The discovery of potent and selective 4-aminothienopyridines as B-Raf kinase inhibitors.

A series of novel, potent 4-aminothienopyridine B-Raf kinase inhibitors was designed and synthesized using knowledge-based design. Compounds 5f, and 6k exhibited not only excellent potency in both enzyme assay (IC(50)=5.1, 16.6 nM) and cellular assay (IC(50)=0.2, 0.2 µM), but also had an outstanding selectivity profile against other kinases.

Knowledge-based design of 7-azaindoles as selective B-Raf inhibitors.

The synthesis of a 7-azaindole series of novel, potent B-Raf kinase inhibitors using knowledge-based design was carried out. Compound 6h exhibits not only excellent potency in both the enzyme assay (IC(50)=2.5 nM) and the cellular assay (IC(50)=63 nM), but also has an outstanding selectivity profile against other kinases.

RET activation inhibits doxorubicin-induced apoptosis in SK-N-MC cells.

BACKGROUND: Medullary thyroid cancer (MTC) is generally resistant to chemotherapy and the frequent constitutive activation of RET (rearranged during transfection gene) in these tumors might inhibit drug-induced apoptosis. MATERIALS AND METHODS: Each RET isoform was separately expressed in SK-N-MC cells (neural crest-derived tumor) and the impact of RET activation on doxorubicin-induced apoptosis was examined. RESULTS: The activation of RET9 and RET51 in the SK-N-MC cells significantly reduced the doxorubicin-induced apoptosis by 50%, compared to untreated cells. RET activation also induced phosphorylation of ERK (extracellular regulated kinase), but no changes in AKT (serine/threonine kinase) phosphorylation were noted. In the presence of a MAP (mitogen-activated protein) kinase inhibitor or a RET kinase inhibitor, the RET-activated/drug-treated cells displayed nearly 75% and 100% of the doxorubicin-induced apoptosis of the drug-treated cells without RET activation, respectively. CONCLUSION: In SK-N-MC cells, downstream activation of MAP kinase, by both RET9 and RET51, appears to mediate the majority of RET-dependent resistance to chemotherapeutically induced apoptosis. MTC might be rendered more responsive to chemotherapeutic agents by the co-administration of a RET kinase inhibitor.

Lessons from the drug discovery of lapatinib, a dual ErbB1/2 tyrosine kinase inhibitor.

Protein Kinases offer many opportunities for drug intervention points since phosphorylation is the most common post-translational modification. Phosphorylation regulates activity, location, degradation, conformation and the aberrant activity is implicated in many diseases, including cancer, inflammation, cardiovascular and central nervous system diseases. The focus of this review will be on the generation of highly effective signaling inhibitors targeting members of the erbB family of receptor tyrosine kinases, EGFR and ErbB-2, also known as transmembrane Type 1 receptor tyrosine kinases of the HER family of receptors. Ligand binding to the receptor causes a conformational change which activates the tyrosine kinase domain leading to autophosphorylation. This autophosphorylation activates the RAS/mitogen activated protein (MAP) kinase and phosphoinositol-3-kinase (PI3K) pathways leading to a myriad of signaling and cellular activities. Type 1 receptors are over-expressed in a variety of cancers and generally correlate with poor prognosis. For this reason, scientists at GlaxoSmithKline and many others in the scientific community, target the ATP binding site of the intracellular portion of the protein to block the aberrant signaling event. This review intends to cover the lessons learned in the discovery of lapatinib (GW572016, GW2016) by pulling together the various different publications that have been generated in distinct disciplines on aspects of the drug discovery program. Data analyses and correlation of assay data to help with the design of drug like molecules will be included and will demonstrate a break from the traditional focus on absolute potency as a guiding factor in lead compound selection.

A unique structure for epidermal growth factor receptor bound to GW572016 (Lapatinib): relationships among protein conformation, inhibitor off-rate, and receptor activity in tumor cells.

GW572016 (Lapatinib) is a tyrosine kinase inhibitor in clinical development for cancer that is a potent dual inhibitor of epidermal growth factor receptor (EGFR, ErbB-1) and ErbB-2. We determined the crystal structure of EGFR bound to GW572016. The compound is bound to an inactive-like conformation of EGFR that is very different from the active-like structure bound by the selective EGFR inhibitor OSI-774 (Tarceva) described previously. Surprisingly, we found that GW572016 has a very slow off-rate from the purified intracellular domains of EGFR and ErbB-2 compared with OSI-774 and another EGFR selective inhibitor, ZD-1839 (Iressa). Treatment of tumor cells with these inhibitors results in down-regulation of receptor tyrosine phosphorylation. We evaluated the duration of the drug effect after washing away free compound and found that the rate of recovery of receptor phosphorylation in the tumor cells reflected the inhibitor off-rate from the purified intracellular domain. The slow off-rate of GW572016 correlates with a prolonged down-regulation of receptor tyrosine phosphorylation in tumor cells. The differences in the off-rates of these drugs and the ability of GW572016 to inhibit ErbB-2 can be explained by the enzyme-inhibitor structures.

Comprehensive characterization of the Published Kinase Inhibitor Set.

Despite the success of protein kinase inhibitors as approved therapeutics, drug discovery has focused on a small subset of kinase targets. Here we provide a thorough characterization of the Published Kinase Inhibitor Set (PKIS), a set of 367 small-molecule ATP-competitive kinase inhibitors that was recently made freely available with the aim of expanding research in this field and as an experiment in open-source target validation. We screen the set in activity assays with 224 recombinant kinases and 24 G protein-coupled receptors and in cellular assays of cancer cell proliferation and angiogenesis. We identify chemical starting points for designing new chemical probes of orphan kinases and illustrate the utility of these leads by developing a selective inhibitor for the previously untargeted kinases LOK and SLK. Our cellular screens reveal compounds that modulate cancer cell growth and angiogenesis in vitro. These reagents and associated data illustrate an efficient way forward to increasing understanding of the historically untargeted kinome.

Small molecule inhibitors of the class 1 receptor tyrosine kinase family.

This review covers literature describing research progress in erbB family tyrosine kinase inhibition over the last year. Excellent recent reviews are available, thus we have focussed on current developments of leading small molecule drug candidates as well as their erbB family inhibition profile. The most advanced erbB family tyrosine kinase (TK) inhibitors are demonstrating promising anti-cancer activity in clinical trials and are discussed. Several inhibition strategies are emerging: EGFR TK selective, irreversible TK inhibition and dual EGFR/erbB2 TK inhibitors. While small structural differences are seen in the leading compounds, the variations in their inhibition profiles and compound properties suggest that biological systems judge structural diversity differently. The readers' attention is drawn to common issues of selectivity and potency generally encountered with kinase inhibitors.

The discovery of substituted 4-(3-hydroxyanilino)-quinolines as potent RET kinase inhibitors.

Substituted 4-(3-hydroxyanilino)-quinoline compounds, initially identified as small-molecule inhibitors of src family kinases, have been evaluated as potential inhibitors of RET kinase. Three compounds, 38, 31, and 40, had K(i)'s of 3, 25, and 50 nM in an in vitro kinase assay; while a cell based kinase assay showed K(i)'s of 300, 100, and 45 nM, respectively. These compounds represent potential new leads for the treatment of medullary and papillary thyroid cancer.

Aza-stilbenes as potent and selective c-RAF inhibitors.

The synthesis of several novel aza-stilbene derivatives was carried out. The compounds were tested for their c-RAF enzyme inhibition. Compound 27 possesses significant potency against c-RAF and demonstrates selectivity over other protein kinases. A hypothesis for the binding mode, activity, and selectivity is proposed.

Optimization and SAR for dual ErbB-1/ErbB-2 tyrosine kinase inhibition in the 6-furanylquinazoline series.

Synthetic modifications on a 6-furanylquinazoline scaffold to optimize the dual ErbB-1/ErbB-2 tyrosine kinase inhibition afforded consistent SAR whereby a 4-(3-fluorobenzyloxy)-3-haloanilino provided the best enzyme potency and cellular selectivity. Changes made to the 6-furanyl group had little impact on the enzyme activity, but appeared to dramatically affect the cellular efficacy. The discovery of lapatinib emerged from this work.

Discovery and in vitro evaluation of potent kinase inhibitors: Pyrido[1',2':1,5]pyrazolo[3,4-d]pyrimidines.

The discovery, synthesis, potential binding mode, and in vitro kinase profile of several pyrido[1',2':1,5]pyrazolo[3,4-d]pyrimidines as potent kinase inhibitors are discussed.

Synthesis and SAR of potent EGFR/erbB2 dual inhibitors.

A series of 6-alkoxy-4-anilinoquinazoline compounds was prepared and evaluated for in vitro inhibition of the erbB2 and EGFR kinase activity. The IC(50) values of the best compounds were below 0.10 uM. Further, several of these compounds inhibit the growth of erbB2 and EGFR over-expressing tumor cell lines at concentrations below 1 uM.

Discovery and in vitro evaluation of potent TrkA kinase inhibitors: oxindole and aza-oxindoles.

The discovery, synthesis, potential binding mode, and in vitro kinase profile of 3-(3-bromo-4-hydroxy-5-(2'-methoxyphenyl)-benzylidene)-5-bromo-1,3-dihydro-pyrrolo[2,3-b]pyridin-2-one, 3-[(1-methyl-1H-indol-3-yl)methylene]-1,3-dihydro-2H-pyrrolo[3,2-b]-pyridin-2-one as potent TrkA inhibitors are discussed.

Comparison of the biochemical and kinetic properties of the type 1 receptor tyrosine kinase intracellular domains. Demonstration of differential sensitivity to kinase inhibitors.

Epidermal growth factor receptor (EGFR), ErbB-2, and ErbB-4 are members of the type 1 receptor tyrosine kinase family. Overexpression of these receptors, especially ErbB-2 and EGFR, has been implicated in multiple forms of cancer. Inhibitors of EGFR tyrosine kinase activity are being evaluated clinically for cancer therapy. The potency and selectivity of these inhibitors may affect the efficacy and toxicity of therapy. Here we describe the expression, purification, and biochemical comparison of EGFR, ErbB-2, and ErbB-4 intracellular domains. Despite their high degree of sequence homology, the three enzymes have significantly different catalytic properties and substrate kinetics. For example, the catalytic activity of ErbB-2 is less stable than that of EGFR. ErbB-2 uses ATP-Mg as a substrate inefficiently compared with EGFR and ErbB-4. The three enzymes have very similar substrate preferences for three optimized peptide substrates, but differences in substrate synergies were observed. We have used the biochemical and kinetic parameters determined from these studies to develop an assay system that accurately measures inhibitor potency and selectivity between the type 1 receptor family. We report that the selectivity profile of molecules in the 4-anilinoquinazoline series can be modified through specific aniline substitutions. Moreover, these compounds have activity in whole cells that reflect the potency and selectivity of target inhibition determined with this assay system.

Discovery and biological evaluation of potent dual ErbB-2/EGFR tyrosine kinase inhibitors: 6-thiazolylquinazolines.

We have identified a novel class of 6-thiazolylquinazolines as potent and selective inhibitors of both ErbB-2 and EGFR tyrosine kinase activity, with IC(50) values in the nanomolar range. These compounds inhibited the growth of both EGFR (HN5) and ErbB-2 (BT474) over-expressing human tumor cell lines in vitro. Using xenograft models of the same cell lines, we found that the compounds given orally inhibited in vivo tumor growth significantly compared with control animals.