Styliani Papadaki

Cancer cells upregulate ribosomal RNA (rRNA) synthesis to sustain the elevated ribosome production that fuels rapid proliferation, creating a dependency that renders RNA polymerase I (Pol I) transcription a pharmacological vulnerability. JP-1302 is a blood-brain barrier-penetrant 9-anilinoacridine derivative developed as an α _2C -adrenergic receptor antagonist, but also recently identified as an RNA Pol II inhibitor at micromolar concentrations (~5–10 μM). Here we show that JP-1302 also suppresses Pol I-driven 47S pre-rRNA synthesis at submicromolar-to-low-micromolar concentrations, evidenced by loss of nascent EU-labelled rRNA and reduced activity of an rDNA promoter-driven luciferase reporter. This was accompanied by preferential proteasome-dependent degradation of the Pol I catalytic subunit POLR1A, independent of α _2C -adrenergic receptor signalling, displacement of POLR1A from the rDNA promoter and progressive disruption of nucleolar morphology. Growth inhibitory IC ₅₀ values across a panel of normal and cancer cell lines, including glioblastoma, ranged from submicromolar to low micromolar. Nucleolar stress stabilised p53 and induced p21 expression at low-to-intermediate concentrations, without evidence of DNA damage at these doses (no γH2AX increase at concentrations sufficient to abrogate Pol I transcription). Interestingly, p53-null and p53-wild type cells showed comparable S-phase depletion in response to JP-1302. At higher concentrations, JP-1302 additionally caused covalent trapping of TOP2A/TOP2B, accompanied by delayed γH2AX induction, and enrichment of the FACT subunits SSRP1 and SPT16 on chromatin. Together, these findings identify JP-1302 as a pharmacologically distinct inhibitor of ribosome biogenesis with broader, dose-dependent chromatin-disruptive activity.

Cancer stem cells (CSCs), a subpopulation of tumor cells with self-renewal capacity, have been associated with tumor initiation, progression, and therapy resistance. While the bulk of tumor cells mainly use glycolysis for energy production, CSCs have gained attention for their ability to switch between glycolysis and oxidative phosphorylation, depending on their energy needs and stimuli from their microenvironment. This metabolic plasticity is mediated by signaling pathways that are also implicated in the regulation of CSC properties, such as the Wnt/β-catenin, Notch, and Hippo networks. Two other stemness-associated processes, autophagy and hypoxia, seem to play a role in the metabolic switching of CSCs as well. Importantly, accumulating evidence has linked the metabolic plasticity of CSCs to their increased resistance to treatment. In this review, we summarize the metabolic signatures of CSCs and the pathways that regulate them; we especially highlight research data that demonstrate the metabolic adaptability of these cells and their role in stemness and therapy resistance. As the development of drug resistance is a major challenge for successful cancer treatment, the potential of specific elimination of CSCs through targeting their metabolism is of great interest and it is particularly examined.

The emergence of drug resistance in cancer poses the greatest hurdle for successful therapeutic results and is associated with most cancer deaths. In triple negative breast cancer (TNBC), due to the lack of specific therapeutic targets, systemic chemotherapy is at the forefront of treatments, but it only benefits a fraction of patients because of the development of resistance. Cancer cells may possess an innate resistance to chemotherapeutic agents or develop new mechanisms of acquired resistance after long-term drug exposure. Such mechanisms involve an interplay between genetic, epigenetic and metabolic alterations that enable cancer cells to evade therapy. In this work, we generated and characterized a chemoresistant TNBC cell line to be used for the investigation of mechanisms that drive resistance to paclitaxel. Transcriptomic analysis highlighted the important role of metabolic-associated pathways in the resistant cells, prompting us to employ ¹H-NMR to explore the metabolome and lipidome of these cells. We identified and described herein numerous metabolites and lipids that were significantly altered in the resistant cells. Integrated analysis of our omics data revealed MSMO1, an intermediate enzyme of cholesterol biosynthesis, as a novel mediator of chemoresistance in TNBC. Overall, our data provide a critical insight into the metabolic adaptations that accompany acquired resistance in TNBC and pinpoint potential new targets.

Stevia rebaudiana Bertoni is a perennial shrub from Paraguay that is nowadays widely cultivated, since it is increasingly being utilized as a sugar substitute in various foodstuffs due to its sweetness and minimal caloric content. These properties of the plant’s derivatives have spurred research on their biological activities revealing a multitude of benefits to human health, including antidiabetic, anticariogenic, antioxidant, hypotensive, antihypertensive, antimicrobial, anti-inflammatory and antitumor actions. To our knowledge, no recent reviews have surveyed and reported published work solely on the latter. Consequently, our main objective was to present a concise, literature-based review of the biological actions of stevia derivatives in various tumor types, as studied in in vitro and in vivo models of the disease. With global cancer estimates suggesting a 47% increase in cancer cases by 2040 compared to 2020, the data reviewed in this article should provide a better insight into Stevia rebaudiana and its products as a means of cancer prevention and therapy within the context of a healthy diet.

Cancer stem cells (CSCs) have been implicated in the development of chemoresistance, tumor recurrence and metastasis in breast cancer, thus emerging as a promising target for novel therapies. To identify novel stemness regulators that could potentially be targeted in luminal ER⁺ tumors, we performed RNA-sequencing (RNA-seq) in MCF-7 adherent monolayer cells and tumorspheres enriched in breast CSCs (bCSCs). We identified 1421 differentially expressed genes (DEGs), with 923 of them being upregulated and 498 downregulated in tumorspheres. Gene ontology and pathway enrichment analyses revealed that distinct gene networks underlie the biology of the two cell systems. We selected the transient receptor potential cation channel subfamily M member 4 (TRPM4) gene that had not been associated with cancer stemness before for further investigation. We confirmed that TRPM4 was overexpressed in tumorspheres and showed that its knock-down affected the stemness properties of bCSCs in vitro. TRPM4 inhibition revealed potential anti-tumor effects by directly targeting the bCSC subpopulation. We suggest that TRPM4 plays a key role in stemness mediation, and its inhibition may represent a novel therapeutic modality against bCSCs contributing in the improvement of breast cancer treatments.

Platelets mediate circulating endothelial progenitor cell (EPC) recruitment and maturation, participating in vascular repair, however the underlying mechanism(s) remain unclear. We investigated the effect of platelet-rich plasma (PRP) on the functionality of CD34 ⁺ -derived late-outgrowth endothelial cells (OECs) in culture. Confluent OECs were coincubated with PRP under platelet aggregation (with adenosine diphosphate; ADP) and nonaggregation conditions, in the presence/absence of the reversible P2Y12 platelet receptor antagonist ticagrelor. Outgrowth endothelial cell activation was evaluated by determining prostacyclin (PGI ₂ ) and monocyte chemoattractant protein-1 (MCP-1) release and intercellular adhesion molecule-1 (ICAM-1) membrane expression. Similar experiments were performed using human umbilical vein endothelial cells (HUVECs). Platelet-rich plasma increased ICAM-1 expression and PGI ₂ and MCP-1 secretion compared with autologous platelet-poor plasma, whereas ADP-aggregated platelets in PRP did not exhibit any effect. Platelet-rich plasma pretreated with ticagrelor prior to activation with ADP increased all markers to a similar extent as PRP. Similar results were obtained using HUVECs. In conclusion, PRP induces OEC activation, a phenomenon not observed when platelets are aggregated with ADP. Platelet inhibition with ticagrelor restores the PRP capability to activate OECs. Since EPC activation is important for endothelial regeneration and angiogenesis, we suggest that agents inhibiting platelet aggregation, such as ticagrelor, may promote platelet-EPC interaction and EPC function.

Background: Type 2 diabetes mellitus is a risk factor for lower extremity arterial disease. Cilostazol expresses antiplatelet, anti‐inflammatory, and vasodilator actions and improves the claudication intermittent symptoms. We investigated the efficacy and safety of adjunctive cilostazol to clopidogrel‐treated patients with type 2 diabetes mellitus exhibiting symptomatic lower extremity arterial disease, in the prevention of ischemic vascular events and improvement of the claudication intermittent symptoms. Methods and Results: In a prospective 2‐arm, multicenter, open‐label, phase 4 trial, patients with type 2 diabetes mellitus with intermittent claudication receiving clopidogrel (75 mg/d) for at least 6 months, were randomly assigned in a 1:1 ratio, either to continue to clopidogrel monotherapy, without receiving placebo cilostazol (391 patients), or to additionally receive cilostazol, 100 mg twice/day (403 patients). The median duration of follow‐up was 27 months. The primary efficacy end point, the composite of acute ischemic stroke/transient ischemic attack, acute myocardial infarction, and death from vascular causes, was significantly reduced in patients receiving adjunctive cilostazol compared with the clopidogrel monotherapy group (sex‐adjusted hazard ratio [HR], 0.468; 95% CI, 0.252–0.870; P =0.016). Adjunctive cilostazol also significantly reduced the stroke/transient ischemic attack events (sex‐adjusted HR, 0.38; 95% CI, 0.15–0.98; P =0.046) and improved the ankle‐brachial index and pain‐free walking distance values ( P =0.001 for both comparisons). No significant difference in the bleeding events, as defined by Bleeding Academic Research Consortium criteria, was found between the 2 groups (sex‐adjusted HR, 1.080; 95% CI, 0.579–2.015; P =0.809). Conclusions: Adjunctive cilostazol to clopidogrel‐treated patients with type 2 diabetes mellitus with symptomatic lower extremity arterial disease may lower the risk of ischemic events and improve intermittent claudication symptoms, without increasing the bleeding risk, compared with clopidogrel monotherapy. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT02983214.

Factor Xa (FXa) and thrombin exert non-hemostatic cellular actions primarily mediated through protease-activated receptors (PARs). We investigated the effect of FXa and thrombin on human late-outgrowth endothelial cells (OECs), a type of endothelial progenitor cells (EPCs), and on human umbilical vein endothelial cells (HUVECs). The effect of direct oral anticoagulants (DOACs), rivaroxaban and dabigatran, was also studied. The membrane expression of intercellular adhesion molecule-1 (ICAM-1) and the secretion of monocyte chemoattractant protein-1 (MCP-1) were used as cell activation markers. FXa and thrombin increase the ICAM-1 expression and the MCP-1 secretion on both cells, being higher on OECs. Vorapaxar, a specific PAR-1 antagonist, completely inhibits FXa-induced activation of both cells and thrombin-induced HUVEC activation, but only partially thrombin-induced OEC activation. Furthermore, thrombin-receptor activating peptide; TRAP-6, only partially activates OECs. OECs do not membrane-express PAR-4, therefore it may not be involved on thrombin-induced OEC activation. Rivaroxaban and dabigatran inhibit OEC and HUVEC activation by FXa and thrombin, respectively. Rivaroxaban enhances thrombin-induced OEC and HUVEC activation, which is completely inhibited by vorapaxar. The inhibition of OEC and HUVEC activation by vorapaxar and DOACs may represent a new pleiotropic effect of these drugs. The pathophysiological and clinical significance of our findings need to be established.

Factor Xa (FXa) is the key serine protease of the coagulation cascade as it is the point of convergence of the intrinsic and extrinsic pathways, leading to the formation of thrombin. Factor Xa is an established target of anticoagulation therapy, due to its central role in coagulation. Over the past years, several direct oral anticoagulants (DOACs) targeting FXa have been developed. Rivaroxaban, apixaban, and edoxaban are used in clinical practice for prevention and treatment of thrombotic diseases. Increasing evidence suggests that FXa exerts nonhemostatic cellular effects that are mediated mainly through protease-activated receptors-1 and -2 and are involved in pathophysiological conditions, such as atherosclerosis, inflammation, and fibrosis. Direct inhibition of FXa by DOACs could be beneficial in these conditions. This is a narrative review that focuses on the cellular effects of FXa in various cell types and conditions, as well as on the possible pleiotropic effects of FXa-targeting DOACs.