Naoyuki Nishiya

Robo4 stabilizes the vascular network by inhibiting pathologic angiogenesis and endothelial hyperpermeability

The angiogenic sprout has been compared to the growing axon, and indeed, many proteins direct pathfinding by both structures. The Roundabout (Robo) proteins are guidance receptors with well-established functions in the nervous system; however, their role in the mammalian vasculature remains ill defined. Here we show that an endothelial-specific Robo, Robo4, maintains vascular integrity. Activation of Robo4 by Slit2 inhibits vascular endothelial growth factor (VEGF)-165-induced migration, tube formation and permeability in vitro and VEGF-165-stimulated vascular leak in vivo by blocking Src family kinase activation. In mouse models of retinal and choroidal vascular disease, Slit2 inhibited angiogenesis and vascular leak, whereas deletion of Robo4 enhanced these pathologic processes. Our results define a previously unknown function for Robo receptors in stabilizing the vasculature and suggest that activating Robo4 may have broad therapeutic application in diseases characterized by excessive angiogenesis and/or vascular leak.

An α 4 integrin–paxillin–Arf-GAP complex restricts Rac activation to the leading edge of migrating cells

Formation of a stable lamellipodium at the front of migrating cells requires localization of Rac activation to the leading edge. Restriction of α4 integrin phosphorylation to the leading edge limits the interaction of α4 with paxillin to the sides and rear of a migrating cell. The α4–paxillin complex inhibits stable lamellipodia, thus confining lamellipod formation to the cell anterior. Here we report that binding of paxillin to the α4 integrin subunit inhibits adhesion-dependent lamellipodium formation by blocking Rac activation. The paxillin LD4 domain mediates this reduction in Rac activity by recruiting an ADP-ribosylation factor GTPase-activating protein (Arf-GAP) that decreases Arf activity, thereby inhibiting Rac. Finally, the localized formation of the α4–paxillin–Arf-GAP complex mediates the polarization of Rac activity and promotes directional cell migration. These findings establish a mechanism for the spatial localization of Rac activity to enhance cell migration.

Slit2-Robo4 signalling promotes vascular stability by blocking Arf6 activity.

Slit–Roundabout (Robo) signalling has a well-understood role in axon guidance. Unlike in the nervous system, however, Slit-dependent activation of an endothelial-specific Robo, Robo4, does not initiate a guidance program. Instead, Robo4 maintains the barrier function of the mature vascular network by inhibiting neovascular tuft formation and endothelial hyperpermeability induced by pro-angiogenic factors. In this study, we used cell biological and biochemical techniques to elucidate the molecular mechanism underlying the maintenance of vascular stability by Robo4. Here, we demonstrate that Robo4 mediates Slit2-dependent suppression of cellular protrusive activity through direct interaction with the intracellular adaptor protein paxillin and its paralogue, Hic-5. Formation of a Robo4–paxillin complex at the cell surface blocks activation of the small GTPase Arf6 and, consequently, Rac by recruitment of Arf-GAPs (ADP-ribosylation factor- directed GTPase-activating proteins) such as GIT1. Consistent with these in vitro studies, inhibition of Arf6 activity in vivo phenocopies Robo4 activation by reducing pathologic angiogenesis in choroidal and retinal vascular disease and VEGF-165 (vascular endothelial growth factor-165)-induced retinal hyperpermeability. These data reveal that a Slit2–Robo4–paxillin–GIT1 network inhibits the cellular protrusive activity underlying neovascularization and vascular leak, and identify a new therapeutic target for ameliorating diseases involving the vascular system.

Small-molecule synergist of the Wnt/β-catenin signaling pathway

The Wnt/β-catenin signaling pathway regulates cell fate and behavior during embryogenesis, adult tissue homeostasis, and regeneration. When inappropriately activated, the pathway has been linked to colorectal cancer and melanoma, and when attenuated it may contribute to Alzheimers disease and osteoporosis. Small molecules that modulate Wnt signaling will likely provide new insights into the regulation of this key developmental pathway and ultimately provide pharmacological agents to control Wnt signaling in vivo. To this end, we screened a library of 100,000 small molecules for activity in a cell-based assay of Wnt/β-catenin signaling and discovered a purine derivative, QS11, that synergizes with Wnt-3a ligand in the activation of Wnt/β-catenin signal transduction. Through affinity chromatography and subsequent functional assays, we showed that QS11 binds and inhibits the GTPase activating protein of ADP-ribosylation factor 1 (ARFGAP1), suggesting that QS11 modulates Wnt/β-catenin signaling through an effect on protein trafficking. Consistent with its function as an ARFGAP inhibitor, QS11 inhibits migration of ARFGAP overexpressing breast cancer cells.

Small molecules inhibiting the nuclear localization of YAP/TAZ for chemotherapeutics and chemosensitizers against breast cancers

YAP and TAZ oncoproteins confer malignancy and drug resistance to various cancer types. We screened for small molecules that inhibit the nuclear localization of YAP/TAZ. Dasatinib, statins and pazopanib inhibited the nuclear localization and target gene expression of YAP and TAZ. All three drugs induced phosphorylation of YAP and TAZ, and pazopanib induced proteasomal degradation of YAP/TAZ. The sensitivities to these drugs are correlated with dependence on YAP/TAZ in breast cancer cell lines. Combinations of these compounds with each other or with other anti‐cancer drugs efficiently reduced cell proliferation of YAP/TAZ‐dependent breast cancer cells. These results suggest that these drugs can be therapeutics and chemosensitizers for YAP/TAZ‐dependent breast cancers.

Multimodal Effects of Small Molecule ROCK and LIMK Inhibitors on Mitosis, and Their Implication as Anti- Leukemia Agents

Accurate chromosome segregation is vital for cell viability. Many cancer cells show chromosome instability (CIN) due to aberrant expression of the genes involved in chromosome segregation. The induction of massive chromosome segregation errors in such cancer cells by small molecule inhibitors is an emerging strategy to kill these cells selectively. Here we screened and characterized small molecule inhibitors which cause mitotic chromosome segregation errors to target cancer cell growth. We screened about 300 chemicals with known targets, and found that Rho-associated coiled-coil kinase (ROCK) inhibitors bypassed the spindle assembly checkpoint (SAC), which delays anaphase onset until proper kinetochore-microtubule interactions are established. We investigated how ROCK inhibitors affect chromosome segregation, and found that they induced microtubule-dependent centrosome fragmentation. Knockdown of ROCK1 and ROCK2 revealed their additive roles in centrosome integrity. Pharmacological inhibition of LIMK also induced centrosome fragmentation similar to that by ROCK inhibitors. Inhibition of ROCK or LIMK hyper-stabilized mitotic spindles and impaired Aurora-A activation. These results suggested that ROCK and LIMK are directly or indirectly involved in microtubule dynamics and activation of Aurora-A. Furthermore, inhibition of ROCK or LIMK suppressed T cell leukemia growth in vitro, but not peripheral blood mononuclear cells. They induced centrosome fragmentation and apoptosis in T cell leukemia cells. These results suggested that ROCK and LIMK can be a potential target for anti-cancer drugs.

Identification of LY83583 as a specific inhibitor of Candida albicans MPS1 protein kinase.

Candida albicans is the most common and virulent fungus causing candidiasis in various parts of the body and can be lethal to immunocompromised patients. All currently known antifungal therapies are drugs which cause serious side effects in the host. An inhibitor specific for fungus survival is an ideal therapeutic. C. albicans MPS1 (monopolar spindle 1) has been reported as a kinase essential to its survival. Because CaMps1p shares limited sequence homology with the human ortholog (hMps1p), we screened for a chemical inhibitor in anticipation of finding one with Candida specific cytotoxicity. In vitro screening using a recombinant catalytic domain of CaMps1p identified LY83583 (6-anilino-5,8-quinolinedione), known as a guanylate cyclase inhibitor, to be blocking CaMps1p kinase activity. In addition to its in vitro kinase inhibition, LY83583 reduced the growth rate of C. albicans. Finally, we compared the inhibitory activity on CaMps1p and hMps1p among inhibitors against those kinases. LY83583 showed specific inhibition for CaMps1p with no effect on hMps1p activity. Conversely, the CaMps1p activity was not affected by known hMps1p inhibitors. These findings suggest that CaMps1p may well be an ideal target molecule for antifungal therapy.

JAK3 inhibitor VI is a mutant specific inhibitor for epidermal growth factor receptor with the gatekeeper mutation T790M

AIM To identify non-quinazoline kinase inhibitors effective against drug resistant mutants of epidermal growth factor receptor (EGFR). METHODS A kinase inhibitor library was subjected to screening for specific inhibition pertaining to the in vitro kinase activation of EGFR with the gatekeeper mutation T790M, which is resistant to small molecular weight tyrosine kinase inhibitors (TKIs) for EGFR in non-small cell lung cancers (NSCLCs). This inhibitory effect was confirmed by measuring autophosphorylation of EGFR T790M/L858R in NCI-H1975 cells, an NSCLC cell line harboring the gatekeeper mutation. The effects of a candidate compound, Janus kinase 3 (JAK3) inhibitor VI, on cell proliferation were evaluated using the MTT assay and were compared between T790M-positive and -negative lung cancer cell lines. JAK3 inhibitor VI was modeled into the ATP-binding pocket of EGFR T790M/L858R. Potential physical interactions between the compound and kinase domains of wild-type (WT) or mutant EGFRs or JAK3 were estimated by calculating binding energy. The gatekeeper residues of EGFRs and JAKs were aligned to discuss the similarities among EGFR T790M and JAKs. RESULTS We found that JAK3 inhibitor VI, a known inhibitor for JAK3 tyrosine kinase, selectively inhibits EGFR T790M/L858R, but has weaker inhibitory effects on the WT EGFR in vitro. JAK3 inhibitor VI also specifically reduced autophosphorylation of EGFR T790M/L858R in NCI-H1975 cells upon EGF stimulation, but did not show the inhibitory effect on WT EGFR in A431 cells. Furthermore, JAK3 inhibitor VI suppressed the proliferation of NCI-H1975 cells, but showed limited inhibitory effects on the WT EGFR-expressing cell lines A431 and A549. A docking simulation between JAK3 inhibitor VI and the ATP-binding pocket of EGFR T790M/L858R predicted a potential binding status with hydrogen bonds. Estimated binding energy of JAK3 inhibitor VI to EGFR T790M/L858R was more stable than its binding energy to the WT EGFR. Amino acid sequence alignments revealed that the gatekeeper residues of JAK family kinases are methionine in WT, similar to EGFR T790M, suggesting that TKIs for JAKs may also be effective for EGFR T790M. CONCLUSION Our findings demonstrate that JAK3 inhibitor VI is a gatekeeper mutant selective TKI and offer a strategy to search for new EGFR T790M inhibitors.

Design, synthesis, and evaluation of A-ring-modified lamellarin N analogues as noncovalent inhibitors of the EGFR T790M/L858R mutant

A series of A-ring-modified lamellarin N analogues were designed, synthesized, and evaluated as potential noncovalent inhibitors of the EGFR T790M/L858R mutant, a causal factor in the drug-resistant non-small cell lung cancer. Several water-soluble ammonium- or guanidinium-tethered analogues exhibited good kinase inhibitory activities. The most promising analogue, 14f, displayed an excellent inhibitory profile against the T790M/L858R mutant [IC50 (WT) = 31.8 nM; IC50 (T790M/L858R) = 8.9 nM]. The effects of A-ring-substituents on activity were rationalized by docking studies.

Augmentation of the therapeutic efficacy of WEE1 kinase inhibitor AZD1775 by inhibiting the YAP–E2F1–DNA damage response pathway axis

The main reasons for failure of cancer chemotherapy are intrinsic and acquired drug resistance. The Hippo pathway effector Yes‐associated protein (YAP) is associated with resistance to both cytotoxic and molecular targeted drugs. Several lines of evidence indicate that YAP activates transcriptional programmes to promote cell cycle progression and DNA damage responses. Therefore, we hypothesised that YAP is involved in the sensitivity of cancer cells to small‐molecule agents targeting cell cycle‐related proteins. Here, we report that the inactivation of YAP sensitises the OVCAR‐8 ovarian cancer cell line to AZD1775, a small‐molecule WEE1 kinase inhibitor. The accumulation of DNA damage and mitotic failures induced by AZD1775‐based therapy were further enhanced by YAP depletion. YAP depletion reduced the expression of the Fanconi anaemia (FA) pathway components required for DNA repair and their transcriptional regulator E2F1. These results suggest that YAP activates the DNA damage response pathway, exemplified by the FA pathway and E2F1. Furthermore, we aimed to apply this finding to combination chemotherapy against ovarian cancers. The regimen containing dasatinib, which inhibits the nuclear localisation of YAP, improved the response to AZD1775‐based therapy in the OVCAR‐8 ovarian cancer cell line. We propose that dasatinib acts as a chemosensitiser for a subset of molecular targeted drugs, including AZD1775, by targeting YAP.