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.

Novel structurally varied N-alkyl 1,4-dihydropyridines as ABCB1 inhibitors: structure-activity relationships, biological activity and first bioanalytical evaluation.

Series of structurally varied N-alkyl 1,4-dihydropyridines and novel benzo-annelated derivatives as 1,4- dihydroquinolines have been characterized as ABCB1 inhibitors. Structure-activity relationships (SARs) are discussed. Cytotoxic activities of selected compounds have been determined. A first bioanalysis of ABCB1 substrate properties has been carried out in a cell-based model. Compounds with highest ABCB1 inhibiting activities were no substrates of ABCB1 and not transported by the efflux pump, thus profiling the new ABCB1 inhibitors.

Discovery of pyridine-2-ones as novel class of multidrug resistance (MDR) modulators: first structure-activity relationships.

A novel facile synthesis led to pyridine-2-one target structures of which first series with varying substituents have been yielded and biologically characterized as novel multidrug resistance (MDR) modulators inhibiting P-glycoprotein (P-gp). Structure-activity relationships prove a dependency of the MDR-modulating properties from the kind and positioning of hydrogen bond acceptor functions within the molecular skeleton. Cyano functions turned out as biologically effective substituents for a potential hydrogen bonding to the protein target structure.

Discovery of 4-benzylamino-substituted α-carbolines as a novel class of receptor tyrosine kinase inhibitors.

Within the last decade, interest in the development of new anticancer drugs increased mainly from emerging resistance against established drugs, which were found to be limited by the multidrug resistance (MDR) phenomenon. Several anticancer targets have been investigated for the development of structurally new drugs which were thought to be unaffected by the MDR phenomenon. Receptor tyrosine kinases (RTKs) make up one interesting group of anticancer targets. The overexpression and mutation of RTKs lead to an ongoing stimulus of cell growth and cancer progression. Early approaches to selective inhibition of single RTKs were generally disappointing in clinical studies, due in part to occurring resistance. Therefore, a new strategy involves the identification of multi-kinase inhibitors to slow the development of potential resistance. Moreover, the expected side effects of the first nonselective inhibitors were less dramatic than had been expected. We have discovered novel 4-benzylamino-α-carbolines as a new class of RTK inhibitors. Docking studies suggest a binding mode to the addressed target structures of the epidermal growth factor receptor (EGFR) and to the vascular endothelial growth factor receptor 2 (VEGFR2). Selectivity profiling against a panel of kinases and antiproliferative studies have highlighted one inhibitor, active in the nanomolar range, as a highly interesting candidate for further clinical studies.

Discovery and selectivity-profiling of 4-benzylamino 1-aza-9-oxafluorene derivatives as lead structures for IGF-1R inhibitors.

Recently the insuline-like growth factor receptor (IGF-1R) emerged as a promising target structure for the development of novel anti-cancer agents. IGF-1R plays a central role in both tumour progression and resistance development against anti-cancer drugs. We discovered 1-aza-9-oxafluorene derivatives as novel lead structures with submicromolar activities against IGF-1R. Structure-activity relationships (SARs) on a series of related receptor tyrosine kinases (RTKs) are discussed in the context of available crystal structures. A preliminary selectivity-profiling is demonstrated for the first compound series. Antiproliferative tumour cell line screening studies yielded one candidate as a promising cytostatic agent without significant toxic effects.

Novel structure-activity relationships and selectivity profiling of cage dimeric 1,4-dihydropyridines as multidrug resistance (MDR) modulators.

Synthesized series of cage dimeric 1,4-dihydropyridines have been systematically evaluated as MDR modulators in in vitro assays to investigate structure-dependent selectivity properties of inhibiting most cancer-relevant efflux pump proteins. Structure-activity relationships of each P-glycoprotein (P-gp) and multidrug resistance associated protein (MRP) 1 and MRP2 inhibition are discussed and prove to be mainly determined by certain aromatic substitution patterns. The characterization of breast cancer resistance protein (BCRP) inhibition results in the discovery of benzyloxy substituted derivatives as selective P-gp inhibitors.

First biological evaluation of developed 3-benzyloxyfluorenes as novel class of MDR modulators.

A series of 3-benzyloxy-1-aza-9-oxafluorenes has been synthesized and biologically evaluated as novel MDR modulators. The concentration dependent inhibition of the efflux pump ABCB1 (P-glycoprotein) has been characterized and is discussed in relation to calculated lipophilicity data. Instead of the molecular lipophilicity the exact positioning of functional groups was found decisive for the biological activities.

Recent advances in the development of multi-kinase inhibitors.

During the last two decades, protein kinases have emerged as a major target for cancer therapy and a large number of selective kinase inhibitors have been developed as potential anticancer drugs. To avoid unpredictable toxic effects, researchers usually aim at designing highly selective inhibitors. But since the formation and progression of a tumor has to be considered as a multifactorial process, which is dependent on different signalling pathways, it seems reasonable to establish anticancer therapies that target several kinases associated with tumor growth. In general, this can be achieved by two different strategies, either by concomitantly using a combination of a set of selective kinase inhibitors or by administering a single agent, which simultaneously inhibits several kinases, a so called multi-kinase inhibitor. In this review, benefits and obstacles of both strategies are discussed. An overview over recently approved and newly upcoming multi-kinase inhibitors is given.

Novel insight in structure-activity relationship and bioanalysis of P-glycoprotein targeting highly potent tetrakishydroxymethyl substituted 3,9-diazatetraasteranes.

Novel 3,9-diazatetraasteranes have been synthesized with varied aromatic substitution patterns and evaluated as P-glycoprotein (P-gp) inhibitors. Structure-activity relationships (SAR) are discussed in relation to determined physicochemical properties. The potential to induce P-gp expression has been evaluated in cancer cell lines. The bioanalytical results indicate favorable noninducing properties compared to P-gp inducing drug standard.

Probing novel 1-aza-9-oxafluorenes as selective GSK-3beta inhibitors.

Within the histopathology of Alzheimer's disease (AD) certain hallmarks are beeing observed. The occurance of protein deposits belong to such characteristic features. Such deposits can be found extracellular as beta-amyloid (Abeta) plaques and intracellular as neurofibrillary tangles (NFTs). In the search for novel AD therapeutics it became of great interest to investigate the formation of NFTs and their contribution to the AD symptomatic. NFTs consist of hyperphosphorylated tau protein. Within the phosphorylation process of tau protein two kinases are of great importance: cyclin dependent kinase 5 (cdk5) and its truncated regulatory subunit p25 and glycogen synthase kinase 3beta (GSK-3beta). The role of both kinases within the NFT formation process is still under debate. To better understand the pathophysiological process highly selective inhibitors of both kinases are of value. Known inhibitors lack the necessary selectivity. We developed novel 1-aza-9-oxafluo-renes as selective GSK-3beta inhibitors. Structure-activity relationships of a series of 4-phenyl substituted derivatives are discussed. Variation of the 3-side chain led to selective carbonyl amide derivatives with selectivity factors of more than 100 at the tested ATP competitor concentrations. Such selectivities permit specific investigation of the role of GSK-3beta within the NFT formation processes.