Non-selective Kinase Inhibitor Research Articles

Affinity enhancement of polo-like kinase 1 polo box domain-binding ligands by a bivalent approach using a covalent kinase-binding component.

The polo-like kinase 1 (Plk1) is an important cell cycle regulator that is recognized as a target molecule for development of anti-cancer agents. Plk1 consists of a catalytic kinase domain (KD) and a polo-box domain (PBD), which engages in protein-protein interactions (PPIs) essential to proper Plk1 function. Recently, we developed extremely high-affinity PBD-binding inhibitors based on a bivalent approach using the Plk1 KD-binding inhibitor, BI2536, and a PBD-binding peptide. Certain of the resulting bivalent constructs exhibited more than 100-fold Plk1 affinity enhancement relative to the best monovalent PBD-binding ligands. Herein, we report an extensive investigation of bivalent ligands that utilize the non-selective kinase inhibitor Wortmannin as a Plk1 KD-binding component. We found that bivalent ligands incorporating Wortmannin demonstrated affinity enhancements that could be similar to what we had obtained with BI2536 and that they could tightly bind to the protein. This suggests that these tight binding ligands might be useful for structural analysis of full-length Plk1.

Abstract A110: Identifying sensitive patient populations for CDK7 inhibitors using cell panel screens and bioinformatic approaches

Abstract Background Dysregulation of cell cycle and transcriptional processes promote tumorigenesis and tumor growth. Due to its dual role in regulating both cellular processes, CDK7 is an attractive therapeutic target, with several CDK7 inhibitors in clinical trials. Preclinical data suggests that such agents could have utility across a range of tumor types particularly those driven by defects in the regulation of cell cycle and transcriptional processes. Consequently, potential patient populations are broad and often lack well-defined patient stratification. To identify specific cancers with greater dependence on CDK7 activity, we employed the use of a cell line panel screen coupled with bioinformatic analysis of association of drug sensitivity to molecular features. Materials and Methods To explore tumor sensitivities to CDK7 inhibition we profiled two CDK7 inhibitors (THZ1 and LY3405105; Eli Lilly) and the non-selective kinase inhibitor staurosporine as a control across a panel of 468 human cancer cell lines with varied genetic backgrounds. Activity area was used to define drug responses whilst multi-omics features of cell lines obtained from DepMap were used to define potential molecular features associated with drug response. Differential gene expression between sensitive and resistant cell lines was used to identify expression signatures associated with sensitivity to CDK7 inhibition. Results were validated in vitro by characterisation of cell line models in viability assays, western blots and RT-qPCR. Our findings were further validated in vivo in a NSCLC mouse xenograft model. Results Cell panel data showed a wide range of sensitives to selective CDK7 inhibition (LY3405105) compared to the profile of the less selective THZ1 which had a similar distribution of sensitivity as the control staurosporine. Bioinformatics analysis identified a global c-MYC signature with a significant correlation between CDK7 expression and c-MYC expression across the entire cell panel which confers sensitivity to CDK7 inhibition and was highly correlated in lung cancer. Further analysis of CDK7 inhibitor sensitivity in lung cancer as a function of c-MYC expression found that SCLC and NSCLC had the highest correlation. Using an independent set of cell lines with varying c-MYC levels, we confirmed these findings and the results were further validated in vivo where we observed partial tumor regressions. Conclusions Cell panel data coupled to bioinformatic analysis was used to define potentially sensitive patient populations for CDK7 inhibitors. This work demonstrates in vitro and in vivo activity of selective CDK7 inhibition in SCLC and NSCLC cancer models with high c-MYC levels. Citation Format: Keisha Hearn, Maria Ahn, Luke Bevan, Jessica Brothwood, Charlotte East, Anna Esteve-Arenys, Lynsey Fazal, Christopher Hindley, Sabrina James, Justyna Kucia-Tran, John Lyons, Joanne Munck, Harpreet Saini, Mathieu Unbekandt, Dhaval Varshney, Steve Wagner, Andrew Woodhead, Nicola Wallis. Identifying sensitive patient populations for CDK7 inhibitors using cell panel screens and bioinformatic approaches [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A110.

Isoform-Selective PI3K Inhibitors for Various Diseases.

Phosphoinositide 3-kinases (PI3Ks) are a family of ubiquitously distributed lipid kinases that control a wide variety of intracellular signaling pathways. Over the years, PI3K has emerged as an attractive target for the development of novel pharmaceuticals to treat cancer and various other diseases. In the last five years, four of the PI3K inhibitors viz. Idelalisib, Copanlisib, Duvelisib, and Alpelisib were approved by the FDA for the treatment of different types of cancer and several other PI3K inhibitors are currently under active clinical development. So far clinical candidates are non-selective kinase inhibitors with various off-target liabilities due to cross-reactivities. Hence, there is a need for the discovery of isoform-selective inhibitors with improved efficacy and fewer side-effects. The development of isoform-selective inhibitors is essential to reveal the unique functions of each isoform and its corresponding therapeutic potential. Although the clinical effect and relative benefit of pan and isoformselective inhibition will ultimately be determined, with the development of drug resistance and the demand for next-generation inhibitors, it will continue to be of great significance to understand the potential mechanism of isoform-selectivity. Because of the important role of type I PI3K family members in various pathophysiological processes, isoform-selective PI3K inhibitors may ultimately have considerable efficacy in a wide range of human diseases. This review summarizes the progress of isoformselective PI3K inhibitors in preclinical and early clinical studies for anticancer and other various diseases.

Abstract 4457: Open science medicinal chemistry: Towards a treatment for DIPG

Abstract Meds4Kids Pharma (M4K)1 is pioneering an open science approach to drug discovery, focussed on the discovery and development of small molecule therapeutics for orphan paediatric cancers. M4K seeks to test the hypothesis that an open science framework can be successfully applied not only to accelerate basic science, using the collective knowledge of the scientific community at large, but also to take an innovative new drug candidate all the way from discovery and clinical proof-of-concept through to product registration, by making use of regulatory data protections and market incentives. Since late 2017, Charles River Early Discovery has been providing in kind drug discovery services to help progress these efforts, including medicinal and synthetic chemistry. The first M4K project aims to generate an orally-available, brain-penetrant therapeutic to treat the diffuse intrinsic pontine glioma (DIPG). DIPG is a rare, aggressive and uniformly fatal childhood brain cancer with a median survival time of 9-12 months and for which there are currently no effective drug treatments. The disease has been shown to be associated with mutations in the ACVR1 gene (activin A receptor, type 1) also known as ALK2 kinase. Early support for the therapeutic hypothesis that an inhibitor of ALK2 kinase would have clinical benefit in DIPG, came from in vivo studies with non-selective ALK2 kinase inhibitors, which both killed DIPG cell lines harbouring the ALK2 mutation and extended lifespan in xenograft mouse models.2 Working collaboratively with M4K and their open science partners, we have made excellent progress towards the identification of potent, selective, brain penetrant ALK2 inhibitors starting from the known inhibitor LDN-214117, previously described for FOP (fibrodysplasia ossificans progressiva).3 Our current lead compound has an excellent in vitro and in vivo profile showing high oral bioavailability and brain penetration in a mouse PK study and is progressing to proof of concept studies. In addition we are progressing with the identification of a back-up series.

Abstract 335: Efficacy of FGFR inhibitors and combination therapies for acquired resistance in FGFR2-fusion cholangiocarcinoma

Abstract Background. The fibroblast growth factor receptor (FGFR) signaling pathway is aberrantly activated in approximately 20% of cases of cholangiocarcinoma through various genomic alterations including gene fusions, point mutations, and copy number amplifications. Currently, several FGFR kinase inhibitors are being assessed in clinical trials for patients with FGFR-altered cholangiocarcinoma. Despite evidence of initial responses and disease control, virtually all tumors eventually develop drug resistance. Overcoming acquired drug resistance to FGFR inhibitors has not been comprehensively studied. Methods. Apatient with metastatic cholangiocarcinoma and an activating FGFR2-KIAA1598fusion was enrolled on a Phase 2 clinical trial for the oral FGFR inhibitor, BGJ398. BGJ398 treatment was initially effective with radiographic and tumor marker response; however, after eight months of BGJ398 therapy, the patient developed disease progression. Sequencing of a post-progression liver biopsy revealed a novel secondary mutation (E566A) in the FGFR2 kinase domain, which was absent in the pre-treatment biopsy suggesting that this mutation may be responsible for the resistance to BGJ398. To confirm this, we conducted in vitrostudies to characterize the sensitivity of the FGFR2 secondary mutation to FGFR inhibitors. Results and Conclusions. In vitrocharacterization of the fusion and putative resistance mutation demonstrated that FGFR2-KIAA1598 WT cells were sensitive to BGJ398 with (IC50value of 10.95 nM) whereas the FGFR2-KIAA1598 E566A cells were resistant (IC50values of 422.4 nM). We investigated additional selective (AZD4547 and JNJ42756493), non-selective (dovtinib and ponatinib), and irreversible (TAS120) FGFR inhibitors. FGFR2-KIAA1598 WT cells were sensitive to AZD4547, JNJ42756493, and TAS120, whereas FGFR2-KIAA1598 E566A cells were resistant to these inhibitors. Interestingly, neither the FGFR2-KIAA1598 WT cells nor the FGFR2-KIAA1598 E566A cells were sensitive to dovitinib, a nonspecific tyrosine kinase inhibitor. Lastly, both populations of cells were equally sensitive to ponatinib, a non-selective FGFR kinase inhibitor. Proteomic analysis by reverse phase protein array (RPPA) revealed upregulation of the mTOR/PI3K/AKT pathway in fusion cells compared to empty controls (FDR: 0.00618), and this expression was further potentiated in FGFR2-KIAA1598 E566A (FDR: 1.96e-19). Furthermore, combination studies with the above FGFR inhibitors and the mTOR inhibitor, INK128, yielded synergistic antitumor effects suggesting that combination therapy may be able to overcome resistance to FGFR inhibitors. Significance. In conclusion, further elucidation of the mechanisms driving resistance to FGFR inhibitors will support the development of next generation FGFR inhibitors as well as combination therapeutic strategies. Citation Format: Melanie A. Krook, Alexandria M. Lenyo, Maxwell J. Wilberding, Hannah D. Barker, Mikayla Dantuono, Hui-Zi Chen, Julie W. Reeser, Michele R. Wing, Jharna Miya, Eric Samorodnitsky, Amy M. Smith, Thuy Dao, Dorrelyn M. Martin, Kristin Dittmar, Kristen K. Ciombor, John L. Hays, Aharon G. Freud, Sameek Roychowdhury. Efficacy of FGFR inhibitors and combination therapies for acquired resistance in FGFR2-fusion cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 335.

Recent developments of c‐Met as a therapeutic target in hepatocellular carcinoma

Aberrant c‐Met activity has been implicated in the development of hepatocellular carcinoma (HCC), suggesting that c‐Met inhibition may have therapeutic potential. However, clinical trials of nonselective kinase inhibitors with c‐Met activity (tivantinib, cabozantinib, foretinib, and golvatinib) in patients with HCC have failed so far to demonstrate significant efficacy. This lack of observed efficacy is likely due to several factors, including trial design, lack of patient selection according to tumor c‐Met status, and the prevalent off‐target activity of these agents, which may indicate that c‐Met inhibition is incomplete. In contrast, selective c‐Met inhibitors (tepotinib, capmatinib) can be dosed at a level predicted to achieve complete inhibition of tumor c‐Met activity. Moreover, results from early trials can be used to optimize the design of clinical trials of these agents. Preliminary results suggest that selective c‐Met inhibitors have antitumor activity in HCC, with acceptable safety and tolerability in patients with Child‐Pugh A liver function. Ongoing trials have been designed to assess the efficacy and safety of selective c‐Met inhibition compared with standard therapy in patients with HCC that were selected based on tumor c‐Met status. Thus, c‐Met inhibition continues to be an active area of research in HCC, with well‐designed trials in progress to investigate the benefit of selective c‐Met inhibitors. (Hepatology 2018;67:1132–1149)

Abstract A097: Phase II trial of the c-Met inhibitor tepotinib in patients with advanced non-small cell lung cancer harboring MET exon 14-skipping mutations

Abstract Background: Approximately 3-4% of non-small cell lung cancers (NSCLCs) harbor activating mutations of the MET proto-oncogene that cause exon 14 skipping (METex14) and accumulation of c-Met lacking a juxtamembrane domain. Such tumors are sensitive to nonselective kinase inhibitors with activity against c-Met, so selective c-Met inhibitors may have greater efficacy and/or tolerability. This single-arm phase II trial (NCT02864992) is investigating the efficacy and safety of the potent and selective c-Met inhibitor tepotinib in patients (pts) with NSCLC harboring METex14. Methods: Eligible patients (pts) are adults with stage IIIB/IV NSCLC and METex14 mutations identified in tumor and/or circulating tumor DNA (ctDNA) in plasma (liquid biopsy) by a central laboratory. Pts with EGFR-activating mutations, ALK rearrangements, or >2 lines of prior therapy are excluded. Pts receive tepotinib 500 mg QD on a 21-day cycle until disease progression, intolerable toxicity, or withdrawal from treatment for other reasons. Primary endpoint: objective response rate (ORR). Secondary endpoints: progression-free and overall survival, safety, pharmacokinetics, and quality of life. Recruitment of up to 120 (minimum 60 tumor, 60 ctDNA METex14-positive) pts in Europe, USA, and Japan is planned. Results: Five pts (age 55-77 years; 4 stage IV, 1 stage IIIB; all male; 4 Caucasian, 1 Asian) have been enrolled. Pts have currently completed 0-8 cycles of tepotinib therapy. Most adverse events observed to date have been grade 1/2 in severity, mostly unrelated to tepotinib treatment. One grade ≥3 tepotinib-related AE has occurred: grade 3 increased serum amylase. One pt has died due to his disease. Of the four pts with post-baseline tumor evaluations, two have confirmed partial response, one unconfirmed partial response, and one (with only one post-baseline assessment) stable disease. Conclusions: Initial data suggest that tepotinib 500 mg QD has promising activity in METex14 NSCLC. The safety profile of tepotinib appears favorable. Recruitment to the trial is ongoing. Citation Format: Enriqueta Felip, Remi Veillon, Santiago Viteri, Jürgen Scheele, Rolf Bruns, Paul K. Paik. Phase II trial of the c-Met inhibitor tepotinib in patients with advanced non-small cell lung cancer harboring MET exon 14-skipping mutations [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A097.

Abstract 3236: Delivering selective and cell-active inhibitors of V804M mutant RET kinase through structure-guided drug discovery

Abstract Activating gene fusions in the RET receptor tyrosine kinase have been found to drive 1-2% of lung adenocarcinomas and therefore offer an attractive target for targeted therapy. Whilst non-selective tyrosine kinase inhibitors with RET activity are efficacious in this setting, their use is generally limited by dose limiting toxicity associated with their more potent activity versus other targets, specifically KDR (VEGFR2) in the case of cabozantinib and vandetanib. Given this limitation, there is considerable interest in developing more selective inhibitors of RET kinase. Tyrosine kinase inhibitors are prone to early clinical failure due to mutations in the kinase ATPase binding domain, which render the kinase catalytically active but no longer sensitive to drug treatment. Such mutations often occur in the so-called “gatekeeper” region and in this specific case, resistance is predicted to arise from a Val-Met or Val-Leu mutation at residue 804. Through a combination of computational methods, structural biology and drug design, we have identified and further optimized a series of inhibitors of the V804M mutant RET kinase which show sub-micromolar cellular activity in cells driven by V804M RET. Moreover, these agents show excellent selectivity against the wtRET kinase and KDR. As such, these agents may offer valuable start-points for second-generation RET inhibitors for use in patents who relapse after treatment with first generation selective RET inhibitors. Citation Format: Allan M. Jordan, Rebecca Newton, Bohdan Waszkowycz, Richard Bayliss, Habiba Begum, Daniel Burschowsky, Aude Echalier, Samantha Hitchin, Colin Hutton, Shaun Johns, Stuart Jones, Li-Ying Lin, Mark Richards, Chitra Seewooruthun, Alex Stowell, Ian Waddell, Mandy Watson, Donald Ogilvie. Delivering selective and cell-active inhibitors of V804M mutant RET kinase through structure-guided drug discovery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3236. doi:10.1158/1538-7445.AM2017-3236

CaMKII in addition to MLCK contributes to phosphorylation of regulatory light chain in cardiomyocytes

The aim was to identify kinase activities involved in the phosphorylation of regulatory light chain (RLC) in situ in cardiomyocytes. In electrically stimulated rat cardiomyocytes, phosphatase inhibition by calyculin A unmasked kinase activities evoking an increase of phosphorylated RLC (P-RLC) from about 16% to about 80% after 80 min. The phosphorylation rate in cardiomyocytes was reduced by about 40% by the myosin light chain kinase (MLCK) inhibitor, ML-7. In rat ventricular muscle strips, calyculin A induced a positive inotropic effect that correlated with P-RLC levels. The inotropic effect and P-RLC elevation were abolished by ML-7 treatment. The kinase activities phosphorylating RLC in cardiomyocytes were reduced by about 60% by the non-selective kinase inhibitor staurosporine and by about 50% by the calmodulin antagonist W7. W7 eliminated the inhibitory effect of ML-7, suggesting that the cardiac MLCK is Ca2+/calmodulin (CaM)-dependent. The CaM-dependent kinase II (CaMKII) inhibitor KN-93 attenuated the calyculin A-induced RLC phosphorylation by about 40%, indicating a contribution from CaMKII. The residual phosphorylation in the presence of W7 indicated that also CaM-independent kinase activities might contribute. RLC phosphorylation was insensitive to protein kinase C inhibition. In conclusion, in addition to MLCK, CaMKII phosphorylates RLC in cardiomyocytes. Involvement of other kinases cannot be excluded.

Abstract 5385: A novel cell-based kinase assay panel paired with high content phenotypic profiling to correlate kinase inhibitor specificity and cellular activity

Abstract In many cancers, drugs that target a single kinase often lack efficacy due to the presence of alternate oncogenic signaling pathways that may compensate for the inhibition of the targeted kinase. Although completely non-selective kinase inhibitors are highly toxic, selective and simultaneous inhibition of a number of kinases can lead to greater responses. Here we describe the development of a multiplexed cellular kinase assay platform in which compounds are simultaneously profiled against more than 12 kinase targets in a single sample. Using this high-throughput platform, target activity and selectivity in cells can be optimized concurrently, enabling the selection of specific multi-targeted compounds. Using this platform, 300 kinase inhibitors were fully characterized for cellular activity and potency across a large panel of tyrosine kinases. These inhibitors were then tested across a panel of diverse cancer cell lines in a phenotypic screen for their ability to affect viability, cell cycle, and apoptosis under different growth conditions. The resulting comprehensive data set of existing in vitro data, cellular kinase data, and phenotypic screening results provided novel insights into the relationship between inhibitor selectivity, cell cycle effects, and the correlation to anti-cancer activity. Citation Format: Tom S. Wehrman, Erika A. O'Donnell, M. Jared Lumpe, Benjamin E. Osetek, Peter O. Krutzik. A novel cell-based kinase assay panel paired with high content phenotypic profiling to correlate kinase inhibitor specificity and cellular activity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5385. doi:10.1158/1538-7445.AM2014-5385

Selective pharmacologic inhibition of a PASTA kinase increases Listeria monocytogenes susceptibility to β-lactam antibiotics.

While β-lactam antibiotics are a critical part of the antimicrobial arsenal, they are frequently compromised by various resistance mechanisms, including changes in penicillin binding proteins of the bacterial cell wall. Genetic deletion of the penicillin binding protein and serine/threonine kinase-associated protein (PASTA) kinase in methicillin-resistant Staphylococcus aureus (MRSA) has been shown to restore β-lactam susceptibility. However, the mechanism remains unclear, and whether pharmacologic inhibition would have the same effect is unknown. In this study, we found that deletion or pharmacologic inhibition of the PASTA kinase in Listeria monocytogenes by the nonselective kinase inhibitor staurosporine results in enhanced susceptibility to both aminopenicillin and cephalosporin antibiotics. Resistance to vancomycin, another class of cell wall synthesis inhibitors, or antibiotics that inhibit protein synthesis was unaffected by staurosporine treatment. Phosphorylation assays with purified kinases revealed that staurosporine selectively inhibited the PASTA kinase of L. monocytogenes (PrkA). Importantly, staurosporine did not inhibit a L. monocytogenes kinase without a PASTA domain (Lmo0618) or the PASTA kinase from MRSA (Stk1). Finally, inhibition of PrkA with a more selective kinase inhibitor, AZD5438, similarly led to sensitization of L. monocytogenes to β-lactam antibiotics. Overall, these results suggest that pharmacologic targeting of PASTA kinases can increase the efficacy of β-lactam antibiotics.

Structure of the β-form of human MK2 in complex with the non-selective kinase inhibitor TEI-L03090.

Mitogen-activated protein kinase-activated protein kinase 2 (MK2 or MAPKAP-K2), a serine/threonine kinase from the p38 mitogen-activated protein kinase signalling pathway, plays an important role in the production of TNF-α and other cytokines. In a previous report, it was shown that MK2 in complex with the selective inhibitor TEI-I01800 adopts an α-helical glycine-rich loop that is induced by the stable nonplanar conformer of TEI-I01800. To understand the mechanism of the structural change, the structure of MK2 bound to TEI-L03090, which lacks the key substituent found in TEI-I01800, was determined. MK2-TEI-L03090 has a β-sheet glycine-rich loop in common with other kinases, as predicted. This result suggests that a small compound can induce a drastic conformational change in the target protein structure and can be used to design potent and selective inhibitors.

Prostate-apoptosis response-4 phosphorylation in vascular smooth muscle

The protein prostate-apoptosis response (Par)-4 has been implicated in the regulation of smooth muscle contraction, based largely on studies with the A7r5 cell line. A mechanism has been proposed whereby Par-4 binding to MYPT1 (the myosin-targeting subunit of myosin light chain phosphatase, MLCP) blocks access of zipper-interacting protein kinase (ZIPK) to Thr697 and Thr855 of MYPT1, whose phosphorylation is associated with MLCP inhibition. Phosphorylation of Par-4 at Thr155 disrupts its interaction with MYPT1, exposing the sites of phosphorylation in MYPT1 and leading to MLCP inhibition and contraction. We tested this “padlock” hypothesis in a well-characterized vascular smooth muscle system, the rat caudal artery. Par-4 was retained in Triton-skinned tissue, suggesting a tight association with the contractile machinery, and indeed Par-4 co-immunoprecipitated with MYPT1. Treatment of Triton-skinned tissue with the phosphatase inhibitor microcystin (MC) evoked phosphorylation of Par-4 at Thr155, but did not induce its dissociation from the contractile machinery. Furthermore, analysis of the time courses of MC-induced phosphorylation of MYPT1 and Par-4 revealed that MYPT1 phosphorylation at Thr697 or Thr855 preceded Par-4 phosphorylation. Par-4 phosphorylation was inhibited by the non-selective kinase inhibitor staurosporine, but not by inhibitors of ZIPK, Rho-associated kinase or protein kinase C. In addition, Par-4 phosphorylation did not occur upon addition of constitutively-active ZIPK to skinned tissue. We conclude that phosphorylation of Par-4 does not regulate contraction of this vascular smooth muscle tissue by inducing dissociation of Par-4 from MYPT1 to allow phosphorylation of MYPT1 and inhibition of MLCP.

Rational Evolution of a Novel Type of Potent and Selective Proviral Integration Site in Moloney Murine Leukemia Virus Kinase 1 (PIM1) Inhibitor from a Screening-Hit Compound

Serine/threonine kinase PIM1 is an emerging therapeutic target for hematopoietic and prostate cancer therapy. To develop a novel PIM1 inhibitor, we focused on 1, a metabolically labile, nonselective kinase inhibitor discovered in our previous screening study. We adopted a rational optimization strategy based mainly on structural information for the PIM1-1 complex to improve the potency and selectivity. This approach afforded the potent and metabolically stable PIM1-selective inhibitor 14, which shows only a marginal increase in molecular weight compared with 1 but has a significantly decreased cLogP. The validity of our design concept was confirmed by X-ray structure analysis. In a cellular study, 14 potently inhibited the growth of human leukemia cell line MV4-11 but had a negligible effect on the growth of WI-38 (surrogate for general toxicity). These results demonstrate the effectiveness of our design strategy for evolving the screening-hit compound 1 into a novel type of PIM1 inhibitor, 14.

Desensitization and Trafficking of μ-Opioid Receptors in Locus Ceruleus Neurons: Modulation by Kinases

The phosphorylation of μ-opioid receptors (MOPRs) by G protein-coupled receptor kinases (GRKs), followed by arrestin binding, is thought to be a key pathway leading to desensitization and internalization. The present study used the combination of intracellular and whole-cell recordings from rats and mice, as well as live cell imaging of Flag-tagged MOPRs from mouse locus ceruleus neurons, to examine the role of protein kinases in acute desensitization and receptor trafficking. Inhibition of GRKs by using heparin or GRK2-mutant mice did not block desensitization or alter the rate of recovery from desensitization. The nonselective kinase inhibitor staurosporine did not reduce the extent of [Met(5)]enkephalin (ME)-induced desensitization but increased the rate of recovery from desensitization. In the presence of staurosporine, ME-activated FlagMOPRs were internalized but did not traffic away from the plasma membrane. The increased rate of recovery from desensitization correlated with the enhancement in the recycling of receptors to the plasma membrane. ME-induced MOPR desensitization persisted and the trafficking of receptors was modified after inhibition of protein kinases. The results suggest that desensitization of MOPRs may be an early step after agonist binding that is modulated by but is not dependent on kinase activity.

Quantitative Chemical Proteomics Reveals New Potential Drug Targets in Head and Neck Cancer

Tumors of the head and neck represent a molecularly diverse set of human cancers, but relatively few proteins have actually been shown to drive the disease at the molecular level. To identify new targets for individualized diagnosis or therapeutic intervention, we performed a kinase centric chemical proteomics screen and quantified 146 kinases across 34 head and neck squamous cell carcinoma (HNSCC) cell lines using intensity-based label-free mass spectrometry. Statistical analysis of the profiles revealed significant intercell line differences for 42 kinases (p < 0.05), and loss of function experiments using siRNA in high and low expressing cell lines identified kinases including EGFR, NEK9, LYN, JAK1, WEE1, and EPHA2 involved in cell survival and proliferation. EGFR inhibition by the small molecule inhibitors lapatinib, gefitinib, and erlotinib as well as siRNA led to strong reduction of viability in high but not low expressing lines, confirming EGFR as a drug target in 10-20% of HNSCC cell lines. Similarly, high, but not low EPHA2-expressing cells showed strongly reduced viability concomitant with down-regulation of AKT and ERK signaling following EPHA2 siRNA treatment or EPHA1-Fc ligand exposure, suggesting that EPHA2 is a novel drug target in HNSCC. This notion is underscored by immunohistochemical analyses showing that high EPHA2 expression is detected in a subset of HNSCC tissues and is associated with poor prognosis. Given that the approved pan-SRC family kinase inhibitor dasatinib is also a very potent inhibitor of EPHA2, our findings may lead to new therapeutic options for HNSCC patients. Importantly, the strategy employed in this study is generic and therefore also of more general utility for the identification of novel drug targets and molecular pathway markers in tumors. This may ultimately lead to a more rational approach to individualized cancer diagnosis and therapy.

Protein Phosphatase 2A as a Potential Target for Anticancer Therapy

The kinase oncogenes are well-characterized drivers of cancer development, and several targeted therapies focused on both specific and selectively nonselective kinase inhibitors have now been approved for clinical use. In contrast, much less is known about the role of protein phosphatases, although modulation of their activities might form the foundation for an effective anti-cancer approach. The serine-threonine protein phosphatase 2A (PP2A) is implicated in the regulation of numerous signaling pathways and may function as a tumor suppressor. Recently pharmacological modulation of PP2A activity has been showed to have a potent anti-tumor activity in both in vitro and in vivo cancer models. These studies implicate PP2A as a promising therapeutic target for the treatment of cancer.

Proteomics Analysis of Cellular Imatinib Targets and their Candidate Downstream Effectors

Inhibition of deregulated protein kinases by small molecule drugs has evolved into a major therapeutic strategy for the treatment of human malignancies. Knowledge about direct cellular targets of kinase-selective drugs and the identification of druggable downstream mediators of oncogenic signaling are relevant for both initial therapy selection and the nomination of alternative targets in case molecular resistance emerges. To address these issues, we performed a proof-of-concept proteomics study designed to monitor drug effects on the pharmacologically tractable subproteome isolated by affinity purification with immobilized, nonselective kinase inhibitors. We applied this strategy to chronic myeloid leukemia cells that express the transforming Bcr-Abl fusion kinase. We used SILAC to measure how cellular treatment with the Bcr-Abl inhibitor imatinib affects protein binding to a generic kinase inhibitor resin and further quantified site-specific phosphorylations on resin-retained proteins. Our integrated approach indicated additional imatinib target candidates, such as flavine adenine dinucleotide synthetase, as well as repressed phosphorylation events on downstream effectors not yet implicated in imatinib-regulated signaling. These included activity-regulating phosphorylations on the kinases Btk, Fer, and focal adhesion kinase, which may qualify them as alternative target candidates in Bcr-Abl-driven oncogenesis. Our approach is rather generic and may have various applications in kinase drug discovery.

Development of a high-throughput AlphaScreen assay measuring full-length LRRK2(G2019S) kinase activity using moesin protein substrate

Mutations within the LRRK2 (leucine-rich repeat kinase 2) gene predispose humans to develop late-onset Parkinson’s disease (PD). The most prevalent of these mutations, G2019S, has been shown to increase LRRK2 kinase activity. Therefore, the discovery of small molecule inhibitors of LRRK2(G2019S) through high-throughput screening (HTS) may provide a novel therapeutic strategy for treating PD. Current biochemical assays monitoring the activity of LRRK2(G2019S) either are radioactive or use short peptidic substrates. Here we describe the development and optimization of a novel HTS AlphaScreen assay for measuring the catalytic activity of full-length LRRK2(G2019S) using its putative physiological protein substrate moesin. The high sensitivity of this optimized 384-well assay allowed the use of enzyme concentrations as low as 0.75 nM. The estimated apparent K m value for adenosine triphosphate (6 μM) using the glutathione S-transferase–moesin substrate was much lower than the one previously reported using LRRKtide, a synthetic peptide derived from moesin. Testing of nonselective kinase inhibitors (staurosporine, H-1152, and Y-27632) generated potencies consistent with published data. Finally, robotic validation of the assay yielded an average Z′ factor of 0.80. Overall, these results indicate that the present HTS AlphaScreen assay might provide a more relevant biochemical approach for the discovery of novel LRRK2(G2019S) inhibitors.

Investigation of leucine‐rich repeat kinase 2

Mutations in leucine-rich repeat kinase 2 (LRRK2) comprise the leading cause of autosomal dominant Parkinson's disease, with age of onset and symptoms identical to those of idiopathic forms of the disorder. Several of these pathogenic mutations are thought to affect its kinase activity, so understanding the roles of LRRK2, and modulation of its kinase activity,may lead to novel therapeutic strategies for treating Parkinson's disease. In this study, highly purified, baculovirus-expressed proteins have been used,for the first time providing large amounts of protein that enable a thorough enzymatic characterization of the kinase activity of LRRK2.Although LRRK2 undergoes weak autophosphorylation, it exhibits high activity towards the peptidic substrate LRRKtide, suggesting that it is a catalytically efficient kinase. We have also utilized a time-resolved fluorescence resonance energy transfer (TR-FRET) assay format (Lantha-ScreenTM) to characterize LRRK2 and test the effects of nonselective kinase inhibitors. Finally, we have used both radiometric and TR-FRETassays to assess the role of clinical mutations affecting LRRK2's kinase activity. Our results suggest that only the most prevalent clinical mutation,G2019S, results in a robust enhancement of kinase activity with LRRKtideas the substrate. This mutation also affects binding of ATP to LRRK2,with wild-type binding being tighter (Km,app of 57 lm) than with theG2019S mutant (Km,app of 134 lm). Overall, these studies delineate the catalytic efficiency of LRRK2 as a kinase and provide strategies by which a therapeutic agent for Parkinson's disease may be identified.