The discovery of nongenotoxic activators of p53: Building on a cell-based high-throughput screen

Recent advances on the intervention sites targeting USP7-MDM2-p53 in cancer therapy

The ubiquitin-specific protease 7 (USP7)-murine double minute 2 (MDM2)-p53 network plays an important role in the regulation of p53, a tumor suppressor which plays critical roles in regulating cell growth, proliferation, cell cycle progression, apoptosis and immune response. The overexpression of USP7 and MDM2 in human cancers contributes to cancer initiation and progression, and their inhibition reactivates p53 signalings and causes cell cycle arrest and apoptosis. Herein, the current state of pharmacological characterization, potential applications in cancer treatment and mechanism of action of small molecules used to target and inhibit MDM2 and USP7 proteins are highlighted, along with the outcomes in clinical and preclinical settings. Moreover, challenges and advantages of these strategies, as well as perspectives in USP7-MDM2-p53 field are analyzed in detail. The investigation and application of MDM2 and USP7 inhibitors will deepen our understanding of the function of USP7-MDM2-p53 network, and feed in the development of effective and safe cancer therapies where USP7-MDM2-p53 network is implicated.

Towards an advanced testing strategy for genotoxicity using image-based 2D and 3D HepG2 DNA damage response fluorescent protein reporters

In vitro assessment of mutagenicity is an essential component in the chemical risk assessment. Given the diverse modes of action by which chemicals can induce DNA damage, it is essential that these in vitro assays are carefully evaluated for their possibilities and limitations. In this study, we used a fluorescent protein HepG2 reporter test system in combination with high content imaging. To measure induction of the DNA damage response (DDR), we used three different green fluorescent protein reporters for p53 pathway activation. These allowed for accurate quantification of p53, p21 and BTG2 (BTG anti-proliferation factor 2) protein expression and cell viability parameters at a single cell or spheroid resolution. The reporter lines were cultured as 2D monolayers and as 3D spheroids. Furthermore, liver maturity and cytochrome P450 enzyme expression were increased by culturing in an amino acid-rich (AAGLY) medium. We found that culture conditions that support a sustained proliferative state (2D culturing with normal DMEM medium) give superior sensitivity when genotoxic compounds are tested that do not require metabolisation and of which the mutagenic mode of action is dependent on replication. For compounds, which are metabolically converted to mutagenic metabolites, more differentiated HepG2 DDR reporters (e.g. 3D cultures) showed a higher sensitivity. This study stratifies how different culture methods of HepG2 DDR reporter cells can influence the sensitivity towards diverse genotoxicants and how this provides opportunities for a tiered genotoxicity testing strategy.

Novel Allosteric Activators for Ferroptosis Regulator Glutathione Peroxidase 4

Glutathione peroxidase 4 (GPX4) is essential for cell membrane repair, inflammation suppression, and ferroptosis inhibition. GPX4 upregulation provides unique drug discovery opportunities for inflammation and ferroptosis-related diseases. However, rational design of protein activators is challenging. Until now, no compound has been reported to activate the enzyme activity of GPX4. Here, we identified a potential allosteric site in GPX4 and successfully found eight GPX4 activators using a novel computational strategy and experimental studies. Compound 1 from the virtual screen increased GPX4 activity, suppressed ferroptosis, reduced pro-inflammatory lipid mediator production, and inhibited NF-κB pathway activation. Further chemical synthesis and structure-activity relationship studies revealed seven more activators. The strongest compound, 1d4, increased GPX4 activity to 150% at 20 μM in the cell-free assay and 61 μM in cell extracts. Therefore, we demonstrated that GPX4 can be directly activated using chemical compounds to suppress ferroptosis and inflammation. Meanwhile, the discovery of GPX4 activators verified the possibility of rational design of allosteric activators.

Synthesis and anticancer activity of acyl thioureas bearing pyrazole moiety

In this work novel organic based compounds, acyl thiourea derivatives were synthesized and their anticancer activities were investigated. A new series of acyl thiourea derivatives containing pyrazole ring were prepared in good yield through one pot reaction of 4-benzoyl-1, 5-diphenyl-1H-pyrazole-3-carbonyl chloride with ammonium thiocyanate and various amines. The structures of the newly synthesized compounds were confirmed by IR, (1)H NMR, (13)C NMR and elemental analysis. Anticancer activities of synthesized compounds were evaluated on human colon, liver and leukemia cancer cell lines. Cell culture studies have demonstrated significant toxicity of the compounds on the cell lines, and the levels of toxicity have altered in the presence of various side groups. These results confirm that novel pyrazolyl acyl thioureas derived compounds may be utilized for cancer treatment. Furthermore, these compounds have a great potential and significance for further investigations.

Tenovin-D3, a novel small-molecule inhibitor of sirtuin SirT2, increases p21 (CDKN1A) expression in a p53-independent manner

While small-molecule inhibitors of class I/II histone deacetylases (HDAC) have been approved for cancer treatment, inhibitors of the sirtuins (a family of class III HDACs) still require further validation and optimization to enter clinical trials. Recent studies show that tenovin-6, a small-molecule inhibitor of sirtuins SirT1 and SirT2, reduces tumor growth in vivo and eliminates leukemic stem cells in a murine model for chronic myelogenous leukemia. Here, we describe a tenovin analogue, tenovin-D3, that preferentially inhibits sirtuin SirT2 and induces predicted phenotypes for SirT2 inhibition. Unlike tenovin-6 and in agreement with its weak effect on SirT1 (a p53 deacetylase), tenovin-D3 fails to increase p53 levels or transcription factor activity. However, tenovin-D3 promotes expression of the cell-cycle regulator and p53 target p21(WAF1/CIP1) (CDKN1A) in a p53-independent manner. Structure-activity relationship studies strongly support that the ability of tenovin-D3 to inhibit SirT2 contributes to this p53-independent induction of p21. The ability of tenovin-D3 to increase p21 mRNA and protein levels is shared with class I/II HDAC inhibitors currently used in the clinic and therefore suggests that SirT2 inhibition and class I/II HDAC inhibitors have similar effects on cell-cycle progression.

Dysregulation of autophagy in chronic lymphocytic leukemia with the small-molecule Sirtuin inhibitor Tenovin-6

Tenovin-6 (Tnv-6) is a bioactive small molecule with anti-neoplastic activity. Inhibition of the Sirtuin class of protein deacetylases with activation of p53 function is associated with the pro-apoptotic effects of Tnv-6 in many tumors. Here, we demonstrate that in chronic lymphocytic leukemia (CLL) cells, Tnv-6 causes non-genotoxic cytotoxicity, without adversely affecting human clonogenic hematopoietic progenitors in vitro, or murine hematopoiesis. Mechanistically, exposure of CLL cells to Tnv-6 did not induce cellular apoptosis or p53-pathway activity. Transcriptomic profiling identified a gene program influenced by Tnv-6 that included autophagy-lysosomal pathway genes. The dysregulation of autophagy was confirmed by changes in cellular ultrastructure and increases in the autophagy-regulatory proteins LC3 (LC3-II) and p62/Sequestosome. Adding bafilomycin-A1, an autophagy inhibitor to Tnv-6 containing cultures did not cause synergistic accumulation of LC3-II, suggesting inhibition of late-stage autophagy by Tnv-6. Thus, in CLL, the cytotoxic effects of Tnv-6 result from dysregulation of protective autophagy pathways.

Synthesis and biological characterisation of sirtuin inhibitors based on the tenovins

The tenovins are small molecule inhibitors of the NAD(+)-dependent family of protein deacetylases known as the sirtuins. There remains considerable interest in inhibitors of this enzyme family due to possible applications in both cancer and neurodegenerative disease therapy. Through the synthesis of novel tenovin analogues, further insights into the structural requirements for activity against the sirtuins in vitro are provided. In addition, the activity of one of the analogues in cells led to an improved understanding of the function of SirT1 in cells.