The pp60c-Src inhibitor PP1 is non-competitive against ATP

ATP non-competitive IGF-1 receptor kinase inhibitors as lead anti-neoplastic and anti-papilloma agents

The insulin-like growth factor-1 receptor (IGF-1 receptor) is a receptor tyrosine kinase, highly homologous to the insulin receptor. In contrast to the insulin receptor, which is mostly involved in metabolic pathways, the IGF-1 system plays a pivotal role in normal and neoplastic cell growth through anti-apoptotic, proliferative and metastatic pathways. Furthermore, IGF-1 receptor over-activation is found to correlate with a variety of tumors, such as breast cancer, prostate cancer, hematological malignancies, colorectal cancer and other proliferative diseases, such as psoriasis and papilloma. In addition, accumulating evidence implies that blockade of IGF-1 receptor activity causes reversal of tumor progression in cell lines as well as in animal tumor models. Because of the central role the IGF-1 receptor plays in oncogenic maintenance and metastatic processes, it is a highly appropriate target for anti-cancer agents. Here we report on a novel substrate-mimic family of IGF-1 receptor inhibitors. These compounds are tertiary aromatic amines, non-competitive with ATP and possess high affinity towards the IGF-1 receptor. The most potent compound, SBL02 inhibited the IGF-1 receptor with an IC(50) of 170 nM in a cell-free kinase assay and was found to inhibit IGF-1 receptor auto-phosphorylation and substrate phosphorylation at the low micromolar range in cellular assays. SBL02 also blocks the formation of colonies in soft agar by cancer cells and inhibits the growth of keratinocytes and of HPV16 immortalized keratinocytes. This new family of non-ATP competitive, IGF-1 receptor inhibitors can serve as a lead for the development of anti-cancer, anti-psoriatic and anti-papilloma agents.

Dendritic Cells Sensitize TCRs through Self-MHC-Mediated Src Family Kinase Activation

It is unclear whether peptide-MHC class II (pMHC) complexes on distinct types of APCs differ in their capacity to trigger TCRs. In this study, we show that individual cognate pMHC complexes displayed by dendritic cells (DCs), as compared with nonprofessional APCs, are far better in productively triggering Ag-specific TCRs independently of conventional costimulation. As we further show, this is accomplished by the unique ability of DCs to robustly activate the Src family kinases (SFKs) Lck and Fyn in T cells even in the absence of cognate peptide. Instead, this form of SFK activation depends on interactions of DC-displayed MHC with TCRs of appropriate restriction, suggesting a central role of self-pMHC recognition. DC-mediated SFK activation leads to "TCR licensing," a process that dramatically increases sensitivity and magnitude of the TCR response to cognate pMHC. Thus, TCR licensing, besides costimulation, is a main mechanism of DCs to present Ag effectively.

Preclinical antitumor activity of BMS-599626, a pan-HER kinase inhibitor that inhibits HER1/HER2 homodimer and heterodimer signaling

PURPOSE

The studies described here are intended to characterize the ability of BMS-599626, a small-molecule inhibitor of the human epidermal growth factor receptor (HER) kinase family, to modulate signaling and growth of tumor cells that depend on HER1 and/or HER2.

EXPERIMENTAL DESIGN

The potency and selectivity of BMS-599626 were assessed in biochemical assays using recombinant protein kinases, as well as in cell proliferation assays using tumor cell lines with varying degrees of dependence on HER1 or HER2 signaling. Modulation of receptor signaling was determined in cell assays by Western blot analyses of receptor autophosphorylation and downstream signaling. The ability of BMS-599626 to inhibit receptor heterodimer signaling in tumor cells was studied by receptor coimmunoprecipitation. Antitumor activity of BMS-599626 was evaluated using a number of different xenograft models that represent a spectrum of human tumors with HER1 or HER2 overexpression.

RESULTS

BMS-599626 inhibited HER1 and HER2 with IC50 of 20 and 30 nmol/L, respectively, and was highly selective when tested against a broad panel of diverse protein kinases. Biochemical studies suggested that BMS-599626 inhibited HER1 and HER2 through distinct mechanisms. BMS-599626 abrogated HER1 and HER2 signaling and inhibited the proliferation of tumor cell lines that are dependent on these receptors, with IC50 in the range of 0.24 to 1 micromol/L. BMS-599626 was highly selective for tumor cells that depend on HER1/HER2 and had no effect on the proliferation of cell lines that do not express these receptors. In tumor cells that are capable of forming HER1/HER2 heterodimers, BMS-599626 inhibited heterodimerization and downstream signaling. BMS-599626 had antitumor activity in models that overexpress HER1 (GEO), as well as in models that have HER2 gene amplification (KPL4) or overexpression (Sal2), and there was good correlation between the inhibition of receptor signaling and antitumor activity.

CONCLUSIONS

BMS-599626 is a highly selective and potent inhibitor of HER1 and HER2 kinases and inhibits tumor cell proliferation through modulation of receptor signaling. BMS-599626 inhibits HER1/HER2 receptor heterodimerization and provides an additional mechanism of inhibiting tumors in which receptor coexpression and heterodimerization play a major role in driving tumor growth. The preclinical data support the advancement of BMS-599626 into clinical development for the treatment of cancer.

RET is constitutively activated by novel tandem mutations that alter the active site resulting in multiple endocrine neoplasia type 2B

Constitutive activation of the RET receptor tyrosine kinase underlies the genesis and progression of multiple endocrine neoplasia type 2 (MEN 2), a dominantly inherited cancer predisposition. Importantly, although kinase activation represents a common theme in neoplasias, not all activating mutations are functionally equivalent. Consistent with this, we ascertained a patient with classical features of MEN 2B, but lacking either of the classical mutations in RET (M918T or A883F). Instead, the patient harbors a novel pair of germ line missense mutations in cis at codons 804 and 805. We evaluated the potential physiochemical effects of these substitutions in silico, predicting both to be moderately deleterious in isolation, but severely deleterious in combination. Consistent with this postulate, we show that the identified tandem mutations (V804M/E805K) are biologically active, transforming cells in culture and that their transforming capacity in combination is distinctly synergistic. Furthermore, the V804M/E805K tandem lesion confers resistance to the small molecule receptor tyrosine kinase inhibitor, PP1, suggesting a mode of action distinct from that known for classical MEN 2B mutations. To address this question, we used homology molecular modeling in silico to model the active site of RET. We predict that RET804 constitutes a critical gatekeeper residue that, when mutated in combination with RET805, induces a conformational change in the hinge region that locks the active site in a position permissive for ATP hydrolysis. Our findings have implications both in the clinic and in the successful development of novel kinase-targeted anticancer drugs.

Tyrosine kinase inhibitors and ATP modulate the conversion of smooth muscle L-type Ca2+ channels toward a second open state

Properties of smooth and cardiac L-type Ca2+ channels differ prominently in several physiological aspects, including sympathetic modulation. To assess the possible underlying mechanisms, we applied the whole cell patch-clamp technique to guinea pig detrusor smooth muscle cells, in which only L-type Ca2+ channel currents are observed in practice. During depolarization to large positive potentials, the conformation of the majority of L-type Ca2+ channels is converted from the normal (O1) to a second open state (O2), which undergoes little inactivation during depolarization. Extracellular application of genistein, a known tyrosine kinase inhibitor, significantly attenuated the voltage-dependent conversion of Ca2+ channels to O2, accompanied by reduction of availability, whereas genistin, an inactive analog, had little effect. In the absence of ATP in the patch pipette, intracellular application of either genistein or tyrphostin-47 suppressed the conversion to O2. Computer calculation revealed that the acceleration of the O1 to an inactivated state qualitatively reconstructs the unique effects of PTK inhibitors antagonized by ATP. We concluded that under normal conditions smooth muscle L-type Ca2+ channels are already modulated by tyrosine-kinase and ATP-related mechanism(s) and thereby easily achieve the second conversion, which yields voltage-dependent modulation of L-type Ca2+ current analogous to that in cardiac myocytes during beta-adrenoceptor stimulation.

Regulation of dendritic branching and spine maturation by semaphorin3A-Fyn signaling

A member of semaphorin family, semaphorin3A (Sema3A), acts as a chemorepellent or chemoattractant on a wide variety of axons and dendrites in the development of the nervous systems. We here show that Sema3A induces clustering of both postsynaptic density-95 (PSD-95) and presynaptic synapsin I in cultured cortical neurons without changing the density of spines or filopodia. Neuropilin-1 (NRP-1), a receptor for Sema3A, is present on both axons and dendrites. When the cultured neurons are exposed to Sema3A, the cluster size of PSD-95 is markedly enhanced, and an extensive colocalization of PSD-95 and NRP-1 or actin-rich protrusion is seen. The effects of Sema3A on spine morphology are blocked by PP2, an Src type tyrosine kinase inhibitor, but not by the PP3, the inactive-related compound. In the cultured cortical neurons from fyn(-/-) mice, dendrites bear few spines, and Sema3A does not induce PSD-95 cluster formation on the dendrites. Sema3A and its receptor genes are highly expressed during the synaptogenic period of postnatal days 10 and 15. The cortical neurons in layer V, but not layer III, show a lowered density of synaptic bouton-like structure on dendrites in sema3A- and fyn-deficient mice. The neurons of the double-heterozygous mice show the lowered spine density, whereas those of single heterozygous mice show similar levels of the spine density as the wild type. These findings suggest that the Sema3A signaling pathway plays an important role in the regulation of dendritic spine maturation in the cerebral cortex neurons.

Src family kinases play multiple roles in differentiation of trophoblasts from human term placenta

Tyrosine phosphorylation plays a major role in controlling many biological processes in different cell types. Src family kinases (SFKs) are one of the most studied groups of tyrosine kinases and can mediate a variety of signalling pathways. However, little is known about the expression of SFKs in human term placenta and their implication in trophoblast differentiation. Therefore, we examined the expression profile of SFK members over time in culture and their implication in differentiation. In vitro, freshly isolated cytotrophoblast cells, cultured in 10% fetal bovine serum (FBS), spontaneously aggregate and fuse to form multinucleated cells that resemble phenotypically mature syncytiotrophoblasts, that concomitantly produce human chorionic gonadotropin (hCG) and human placental lactogen (hPL). In this study, we showed that trophoblasts expressed all SFK members and some of them are expressed as different splice variants. Moreover, using real-time PCR, this study showed two different expression profiles of SFKs in human trophoblasts during culture. In addition, the protein level and phosphorylation status of Src were evaluated using specific antibodies. Src was rapidly phosphorylated at Tyr-416 and dephosphorylated at Tyr-527 after FBS addition. Surprisingly, inhibition of SFKs by 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2) or herbimycin A had different effects on trophoblast differentiation. While herbimycin A inhibited morphological and hormonal differentiation, PP2 stimulated hormonal differentiation and inhibited cell adhesion and spreading with no effect on cell fusion. In summary, this study showed that SFKs play different roles in trophoblast differentiation, probably depending on SFK members activated. Thus, this study increases our knowledge and understanding of pathology related to impaired trophoblast differentiation such as pre-eclampsia and trophoblast neoplasm.

Microarrays for the functional analysis of the chemical-kinase interactome

A central challenge in chemical biology is profiling the activity of a large number of chemical structures against hundreds of biological targets, such as kinases. Conventional 32P-incorporation or immunoassay of phosphorylated residues produces high-quality signals for monitoring kinase reactions but is difficult to use in high-throughput screening (HTS) because of cost and the need for well-plate washing. The authors report a method for densely archiving compounds in nanodroplets on peptide or protein substrate-coated microarrays for subsequent profiling by aerosol deposition of kinases. Each microarray contains over 6000 reaction centers (1.0 nL each) whose phosphorylation progress can be detected by immunofluorescence. For p60c-src, the microarray produced a signal-to-background ratio of 36.3 and Z' factor of 0.63 for HTS and accurate enzyme kinetic parameters (KmATP = 3.3 microM) and IC50 values for staurosporine (210 nM) and PP2 (326 nM) at 10 microM adenosine triphosphate (ATP). Similarly, B-Raf phosphorylation of MEK-coated microarrays was inhibited in the nanoliter reactions by GW5074 at the expected IC50 of 9 nM. Common kinase inhibitors were printed on microarrays, and their inhibitory activities were systematically profiled against B-Raf (V599E), KDR, Met, Flt-3 (D835Y), Lyn, EGFR, PDGFRbeta, and Tie2. All results indicate that this platform is well suited for kinetic analysis, HTS, large-scale IC50 determinations, and selectivity profiling.

Focal adhesion kinase signaling regulates cardiogenesis of embryonic stem cells

The signaling steps that induce cardiac differentiation in embryonic stem (ES) cells are incompletely understood. We examined the effect of adhesion signaling including Src and focal adhesion kinase (FAK) on cardiogenesis in mouse ES cells using alpha-myosin heavy chain promoter-driven enhanced green fluorescent protein or luciferase as reporters. Cardiac transcription factors including Nkx2.5 and Tbx5 mRNA were first expressed at day 4 in hanging drop embryoid bodies, and adhesion of embryoid bodies to surfaces at or before that day strongly inhibited differentiation of ES cells to cardiomyocytes. Since adhesion signaling could suppress cardiogenesis through Src kinases, embryoid bodies were exposed to the small molecule PP2, known as a Src family kinase inhibitor. PP2 during embryoid body adhesion dramatically increased cardiomyocyte differentiation and decreased mRNA expression of neuronal cellular adhesion molecule and alpha-fetoprotein, neuroectodermal, and endodermal markers, respectively. Surprisingly, although there was an interaction between Src and FAK in cardiogenesis, the procardiogenic effect of PP2 appeared incompletely explained by Src kinase inhibition, since another Src family kinase inhibitor, SU6656, failed to induce cardiogenesis. Instead, PP2 specifically inhibited adhesion-induced FAK phosphorylation. In ES cells stably expressing FAK-related nonkinase, which functions as a dominant negative FAK, cell migration from embryoid bodies was inhibited, whereas alpha-myosin heavy chain expression and myosin-stained cardiomyocytes were increased, suggesting that reducing cell motility may contribute to cardiogenesis. These data indicate that FAK is a key regulator of cardiogenesis in mouse ES cells and that FAK signaling within embryoid bodies can direct stem cell lineage commitment.

Antiproliferative plant and synthetic polyphenolics are specific inhibitors of vertebrate inositol-1,4,5-trisphosphate 3-kinases and inositol polyphosphate multikinase

Inositol-1,4,5-trisphosphate 3-kinases (IP3K) A, B, and C as well as inositol polyphosphate multikinase (IPMK) catalyze the first step in the formation of the higher phosphorylated inositols InsP5 and InsP6 by metabolizing Ins(1,4,5)P3 to Ins(1,3,4,5)P4. In order to clarify the special role of these InsP3 phosphorylating enzymes and of subsequent anabolic inositol phosphate reactions, a search was conducted for potent enzyme inhibitors starting with a fully active IP3K-A catalytic domain. Seven polyphenolic compounds could be identified as potent inhibitors with IC50 < 200 nM (IC50 given): ellagic acid (36 nM), gossypol (58 nM), (-)-epicatechin-3-gallate (94 nM), (-)-epigallocatechin-3-gallate (EGCG, 120 nM), aurintricarboxylic acid (ATA, 150 nM), hypericin (170 nM), and quercetin (180 nM). All inhibitors displayed a mixed-type inhibition with respect to ATP and a non-competitive inhibition with respect to Ins(1,4,5)P3. Examination of these inhibitors toward IP3K-A, -B, and -C and IPMK from mammals revealed that ATA potently inhibits all kinases while the other inhibitors do not markedly affect IPMK but differentially inhibit IP3K isoforms. We identified chlorogenic acid as a specific IPMK inhibitor whereas the flavonoids myricetin, 3',4',7,8-tetrahydroxyflavone and EGCG inhibit preferentially IP3K-A and IP3K-C. Mutagenesis studies revealed that both the calmodulin binding and the ATP [corrected] binding domain in IP3K are involved in inhibitor binding. Their absence in IPMK and the presence of a unique insertion in IPMK were found to be important for selectivity differences from IP3K. The fact that all identified IP3K and IPMK inhibitors have been reported as antiproliferative agents and that IP3Ks or IPMK often are the best binding targets deserves further investigation concerning their antitumor potential.

New pyrazolo[3,4-d]pyrimidines endowed with A431 antiproliferative activity and inhibitory properties of Src phosphorylation

New 4-aminopyrazolo[3,4-d]pyrimidines bearing various substituents at the position 1 and 6, were synthesized. The new compounds showed antiproliferative activity toward A431 cells, were found to be inhibitors of Src phosphorylation, and induced apoptotic cell death. In particular, 2h was a better inhibitor of Src phosphorylation than the reference compound PP2.

Oncogenic mutations reduce the stability of SRC kinase

The oncogenic potential of the viral tyrosine kinase v-Src is due to its constitutive activity. Unlike the highly homologous cellular c-Src kinase, a C-terminal deletion of the regulatory tail and numerous point mutations make the viral kinase uncontrollable. To determine the basis of these differences, we analysed the structure and stability of v-Src and c-Src in vitro. We show that the stability of v-Src against unfolding and irreversible aggregation is significantly lower than that of c-Src. Furthermore, in v-Src hydrophobic residues are more exposed already in the native state. In consequence, v-Src was found to be inactive close to physiological temperatures. We thus suggest that the ensemble of mutations that transform c-Src into the oncogenic variant cause a concomitant destabilisation of the kinase.

Inhibitors of JAKs/STATs and the kinases: a possible new cluster of drugs

JAK(s)/STAT(s) relay cytokine signals through tyrosine site-specific phosphorylation of the proteins involved in cellular responses for the activation and proliferation of bone marrow-derived cells. In recent years, the constitutive or elevated expression of JAK/STAT has been found in cancer cells and oncogene transfected cells, and has been shown to be involved in the immune rejection of allografts and the inflammatory processes of autoimmune diseases. This review discusses the strategies for screening and rational design of selective, potent JAK/STAT and kinase inhibitors that are either ATP-competitive or non-ATP competitive, naturally derived or synthetic, as well as other unique inhibitors and analogues for different therapeutic indications.

Pyrazolo[3,4-d]pyrimidines Endowed with Antiproliferative Activity on Ductal Infiltrating Carcinoma Cells

Novel 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines are reported with preliminary in vitro activity data indicating that several of them are potent inhibitors (better than the reference compound) of Src phosphorylation of the breast cancer cells 8701-BC, known to overexpress Src. The ability of such compounds to significantly reduce 8701-BC cell proliferation suggests that this scaffold could be a promising lead for the development of antitumoral agents able to block Src phosphorylation of breast cancer cells.

Sequence-based Design of Kinase Inhibitors Applicable for Therapeutics and Target Identification

A platform for specifically modulating kinase-dependent signaling using peptides derived from the catalytic domain of the kinase is presented. This technology, termed KinAce, utilizes the canonical structure of protein kinases. The targeted regions (subdomain V and subdomains IX and X) are analyzed and their sequence, three-dimensional structure, and involvement in protein-protein interaction are highlighted. Short myristoylated peptides were derived from the target regions of the tyrosine kinases c-Kit and Lyn and the serine/threonine kinases 3-phosphoinositide-dependent kinase-1 (PDK1) and Akt/protein kinase B (PKB). For each kinase an active designer peptide is shown to selectively inhibit the signaling of the kinase from which it is derived, and to inhibit cancer cell proliferation in the micromolar range. This technology emerges as an applicable tool for deriving sequence-based selective inhibitors for a broad range of protein kinases as hits that may be further developed into drugs. Moreover, it enables identification of novel kinase targets for selected therapeutic indications as demonstrated in the KinScreen application.

Pyrazolo Pyrimidine-Type Inhibitors of Src Family Tyrosine Kinases Promote Ovarian Steroid-Induced Differentiation of Human Endometrial Stromal Cells In Vitro1

Reversible protein tyrosine phosphorylation, coordinately controlled by protein tyrosine kinases and phosphatases, is a critical element in signal transduction pathways regulating a wide variety of biological processes, including cell growth, differentiation, and tumorigenesis. We have previously reported that c-Src belonging to the Src family tyrosine kinase (SFK) becomes dephosphorylated at tyrosine 530 (Y530) and thereby activated during progestin-induced differentiation of human endometrial stromal cells (i.e., decidualization). In this study, to elucidate the role of decidual c-Src activation, we examined whether 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), both potent and selective SFK inhibitors, affected the ovarian steroid-induced decidualization in vitro. Unexpectedly, PP1 paradoxically increased the kinase activity of decidual c-Src together with dephosphorylation of Y530 in the presence of ovarian steroids. Concomitantly, PP1 enhanced morphological and functional decidualization, as determined by induction of decidualization markers, such as insulin-like growth factor binding protein-1 and prolactin. PP2 also advanced decidualization along with up-regulation of the active form of c-Src whose Y-530 was dephosphorylated. In contrast to PP1 and PP2, herbimycin A, a tyrosine kinase inhibitor with less specificity for SFKs, showed little enhancing effect on the expression of both IGFBP-1 and active c-Src. These results suggest that SFKs, including c-Src, may play a significant role in stromal cell differentiation, providing a clue for a possible therapeutic strategy to modulate endometrial function by targeting signaling pathway(s) involving SFKs.

Development of new insulin-like growth factor-1 receptor kinase inhibitors using catechol mimics

Because insulin-like growth factor-1 (IGF-1) and its receptor play a pivotal role in many cancers, it is an attractive target for the design of inhibitors. Here we present a new family of bioisostere inhibitors, based on the structure of AG 538. AG 538 is a substrate-competitive inhibitor of the IGF-1 receptor (IGF-1R), with an IC50 = 61 nM in a cell-free kinase assay (Blum, G., Gazit, A., and Levitzki, A. (2000) Biochemistry 39, 15705-15712). AG 538 is a low molecular weight compound containing two catechol rings, which are sensitive to oxidation in cells. We have therefore prepared and examined catechol bioisosteres of AG 538. These AG 538 bioisosteres possess similar biological properties to AG 538; they inhibit IGF-1R by a substrate-competitive mechanism and are non-competitive vis à vis ATP. They inhibit IGF-1R kinase activity in the sub-micromolar concentration range in cell-free assays. IGF-1 induced IGF-1R autophosphorylation; IRS-1 phosphorylation and protein kinase B activation are inhibited at a low micromolar concentration range when applied to intact cells. These inhibitors also block the formation of colonies in soft agar by prostate and breast cancer cells. The ability to replace catechol groups with a moiety that is more stable in cells may aid in developing non-catechol-containing substrate-competitive inhibitors targeted toward IGF-1R and possibly against other protein-tyrosine kinases.