Mithramycin A suppresses basal triple-negative breast cancer cell survival partially via down-regulating Krüppel-like factor 5 transcription by Sp1

LN-439A, a novel BAP1 inhibitor, suppresses the growth of basal-like breast cancer by degrading KLF5

Basal-like breast cancer (BLBC) is the most malignant subtype of breast cancer because of its aggressive clinical behaviour and lack of effective targeted agents. Krüppel-like factor 5 (KLF5) is an oncogenic transcription factor that is highly expressed in BLBC. The deubiquitinase (DUB) BRCA1-associated protein 1 (BAP1) stabilizes KLF5 and promotes BLBC growth and metastasis. Therefore, pharmacological inhibition of the BAP1‒KLF5 axis is an effective therapeutic strategy for BLBC. Here, through screening, we identified a series of tetrahydro-β-carboline derivatives that effectively reduced the protein expression of KLF5 and exhibited strong antitumour activity. Among the investigated compounds, the lead compound LN-439A presented the strongest antitumour activity and inhibitory effect on KLF5 expression. LN-439A suppressed the proliferation and migration of BLBC cells, induced G2/M arrest, and induced apoptosis. Mechanistically, LN-439A functions as a small molecule catalytic inhibitor of BAP1 by binding to the catalytic pocket of BAP1, leading to the ubiquitination and degradation of KLF5. Consistent with this finding, the overexpression of KLF5 suppressed the antitumour effects of LN-439A. In summary, LN-439A is a promising therapeutic agent for BLBC that functions by targeting the BAP1‒KLF5 axis.

Kv1.3-induced hyperpolarization is required for efficient Kaposi's sarcoma-associated herpesvirus lytic replication

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic herpesvirus that is linked directly to the development of Kaposi's sarcoma. KSHV establishes a latent infection in B cells, which can be reactivated to initiate lytic replication, producing infectious virions. Using pharmacological and genetic silencing approaches, we showed that the voltage-gated K+ channel Kv1.3 in B cells enhanced KSHV lytic replication. The KSHV replication and transcription activator (RTA) protein increased the abundance of Kv1.3 and led to enhanced K+ channel activity and hyperpolarization of the B cell membrane. Enhanced Kv1.3 activity promoted intracellular Ca2+ influx, leading to the Ca2+-driven nuclear localization of KSHV RTA and host nuclear factor of activated T cells (NFAT) proteins and subsequently increased the expression of NFAT1 target genes. KSHV lytic replication and infectious virion production were inhibited by Kv1.3 blockers or silencing. These findings highlight Kv1.3 as a druggable host factor that is key to the successful completion of KSHV lytic replication.

Decoding gene regulatory circuitry underlying TNBC chemoresistance reveals biomarkers for therapy response and therapeutic targets

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype characterised by extensive intratumoral heterogeneity, high rates of metastasis and chemoresistance, leading to poor clinical outcomes. Despite progress, the mechanistic basis of chemotherapy resistance in TNBC patients remains poorly understood. Here, leveraging single-cell transcriptome datasets of matched longitudinal TNBC chemoresponsive and chemoresistant patient cohorts, we unravel distinct cell subpopulations intricately associated with chemoresistance and the signature genes defining these populations. Notably, using genome-wide mapping of the H3K27ac mark, we show that the expression of these chemoresistance genes is driven via a set of TNBC super-enhancers and associated transcription factor networks across TNBC subtypes. Furthermore, genetic screens reveal that a subset of these transcription factors is essential for the survival of TNBC cells, and their loss increases sensitivity to chemotherapeutic agents. Overall, our study has revealed epigenetic and transcription factor networks underlying chemoresistance and suggests novel avenues to stratify and improve the treatment of patients with a high risk of developing resistance.

Demethylase FTO inhibits the occurrence and development of triple-negative breast cancer by blocking m 6A-dependent miR-17-5p maturation-induced ZBTB4 depletion

Triple-negative breast cancer (TNBC) is a subtype of breast cancer, and its mechanisms of occurrence and development remain unclear. In this study, we aim to investigate the role and molecular mechanisms of the demethylase FTO (fat mass and obesity-associated protein) in TNBC. Through analysis of public databases, we identify that FTO may regulate the maturation of miR-17-5p and subsequently influence the expression of zinc finger and BTB domain-containing protein 4 (ZBTB4), thereby affecting the occurrence and progression of TNBC. We screen for relevant miRNAs and mRNAs from the GEO and TCGA databases and find that the FTO gene may play a crucial role in TNBC. In vitro cell experiments demonstrate that overexpression of FTO can suppress the proliferation, migration, and invasion ability of TNBC cells and can regulate the maturation of miR-17-5p through an m 6A-dependent mechanism. Furthermore, we establish a xenograft nude mouse model and collect clinical samples to further confirm the role and impact of the FTO/miR-17-5p/ZBTB4 regulatory axis in TNBC. Our findings unveil the potential role of FTO and its underlying molecular mechanisms in TNBC, providing new perspectives and strategies for the research and treatment of TNBC.

CircSNX25 mediated by SP1 promotes the carcinogenesis and development of triple-negative breast cancer

Circular RNAs (circRNAs), according to a growing body of research, are thought to be important in the initiation and development of a number of cancers. However, more research is needed to fully understand how circRNAs work at the molecular level in triple-negative breast cancer (TNBC). RNA sequencing was conducted on four sets of TNBC samples and their corresponding adjacent noncancerous tissues (ANTs). The circSNX25 expression was assessed using quantitative real-time PCR in TNBC tissues and cells. Several in vitro and in vivo experiments were conducted in order to examine the function of circSNX25 in TNBC carcinogenesis. Through luciferase reporter and chromatin immunoprecipitation (ChIP) assays, we also investigated the potential regulation of circSNX25 biogenesis by specificity protein 1 (SP1). To further validate the relationship between circSNX25 and COPI coat complex subunit beta 1 (COPB1) in TNBC, we conducted circRNA pull-down and RNA immunoprecipitation (RIP) assays using the MS2/MS2-CP system. Online databases were analyzed to examine the clinical implications and prognostic value of COPB1 in TNBC. A higher circSNX25 expression levels were observed in tissues and cells of TNBC. Silencing circSNX25 notably inhibited TNBC cell proliferation, triggered apoptosis, and hindered tumor growth in vivo. Conversely, upregulation of circSNX25 had the opposite effects. Mechanistically, circSNX25 was found to physically interact with COPB1. Importantly, we identified that SP1 may enhance circSNX25 biogenesis. COPB1 levels were markedly higher in TNBC cells. Analysis of online databases revealed that TNBC patients with elevated COPB1 levels had a poorer prognosis. Our findings demonstrate that SP1-mediated circSNX25 promotes TNBC carcinogenesis and development. CircSNX25 may therefore serve as both a diagnostic and therapeutic biomarker for TNBC patients.

SP1-Induced Upregulation of LncRNA AFAP1-AS1 Promotes Tumor Progression in Triple-Negative Breast Cancer by Regulating mTOR Pathway

The long non-coding RNA (lncRNA) actin fiber-associated protein-1 antisense RNA 1 (AFAP1-AS1) exerted oncogenic activity in triple-negative breast cancer (TNBC). We designed this study and conducted it to investigate the upstream regulation mechanism of AFAP1-AS1 in TNBC tumorigenesis. In this work, we proved the localization of AFAP1-AS1 in the cytoplasm. We elucidated the mechanism by which the transcription factor specificity protein 1 (SP1) modulated AFAP1-AS1 in TNBC progression, which has yet to be thoroughly studied. Dual luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay revealed a strong affinity of SP1 toward the promoter regions P3 of AFAP1-AS1, proving the gene expression regulation of AFAP1-AS1 via SP1 in TNBC. Additionally, SP1 could facilitate the tumorigenesis of TNBC cells in vitro and in vivo by regulating the AFAP1-AS1 expression. Furthermore, silenced AFAP1-AS1 suppressed the expression of genes in the mTOR pathway, such as eukaryotic translation initiation factor 4B (EIF4B), mitogen-activated protein kinase-associated protein 1 (MAPKAP1), SEH1-like nucleoporin (SEH1L), serum/glucocorticoid regulated kinase 1 (SGK1), and its target NEDD4-like E3 ubiquitin protein ligase (NEDD4L), and promoted the gene expression of s-phase kinase-associated protein 2 (SKP2). Overall, this study emphasized the oncogenic role of SP1 and AFAP1-AS1 in TNBC and illustrated the AFAP1-AS1 upstream interaction with SP1 and the downstream modulatory of mTOR signaling, thus offering insights into the tumorigenesis mechanism in TNBC.

Cell cycle arrest and apoptosis are early events in radiosensitization of EWS::FLI1+ Ewing sarcoma cells by Mithramycin A

PURPOSE

The oncogenic fusion protein EWS::FLI1 is an attractive therapeutic target in Ewing sarcoma (ES). Mithramycin A (MithA) is a potent and specific inhibitor of EWS::FLI1 that can selectively radiosensitize ES cells through transcriptional inhibition of DNA double-strand break (DSB) repair. Here, we evaluate temporal changes in cell cycle progression and apoptosis in ES cells treated with MithA and/or ionizing radiation (RTx), testing the hypothesis that combining MithA with ionizing radiation would synergistically impair cell cycle progression and enhance apoptotic elimination to a greater extent than either agent alone.

MATERIALS AND METHODS

Four EWS::FLI1+ ES cell lines TC-71, RD-ES, SK-ES-1, and A673, and one EWS::ERG cell line (CHLA-25) were exposed to 10nM MithA or vehicle and followed 24 h later by exposure to 2 Gy x-radiation or sham irradiation. Reactive oxygen species (ROS) activity was evaluated by cytometric assay, and assay of antioxidant gene expression by RT-qPCR. Cell cycle changes were evaluated by flow cytometry of nuclei stained with propidium iodide. Apoptosis was assessed by cytometric assessment of Caspase-3/7 activity and by immunoblotting of PARP-1 cleavage. Radiosensitization was evaluated by clonogenic survival assay. Proliferation (EdU) and apoptosis (TUNEL) were evaluated in SK-ES-1 xenograft tumors following pretreatment with 1 mg/kg MithA, followed 24 h later by a single 4 Gy fraction of x-radiation.

RESULTS

MithA-treated cells showed reduced levels of ROS, and were associated with increased expression of antioxidant genes SOD1, SOD2, and CAT. It nonetheless induced persistent G0/G1 arrest and a progressive increase of the sub-G1 fraction, suggesting apoptotic degeneration. In vitro assays of Caspase-3/7 activity and immunoblotting of Caspase-3/7 dependent cleavage of PARP-1 indicated that apoptosis began as early as 24 h after MithA exposure, reducing clonogenic survival. Tumors from xenograft mice treated with either radiation alone, or in combination with MithA showed a significant reduction of tumor cell proliferation, while apoptosis was significantly increased in the group receiving the combination of MithA and RTx.

CONCLUSIONS

Taken together, our data show that the anti-proliferative and cytotoxic effects of MithA are the prominent components of radiosensitization of EWS::FLI1+ ES, rather than the result of acutely enhanced ROS levels.

Sp3 is essential for normal lung morphogenesis and cell cycle progression during mouse embryonic development

Members of the Sp family of transcription factors regulate gene expression via binding GC boxes within promoter regions. Unlike Sp1, which stimulates transcription, the closely related Sp3 can either repress or activate gene expression and is required for perinatal survival in mice. Here, we use RNA-seq and cellular phenotyping to show how Sp3 regulates murine fetal cell differentiation and proliferation. Homozygous Sp3-/- mice were smaller than wild-type and Sp+/- littermates, died soon after birth and had abnormal lung morphogenesis. RNA-seq of Sp3-/- fetal lung mesenchymal cells identified alterations in extracellular matrix production, developmental signaling pathways and myofibroblast/lipofibroblast differentiation. The lungs of Sp3-/- mice contained multiple structural defects, with abnormal endothelial cell morphology, lack of elastic fiber formation, and accumulation of lipid droplets within mesenchymal lipofibroblasts. Sp3-/- cells and mice also displayed cell cycle arrest, with accumulation in G0/G1 and reduced expression of numerous cell cycle regulators including Ccne1. These data detail the global impact of Sp3 on in vivo mouse gene expression and development.

Proline/serine-rich coiled-coil protein 1 inhibits macrophage inflammation and delays atherosclerotic progression by binding to Annexin A2

BACKGROUND

Atherosclerosis (AS), the main pathological basis of life-threatening cardiovascular disease, is essentially caused by chronic macrophage inflammation. Overexpression of proline/serine-rich coiled-coil protein 1 (PSRC1) reduces macrophage inflammatory responses and delays AS development. However, the exact mechanism of PSRC1 is unclear.

METHODS

Proteins interacting with PSRC1 were screened by proteomics in RAW264.7 cells, followed by RT-qPCR, immunoprecipitation and immunofluorescence to explore the specific mechanistic pathways affecting inflammation. CRISPR-Cas9 constructs for PSRC1^-/- ApoE^-/- (DKO) mice and high-fat diet-fed ApoE^-/- and DKO mice were used for AS models for in vivo experiments. Upstream transcription factors of PSRC1 were predicted by ATAC-seq, ChIP-seq and UCSC, and the regulatory mechanism was verified by ChIP-qPCR and dual luciferase assays. Peripheral blood serum and monocytes were collected from coronary artery disease (CAD) patients and non-CAD patients.

RESULTS

Increased binding of ANXA2 to PSRC1 in macrophages under oxidized low-density lipoprotein stimulation and decreased release of ANXA2 to the extracellular compartment were observed. Knockdown of ANXA2 in AS model mice delayed AS progression. Knockdown of ANXA2 in DKO mice reversed the AS-promoting effect of PSRC1 knockdown. Mechanistically, ANXA2 promotes STAT3 phosphorylation, which in turn promotes inflammatory responses. In addition, SP1 is a PSRC1 upstream repressive transcription factor, and the SP1 inhibitor mithramycin (Mith) elevated PSRC1 expression and exerted anti-AS effects in AS model mice. Patients with CAD had considerably greater serum levels of ANXA2 than those without CAD, and Mith reduced the secretion of ANXA2 in peripheral blood monocytes of CAD patients.

CONCLUSION

In macrophages, PSRC1 can interact with ANXA2 to inhibit its extracellular release and delay AS development. SP1 is an upstream transcription factor of PSRC1 and inhibits the transcription of PSRC1. The SP1 inhibitor Mith can elevate PSRC1 levels and slow AS progression while reducing ANXA2 release from monocytes in CAD patients. Mith is expected to be a new agent for AS treatment.

The addition of arginine deiminase potentiates Mithramycin A-induced cell death in patient-derived glioblastoma cells via ATF4 and cytochrome C

BACKGROUND

Arginine auxotrophy constitutes a shortcoming for ~ 30% of glioblastoma multiforme (GBM). Indeed, arginine-depleting therapy using arginine deiminase from Streptococcus pyogenes (SpyADI) has proven activity against GBM in preclinical studies. The good safety profile of SpyADI renders this agent an ideal combination partner for cytostatic therapy.

METHODS

In this study, we combined the antineoplastic antibiotic Mithramycin A (MitA) with SpyADI to boost single-agent activity and analyzed underlying response mechanisms in-depth.

RESULTS

MitA monotherapy induced a time- and dose-dependent cytotoxicity in eight patient-derived GBM cell lines and had a radiosensitizing effect in all but one cell line. Combination treatment boosted the effects of the monotherapy in 2D- and 3D models. The simultaneous approach was superior to the sequential application and significantly impaired colony formation after repetitive treatment. MitA monotherapy significantly inhibited GBM invasiveness. However, this effect was not enhanced in the combination. Functional analysis identified SpyADI-triggered senescence induction accompanied by increased mitochondrial membrane polarization upon mono- and combination therapy. In HROG63, induction of lysosomes was seen after both monotherapies, indicative of autophagy. These cells seemed swollen and had a more pronounced cortically formed cytoskeleton. Also, cytochrome C and endoplasmatic reticulum-stress-associated proteins ATF4 and Calnexin were enhanced in the combination, contributing to apoptosis. Notably, no significant increases in glioma-stemness marker were seen.

CONCLUSIONS

Therapeutic utilization of a metabolic defect in GBM along with cytostatic therapy provides a novel combination approach. Whether this SpyADI/MitA regimen will provide a safe alternative to combat GBM, will have to be addressed in subsequent (pre-)clinical trials.

KLF5 inhibition potentiates anti-PD1 efficacy by enhancing CD8+ T-cell-dependent antitumor immunity

Background: Immune checkpoint blockers (ICBs) are revolutionized therapeutic strategies for cancer, but most patients with solid neoplasms remain resistant to ICBs, partly because of the difficulty in reversing the highly immunosuppressive tumor microenvironment (TME). Exploring the strategies for tumor immunotherapy is highly dependent on the discovery of molecular mechanisms of tumor immune escape and potential therapeutic target. Krüppel-like Factor 5 (KLF5) is a cell-intrinsic oncogene to promote tumorigenesis. However, the cell-extrinsic effects of KLF5 on suppressing the immune response to cancer remain unclear. Methods: We analyzed the immunosuppressive role of KLF5 in mice models transplanted with KLF5-deleted/overexpressing tumor cells. We performed RNA sequencing, immunohistochemistry, western blotting, real time-PCR, ELISA, luciferase assay, chromatin immunoprecipitation (ChIP), and flow cytometry to demonstrate the effects of KLF5 on CD8⁺ T cell infiltration and related molecular mechanism. Single-cell RNA sequencing and spatial transcriptomics analysis were applied to further decipher the association between KLF5 expression and infiltrating immune cells. The efficacy of KLF5/COX2 inhibitors combined with anti-programmed cell death protein 1 (anti-PD1) therapy were explored in pre-clinical models. Finally, a gene-expression signature depending on KLF5/COX2 axis and associated immune markers was created to predict patient survival. Results: KLF5 inactivation decelerated basal-like breast tumor growth in a CD8⁺ T-cell-dependent manner. Transcriptomic profiling revealed that KLF5 loss in tumors increases the number and activated function of T lymphocytes. Mechanistically, KLF5 binds to the promoter of the COX2 gene and promotes COX2 transcription; subsequently, KLF5 deficiency decreases prostaglandin E2 (PGE2) release from tumor cells by reducing COX2 expression. Inhibition of the KLF5/COX2 axis increases the number and functionality of intratumoral antitumor T cells to synergize the antitumorigenic effects of anti-PD1 therapy. Analysis of patient datasets at single-cell and spatial resolution shows that low expression of KLF5 is associated with an immune-supportive TME. Finally, we generate a KLF5/COX2-associated immune score (KC-IS) to predict patient survival. Conclusions: Our results identified a novel mechanism responsible for KLF5-mediated immunosuppression in TME, and targeting the KLF5/COX2/PGE2 axis is a critical immunotherapy sensitizer.

Recent developments in the identification and biosynthesis of antitumor drugs derived from microorganisms

Secondary metabolites in microorganisms represent a resource for drug discovery and development. In particular, microbial-derived antitumor agents are in clinical use worldwide. Herein, we provide an overview of the development of classical antitumor drugs derived from microorganisms. Currently used drugs and drug candidates are comprehensively described in terms of pharmacological activities, mechanisms of action, microbial sources, and biosynthesis. We further discuss recent studies that have demonstrated the utility of gene-editing technologies and synthetic biology tools for the identification of new gene clusters, expansion of natural products, and elucidation of biosynthetic pathways. This review summarizes recent progress in the discovery and development of microbial-derived anticancer compounds with emphasis on biosynthesis.

DNA damage and reticular stress in cytotoxicity and oncotic cell death of MCF-7 cells treated with fluopsin C

Fluopsin C is an antibiotic compound derived from secondary metabolism of different microorganisms, which possesses antitumor, antibacterial, and antifungal activity. Related to fluopsin C antiproliferative activity, the aim of this study was to examine the following parameters: cytotoxicity, genotoxicity, cell cycle arrest, cell death induction (apoptosis), mitochondrial membrane potential (MMP), colony formation, and mRNA expression of genes involved in adaptive stress responses and cellular death utilizing a monolayer. In addition, a three-dimensional cell culture was used to evaluate the effects on growth of tumor spheroids. Fluopsin C was cytotoxic (1) producing cell division arrest in the G₁ phase, (2) elevating expression of mRNA of the CDKN1A gene and (3) decrease in expression of mRNA H2AFX gene. Further, fluopsin C enhanced DNA damage as evidenced by increased expression of mRNA of GADD45A and GPX1 genes, indicating that reactive oxygen species (ROS) may be involved in the observed genotoxic response. Reticulum stress was also detected as noted from activation of the ribonuclease inositol-requiring protein 1 (IRE1) pathway, since a rise in mRNA expression of the ERN1 and TRAF2 genes was observed. During the cell death process, an increase in mRNA expression of the BBC3 gene was noted, indicating participation of this antibiotic in oncotic (ischemic) cell death. Data thus demonstrated for the first time that fluopsin C interferes with the volume of tumor spheroids, in order to attenuate their growth. Our findings show that fluopsin C modulates essential molecular processes in response to stress and cell death.

Inhibitory effect of the novel tyrosine kinase inhibitor DCC-2036 on triple-negative breast cancer stem cells through AXL-KLF5 positive feedback loop

Triple-negative breast cancer (TNBC), an aggressive histological subtype of breast cancer, exhibits a high risk of early recurrence rate and a poor prognosis, and it is primarily associated with the abundance of cancer stem cells (CSCs). At present, the strategies for effectively eradicating or inhibiting TNBC CSCs are still limited, which makes the development of novel drugs with anti-CSCs function be of great value for the treatment of TNBC, especially the refractory TNBC. In this study, we found that the small-molecule tyrosine kinase inhibitor DCC-2036 suppressed TNBC stem cells by inhibiting the tyrosine kinase AXL and the transcription factor KLF5. DCC-2036 downregulated the expression of KLF5 by decreasing the protein stability of KLF5 via the AXL-Akt-GSK3β signal axis, and in turn, the downregulation of KLF5 further reduced the expression of AXL via binding to its promotor (-171 to -162 bp). In addition, p-AXL/AXL levels were positively correlated with KLF5 expression in human TNBC specimens. These findings indicated that DCC-2036 is able to suppress the CSCs in TNBC by targeting the AXL-KLF5 positive feedback loop. Moreover, our findings indicated that DCC-2036 increased the sensitivity of TNBC chemotherapy. Therefore, this study proposes a potential drug candidate and several targets for the treatment of refractory TNBC.

Inflammatory-Dependent Bidirectional Effect of Bile Acids on NLRP3 Inflammasome and Its Role in Ameliorating CPT-11-Induced Colitis

Irinotecan (CPT-11) in combination with 5-fluorouracil and leucovorin is a first-line chemotherapy regimen for the treatment of colorectal cancer; however, its clinical application is limited by the dose-limiting gastrointestinal toxicity of colitis. In our previous studies, several bile acids (BAs) were found significantly elevated in the colon of the CPT-11-induced rat colitis model. On the other hand, NLRP3 inflammasome has been reported to play important roles in mediating colitis. Interestingly, BA was stated to activate the NLRP3 inflammasome in some studies, while in some other reports, it showed an inhibitory effect. We assumed that the inflammatory status in different circumstances might have contributed to the controversial findings. In this study, we first discovered, under non-inflammatory conditions, that supplementing BA could activate the NLRP3 inflammasome in THP-1-differentiated macrophages and promote inflammation. In lipopolysaccharide (LPS)-induced inflammatory macrophages, however, BA inhibited the NLRP3 inflammasome and reduced inflammation. Further experiments demonstrated that Takeda G protein-coupled receptor 5 (TGR5) is essential in mediating the inhibitory effect of BA, while phospho-SP1 (p-SP1) is key to the activation. Furthermore, we applied the above findings to ameliorate CPT-11-caused colitis in rats by inhibiting SP1 with mithramycin A (MitA) or activating TGR5 using oleanolic acid (OA). Our findings may shed light on the discovery of effective interventions for reducing dose-limiting chemotherapy-induced colitis.

The curcumin analog EF24 inhibits proliferation and invasion of triple-negative breast cancer cells by targeting the lncRNA HCG11/Sp1 axis

EF24, a curcumin analog, exerts a potent anti-tumor effect on various cancers. However, whether EF24 retards the progression of triple-negative breast cancer (TNBC) remains unclear. In this study, we explored the role of EF24 in TNBC and clarified the underlying mechanism. In a mouse model of TNBC xenograft, EF24 administration reduced the tumor volume, suppressed cell proliferation, promoted cell apoptosis, and downregulated long non-coding RNA human leukocyte antigen complex group 11 (HCG11) expression. In TNBC cell lines, EF24 administration reduced cell viability, suppressed cell invasion, and downregulated HCG11 expression. HCG11 overexpression re-enhanced the proliferation and invasion of TNBC cell lines suppressed by EF24. The following mechanism research revealed that HCG11 overexpression elevated Sp1 transcription factor (Sp1) expression by reducing its ubiquitination, thereby enhanced Sp1-mediated cell survival and invasion in the TNBC cell line. Finally, the in vivo study showed that HCG11-overexpressed TNBC xenografts exhibited lower responsiveness in response to EF24 treatment. In conclusion, EF24 treatment reduced HCG11 expression, resulting in the degradation of Sp1 expression, thereby inhibiting the proliferation and invasion of TNBC cells.

Fasting-mimicking diet blocks triple-negative breast cancer and cancer stem cell escape

Metastatic tumors remain lethal due to primary/acquired resistance to therapy or cancer stem cell (CSC)-mediated repopulation. We show that a fasting-mimicking diet (FMD) activates starvation escape pathways in triple-negative breast cancer (TNBC) cells, which can be identified and targeted by drugs. In CSCs, FMD lowers glucose-dependent protein kinase A signaling and stemness markers to reduce cell number and increase mouse survival. Accordingly, metastatic TNBC patients with lower glycemia survive longer than those with higher baseline glycemia. By contrast, in differentiated cancer cells, FMD activates PI3K-AKT, mTOR, and CDK4/6 as survival/growth pathways, which can be targeted by drugs to promote tumor regression. FMD cycles also prevent hyperglycemia and other toxicities caused by these drugs. These data indicate that FMD has wide and differential effects on normal, cancer, and CSCs, allowing the rapid identification and targeting of starvation escape pathways and providing a method potentially applicable to many malignancies.

The roles and regulation of the KLF5 transcription factor in cancers

Krüppel‐like factor 5 (KLF5) is a member of the KLF family. Recent studies have suggested that KLF5 regulates the expression of a large number of new target genes and participates in diverse cellular functions, such as stemness, proliferation, apoptosis, autophagy, and migration. In response to multiple signaling pathways, various transcriptional modulation and posttranslational modifications affect the expression level and activity of KLF5. Several transgenic mouse models have revealed the physiological and pathological functions of KLF5 in different cancers. Studies of KLF5 will provide prognostic biomarkers, therapeutic targets, and potential drugs for cancers.

Isochromanoindolenines suppress triple-negative breast cancer cell proliferation partially via inhibiting Akt activation

As the most malignant subtype of breast cancers, triple-negative breast cancer (TNBC) lacks effective targeted therapeutics clinically to date. In this study, one lead compound FZU-0025-065 with isochromanoindolenine scaffold was identified by a cell-based screening. Among nine breast cancer cell lines tested, TNBC are the most sensitive cell lines to FZU-0025-065. FZU-0025-065 inhibits TNBC cell growth in a time- and dosage-dependent manner. FZU-0025-065 suppresses the expression of cell cycle dependent kinase 4 (CDK4), Cyclin D1 and Cyclin B1; meanwhile, elevates the expression of cell cycle dependent kinase inhibitor p21 and p27. Importantly, we found that FZU-0025-065 suppresses AKT activation in a time- and dosage-dependent manner. Over-expression of constitutive active AKT partially rescues FZU-0025-065 induced cell growth inhibition in MDA-MB-468 cells, indicating FZU-0025-065 suppresses TNBC cell growth partially via inhibiting AKT activation. Finally, FZU-0025-065 suppresses TNBC cell growth in a xenograft mouse model. Taken together, our findings suggested that isochromanoindolenine derivative FZU-0025-065 inhibits TNBC via suppressing the AKT signaling and that FZU-0025-065 may be useful for TNBC treatment.

New anti-mesothelin single-domain antibodies and cell models for developing targeted breast cancer therapy

Most triple negative breast cancers (TNBC) are characterized by elevated expression of mesothelin (MSLN), a cell surface antigen and one of the preferred targets for the therapy of solid tumors. Most continuous TNBC cell lines are MSLN-negative, which obstructs the development of MSLN-targeted therapy for TNBC. The aim of this study was to identify TNBC cell lines with MSLN hyperexpression and to obtain single-domain antibodies (nanobodies) capable of recognizing MSLN in TNBC cells. Mesothelin expression levels were measured in the panel of TNBC cell lines by real-time reverse-transcription PCR. PCR results were verified by measuring concentrations of the megakaryocyte potentiating factor (the secreted fragment of the mesothelin precursor) using sandwich ELISA. Immune phage-display VHH fragment libraries were prepared from mononuclear cells of Vicugna pacos using a modified library enrichment protocol. Two nanobody variants with high specificity for the target and Kd of about 140 and 95 nmol, respectively were obtained. Two MSLN+ and three MSLN– cell lines were identified in the TNBC cell lines panel. The nanobodies demonstrated the ability to recognize the target antigen in MSLN+ cells and had the low ability to bind to MSLN– cells. Thus, we found a convenient MSLN+ TNBC cell model for MSLN-targeted therapy testing. The new single-domain antibodies can be used as targeting components of chimeric antigen receptors.

Mithramycin A and Mithralog EC-8042 Inhibit SETDB1 Expression and Its Oncogenic Activity in Malignant Melanoma

Malignant melanoma is the most deadly skin cancer, associated with rising incidence and mortality rates. Most of the patients with melanoma, treated with current targeted therapies, develop a drug resistance, causing tumor relapse. The attainment of a better understanding of novel cancer-promoting molecular mechanisms driving melanoma progression is essential for the development of more effective targeted therapeutic approaches. Recent studies, including the research previously conducted in our laboratory, reported that the histone methyltransferase SETDB1 contributes to melanoma pathogenesis. In this follow-up study, we further elucidated the role of SETDB1 in melanoma, showing that SETDB1 modulated relevant transcriptomic effects in melanoma, in particular, as activator of cancer-related secreted (CRS) factors and as repressor of melanocyte-lineage differentiation (MLD) and metabolic enzymes. Next, we investigated the effects of SETDB1 inhibition via compounds belonging to the mithramycin family, mithramycin A and mithramycin analog (mithralog) EC-8042: melanoma cells showed strong sensitivity to these drugs, which effectively suppressed the expression of SETDB1 and induced changes at the transcriptomic, morphological, and functional level. Moreover, SETDB1 inhibitors enhanced the efficacy of mitogen-activated protein kinase (MAPK) inhibitor-based therapies against melanoma. Taken together, this work highlights the key regulatory role of SETDB1 in melanoma and supports the development of SETDB1-targeting therapeutic strategies for the treatment of melanoma patients.

Krüppel-like factors in breast cancer: Function, regulation and clinical relevance

Breast cancer has accounted for the leading cause of cancer-related mortality among women worldwide. Although the progress in its diagnosis and treatment has come at a remarkable pace during the past several decades, there are still a wide array of problems regarding its progression, metastasis and treatment resistance that have not yet been fully clarified. Recently, an increasing number of studies have revealed that some members of Krüppel-like factors(KLFs) are significantly associated with cell proliferation, apoptosis, metastasis, cancer stem cell regulation and prognostic and predictive value for patients in breast cancer, indicating their promising prognostic and predictive potential for breast cancer survival and outcome. In this review, we will summarize our current knowledge of the functions, regulations and clinical relevance of KLFs in breast cancer.

USP3 promotes breast cancer cell proliferation by deubiquitinating KLF5

The Krüppel-like factor 5 (KLF5) transcription factor is highly expressed in basal type breast cancer and promotes breast cancer cell proliferation, survival, migration, and tumorigenesis. KLF5 protein stability is regulated by ubiquitination. In this study, ubiquitin-specific protease 3 (USP3) was identified as a new KLF5 deubiquitinase by genome-wide siRNA library screening. We demonstrated that USP3 interacts with KLF5 and stabilizes KLF5 via deubiquitination. USP3 knockdown inhibits breast cancer cell proliferation in vitro and tumorigenesis in vivo, which can be partially rescued by ectopic expression of KLF5. Furthermore, we observed a positive correlation between USP3 and KLF5 protein expression levels in human breast cancer samples. These findings suggest that USP3 is a new KLF5 deubiquitinase and that USP3 may represent a potential therapeutic target for breast cancer.

Direct and Indirect Targeting of HOXA9 Transcription Factor in Acute Myeloid Leukemia

HOXA9 (Homeobox A9) is a homeotic transcription factor known for more than two decades to be associated with leukemia. The expression of HOXA9 homeoprotein is associated with anterior-posterior patterning during embryonic development, and its expression is then abolished in most adult cells, with the exception of hematopoietic progenitor cells. The oncogenic function of HOXA9 was first assessed in human acute myeloid leukemia (AML), particularly in the mixed-phenotype associated lineage leukemia (MPAL) subtype. HOXA9 expression in AML is associated with aggressiveness and a poor prognosis. Since then, HOXA9 has been involved in other hematopoietic malignancies and an increasing number of solid tumors. Despite this, HOXA9 was for a long time not targeted to treat cancer, mainly since, as a transcription factor, it belongs to a class of protein long considered to be an "undruggable" target; however, things have now evolved. The aim of the present review is to focus on the different aspects of HOXA9 targeting that could be achieved through multiple ways: (1) indirectly, through the inhibition of its expression, a strategy acting principally at the epigenetic level; or (2) directly, through the inhibition of its transcription factor function by acting at either the protein/protein interaction or the protein/DNA interaction interfaces.

Inhibition of super enhancer downregulates the expression of KLF5 in basal-like breast cancers

The transcription factor KLF5 (Krüpple-like factor 5) is highly expressed in basal-like breast cancer (BLBC), which promotes cell proliferation, survival, migration and stemness, serving as a potential therapeutic target. In the current study, a super-enhancer (SE) was identified to be located downstream of the KLF5 gene in BLBC cell lines, HCC1806 and HCC1937. JQ-1, a BRD4 inhibitor, inhibits the expression and activity of KLF5 in both HCC1806 and HCC1937 cells in a time- and dose-dependent manner. Compound 870, an in-house BRD4 inhibitor, exhibited higher potency than JQ-1 to inhibit KLF5 and BLBC growth by arresting cells in G1 phase. Additionally, THZ1, a CDK7 inhibitor, also inhibits KLF5 and BLBC growth in a similar manner. Our findings suggested that KLF5 is regulated by SE, and modulation of SE could be an effective therapeutic strategy for treating BLBC.

Activin A regulates the epidermal growth factor receptor promoter by activating the PI3K/SP1 pathway in oral squamous cell carcinoma cells

Epidermal growth factor receptor (EGFR) and activin A are both overexpressed in oral cavity squamous cell carcinoma (OSCC). We evaluated their clinical correlation and activin A-mediated EGFR regulation in this study. Overexpression of both transcripts/proteins indicated a poorer prognosis in OSCC patients. Knockdown of endogenous INHBA repressed the expression of EGFR and inhibited activin A-mediated canonical Smads, noncanonical phosphorylation of AKT (ser473) (p-AKT ser473) and SP1. Inhibition of PI3K signaling via its inhibitor attenuated p-AKT ser473 and in turn reduced SP1 and EGFR expression in the presence of recombinant activin A (rActivin A) in OSCC cells, as revealed via a luciferase assay and western blotting. However, canonical Smad signaling repressed the EGFR promoter, as revealed by a luciferase assay. The transcription factor SP1, its coactivator CBP/p300, and Smad proteins were recruited to the EGFR proximal promoter following rActivin A treatment, as revealed by chromatin immunoprecipitation (ChIP). Smad2/3/4 dramatically outcompeted SP1 binding to the EGFR proximal promoter following mithramycin A treatment. Activin A activates the PI3K and Smad pathways to compete for binding to overlapping SP1 consensus sequences on the EGFR proximal promoter. Nevertheless, canonical p-Smad2 was largely repressed in OSCC tumor tissues, suggesting that the activin A-mediated noncanonical pathway is essential for the carcinogenesis of OSCC.

Targeting Transcription Factors for Cancer Treatment

Transcription factors are involved in a large number of human diseases such as cancers for which they account for about 20% of all oncogenes identified so far. For long time, with the exception of ligand-inducible nuclear receptors, transcription factors were considered as “undruggable” targets. Advances knowledge of these transcription factors, in terms of structure, function (expression, degradation, interaction with co-factors and other proteins) and the dynamics of their mode of binding to DNA has changed this postulate and paved the way for new therapies targeted against transcription factors. Here, we discuss various ways to target transcription factors in cancer models: by modulating their expression or degradation, by blocking protein/protein interactions, by targeting the transcription factor itself to prevent its DNA binding either through a binding pocket or at the DNA-interacting site, some of these inhibitors being currently used or evaluated for cancer treatment. Such different targeting of transcription factors by small molecules is facilitated by modern chemistry developing a wide variety of original molecules designed to specifically abort transcription factor and by an increased knowledge of their pathological implication through the use of new technologies in order to make it possible to improve therapeutic control of transcription factor oncogenic functions.