The radical reactions of dimethylsulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) with reactive oxygen species (ROS) in the presence of a nitroxide radical scavenger have been evaluated both synthetically and in analytical practice.

Human single-stranded DNA binding protein 1 (hSSB1) is critical to preserving genome stability, interacting with single-stranded DNA (ssDNA) through an oligonucleotide/oligosaccharide binding-fold. The depletion of hSSB1 in cell-line models leads to aberrant DNA repair and increased sensitivity to irradiation. hSSB1 is over-expressed in several types of cancers, suggesting that hSSB1 could be a novel therapeutic target in malignant disease. hSSB1 binding studies have focused on DNA; however, despite the availability of 3D structures, small molecules targeting hSSB1 have not been explored. Quinoline derivatives targeting hSSB1 were designed through a virtual fragment-based screening process, synthesizing them using AlphaLISA and EMSA to determine their affinity for hSSB1. In parallel, we further screened a structurally diverse compound library against hSSB1 using the same biochemical assays. Three compounds with nanomolar affinity for hSSB1 were identified, exhibiting cytotoxicity in an osteosarcoma cell line. To our knowledge, this is the first study to identify small molecules that modulate hSSB1 activity. Molecular dynamics simulations indicated that three of the compounds that were tested bound to the ssDNA-binding site of hSSB1, providing a framework for the further elucidation of inhibition mechanisms. These data suggest that small molecules can disrupt the interaction between hSSB1 and ssDNA, and may also affect the ability of cells to repair DNA damage. This test study of small molecules holds the potential to provide insights into fundamental biochemical questions regarding the OB-fold.

Chemoresistance and limited broad-spectrum efficacy remain major challenges in cancer therapy. The development of agents capable of overcoming resistance and exhibiting activity across diverse tumour types is therefore critical to improving treatment outcomes. Here, we demonstrate the antiproliferative activity of a steroidal-nitroxide hybrid across multiple cell lines. CS187, a first-generation hybrid identified from previous work in cervical cancer, exhibited concentration-dependent antiproliferative activity with associated morphological changes in prostate (C4-2B), breast (MCF-7), and lung cancer (H460 and A549) cells at concentrations of 11-50 µM. In-combination with cisplatin, CS187 potentiated antiproliferative effects, achieving comparable growth inhibition at reduced cisplatin doses. Assessment of reactive oxygen species (ROS) levels revealed that CS187, both alone and in-combination with cisplatin, induced sustained intracellular oxidative stress, whereas cisplatin monotherapy exhibited attenuation over the time course. Together, these findings suggest that CS187 acts predominantly through a cytostatic mechanism and may interfere with redox-mediated adaptive responses that typically limit cisplatin efficacy. This work identifies CS187 as a promising redox-modulating scaffold capable of enhancing chemotherapeutic efficacy while potentially enabling dose reduction across multiple cancer types.

Inflammation and redox imbalance are hallmarks of many diseases. Here, we report the synthesis and systematic evaluation of steroid-nitroxide hybrid compounds as dual-acting anti-inflammatory and redox-modulating agents. Hybrids were generated via ester (1a-c, 2a-b), amide (1d-h), and ether (3a-c) linkages at the C21 position of corticosteroids prednisolone, cortisol, and dexamethasone. The hybrids exhibit glucocorticoid receptor (GR) activity and suppress IL-6 secretion in vitro at variable potencies, some comparable to commercial corticosteroids. Cellular metabolic evaluation demonstrates various rates of intracellular cleavage for ester- and amide-linked hybrids, while ether-linked hybrids remain intact. Assessment of general reactive oxygen species (ROS) levels via the fluorogenic probe 2',7'-dichlorofluorescein diacetate (DCFDA) demonstrated linker-dependent pro-oxidative effects, with poorly labile and non-cleavable compounds (1a, 3a-c) causing sustained ROS elevation, while cleavable hybrids produced only transient, recoverable increases. Notably, one hybrid (1a) demonstrated higher ROS elevation in A549 cells over normal human fibroblasts (i.e. NFF cells) suggesting certain structural features of this hybrid induce specificity. Live-cell imaging using fluorescent analogues supports the mechanism of intracellular cleavage and efflux for cleavable hybrids, while non-cleavable hybrids remain within the cell. These findings demonstrate that steroidal-nitroxide hybrids harness both anti-inflammatory and redox modulation pathways, positioning them as a novel treatment strategy where dual anti-inflammatory and pro-oxidant strategies are advantageous.

The accurate detection of airborne pollutants remains critical for safeguarding both environmental integrity and public health. Equally important is the consideration of method stability and susceptibility to degradation by common reactive atmospheric species, such as ozone. This study examines the reactivity of ozone towards the profluorescent nitroxide (PFN) BPEAnit, a molecular probe that is used in an acellular assay for detecting reactive oxygen species (ROS) from particulate pollution. Online fluorescence measurements revealed a dose-dependent increase in fluorescence when a BPEAnit/DMSO solution was exposed to low-level ozone concentrations (0–544 ppb). Exposure to excess ozone (ca. 9.5 ppm) produced sufficient fluorescent products for LC-MS analysis, which, when combined with isotope labelling, enabled structural characterization of several products, accounting for 43.5% of the total fluorescent signal. Under similar conditions the parent fluorophore (BPEA) showed no reactivity toward ozone, confirming the specificity of BPEAnit. The primary mechanism is proposed as a single-electron transfer between BPEAnit and ozone, forming an oxoammonium cation and ozone radical anion, which react with DMSO to yield carbon- and sulfur-based adducts. Increased moisture significantly altered the product distribution, highlighting the need to consider ambient humidity in these atmospheric assays. Preliminary evaluation of alternative solvent systems, ethanol and cyclohexane, revealed simpler reaction profiles with fewer products; however factors such as solvent volatility, ozone dose-response, and product stability require further investigation. These findings support the reliability of the BPEAnit probe towards ozone, as well as demonstrating a sensitive, ozone-responsive fluorescence profile, offering potential for broader application in atmospheric monitoring.