Targeting FOXM1 auto-regulation in cancer

Structure–Activity Relationship of N-Phenylthieno[2,3-b]pyridine-2-carboxamide Derivatives Designed as Forkhead Box M1 Inhibitors: The Effect of Electron-Withdrawing and Donating Substituents on the Phenyl Ring

We report synthesis, characterization, biological evaluation, and molecular-docking studies of 18 thieno[2,3-b]pyridines with a phenylacetamide moiety at position 2, which is disubstituted with F, Cl, Br, or I at position 4, and with electron-withdrawing and electron-donating groups (-CN, -NO₂, -CF₃, and -CH₃) at position 2, to study how the electronic properties of the substituents affected the FOXM1-inhibitory activity. Among compounds 1–18, only those bearing a -CN (regardless of the halogen) decreased FOXM1 expression in a triple-negative breast cancer cell line (MDA-MB-231), as shown by Western blotting. However, only compounds 6 and 16 decreased the relative expression of FOXM1 to a level lower than 50%, and hence, we determined their anti-proliferative activity (IC₅₀) in MDA-MB-231 cells using the MTT assay, which was comparable to that observed with FDI-6, in contrast to compound 1, which was inactive according to both Western blot and MTT assays. We employed molecular docking to calculate the binding interactions of compounds 1–18 in the FOXM1 DNA-binding site. The results suggest a key role for residues Val296 and Leu289 in this binding. Furthermore, we used molecular electrostatic potential maps showing the effects of different substituents on the overall electron density.

FOXM1 inhibitors as potential diagnostic agents: 1st generation of a PET probe targeting FOXM1 to detect triple negative-breast cancer in vitro and in vivo

The FOXM1 protein controls the expression of essential genes related to cancer cell cycle progression, metastasis, and chemoresistance. We hypothesize that FOXM1 inhibitors could represent a novel approach to develop 18 F-based radiotracers for Positron Emission Tomography (PET). Therefore, in this report we describe the first attempt to use 18 F-labeled FOXM1 inhibitors to detect triple-negative breast cancer (TNBC). Briefly, we replaced the original amide group in the parent drug FDI-6 for a ketone group in the novel AF-FDI molecule, to carry out an aromatic nucleophilic ( 18 F)-fluorination. AF-FDI dissociated the FOXM1-DNA complex, decreased FOXM1 levels, and inhibited cell proliferation in a TNBC cell line (MDA-MB-231). [ 18 F]AF-FDI was internalized in MDA-MB-231 cells. Cell uptake inhibition experiments showed that AF-FDI and FDI-6 significantly decreased the maximum uptake of [ 18 F]AF-FDI, suggesting specificity towards FOXM1. [ 18 F]AF-FDI reached a tumor uptake of SUV = 0.31 in MDA-MB-231 tumor-bearing mice and was metabolically stable 60 min post-injection. These results provide preliminary evidence supporting the potential role of FOXM1 to develop PET radiotracers.

Rosmarinic Acid Methyl Ester Regulates Ovarian Cancer Cell Migration and Reverses Cisplatin Resistance by Inhibiting the Expression of Forkhead Box M1

Rosmarinic acid methyl ester (RAME), a derivative of rosmarinic acid (RA), is reported to have several therapeutic effects, including anti-tumor effects against cervical cancer. However, its anti-tumor effects in ovarian cancer is unclear. In this study, we studied the molecular pathways associated with the anti-tumor effects of RAME in ovarian cancer. To identify the effects of RAME in ovarian cancer, RNA sequencing was performed in RAME-treated ovarian cancer cells; we found that RAME treatment downregulated the genes closely involved with the target genes of the transcription factor Forkhead box M1 (FOXM1). It was reported that FOXM1 is overexpressed in a variety of cancer cells and is associated with cell proliferation and tumorigenesis. Therefore, we hypothesized that FOXM1 is a key target of RAME; this could result in its anti-tumor effects. Treatment of ovarian cancer cells with RAME-inhibited cell migration and invasion, as shown by wound healing and transwell migration assays. To examine whether RAME represses the action of FOXM1, we performed quantitative RT-PCR and ChIP-qPCR. Treatment of ovarian cancer cells with RAME decreased the mRNA expression of FOXM1 target genes and the binding of FOXM1 to its target genes. Moreover, FOXM1 expression was increased in cisplatin-resistant ovarian cancer cells, and combination treatment with RAME and cisplatin sensitized the cisplatin-resistant ovarian cancer cells, which was likely due to FOXM1 inhibition. Our research suggests that RAME is a promising option in treating ovarian cancer patients, as it revealed a novel molecular pathway underlying its anti-tumor effects.

A structure-activity relationship study of Forkhead Domain Inhibitors (FDI): The importance of halogen binding interactions

The Forkhead boX M1 (FOXM1) protein is an essential transcription factor required for the normal activation of human cell cycle. However, increasing evidence supports a correlation between FOXM1 overexpression and the onset of several types of cancer. Based on a previously reported molecular modeling and molecular dynamics simulations (MD) study, we hypothesized the role of an essential halogen-bonding interaction between the 4-fluorophenyl group in the forkhead domain inhibitor-6 (FDI-6) and an Arg297 residue inside the FOXM1-DNA binding domain (DBD). To prove the importance of this binding interaction, we synthesized and screened ten FDI-6 derivatives possessing different groups at the 4-fluorophenyl position of the lead molecule. Briefly, we found that derivatives possessing a 4-chlorophenyl, 4-bromophenyl, or a 4-iodophenyl group, were equipotent to the original 4-fluorophenyl moiety present in FDI-6, whereas derivatives without this 4-halogen moiety were inactive. We also observed that positional isomers in which the halogen was relocated to positions 2- or 3- on the phenyl group were significantly less active. These results provide evidence to support the essential role of a 4-halophenyl bonding interaction, with the Arg297 residue in the FOXM1-DBD, to exert inhibition of transcriptional activity.

Molecular mechanism of Forkhead box M1 inhibition by thiostrepton in breast cancer cells

Breast cancer is the most common type of malignancies in women worldwide, and genotoxic chemotherapeutic drugs are effective by causing DNA damage in cancer cells. However, >90% of patients with metastatic cancer are resistant to chemotherapy. The Forkhead box M1 (FOXM1) transcription factor plays a pivotal role in the resistance of breast cancer cells to chemotherapy by promoting DNA damage repair following genotoxic drug treatment. The aim of the present study was to investigate the inhibition of the FOXM1 protein by thiostrepton, a natural antibiotic produced by the Streptomyces species. Experimental studies were designed to examine the effectiveness of thiostrepton in downregulating FOXM1 mRNA expression and activity, leading to senescence and apoptosis of breast cancer cells. The cytotoxicity of thiostrepton in breast cancer was determined using cell viability assay. Additionally, thiostrepton treatment decreased the mRNA expression of cyclin B1 (CCNB1), a downstream target of FOXM1. The present results indicated that thiostrepton inhibited FOXM1 mRNA expression and its effect on CCNB1. Molecular dynamic simulations were performed to study the interactions between FOXM1-DNA and thiostrepton after molecular docking. The results revealed that the possible mechanism underlying the inhibitory effect of thiostrepton on FOXM1 function was by forming a tight complex with the DNA and FOXM1 via its binding domain. Collectively, these results indicated that thiostrepton is a specific and direct inhibitor of the FOXM1 protein in breast cancer. The findings of the present study may lead to the development of novel therapeutic strategies for breast cancer and help overcome resistance to conventional chemotherapeutic drugs.

FOXM1 plays a role in autophagy by transcriptionally regulating Beclin-1 and LC3 genes in human triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) is associated with poor prognosis owing to its aggressive and heterogeneous nature, and the lack of therapeutic targets. Although Forkhead Box M1 (FOXM1) is one of the most important oncogenes contributing to tumorigenesis, progression, and drug resistance in TNBC, the underlying molecular mechanisms are not well understood. Emerging evidence indicates that autophagy plays a critical role in cell survival and protective mechanism in TNBC. However, signaling pathways that are involved in the regulation of autophagy remain to be elucidated. In the present study, we examined the role of FOXM1 in regulating autophagy in TNBC cells and found that FOXM1 is upregulated during induction of autophagy. We found that inhibition of FOXM1 suppressed starvation and rapamycin-induced autophagy and expression of the major autophagy regulators, LC3 and Beclin-1. Further studies demonstrated that FOXM1 directly binds to the promotors of LC3 and Beclin-1 genes and transcriptionally regulates their expression by chromatin immunoprecipitation (ChIP) and luciferase gene reporter assays. In conclusion, our study provides the first evidence about the role of FOXM1 in regulating expression of LC3 and Beclin-1 and autophagy in TNBC cells. Our findings provide novel insight into the role of FOXM1 regulation of the autophagic survival pathway and potential molecular target for treating TNBC. KEY MESSAGES: • FOXM1 promotes tumorigenesis and progression of TNBC. However, the underlying molecular mechanism by which FOXM1 promotes TNBC tumorigenesis is unclear. The goal of our study was to determine the role of FOXM1 in the regulation of autophagy that plays a role in TNBC progression. Our findings show that FOXM1 binds to promoters of the genes encoding the major autophagy proteins, Beclin and LC3, and provide new insights into the regulation of autophagy, which is being targeted in many clinical trials.

Regulation of the master regulator FOXM1 in cancer

FOXM1 (forkhead box protein M1) is a critical proliferation-associated transcription factor that is widely spatiotemporally expressed during the cell cycle. It is closely involved with the processes of cell proliferation, self-renewal, and tumorigenesis. In most human cancers, FOXM1 is overexpressed, and this indicates a poor prognosis for cancer patients. FOXM1 maintains cancer hallmarks by regulating the expression of target genes at the transcriptional level. Due to its potential role as molecular target in cancer therapy, FOXM1 was named the Molecule of the Year in 2010. However, the mechanism of FOXM1 dysregulation remains indistinct. A comprehensive understanding of FOXM1 regulation will provide novel insight for cancer and other diseases in which FOXM1 plays a major role. Here, we summarize the transcriptional regulation, post-transcriptional regulation and post-translational modifications of FOXM1, which will provide extremely important implications for novel strategies targeting FOXM1.

A Novel Function of Molecular Chaperone HSP70: SUPPRESSION OF ONCOGENIC FOXM1 AFTER PROTEOTOXIC STRESS

The oncogenic transcription factor FOXM1 is overexpressed in the majority of human cancers, and it is a potential target for anticancer therapy. We identified proteasome inhibitors as the first type of drugs that target FOXM1 in cancer cells. Here we found that HSP90 inhibitor PF-4942847 and heat shock also suppress FOXM1. The common effector, which was induced after treatment with proteasome and HSP90 inhibitors or heat shock, was the molecular chaperone HSP70. We show that HSP70 binds to FOXM1 following proteotoxic stress and that HSP70 inhibits FOXM1 DNA-binding ability. Inhibition of FOXM1 transcriptional autoregulation by HSP70 leads to the suppression of FOXM1 protein expression. In addition, HSP70 suppression elevates FOXM1 expression, and simultaneous inhibition of FOXM1 and HSP70 increases the sensitivity of human cancer cells to anticancer drug-induced apoptosis. Overall, we determined the unique and novel mechanism of FOXM1 suppression by proteasome inhibitors.