Identification of an Aurora kinase inhibitor specific for the Aurora B isoform

Discovery of a novel Aurora B inhibitor GSK650394 with potent anticancer and anti-aspergillus fumigatus dual efficacies in vitro

Invasive fungal infections including Candidiasis and Aspergillosis are associated with considerable morbidity and mortality in immunocompromised individuals, such as cancer patients. Aurora B is a key mitotic kinase required for the cell division of eukaryotes from fungus to man. Here, we identified a novel Aurora B inhibitor GSK650394 that can inhibit the recombinant Aurora B from human and Aspergillus fumigatus, with IC₅₀ values of 5.68 and 1.29 µM, respectively. In HeLa and HepG2 cells, GSK650394 diminishes the endogenous Aurora B activity and causes cell cycle arrest in G2/M phase. Further cell-based assays demonstrate that GSK650394 efficiently suppresses the proliferation of both cancer cells and Aspergillus fumigatus. Finally, the molecular docking calculation and site-directed mutagenesis analyses reveal the molecular mechanism of Aurora B inhibition by GSK650394. Our work is expected to provide new insight into the combinational therapy of cancer and Aspergillus fumigatus infection.

Targeting Aurora B kinase prevents and overcomes resistance to EGFR inhibitors in lung cancer by enhancing BIM- and PUMA-mediated apoptosis

The clinical success of EGFR inhibitors in EGFR-mutant lung cancer is limited by the eventual development of acquired resistance. We hypothesize that enhancing apoptosis through combination therapies can eradicate cancer cells and reduce the emergence of drug-tolerant persisters. Through high-throughput screening of a custom library of ∼1,000 compounds, we discover Aurora B kinase inhibitors as potent enhancers of osimertinib-induced apoptosis. Mechanistically, Aurora B inhibition stabilizes BIM through reduced Ser87 phosphorylation, and transactivates PUMA through FOXO1/3. Importantly, osimertinib resistance caused by epithelial-mesenchymal transition (EMT) activates the ATR-CHK1-Aurora B signaling cascade and thereby engenders hypersensitivity to respective kinase inhibitors by activating BIM-mediated mitotic catastrophe. Combined inhibition of EGFR and Aurora B not only efficiently eliminates cancer cells but also overcomes resistance beyond EMT.

Structural insights of oxindole based kinase inhibitors as anticancer agents: Recent advances

Small-molecule kinase inhibitors are being continuously explored as new anticancer therapeutics. Kinases are the phosphorylating enzymes which regulate numerous cellular functions such as proliferation, differentiation, migration, metabolism, and angiogenesis by activating several signalling pathways. Kinases have also been frequently found to be deregulated and overexpressed in cancerous tissues. Therefore, modulating the kinase activity by employing small molecules has emerged as a strategic approach for cancer treatment. On the other hand, oxindole motifs have surfaced as privileged scaffolds with significant multi-kinase inhibitory activity. The present review summarises recent advances in the development of oxindole based kinase inhibitors. The role of distinguished structural frameworks of oxindoles, such as 3-alkenyl oxindoles, spirooxindoles, 3-iminooxindoles and similar hydrazone derivatives have been described based on their kinase inhibition potential. Furthermore, the design strategies, mechanism of actions, structure activity relationships (SARs) and their mode of interaction with target protein have been critically highlighted.

Effect of stress-induced polyploidy on melanoma reprogramming and therapy resistance

Melanomas and their precursors, the melanocytes, are frequently exposed to UV due to their anatomic location, leading to DNA damage and reactive oxygen stress related harm. Such damage can result in multinucleation or polyploidy, in particularly in presence of mitotic or cell division failure. As a consequence, the cell encounters either of two fates: mitotic catastrophe, resulting in cell death, or survival and recovery, the latter occurring less frequently. However, when cells manage to recover in an polyploid state, they have often acquired new features, which allow them to tolerate and adapt to oncogene- or therapy induced stress. This review focuses on polyploidy inducers in melanoma and their effects on transcriptional reprogramming and phenotypic adaptation as well as the relevance of polyploid melanoma cells for therapy resistance.

Promising Therapy in Lung Cancer: Spotlight on Aurora Kinases

Simple Summary

Lung cancer has remained one of the major causes of death worldwide. Thus, a more effective treatment approach is essential, such as the inhibition of specific cancer-promoting molecules. Aurora kinases regulate the process of mitosis—a process of cell division that is necessary for normal cell proliferation. Dysfunction of these kinases can contribute to cancer formation. In this review, we present studies indicating the implication of Aurora kinases in tumor formation, drug resistance, and disease prognosis. The effectivity of using Aurora kinase inhibitors in the pre-clinical and clinical investigations has proven their therapeutic potential in the setting of lung cancer. This work may provide further information to broaden the development of anticancer drugs and, thus, improve the conventional lung cancer management.

Abstract

Despite tremendous efforts to improve the treatment of lung cancer, prognosis still remains poor; hence, the search for efficacious therapeutic option remains a prime concern in lung cancer research. Cell cycle regulation including mitosis has emerged as an important target for cancer management. Novel pharmacological agents blocking the activities of regulatory molecules that control the functional aspects of mitosis such as Aurora kinases are now being investigated. The Aurora kinases, Aurora-A (AURKA), and Aurora B (AURKB) are overexpressed in many tumor entities such as lung cancer that correlate with poor survival, whereby their inhibition, in most cases, enhances the efficacy of chemo-and radiotherapies, indicating their implication in cancer therapy. The current knowledge on Aurora kinase inhibitors has increasingly shown high potential in ensuing targeted therapies in lung malignancies. In this review, we will briefly describe the biology of Aurora kinases, highlight their oncogenic roles in the pre-clinical and clinical studies in lung cancer and, finally, address the challenges and potentials of Aurora kinases to improve the therapy of this malignancy.

HI-511 overcomes melanoma drug resistance via targeting AURKB and BRAF V600E

Rationale: Melanoma is an aggressive tumor of the skin and drug resistance is still a major problem in melanoma therapy. Novel targets and effective agents to overcome drug resistant melanoma are urgently needed in clinical therapy.

Methods: Gene Expression Omnibus (GEO) database analysis, pathway enrichment analysis, and survival rate analysis were utilized to identify a candidate target. An anchorage-independent cell growth assay, flow cytometry, Western blot, and a xenograft mouse model were used to study the function of Aurora kinase B (AURKB) in both drug-sensitive and drug-resistant melanoma. Next, HI-511, a novel dual-target inhibitor targeting both AURKB and BRAF V600E, was designed and examined by an in vitro kinase assay. Methods as indicated above in addition to a BRAF V600E/PTEN-loss melanoma mouse model were used to demonstrate the effect of HI-511 on melanoma development in vitro and in vivo.

Results: AURKB is highly expressed in melanoma and especially in vemurafenib-resistant melanoma and the expression was correlated with patient survival rate. Knocking down AURKB inhibited cell growth and induced apoptosis in melanoma, which was associated with the BRAF/MEK/ERKs and PI3-K/AKT signaling pathways. Importantly, we found that HI-511, a novel dual-target inhibitor against AURKB and BRAF V600E, suppresses both vemurafenib-sensitive and vemurafenib-resistant melanoma growth in vitro and in vivo by inducing apoptosis and mediating the inhibition of the BRAF/MEK/ERKs and PI3K/AKT signaling pathways.

Conclusion: AURKB is a potential target for melanoma treatment. HI-511, a novel dual-target inhibitor against both AURKB and BRAF V600E, could achieve durable suppression of melanoma growth, even drug-resistant melanoma growth.

Cascade [1,5]-Hydride Transfer/Cyclization for Synthesis of [3,4]-Fused Oxindoles

The scandium-catalyzed redox-neutral cascade [1,5]-hydride transfer/cyclization between C4-amine-substituted isatins and 1,3-dicarbonyl compounds has been developed. This protocol enabled the synthesis of tricyclic [3,4]-fused oxindoles in good to high yields and excellent diastereoselectivities, featuring high atom- and step economy as well as good functional group tolerance.

AURKB as a target in non-small cell lung cancer with acquired resistance to anti-EGFR therapy

Non-small cell lung cancer (NSCLC) tumors harboring mutations in EGFR ultimately relapse to therapy with EGFR tyrosine kinase inhibitors (EGFR TKIs). Here, we show that resistant cells without the p.T790M or other acquired mutations are sensitive to the Aurora B (AURKB) inhibitors barasertib and S49076. Phospho-histone H3 (pH3), a major product of AURKB, is increased in most resistant cells and treatment with AURKB inhibitors reduces the levels of pH3, triggering G1/S arrest and polyploidy. Senescence is subsequently induced in cells with acquired mutations while, in their absence, polyploidy is followed by cell death. Finally, in NSCLC patients, pH3 levels are increased after progression on EGFR TKIs and high pH3 baseline correlates with shorter survival. Our results reveal that AURKB activation is associated with acquired resistance to EGFR TKIs, and that AURKB constitutes a potential target in NSCLC progressing to anti-EGFR therapy and not carrying resistance mutations.

Non-small cell lung cancer with EGFR mutations are known to develop resistance to EGFR tyrosine kinase inhibitors. Here, the authors show AURKB activation to be associated with resistance in EGFR mutant lung cancer cells, and that AURKB is a therapeutic target in resistant tumours that lack the p.T790M or other acquired mutations.

Aurora B kinase as a novel molecular target for inhibition the growth of osteosarcoma

Osteosarcoma is the primary human malignant tumor affecting bone. This cancer most frequently arises in children and adolescents, with a second peak in those over the age of 50. Currently, surgery followed by radiotherapy and chemotherapy are the main treatments, but long-term positive effects are very poor. Aurora B kinase is a serine/threonine kinase that is a key regulator of cell cycle and mitosis. Tissue array analysis revealed that Aurora B kinase is overexpressed in osteosarcoma compared with normal bone tissue. We developed a compound, HOI-07 (i.e., (E)-3-((E)-4-(benzo[d] [1,3]dioxol-5-yl)-2-oxobut-3-en-1-ylidene)indolin-2-one), as a specific Aurora B kinase inhibitor and examined its effectiveness against osteosarcoma cell growth in this study. This compound inhibited Aurora B kinase activity in osteosarcoma and induced apoptosis, caused G2-M phase arrest, and attenuated osteosarcoma anchorage-independent cell growth. Moreover, knocking down the expression of Aurora B effectively reduced the sensitivity of osteosarcoma to HOI-07. Results of a xenograft mouse study indicated that HOI-07 treatment effectively suppressed the growth of 143B and KHOS xenografts, without affecting the body weight of mice. The expression of phosphorylated histone H3 (Ser10) was reduced in mice treated with HOI-07. Overall, we identified HOI-07 as a specific Aurora B kinase inhibitor for osteosarcoma treatment and this compound warrants further investigation.

APIO-EE-9 is a novel Aurora A and B antagonist that suppresses esophageal cancer growth in a PDX mouse model

Esophageal cancer (EC) is one of the most aggressive malignancies of the upper aerodigestive tract. Over the past three decades, with advances in surgical techniques and treatment, the prognosis of esophageal cancer has only slowly improved. Thus identifying novel molecular targets and developing therapeutic agents are critical. Aurora kinases play a crucial role in mitosis and selective inhibitors might provide an effective therapeutic treatment for cancer. However, the role of Aurora kinases in EC is still inadequately studied. Here, we identified a novel compound, referred to as APIO-EE-9, which inhibits growth and colony formation and induces apoptosis of esophageal cancer cells. Using computer modeling, we found that APIO-EE-9 interacted with both Aurora A and B in the ATP-binding pocket. APIO-EE-9 inhibited both Aurora A and B kinase activities in a dose-dependent manner. Treatment with APIO-EE-9 substantially reduced the downstream Aurora kinase phosphorylation of histone H3 (Ser10), resulting in formation of multiple nuclei and centrosomes. Additionally, esophageal cancer cells expressing shAurora A or shAurora B kinase exhibited a dramatic reduction in proliferation and colony formation. Injection of these cells as xenografts in mice reduced tumor formation compared to wildtype cells. Importantly, APIO-EE-9 significantly decreased the size of esophageal patient-derived xenograft (PDX) tumors implanted in SCID mice. These results demonstrated that APIO-EE-9 is a specific Aurora kinase inhibitor that could be developed as a therapeutic agent against esophageal cancer.

Synthesis of Functionalized 6-Hydroxy-2-oxindole Derivatives by Phenoxide Cyclization

An apparent intramolecular cross-dehydrogenative coupling of N-(3-hydroxy)monoanilide of maleic esters comprising base promoted phenoxide cyclization and subsequent base-mediated aerobic oxidation was developed to synthesize a variety of 2-(6-hydroxy-2-oxoindolin-3-ylidene)acetate derivatives. The isolation of intermediate cyclized products during the large scale reactions and their ready dehydrogenation with 1 equiv of base support this proposed two-step path.

Quercetin suppresses lung cancer growth by targeting Aurora B kinase

aurora B kinase is highly expressed in several cancer cells and promotes tumorigenesis and progression, and therefore, it is an important target for drug to treat tumors. Quercetin was identified to be an antitumor agent. Herein, we report for the first time that quercetin inhibited aurora B activities by directly binding with aurora B in vitro and in vivo. Ex vivo studies showed that quercetin inhibited aurora B activities in JB6 Cl41 cells and A549 lung cancer cells. Moreover, knockdown of aurora B in A549 cells decreased their sensitivities to quercetin. In vivo study demonstrated that injection of quercetin in A549 tumor‐bearing mice effectively suppressed cancer growth. The phosphorylation of histone 3 in tumor tissues was also decreased after quercetin treatment. In short, quercetin can suppress growth of lung cancer cells as an aurora B inhibitor both in vitro and in vivo.

Effective Concentration of a Multikinase Inhibitor within Bone Marrow Correlates with In Vitro Cell Killing in Therapy-Resistant Chronic Myeloid Leukemia

Leukemia cells escape BCR-ABL-targeted therapy by developing mutations, such as T315I, in the p210(BCR-ABL) fusion protein in Philadelphia chromosome-positive chronic myeloid leukemia (CML). Although most effort has been focused on development of new tyrosine kinase inhibitors, enrichment of these small-molecule inhibitors in the tumor tissue can also have a profound impact on treatment outcomes. Here, we report that a 2-hour exposure of the T315I-mutant CML cells to 10 μmol/L of the multikinase inhibitor TG101209 suppressed BCR-ABL-independent signaling and caused cell-cycle arrest at G2-M. Further increase in drug concentration to 17.5 μmol/L blocked phosphorylation of the mutant BCR-ABL kinase and its downstream JAK2 and STAT5. The effective dosage to overcome therapy resistance identified in an in vitro setting serves as a guidance to develop the proper drug formulation for in vivo efficacy. A targeted formulation was developed to achieve sustained bone marrow TG101209 concentration at or above 17.5 μmol/L for effective killing of CML cells in vivo Potent inhibition of leukemia cell growth and extended survival were observed in two murine models of CML treated with 40 mg/kg intravenously administered targeted TG101209, but not with the untargeted drug at the same dosage. Our finding provides a unique approach to develop treatments for therapy-resistant CML. Mol Cancer Ther; 15(5); 899-910. ©2016 AACR.

Tubulin Beta3 Serves as a Target of HDAC3 and Mediates Resistance to Microtubule-Targeting Drugs

We investigated the role of HDAC3 in anti-cancer drug-resistance. The expression of HDAC3 was decreased in cancer cell lines resistant to anti-cancer drugs such as celastrol and taxol. HDAC3 conferred sensitivity to these anti-cancer drugs. HDAC3 activity was necessary for conferring sensitivity to these anti-cancer drugs. The down-regulation of HDAC3 increased the expression of MDR1 and conferred resistance to anti-cancer drugs. The expression of tubulin β3 was increased in drug-resistant cancer cell lines. ChIP assays showed the binding of HDAC3 to the promoter sequences of tubulin β3 and HDAC6. HDAC6 showed an interaction with tubulin β3. HDAC3 had a negative regulatory role in the expression of tubulin β3 and HDAC6. The down-regulation of HDAC6 decreased the expression of MDR1 and tubulin β3, but did not affect HDAC3 expression. The down-regulation of HDAC6 conferred sensitivity to taxol. The down-regulation of tubulin β3 did not affect the expression of HDAC6 or MDR1. The down-regulation of tubulin β3 conferred sensitivity to anti-cancer drugs. Our results showed that tubulin β3 serves as a downstream target of HDAC3 and mediates resistance to microtubule-targeting drugs. Thus, the HDAC3-HDAC6-Tubulin β axis can be employed for the development of anti-cancer drugs.

Targeting epidermal fatty acid binding protein for treatment of experimental autoimmune encephalomyelitis

Background

Multiple sclerosis (MS) is an autoimmune disease in which dysregulated immune cells attack myelin in the central nervous system (CNS), leading to irreversible neuronal degeneration. Our previous studies have demonstrated that epidermal fatty acid binding protein (E-FABP), widely expressed in immune cells, in particular in dendritic cells (DCs) and T lymphocytes, fuels the overactive immune responses in the mouse model of experimental autoimmune encephalomyelitis (EAE).

Methods

In the present study, we conducted an intensive computational docking analysis to identify novel E-FABP inhibitors for regulation of immune cell functions and for treatment of EAE.

Results

We demonstrate that compound [2-(4-acetylphenoxy)-9,10-dimethoxy-6,7-dihydropyrimido[6,1-a]isoquinolin-4-one; designated as EI-03] bound to the lipid binding pocket of E-FABP and enhanced the expression of peroxisome proliferator-activating receptor (PPAR) γ. Further in vitro experiments showed that EI-03 regulated DC functions by inhibition of TNFα production while promoting IL-10 secretion. Moreover, EI-03 treatment counterregulated T cell balance by decreasing effector T cell differentiation (e.g. Th17, Th1) while increasing regulatory T cell development. Most importantly, mice treated with this newly identified compound exhibited reduced clinical symptoms of EAE in mouse models.

Conclusions

Taken together, we have identified a new compound which displays a potential therapeutic benefit for treatment of MS by targeting E-FABP.

A phase 1 dose escalation study of BI 831266, an inhibitor of Aurora kinase B, in patients with advanced solid tumors

Purpose BI 831266 is a potent, selective, low-molecular-weight inhibitor of Aurora kinase B. This trial aimed to determine the maximum tolerated dose (MTD) of BI 831266 in patients with advanced solid tumors (NCT00756223; EudraCT 2008-001631-36; 1257.1). Methods BI 831266 (4–130 mg) was administered over 24 h on days 1 and 15 of a 4-week schedule. A modified 3 + 3 dose-escalation design was utilized to evaluate the MTD. Safety, pharmacokinetics, pharmacodynamics, objective response rate, progression-free survival (PFS) and exploratory biomarkers were secondary endpoints. Results Twenty-five patients received BI 831266. The most frequent tumor type was colorectal cancer (48 %). One patient (130 mg) experienced a dose-limiting toxicity of grade 3 febrile neutropenia. The trial was prematurely terminated (sponsor decision) without further dose-escalation. The most frequent treatment-related adverse events (AEs) were fatigue (20 %), neutropenia, alopecia (16 % each), anemia, dry skin, and nausea (12 % each). Treatment-related grade ≥3 AEs were neutropenia (12 %), anemia (8 %), and febrile neutropenia (4 %); 15 patients experienced serious AEs. High variability in the pharmacokinetic profiles precluded definitive pharmacokinetic conclusions. Exploratory biomarker determination revealed consistency with the mode of action as an Aurora kinase B inhibitor. One patient (4 %; 32 mg) with cervical cancer demonstrated a confirmed partial response (duration 141 days, PFS 414 days). Four patients had stable disease. Conclusion The MTD of BI 831266 was not reached because of early trial termination. BI 831266 demonstrated a generally manageable safety profile and signs of antitumor activity in some patients’ solid tumors.

Dose selection for the investigational anticancer agent alisertib (MLN8237): Pharmacokinetics, pharmacodynamics, and exposure-safety relationships

We report population pharmacokinetic, pharmacodynamic, and pharmacokinetic-safety analyses to support phase II/III dose/regimen selection of alisertib, a selective Aurora A kinase (AAK) inhibitor. Phase I studies in adult cancer patients evaluated dosing on Days 1-7 in 21-day cycles or Days 1-21 in 35-day cycles, with corresponding maximum tolerated doses of 50 mg twice daily (BID) and 50 mg QD, respectively. Population pharmacokinetic analyses supported dose- and time-linear pharmacokinetics without identification of clinically meaningful covariates. Exposure-related increases in skin mitotic index and decreases in chromosomal alignment/spindle bipolarity in tumor mitotic cells confirmed AAK inhibition. Exposures in the 7-day schedule at or near 50 mg BID are expected to result in tumor AAK inhibition based on pharmacodynamic assessment in patient tumors. Exposure-safety analyses of data from patients receiving doses of 5-200 mg/day in the 7-day schedule support a low (∼7%) predicted incidence of dose-limiting toxicity at 50 mg BID. Taken together, these analyses support a pharmacologically active and acceptably tolerated dose range of alisertib for future clinical development.

3,6,2',4',5'-Pentahydroxyflavone, an orally bioavailable multiple protein kinase inhibitor, overcomes gefitinib resistance in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the most lethal cancer, causing more than 150,000 deaths in the United States in 2013. The receptor tyrosine kinase inhibitors such as gefitinib are not perfect clinical therapeutic agents for NSCLC treatment due to primary or acquired tyrosine kinase inhibitor resistance. Herein, 3,6,2',4',5'-pentahydroxyflavone (36245-PHF) was identified as a multiple kinase inhibitor for NSCLC treatment based on the computational screening of a natural products database. 36245-PHF was shown to inhibit PI3K and Aurora A and B kinases and overcome gefitinib-resistant NSCLC growth. Our data clearly showed that 36245-PHF markedly inhibited anchorage-independent growth of gefitinib-resistant NSCLC cell lines and exerted a substantial chemotherapeutic effect following oral administration in a gefitinib-resistant NSCLC xenograft model. The evidence from three different subsequent methodological approaches, in vitro, ex vivo, and in vivo, all confirmed that 36245-PHF as a multiple protein kinase inhibitor. Overall, we identified 36245-PHF as a multiple protein kinase inhibitor and as a novel therapeutic agent to overcome gefitinib-resistant NSCLC growth, which could provide a new option for clinical NSCLC oral treatment.

Use of rodents as models of human diseases

Advances in molecular biology have significantly increased the understanding of the biology of different diseases. However, these discoveries have not yet been fully translated into improved treatments for patients with diseases such as cancers. One of the factors limiting the translation of knowledge from preclinical studies to the clinic has been the limitations of in vivo diseases models. In this brief review, we will discuss the advantages and disadvantages of rodent models that have been developed to simulate human pathologies, focusing in models that employ xenografts and genetic modification. Within the framework of genetically engineered mouse (GEM) models, we will review some of the current genetic strategies for modeling diseases in the mouse and the preclinical studies that have already been undertaken. We will also discuss how recent improvements in imaging technologies may increase the information derived from using these GEMs during early assessments of potential therapeutic pathways. Furthermore, it is interesting to note that one of the values of using a mouse model is the very rapid turnover rate of the animal, going through the process of birth to death in a very short timeframe relative to that of larger mammalian species.

Inhibition of Aurora-B suppresses osteosarcoma cell migration and invasion

Previous studies have suggested that Aurora-B may be involved in cancer metastasis. However, its role has been poorly evaluated in osteosarcoma (OS). The aim of this study was to investigate the correlation between Aurora-B expression and metastasis in human OS. The human OS cell line, U2-OS, and OS biopsy specimens were used in the study. The expression of Aurora-B protein was examined using immunohistochemistry and western blotting in OS tissues and U2-OS cells, respectively. AZD1152-hydroxyquinazoline-pyrazol-anilide, an inhibitor of Aurora-B, was used to inhibit Aurora-B expression in U2-OS cells. The effect of Aurora-B inhibition on U2-OS cell proliferation, invasion and migration was assessed using MTT, colony formation, wound healing and Transwell assays. The results showed that positive expression of the Aurora-B protein was observed in the nucleus, and that Aurora-B expression levels in the cases with pulmonary metastases were significantly higher than in those without metastasis. In vitro, the proliferation, invasion and migration of U2-OS cells were suppressed by the inhibition of Aurora-B. These results suggest that Aurora-B may be involved in OS metastasis, and may be a promising target in the treatment of OS metastasis.

A derivative of chrysin suppresses two-stage skin carcinogenesis by inhibiting mitogen- and stress-activated kinase 1

Mitogen- and stress-activated kinase 1 (MSK1) is a nuclear serine/threonine protein kinase that acts downstream of both extracellular signal-regulated kinases and p38 mitogen-activated protein kinase in response to stress or mitogenic extracellular stimuli. Increasing evidence has shown that MSK1 is closely associated with malignant transformation and cancer development. MSK1 should be an effective target for cancer chemoprevention and chemotherapy. However, very few MSK1 inhibitors, especially natural compounds, have been reported. We used virtual screening of a natural products database and the active conformation of the C-terminal kinase domain of MSK1 (PDB id 3KN) as the receptor structure to identify chrysin and its derivative, compound 69407, as inhibitors of MSK1. Compared with chrysin, compound 69407 more strongly inhibited proliferation and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation of JB6 P+ cells with lower cytotoxicity. Western blot data demonstrated that compound 69407 suppressed phosphorylation of the MSK1 downstream effector histone H3 in intact cells. Knocking down the expression of MSK1 effectively reduced the sensitivity of JB6 P+ cells to compound 69407. Moreover, topical treatment with compound 69407 before TPA application significantly reduced papilloma development in terms of number and size in a two-stage mouse skin carcinogenesis model. The reduction in papilloma development was accompanied by the inhibition of histone H3 phosphorylation at Ser10 in tumors extracted from mouse skin. The results indicated that compound 69407 exerts inhibitory effects on skin tumorigenesis by directly binding with MSK1 and attenuates the MSK1/histone H3 signaling pathway, which makes it an ideal chemopreventive agent against skin cancer.