity at other cancer targets of interest; however, it exhibits selective cellular cytotoxicity for BRAF(V600E) versus wild-type cells. CEP-32496 is orally bioavailable in multiple preclinical species (>95% in rats, dogs, and monkeys) and has single oral dose pharmacodynamic inhibition (10-55 mg/kg) of both pMEK and pERK in BRAF(V600E) colon carcinoma xenografts in nude mice. Sustained tumor stasis and regressions are observed with oral administration (30-100 mg/kg twice daily) against BRAF(V600E) melanoma and colon carcinoma xenografts, with no adverse effects. Little or no epithelial hyperplasia was observed in rodents and primates with prolonged oral administration and sustained exposure. CEP-32496 benchmarks favorably with respect to other kinase inhibitors, including RAF-265 (phase I), sorafenib, (approved), and vemurafenib (PLX4032/RG7204, approved). CEP-32496 represents a novel and pharmacologically active BRAF inhibitor with a favorable side effect profile currently in clinical development.

Discovery of AC710, a Globally Selective Inhibitor of Platelet-Derived Growth Factor Receptor-Family Kinases.

A series of potent, selective platelet-derived growth factor receptor-family kinase inhibitors was optimized starting from a globally selective lead molecule 4 through structural modifications aimed at improving the physiochemical and pharmacokinetic properties, as exemplified by 18b. Further clearance reduction via per-methylation of the α-carbons of a solubilizing piperidine nitrogen resulted in advanced leads 22a and 22b. Results from a mouse tumor xenograft, a collagen-induced arthritis model, and a 7 day rat in vivo tolerability study culminated in the selection of compound 22b (AC710) as a preclinical development candidate.

Identification of 1-(3-(6,7-dimethoxyquinazolin-4-yloxy)phenyl)-3-(5-(1,1,1-trifluoro-2-methylpropan-2-yl)isoxazol-3-yl)urea hydrochloride (CEP-32496), a highly potent and orally efficacious inhibitor of V-RAF murine sarcoma viral oncogene homologue B1 (BRAF) V600E.

The Ras/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) signaling pathway plays a central role in the regulation of cell growth, differentiation, and survival. Expression of mutant BRAF(V600E) results in constitutive activation of the MAPK pathway, which can lead to uncontrolled cellular growth. Herein, we describe an SAR optimization campaign around a series of quinazoline derived BRAF(V600E) inhibitors. In particular, the bioisosteric replacement of a metabolically sensitive tert-butyl group with fluorinated alkyl moieties is described. This effort led directly to the identification of a clinical candidate, compound 40 (CEP-32496). Compound 40 exhibits high potency against several BRAF(V600E)-dependent cell lines and selective cytotoxicity for tumor cell lines expressing mutant BRAF(V600E) versus those containing wild-type BRAF. Compound 40 also exhibits an excellent PK profile across multiple preclinical species. In addition, significant oral efficacy was observed in a 14-day BRAF(V600E)-dependent human Colo-205 tumor xenograft mouse model, upon dosing at 30 and 100 mg/kg BID.

4-Quinazolinyloxy-diaryl ureas as novel BRAFV600E inhibitors.

Aryl phenyl ureas with a 4-quinazolinoxy substituent at the meta-position of the phenyl ring are potent inhibitors of mutant and wild type BRAF kinase. Compound 7 (1-(5-tert-butylisoxazol-3-yl)-3-(3-(6,7-dimethoxyquinazolin-4-yloxy)phenyl)urea hydrochloride) exhibits good pharmacokinetic properties in rat and mouse and is efficacious in a mouse tumor xenograft model following oral dosing.

Heterocycle-substituted proline dipeptides as potent VLA-4 antagonists.

A variety of N-linked tertiary amines and heteroarylamines were examined at the 4-position of sulfonylated proline dipeptides in order to improve VLA-4 receptor off-rates and overcome the issue of CYP3A4 time-dependent inhibition of ester prodrugs. A tight-binding inhibitor 5j with a long off-rate provided sustained receptor occupancy despite poor oral pharmacokinetics.

Identification of N-(5-tert-butyl-isoxazol-3-yl)-N'-{4-[7-(2-morpholin-4-yl-ethoxy)imidazo[2,1-b][1,3]benzothiazol-2-yl]phenyl}urea dihydrochloride (AC220), a uniquely potent, selective, and efficacious FMS-like tyrosine kinase-3 (FLT3) inhibitor.

Treatment of AML patients with small molecule inhibitors of FLT3 kinase has been explored as a viable therapy. However, these agents are found to be less than optimal for the treatment of AML because of lack of sufficient potency or suboptimal oral pharmacokinetics (PK) or lack of adequate tolerability at efficacious doses. We have developed a series of extremely potent and highly selective FLT3 inhibitors with good oral PK properties. The first series of compounds represented by 1 (AB530) was found to be a potent and selective FLT3 kinase inhibitor with good PK properties. The aqueous solubility and oral PK properties at higher doses in rodents were found to be less than optimal for clinical development. A novel series of compounds were designed lacking the carboxamide group of 1 with an added water solubilizing group. Compound 7 (AC220) was identified from this series to be the most potent and selective FLT3 inhibitor with good pharmaceutical properties, excellent PK profile, and superior efficacy and tolerability in tumor xenograft models. Compound 7 has demonstrated a desirable safety and PK profile in humans and is currently in phase II clinical trials.

AC220 is a uniquely potent and selective inhibitor of FLT3 for the treatment of acute myeloid leukemia (AML).

Activating mutations in the receptor tyrosine kinase FLT3 are present in up to approximately 30% of acute myeloid leukemia (AML) patients, implicating FLT3 as a driver of the disease and therefore as a target for therapy. We report the characterization of AC220, a second-generation FLT3 inhibitor, and a comparison of AC220 with the first-generation FLT3 inhibitors CEP-701, MLN-518, PKC-412, sorafenib, and sunitinib. AC220 exhibits low nanomolar potency in biochemical and cellular assays and exceptional kinase selectivity, and in animal models is efficacious at doses as low as 1 mg/kg given orally once daily. The data reveal that the combination of excellent potency, selectivity, and pharmacokinetic properties is unique to AC220, which therefore is the first drug candidate with a profile that matches the characteristics desirable for a clinical FLT3 inhibitor.

Discovery of N-{N-[(3-cyanobenzene) sulfonyl]-4(R)-(3,3-difluoropiperidin-1-yl)-(l)-prolyl}-4-[(3',5'-dichloro-isonicotinoyl) amino]-(l)-phenylalanine (MK-0617), a highly potent and orally active VLA-4 antagonist.

A series of prolyl-N-isonicotinoyl-(L)-4-aminophenylalanine derivatives substituted at the proline 4-position with cyclic amines was evaluated as VLA-4 antagonists. The ring size and presence or absence of fluorine affected potency and receptor occupancy. The analog with 3,3-difluoropiperidine at the proline 4-position (13) was the most potent compound and had very good duration of receptor occupancy in vitro. The ethyl ester prodrug of 13 demonstrated excellent receptor occupancy after oral dosing in rats.

Benzazoles as allosteric potentiators of metabotropic glutamate receptor 2 (mGluR2): efficacy in an animal model for schizophrenia.

Metabotropic glutamate receptor 2 (mGluR2) has been implicated in a variety of CNS disorders, including schizophrenia. Disclosed herein is the development of a new series of allosteric potentiators of mGluR2. Structure-activity relationship studies in conjunction with pharmacokinetic data led to the discovery of indole 5, which is active in an animal model for schizophrenia.

Influence of acid surrogates toward potency of VLA-4 antagonist.

A series of VLA-4 antagonist were synthesized wherein carboxylic acid was replaced by various acid surrogates. The effect of these acid surrogates toward potency was evaluated in a binding assay. A number of acid surrogates were potent antagonist of VLA-4, albeit significantly less potent than the corresponding carboxylic acid. Heterocyclic acid surrogate, oxadiazolidinone 3, demonstrated an improved pharmacokinetic property when dosed intravenously.

Biphenyl-indanones: allosteric potentiators of the metabotropic glutamate subtype 2 receptor.

We have identified and synthesized a series of biphenyl-carboxylic acid indanones as allosteric potentiators of the metabotropic glutamate receptor 2. Structure-activity relationship studies directed toward improving the potency and the brain to plasma ratio of the initial lead led to the discovery of 5 and 23 (EC50=111 and 5 nM, respectively).

3-(2-Ethoxy-4-{4-[3-hydroxy-2-methyl-4-(3-methylbutanoyl)phenoxy]butoxy}phenyl)propanoic acid: a brain penetrant allosteric potentiator at the metabotropic glutamate receptor 2 (mGluR2).

We have identified and synthesized a brain penetrant propanoic acid as an allosteric potentiator of the metabotropic glutamate receptor 2. Structure-activity relationship studies directed toward improving the potency, level of potentiation and brain penetration led to the discovery of 8 (EC50=1200 nM, 77% potentiation, 119% brain/plasma in rat, 20 mpk i.p., brain level of 5700 nM).

Allosteric potentiators of the metabotropic glutamate receptor 2 (mGlu2). Part 3: Identification and biological activity of indanone containing mGlu2 receptor potentiators.

We have identified and synthesized a series of phenyl-tetrazolyl and 4-thiopyridyl indanones as allosteric potentiators of the metabotropic glutamate receptor 2. Structure activity relationship studies directed toward improving the potency and level of potentiation, as well as PK properties, led to the discovery of 28 (EC50=186 nM), which displayed activity in a rodent model for schizophrenia.

Allosteric potentiators of the metabotropic glutamate receptor 2 (mGlu2). Part 2: 4-thiopyridyl acetophenones as non-tetrazole containing mGlu2 receptor potentiators.

We have identified and synthesized a series of 4-thiopyridyl acetophenones as positive allosteric potentiators of the metabotropic glutamate receptor 2. Structure-activity relationship studies directed toward replacement of the tetrazole in the initial lead led to the discovery of 16 (EC(50)=340 nM), which showed improved brain penetration over the initial lead.

Discovery of novel modulators of metabotropic glutamate receptor subtype-5.

A series of potent and selective mGluR5 antagonists were synthesized and evaluated in vitro and in vivo. It was found that a pyridyl functionality is a potential replacement for acetonitrile in the lead structure, with 2-pyridyl being most favored. Additionally, the benzoxazole moiety could also be replaced by other heterobicyclic rings such as imidazothiazole.

In vivo pharmacological characterization of (+/-)-4-[2-(1-methyl-2-pyrrolidinyl)ethyl]thiophenol hydrochloride (SIB-1553A), a novel cholinergic ligand: microdialysis studies.

SIB-1553A ((+/-)-4-[2-(1-methyl-2-pyrrolidinyl)ethyl]thiophenol HCl) is a neuronal nicotinic acetylcholine receptor (nAChR) ligand which is active in rodent and primate models of cognition. In functional assays, SIB-1553A exhibits marked subtype selectivity for nAChRs as compared to nicotine. In addition SIB-1553A also exhibits affinities to histaminergic (H3) and serotonergic (5-HT1 and 5HT2) receptors and sigma binding sites. In the present investigation, we characterized SIB-1553A-induced neurotransmitter release in vivo. Following subcutaneous injection (s.c., 10 mg/kg), SIB-1553A rapidly entered the brain achieving concentration of approximately 20 microM 15 min post-injection and was eliminated from plasma with a terminal half-life of approximately 32 min. In freely moving rats, SIB-1553A (1-40 mg/kg, s.c.), markedly increased ACh release in the hippocampus and prefrontal cortex. In both regions, the magnitude of SIB-1553A-induced ACh release was greater than that seen with the prototypical nAChR agonist, nicotine (0.4 mg/kg, s.c.). Both isomers of SIB-1553A induced similar levels of increase in hippocampal ACh release. Increased hippocampal ACh release was also observed following oral administration of SIB-1553A (40 mg/kg) or after local perfusion into the hippocampus (1 mM). SIB-1553A-induced hippocampal ACh release was significantly attenuated by two nAChR antagonists, mecamylamine (MEC) and dihydro-beta-erythroidine (DHbetaE), and by the dopamine (DA) (D1) antagonist, SCH-23390, arguing that ACh release, in part, involves activation of nAChRs and a permissive DA synapse. In contrast to its robust effects on ACh release, SIB-1553A (40 mg/kg, s.c.) modestly increased striatal DA release (approximately 180% of baseline). Due to the proposed role of cholinergic pathways in learning and memory, the neurochemical profile of SIB-1553A suggests a potential for it to treat cognitive dysfunction.

Ganciclovir release rates in vitreous from different formulations of 1-O-hexadecylpropanediol-3-phospho-ganciclovir.

PURPOSE: To determine the optimal formulation of lipid prodrug, 1-O-hexadecyloxypropyl-phospho-ganciclovir (HDP-P-GCV), for intravitreal delivery. METHODS: Equal concentrations of crystalline or liposomal HDP-P-GCV were exposed to rabbit whole vitreous, core vitreous, peripheral vitreous, human plasma, and heat inactivated rabbit vitreous, and the samples were incubated at 37 degrees C for one week. Aliquots were taken at day 1, 2, 3, and 7 and subjected to HPLC analysis for conversion to GCV. RESULTS: The resultant concentration of GCV from crystalline HDP-P-GCV in vitreous was 198 +/- 49 microM (n = 3) at day 1 and 1253 +/- 248 microM (n = 3) at day 7. The resultant concentration of GCV from the liposomal formulation of HDP-P-GCV in vitreous was much lower, yielding a concentration of 66 +/- 7 microM (n = 3) at day 1 and 243 +/- 39 microM (n = 3) at day 7 (P < 0.001, t Test). When the crystalline HDP-P-GCV was incubated with heat-inactivated vitreous, the detectable GCV concentrations were low (22 microM) and did not increase over time. The concentration of GCV detected from the crystalline HDP-P-GCV in the core vitreous was 19.69 +/- 3.84 microM (n = 3) at day 1 and 1537.36 +/- 177.14 microM (n = 3) at day 7. The concentration of GCV released from crystalline HDP-P-GCV in peripheral vitreous was 32.86 +/- 5.07 microM (n = 3) at day 1 and 1805.78 +/- 327.94 microM (n = 3) at day 7. Detectable GCV concentration from both core and peripheral vitreous samples increased over time, however, the magnitude of GCV release from peripheral vitreous samples was higher (P < 0.05, t Test). CONCLUSION: In vitreous, HDP-P-GCV as a crystalline formulation was converted to GCV more rapidly than liposomal formulation of HDP-P-GCV. Vitreous cells may play an important role in the metabolism of either formulation of HDP-P-GCV delivered into vitreous.

Treatment or prevention of herpes simplex virus retinitis with intravitreally injectable crystalline 1-O-hexadecylpropanediol-3-phospho-ganciclovir.

PURPOSE: To evaluate an intraocular drug delivery system consisting of the crystalline ammonium salt of 1-O-hexadecylpropanediol-3-phospho-ganciclovir (HDP-P-GCV) as a slow-release form of the drug. METHODS: A dosage of 0.885, 1.57, 2.8, 4.486, or 8.85 micromol of ammonium salt HDP-P-GCV in 0.1 mL was intravitreally injected into rabbit vitreous. The toxicity and safety were evaluated with ophthalmoscopy, electroretinography, and pathology. Drug vitreous levels were determined at various time intervals by means of HPLC. The treatment efficacy and duration of efficacy were tested in a herpes simplex virus (HSV)-1 retinitis rabbit model. RESULTS: Intravitreal injections of the compound revealed clear vitreous of optic axis, a desirable drug depot in the inferior vitreous cavity, and no clinical toxicity, except for variable mild local posterior subcapsular cataract and local retinal toxicity with high doses. HPLC analysis showed free ammonium salt of HDP-P-GCV in the upper vitreous at a level of 0.2 microM 12 weeks after the 2.8-micromol initial intravitreal dose. Drug concentration was still 1.95 microM 20 weeks after the 8.85-micromol initial intravitreal dose. These concentrations (0.2 and 1.95 microM) were 10 and 100 times higher, respectively, than the median inhibitory concentration (IC(50)) of HSV-1 (0.023 microM). Treatment with the highest nontoxic dose (2.8 micromol) and the highest dose (8.85 micromol) showed significant protection from HSV-1 infection (P < 0.05) and provided sustained antiviral effect after a single intravitreal drug injection. CONCLUSIONS: The crystalline ammonium salt of HDP-P-GCV may be a very useful local therapy for herpes family viral retinitis.