Quantitative high-throughput cell-based assays for inhibitors of ROCK kinases

Chemically induced neurite-like outgrowth reveals a multicellular network function in patient-derived glioblastoma cells

Tumor stem cells and malignant multicellular networks have been separately implicated in the therapeutic resistance of glioblastoma multiforme (GBM), the most aggressive type of brain cancer in adults. Here, we show that small-molecule inhibition of RHO-associated serine/threonine kinase proteins (ROCKi) significantly promoted the outgrowth of neurite-like cell projections in cultures of heterogeneous patient-derived GBM stem-like cells. These projections formed de novo-induced cellular network (iNet) 'webs', which regressed after withdrawal of ROCKi. Connected cells within the iNet web exhibited long range Ca²⁺ signal transmission, and significant lysosomal and mitochondrial trafficking. In contrast to their less-connected vehicle control counterparts, iNet cells remained viable and proliferative after high-dose radiation. These findings demonstrate a link between ROCKi-regulated cell projection dynamics and the formation of radiation-resistant multicellular networks. Our study identifies means to reversibly induce iNet webs ex vivo, and may thereby accelerate future studies into the biology of GBM cellular networks.

Inhibition of ROCK1 kinase modulates both tumor cells and stromal fibroblasts in pancreatic cancer

ROCK, or Rho-associated coiled coil-containing protein kinase, is a member of the AGC kinase family and has been shown to play a role in cell migration, ECM synthesis, stress-fiber assembly, and cell contraction. Increased ROCK expression has been reported in multiple pathological conditions, including cancer. Here, we report increased expression of ROCK 1 in pancreatic tumor epithelial cells as well as in cancer associated fibroblasts (CAF). In our analysis, 62% of tumor samples exhibited ≥2+ in staining intensity by IHC analysis, versus 40% of adjacent normal tissue samples (P<0.0001). Thus, we hypothesized that ROCKs may play a significant role in pancreatic cancer progression, and may serve as a suitable target for treatment. We report a low frequency (4/34) amplification of the ROCK1 gene locus at chromosome 18q11.1 in pancreatic ductal adenocarcinoma (PDAC) patient tissue samples by aCGH analysis. Inhibition of ROCK kinase activity by a small molecule inhibitor (fasudil) resulted in moderate (IC50s of 6-71 μM) inhibition of PDAC cell proliferation, migration, and activation of co-cultured stellate cells. In the KPC mouse model for pancreatic cancer, fasudil decreased tumor collagen deposition. This translated to an enhanced overall survival of the mice and an increase in gemcitabine uptake. Though fasudil may target both the tumor epithelial cells and the CAFs, our findings are consistent with the hypothesis that inhibition of tumor stroma enhances drug penetration and efficacy in PDAC. Overall, our data suggests that ROCK1 may serve as a potential therapeutic target to enhance current treatment regimens for pancreatic cancer.

Inhibitors of the ROCK serine/threonine kinases: key effectors of the RhoA small GTPase

Aberrant activation of the RhoA small GTPase has been implicated in cancer and other human diseases. Therefore, inhibitors of RhoA may have important therapeutic value. However, similar to the Ras small GTPases, RhoA itself is not considered a tractable target and is currently considered to be "undruggable." While recent efforts suggest that direct inhibitors of the Ras oncoprotein may yet be developed, the most promising directions for anti-Ras inhibitors involve inhibitors of protein kinases that are activated downstream of Ras. By analogy, protein kinases activated downstream of RhoA may provide more attractive directions for the development of anti-RhoA inhibitors. Among the multitude of RhoA effectors, the ROCK serine/threonine kinases have emerged as attractive targets for anti-RhoA drug discovery. In this review, we summarize the current status of the development of small molecule inhibitors of ROCK.

PTK7-Src signaling at epithelial cell contacts mediates spatial organization of actomyosin and planar cell polarity

Actomyosin contractility plays a key role in tissue morphogenesis. During mammalian development, PTK7 regulates epithelial morphogenesis and planar cell polarity (PCP) through modulation of actomyosin contractility, but the underlying mechanism is unknown. Here, we show that PTK7 interacts with the tyrosine kinase Src and stimulates Src signaling along cell-cell contacts. We further identify ROCK2 as a target of junctional PTK7-Src signaling. PTK7 knockdown in cultured epithelial cells reduced the level of active Src at cell-cell contacts, resulting in delocalization of ROCK2 from cell-cell contacts and decreased junctional contractility, with a concomitant increase in actomyosin on the basal surface. Moreover, we present in vivo evidence that Src family kinase (SFK) activity is critical for PCP regulation in the auditory sensory epithelium and that PTK7-SFK signaling regulates tyrosine phosphorylation of junctional ROCK2. Together, these results delineate a PTK7-Src signaling module for spatial regulation of ROCK activity, actomyosin contractility, and epithelial PCP.

Linking phenotype to kinase: identification of a novel benzoxaborole hinge-binding motif for kinase inhibition and development of high-potency rho kinase inhibitors

Benzoxaboroles are a novel class of drug-like compounds that have been rich sources of novel inhibitors for various enzymes and of new drugs. While examining benzoxaborole activity in phenotypic screens, our attention was attracted by the (aminomethylphenoxy)benzoxaborole family, which potently inhibited Toll-like receptor-stimulated cytokine secretion from leukocytes. After considering their structure-activity relationships and the central role of kinases in leukocyte biology, we performed a kinome-wide screen to investigate the members of the (aminomethylphenoxy)benzoxaborole family. This technique identified Rho-activated kinase (ROCK) as a target. We showed competitive behavior, with respect to ATP, and then determined the ROCK2-drug cocrystal structure. The drug occupies the ATP site in which the oxaborole moiety provides hydrogen bond donors and acceptors to the hinge, and the aminomethyl group interacts with the magnesium/ATP-interacting aspartic acid common to protein kinases. The series exhibits excellent selectivity against most of the kinome, with greater than 15-fold selectivity against the next best member of the AGC protein kinase subfamily. Medicinal chemistry efforts with structure-based design resulted in a compound with a Ki of 170 nM. Cellular studies revealed strong enzyme inhibition rank correlation with suppression of intracellular phosphorylation of a ROCK substrate. The biochemical potencies of these compounds also translated to functional activity, causing smooth muscle relaxation in rat aorta and guinea pig trachea. The series exhibited oral availability and one member reduced rat blood pressure, consistent with ROCK's role in smooth muscle contraction. Thus, the benzoxaborole moiety represents a novel hinge-binding kinase scaffold that may have potential for therapeutic use.

Myosin phosphatase modulates the cardiac cell fate by regulating the subcellular localization of Nkx2.5 in a Wnt/Rho-associated protein kinase-dependent pathway

RATIONALE

Nkx2.5 is a transcription factor that regulates cardiomyogenesis in vivo and in embryonic stem cells. It is also a common target in congenital heart disease. Although Nkx2.5 has been implicated in the regulation of many cellular processes that ultimately contribute to cardiomyogenesis and morphogenesis of the mature heart, relatively little is known about how it is regulated at a functional level.

OBJECTIVE

We have undertaken a proteomic screen to identify novel binding partners of Nkx2.5 during cardiomyogenic differentiation in an effort to better understand the regulation of its transcriptional activity.

METHODS AND RESULTS

Purification of Nkx2.5 from differentiating cells identified the myosin phosphatase subunits protein phosphatase 1β and myosin phosphatase targeting subunit 1 (Mypt1) as novel binding partners. The interaction with protein phosphatase 1 β/Mypt1 resulted in exclusion of Nkx2.5 from the nucleus and, consequently, inhibition of its transcriptional activity. Exclusion of Nkx2.5 was inhibited by treatment with leptomycin B and was dependent on an Mypt1 nuclear export signal. Furthermore, in transient transfection experiments, Nkx2.5 colocalized outside the nucleus with phosphorylated Mypt1 in a manner dependent on Wnt signaling and Rho-associated protein kinase. Treatment of differentiating mouse embryonic stem cells with Wnt3a resulted in enhanced phosphorylation of endogenous Mypt1, increased nuclear exclusion of endogenous Nkx2.5, and a failure to undergo terminal cardiomyogenesis. Finally, knockdown of Mypt1 resulted in rescue of Wnt3a-mediated inhibition of cardiomyogenesis, indicating that Mypt1 is required for this process.

CONCLUSIONS

We have identified a novel interaction between Nkx2.5 and myosin phosphatase. Promoting this interaction represents a novel mechanism whereby Wnt3a regulates Nkx2.5 and inhibits cardiomyogenesis.

ROCK1 and ROCK2 are required for non-small cell lung cancer anchorage-independent growth and invasion

Evidence is emerging that the closely related ROCK1 and ROCK2 serine/threonine kinases support the invasive and metastatic growth of a spectrum of human cancer types. Therefore, inhibitors of ROCK are under preclinical development. However, a key step in their development involves the identification of genetic biomarkers that will predict ROCK inhibitor antitumor activity. One identified mechanism for ROCK activation in cancer involves the loss of function of the DLC1 tumor suppressor gene, which encodes a GTPase activating protein (RhoGAP) for the RhoA and RhoC small GTPases. DLC-1 loss may lead to hyperactivation of RhoA/C and its downstream effectors, the ROCK kinases. We therefore determined whether loss of DLC-1 protein expression identifies non-small cell lung carcinoma (NSCLC) cell lines whose growth and invasion phenotypes are sensitive to ROCK inhibition. We identified and characterized a novel small molecule pharmacologic inhibitor of ROCK and additionally applied genetic approaches to impair ROCK1 and/or ROCK2 activity, and we determined that although NSCLC anchorage-dependent growth was ROCK-independent, both anchorage-independent growth and Matrigel invasion were ROCK-dependent. However, loss of DLC-1 expression did not correlate with ROCK activation or with OXA-06 sensitivity. Unexpectedly, suppression of ROCK1 or ROCK2 expression alone was sufficient to impair anchorage-independent growth, supporting their nonoverlapping roles in oncogenesis. Mechanistically, the block in anchorage-independent growth was associated with accumulation of cells in the G(0)-G(1) phase of the cell cycle, but not increased anoikis. We conclude that ROCK may be a useful therapeutic target for NSCLC.

ROCK1 and ROCK2 are required for non-small cell lung cancer anchorage-independent growth and invasion

Evidence is emerging that the closely related ROCK1 and ROCK2 serine/threonine kinases support the invasive and metastatic growth of a spectrum of human cancer types. Therefore, inhibitors of ROCK are under preclinical development. However, a key step in their development involves the identification of genetic biomarkers that will predict ROCK inhibitor antitumor activity. One identified mechanism for ROCK activation in cancer involves the loss of function of the DLC1 tumor suppressor gene, which encodes a GTPase activating protein (RhoGAP) for the RhoA and RhoC small GTPases. DLC-1 loss may lead to hyperactivation of RhoA/C and its downstream effectors, the ROCK kinases. We therefore determined whether loss of DLC-1 protein expression identifies non-small cell lung carcinoma (NSCLC) cell lines whose growth and invasion phenotypes are sensitive to ROCK inhibition. We identified and characterized a novel small molecule pharmacologic inhibitor of ROCK and additionally applied genetic approaches to impair ROCK1 and/or ROCK2 activity, and we determined that although NSCLC anchorage-dependent growth was ROCK-independent, both anchorage-independent growth and Matrigel invasion were ROCK-dependent. However, loss of DLC-1 expression did not correlate with ROCK activation or with OXA-06 sensitivity. Unexpectedly, suppression of ROCK1 or ROCK2 expression alone was sufficient to impair anchorage-independent growth, supporting their nonoverlapping roles in oncogenesis. Mechanistically, the block in anchorage-independent growth was associated with accumulation of cells in the G(0)-G(1) phase of the cell cycle, but not increased anoikis. We conclude that ROCK may be a useful therapeutic target for NSCLC.

Rho kinase-2 activation in human endothelial cells drives lysophosphatidic acid-mediated expression of cell adhesion molecules via NF-kappaB p65

Endothelial cells play an important role in the recruitment of immune cells to a disease locus through the induced expression of chemokines and cell adhesion molecules (CAMs). The proinflammatory lysophospholipid, lysophosphatidic acid (LPA), which is elevated in multiple inflammatory diseases, is a potent activator of the RhoA/Rho kinase signaling pathway and has been shown to induce the expression of CAMs in endothelial cells. The present study was undertaken to map signal transduction downstream of LPA and to investigate the contributions of the Rho kinase isoforms ROCK1 and ROCK2 to adhesion molecule expression in human umbilical vein endothelial cells. LPA activated Rho kinase within minutes and subsequently the NF-kappaB pathway through phosphorylation of the p65 subunit. The lipid also induced the late expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Pharmacologic inhibition of Rho kinase signaling blocked LPA-induced p65 phosphorylation and suppressed ICAM-1 and VCAM-1 expression. Inhibition of the NF-kappaB pathway had no impact on LPA-induced Rho kinase activation, but inhibited adhesion molecule expression. Small interfering RNA-facilitated knockdown of each isoform identified ROCK2 as the mediator of LPA-driven phosphorylation of NF-kappaB p65 and of ICAM-1 and VCAM-1 mRNA and protein induction. Taken collectively, our data are consistent with Rho kinase being upstream of NF-kappaB in driving LPA-mediated adhesion molecule expression. This study also provides the first evidence of the critical involvement of ROCK2 in LPA-induced CAM expression through activation of the NF-kappaB pathway in human endothelial cells.

Integrins stimulate E-cadherin-mediated intercellular adhesion by regulating Src-kinase activation and actomyosin contractility

Cadherins and integrins are major adhesion molecules regulating cell-cell and cell-matrix interactions. In vitro and in vivo studies have demonstrated the existence of crosstalk between integrins and cadherins in cell adhesion and motility. We used a dual pipette assay to measure the force required to separate E-cadherin-producing cell doublets and to investigate the role of integrin in regulating the strength of intercellular adhesion. A greater force was required to separate cell doublets bound to fibronectin or vitronectin-coated beads than for doublets bound to polylysine-coated beads. This effect depended on cell spreading and the duration of stimulation. Cells expressing type II cadherin-7 also responded to fibronectin stimulation to produce a higher intercellular adhesion. Establishment of cadherin-mediated adhesion needed ROCK, MLCK and myosin ATPase II activity. The regulation of intercellular adhesion strength by integrin stimulation required activation of Src family kinases, ROCK and actomyosin contractility. These findings highlight the importance and mechanisms of molecular crosstalk between cadherins and integrins in the control of cell plasticity during histogenesis and morphogenesis.