Makoto Muroi

The identification of an osteoclastogenesis inhibitor through the inhibition of glyoxalase I

Osteoclasts, bone-resorptive multinucleated cells derived from hematopoietic stem cells, are associated with many bone-related diseases, such as osteoporosis. Osteoclast-targeting small-molecule inhibitors are valuable tools for studying osteoclast biology and for developing antiresorptive agents. Here, we have discovered that methyl-gerfelin (M-GFN), the methyl ester of the natural product gerfelin, suppresses osteoclastogenesis. By using M-GFN-immobilized beads, glyoxalase I (GLO1) was identified as an M-GFN-binding protein. GLO1 knockdown and treatment with an established GLO1 inhibitor in osteoclast progenitor cells interfered with osteoclast generation, suggesting that GLO1 activity is required for osteoclastogenesis. In cells, GLO1 plays a critical role in the detoxification of 2-oxoaldehydes, such as methylglyoxal. M-GFN inhibited the enzymatic activity of GLO1 in vitro and in situ. Furthermore, the cocrystal structure of the GLO1/M-GFN complex revealed the binding mode of M-GFN at the active site of GLO1. These results suggest that M-GFN targets GLO1, resulting in the inhibition of osteoclastogenesis.

Prodigiosin 25-C uncouples vacuolar type H+-ATPase, inhibits vacuolar acidification and affects glycoprotein processing

Prodigiosin 25‐C inhibited the accumulation of 3‐(2,4‐dinitroanilino)‐3′‐amino‐N‐methyldipropylamine and acridine orange in the acidic compartments of baby hamster kidney cells with little perturbation of cellular ATP levels. In rat liver lysosomes, prodigiosin 25‐C inhibited the proton pump activity with an IC50 of approximately 30 nM, but did not affect ATPase activity up to 1 μM. It also delayed the transport of vesicular stomatitis virus G protein and induced a drastic swelling of Golgi apparatus and mitochondria. These results indicate that prodigiosin 25‐C raises the pH of acidic compartments through inhibition of the proton pump activity of vacuolar type H+‐ATPase, thereby causing the functional and morphological changes to the Golgi apparatus.

Fusarisetin A, an Acinar Morphogenesis Inhibitor from a Soil Fungus, Fusarium sp. FN080326

An acinar morphogenesis inhibitor named fusarisetin A (1) that possesses both an unprecedented carbon skeleton and a new pentacyclic ring system has been identified from an in-house fractionated fungal library using a three-dimensional matrigel-induced acinar morphogenesis assay system. The structure of 1 was determined in detail by NMR and circular dichroism spectroscopy, X-ray analysis, and chemical reaction experiments.

Application of Proteomic Profiling Based on 2D-DIGE for Classification of Compounds According to the Mechanism of Action

The development of new anticancer agents derived from natural resources requires a rapid identification of their molecular mechanism of action. To make this step short, we have initiated the proteomic profiling of HeLa cells treated with anticancer drugs representing a wide spectrum of mechanisms of action using two-dimensional difference gel electrophoresis (2D-DIGE). Unique proteome patterns were observed in HeLa cells treated with the HSP90 inhibitor geldanamycin, and were similar to the patterns induced by radicicol, a structurally different HSP90 inhibitor. On the other hand, etoposide and ICRF-193, compounds claimed to be topoisomerase II inhibitors, showed different proteomic profiles, which reflect their different biological activities as revealed by cell-cycle analysis. Thus far, combined data from 19 compounds have allowed their successful classification by cluster analysis according to the mechanism of action.

Morphobase, an Encyclopedic Cell Morphology Database, and Its Use for Drug Target Identification

Visual observation is a powerful approach for screening bioactive compounds that can facilitate the discovery of attractive druggable targets following their chemicobiological validation. So far, many high-content approaches, using sophisticated imaging technology and bioinformatics, have been developed. In our study, we aimed to develop a simpler method that focuses on intact cell images because we found that dynamic changes in morphology are informative, often reflecting the mechanism of action of a drug. Here, we constructed a chemical-genetic phenotype profiling system, based on the high-content cell morphology database Morphobase. This database compiles the phenotypes of cancer cell lines that are induced by hundreds of reference compounds, wherein those of well-characterized anticancer drugs are classified by mode of action. Furthermore, we demonstrate the applicability of this system in identifying NPD6689, NPD8617, and NPD8969 as tubulin inhibitors.

Xanthohumol Impairs Autophagosome Maturation through Direct Inhibition of Valosin-Containing Protein

Autophagy is a bulk, nonspecific protein degradation pathway that is involved in the pathogenesis of cancer and neurodegenerative disease. Here, we observed that xanthohumol (XN), a prenylated chalcone present in hops (Humulus lupulus L.) and beer, modulates autophagy. By using XN-immobilized beads, valosin-containing protein (VCP) was identified as a XN-binding protein. VCP has been reported to be an essential protein for autophagosome maturation. Using an in vitro pull down assay, we showed that XN bound directly to the N domain, which is known to mediate cofactor and substrate binding to VCP. These data indicated that XN inhibited the function of VCP, thereby allowing the impairment of autophagosome maturation and resulting in the accumulation of microtubule-associated protein 1 light chain 3-II (LC3-II). This is the first report demonstrating XN as a VCP inhibitor that binds directly to the N domain of VCP. Our finding that XN bound to and inactivated VCP not only reveals the molecular mechanism of XN-modulated autophagy but may also explain how XN exhibits various biological activities that have been reported previously.

Iejimalides Show Anti-Osteoclast Activity via V-ATPase Inhibition

Iejimalides (IEJLs), 24-membered macrolides, are potent antitumor compounds, but their molecular targets remain to be revealed. In the course of screening, we identified IEJLs as potent osteoclast inhibitors. Since it is known that osteoclasts are sensitive to vacuolar H+-ATPase (V-ATPase) inhibitor, we investigated the effect of IEJLs on V-ATPases. IEJLs inhibited the V-ATPases of both mammalian and yeast cells in situ, and of yeast V-ATPases in vitro. A bafilomycin-resistant yeast mutant conferred IEJL resistance, suggesting that IEJLs bind a site similar to the bafilomycins/concanamycins-binding site. These results indicate that IEJLs are novel V-ATPase inhibitors, and that antitumor and antiosteporotic activities are exerted via V-ATPase inhibition.

Involvement of Disulfide Bond Formation in the Activation of Heparanase

Heparanase is overexpressed in many solid tumor cells and is capable of specifically cleaving heparan sulfate, and this activity is associated with the metastatic potential of tumor cells; however, the activation mechanism of heparanase has remained unknown. In this study, we investigated the link between disulfide bond formation and the activation of heparanase in human tumor cells. Mass spectrometry analysis of heparanase purified from a conditioned medium of human fibrosarcoma cells revealed two disulfide bonds, Cys127-Cys179 and Cys437-Cys542, and one S-cysteinylation at the Cys211 residue. It was shown that, although the formation of the Cys127-Cys179 bond and S-cysteinylation at Cys211 have little effect on heparanase function, the disulfide bond between Cys437 and Cys542 is necessary for the secretion and activation of heparanase. Thus, the present findings will provide a basis for the further refinement of heparanase structural studies and for the development of novel heparanase inhibitors.

Polo-like kinase 1 phosphorylates and regulates Bcl-x L during pironetin-induced apoptosis

Bcl-xL, an anti-apoptotic Bcl-2 family member protein, contributes to the resistance against chemotherapies such as tubulin-binder treatment in many human tumors. Although Bcl-xL is phosphorylated after tubulin-binder treatment, the role of the phosphorylation and its responsible kinase(s) are poorly understood. Here, we identified Plk1 (polo-like kinase 1) as a Bcl-xL kinase. Same location of Bcl-xL and Plk1 was revealed by immunocytochemical analyses at M-phase in situ. Plk1 phosphorylates Bcl-xL in vitro, and we identified Plk1 phosphorylation sites in Bcl-xL. When all of these phosphorylation sites were substituted to alanines, the anti-apoptotic activity of the Bcl-xL mutant against the apoptosis induced by pironetin, but not against ultraviolet-induced apoptosis, was increased. These observations suggest that Plk1 is a regulator of Bcl-xL phosphorylation and controls the anti-apoptotic activity of Bcl-xL during pironetin-induced apoptosis.

Proteomics accelerating the identification of the target molecule of bioactive small molecules

Failures in many drug development programs in the past decades were related to unspecified mechanism of action and poor pharmacokinetic (PK) properties. Recent developments are focused on well defined targets, improved PK profiles, however, not much is known about off-target effects, especially those responsible for diminishing drug activity. Steadily increasing application of proteomics in drug development should expose clinically relevant proteins for the analysis of drug effects, to show what group of patients will respond and who should not be treated with an agent.