7-(2-Anilinopyrimidin-4-yl)-1-benzazepin-2-ones Designed by a "Cut and Glue" Strategy Are Dual Aurora A/VEGF-R Kinase Inhibitors.

Although overexpression and hyperactivity of protein kinases are causative for a wide range of human cancers, protein kinase inhibitors currently approved as cancer drugs address only a limited number of these enzymes. To identify new chemotypes addressing alternative protein kinases, the basic structure of a known PLK1/VEGF-R2 inhibitor class was formally dissected and reassembled. The resulting 7-(2-anilinopyrimidin-4-yl)-1-benzazepin-2-ones were synthesized and proved to be dual inhibitors of Aurora A kinase and VEGF receptor kinases. Crystal structures of two representatives of the new chemotype in complex with Aurora A showed the ligand orientation in the ATP binding pocket and provided the basis for rational structural modifications. Congeners with attached sulfamide substituents retained Aurora A inhibitory activity. In vitro screening of two members of the new kinase inhibitor family against the cancer cell line panel of the National Cancer Institute (NCI) showed antiproliferative activity in the single-digit micromolar concentration range in the majority of the cell lines.

Novel Protein Kinase Inhibitors Related to Tau Pathology Modulate Tau Protein-Self Interaction Using a Luciferase Complementation Assay.

The current number of drugs available for the treatment of Alzheimer's disease (AD) is strongly limited and their benefit for therapy is given only in the early state of the disease. An effective therapy should affect those processes which mainly contribute to the neuronal decay. There have been many approaches for a reduction of toxic Aß peptides which mostly failed to halt cognitive deterioration in patients. The formation of neurofibrillary tangles (NFT) and its precursor tau oligomers have been suggested as main cause of neuronal degeneration because of a direct correlation of their density to the degree of dementia. Reducing of tau aggregation may be a viable approach for the treatment of AD. NFT consist of hyperphosphorylated tau protein and tau hyperphosphorylation reduces microtubule binding. Several protein kinases are discussed to be involved in tau hyperphosphorylation. We developed novel inhibitors of three protein kinases (gsk-3ß, cdk5, and cdk1) and discussed their activity in relation to tau phosphorylation and on tau⁻tau interaction as a nucleation stage of a tau aggregation in cells. Strongest effects were observed for those inhibitors with effects on all the three kinases with emphasis on gsk-3ß in nanomolar ranges.

Bioactive pyrrole alkaloids isolated from the Red Sea: marine sponge Stylissa carteri.

Fifteen pyrrole alkaloids were isolated from the Red Sea marine sponge Stylissa carteri and investigated for their biological activities. Four of them were dibrominated [(+) dibromophakelline, Z-3-bromohymenialdisine, (±) ageliferin and 3,4-dibromo-1H-pyrrole-2-carbamide], nine compounds were monobrominated [(-) clathramide C, agelongine, (+) manzacidin A, (-) 3-bromomanzacidin D, Z-spongiacidin D, Z-hymenialdisine, 2-debromostevensine, 2-bromoaldisine and 4-bromo-1H-pyrrole-2-carbamide)] and finally, two compounds were non-brominated derivatives viz., E-debromohymenialdisine and aldisine. The structure elucidations of isolated compounds were based on 1D & 2D NMR spectroscopic and MS studies, as well as by comparison with literature. In-vitro, Z-spongiacidin D exhibited a moderate activity on (ARK5, CDK2-CycA, CDK4/CycD1, VEGF-R2, SAK and PDGFR-beta) protein kinases. Moreover, Z-3-bromohymenialdisine showed nearly similar pattern. Furthermore, Z-hymenialdisine displayed a moderate effect on (ARK5 & VEGF-R2) and (-) clathramide C showed a moderate activity on AURORA-A protein kinases. While, agelongine, (+) manzacidin A, E-debromohymenialdisine and 3,4-dibromo-1H-pyrrole-2-carbamide demonstrated only marginal inhibitory activities. The cytotoxicity study was evaluated in two different cell lines. The most effective secondary metabolites were (+) dibromophakelline and Z-3-bromohymenialdisine on L5178Y. Finally, Z-hymenialdisine, Z-3-bromohymenialdisine and (±) ageliferin exhibited the highest cytotoxic activity on HCT116. No report about inhibition of AURORA-A and B by hymenialdisine/hymenialdisine analogs existed and no reported toxicity of ageliferin existed in literature.

Scaffold hopping identifies 6,8-disubstituted purines as novel anaplastic lymphoma kinase inhibitors.

Rearrangements of anaplastic lymphoma kinase (ALK) are associated with several cancer diseases. Due to resistance development against existing ALK-inhibitors, new, structurally unrelated inhibitors are required. By a scaffold hopping strategy, 6,8-disubstituted purines were designed as analogues of similar ALK-inhibiting thieno[3,2-d]pyrimidines. While the new title compounds indeed inhibited ALK and several ALK mutants in submicromolar concentrations, they retained poor water solubility.

Discovery of novel dual inhibitors of receptor tyrosine kinases EGFR and PDGFR-ß related to anticancer drug resistance.

With ongoing resistance problems against the marketed EGFR inhibitors having a quinazoline core scaffold there is a need for the development of novel inhibitors having a modified scaffold and, thus, expected lower EGFR resistance problems. An additional problem concerning EGFR inhibitor resistance is an observed heterodimerization of EGFR with PDGFR-ß that neutralises the sole inhibitor activity towards EGFR. We developed novel pyrimido[4,5-b]indoles with varied substitution patterns at the 4-anilino residue to evaluate their EGFR and PDGFR-ß inhibiting properties. We identified dual inhibitors of both EGFR and PDGFR-ß in the nanomolar range which have been initially screened in cancer cell lines to prove a benefit of both EGFR and PDGFR-ß inhibition.

Discovery of novel substituted benzo-anellated 4-benzylamino pyrrolopyrimidines as dual EGFR and VEGFR2 inhibitors.

The quinazoline scaffold is the main part of many marketed EGFR inhibitors. Resistance developments against those inhibitors enforced the search for novel structural lead compounds. We developed novel benzo-anellated 4-benzylamine pyrrolopyrimidines with varied substitution patterns at both the molecular scaffold and the attached residue in the 4-position. The structure-dependent affinities towards EGFR are discussed and first nanomolar derivatives have been identified. Docking studies were carried out for EGFR in order to explore the potential binding mode of the novel inhibitors. As the receptor tyrosine kinase VEGFR2 recently gained an increasing interest as an upregulated signaling kinase in many solid tumors and in tumor metastasis we determined the affinity of our compounds to inhibit VEGFR2. So we identified novel dually acting EGFR and VEGFR2 inhibitors for which first anticancer screening data are reported. Those data indicate a stronger antiproliferative effect of a VEGFR2 inhibition compared to the EGFR inhibition.

Discovery of novel dual inhibitors of receptor tyrosine kinases EGFR and IGF-1R.

Novel 4-benzylamino benzo-anellated pyrrolo[2,3-b]pyridines have been synthesized with varied substitution patterns both at the molecular scaffold of the benzo-anellated ring and at the 4-benzylamino residue. With a structural similarity to substituted thieno[2,3-d]pyrimidines as epidermal growth factor receptor (EGFR) inhibitors, we characterized the inhibition of EGFR for our novel compounds. As receptor heterodimerization gained certain interest as mechanism of cancer cells to become resistant against novel protein kinase inhibitors, we additionally measured the inhibition of insulin-like growth factor receptor IGF-1R which is a prominent receptor for such heterodimerizations with EGFR. Structure-activity relationships are discussed for both kinase inhibitions depending on the varied substitution patterns. We discovered novel dual inhibitors of both receptor tyrosine kinases with interest for further studies to reduce inhibitor resistance developments in cancer treatment.

Cytotoxic effects of the anthraquinone derivatives 1'-deoxyrhodoptilometrin and (S)-(-)-rhodoptilometrin isolated from the marine echinoderm Comanthus sp.

We investigated cytotoxic effects of the anthraquinone derivatives 1'-deoxyrhodoptilometrin (SE11) and (S)-(-)-rhodoptilometrin (SE16) isolated from the marine echinoderm Comanthus sp. in two tumor cell lines (C6 glioma, Hct116 colon carcinoma). Both compounds showed cytotoxic effects, with SE11 [IC50-value (MTT assay): 13.1 µM in Hct116 cells] showing a higher potency to induce apoptotic and necrotic cell death. No generation of oxidative stress was detectable (DCF assay), and also no modulation of Nrf2/ARE and NFκB signaling could be shown. Investigation of 23 protein kinases associated with cell proliferation, survival, metastasis, and angiogenesis showed that both compounds were potent inhibitors of distinct kinases, e.g., IGF1-receptor kinase, focal adhesion kinase, and EGF receptor kinase with SE11 being a more potent compound (IC50 values: 5, 18.4 and 4 µM, respectively). SE11 caused a decrease in ERK phosphorylation which may be a consequence of the inhibition of EGF receptor kinase by this compound. Since an inhibition of the EGF receptor/MAPK pathway is an important target for diverse cytostatic drugs, we suggest that the anthraquinone derivative 1'-deoxyrhodoptilometrin (SE11) may be an interesting lead structure for the development of new anticancer drugs.

Drug Development of Small-Molecule Inhibitors of AD-Relevant Kinases as Novel Perspective Multitargeted Approach.

So far monotargeted therapies in Alzheimers disease (AD) led to insufficient results. Slight improvements in the AD symptomatics have been limited to patients in the early stage of the disease. So multitargeting approaches have been started addressing amyloid plaques as preferred primary target structures beside acetylcholine esterase inhibition. Various protein kinases have been discussed to make a contribution to the progression of AD. So protein kinases are promising target structures for a perspective multitargeting. We identified substituted smallmolecule protein kinase inhibitors of the tricyclic benzofuropyridine type which showed partly nanomolar affinities to AD-relevant glycogen synthase kinase (gsk) 3ß, extracellular-signal regulated kinase (ERK) 2 and C-Jun-N-terminal kinase (JNK) 3. Substituent-dependent effects on the respective kinase inhibitions are discussed and inhibitor binding modes to those kinases are presented based on enzyme docking studies. Inhibitor effects on the tau protein target structure are shown for first compounds in cellular studies to prove the enzyme conditioned effects.

Optimization of potent DFG-in inhibitors of platelet derived growth factor receptorß (PDGF-Rß) guided by water thermodynamics.

In this study we report on the hit optimization of substituted 3,5-diaryl-pyrazin-2(1H)-ones toward potent and effective platelet-derived growth factor receptor (PDGF-R) ß-inhibitors. Originally, the 3,5-diaryl-pyrazin-2-one core was derived from the marine sponge alkaloid family of hamacanthins. In our first series compound 2 was discovered as a promising hit showing strong activity against PDGF-Rß in the kinase assay (IC50 = 0.5 µM). Furthermore, 2 was shown to be selective for PDGF-Rß in a panel of 24 therapeutically relevant protein kinases. Molecular modeling studies on a PDGF-Rß homology model using prediction of water thermodynamics suggested an optimization strategy for the 3,5-diaryl-pyrazin-2-ones as DFG-in binders by using a phenolic OH function to replace a structural water molecule in the ATP binding site. Indeed, we identified compound 38 as a highly potent inhibitor with an IC50 value of 0.02 µM in a PDGF-Rß enzymatic assay also showing activity against PDGF-R dependent cancer cells.

Development of first lead structures for phosphoinositide 3-kinase-C2γ inhibitors.

The importance of complete elucidation of the biological functions of phosphoinositide 3-kinases (PI3K) was realized years ago. They generate 3-phosphoinositides, which are known to function as important second messengers in many inter- and intracellular signaling pathways. However, the functional role of class II PI3Ks is still unclear. Herein, we describe the synthesis of a panel of compounds that were tested against all eight mammalian PI3K-isoforms. We found inhibitors with some selectivity for class II PI3K-C2γ and also compounds with preferred inhibition of class II PI3K-C2ß, providing structural leads to develop selective tool compounds.

Cell lines expressing recombinant transmembrane domain-activated receptor kinases as tools for drug discovery.

Many receptor tyrosine kinases (RTKs) represent bona fide drug targets in oncology. Effective compounds are available, but treatment invariably leads to resistance, often due to RTK mutations. The discovery of second-generation inhibitors requires cellular models of resistant RTKs. An approach using artificial transmembrane domains (TMDs) to activate RTKs was explored for the rapid generation of simple, ligand-independent cellular RTK assays, including resistance mutants. The RTKs epidermal growth factor receptor (EGFR), MET, and KIT were chosen in a proof-of-concept study. Their intracellular domains were inserted into a series of expression vectors encoding artificial TMDs, and they were tested for autophosphorylation activity in transient transfection assays. Active constructs could be identified for MET and EGFR, but not for KIT. Rat1 cell pools were generated expressing the MET or EGFR constructs, and their sensitivity to reference tool compounds was compared to that of MKN-45 or A431 cells. A good correlation between natural and recombinant cells led us to build a panel of clinically relevant MET mutant cell pools, based on the wild-type construct, which were then profiled via MET autophosphorylation and soft agar assays. In summary, a platform was established that allows for the rapid generation of cellular models for RTKs and their resistance mutants.

Discovery of 4-anilino α-carbolines as novel Brk inhibitors.

Dysregulation of cell signalling processes caused by an enhanced activity of protein kinases mainly contributes to cancer progression. Protein kinase inhibitors have been established as promising drugs that inhibit such overactive protein kinases in cancer cells. The formation of metastases, which makes a therapy difficult, remains a great challenge for cancer treatment. Recently, breast tumor kinase (Brk) was discovered as novel and interesting target for a cancer therapy because Brk participates in both cell dysregulation and metastasis. We discovered 4-anilino substituted α-carboline compounds as a novel class of highly active Brk inhibitors. In the current work, structure-activity relationships are discussed including docking results obtained for 4-anilino α-carbolines. A first profiling of selective kinase inhibition and a proof of concept for the antiproliferative effects is demonstrated. These results qualify the compounds as a promising class of novel antitumor agents.

Approaches to a multitargeting drug development: first profiled 3- ethoxycarbonyl-1-aza-9-oxafluorenes representing a perspective compound class targeting Alzheimer disease relevant kinases CDK1, CDK5 and GSK-3ß.

Since Alzheimer disease (AD) is a multifactorial disease, recent therapeutical approaches concentrate on the development of a multitargeting drug. Various protein kinases are known to be involved in the progression of AD. A first series of 3-ethoxycarbonyl-1-aza-9-oxafluorenes has been synthesized and biologically evaluated as AD-relevant protein kinase inhibitors. A concentration-dependent inhibition of important AD-relevant kinases has been characterized after the selectivity of kinase inhibition had been demonstrated. Structure-activity relationships of protein kinase inhibition are discussed and first multitargeting inhibitors have been identified.

Novel 2-chloro-4-anilino-quinazoline derivatives as EGFR and VEGFR-2 dual inhibitors.

Novel 2-chloro-4-anilino-quinazolines designed as EGFR and VEGFR-2 dual inhibitors were synthesized and evaluated for inhibitory effects. EGFR and VEGFR-2 are validated targets in cancer therapy and combined inhibition might be synergistic for both antitumor activity and resistance prevention. The biological data obtained proved the potential of 2-chloro-4-anilino-quinazoline derivatives as EGFR and VEGFR-2 dual inhibitors, highlighting compound 8o, which was approximately 7-fold more potent on VEGFR-2 and approximately 11-fold more potent on EGFR compared to the prototype 7. SAR and docking studies allowed the identification of pharmacophoric groups for both kinases and demonstrated the importance of a hydrogen bond donor at the para position of the aniline moiety for interaction with conserved Glu and Asp amino acids in EGFR and VEGFR-2 binding sites.

Marine derived hamacanthins as lead for the development of novel PDGFRß protein kinase inhibitors.

In this study, we report on pyrazin-2(1H)-ones as lead for the development of potent adenosine triphosphate (ATP) competitive protein kinase inhibitors with implications as anti-cancer drugs. Initially, we identified the pyrazin-2(1H)-one scaffold from hamacanthins (deep sea marine sponge alkaloids) by Molecular Modeling studies as core binding motif in the ATP pocket of receptor tyrosine kinases (RTK), which are validated drug targets for the treatment of various neoplastic diseases. Structure-based design studies on a human RTK member PDGFR (platelet-derived growth factor receptor) suggested a straight forward lead optimization strategy. Accordingly, we focused on a Medicinal Chemistry project to develop pyrazin-2(1H)-ones as optimized PDGFR binders. In order to reveal Structure-Activity-Relationships (SAR), we established a flexible synthetic route via microwave mediated ring closure to asymmetric 3,5-substituted pyrazin-2(1H)-ones and produced a set of novel compounds. Herein, we identified highly potent PDGFR binders with IC50 values in an enzymatic assay below µM range, and possessing significant activity against PDGFR dependent cancer cells. Thus, marine hamacanthin-derived pyrazin-2(1H)-ones showing interesting properties as lead for their further development towards potent PDGFR-inhibitors.

Compounds isolated from Psoralea corylifolia seeds inhibit protein kinase activity and induce apoptotic cell death in mammalian cells.

OBJECTIVES: Psoralea corylifolia is a plant widely used in traditional Chinese medicine, e.g. for its chemopreventive effect. To identify active substances responsible for this effect, we investigated pharmacological effects of 11 compounds isolated from the seeds of this plant (newly described substances: 7, 2', 4'-trihydroxy-3-arylcoumarin and psoracoumestan). METHODS: The influence of distinct compounds on different signal transduction pathways (cell proliferation, survival, angiogenesis and metastasis) was screened via analysis of the activity of 24 protein kinases, mitogen activated protein kinase phosphorylation via Western blot, cytotoxicity was shown using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and determination of caspase activity. Oxidative stress was detected via 2',7'-dichlorofluorescein fluorescence. KEY FINDINGS: Some compounds showed cytotoxic effects (H4IIE, Hct116, C6 cells) mainly mediated via induction of apoptosis. Distinct compounds caused a strong inhibition of MAPK/ERK kinase (MEK) phosphorylation, weak effects on extracellular-signal regulated kinase (ERK) phosphorylation and no significant effect on p38 and c-Jun amino-terminal kinase. Corylifol C and, to a lesser extent, xanthoangelol are potent protein kinase inhibitors (inhibitory concentration 50% values for epidermal growth factor receptor (EGFR): 1.1 and 4.4 × 10(-6) µg/ml, respectively). Because EGFR, MEK and ERK are kinases involved in cellular proliferation, an inhibition of these enzymes may be useful to cause chemopreventive effects. CONCLUSIONS: Distinct compounds isolated from P. corylifolia showed a high potential to influence cellular pathways, e.g. by inhibition of protein kinases that may be interesting for pharmacological purposes.

Assessing the target differentiation potential of imidazole-based protein kinase inhibitors.

A library of 484 imidazole-based candidate inhibitors was tested against 24 protein kinases. The resulting activity data have been systematically analyzed to search for compounds that effectively differentiate between kinases. Six imidazole derivatives with high kinase differentiation potential were identified. Nearest neighbor analysis revealed the presence of close analogues with varying differentiation potential. Small structural modifications of active compounds were found to shift their inhibitory profiles toward kinases with different functions.

Multitargeted drug development: Discovery and profiling of dihydroxy substituted 1-aza-9-oxafluorenes as lead compounds targeting Alzheimer disease relevant kinases.

Alzheimer disease (AD) turned out to be a multifactorial process leading to neuronal decay. So far merely single target structures which attribute to the AD progression have been considered to develop specific drugs. However, such drug developments have been disappointing in clinical stages. Multitargeting of more than one target structure determines recent studies of developing novel lead compounds. Protein kinases have been identified to contribute to the neuronal decay with CDK1, GSK-3ß and CDK5/p25 being involved in a pathological tau protein hyperphosphorylation. We discovered novel lead structures of the dihydroxy-1-aza-9-oxafluorene type with nanomolar activities against CDK1, GSK-3ß and CDK5/p25. Structure-activity relationships (SAR) of the protein kinase inhibition are discussed within our first compound series. One nanomolar active compound profiled as selective protein kinase inhibitor. Bioanalysis of a harmless cellular toxicity and of the inhibition of tau protein phosphorylation qualifies the compound for further studies.

Novel indeno[1,2-b]indoloquinones as inhibitors of the human protein kinase CK2 with antiproliferative activity towards a broad panel of cancer cell lines.

We previously reported indeno[1,2-b]indoles as a novel class of potent inhibitors of the human protein kinase CK2. In the present study we prepared two novel quinoid derivatives, the indeno[1,2-b]indoloquinones 6b and 6c, and demonstrated inhibition of the human CK2 by the compounds. Furthermore, we showed substantial antiproliferative activity of both compounds towards a broad panel of human cancer cell lines in the low micromolar range. Whereas the earlier indeno[1,2-b]indoles have been shown to be selective for CK2, the indeno[1,2-b]indoloquinones 6b and 6c also inhibited the AMPK activated protein kinase ARK5, potentially contributing to the anti-cancer effects of the compounds. In addition, with compound 6b we found a very potent inhibitor of the leukemia-associated receptor tyrosine kinase FLT3, with an IC(50) of 0.18 µM.