3-amino-benzo[d]isoxazoles as novel multitargeted inhibitors of receptor tyrosine kinases.

A series of benzoisoxazoles and benzoisothiazoles have been synthesized and evaluated as inhibitors of receptor tyrosine kinases (RTKs). Structure-activity relationship studies led to the identification of 3-amino benzo[ d]isoxazoles, incorporating a N, N'-diphenyl urea moiety at the 4-position that potently inhibited both the vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor families of RTKs. Within this series, orally bioavailable compounds possessing promising pharmacokinetic profiles were identified, and a number of compounds demonstrated in vivo efficacy in models of VEGF-stimulated vascular permeability and tumor growth. In particular, compound 50 exhibited an ED 50 of 2.0 mg/kg in the VEGF-stimulated uterine edema model and 81% inhibition in the human fibrosarcoma (HT1080) tumor growth model when given orally at a dose of 10 mg/kg/day.

Discovery of N-(4-(3-amino-1H-indazol-4-yl)phenyl)-N'-(2-fluoro-5-methylphenyl)urea (ABT-869), a 3-aminoindazole-based orally active multitargeted receptor tyrosine kinase inhibitor.

In our continued efforts to search for potent and novel receptor tyrosine kinase (RTK) inhibitors as potential anticancer agents, we discovered, through a structure-based design, that 3-aminoindazole could serve as an efficient hinge-binding template for kinase inhibitors. By incorporating an N,N'-diaryl urea moiety at the C4-position of 3-aminodazole, a series of RTK inhibitors were generated, which potently inhibited the tyrosine kinase activity of the vascular endothelial growth factor receptor and the platelet-derived growth factor receptor families. A number of compounds with potent oral activity were identified by utilizing an estradiol-induced mouse uterine edema model and an HT1080 human fibrosarcoma xenograft tumor model. In particular, compound 17p (ABT-869) was found to possess favorable pharmacokinetic profiles across different species and display significant tumor growth inhibition in multiple preclinical animal models.

1,4-Dihydroindeno[1,2-c]pyrazoles with acetylenic side chains as novel and potent multitargeted receptor tyrosine kinase inhibitors with low affinity for the hERG ion channel.

The synthesis of a novel series of 1,4-dihydroindeno[1,2-c]pyrazoles with acetylene-type side chains is described. Optimization of those compounds as KDR kinase inhibitors identified 8, which displayed an oral activity in an estradiol-induced murine uterine edema model (ED50 = 3 mg/kg) superior to Sutent (ED50 = 9 mg/kg) and showed potent antitumor efficacy in an MX-1 human breast carcinoma xenograft tumor growth model (tumor growth inhibition = 90% at 25 mg/kg.day po). The compound was docked into a homology model of the homo-tetrameric pore domain of the hERG potassium channel to identify strategies to improve its cardiac safety profile. Systematic interruption of key binding interactions between 8 and Phe656, Tyr652, and Ser624 yielded 90, which only showed an IC50 of 11.6 microM in the hERG patch clamp assay. The selectivity profile for 8 and 90 revealed that both compounds are multitargeted receptor tyrosine kinase inhibitors with low nanomolar potencies against the members of the VEGFR and PDGFR kinase subfamilies.

Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor.

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC50 = 4 nmol/L) but has much less activity (IC50s > 1 micromol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC50 = 2, 4, and 7 nmol/L for PDGFR-beta, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC50 = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED50 = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED50 = 1.5-5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC50 corrected for plasma protein binding = 0.08 microg/mL, >or=7 hours) than with plasma area under the curve or Cmax. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer.

Thienopyrimidine ureas as novel and potent multitargeted receptor tyrosine kinase inhibitors.

A series of novel thienopyrimidine-based receptor tyrosine kinase inhibitors has been discovered. Investigation of structure-activity relationships at the 5- and 6-positions of the thienopyrimidine nucleus led to a series of N,N'-diaryl ureas that potently inhibit all of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor tyrosine kinases. A kinase insert domain-containing receptor (KDR) homology model suggests that these compounds bind to the "inactive conformation" of the enzyme with the urea portion extending into the back hydrophobic pocket adjacent to the adenosine 5'-triphosphate (ATP) binding site. A number of compounds have been identified as displaying excellent in vivo potency. In particular, compounds 28 and 76 possess favorable pharmacokinetic (PK) profiles and demonstrate potent antitumor efficacy against the HT1080 human fibrosarcoma xenograft tumor growth model (tumor growth inhibition (TGI) = 75% at 25 mg/kg.day, per os (po)).

Distinct spatiotemporal pattern of CNS lesions revealed by USPIO-enhanced MRI in MOG-induced EAE rats implicates the involvement of spino-olivocerebellar pathways.

USPIO-enhanced MRI allows non-invasive visualization of mononuclear cell infiltration into CNS lesions in MS and EAE. Herein, we show a distinct spatiotemporal pattern of CNS lesions that reveals the involvement of spino-olivocerebellar pathways in MOG-induced EAE rats using USPIO-enhanced MRI. Specifically, lesions of the inferior olives were observed primarily in the acute phase whereas lesions of cerebellum or spinal cord/brainstem were observed during the relapse phase. Further, behavioral deficits observed from these animals are consistent with the functional role of spino-olivocerebellar pathways in coordination and movement. Collectively, our results provide new insights into the pathophysiology of this animal model of MS.

Synthesis and biological evaluation of 5-substituted 1,4-dihydroindeno[1,2-c]pyrazoles as multitargeted receptor tyrosine kinase inhibitors.

We report the synthesis and biological evaluation of 5-substituted 1,4-dihydroindeno[1,2-c]pyrazoles as multitargeted kinase inhibitors. Initial efforts focused on the development of selective KDR inhibitors, while later strategies involved the improvement of potency toward multiple kinase targets. Thus, several compounds were identified as potent KDR, Flt1, Flt3, and c-Kit inhibitors.

Thienopyridine urea inhibitors of KDR kinase.

A series of substituted thienopyridine ureas was prepared and evaluated for enzymatic and cellular inhibition of KDR kinase activity. Several of these analogs, such as 2, are potent inhibitors of KDR (<10 nM) in both enzymatic and cellular assays. Further characterization of inhibitor 2 indicated that this analog possessed excellent in vivo potency (ED50 2.1 mg/kg) as measured in an estradiol-induced mouse uterine edema model.

1,4-Dihydroindeno[1,2-c]pyrazoles as novel multitargeted receptor tyrosine kinase inhibitors.

A series of 1,4-dihydroindeno[1,2-c]pyrazoles with a 3-thiophene substituent carrying a urea-type side chain were identified as potent multitargeted (VEGFR and PDGFR families) receptor tyrosine kinase inhibitors. A KDR homology model suggested that the urea moiety is able to interact with a recognition motif in the hydrophobic specificity pocket of the enzyme.

Isothiazolopyrimidines and isoxazolopyrimidines as novel multi-targeted inhibitors of receptor tyrosine kinases.

A series of isothiazolopyrimidines and isoxazolopyrimidines were synthesized and identified as potent KDR inhibitors. SAR studies led to isothiazolopyrimidine urea analogs that potently inhibit VEGFR tyrosine kinases (KDR enzymatic and cellular IC(50) values below 10 nM) as well as cKIT and TIE2. The selected compounds 8 and 13 display 56% and 48% oral bioavailability in mice, respectively.

Hit-to-lead optimization of 1,4-dihydroindeno[1,2-c]pyrazoles as a novel class of KDR kinase inhibitors.

A series of 1,4-dihydroindeno[1,2-c]pyrazoles was prepared and evaluated for their enzymatic inhibition of KDR kinase. Computer modeling studies revealed the importance of attaching a basic side chain in predicting the binding mode of those compounds. Further investigation of structure-activity relationships led to 19, a lead compound with an acceptable selectivity profile, activity in whole cells, and good oral efficacy in an estradiol-induced murine uterine edema model of VEGF activity.

Isoindolinone ureas: a novel class of KDR kinase inhibitors.

A series of substituted isoindolinone ureas was prepared and evaluated for enzymatic and cellular inhibition of KDR kinase activity. Several of these analogs, such as 14c, are potent inhibitors of KDR both enzymatically (< 50 nM) and cellularly < or = 100 nM). A 3D KDR/CDK2/MAP kinase overlay model with several structurally related tyrosine kinase inhibitors was used to predict the binding interactions of the isoindolinone ureas with the KDR active site.