Abstract 2456: Discovery of orally active 4-amino-6-arylaminopyrimidine-5-carbaldehyde oximes with dual EGFR and HER2 inhibitory activity

Growth factor receptors of the ErbB family, especially ErbB1 (EGFR) and ErbB2 (HER2), have attracted considerable attention in recent years as therapeutic targets for the treatment of numerous malignancies including cancers of the lung, colon, and breast, either through blockade of the extracellular ligand binding site by monoclonal antibodies (e.g. anti-EGFR antibodies cetuximab and panitumumab, and anti-HER2 antibody trastuzumab) or inhibition of the intracellular tyrosine kinase domain by small molecule inhibitors (e.g. EGFR kinase inhibitors gefitinib and erlotinib, and dual EGFR/HER2 inhibitor lapatinib). The abundance of small molecule kinase inhibitors in clinical development or on the market attests to the acceptance of ErbB inhibition as a clinically relevant paradigm. Nevertheless, the emergence of resistance mechanisms in ErbB driven or dependent tumors indicates that continued research is required to discover more effective drugs. We previously reported the discovery of JNJ-28871063, a potent inhibitor of EGFR and HER2 kinases in vitro that also showed excellent antitumor efficacy in EGFR (A431 epidermoid carcinoma) and HER2 (N87 gastric carcinoma) overexpressing xenograft models and significant extension of survival in a mouse intracranial tumor model. This compound is a 4-amino-6-arylaminopyrimidine-5-carbaldehyde oxime, a monocyclic chemotype that mimics the traditional bicyclic quinazoline scaffold via an intramolecular hydrogen-bonded pseudocycle involving the adjacent 4-amino and 5-oximino groups. In this study, we present results of a structure-guided analog program designed to optimize in vitro kinase potency and in vivo antitumor efficacy of the pyrimidine-oximes. While substituents on the 6-arylamino group are critical for ErbB inhibitory potency and kinase selectivity, substitution on the oxime oxygen may be changed to modify physico-chemical properties and bioavailability. We will discuss structure-activity relationships for the 5-oximino and 6-arylamino groups as well as the important role played by O-aminoalkyl oxime substituents in improving in vivo activity.

Citation Format: Peter J. Connolly, Mary Adams, Amanda K. Beck, Stuart L. Emanuel, Angel R. Fuentes-Pesquera, Lee M. Greenberger, Robert H. Gruninger, Terry V. Hughes, Stephen A. Middleton, Sandra Moreno-Mazza, Niranjan Pandey, Steven K. Wetter, Guozhang Xu. Discovery of orally active 4-amino-6-arylaminopyrimidine-5-carbaldehyde oximes with dual EGFR and HER2 inhibitory activity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2456. doi:10.1158/1538-7445.AM2013-2456

Discovery of novel 4-amino-6-arylaminopyrimidine-5-carbaldehyde oximes as dual inhibitors of EGFR and ErbB-2 protein tyrosine kinases

We herein disclose a novel series of 4-aminopyrimidine-5-carbaldehyde oximes that are potent and selective inhibitors of both EGFR and ErbB-2 tyrosine kinases, with IC(50) values in the nanomolar range. Structure-activity relationship (SAR) studies elucidated a critical role for the 4-amino and C-6 arylamino moieties. The X-ray co-crystal structure of EGFR with 37 was determined and validated our design rationale.

Cellular and in vivo activity of JNJ-28871063, a nonquinazoline pan-ErbB kinase inhibitor that crosses the blood-brain barrier and displays efficacy against intracranial tumors

JNJ-28871063 is a potent and highly selective pan-ErbB kinase inhibitor from a novel aminopyrimidine oxime structural class that blocks the proliferation of epidermal growth factor receptor (EGFR; ErbB1)- and ErbB2-overexpressing cells but does not affect the growth of non-ErbB-overexpressing cells. Treatment of human cancer cells with JNJ-28871063 inhibited phosphorylation of functionally important tyrosine residues in both EGFR and ErbB2 and blocked downstream signal transduction pathways responsible for proliferation and survival. A single dose of compound reduced phosphorylation of ErbB2 receptors in tumor-bearing mice, demonstrating target suppression in vivo. Tissue distribution studies show that JNJ-28871063 crosses the blood-brain barrier and penetrates into tumors, where it is able to accumulate to higher levels than those found in the plasma. JNJ-28871063 showed oral antitumor activity in human tumor xenograft models that overexpress EGFR and ErbB2. In an intracranial ErbB2-overexpressing tumor model, JNJ-28871063 extended survival relative to untreated animals. The brain is a primary site of metastasis for EGFR-overexpressing lung cancers and ErbB2-overexpressing breast cancers. Therefore, the ability to penetrate into the brain could be an advantage over existing therapies such as trastuzumab (Herceptin) and cetuximab (Erbitux), which are antibodies and do not cross the blood-brain barrier. These results show that JNJ-28871063 is orally bioavailable, has activity against EGFR and ErbB2-dependent tumor xenografts, and can penetrate into the brain and inhibit ErbB2-overexpressing tumor growth.

4-Aryl-5-cyano-2-aminopyrimidines as VEGF-R2 inhibitors: Synthesis and biological evaluation

A novel series of 4-aryl-5-cyano-2-aminopyrimidines were synthesized and found to have potent VEGF-R2 kinase inhibitory activity. Structure-activity relationships were investigated and compound 14a was shown to be efficacious in a mouse model of corneal neovascularization.

Synthesis and evaluation of pyrazolo[3,4-b]pyridine CDK1 inhibitors as anti-tumor agents

A series of 3,5-disubstituted pyrazolo[3,4-b]pyridine cyclin-dependent kinase (CDK) inhibitors was synthesized. These compounds showed potent and selective CDK inhibitory activities and inhibited in vitro cellular proliferation in cultured human tumor cells. Selected compounds were evaluated in an in vivo tumor xenograft model. The synthesis and biological evaluation of these pyrazolo[3,4-b]pyridines and related compounds are reported.

Synthesis and biological study of 2-amino-4-aryl-5-chloropyrimidine analogues as inhibitors of VEGFR-2 and cyclin dependent kinase 1 (CDK1)

The series of 2-amino-4-aryl-5-chloropyrimidines was discovered to be potent for both VEGFR-2 and CDK1. Described here are the chemistry for analogue synthesis, SAR study, and its kinase selectivity prolifing. The full rat PK data and in vivo efficacy study are also included.

(6,7-Dimethoxy-2,4-dihydroindeno[1,2-c]pyrazol-3-yl)phenylamines: platelet-derived growth factor receptor tyrosine kinase inhibitors with broad antiproliferative activity against tumor cells

A series of (6,7-dimethoxy-2,4-dihydroindeno[1,2-c]pyrazol-3-yl)phenylamines has been optimized to preserve both potent kinase inhibition activity against the angiogenesis target, the receptor tyrosine kinase of Platelet-Derived Growth Factor-BB (PDGF-BB), and to improve the broad tumor cell antiproliferative activity of these compounds. This series culminates in the discovery of 17 (JNJ-10198409), a compound with anti-PDGFR-beta kinase activity (IC(50)=0.0042 microM) and potent antiproliferative activity in six of eight human tumor cell lines (IC(50) < 0.033 microM).

TheIn vitroandIn vivoEffects of JNJ-7706621: A Dual Inhibitor of Cyclin-Dependent Kinases and Aurora Kinases

Modulation of aberrant cell cycle regulation is a potential therapeutic strategy applicable to a wide range of tumor types. JNJ-7706621 is a novel cell cycle inhibitor that showed potent inhibition of several cyclin-dependent kinases (CDK) and Aurora kinases and selectively blocked proliferation of tumor cells of various origins but was about 10-fold less effective at inhibiting normal human cell growth in vitro. In human cancer cells, treatment with JNJ-7706621 inhibited cell growth independent of p53, retinoblastoma, or P-glycoprotein status; activated apoptosis; and reduced colony formation. At low concentrations, JNJ-7706621 slowed the growth of cells and at higher concentrations induced cytotoxicity. Inhibition of CDK1 kinase activity, altered CDK1 phosphorylation status, and interference with downstream substrates such as retinoblastoma were also shown in human tumor cells following drug treatment. Flow cytometric analysis of DNA content showed that JNJ-7706621 delayed progression through G1 and arrested the cell cycle at the G2-M phase. Additional cellular effects due to inhibition of Aurora kinases included endoreduplication and inhibition of histone H3 phosphorylation. In a human tumor xenograft model, several intermittent dosing schedules were identified that produced significant antitumor activity. There was a direct correlation between total cumulative dose given and antitumor effect regardless of the dosing schedule. These results show the therapeutic potential of this novel cell cycle inhibitor and support clinical evaluation of JNJ-7706621.

1-Acyl-1H-[1,2,4]triazole-3,5-diamine analogues as novel and potent anticancer cyclin-dependent kinase inhibitors: synthesis and evaluation of biological activities

A series of 1-acyl-1H-[1,2,4]triazole-3,5-diamine analogues were synthesized as cyclin-dependent kinase (CDK) inhibitors. These compounds showed potent and selective CDK1 and CDK2 inhibitory activities and inhibited in vitro cellular proliferation in various human tumor cells. Representative compound 3b demonstrated in vivo efficacy in a human melanoma A375 xenograft model in nude mice.

Synthesis and identification of [1,3,5]triazine-pyridine biheteroaryl as a novel series of potent cyclin-dependent kinase inhibitors

On the basis of previous studies, we identified pyrazine-pyridine A as a potent vascular endothelial growth factor inhibitor and pyrimidine-pyridine B as a moderately potent cyclin dependent kinase (CDK) inhibitor. A proposed combination of CGP-60474 and compound B led to the discovery of [1,3,5]triazine-pyridine as a new series of potent CDK inhibitors. Palladium-catalyzed C-C bond formation reactions, particularly the Negishi coupling reaction, were used to assemble various triazine-heteroaryl analogues effectively. Among them, compound 20 displayed high inhibitory potency at CDK1 (IC(50) = 0.021 microM), CDK2, and CDK5 and submicromolar potency at CDK4, CDK6, and CDK7. Compound 20 also displayed high potency at GSK-3beta. It demonstrated potent antiproliferative activity on various tumor cell lines, including HeLa, HCT-116, U937, and A375. When 20 was administered intraperitoneally at 150 and 125 mg/kg to nude mice bearing human A375 xenografts, the compound produced a significant survival increase. Molecular docking studies were conducted in an attempt to enhance the understanding of the observed structure-activity relationship.

Synthesis and Structure−Activity Relationships of Pyrazine-Pyridine Biheteroaryls as Novel, Potent, and Selective Vascular Endothelial Growth Factor Receptor-2 Inhibitors

There is much evidence that direct inhibition of the kinase activity of vascular endothelial growth factor receptor-2 (VEGFR-2) will result in the reduction of angiogenesis and the suppression of tumor growth. Palladium-catalyzed C-C bond, C-N bond formation reactions were used to assemble various pyrazine-pyridine biheteroaryls as potent VEGFR-2 inhibitors. Among them, 4-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-ylamino}-butan-1-ol (39) and N-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-yl}-N',N'-dimethyl-ethane-1,2-diamine (41) exhibited the highest kinase selectivity against fibroblast growth factor receptor kinase, platelet-derived growth factor receptor kinase, and glycogen synthase kinase-3. All of these compounds showed good cellular potency to inhibit VEGF-stimulated proliferation of human umbilical vein endothelial cells (HUVEC) but with modest effects on the unstimulated growth of HUVEC. The low inhibition of these compounds to the growth of tumor cell lines, such as HeLa, HCT-116, and A375 further confirms that these VEGFR-2 inhibitors are not cytotoxic agents. The in vivo antitumor activity of 39 and 41 were demonstrated in the A375 human melanoma xenograft nude mice model. Molecular modeling (QSAR analysis) was conducted in an attempt to rationalize the observed structure-activity relationship.

Synthesis and discovery of pyrazine-pyridine biheteroaryl as a novel series of potent vascular endothelial growth factor receptor-2 inhibitors

Pathological angiogenesis is associated with disease states such as cancer, diabetic retinopathy, rheumatoid arthritis, endometriosis, and psoriasis. There is much evidence that direct inhibition of the kinase activity of vascular endothelial growth factor receptor-2 (VEGFR-2) will result in the reduction of angiogenesis and the suppression of tumor growth. Attempts to optimize a cyclin-dependent kinase-1 (CDK1) inhibitor by using palladium-catalyzed C-C bond, C-N bond formation reactions to assemble diverse biheteroaryl molecules led to the unexpected discovery of a pyrazine-pyridine biheteroaryl as a novel series of potent VEGFR-2 inhibitors. Compound 15, which had IC(50) = 0.084 microM at VEGFR-2, showed very modest selectivity against fibroblast growth factor receptor-2 (IC(50) = 0.21 microM), platelet-derived growth factor receptor (IC(50) = 0.36 microM), and glycogen synthase kinase-3 (IC(50) = 0.478 microM), while it exhibited more than 10-fold selectivity against epidermal growth factor receptor (IC(50) = 1.36 microM) and insulin-R kinase (IC(50) = 1.69 microM). On the other hand, compound 15 exhibited more than 100-fold selectivity against calmodulin kinase 2; casein kinase-1 and -2; CDK1 and -4; mitogen-activated protein kinase; and protein kinase A, Cbeta2, and Cgamma (IC(50) >10 microM). Compound 15 also displayed high inhibitory potency on VEGF-stimulated human umbilical vein endothelial cell (HUVEC) proliferation (IC(50) = 0.005 microM) and good selectivity against cell lines such as HUVEC, human aortic smooth muscle cells, and MRC5 lung fibroblasts. Molecular docking studies were conducted in an attempt to rationalize the unexpected high VEGFR-2 selectivity of 15.

3-Acyl-2,6-diaminopyridines as cyclin-dependent kinase inhibitors: synthesis and biological evaluation

A novel series of 2,6-diamino-3-acylpyridines were designed and synthesized as cyclin-dependent kinase (CDK) inhibitors. The representative compounds 2r and 11 showed potent CDK1 and CDK2 inhibitory activities and inhibited cellular proliferation in HeLa, HCT116, and A375 tumor cells.

A Vascular Endothelial Growth Factor Receptor-2 Kinase Inhibitor Potentiates the Activity of the Conventional Chemotherapeutic Agents Paclitaxel and Doxorubicin in Tumor Xenograft Models

Inhibition of angiogenesis may have wide use in the treatment of cancer; however, this approach alone will not cause tumor regression but may only slow the growth of solid tumors. The clinical potential of antiangiogenic agents may be increased by combining them with conventional chemotherapeutics. 4-[4-(1-Amino-1-methylethyl)phenyl]-2-[4-(2-morpholin-4-yl-ethyl)phenylamino]pyrimidine-5-carbonitrile (JNJ-17029259) represents a novel structural class of 5-cyanopyrimidines that are orally available, selective, nanomolar inhibitors of the vascular endothelial growth factor receptor-2 (VEGF-R2) and other tyrosine kinases involved in angiogenesis, such as platelet-derived growth factor receptor, fibroblast growth factor receptor, VEGF-R1, and VEGF-R3, but have little activity on other kinase families. At nanomolar levels, JNJ-17029259 blocks VEGF-stimulated mitogen-activated protein kinase signaling, proliferation/migration, and VEGF-R2 phosphorylation in human endothelial cells; inhibits the formation of vascular sprouting in the rat aortic ring model of angiogenesis; and interferes with the development of new veins and arteries in the chorioallantoic membrane assay. At higher concentrations of 1 to 3 microM, this compound shows antiproliferative activity on cells that may contribute to its antitumor effects. JNJ-17029259 delays the growth of a wide range of human tumor xenografts in nude mice when administered orally as single-agent therapy. Histological examination revealed that the tumors have evidence of reduced vascularity after treatment. In addition, JNJ-17029259 enhances the effects of the conventional chemotherapeutic drugs doxorubicin and paclitaxel in xenograft models when administered orally in combination therapy. An orally available angiogenesis inhibitor that can be used in conjunction with standard chemotherapeutic agents to augment their activity may have therapeutic benefit in stopping the progression of cancer and preventing metastasis.

Mutagenesis studies of the human erythropoietin receptor. Establishment of structure-function relationships

Mutagenesis of the erythropoietin receptor (EPOR) permits analysis of the contribution that individual amino acid residues make to erythropoietin (EPO) binding. We employed both random and site-specific mutagenesis to determine the function of amino acid residues in the extracellular domain (referred to as EPO binding protein, EBP) of the EPOR. Residues were chosen for site-specific alanine substitution based on the results of the random mutagenesis or on their homology to residues that are conserved or have been reported to be involved in ligand binding in other receptors of the cytokine receptor family. Site-specific mutants were expressed in Escherichia coli as soluble EBP and analyzed for EPO binding in several different assay formats. In addition, selected mutant proteins were expressed as full-length EPOR on the surface of COS cells and analyzed for 125I-EPO binding in receptor binding assays. Using these methods, we have identified residues that appear to be involved in EPO binding as well as other residues, most of which are conserved in receptors of the cytokine receptor family, that appear to be necessary for the proper folding and/or stability of the EPOR. We present correlations between these mutagenesis data and the recently solved crystal structure of the EBP with a peptide ligand.

Identification of a critical ligand binding determinant of the human erythropoietin receptor. Evidence for common ligand binding motifs in the cytokine receptor family

The erythropoietin receptor (EPOR) is a member of a family of cytokine and growth factor receptors that share conserved features in their extracellular and cytoplasmic domains. We have used site-specific mutagenesis within the extracellular domain of the EPOR to search for amino acid residues involved in erythropoietin (EPO) binding. Mutant proteins were expressed in bacteria as soluble EPO binding proteins (EBP) and characterized for EPO binding activity in a number of different assays. Substitution of phenylalanine at position 93 (Phe93) with alanine (F93A mutation) resulted in a drastic reduction in EPO binding in the EBP. More conservative tyrosine or tryptophan substitutions at Phe93 resulted in much less dramatic effects on EPO binding. Biophysical studies indicated that the F93A mutation does not result in gross structural alterations in the EBP. Furthermore, the F93A mutation in full-length EPOR expressed in COS cells abolished detectable EPO binding. This was not a result of processing or transport defects, since mutant receptor was present on the surface of the cells. Mutations in the region immediately around Phe93 and in residues homologous to other reported ligand binding determinants of the cytokine receptor family had small to moderate effects on EPO binding. These data indicate that Phe93 is a critical EPO binding determinant of the EPOR. Furthermore, since Phe93 aligns with critical ligand binding determinants in other receptors of the cytokine receptor family, these data suggest that receptors of this family may use common structural motifs to bind their cognate ligands.

Erythropoietin receptor: application in drug development

Erythropoietin (EPO) is the primary hormone responsible for the growth and maturation of red blood cells in mammals. In contrast to many other growth factors, the specificity of EPO for mature erythroid cells has lead to its development as a safe and efficacious therapeutic, EPREX. The medical benefits of EPREX have been well established in the treatment of anaemic chronic renal failure patients, anaemic HIV patients treated with AZT, cancer chemotherapy patients, and patients wishing to donate their own blood prior to elective surgery (autologous predonation). Due to the chronic nature of EPO therapy, it would be desirable to have an orally administered 'second generation' molecule. An understanding of the structural basis of the interaction of EPO with its receptor will aid in the design of an oral anaemia drug. In this study, a series of mutations have been generated in a truncated form of the receptor comprising the extracellular region, termed EPO binding protein (EBP). One mutant, in which alanine replaces phenylalanine at position 93 (F93A) has a 500-fold reduction in binding compared to wild-type EBP. A neutralizing anti-EBP antibody binds poorly to the F93A mutant, while a non-neutralizing anti-EBP antibody binds wild-type and F93A equally well. Information from this mutational analysis can be applied to a receptor 3-D model and ultimately used in drug development.

Erythropoietin structure-function relationships: high degree of sequence homology among mammals

To investigate structure-function relationships of erythropoietin (Epo), we have obtained cDNA sequences that encode the mature Epo protein of a variety of mammals. A first set of primers, corresponding to conserved nucleotide sequences between mouse and human DNAs, allowed us to amplify by polymerase chain reaction (PCR) intron 1/exon 2 fragments from genomic DNA of the hamster, cat, lion, dog, horse, sheep, dolphin, and pig. Sequencing of these fragments permitted the design of a second generation of species-specific primers. RNA was prepared from anemic kidneys and reverse-transcribed. Using our battery of species-specific 5' primers, we were able to successfully PCR-amplify Epo cDNA from Rhesus monkey, rat, sheep, dog, cat, and pig. Deduced amino acid sequences of mature Epo proteins from these animals, in combination with known sequences for human, Cynomolgus monkey, and mouse, showed a high degree of homology, which explains the biologic and immunological cross-reactivity that has been observed in a number of species. Human Epo is 91% identical to monkey Epo, 85% to cat and dog Epo, and 80% to 82% to pig, sheep, mouse, and rat Epos. There was full conservation of (1) the disulfide bridge linking the NH2 and COOH termini; (2) N-glycosylation sites; and (3) predicted amphipathic alpha-helices. In contrast, the short disulfide bridge (C29/C33 in humans) is not invariant. Cys33 was replaced by a Pro in rodents. Most of the amino acid replacements were conservative. The C-terminal part of the loop between the C and D helices showed the most variation, with several amino acid substitutions, deletions, and/or insertions. Calculations of maximum parsimony for intron 1/exon 2 sequences as well as coding sequences enabled the construction of cladograms that are in good agreement with known phylogenetic relationships.