Osteogenic effects of a potent Src-over-Abl-selective kinase inhibitor in the mouse.

Src-null mice have higher bone mass because of decreased bone resorption and increased bone formation, whereas Abl-null mice are osteopenic, because of decreased bone formation. Compound I, a potent inhibitor of Src in an isolated enzyme assay (IC(50) 0.55 nM) and a Src-dependent cell growth assay, with lower activity on equivalent Abl-based assays, potently, but biphasically, accelerated differentiation of human mesenchymal stem cells to an osteoblast phenotype (1-10 nM). Compound I (≥0.1 nM) also activated osteoblasts and induced bone formation in isolated neonatal mouse calvariae. Compound I required higher concentrations (100 nM) to inhibit differentiation and activity of osteoclasts. Transcriptional profiling (TxP) of calvaria treated with 1 µM compound I revealed down-regulation of osteoclastic genes and up-regulation of matrix genes and genes associated with the osteoblast phenotype, confirming compound I's dual effects on bone resorption and formation. In addition, calvarial TxP implicated calcitonin-related polypeptide, ß (ß-CGRP) as a potential mediator of compound I's osteogenic effect. In vivo, compound I (1 mg/kg s.c.) increased vertebral trabecular bone volume 21% (microcomputed tomography) in intact female mice. Increased trabecular volume was also detected histologically in a separate bone, the femur, particularly in the secondary spongiosa (100% increase), which underwent a 171% increase in bone formation rate, a 73% increase in mineralizing surface, and a 59% increase in mineral apposition rate. Similar effects were observed in ovariectomized mice with established osteopenia. We conclude that the Src inhibitor compound I is osteogenic, presumably because of its potent stimulation of osteoblast differentiation and activation, possibly mediated by ß-CGRP.

Discovery of a stable macrocyclic o-aminobenzamide Hsp90 inhibitor which significantly decreases tumor volume in a mouse xenograft model.

An extension of our previously reported series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. Addition of a second methyl group to the tether provided analogs that show increased potency in binding as well as cell-proliferation assays and, more importantly, are stable toward microsomes. We wish to disclose the discovery of a macrocycle which showed impressive biomarker activity 24-h post dosing and which demonstrated prolonged exposure in tumors. When studied in a lung cancer xenograft model, the compound demonstrated significant tumor size reduction.

Discovery of a macrocyclic o-aminobenzamide Hsp90 inhibitor with heterocyclic tether that shows extended biomarker activity and in vivo efficacy in a mouse xenograft model.

A novel series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. In continuation of our research, heterocycle-containing tethers were explored with the intent to further improve potency and minimize hERG liabilities. This effort culminated in the discovery of compound 10, which efficiently suppressed proliferation of HCT116 and U87 cells. This compound showed prolonged Hsp90-inhibitory activity at least 24h post-administration consistent with elevated and prolonged exposure in the tumor. When studied in a xenograft model, the compound demonstrated significant suppression of tumor growth.

Macrocyclic lactams as potent Hsp90 inhibitors with excellent tumor exposure and extended biomarker activity.

A novel series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. In continuation of our research in this area, macrocyclic amides and lactams were explored to reduce the risk of hERG liabilities. This effort culminated in the discovery of compound 38, which showed a favorable in vitro profile, and efficiently suppressed proliferation of several relevant cell lines. This compound showed prolonged Hsp90-inhibitory activity at least 24 h post-administration, consistent with elevated and prolonged exposure in the tumor.

Design and SAR of macrocyclic Hsp90 inhibitors with increased metabolic stability and potent cell-proliferation activity.

A novel series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. A basic nitrogen within the tether linking the aniline nitrogen atom to a tetrahydroindolone moiety allowed access to compounds with good physical properties. Important structure-activity relationship information was obtained from this series which led to the discovery of a soluble and stable compound which is potent in an Hsp90 binding and cell-proliferation assay.

A cell-based screen for inhibitors of protein folding and degradation.

Cancer cells are exposed to external and internal stresses by virtue of their unrestrained growth, hostile microenvironment, and increased mutation rate. These stresses impose a burden on protein folding and degradation pathways and suggest a route for therapeutic intervention in cancer. Proteasome and Hsp90 inhibitors are in clinical trials and a 20S proteasome inhibitor, Velcade, is an approved drug. Other points of intervention in the folding and degradation pathway may therefore be of interest. We describe a simple screen for inhibitors of protein synthesis, folding, and proteasomal degradation pathways in this paper. The molecular chaperone-dependent client v-Src was fused to firefly luciferase and expressed in HCT-116 colorectal tumor cells. Both luciferase and protein tyrosine kinase activity were preserved in cells expressing this fusion construct. Exposing these cells to the Hsp90 inhibitor geldanamycin caused a rapid reduction of luciferase and kinase activities and depletion of detergent-soluble v-Src::luciferase fusion protein. Hsp70 knockdown reduced v-Src::luciferase activity and, when combined with geldanamycin, caused a buildup of v-Src::luciferase and ubiquitinated proteins in a detergent-insoluble fraction. Proteasome inhibitors also decreased luciferase activity and caused a buildup of phosphotyrosine-containing proteins in a detergent-insoluble fraction. Protein synthesis inhibitors also reduced luciferase activity, but had less of an effect on phosphotyrosine levels. In contrast, certain histone deacetylase inhibitors increased luciferase and phosphotyrosine activity. A mass screen led to the identification of Hsp90 inhibitors, ubiquitin pathway inhibitors, inhibitors of Hsp70/Hsp40-mediated refolding, and protein synthesis inhibitors. The largest group of compounds identified in the screen increased luciferase activity, and some of these increase v-Src levels and activity. When used in conjunction with appropriate secondary assays, this screen is a powerful cell-based tool for studying compounds that affect protein synthesis, folding, and degradation.

Optimization of 7-alkene-3-quinolinecarbonitriles as Src kinase inhibitors.

The 7-alkene-3-quinolinecarbonitrile 20, a potent inhibitor of Src enzymatic and cellular activity with IC(50) values of 2.1 and 58 nM, respectively, had comparable efficacy to bosutinib in a colon tumor xenograft study.

4-Anilino-7-pyridyl-3-quinolinecarbonitriles as Src kinase inhibitors.

A series of 4-anilino-7-pyridyl-3-quinolinecarbonitriles was prepared as Src kinase inhibitors. A systematic SAR study of substitutions on both the pyridine ring and the 3-quinolinecarbonitrile core established the requirements for optimal activity. The lead compound, 17, showed potent activity in both the Src enzyme assay and cell assays, and demonstrated in vivo anti-tumor activity in a xenograft model.

Discovery of benzisoxazoles as potent inhibitors of chaperone heat shock protein 90.

Heat shock protein 90 (Hsp90) is a molecular chaperone that is responsible for activating many signaling proteins and is a promising target in tumor biology. We have identified small-molecule benzisoxazole derivatives as Hsp90 inhibitors. Crystallographic studies show that these compounds bind in the ATP binding pocket interacting with the Asp93. Structure based optimization led to the identification of potent analogues, such as 13, with good biochemical profiles.

Facile preparation of new 4-phenylamino-3-quinolinecarbonitrile Src kinase inhibitors via 7-fluoro intermediates: identification of potent 7-amino analogs.

A more efficient preparation of 4-[(2,4-dichloro-5-methoxyphenyl)amino]-7-fluoro-6-methoxy-3-quinolinecarbonitrile (2), the penultimate intermediate in the synthesis of bosutinib (1a), was developed. New 7-alkoxy-4-phenylamino-3-quinolinecarbonitrile Src inhibitors were prepared from 5 and 9, the 6-ethoxy and 6-hydrogen analogs of 2. In addition, the fluoro group of 2 was readily displaced by primary and secondary amines to give 7-amino analogs. Two of these 7-amino analogs, 15 and 18, were potent Src inhibitors with in vivo activity.

Inhibition of Src kinase activity by 7-ethynyl-4-phenylamino-3-quinolinecarbonitriles: identification of SKS-927.

Of a series of 7-ethynyl-3-quinolinecarbonitriles, the most potent Src inhibitory activity was observed with 4-[(2,4-dichloro-5-methoxyphenyl)amino]-6-methoxy-7-[4-(4-methylpiperazin-1-yl)but-1-ynyl]-3-quinolinecarbonitrile (SKS-927). Variation of the solubilizing amine tail or removal of the methoxy group from either C-6 of the quinoline core or C-5 of the aniline headpiece led to reduced activity.

Synthesis and Src kinase inhibitory activity of a series of 4-[(2,4-dichloro-5-methoxyphenyl)amino]-7-furyl-3-quinolinecarbonitriles.

Compound 1 (SKI-606, bosutinib), a 7-alkoxy-4-[(2,4-dichloro-5-methoxyphenyl)amino]-3-quinolinecarbonitrile, is a potent inhibitor of Src kinase activity. We previously reported that analogs of 1 with thiophene groups at C-7 retained the Src activity of the parent compound. The corresponding C-7 furan analogs were prepared and it was found that the 3,5-substituted furan analog had increased activity compared to that of the 2,5-substituted furan isomer. Addition of a methoxy group at C-6 decreased the Src inhibitory activity of the C-7 2,5-substituted furan analog but increased the activity of the C-7 3,5-substituted furan isomer. This compound, 10, was a more potent Src inhibitor than 1 in both enzymatic and cell-based assays. The kinase selectivity profile of 10 was similar to that of 1, with 10 also inhibiting the activity of Abl and Lck. When tested in a solid tumor xenograft model, 10 had comparable oral activity to that of 1.

7-(aryl/heteroaryl-2-ylethynyl)-4-phenylamino-3-quinolinecarbonitriles as new Src kinase inhibitors: addition of water solubilizing groups.

New 4-phenylamino-3-quinolinecarbonitriles with a 7-ethynyl group substituted by a pyridine, phenyl or thiophene ring containing basic water solubilizing groups were prepared and evaluated as Src kinase inhibitors. Of these new analogs, potent activity was observed with compounds having a (2,4-dichloro-5-methoxyphenyl)amino group at C-4, a methoxy or ethoxy group at C-6, and a pyridyl group bearing a dimethylamine or N-methylpiperazine on the ethynyl group at C-7.

4-Anilino-7,8-dialkoxybenzo[g]quinoline-3-carbonitriles as potent Src kinase inhibitors.

It has been previously reported that appropriately substituted 4-anilinoquinoline-3-carbonitriles are potent inhibitors of Src kinase, with biological activity in vitro and in vivo. Structural modifications to these compounds have been explored, providing the 4-anilinobenzo[g]quinoline-3-carbonitriles as a series with enhanced Src inhibitory properties. The synthesis and structure-activity relationships of these 4-anilino-7,8-dialkoxybenzo[g]quinoline-3-carbonitriles are presented here. Analogues with cyclic basic amine groups attached via ethoxy linkages at the C-8 position were the most active in vitro, with subnanomolar IC50 values against Src kinase observed for a majority of the compounds synthesized. Compound 17d was more potent in vitro than the analogously substituted 4-anilinoquinoline-3-carbonitrile SKI-606, which is undergoing evaluation in clinical trials. The most potent analogue synthesized was 17a, with an IC50 of 0.15 nM against Src kinase and with an IC50 of 10 nM against Src-transformed fibroblasts. Molecular modeling studies provided a rationale for the exceptional activity observed for these compounds, with favorable van der Waals interactions playing the major role. Compound 17c was found to be highly selective for Src kinase when tested against a panel of other kinases, with modest selectivity versus the Src family kinases Lyn and Fyn. Following ip dosing at 50 mg/kg, analogues 17c and 17d were shown to have plasma levels that significantly exceeded the cellular IC50 values against Src-transformed fibroblasts. In an Src-transformed fibroblast xenograft model, both compounds exhibited a significant inhibition of tumor growth.

Inhibition of Src kinase activity by 7-[(2,4-dichloro-5-methoxyphenyl)amino]-2-heteroaryl-thieno[3,2-b]pyridine-6-carbonitriles.

7-[(2,4-Dichloro-5-methoxyphenyl)amino]thieno[3,2-b]pyridine-6-carbonitriles with various heteroaryl groups at C-2 are inhibitors of Src kinase activity. Of these new analogs, compounds substituted at C-2 by a 3,5-furan or a 2,5-pyridine had the best activity in the Src enzyme and cell assays.

SKI-606, a Src/Abl inhibitor with in vivo activity in colon tumor xenograft models.

Src up-regulation is a common event in human cancers. In colorectal cancer, increased Src levels are an indicator of poor prognosis, and progression to metastatic disease is associated with substantial increases in Src activity. Therefore, we examined the activity of SKI-606, a potent inhibitor of Src and Abl kinases, against colon tumor lines in vitro and in s.c. tumor xenograft models. SKI-606 inhibited Src autophosphorylation with an IC(50) of approximately 0.25 micromol/L in HT29 cells. Phosphorylation of Tyr(925) of focal adhesion kinase, a Src substrate, was reduced by similar concentrations of inhibitor. Antiproliferative activity on plastic did not correlate with Src inhibition in either HT29 or Colo205 cells (IC(50)s, 1.5 and 2.5 micromol/L, respectively), although submicromolar concentrations of SKI-606 inhibited HT29 cell colony formation in soft agar. SKI-606 also caused loosely aggregated Colo205 spheroids to condense into compact spheroids. On oral administration to nude mice at the lowest efficacious dose, peak plasma concentrations of approximately 3 micromol/L, an oral bioavailability of 18%, and a t(1/2) of 8.6 hours were observed. SKI-606 was orally active in s.c. colon tumor xenograft models and caused substantial reductions in Src autophosphorylation on Tyr(418) in HT29 and Colo205 tumors. SKI-606 inhibited HT29 tumor growth on once daily administration, whereas twice daily administration was necessary to inhibit Colo205, HCT116, and DLD1 tumor growth. These results support development of SKI-606 as a therapeutic agent for treatment of colorectal cancer.

Synthesis and Src kinase inhibitory activity of 2-phenyl- and 2-thienyl-7-phenylaminothieno[3,2-b]pyridine-6-carbonitriles.

2-phenyl-7-phenylaminothieno[3,2-b]pyridine-6-carbonitriles were recently reported to be inhibitors of Src kinase activity. In this study we present structure-activity relationships for additional thieno[3,2-b]pyridine-6-carbonitriles, modifying the substituents on the C-2 phenyl and C-7 phenylamino groups. Derivatives with various aminomethyl and aminoethyl substituents on the para position of the C-2 phenyl group retained the activity of the initial analogues. However, direct attachment of an amino group led to decreased activity. A 2,4-dichloro-5-methoxyphenylamino group at C-7 provided superior inhibition of Src enzymatic activity. Replacement of the C-2 phenyl group with a 3,5-substituted thiophene led to improved Src inhibitory activity compared to the parent compound, but other thiophene isomers were less active. One of the analogues reported here exhibited in vivo activity comparable to that of SKI-606, a related 3-quinolinecarbonitrile currently in clinical trials.

Further studies on ethenyl and ethynyl-4-phenylamino-3-quinolinecarbonitriles: identification of a subnanomolar Src kinase inhibitor.

Several new ethynyl- and ethenyl-4-phenylamino-3-quinolinecarbonitriles were synthesized and tested for Src inhibition. Derivatives bearing an ethenyl or ethynyl substituent at C-6 showed decreased Src inhibitory activity. Incorporation of an ethenylpyridine N-oxide group at C-7 provided 20b, a 0.6 nM inhibitor of Src enzymatic activity with excellent cellular potency.

Identification of 7-phenylaminothieno- [3,2-b]pyridine-6-carbonitriles as a new class of Src kinase inhibitors.

We disclose here a new class of kinase inhibitors, obtained by replacing the phenyl ring of a 3-quinolinecarbonitrile system with a thiophene ring. When suitably substituted, the resultant 7-phenylaminothieno[3,2-b]pyridine-6-carbonitrile analogues show potent inhibition of Src kinase activity.

Synthesis and inhibition of Src kinase activity by 7-ethenyl and 7-ethynyl-4-anilino-3-quinolinecarbonitriles.

A series of 7-ethynyl and 7-ethenyl-4-anilino-3-quinolinecarbonitriles were synthesized and tested for Src inhibition. Derivatives bearing a C-6 methoxy group and 2,4-dichloro-5-methoxyaniline at C-4 showed optimal inhibition of Src enzymatic and cellular activity. The ethenyl and ethynyl groups were incorporated at C-7 utilizing a Stille, Heck, or Sonogashira coupling reaction.