Chemistry – A European Journal

Biosynthetic gene clusters (BGC) involved in aryl polyene (APE) biosynthesis are supposed to represent the most widespread BGC in the bacterial world.[1-3] Still, only hydrolysis products[4-8] and not the full-length product(s) have been identified, hindering studies on their biosynthesis and natural function. Here, we apply subsequent chromatographic separations to purify the aryl polyene-containing lipids (APELs) from the entomopathogenic bacterium Xenorhabdus doucetiae. Structure elucidation using a combination of isotope labeling, nuclear magnetic resonance techniques, and tandem mass spectrometry reveals an array of APELs featuring an all-trans C26:5 conjugated fatty acyl and a galactosamine-phosphate-glycerol moiety. In combination with extensive genetic studies, this research broadens the bacterial natural product repertoire and paves the way for future functional characterization of this almost universal microbial compound class. Due to their protective function against reactive oxygen species,[5,9] APELs might be important for virulence or symbiosis, mediating organismic interactions in several ecological niches.

Heme peroxygenases are attractive biocatalysts for incorporating oxygen into the organic molecules using H2O2 as oxygen source under mild conditions. However, their practical applications are hindered by irreversible oxidative inactivation caused by exogenous H2O2 usage. Herein, we report a novel catalytic pathway in heme peroxygenases that relies on O2 and small-molecule reductants such as ascorbate acid (AscA), dehydroascorbic acid (DHA), gallic acid (GA), or pyrogallol (PA) to drive reactions. For reactions of unspecific peroxygenase (UPO) with either AscA or DHA, experimental and computational studies revealed that DHAA (the hydrated form of DHA) is the actual co-substrate responsible for activating oxygen to generate oxyferryl heme (compound I, Cpd I) as the oxygenation species. Subsequently, we demonstrate the universality of this O2/reductant-dependent route across various heme peroxygenases, highlighting its biological significance as monooxygenases. Compared to the conventional H2O2-dependent process, this innovative route can efficiently eliminate the excessive production of H2O2, thereby preventing the heme destruction and related enzyme inactivation. Finally, scale-up reactions were performed for the preparations of chiral, value-added products with unprecedented productivity, underscoring the great synthetic capabilities of the developed peroxygenase technology, which paves the way for sustainable and practical applications in various chemical transformations.

Photodynamic Therapy (PDT), which involves the combined action of a drug and its activation by suitable light, is a particularly attractive novel cancer therapy method due to less systemic side-effects. However, the delivery and accumulation of the PDT drug into cancer cells is still problematic. Here, by using -scale molecular dynamic simulations combined with quantum mechanics/molecular mechanics approaches, we examine the behavior of a PDT drug functionalized with a folic acid unit targeting the folate receptor (FR-), which is overexpressed in ovarian cancer cells. We show that the PDT drug forms a stable complex with the folate receptor, albeit slightly disrupting the main interaction patterns as compared to the parent folate ligand. Furthermore, we also show that the optical properties of the PDT drug are not altered by its interaction with the protein. Our results confirm that coupling with folate is an attractive strategy for selective active delivery of PDT agents.

Fluorogenic dyes that light up in complexes with genetically encodable RNA aptamers are increasingly used for intracellular RNA imaging. The growing toolbox of dyes and aptamers allows simultaneous or sequential monitoring of different RNAs. However, few orthogonal aptamer-dye pairs meet all the requirements of multiplex imaging in terms of brightness, contrast, etc., thus necessitating their optimization and further diversification. Here, we report new fluorogenic ligands for the Mango II aptamer, one of the most stable and widely used RNA tags. They are based on the cognate Mango ligand TO1-B, which is a thiazole orange (TO) derivative with a biotinylated tetraethylene glycol (TEG) residue attached via an amide linker, and its analogue with an isosteric triazolyl linker (TO1-triazolyl-TEG-biotin). Structural data suggested that the biotin residue might be dispensable for interactions with Mango, so we replaced it with a second TO residue or the alternative push-pull system, namely the dimethylaminophenyl (DMAP) group linked to the benzothiazolyl (BzT) group via the ethenyl linker. The resulting "double-headed" symmetric and asymmetric dyes showed reduced fluorescence in the free state due to intramolecular TO/TO or TO/DMAP-BzT interactions. The asymmetric dye exhibited intramolecular FRET in complex with Mango, resulting in a remarkably large (130 nm) Stocks shift, which may be advantageous for multiplex imaging. The main limitation of the "double-headed" dyes was their low brightness. To improve brightness, we further optimized the truncated (biotin-free) TO1-triazolyl-TEG dye by introducing a hydroxy or a methoxy group into the methylqunolinium (MQ) fragment of its push-pull system. The brightness of the methoxy-MQ derivative was increased by 40% compared to the reported TO1-triazolyl-TEG-biotin. Importantly, the methoxy-MQ derivative also showed increased selectivity for Mango over other noncanonical nucleic acids structures, making it a promising alternative to known TO-based dyes for high-contrast RNA imaging.

Despite the vital role of nicotinamide adenine dinucleotide (NAD) as a cofactor in all living organisms, the diversity of its functions is poorly understood. Particularly in interaction with ultraviolet (UV) light, a variety of photorelaxation channels can be accessed, which current models lack to explain. In this work, for the first time, we used picosecond UV pump, mid-infrared (mIR) probe spectroscopy and accurate quantum-chemical calculations to elucidate the ultrafast photodynamics of NAD+ and NADH to unify contradictory mechanisms from the past decades in the big picture. We found direct evidence for a long-lived ([~]900 ps) charge-separated state in NADH, which has been unobserved previously and results in the parallel population of a fluorescent state. The photochemical pathways demonstrated here open up functions of NAD in chemistry and molecular biology, such as an electron donor, as a FRET agent or as a redox pair switch, which have not been considered previously. TOC GRAPHICS O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=194 SRC="FIGDIR/small/563164v1_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@740620org.highwire.dtl.DTLVardef@13e2c71org.highwire.dtl.DTLVardef@d7cb0corg.highwire.dtl.DTLVardef@153ab51_HPS_FORMAT_FIGEXP M_FIG C_FIG

This study focuses on the synthesis of Biguanide-PROTACs, formed by conjugating the biguanide motif with diverse E3 enzyme ligands and spacers. Evaluation of their activity on pancreatic cancer cell (KP4) proliferation established a correlation between membrane permeability and median effective concentration. Mechanistic insights revealed that only two compounds exhibited biguanide-like AMPK activation, while only one hydrophobic compound uniquely altered mitochondrial protein levels. The prospect of developing and expanding the Biguanide-PROTAC library holds promises, offering potential insights into biguanide mechanisms and the creation of more potent anticancer agents. This study contributes to understanding the intricate interplay between compound structure, permeability, and anticancer activity, paving the way for targeted drug development in pancreatic cancer treatment.

Multiple-drug resistant (MDR) Staphylococcus aureus strains (like methicillin-resistant S. aureus or MRSA) uses an arsenal of antioxidant enzymes to mitigate host-induced oxidative stress. Among them the non-canonical Staphylococcal glutathione peroxidase (SaGpx) plays a crucial role in bacterial redox homeostasis by reducing peroxides via thioredoxin-dependent pathways. Thus, enabling oxidative stress mitigation during host infection. Despite its importance in S. aureus, its role in bacterial pathogenesis remains unexplored. This study aimed to elucidate the possible role of SaGpx in Staphylococcal virulence. First, we determined the high-resolution crystal structure of SaGpx (at 1.65 [A] resolution) using X-ray crystallography. Guided by the catalytic cleft architecture of SaGpx, small-molecule based inhibitors were then rationally designed and synthesized. These inhibitors exhibited good binding affinity to SaGpx and complete enzymatic blockade. These inhibitors exhibited potent anti-S. aureus activity (MICs 6.25-31.25 M) along with no cytotoxicity in L929 fibroblast wound-healing assays. Furthermore, the in vivo antibacterial ability of these inhibitors was evaluated using S. aureus-infected skin wound mouse model, where these compounds show potent antibacterial and wound healing ability supported by subsequent histological as well as immunohistochemical analysis. These findings suggest SaGpx as a possible virulence determinant in S. aureus and position these synthesized inhibitors as promising antivirulence therapeutics. HighlightsO_LIThe high-resolution crystal structure of Staphylococcal glutathione peroxidase is solved. C_LIO_LIBased on the SaGpx catalytic site, ,{beta}-unsaturated ketoesters derivatives are synthesized. C_LIO_LISynthesized ,{beta}-unsaturated ketoesters derivatives inhibit SaGpx activity and binds the protein at M range. C_LIO_LISynthesized ,{beta}-unsaturated ketoesters derivatives show in vitro antibacterial activity against S. aureus at low M range. C_LIO_LISynthesized ,{beta}-unsaturated ketoesters derivatives show in vivo antibacterial and wound healing ability S. aureus-infected skin wound mouse model. C_LI

A large series of dipeptides containing sulfur groups and antimony SbV were modeled to understand their inhibitor activity against Leishmaniasis. The trypanothione reductase (TR), which acts as a reducing agent in several vital processes, is responsible for maintaining the parasite’s cellular thiol redox balance. The antimonic SbV acid (Sb2O5·nH2O) is being evaluated as a drug with inhibitory activity against Leishmaniasis. In the present work, we investigated the inhibitory effect of antimony oxide on (TR) activity modeled as a substrate by probing two model clusters in gas phase and continuum water medium: A [(Sb2O10H8)]−2 coordinated to cysteine, and B [Sb7O28H21] coordinated to trypanothione, including glucose adduct. We report here density functional theory (DFT and DFT-D3) using (B3LYP/LANL2DZ and (TPSS/def2TZVP) results on the binding energy of cysteine and trypanthione complexed to these clusters as possible sites promoting the inhibition process. Upon viewing the results of the computational studies of cluster models and theoretical thermochemistry data for receptor-substrate interactions, identification of ligand-cluster interactions helps to unravel the mechanism of inhibition. The acidity of (Sb2O5,nH2O) leads to great cluster-dipeptide passivation. The electrostatic forces between cluster interface and dipeptide interaction present relevant inhibition effects through proton transfer or mobility from the different amine and ketone groups. The reactivity differences come from the unoccupied lone pairs 5pSb which lie at higher energy but remain available to make a good interaction with the lowest orbital p nitrogen in NH2, and in the CO groups substrate fragment in the zone HOMO-LUMO. Further cluster stability comparisons show a lower Gibbs free energy in B3 (B/trypanthione/glucose) (18 – 30 kcal/mol) at both used level in this study and gives good accurate intramolecular interactions, confirmed by the use of the dispersion-corrected density functional (DFT-D3). Given the dipeptide H-mobility and the (Sb2O5,nH2O) cluster acidity, (donor-acceptor duality), the system is predicted to be potent cluster of the inhibitors by endothermic and spontaneous reaction requiring 3.10 kcal/mol in aqueous medium.View Full Text

Guanine-quadruplexes (G4s) are non-canonical DNA structures that play important protective and regulatory roles within cells, influencing, for instance, gene expression. Although the secondary structure of many human G4s is well characterized, in several gene-promoter regions multiple G4s are located in close proximity and may form three-dimensional structures which could ultimately influence their biological roles. In this contribution, we analyze the interplay between the three neighboring G4s present in the c-KIT proto-oncogene promoter, namely WK1, WSP and WK2. In particular, we highlight how these three G4s are structurally linked and how their crosstalk favors the formation of a parallel structure for WSP, differently from what observed for this isolated G4 in solution. Relying on all-atom molecular dynamic simulations exceeding the s time-scale and using enhanced sampling methods, we provide the first computationally-resolved structure of a well-organized G4 cluster in the promoter of a crucial gene involved in cancer development. Our results indicate that neighboring G4s influence their mutual three-dimensional arrangement and provide a powerful tool to predict and interpret complex DNA structures that ultimately can be used as starting point for drug discovery purposes.

The bacterial plant pathogen Pseudomonas syringae causes significant damage to economically important crops worldwide. These bacteria coordinate their behavior and virulence through specific signaling compounds, such as the diazeniumdiolate leudiazen. Conventional antibacterial treatments enable the development of resistant strains. A more attractive treatment strategy would involve antagonists that suppress the expression of virulence factors without killing the pathogen, potentially reducing the risk of resistance development. Herein, we present the design and synthesis of analogs of leudiazen, which positively regulates the production of mangotoxin in P. syringae pv. syringae (Pss). Several compounds display inhibitory activity towards mangotoxin production, and a lead compound abolishes necrosis in infected tomato leaves, without significantly affecting bacterial growth. Thus, this study represents a promising advance towards developing effective and sustainable methods for bacterial disease control.

Xenorhabdus strains, Gram-negative bacteria pathogenic to insects and symbionts to nematodes of the genus Steinernema are prolific producers of various natural products. Here we describe the xisABCDE biosynthesis gene cluster from Xenorhabdus hominickii responsible for the production of xildivalines. These non-ribosomal peptide and polyketide hybrids act as peptide deformylase inhibitor (PDI) and occur also in other Gammaproteobacteria, especially Vibrio. Their structure and biosynthesis were fully elucidated despite their instability, highlighting a rare trans-methylation of their N-terminus. Subsequently, the structure of the responsible methyltransferase XisE and the peptide deformylase XisD, serving as resistance mechanism, were elucidated by X-ray crystallography, allowing insights into the function and the mode of action of this novel class of PDIs.

Chemically modified nucleic acids have become a powerful platform for basic research and applied technologies. Universal nucleobases are used in PCR,sequencing, and the design of nanodevices and aptamers. Fluorescent universal nucleobases have an even wider range of applications, including the development of nucleic acid-based sensors, switches, and relay logic gates. However, few such nucleobases have been proposed to date, and most of them have suboptimal optical properties. Here, we propose an adenine-based molecular rotor, 7,8-dihydro-8-oxo-6-(3-methylbenzo[d]thiazol-2(3H)-ylidene)adenine (oxo-Ade BZT), as a new, remarkably bright and potent fluorescent universal nucleobase. Its brightness in both oligodeoxyribonucleotides (ODNs) and DNA duplexes (4200 - 10000 M-1 x cm-1) originates from a high molar extinction coefficient (averaged{varepsilon} 368 37000 M-1 x cm-1), provided by the appended 3-methylbenzo[d]thiazolyl moiety, and a relatively high quantum yield (0.11 - 0.27). Melting temperature variations observed upon the incorporation of oxo-Ade BZT opposite native nucleobases in a duplex context did not exceed 10%. The basis of these universal hybridizing properties was unveiled using computational methods. According to molecular dynamics simulations, oxo-Ade BZT pushes the opposite nucleobase out of the DNA double helix and forms multiple hydrophobic contacts with the flanking base pairs. At the same time, the rotational mobility of the bonds between the oxo-Ade BZT-constituting heterobicycles decreases, and oxo-Ade BZT adopts a planar conformation in both ODNs and their duplexes, resulting in the light-up effect. These properties make oxo-Ade BZT a promising molecular tool for analytical, biophysical and biochemical studies.

The increasing prevalence of antimicrobial resistance among ESKAPE group pathogens presents a significant challenge in the healthcare sector, contributing to higher morbidity and mortality rates globally. Thus, it is essential to develop novel antimicrobial agents effective against drug-resistant pathogens. In this study, we report the synthesis and in vitro antimicrobial activity characterization of novel N-substituted {beta}-amino acid derivatives bearing 2-hydroxyphenyl core against multidrug-resistant bacterial pathogens. The synthesized compounds (2-26) exhibited promising antimicrobial activity specifically against Gram-positive bacteria, with minimum inhibitory concentrations (MIC) ranging from 4 to 128 {micro}g/mL. None of the compounds demonstrated activity against Gram-negative pathogens or drug-resistant fungi. Compounds 9 (R = 4-nitrophenyl), 17 (R = 5-nitro-2-thienyl), 18 (R = 5-nitro-2-furyl), thiosemicarbazide 16, and 26 exhibited the most promising activity against Staphylococcus aureus MRSA USA300 lineage strain TCH-1516, with MIC values between 4 and 16 {micro}g/mL. Compound 26 demonstrated strong antimicrobial activity against both S. aureus TCH-1516 and E. faecalis AR-0781, with the activity comparable to control antibiotics. These findings indicate that N-substituted {beta}-amino acid derivatives with a 2-hydroxyphenyl core warrant further investigation as a potential scaffold for the further development of antimicrobial agents based on compound 26 targeting Gram-positive pathogens.

A substantial number of Orange Carotenoid Protein (OCP) studies have aimed to describe the evolution of singlet excited states leading to the formation of photo-activated form, OCPR. The most recent one suggests that three picosecond-lived excited states are formed after the sub-100 fs decay of the initial S2 state. The S* state which has the longest reported lifetime of a few to tens of picoseconds is considered to be the precursor of the first red photoproduct P1. Here, we report the ultrafast photo-dynamics of the OCP from Synechocystis PCC 6803, carried out using Visible-NIR femtosecond time-resolved absorption spectroscopy as a function of the excitation pulse power and wavelength. We found that a carotenoid radical cation can form even at relatively low excitation power, obscuring the determination of photo-activation yields for P1. Moreover, the comparison of green (540 nm) and blue (470 nm) excitations revealed the existence of an hitherto uncharacterized excited state, denoted as S[~], living a few tens of picoseconds and formed only upon 470 nm excitation. Since neither the P1 quantum yield nor the photo-activation speed over hundreds of seconds vary under green and blue continuous irradiation, this S[~] species is unlikely to be involved in the photo-activation mechanism leading to OCPR. We also addressed the effect of His-tagging at the N- or C-termini on excited state photo-physical properties. Differences in spectral signatures and lifetimes of the different excited states were observed, at variance with the usual assumption that His-tagging hardly influences protein dynamics and function. Altogether our results advocate for careful consideration of the excitation power and His-tag position when comparing the photo-activation of different OCP variants, and beg to revisit the notion that S* is the precursor of photoactivated OCPR. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=166 SRC="FIGDIR/small/474187v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@1064473org.highwire.dtl.DTLVardef@77e3c7org.highwire.dtl.DTLVardef@10b1e0eorg.highwire.dtl.DTLVardef@e24977_HPS_FORMAT_FIGEXP M_FIG C_FIG

The discovery of microbial-derived DNA-interacting agents, which hold broad therapeutic potential, is inherently challenging due to the limited sensitivity and specificity of conventional methodologies. Our study introduces a pioneering application of single-molecule stretching assay (SMSA) in natural product chemistry to identify DNA-intercalating agents directly from microbial cultures or extracts. We demonstrate that mechanical force can enhance sensitivity by increasing both the binding affinity Ka and the quantity of ligands bound. The changes induced by intercalators in the counter length and overstretching transition of dsDNA yield a distinctive and highly specific signature indicative of DNA intercalative binding, thereby enabling straightforward detection of DNA intercalators even in trace amounts from microbial cultures. This methodology eliminates the need for extensive large-scale fermentation and purification processes, thus offering a more streamlined approach to DNA-intercalating natural product discovery. By applying SMSA to 17 microorganisms, we identified two DNA intercalator-producing strains: Streptomyces tanashiensis and Talaromyces funiculosus. Subsequently, three DNA intercalators, namely medermycin, kalafungin, and ligustrone B, were isolated and characterized. Among them, medermycin and kalafungin showed significant inhibitory effects against HCT-116 cancer cells, with IC50 values of 52 {+/-} 6 nM and 70 {+/-} 7 nM, respectively.

[FeFe]-hydrogenases are metalloenzymes that catalyze the reversible oxidation and production of H2, making them potential candidates for sustainable energy solutions. However, their practical application is restricted by their extreme O2 sensitivity, which leads to irreversible active site degradation. A newly characterized Group B hydrogenase, ToHydA from Thermosediminibacter oceani, has exhibited exceptional O2-stability even after longtime exposure to air. In ToHydA, the highly conserved proton-transporting cysteine (C212) safeguards the H-cluster from O2-induced degradation by formation of the Hinact state. In this study, we investigate the effects of replacing the azadithiolate (ADT) ligand of [2Fe]H with propanedithiolate (PDT), revealing that this substitution prevents the formation of the Hinact and Htrans states observed in ToHydA WT (bearing the ADT ligand). By combining ATR-FTIR spectroscopy and molecular dynamics (MD) simulations, we show that a hydrogen bond between the nitrogen bridgehead of the ADT ligand and the C212 sidechain is crucial for stabilizing these states. The absence of this interaction in ToHydAPDT (bearing the PDT ligand) prevents the C212 sidechain from approaching the Fed center of [2Fe]H, thereby reducing Hinact accumulation. Moreover, as-isolated ToHydAPDT predominantly exhibits the Hhyd state, which is unusual for [FeFe]-hydrogenases with bound PDT ligand. These findings demonstrate how ligand substitution at the [2Fe]H site of ToHydA affects the structural dynamics, offering detailed molecular insights into the ligand-dependent modulation of [FeFe]-hydrogenases.

The repair of photo-induced DNA lesions through nucleotide excision repair machinery is still the source of important questions. It has been observed that the repair rate of the different cyclobutane pyrimidine dimers, i.e. the photoproducts induced by dimerization of two {pi}-stacked pyrimidines (T<>T, T<>C, C<>T, C<>C), depends on the nucleobases involved in the lesion. TT derivatives (T<>T) are removed more slowly than those containing cytosine, especially in 5. Using all-atom molecular dynamics simulations and free-energy calculations, we demonstrate that the variation of the repair rate observed in human skin and in cultured cutaneous cell is associated to the recognition of the four lesions by the DDB2 protein moiety, and more specifically by the differential structural deformation induced on the complementary strand. Indeed, while C<>C and C<>T induce a larger deviation on the groove parameters, T<>T and T<>C, instead, affect DNA structure to a lesser extent. less affected. These effects then hamper differentially the downstream recruitment of the repair complexes. The observed DNA deformation correlates with the experimental repair rate and provides a structural rationale for the different repair rates of CPD by nucleotide excision repair machinery. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/724087v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@cf6b6dorg.highwire.dtl.DTLVardef@195e35forg.highwire.dtl.DTLVardef@1829296org.highwire.dtl.DTLVardef@165baba_HPS_FORMAT_FIGEXP M_FIG C_FIG

VdtB, the multiple-copper oxidase (MCO) from the bisnaphthopyrone (M)-viriditoxin biosynthetic pathway in Paecilomyces variotii, was shown to catalyze regioselective 6,6'-coupling of semi-viriditoxin (1). The stereoselectivity of the oxidative coupling reaction for the production of the atropisomer (M)-viriditoxin, however, was controlled by VdtD, a non-catalytic dirigent protein from the pathway. In this work, VdtB either alone or together with VdtD were investigated for its stereoselective control upon coupling of other monomeric naphthopyrone derivatives from the pathway with different minor structural variations in terms of presence/absence of O-methylation at C7-position and C3-C4{Delta} 2 double bond on the pyrone ring, and the different side-chain modifications. We showed that VdtB could favour either M- or P-form coupling in a substrate-dependent manner. For some substrates, VdtB could catalyze oxidative coupling in an enantiomerically selective manner. The efficiency of the VdtD in exerting stereoselective control of the oxidative coupling reaction also varies between substrates. The results point to a model whereby VdtB and VdtD form a VdtB-ligand-VdtD complex in which the stereochemical outcome of the coupling reaction depends on how the substrate interacts with both proteins, based on the substrate structure. Our findings contributed to a more comprehensive understanding of dirigent protein-mediated MCO-catalyzed stereoselective oxidative coupling reactions in fungi.

I-motif (iM) DNA structures, formed by cytosine-rich sequences, are increasingly acknowledged for their involvement in gene regulation, maintenance of genomic stability, and their emerging potential as therapeutic targets, particularly in cancer. Despite their biological relevance, the discovery of selective small-molecule probes that can specifically recognize and interact with iM DNA remains an ongoing challenge. In this study, we have used TMPyP4 and screened for its ability to bind various iM DNA constructs, including HRAS1, HRAS2, VEGF, CMYC, CKIT and H-Telo. Structure-activity relationship analyses revealed that specific substitution patterns conferred selectivity towards HRAS2 iM target. Comprehensive spectroscopic investigations, including UV-Vis absorption, steady-state and time-resolved fluorescence, and fluorescence anisotropy, uncovered key photophysical signatures of binding, including significant hypochromic and bathochromic shifts, enhanced fluorescence emission, and prolonged fluorescence lifetimes. Circular dichroism (CD),thermal denaturation (UV-melting) and thermodynamic investigations confirmed that TMPyP4 effectively stabilized the HRAS2 iM structures without disrupting their native topologies. Meanwhile, FT-IR spectroscopy revealed local structural rearrangements upon TMPyP4 binding, offering further evidence of molecular interaction. Collectively, these findings provide valuable insights into the molecular recognition of iM DNA by TMPyP4 and highlight its promise as both selective HRAS2 iM-binding agent and responsive fluorescent probe. This work lays a strong foundation for the development of novel tools for studying iM structures in biological systems and for designing future therapeutics targeting iM DNA in cancer and related diseases.

Lung cancer remains the leading cause of cancer-related deaths worldwide, with cisplatin as the primary chemotherapy despite its limitations. Organotin(IV) dithiocarbamates have emerged as promising anticancer agents due to their potent cytotoxicity and stability. This study reports the successful synthesis of four novel organotin(IV) dithiocarbamates: dimethyltin(IV) N-methyl-N-benzyldithiocarbamate (DioSn-1), diphenyltin(IV) N-methyl-N-benzyldithiocarbamate (DioSn-2), triphenyltin(IV) N-methyl-N-benzyldithiocarbamate (TriSn-3), and triphenyltin(IV) N-ethyl-N-benzyldithiocarbamate (TriSn-4). Their cytotoxicity against A549 lung carcinoma cells was evaluated via MTT assay, while Annexin V-FITC/PI staining determined the mode of cell death. DioSn-2, TriSn-3, and TriSn-4 exhibited potent cytotoxicity (IC: 0.52-1.86 M), whereas DioSn-1 was inactive (IC > 50 M). Apoptotic features such as cell shrinkage and membrane blebbing were observed, with apoptosis rates ranging from 58% to 91%. DioSn-2 was the most selective (SI = 6.45) and induced early DNA damage within 30 minutes, followed by mitochondrial depolarization and excessive ROS generation. Caspase-9 activation exceeded caspase-8, confirming intrinsic apoptosis. NAC treatment reduced apoptosis by 52%, highlighting oxidative stress as a key cytotoxic mechanism. These findings suggest DioSn-2 as a promising alternative to cisplatin for lung cancer therapy.