Research ArticleRegenerative Medicine

Pharmacological targeting of kinases MST1 and MST2 augments tissue repair and regeneration

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Science Translational Medicine  17 Aug 2016:
Vol. 8, Issue 352, pp. 352ra108
DOI: 10.1126/scitranslmed.aaf2304

Drug-induced regeneration

Popping a pill to repair an organ may eventually become reality. Turning away from conventional scaffolds, materials, and cell-based regenerative medicine strategies, Fan and colleagues sought a small molecule that could specifically target a critical signaling molecule in the Hippo pathway. Loss of kinases in this pathway, MST1/2, increases cell proliferation during development; thus, the authors hypothesized that inhibiting their activity in mature organs could help repair any damage. They discovered a drug, XMU-MP-1, that blocked MST1/2 activity and found that it promoted liver repair and regeneration in four different mouse models of acute and chronic injuries, including acetaminophen-induced injury, which is a common cause of liver failure worldwide. Such a pharmacological strategy could make tissue regeneration easier for many, compared to complex biomaterial and cell therapies.

Abstract

Tissue repair and regenerative medicine address the important medical needs to replace damaged tissue with functional tissue. Most regenerative medicine strategies have focused on delivering biomaterials and cells, yet there is the untapped potential for drug-induced regeneration with good specificity and safety profiles. The Hippo pathway is a key regulator of organ size and regeneration by inhibiting cell proliferation and promoting apoptosis. Kinases MST1 and MST2 (MST1/2), the mammalian Hippo orthologs, are central components of this pathway and are, therefore, strong target candidates for pharmacologically induced tissue regeneration. We report the discovery of a reversible and selective MST1/2 inhibitor, 4-((5,10-dimethyl-6-oxo-6,10-dihydro-5H-pyrimido[5,4-b]thieno[3,2-e][1,4]diazepin-2-yl)amino)benzenesulfonamide (XMU-MP-1), using an enzyme-linked immunosorbent assay–based high-throughput biochemical assay. The cocrystal structure and the structure-activity relationship confirmed that XMU-MP-1 is on-target to MST1/2. XMU-MP-1 blocked MST1/2 kinase activities, thereby activating the downstream effector Yes-associated protein and promoting cell growth. XMU-MP-1 displayed excellent in vivo pharmacokinetics and was able to augment mouse intestinal repair, as well as liver repair and regeneration, in both acute and chronic liver injury mouse models at a dose of 1 to 3 mg/kg via intraperitoneal injection. XMU-MP-1 treatment exhibited substantially greater repopulation rate of human hepatocytes in the Fah-deficient mouse model than in the vehicle-treated control, indicating that XMU-MP-1 treatment might facilitate human liver regeneration. Thus, the pharmacological modulation of MST1/2 kinase activities provides a novel approach to potentiate tissue repair and regeneration, with XMU-MP-1 as the first lead for the development of targeted regenerative therapeutics.

INTRODUCTION

The mechanisms controlling tissue repair and regeneration have long been of enormous interest and fascination to biologists (1, 2). Stem cells enable the human body to develop, grow, and repair throughout life. Although much progress has been made in exploring the therapeutic potential of induced pluripotent stem cells, embryonic stem cells, and mesenchymal stem cells, we are still unable to harness their potential to repair or regenerate damaged human organs (3). Therapeutically enhancing tissue regeneration has proven to be challenging. However, recent studies demonstrated that several compounds capable of promoting tissue regeneration in mice might have clinical applications. For example, inhibition of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) by a small-molecule inhibitor of 15-PGDH (SW033291) promoted tissue regeneration in mouse models of colon and liver injury (4). Subcutaneous injection of the drug 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid, which blocks the degradation of hypoxia-inducible factor–1α into Swiss Webster mice that do not show a regenerative phenotype, led to regenerative wound healing after earhole punch injury (5). Administration of the recombinant growth factor neuregulin-1 to postnatal mice stimulated regeneration of heart muscle cells, further improved myocardial function, and reduced the prevalence of transmural scars when mice were subjected to cryoinjury (6).

Some new targets for regenerative medicine have been identified, including miR302-367 and the RNA-binding protein LIN28A. Postnatal reexpression of miR302-367 reactivated the cell cycle in cardiomyocytes by repressing Hippo signaling, resulting in reduced scar formation after experimental myocardial infarction (7). Reexpression of LIN28A, which is highly expressed during embryogenesis and in embryonic stem cells, enhanced tissue repair in mice by increasing oxidative metabolism (8). Some of the above techniques need to be used right after birth to achieve a therapeutic effect, where a critical time point is a prerequisite. It is unknown whether the others will induce a regenerative healing response to wounds in multiple tissue injury sites. Therefore, novel therapeutic strategies and tissue engineering techniques with broader scope are needed to coax organ recovery after injury.

The Sterile 20–like kinases MST1 and MST2 (MST1/2), the mammalian Hippo orthologs, are key components of the Hippo signaling cascade that play a pivotal role in stem cell self-renewal, tissue regeneration, and organ size control (917). Central to this pathway is a kinase cascade formed by kinases MST1/2; a scaffolding protein, Salvador/WW45 (Sav); nuclear Dbf2–related family kinases LATS1 and LATS2 (LATS1/2); and an adaptor protein, MOB1. MST1/2 phosphorylates and activates LATS1/2–MOB1, which then phosphorylates Yes-associated protein/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). Phospho-YAP/TAZ is either degraded or sequestered in the cytoplasm by the 14-3-3 protein. When the Hippo pathway is off, YAP/TAZ translocates to the nucleus and forms a functional hybrid transcriptional factor with TEA domain transcription factor (TEAD) to turn on pro-proliferative and prosurvival genes, thereby enabling cell proliferation. Genetic defects in this pathway in mice lead to sustained tissue growth and can lead to cancer (12, 13, 16). Although Hippo kinase MST1/2 structures have been determined, small-molecule MST1/2 inhibitors have yet been disclosed (18, 19). Therefore, small molecules targeting Hippo signaling in a reversible and dose-dependent manner have drawn significant attention as novel, molecularly targeted therapeutics for regenerative medicine.

Here, we report the discovery of a potent and selective inhibitor of MST1/2, 4-((5,10-dimethyl-6-oxo-6,10-dihydro-5H-pyrimido[5,4-b]thieno[3,2-e][1,4]diazepin-2-yl)amino)benzenesulfonamide (XMU-MP-1), using an enzyme-linked immunosorbent assay (ELISA)–based high-throughput screen of a kinase-directed compound library. A 2.47 Å cocrystal structure of the MST2 with XMU-MP-1 reveals the molecular basis for selectivity. The development of inhibitor-resistant alleles of MST1/2 in conjunction with structure-activity relationship (SAR) studies confirmed that the cellular effects of XMU-MP-1 are “on-target” to MST1/2. The pharmacokinetic properties of XMU-MP-1 were sufficient to enable inhibition of MST1/2 activities in mice, and the compound exhibited in vivo efficacy in multiple models of liver and intestinal repair and regeneration. Thus, the pharmacological manipulation of the Hippo signaling pathway using XMU-MP-1 might provide new avenues for research in regenerative medicine and novel therapeutic options for tissue repair.

RESULTS

High-throughput screening identifies small molecules that inhibit kinases MST1 and MST2

To identify the pharmacological modulators of MST1/2 kinase activities, we designed and optimized an ELISA-based high-throughput screening assay using their physiological substrate MOB1 protein as the reaction substrate (fig. S1, A to D). After screening an in-house compound library (~3000 compounds) designed to target the adenosine triphosphate (ATP)–binding site of the kinases MST1/2, we obtained preliminary hits that inhibited MST2 kinase activity by more than 50% at 10 μM. The selected hits (with MOB1 phosphorylation <5%) were derived from four chemical scaffolds shown in Fig. 1A and fig. S1E.

Fig. 1.

High-throughput screening identifies XMU-MP-1 as a potent, ATP-competitive inhibitor of kinases MST1/2. (A) Overview of the primary screening data for an in-house library. Each spot represents a compound at 10 μM. Data are relative to the dimethyl sulfoxide (DMSO)–treated control. (B) The chemical structure of XMU-MP-1. Synthetic steps are shown in fig. S2. (C) The inhibitory activities of XMU-MP-1 for MST1 and MST2, measured as percentage of MOB1a phosphorylation. Data are means ± SD relative to DMSO-treated controls (n = 3). IC50, median inhibitory concentration. (D and E) Immunoblot analysis of phosphorylated (p-) MOB1 in a cell-free reaction system at different doses of XMU-MP-1 for 15 min (D) or 1 μM XMU-MP-1 for different incubation times (E). His, histidine; GST, glutathione S-transferase. (F) The thermal denaturation curve shift of MST2 (10 μM) via XMU-MP-1 (100 μM). Tm, melting transition temperature; RFU, relative fluorescence units. (G) IC50 values of XMU-MP-1 against MST1 or MST2 at different ATP concentrations. Data are means ± SD relative to DMSO controls (n = 3). (H) The KINOMEscan result of XMU-MP-1 against a panel of 468 kinases. S(10) and Kd’s of XMU-MP-1 against kinases with ctrl% ≤10% containing MST1-4 highlighted as blue (see tables S1 and S2 for the full list and see Materials and Methods for the detailed kinase group names) were shown. Data are from one experiment representative of three (C to H) or two (A) independent experiments. Full blots are shown in fig. S11.

Through iterative rounds of structure-activity optimization, XMU-MP-1 (Fig. 1B and fig. S2) was identified as having the best inhibitory activity, with IC50 values of 71.1 ± 12.9 nM and 38.1 ± 6.9 nM against MST1 and MST2, respectively (Fig. 1C). XMU-MP-1 inhibited phosphorylation of MOB1 in a dose-dependent manner (Fig. 1, D and E, and fig. S3, A to D). XMU-MP-1 also demonstrated a high-affinity interaction with the MST2 protein, as shown by a shift of 8.5°C in the melting temperature (Fig. 1F). Furthermore, with increasing ATP concentration, XMU-MP-1 exhibited a proportional increase in IC50 against MST1/2 (Fig. 1G), as well as an attenuated inhibition of the MST2-mediated phosphorylation of MOB1 (fig. S3E). Together with substrate kinetic analyses (fig. S3F), these data suggest that XMU-MP-1 is an ATP-competitive inhibitor for MST1/2.

Kinase selectivity of XMU-MP-1 was determined using KINOMEscan, which profiled the inhibitor at a concentration of 1 μM against a panel of 468 diverse kinases using an in vitro ATP-site competition binding assay (20). The KINOMEscan results are reported as the percentage of the DMSO negative control signal (ctrl%) set at 100%, and a lower number represents higher-affinity binding. There were 23 kinases with ctrl% ≤10% in total containing MST1-4, indicating very strong inhibition. The dissociation constants (Kd) of XMU-MP-1 against these kinases were determined (Fig. 1H and tables S1 and S2). A selectivity score [S(10)] of 0.05 was determined for XMU-MP-1, calculated by dividing the number of kinases with ctrl% ≤10% (n = 23) by the total number of kinases tested (n = 468). Cumulatively, these studies demonstrate that XMU-MP-1 is a potent and highly selective inhibitor of MST1/2 kinases.

Compound XMU-MP-1 abrogates the MST1/2-mediated signaling cascade

We investigated whether XMU-MP-1 was capable of inhibiting MST1/2 kinase activities within cells. At concentrations ranging from 0.1 to 10 μM, XMU-MP-1 reduced the phosphorylation of endogenous MOB1, LATS1/2, and YAP in human liver carcinoma (HepG2) cells in a dose-dependent manner (fig. S4A). Similarly, XMU-MP-1 treatment inhibited hydrogen peroxide (H2O2)–stimulated MOB1 phosphorylation and MST1/2 autophosphorylation in a variety of cell lines, including mouse macrophage-like cells (RAW264.7), human osteosarcoma (U2OS), human colorectal adenocarcinoma (SW480), immortalized human retinal pigment epithelial cells (RPE1), human pleomorphic hepatocellular carcinoma (SNU-423), and HepG2, as well as primary mouse hepatocytes, without affecting the phosphorylation of JNK (c-Jun N-terminal kinase), which is a positive control for H2O2 stimulation (Fig. 2A and fig. S4B).

Fig. 2.

Inhibition of MST1/2 signaling by XMU-MP-1 in vitro in various cell types. (A) Relative levels of p-MOB1 and p-MST in a variety of cell lines or primary mouse hepatocytes stimulated with or without H2O2 after treatment with various concentrations of XMU-MP-1. (B) Immunoblot analysis of YAP, poly(ADP-ribose) polymerase (PARP), and α-tubulin, and quantification of relative levels of YAP in cytoplasmic (c) and nuclear (n) fractions of human HepG2 cells treated with various concentrations of XMU-MP-1. (C) Real-time quantitative polymerase chain reaction (RT-qPCR) analysis of the expression levels of CTGF and CYR61 in HepG2 cells after XMU-MP-1 treatment for 6 hours. (D) Confocal microscopy of YAP distribution in HepG2 cells overexpressing MST2 (or not) at about 30% confluence after DMSO or XMU-MP-1 treatment for 4hours. Nuclei were counterstained with 4′,6-diamidino-2-phenylindole (DAPI). Cells transfected with or without MST2 are indicated with a star or an arrow, respectively. Scale bars, 10 μm. (E) Confocal microscopy of YAP distribution in HepG2 cells cultured at high density (100% confluent) after DMSO or XMU-MP-1 treatment for 4 hours. Nuclei were counterstained with DAPI. Scale bars, 10 μm. (F) Confocal microscopy of YAP distribution in HepG2 cells treated with 3 μM XMU-MP-1 for 0 to 8 hours (top two panels) or washed with fresh medium after 4 hours of treatment with XMU-MP-1 (bottom). Cells counterstained with DAPI are inset. Scale bars, 10 μm. (G and H) Quantification of relative levels of p-MOB1 and p-YAP in HepG2 cells treated with various concentrations of XMU-MP-1 for 0 to 8 hours (G) or for 4 hours followed by depleting XMU-MP-1 (5 to 8 hours) (H). Data are means ± SD relative to DMSO controls (n = 3). In (A) to (C), *P < 0.05, **P < 0.01, ***P < 0.001, Student’s t test. All data are from one experiment, representing three independent experiments. Full blots are shown in fig. S11.

MST1/2 proteins are proapoptotic kinases. XMU-MP-1 treatment prevented cell death induced by adenovirus-mediated overexpression of MST2 (fig. S4C). Another downstream effect of MST1/2 activation is to induce phosphorylation and nuclear exit of YAP. XMU-MP-1 treatment increased YAP nuclear translocation (Fig. 2B), leading to a significant up-regulation of the YAP target genes CTGF and CYR61 in HepG2 cells (Fig. 2C). Furthermore, in HepG2 cells overexpressing MST2, the enhanced phosphorylation of LATS1/2, MOB1, and YAP and the increased YAP cytoplasmic localization were prevented by XMU-MP-1 (Fig. 2D and fig. S4D). Previous studies have shown that cell-cell contact and high cell density activate Hippo signaling to inhibit YAP activity by promoting cytoplasmic retention (21). We found that YAP was exclusively located in the cytosol when HepG2 cells were grown at high density and XMU-MP-1 treatment induced predominant nuclear localization of YAP, regardless of the cell density (Fig. 2E).

To investigate whether the inhibition of kinases MST1/2 via XMU-MP-1 is reversible, we performed cellular washaway experiments in HepG2 cells. One hour after washing, the cells displayed a greatly reduced amount of YAP in the nucleus, and the YAP subcellular distribution was restored to control levels 2 hours after washing (Fig. 2F). Consistently, Western blotting analysis indicated that the XMU-MP-1 treatment greatly reduced the phosphorylation levels of MOB1 and YAP, which were restored to normal levels 2 hours after washing (Fig. 2, G and H, and fig. S4, E and F). These data establish that XMU-MP-1 can potently and reversibly suppress the activities of kinases MST1/2 and enhance their downstream YAP activation in cells.

Cocrystal structure and SAR reveal that XMU-MP-1 is on-target to MST2

To study how XMU-MP-1 recognizes the MST1/2 kinases, we determined the protein/inhibitor complex structure via cocrystallization. MST2 in this complex adopted the typical active conformation closely resembling the wild-type MST1 crystal structure [Protein Data Bank (PDB) 3COM; fig. S5A] as evidenced by the extended activation loop (A-loop) and the phosphorylated Thr174 and Thr180 residues (residues 177 and 183 in MST1) (Fig. 3A). In contrast, the previously reported apo-bound and AMP-PNP–bound kinase–dead mutant MST2 D146N structures (PDB 4LG4 and 4LGD) were in the inactive conformation (fig. S5B) (18, 19). XMU-MP-1 bound deeply into the ATP-binding pocket, sandwiched between the N- and C-lobes, and closely associated with the hinge of the kinase (Fig. 3B and fig. S5C). The pyrimido[4,5-b]thieno[3,2-e][1,4]diazepine scaffold adopted a bent conformation that optimally fit the hydrophobic Val41 and Leu153 side chains; the phenyl ring of the compound contacted the side chain of Leu33 through a hydrophobic interaction. The compound was well accommodated in the ATP-binding pocket and interacted with the bulky Met gatekeeper (residue 99) through its methyl moiety (Fig. 3B and fig. S5C).

Fig. 3.

XMU-MP-1 is on-target to MST2. (A) Overall structure of the MST2/XMU-MP-1 complex (PDB 5DH3) (stereo view). The MST2 protein and the compound are shown as slate cartoons and sticks, respectively. (B) XMU-MP-1 interacts with MST2 at the ATP-binding site. The MST2 kinase is shown as a slate cartoon except for the P-loop, which is a Cα trace (thin line), to enable a better view of the compound. The αC-helix, A-loop, and P-loop are red, orange, and deep blue (thin line), respectively. The side chains of the residues of Met99, Tyr101, Leu33, Val41, Leu153, Asp109, Lys56, and Glu70 are shown as sticks. The compound is shown as sticks, with C (yellow), O (red), S (orange), and N (blue) atoms. (C) IC50 values for the inhibition of wild-type MST2 (WT) or mutant MST2 (Y101F, D109A, or both Y101F and D109A) by XMU-MP-1 for 15 min. Data are means ± SD relative to DMSO controls (n = 3). (D) p-MOB1 in HepG2 cells expressing Flag-tagged various forms of MST2 as indicated or control vectors after DMSO or XMU-MP-1 treatment for 3 hours. Data are means ± SD relative to DMSO controls (n = 3). ns, not significant; *P < 0.05, **P < 0.01, Student’s t test. (E) Confocal microscopy of the distribution of YAP in HepG2 cells overexpressing Flag-tagged various forms of MST2, as indicated, after DMSO or XMU-MP-1 treatment for 4 hours. Nuclei were counterstained with DAPI. Cells transfected with or without MST2 (WT or mutant, as indicated) are labeled with a star or an arrow, respectively. Scale bars, 10 μm. Data in (C) to (E) are from one experiment representative of three independent experiments.

The sulfonamide moiety of XMU-MP-1 interacted with the kinase through at least two interactions, including the direct polar interaction with the Asp109 side chain and the indirect interaction with a Tyr101 side-chain hydroxyl through a water bridge. Because of these interactions, the conformation of the sulfonamide group was fixed, as shown by the well-defined electron density (fig. S5D). Notably, unlike other kinases, the MST1/2 kinases have a C-terminal helix (αJ) located near the sulfonamide group, which might provide extra determinants for further optimization of the compound (for instance, to increase the binding potency or selectivity through careful tailoring of the tail group of the compound).

To corroborate the functional relevance of these interactions and to develop inhibitor-resistant alleles of the kinase, we performed mutagenesis and biochemical studies. Introduction of single mutations at Y101F or D109A did not compromise kinase activity; however, the inhibition potency (IC50) of XMU-MP-1 was remarkably reduced by ~10-fold to 361.1 nM for MST2 (Y101F) and by ~27-fold to 1040 nM for MST2 (D109A) relative to wild-type kinase (Fig. 3C). For the double mutation Y101F/D109A, an even higher IC50 of 1678 nM was observed (Fig. 3C). Consistent with these biochemical data, the similar inhibitory effects of XMU-MP-1 in HepG2 cells transfected with various MST1/2 mutations were observed (Fig. 3, D and E, and figs. S6 and S7). These findings confirm the importance of interactions identified by the structural studies and further demonstrate that XMU-MP-1 is on-target to MST1/2 kinase.

Additional SAR studies of XMU-MP-1 (1a) revealed the key chemical features for efficacy (fig. S8, A and B). The importance of the free hydrogens of -NH2 in sulfonamide (1a) was demonstrated by the gradual loss of efficacy when replacing the amide with cyclopropanylamine (1b) and 4-methylpiperazine (1c). Without the oxygen substitution of sulfur, the biochemical activity was also greatly reduced (1e versus 1d). The cellular efficacies of these analogs to inhibit MOB1 phosphorylation under H2O2 stimulation (fig. S8C) and YAP cytoplasmic retention (fig. S8D) in HepG2 cells were compromised, consistent with in vitro biochemical activities (Fig. 2, A and B).

XMU-MP-1 promotes liver repair and regeneration in mice

Liver-specific deletion of MST1/2 using a Cre-expressing adenovirus leads to immediate and pronounced liver overgrowth in mice (22, 23). We next explored whether the pharmacological inhibition of MST1/2 would similarly potentiate liver repair and regeneration in vivo. The pharmacokinetic properties of XMU-MP-1 were first evaluated in Sprague-Dawley rats administered a single intravenous or oral dose. XMU-MP-1 exhibited favorable pharmacokinetics with a half-life of 1.2 hours, an area under the curve of 1035 (h·ng)/ml, and a bioavailability of 39.5% (table S3). In pharmacodynamic experiments, the maximal phosphorylation inhibition of MOB1 and YAP was achieved between 1.5 and 6 hours after intraperitoneal dosing with XMU-MP-1 (1 mg/kg) (Fig. 4A). A dose escalation study of XMU-MP-1 revealed that the phosphorylation of MOB1 in liver tissue was blocked at a minimal dose (1 mg/kg, intraperitoneally) (Fig. 4B).

Fig. 4.

Inhibition of MST1/2 signaling by XMU-MP-1 in mouse liver. (A and B) Immunoblots and quantification of p-MOB1 and p-YAP in lysates of livers from wild-type mice treated with XMU-MP-1 (1 mg/kg) over time (0 to 12 hours) (A) or different doses of XMU-MP-1 for 3 hours (B). Data are means ± SD relative to DMSO controls (n = 3). *P < 0.05, **P < 0.01, ***P < 0.001 versus control, Student’s t test. GAPDH, glyceraldehyde-3-phosphate dehydrogenase. (C) Hematoxylin and eosin (H&E) or immunohistochemical (IHC) staining of the oval cell marker CK19 in liver sections of Mst1fl/flMst2fl/fl and Mst1fl/flMst2fl/flAlb-Cre mice. Scale bars, 100 μm. (D and E) H&E and IHC staining and quantification of CK19- and BrdU-positive cells in liver sections (n = 3) (D) or liver/body weight ratio (n = 6) (E) of wild-type mice treated with a vehicle or XMU-MP-1 (1 mg/kg) daily for 2 months, or after 2 weeks of XMU-MP-1 withdrawal. ND, not determined. Data are means ± SD. P values were determined by Student’s t test. Scale bars, 100 μm. (F) Ki67 staining in tissue sections from wild-type mice treated with a vehicle or XMU-MP-1 (3 mg/kg) daily for 7 days. Quantification of the Ki67-positive cells in various tissues. Data are means ± SD (n = 6). P values were determined by Student’s t test. Scale bars, 100 μm. Data are from one experiment representative of three (A to C) or two (D to F) independent experiments. Full blots are shown in fig. S11.

Liver-specific deletion of MST1/2 using Alb-Cre (Mst1fl/flMst2fl/flAlb-Cre) resulted in a two- to threefold increase in liver/body weight ratio and overexpansion of bile duct–like liver progenitor cells (oval cells) compared to control wild-type mice (Mst1fl/flMst2fl/fl) within 2 months (Fig. 4C). Wild-type mice treated with XMU-MP-1 daily for 2 months had moderately increased ratios (around 20 to 30%) of liver/body weight and very low levels of oval cell expansion, as indicated by staining for the marker cytokeratin 19 (CK19) (Fig. 4, D and E). These treated mice did not exhibit any cancer growth and had no detectable levels of α-fetoprotein, a marker for hepatocellular carcinoma. Moreover, the liver/body weight ratio and the percentage of CK19-positive and bromodeoxyuridine (BrdU)–positive cells were restored to normal levels after 2 weeks of XMU-MP-1 withdrawal (Fig. 4, D and E). Furthermore, mice treated with XMU-MP-1 at a threefold higher dose (3 mg/kg) daily for 7 days showed equivalent daily weights and physical activity compared with those treated with a vehicle control, showing no significant changes in cell proliferation among various tissues (Fig. 4F) and serum chemistry (table S4). Thus, XMU-MP-1 was well tolerated, and the mice appeared healthy with no signs of distress in the tolerability experiments.

To investigate the effect of XMU-MP-1 on liver regeneration, we treated wild-type mice with XMU-MP-1 once a day before a two-thirds partial hepatectomy followed by daily treatment for 7 days. Similarly, XMU-MP-1 treatment significantly decreased the phosphorylation levels of MOB1 and YAP (fig. S9A). After partial hepatectomy, the mice treated with XMU-MP-1 exhibited substantially enhanced liver regeneration. Between postoperative days 1 and 7, the number of Ki67-positive cells increased rapidly in the liver and was significantly higher in the XMU-MP-1–treated mice than in controls (Fig. 5A). Moreover, the number of nuclear YAP-positive cells and the expression levels of YAP target gene Ctgf were significantly higher in the XMU-MP-1–treated mice than in controls (fig. S9, B and C). The XMU-MP-1–treated mice also increased their liver/body weight ratio faster than controls, although the two groups were similar by day 6 (Fig. 5B). XMU-MP-1, therefore, seems to have a strong effect in vivo when hepatocytes are actively proliferating.

Fig. 5.

XMU-MP-1 promotes human and mouse liver cell proliferation. (A and B) Ki67-positive cells in liver sections (A) or the liver/body weight ratio (B) of partially hepatectomized mice treated with a vehicle or XMU-MP-1 (1 mg/kg) twice per day. Data are means ± SD (n = 5). (C and D) H&E staining and IHC staining of CK19 and BrdU (C), as well as quantifications of CK19- and BrdU-positive cells in liver sections (n = 3) or the liver/body weight ratio of postnatal mice (n = 4) (D) treated with a vehicle or XMU-MP-1 (1 mg/kg) once per day for 21 days. Data are means ± SD. Scale bars, 100 μm. (E) Ki67-positive cells in liver sections of partially hepatectomized Mst1fl/flMst2fl/fl or Mst1fl/flMst2fl/flAlb-Cre mice treated with a vehicle or XMU-MP-1 (1 mg/kg) twice per day for 2 days. Data are means ± SD (n = 3). (F) The repopulation of transplanted human hepatocytes in FRG livers was determined by measuring serum human albumin (hALB) levels. Two weeks after transplantation, animals were treated with a vehicle or XMU-MP-1 (1 mg/kg) once per day. Data are means ± SD (n = 9). (G) H&E staining and IHC staining of FAH, BrdU, and TUNEL in FRG livers. H, human hepatocytes. Quantifications of the ratio of BrdU+/FAH+ cells and the number of TUNEL-positive cells in nonhuman hepatocyte region (FAH cells) in liver sections of mice treated with a vehicle or XMU-MP-1 (1 mg/kg) once per day for 28 days. Data are means ± SD (n = 3). Scale bars, 200 μm. (H) IHC staining of YAP and human hepatic functional proteins cytochrome P-450 (CYP) 3A4, CYP2D6, α-1 antitrypsin (AAT), and CK18 in FRG livers. Scale bars, 50 μm. *P < 0.05, **P < 0.01, ***P < 0.001 versus control, unless otherwise indicated, Student’s t test. Data are from one experiment representative of three (A to E) or two (F to H) independent experiments.

Previous studies showed that YAP is involved in proliferation and differentiation during postnatal liver development (24, 25). To assess the synergistic effect of XMU-MP-1 with proliferative signals in postnatal mice, 10-day-old mice were treated daily with XMU-MP-1 for 3 weeks. XMU-MP-1 treatment significantly increased the number of CK19- and BrdU-positive cells, as well as the liver/body weight ratio, by 15 to 20% compared to that of vehicle control (Fig. 5, C and D). Moreover, the XMU-MP-1–treated MST1/2 double-knockout (Mst1fl/flMst2fl/flAlb-Cre) mice did not increase the number of Ki67-positive cells 36 hours after partial hepatectomy compared to those of vehicle-treated MST1/2-null mice (Fig. 5E and fig. S9D), indicating that liver overgrowth was due to the inhibition of MST1/2 by XMU-MP-1 in vivo.

Next, we sought to determine the effects of XMU-MP-1 on facilitating the repopulation of human hepatocytes using Fah−/−/Rag2−/−/Il2rg−/− (FRG) mice, which are excellent recipients of human hepatocyte xenografts (26, 27). These mice, when removed from NTBC [(2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione)], a drug that inhibits the formation of hepatotoxic levels of fumaryl acetoacetate, undergo liver failure unless they receive intrasplenic injection of hepatocytes. The FRG mice received human hepatocytes, followed by either vehicle control or XMU-MP-1, and engraftment was evaluated by histology, immunohistochemistry, and serum human albumin level (Fig. 5, F to H). Compared with the vehicle-treated controls, XMU-MP-1 significantly increased serum human albumin levels within 6 weeks (Fig. 5F). XMU-MP-1–treated livers were more greatly repopulated than controls, as assessed by H&E staining and the liver enzyme marker fumaryl acetoacetate hydrolase (FAH) (Fig. 5G). XMU-MP-1 treatment resulted in a significant increase in the ratio of BrdU+/FAH+ cells, indicating enhanced proliferation rate of human hepatocytes (Fig. 5G). Similar numbers of terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick end labeling (TUNEL)–positive cells in nonhuman (murine) hepatocyte areas (FAH) suggested that XMU-MP-1 did not promote Fah-deficient hepatocyte survival (Fig. 5G). However, there were more nuclear YAP in Fah-deficient liver cells treated with XMU-MP-1, indicating the inhibition of Hippo signaling (Fig. 5H). In addition to FAH, the indicators of functional hepatocytes, AAT, CYP3A4, CYP2D6, and CK18, were equivalent in both controls and XMU-MP-1–treated animals (Fig. 5H).

XMU-MP-1 attenuates acetaminophen-induced liver injury

Acetaminophen (APAP) overdose is the leading cause of acute liver failure worldwide (28). Currently, N-acetylcysteine (NAC), an antioxidant, is the antidote for APAP toxicity. However, NAC is effective only for patients who present within hours of an acute overdose (29). In addition, prolonged (>24 hours) treatment with NAC can be toxic and delay liver regeneration in patients with APAP hepatotoxicity (30). NAC efficiently blocks APAP-induced injury in mice when NAC treatment occurs within 1.5 hours of APAP administration (31). MST1/2 proteins are proapoptotic kinases. Thus, blocking MST1/2 might ameliorate APAP-induced liver cell death.

NAC (250 mg/kg) administered at 1.5 hours, but not at 2.5 or 3.5 hours after APAP administration, protected mice from liver centrilobular necrosis (Fig. 6A and fig. S10A). Extending this therapeutic window, XMU-MP-1 administered within 2.5 hours after APAP administration effectively prevented the continual expansion of centrilobular necrotic lesions in APAP-treated mouse livers (Fig. 6B and fig. S10, B to D). NAC treatment alone at 1.5 hours after APAP administration treated about 80% of mice, whereas the combination of NAC and XMU-MP-1 (1 mg/kg) at 1.5 hours after APAP administration protected 100% of mice from APAP-induced death (Fig. 6A). The combination of NAC and XMU-MP-1, or XMU-MP-1 treatment alone, effectively extended the protective effects to 2.5 hours after APAP administration, as shown by the increased survival rate from ~40% (NAC alone or vehicle control) to ~75% (Fig. 6B), as well as the smaller liver centrilobular necrotic lesions compared with the control groups (Fig. 6C and fig. S10D). Furthermore, compared with the vehicle controls, all treatments given at either 1.5 or 2.5 hours after APAP treatment significantly decreased serum alanine transaminase (ALT) levels at 24 hours after APAP treatment (Fig. 6C). Of the treatments provided at 2.5 hours after APAP administration, however, only XMU-MP-1 alone or the combination of NAC and XMU-MP-1 significantly decreased the mortality rate (Fig. 6A).

Fig. 6.

XMU-MP-1 promotes liver and intestinal tissue repair and regeneration after acute injury. (A) The mortality of wild-type mice injected intraperitoneally with vehicle (n = 11), NAC (n = 10), XMU-MP-1 (n = 11), or NAC + XMU-MP-1 (n = 11) at 1.5 or 2.5 hours after the oral administration of APAP (400 mg/kg). P values versus control were determined by Mantel-Cox test. (B) TUNEL staining of liver sections at indicated post-APAP time points from wild-type mice treated 2.5 hours after a sublethal dose of APAP (200 mg/kg) administration. Scale bars, 200 μm. (C) Serum ALT levels at 24 hours after APAP administration among wild-type mice injected intraperitoneally with vehicle (n = 7), NAC (n = 5 at 1.5 hours; n = 4 at 2.5 hours), XMU-MP-1 (n = 7 at 1.5 hours; n = 4 at 2.5 hours), or NAC + XMU-MP-1 (n = 5 at 1.5 hours; n = 4 at 2.5 hours) after APAP administration. P values were determined by Mantel-Cox test. (Dand E) Body weight (D) and DAI (E) over days 1 to 21 of mice with colitis induced by DSS (days 1 to 7) that were also treated with a vehicle (n = 12) or XMU-MP-1 (1 mg/kg) (n = 12) daily. Data are means ± SD. Plots of daily weights were graphed as the percentage of the day 1 value (D). Plots of daily DAI are shown in (E). *P < 0.05 compared between the vehicle-treated and XMU-MP-1–treated groups at the same time point via Student’s t test. (F) IHC staining of YAP, BrdU, and Ki67 in the colon sections of wild-type mice after the oral administration of DSS for 7 days after vehicle or XMU-MP-1 (1 mg/kg) each day. BrdU- and Ki67-positive cells in the colon sections were quantified in tissue sections from individual animals. Data are means ± SD (n = 10). P values were determined by Student’s t test. Scale bars, 100 μm. All data are from one experiment representative of three independent experiments.

Genetic disruption of the components of the Hippo pathway has been shown to result in eventual tumor formation (12, 13). Nevertheless, mice with APAP-induced injury that were treated daily with XMU-MP-1 (1 mg/kg) for 1 week did not exhibit cancerous phenotypes for more than 10 months when examined by gross necropsy. They, like control mice, which were subjected to a sublethal dose of APAP followed by the treatment of PBS or NAC, remained healthy (n = 10 per group). In addition, wild-type mice treated daily with XMU-MP-1 at the same dose (1 mg/kg) but for a longer period of time (2 months) did not exhibit any cancer growth. These results indicate that the pharmacological blockage of MST1/2 activities can halt the negative sequelae of APAP-induced liver injury and increase the animal survival rate beyond that obtained with NAC alone—the current clinical standard of care.

XMU-MP-1 protects mice from DSS-induced colitis

To determine whether the MST1/2 inhibitor XMU-MP-1 promotes regeneration in intestinal tissues where Hippo signaling plays an important role (32, 33), we examined the effects of XMU-MP-1 in the colons of mice treated for 7 days with oral dextran sodium sulfate (DSS), an agent that induces the colon tissue ulcerations similar to those found in humans with ulcerative colitis. Wild-type mice treated daily with XMU-MP-1 showed a marked resistance to DSS-induced colitis compared with controls. XMU-MP-1–treated mice showed significantly less weight loss (Fig. 6D) and suppression of colitis symptoms, with substantially less diarrhea and rectal bleeding, as assessed by the disease activity index (DAI) (Fig. 6E) (34).

To further characterize the mechanism through which MST1/2 inhibition protects the colon epithelium, we assessed the effects of XMU-MP-1 on the cell proliferation in the colon crypts. The numbers of nuclear YAP-positive cells and BrdU incorporation or Ki67-positive proliferating cells were significantly higher in the XMU-MP-1 treatment group than in controls (Fig. 6F). Mice treated daily with XMU-MP-1 (1 mg/kg) for 1 week in the model of DSS-induced injury did not exhibit cancerous phenotypes for more than 10 months. Thus, MST1/2 inhibition confers protection primarily by helping to maintain colonocyte proliferation in damaged mucosa.

XMU-MP-1 ameliorates chronic liver injury

Next, we evaluated the regenerative effect of XMU-MP-1 in chronic liver injury, which is of great clinical interest. The two most commonly used models of experimental chronic liver injury are iterative toxic damage (for example, elicited by CCl4 intoxication) and bile duct ligation (35). Chronic liver injury was induced by the administration of CCl4 twice per week for 4 weeks (Fig. 7A) or by bile duct ligation (Fig. 7B). Liver fibrosis is the common result of chronic hepatic injury. Liver fibrosis and cell death were assessed by Sirius Red and TUNEL staining, respectively. In the model of CCl4-induced liver chronic injury, mice treated with XMU-MP-1 (1 mg/kg) daily for 10 days (starting at day 30 after toxic insult) had a small amount of collagen deposition as well as few dead cells, whereas mice treated with vehicle control demonstrated bridging fibrosis and significantly more TUNEL-positive cells, suggesting that inhibition of MST1/2 by XMU-MP-1 is capable of partially rescuing fibrosis (Fig. 7C). XMU-MP-1 treatment exhibited a similar effect in the model of duct ligation–induced chronic liver injury, with MST1/2 inhibition reducing fibrosis and cell proliferation (Fig. 7D).

Fig. 7.

XMU-MP-1 potentiates tissue repair and regeneration after chronic liver injury. (A and B) Schematics for CCl4-induced (A) and bile duct ligation (BDL)–induced (B) chronic liver injury and fibrosis evaluation in mice. (C) Sirius Red and TUNEL staining and corresponding quantifications in liver sections 10 days after CCl4 administration. Injured mice were treated with a vehicle or XMU-MP-1 (1 mg/kg) for 10 days. Scale bars, 100 μm. (D) H&E, Sirius Red, and TUNEL staining and corresponding quantifications in liver sections after 30 days of BDL. Injured mice were treated with a vehicle or XMU-MP-1 (1 mg/kg) for 10 days. L, lesions. Scale bars, 200 μm. P values were determined by Student’s t test. Data in (C) and (D) are means ± SD (n = 3) from one experiment representative of two independent experiments.

DISCUSSION

Pharmacological manipulation of the Hippo pathway could open doors to facile tissue regeneration with drugs, rather than complex biomaterial and cell therapies. MST1/2 kinases, for instance, play major roles in organ growth control. Our present study demonstrates that XMU-MP-1 is a selective and reversible small-molecule MST1/2 inhibitor with in vivo efficacy in four different rodent models of liver injury, attenuating Hippo signaling and augmenting tissue repair. Additionally, this new agent could be used to study the mechanisms of Hippo signaling–mediated pathobiology in other experimental models of organ disease and damage.

Genetic disruption of the components of the Hippo pathway results in YAP activation and, eventually, tumor formation; thus, developing tissue-regenerative therapeutics by targeting Hippo signaling is a daunting challenge (12, 13). Recent studies demonstrated that the downstream effector protein YAP of kinases MST1/2 could be a promising target for cancer prevention (36, 37). One study showed that the enantiopure organoruthenium might inhibit MST1 kinase in vitro using a nonphysiological substrate of MST1/2 kinase, but the authors did not provide further evidence about whether it could target MST2 kinase or about inhibitor selectivity and in vivo efficacy (38). With XMU-MP-1 in hand, we demonstrated that pharmacological inhibition of MST1/2 can augment tissue repair and regeneration after injuries such as partial hepatectomy, APAP-induced liver hepatotoxicity, and chemically induced liver chronic injury and colitis. Healthy or injured mice treated with XMU-MP-1 (1 mg/kg) daily for 2 months or 1 week, respectively, did not exhibit cancerous growth. To some extent, these results differ from the MST1/2 double-knockout phenotype, suggesting that remaining MST1/2 activities in wild-type mice treated with XMU-MP-1 are sufficient to control the cell overproliferation that persists in intact tissues. Previous studies showed that Hippo signaling is suppressed to some extent during tissue regeneration (25, 39). Thus, XMU-MP-1 treatment could facilitate the damaged tissue repair and regeneration but not affect intact, healthy organs. Moreover, we demonstrated that the inhibitory effect of XMU-MP-1 on MST1/2 is reversible. Thus, XMU-MP-1 appears to be safe as a targeted therapeutic to treat tissue injury.

Liver fibrosis occurs as an attempt to limit tissue damage in response to chronic liver injury. However, progressive fibrosis eventually results in cirrhosis. Antifibrotic therapies should inhibit matrix deposition, collagen synthesis, and hepatic stellate cell activation. A previous study showed that macrophage depletion in mice during injury resulted in a marked loss of stellate cells and matrix deposition (40); thus, macrophages are likely essential for regeneration. Additionally, reactive oxygen species could augment fibrogenesis (41). We previously found that MST1/2 kinases are essential for macrophage activation and that the elimination of MST1/2 from the liver resulted in increased expression of enzymes that scavenge oxidants (25, 42). Another study showed that the Hippo downstream effector protein YAP promoted stellate cell activation (43). The complex interplay between MST1/2 kinase activity and cellular activity during regeneration, evidenced by these contradictory findings, might explain why pharmacological inhibition of MST1/2 results in only a partial rescue of liver fibrosis in mice. Thus, more work is needed to determine the antifibrotic mechanisms of XMU-MP-1 and to further optimize the dosage to achieve better antifibrotic efficacy.

Together, our results show that XMU-MP-1 is a valuable chemical probe to study the Hippo signaling pathway, and it provides a starting point for medicinal chemistry efforts aimed at developing therapeutics that target the Hippo-signaling cascade. The major challenges in human hepatocyte transplantation are the limited supply of donor organs and the lack of effective methods to improve engraftment and proliferation of donor hepatocytes after transplantation. Targeting Hippo signaling by XMU-MP-1 or other therapeutics (7) might support hepatocyte expansion after transplant in patients. The future success of such trial would lead to autologous live cell therapy. Although our studies involve several mouse models, in addition to liver and intestinal tissues, the loss of MST1/2 in other tissues, including the pancreas, skin, and heart, also promotes tissue growth (11). It will be of interest to determine the protective effect of XMU-MP-1 on injuries to those tissues. In summary, pharmacological manipulation of Hippo signaling unlocks new opportunities for regeneration of multiple tissues that, to date, have seen minimal success in clinical approaches centered on cell- and biomaterial-based therapies.

MATERIALS AND METHODS

Study design

The purpose of this study was to explore a therapeutic regenerative medicine path that pharmacologically targets the Hippo pathway kinases MST1/2. We developed an ELISA-based screen approach to identify potential inhibitors and designed in vitro studies in murine and human cell lines, as well as primary murine hepatocytes, and in vivo efficacy studies in four mouse models of acute and chronic tissue injuries: partial hepatectomy, hepatocyte repopulation in FRG mice, APAP-induced hepatotoxicity, and DSS-induced colitis (all described in Supplementary Methods). At least 3 to 4 biological replicates were used for each biochemical analysis, whereas a sample size of at least 6 to 12 biological replicates per group was used for animal testing to achieve a 90% power. The detailed sample size for each animal study determined the mean value and SD (σ) and defined the difference in means (δ) of the measurement marker, using an online calculator (http://hedwig.mgh.harvard.edu/sample_size/js/js_parallel_quant.html), assuming 90% power (1 − β), a 5% significance level (α), and a two-sided test.

Data collection occurred for a predetermined period of time, as dictated by literature- or core facility–based standard, and no exclusion criteria were applied. All analyses were performed by examiners blinded to genotype and/or treatment arm. For drug treatments, age- and gender-matched animals were randomly assigned to treatment arms with about equivalent numbers in each group. Box-and-whisker plots were identified using RStudio-defined outliers (shown as circles), but all data points were used in statistical analyses.

General synthesis of XMU-MP-1 and its analogs

MST1/2 kinase inhibitor XMU-MP-1 and its analogs were synthesized from a starting mixture of methyl 3-aminothiophene-2-carboxylate, diisopropylethylamine, and 2,4-dichloro-5-nitropyrimidine in isopropanol, as described in Supplementary Methods (figs. S2 and S8A). For biochemical assays and cellular studies, XMU-MP-1 was dissolved in DMSO (stock concentration, 10 mM). For animal treatments, XMU-MP-1 was dissolved in 0.1% citric acid aqueous solution containing 20% Kolliphor HS 15.

In vitro and in vivo kinase inhibition assays

For the in vivo inhibition assays, human embryonic kidney (HEK) 293T cells were transfected with 0.5 μg of empty plasmid or pCMV plasmids expressing various forms of Flag-tagged full-length MST1 or MST2 kinase in 12-well plates each. Twenty-four hours after transfection, cells were treated with the indicated doses of XMU-MP-1 for 3 hours. Cell lysates were analyzed via immunoblotting with the indicated antibodies. For the in vitro kinase inhibition assays, recombinant GST-tagged MOB1a and various forms of recombinant His-tagged full-length MST1 or MST2 kinase were expressed and purified from Escherichia coli. The enzyme, ATP, and GST-MOB1 consumption were kept consistent with the previously optimized conditions. The assays were performed with the indicated doses of XMU-MP-1 in the kinase assay buffer for 30 min at 30°C followed by SDS–polyacrylamide gel electrophoresis and immunoblot analyses.

KINOMEscan profiling of XMU-MP-1

XMU-MP-1 was profiled against a panel of 468 kinases using KINOMEscan technology, an active-site–dependent competition-binding assay at 1 μM (DiscoverX Corp.). The KINOMEscan selectivity score is a quantitative measure of a compound’s selectivity (20). It is calculated by dividing the number of kinases that bind to the compound by the total number of kinases tested. The results are reported as “control%” (ctrl%) in which lower numbers represent higher-affinity binding; ctrl% = (test compound signal − positive control signal)/(negative control signal − positive control signal) × 100, where the negative control = DMSO (ctrl% = 100%) and the positive control = control compound (ctrl% = 0%); S(10) = (number of kinases with ctrl% ≤10%)/(number of kinases tested). ctrl% <10% means very strong inhibition, and ctrl% >70% means very weak inhibition. Kinome illustration reproduced courtesy of Cell Signaling Technology (www.cellsignal.com). The kinase group or individual kinase names in the current study includes TK (tyrosine kinase), TKL (TK-like), STE (homologs of yeast Sterile 7, Sterile 11, and Sterile 20 kinases), AGC [protein kinase A, G, and C families], CAMK (calcium/calmodulin-dependent protein kinase), CK1 (casein kinase 1), and CMGC [cyclin-dependent kinase (CDK), mitogen-activated protein kinase (MAPK), glycogen synthase kinase 3 (GSK3), and CDC2-like kinase (CLK) families].

Real-time quantitative polymerase chain reaction

One microgram of total RNA from the liver tissue or cells was reverse-transcribed with oligo(dT) and SuperScript III Reverse Transcriptase (Invitrogen). RT-qPCR was performed using a Bio-Rad iQ SYBR Green Supermix Kit and the Bio-Rad iCycler iQ system (Bio-Rad). All runs were accompanied by the internal control Gapdh gene. The samples were run in triplicate and normalized to GAPDH using a ΔΔ cycle threshold–based algorithm to provide arbitrary units representing relative expression levels. The primer sequences for specific genes are shown in table S6.

Statistical analysis

All statistical analyses were performed using Prism 5 (GraphPad Software). The liver weights and liver/body weight ratios, BrdU or TUNEL labeling count, relative mRNA levels, and quantification of immune blots were tabulated graphically with error bars corresponding to means ± SD and compared using two-tailed Student’s t test. Body weight changes and DAI scores in the DSS model with the different treatment arms were compared across the time course of study using two-tailed paired-samples Student’s t test. Survival data were analyzed by the Kaplan-Meier statistical method. P < 0.05 was considered statistically significant.

SUPPLEMENTARY MATERIALS

www.sciencetranslationalmedicine.org/cgi/content/full/8/352/352ra108/DC1

Materials and Methods

Fig. S1. Identification, characterization, and optimization of a potent and selective inhibitor of MST1/2.

Fig. S2. General synthetic scheme of XMU-MP-1 and its analogs.

Fig. S3. Identification, characterization, and optimization of a potent and selective inhibitor of MST1/2.

Fig. S4. Effects of XMU-MP-1 on the MST1/2-mediated signaling cascade in HepG2 liver cells.

Fig. S5. The complex structure of MST2/XMU-MP-1.

Fig. S6. Effects of XMU-MP-1 on wild-type or mutated MST2-mediated signaling cascade in human HepG2 cells.

Fig. S7. Effects of XMU-MP-1 on wild-type or mutated MST1-mediated signaling cascade in human HepG2 cells.

Fig. S8. Inhibition of MST2 by various XMU-MP-1 analogs.

Fig. S9. Effects of XMU-MP-1 on MST1/2 signaling-mediated liver regeneration in mice.

Fig. S10. XMU-MP-1 stimulates MST1/2 signaling-mediated liver tissue repair and regeneration in mice.

Fig. S11. Full scans of Western blots for Figs. 1 (D and E), 2B, and 4 (A and B), and figs. S2A and S3 (C and D).

Fig. S12. Full scans of Western blots for figs. S3E and S4.

Fig. S13. Full scans of Western blots for fig. S6.

Fig. S14. Full scans of Western blots for fig. S7.

Fig. S15. Full scans of Western blots for figs. S8C and S9A.

Table S1. Full list of KINOMEscan profiling data of XMU-MP-1.

Table S2. Kinase profiling data of XMU-MP-1.

Table S3. Pharmacokinetics of XMU-MP-1 in rats.

Table S4: Blood chemistry in tolerability studies.

Table S5. Crystallographic data collection and refinement statistics for MST2 (residues 16–313) bound to XMU-MP-1.

Table S6. The sequences of primers used in this study.

Data S1. Tabulated raw data. (Microsoft Excel format)

REFERENCES AND NOTES

Acknowledgments: We thank J. Avruch for his discussions and comments on the manuscript. Funding: This work was supported by the National Basic Research Program (973) of China [2015CB910502 (to L.C.) and 2012CB917202 (to C.-H.Y.)], the National Natural Science Foundation of China [31270918, U1505224, and J1310027 (to D.Z.); 81422045, U1405223, and 21272195 (to X.D.); 81372617, 81422018, and U1405225 (to L.C.); 31270769 (to C.-H.Y.); and 81472229 (to L.H.)], the 111 Projects (B12001 and B06016), the Fundamental Research Funds for the Central Universities of China-Xiamen University [CXB2014004 (to Z.J.), 20720140551 (to L.C.), 20720160064 and 2013121032 (to X.D.), and 2013121034 and 20720140537 (to D.Z.)]. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Author contributions: D.Z., X.D., C.-H.Y., and L.C. conceived the project. D.Z., L.C., X.D., and F.F. performed data analysis/statistics. X.D., N.S.G., and Z.H. conceived and performed chemical synthesis of XMU-MP-1 and its analogs and small-molecule structure determination. L.-L.K. and C.-H.Y. designed and performed cocrystal structure study of MST2 with XMU-MP-1. D.Z. and L.C. conceived the biological study. F.F., S.Z., J.Y., C.X., Xihuan Sun, L. Huang, X.W., and Z.J. performed biochemical assay. F.F., J.G., P.W., L. Hong, and Q.W. performed cellular experiments. Q.C., S.Z., H.L., Xiufeng Sun, W.Z., and Y.L. performed animal model study. D.Z., Q.Y., N.-S.X., and L.Y. designed and performed the human hepatocyte in vivo study. C.-H.Y., X.D., L.C., and D.Z. co-wrote the paper. All authors edited the manuscript. Competing interests: A patent has been filed with Chinese patent application no. 201610121108.5. Data and materials availability: The structure was deposited in the PDB with ID 5DH3.
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