Guanine Residues Research Articles

The HNRNPF/H RNA binding proteins and disease.

The members of the HNRNPF/H family of heterogeneous nuclear RNA proteins-HNRNPF, HNRNPH1, HNRNPH2, HNRNPH3, and GRSF1, are critical regulators of RNA maturation. Documented functions of these proteins include regulating splicing, particularly alternative splicing, 5' capping and 3' polyadenylation of RNAs, and RNA export. The assignment of these proteins to the HNRNPF/H protein family members relates to differences in the amino acid composition of their RNA recognition motifs, which differ from those of other RNA binding proteins (RBPs). HNRNPF/H proteins typically bind RNA sequences enriched with guanine (G) residues, including sequences that, in the presence of a cation, have the potential to form higher-order G-quadruplex structures. The need to further investigate members of the HNRNPF/H family of RBPs has intensified with the recent descriptions of their involvement in several disease states, including the pediatric tumor Ewing sarcoma and the hematological malignancy mantle cell lymphoma; newly described groups of developmental syndromes; and neuronal-related disorders, including addictive behavior. Here, to foster the study of the HNRNPF/H family of RBPs, we discuss features of the genes encoding these proteins, their structures and functions, and emerging contributions to disease. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

In situ Electrochemical Evaluation of the Interaction of dsDNA with the Proteasome Inhibitor Anticancer Drug Bortezomib

Bortezomib is an inhibitor of proteasomes and an anti-cancer drug. Although bortezomib is considered a safe drug, as confirmed by cytotoxicity assays, recent reports highlighted the possibility of interaction between bortezomib and cellular components, with detrimental long-term effects. The evaluation of the interaction between bortezomib and dsDNA was investigated in bulk solution and using a dsDNA electrochemical biosensor. The binding of bortezomib to dsDNA involved its electroactive centers and led to small morphological modifications in the dsDNA double helix, which were electrochemically identified through changes in the guanine and adenine residue oxidation peaks and confirmed by electrophoretic and spectrophotometric measurements. The redox product of bortezomib amino group oxidation was electrochemically generated in situ on the surface of the dsDNA electrochemical biosensor. The redox product of bortezomib was shown to interact primarily with guanine residues, preventing their oxidation and leading to the formation of bortezomib-guanine adducts, which was confirmed by control experiments with polyhomonucleotides electrochemical biosensors and mass spectrometry. An interaction mechanism between dsDNA and bortezomib is proposed, and the formation of the bortezomib redox product-guanine adduct explained.

Abstract 6209: O6-methylguanine as the junction of MGMT and PARP1-mediated repair pathways

Abstract Temozolomide is the first-choice DNA alkylating agent and has been commonly used in oncology over the last several decades. The cytotoxicity that temozolomide elicits through the methylation of guanine and adenine residues often becomes the limiting factor in effective treatment. Despite growing evidence of dysregulated alkylating DNA damage repair as a driving force of genome instability leading to cancer, neurological diseases, and premature aging, little is currently known about the coordinated role of PARP1 and MGMT (O6-methylguanine methyltransferase) enzymes in the repair of temozolomide-induced methylated DNA lesions. A major PARP1 function in DNA damage is facilitation of repair of the methylated DNA lesions, N6-methyladenine and N7-methylguanine, via base excision repair (BER); while MGMT restores guanine in O6-methylguanine (O6meG), the most cytotoxic adduct, by a one-step catalysis. It is generally thought that BER and MGMT represent two distinct mechanisms for removing DNA damage induced by alkylating agents; however, using a number of advanced cell-free and cell-based approaches, we provided evidence for direct (DNA-independent) and indirect (through PARylation) interaction between PARP1 and MGMT and demonstrated a functional crosstalk between these repair pathways. Particularly, O6meG repair activity is increased once PARP1 PARylates MGMT. Further, longer (more clinically relevant) exposure to temozolomide induced stronger MGMT PARylation in cells, indicating that the PARP1-MGMT interaction is important for enhanced O6meG repair and cell survival. As PARP1-MGMT complex forms in a variety of cancer cell types, our findings have strong implications for the development of an effective cancer therapy for cells dependent on PARP1 and MGMT mediated DNA repair. Citation Format: Jodie D. Cropper, Dauren S. Alimbetov, Kevin T. Brown, Andrew Robles, Rostislav I. Likhotvorik, James T. Guerra, Yidong Chen, Youngho Kwon, Raushan T. Kurmasheva. O6-methylguanine as the junction of MGMT and PARP1-mediated repair pathways. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6209.

Singlet oxygen production analysis of reduced berberine analogs via NMR spectroscopy

Berberine is a natural product isoquinoline alkaloid derived from plants of the genus Berberis. When exposed to photoirradiation, it produces singlet oxygen through photosensitization of triplet oxygen. The production of singlet oxygen grants Berberine its biological activity, as singlet oxygen forms an activated complex with DNA, oxidizing its guanine residues, halting cell replication and leading to cell death, which can be applied in photodynamic therapy of cancer. Through qNMR analysis of 1H NMR spectra gathered through kinetic experiments, we were able to track the generation of a product between singlet oxygen and alpha terpinene, allowing us to quantitatively measure the photosensitizing properties of our scaffolds. Moreover, we implemented 7,8-dihydroberberine and tetrahydroberberine, the reduced and over-reduced forms of berberine, respectively, in the studies to test the effect of the reduction of a compound on its singlet oxygen production.

Integrase and reversetranscriptase: New insights into the HIV genome replication system in line.

Reverse transcriptase (RT) and integrase (IN) are retrovirus enzymes to convert virus genomic RNA into provirus DNA state in host cells. The RT and IN encoded tandemly in the pol gene, are translated as a fused form and incorporated into the virus particles. Recently, we discovered the potential role of HIV-1 IN to regulate the reverse transcription through the fused state with RT (RT-IN). On the other hand, analysis of HIV-1 transcripts have revealed the variations in number of guanine residue at the 5' end (5'G) due to fluctuations in the transcription initiation point within HIV-1 provirus DNA. Importantly, the number of 5'G dictates the packaging of HIV genome RNA into virus particles serving as a template for the reverse transcription reaction. In this review, we provide new insights into the mechanism of HIV genome replication based on our recent findings of the structural-functional correlation of HIV enzymes (RT and IN) and virus genomic RNA.

Bifunctional Epimerase/Reductase Enzymes Facilitate the Modulation of 6-Deoxy-Heptoses Found in the Capsular Polysaccharides of Campylobacter jejuni.

Campylobacter jejuni is a human pathogen and the leading cause of food poisoning in the United States and Europe. Surrounding the exterior surface of this bacterium is a capsular polysaccharide (CPS) that consists of a repeating sequence of common and unusual carbohydrate segments. At least 10 different heptose sugars have thus far been identified in the various strains of C. jejuni. The accepted biosynthetic pathway for the construction of the 6-deoxy-heptoses begins with the 4,6-dehydration of GDP-d-glycero-d-manno-heptose by a dehydratase, followed by an epimerase that racemizes C3 and/or C5 of the product GDP-6-deoxy-4-keto-d-lyxo-heptose. In the final step, a C4-reductase catalyzes the NADPH reduction of the resulting 4-keto product. However, in some strains and serotypes of C. jejuni, there are two separate C4-reductases with different product specificities in the gene cluster for CPS formation. Five pairs of these tandem C4-reductases were isolated, and the catalytic properties were ascertained. In four out of five cases, one of the two C4-reductases is able to catalyze the isomerization of C3 and C5 of GDP-6-deoxy-4-keto-d-lyxo-heptose, in addition to the catalysis of the reduction of C4, thus bypassing the requirement for a separate C3/C5-isomerase. In each case, the 3'-end of the gene for the first C4-reductase contains a poly-G tract of 8-10 guanine residues that may be used to control the expression and/or catalytic activity of either C4-reductase. The three-dimensional structure of the C4-reductase from serotype HS:15, which only does a reduction of C4, was determined to 1.45 Å resolution in the presence of NADPH and GDP.

Genosensing Applications of Glassy Carbon Electrodes Modified with Multi-Walled Carbon Nanotubes Non-Covalently Functionalized with Polyarginine.

We report the advantages of glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with polyarginine (PolyArg) for the adsorption and electrooxidation of different DNAs and the analytical applications of the resulting platform. The presence of the carbon nanostructures, and mainly the charge of the PolyArg that supports them, facilitates the adsorption of calf-thymus and salmon sperm double-stranded DNAs and produces an important decrease in the overvoltages for the oxidation of guanine and adenine residues and a significant enhancement in the associated currents. As a proof-of-concept of possible GCE/MWCNTs-PolyArg biosensing applications, we develop an impedimetric genosensor for the quantification of microRNA-21 at femtomolar levels, using GCE/MWCNTs-PolyArg as a platform for immobilizing the DNA probe, with a detection limit of 3fM, a sensitivity of 1.544 × 103 Ω M-1, and a successful application in enriched biological fluids.

The Promoter Region of the Proto-Oncogene MST1R Contains the Main Features of G-Quadruplexes Formation

MST1R (RON) is a receptor of the MET tyrosine kinase receptor family involved in several cancers such as pancreas, breast, ovary, colon, and stomach. Some studies have shown that overexpression of MST1R increases the migratory and invasive properties of cancer cells. The promoter region of the oncogene MST1R is enriched in guanine residues that can potentially form G-quadruplexes (G4s), as it was observed in other oncogenic promoters such as KRAS and c-MYC. There is abundant literature that links the presence of G4s in promoter regions of oncogenes to diverse gene regulation processes that are not well understood. In this work, we have studied the reverse and forward sequence of MST1R promoter region using the G4Hunter software and performed biophysical studies to characterize the best scored sequences.

Photo-Oxidizing Ruthenium(II) Complexes with Enhanced Visible-Light Absorption and G-quadruplex DNA Binding Abilities.

Photosensitizers that gather high photo-oxidizing power and strong visible-light absorption are of great interest in the development of new photo-chemotherapeutics. Indeed, such compounds constitute attractive candidates for the design of type I photosensitizers that are not dependent on the presence of oxygen. In this paper, we report on the synthesis and studies of new ruthenium(II) complexes that display strong visible-light absorption and can oxidize guanine residues under visible-light irradiation, as evidenced by nanosecond transient absorption spectroscopy. The reported compounds also tightly bind to G-quadruplex DNA structures from the human telomeric sequence (TTAGGG repeat). The kinetic and thermodynamic parameters of the interaction of these Ru(II) complexes with G-quadruplex and duplex DNA were studied thanks to luminescence titrations and bio-layer interferometry measurements, which revealed higher affinities towards the non-canonical G-quadruplex architecture. Docking experiments and non-covalent ionic analysis allowed us to gain information on the mode and the strength of the interaction of the compounds towards G-quadruplex and duplex DNA. The different studies emphasize the substantial influence of the position and the number of non-chelating nitrogen atoms on the interaction with both types of DNA secondary structures.

Covalent Catalytic Strategies for Enzymes That Modify RNA Molecules on their Tripartite Building Blocks.

The tripartite structures of the four 5'-nucleotide monophosphate (NMP) building blocks in all RNAs enable enzyme-catalyzed chemical modifications to three types of sites: the heterocyclic bases via N- and C-methylations and other alkylations, conversion of the N-glycoside linkages of the uridine moiety to the C-C glycoside link in pseudouridines, and the phosphodiester-mediated processes of 5'-capping, splicing, and 3'-tailing of premRNAs. We examine known cases for enzymatic covalent catalytic strategies that entail transient formation and breakdown of covalent enzyme-RNA adducts in each catalytic cycle. One case involves generation of the required carbon nucleophile during C5 methylation of cytosine residues in RNAs. A second examines the mechanism proposed for pseudouridine synthases and for replacement of a guanine residue in tRNAs by queuosine. The third category involves phosphoric anhydride and phosphodiester chemistry by which viral RNAs encode enzymes for making their own mRNA 5'-caps. This strategy includes the recent finding that the SARS-CoV2 proteins assemble a canonical 5',5'-GTP cap on their 28 900 nucleotide genomic RNA to enable its translation as an mRNA by host translational machinery by way of a covalent RNA-viral enzyme intermediate.

DNA methyltransferase DNMT3A forms interaction networks with the CpG site and flanking sequence elements for efficient methylation

Specific DNA methylation at CpG and non-CpG sites is essential for chromatin regulation. The DNA methyltransferase DNMT3A interacts with target sites surrounded by variable DNA sequences with its TRD and RD loops, but the functional necessity of these interactions is unclear. We investigated CpG and non-CpG methylation in a randomized sequence context using WT DNMT3A and several DNMT3A variants containing mutations at DNA-interacting residues. Our data revealed that the flanking sequence of target sites between the −2 and up to the +8 position modulates methylation rates >100-fold. Non-CpG methylation flanking preferences were even stronger and favor C(+1). R836 and N838 in concert mediate recognition of the CpG guanine. R836 changes its conformation in a flanking sequence-dependent manner and either contacts the CpG guanine or the +1/+2 flank, thereby coupling the interaction with both sequence elements. R836 suppresses activity at CNT sites but supports methylation of CAC substrates, the preferred target for non-CpG methylation of DNMT3A in cells. N838 helps to balance this effect and prevent the preference for C(+1) from becoming too strong. Surprisingly, we found L883 reduces DNMT3A activity despite being highly conserved in evolution. However, mutations at L883 disrupt the DNMT3A-specific DNA interactions of the RD loop, leading to altered flanking sequence preferences. Similar effects occur after the R882H mutation in cancer cells. Our data reveal that DNMT3A forms flexible and interdependent interaction networks with the CpG guanine and flanking residues that ensure recognition of the CpG and efficient methylation of the cytosine in contexts of variable flanking sequences.

Electrochemical characterization of shikonin and in-situ evaluation of interaction with DNA

• Shikonin, a natural compound with pharmaceutical properties; • Shikonin reduction results in semiquinone radical and superoxide; • Shikonin induces DNA conformational modification. • In-situ shikonin reduction leads to occurrence 8-oxo-guanine. • Shikonin-DNA interaction mechanism proposed. Shikonin, a natural compound with pharmaceutical properties, has attracted interest due to its anti-oxidant properties, potential anti-cancer activity and activity over several biological pathways, such as dsDNA transcription/replication of cancer cells and inhibition of pyruvate kinase M2. The electrochemical behavior of shikonin in aqueous media was investigated at glassy carbon electrodes by cyclic and differential pulse voltammetry. The reduction involves the quinone moiety and formation of a semiquinone intermediate. In the absence of dissolved oxygen, the reduction is reversible while in normal atmosphere leads to formation of superoxide cation. The oxidation occurs at the dihydroxy moiety and reversibility was only observed in acid electrolytes. A redox mechanism was proposed. The interaction between shikonin and ds DNA was evaluated in incubated solutions and in situ with the dsDNA-electrochemical biosensor. The mechanism of interaction is time-dependent and follows an initial binding step at the grooves of the double strand leading to conformational modifications recognized through the variation of guanine and adenine oxidation peaks. The in-situ electrochemical production of the semiquinone intermediate leads to a preferential interaction with guanine residues, promoting their oxidation and consequently occurrence 8-oxo-guanine. An interaction mechanism was proposed.

Discovery and Genomic Characterization of a Novel Henipavirus, Angavokely Virus, from Fruit Bats in Madagascar.

The genus Henipavirus (family Paramyxoviridae) currently comprises seven viruses, four of which have demonstrated prior evidence of zoonotic capacity. These include the biosafety level 4 agents Hendra (HeV) and Nipah (NiV) viruses, which circulate naturally in pteropodid fruit bats. Here, we describe and characterize Angavokely virus (AngV), a divergent henipavirus identified in urine samples from wild, Madagascar fruit bats. We report the nearly complete 16,740-nucleotide genome of AngV, which encodes the six major henipavirus structural proteins (nucleocapsid, phosphoprotein, matrix, fusion, glycoprotein, and L polymerase). Within the phosphoprotein (P) gene, we identify an alternative start codon encoding the AngV C protein and a putative mRNA editing site where the insertion of one or two guanine residues encodes, respectively, additional V and W proteins. In other paramyxovirus systems, C, V, and W are accessory proteins involved in antagonism of host immune responses during infection. Phylogenetic analysis suggests that AngV is ancestral to all four previously described bat henipaviruses-HeV, NiV, Cedar virus (CedV), and Ghanaian bat virus (GhV)-but evolved more recently than rodent- and shrew-derived henipaviruses, Mojiang (MojV), Gamak (GAKV), and Daeryong (DARV) viruses. Predictive structure-based alignments suggest that AngV is unlikely to bind ephrin receptors, which mediate cell entry for all other known bat henipaviruses. Identification of the AngV receptor is needed to clarify the virus's potential host range. The presence of V and W proteins in the AngV genome suggest that the virus could be pathogenic following zoonotic spillover. IMPORTANCE Henipaviruses include highly pathogenic emerging zoonotic viruses, derived from bat, rodent, and shrew reservoirs. Bat-borne Hendra (HeV) and Nipah (NiV) are the most well-known henipaviruses, for which no effective antivirals or vaccines for humans have been described. Here, we report the discovery and characterization of a novel henipavirus, Angavokely virus (AngV), isolated from wild fruit bats in Madagascar. Genomic characterization of AngV reveals all major features associated with pathogenicity in other henipaviruses, suggesting that AngV could be pathogenic following spillover to human hosts. Our work suggests that AngV is an ancestral bat henipavirus that likely uses viral entry pathways distinct from those previously described for HeV and NiV. In Madagascar, bats are consumed as a source of human food, presenting opportunities for cross-species transmission. Characterization of novel henipaviruses and documentation of their pathogenic and zoonotic potential are essential to predicting and preventing the emergence of future zoonoses that cause pandemics.

Site-Specific and Enzymatic Cross-Linking of sgRNA Enables Wavelength-Selectable Photoactivated Control of CRISPR Gene Editing.

Chemical cross-linking enables rapid identification of RNA-protein and RNA-nucleic acid inter- and intramolecular interactions. However, no method exists to site-specifically and covalently cross-link two user-defined sites within an RNA. Here, we develop RNA-CLAMP, which enables site-specific and enzymatic cross-linking (clamping) of two selected guanine residues within an RNA. Intramolecular clamping can disrupt normal RNA function, whereas subsequent photocleavage of the cross-linker restores activity. We used RNA-CLAMP to clamp two stem loops within the single-guide RNA (sgRNA) of the CRISPR-Cas9 gene editing system via a photocleavable cross-linker, completely inhibiting gene editing. Visible light irradiation cleaved the cross-linker and restored gene editing with high spatiotemporal resolution. Design of two photocleavable linkers responsive to different wavelengths of light allowed multiplexed photoactivation of gene editing in mammalian cells. This photoactivated CRISPR-Cas9 gene editing platform benefits from undetectable background activity, provides a choice of activation wavelengths, and has multiplexing capabilities.

Ruthenium(II) Polypyridyl Complexes and Their Use as Probes and Photoreactive Agents for G-quadruplexes Labelling.

Due to their optical and electrochemical properties, ruthenium(II) polypyridyl complexes have been used in a wide array of applications. Since the discovery of the light-switch ON effect of [Ru(bpy)2dppz]2+ when interacting with DNA, the design of new Ru(II) complexes as light-up probes for specific regions of DNA has been intensively explored. Amongst them, G-quadruplexes (G4s) are of particular interest. These structures formed by guanine-rich parts of DNA and RNA may be associated with a wide range of biological events. However, locating them and understanding their implications in biological pathways has proven challenging. Elegant approaches to tackle this challenge relies on the use of photoprobes capable of marking, reversibly or irreversibly, these G4s. Indeed, Ru(II) complexes containing ancillary π-deficient TAP ligands can create a covalently linked adduct with G4s after a photoinduced electron transfer from a guanine residue to the excited complex. Through careful design of the ligands, high selectivity of interaction with G4 structures can be achieved. This allows the creation of specific Ru(II) light-up probes and photoreactive agents for G4 labelling, which is at the core of this review composed of an introduction dedicated to a brief description of G-quadruplex structures and two main sections. The first one will provide a general picture of ligands and metal complexes interacting with G4s. The second one will focus on an exhaustive and comprehensive overview of the interactions and (photo)reactions of Ru(II) complexes with G4s.

Residue interactions affecting the deprotonation of internal guanine moieties in oligodeoxyribonucleotides, calculated by FMO methods.

The effect of vicinal molecular groups on the intrinsic acidity of a central guanine residue in short single-stranded DNA models and the potentials exerted by the backbone and the nucleobases on the leaving proton were determined by the fragment molecular orbital (FMO) method, in terms of quantum descriptors (QDs) and pair interaction interfragment decomposition analysis (PIEDA). The acidity of the central guanine moiety decreased with increasing oligonucleotide length, in response to changes by less than 1 eV in the ionization potential, global softness, electrophilicity index, and electronegativity descriptors. The differences in these descriptors were majorly interpreted in terms of the electrostatic influence of the negative charges residing on the backbone of the molecule. Additionally, this electric-field effect was determined explicitly for the displacement of the test hydronium ion to a distance of 250 Å from its original position, resulting in good agreement with calculations of the variation in Gibbs free energies, obtained from physical experiments conducted on the identical oligonucleotide sequences. The reported results are useful for biophysical applications of deoxyriboligonucleotides containing guanine residues in order to induce local negative charges at specific positions in the DNA chain.

Structural analysis of thrombin-binding G-aptamers in presence of bivalent ions

The aim of this study was to examine 3D structures of DNA aptamers, thrombin inhibitors. •The main objective was to study 3D structure 15TBA, RE31, NU172 aptamers using the small-angle X-ray scattering method. The size of 15TBA was 4.5 nm, which corresponds to a partially unfolded conformation. The CD spectrum of Nu172 in the presence of 50 mM strontium ions indicates the presence of an antiparallel G-quadruplex, the concentration o f which drops at 50°C. NU172 does not have a rigid structure, apparently due to the presence of a guanine residue in the GT loop. The NU172 aptamer does not form a stable conformation in solution either without ions or with Ba2+ and Sr2+ ions. • It was shown that there is possibility of aptamers transition from one conformation to another dependently on concentration and temperature confirms that the potassium ion is a unique stabilizing ion of natural molecules containing G-quadruplexes

Evaluation of Ceftriaxone Residue in Cow Milk and its Toxicity on Danio rerio

Ceftriaxone (CEFT), a widely used broad-spectrum beta -lactam cephalosporin antibiotic, is used to treat bovine mastitis, caused by a variety of bacteria. If used injudiciously, this antibiotic leaves a residue that persists after pasteurization. Antibiotic residue contamination occurs when antibiotic residue exceeds its Maximum Residue Limits (MRLs). This has negative impacts on both public health and the environment. The aim of a recent study was to determine the concentration of ceftriaxone residue (CEFTR) in raw and pasteurized mastitis cow milk, and its role in developmental toxicity and genotoxicity in the zebra fish model. The CEFTR concentrations in raw and pasteurized milk were several times higher than CEFT's MRL. CEFTR showed a decrease in body length and yolk sac region of zebra fish larvae 7-amino cephalosporanic acid (7-ACA), C3 and C7 are the cephalosporin components produced by the degradation of CEFT that may present in CEFTR, and have an impact on the zebra fish embryo in this stage of development. Comet Assay or Single Cell Gel Electrophoresis (SCGE) also exhibited highest percentage of tail DNA, and tail moment (DNA migration) that is the ultimate indicator of DNA damage by breaking DNA strands and incorporating guanine residue into the genome that ultimately damages the DNA. As a result, the CEFTR is extremely concerning for public health and the environment. The toxic effects of the CEFTR in zebra fish model have not yet been studied. This may be the first comprehensive study.

Structural specificity of groove binding mechanism between imidazolium-based ionic liquids and DNA revealed by synchrotron-UV Resonance Raman spectroscopy and molecular dynamics simulations

The predicted capability of Ionic Liquids (ILs) in stabilizing the native structure of nucleic acids is relevant in biotechnology, especially for DNA storage and handling. In the present work, we implement a joint combination of advanced spectroscopic techniques such as synchrotron radiation-UV Resonance Raman spectroscopy (SR-UVRR) and molecular dynamics (MD) simulations for deepening insight into the sequence and structural specificity of the binding interactions between imidazolium-based ILs and both the phosphate groups and nucleobases in the minor and major grooves of double-stranded DNA. A 30-base pair double-stranded DNA structure has been chosen as a model of natural DNA. The experimental and simulation results give evidence of the predominance of a groove binding mechanism between ILs cations and DNA, with preferential interactions among guanine residues and the shorter alkyl-chain length on imidazolium cations. Raman experiments allowed us to detect both cooperative transition and reversible pre-melting structural transformations that involve specific tracts in the structure of DNA and are turned on at lower temperatures for guanine residues than for adenine ones. The more marked effect on the pre-melting states of adenine operated by the imidazolium-based ILs with chloride as anion suggests a selective strong interaction of this anion with the DNA’s adenine-rich tracts. MD simulation results reveal the influence of ILs on the structural properties of DNA and provide more details about the solvation, interaction, stability and flexibility of DNA in the hydrated ILs. According to MD analyses, simultaneous electrostatic and hydrophobic interactions drive the shorter alkyl-chain length of imidazolium cations to have greater interplays with the DNA major groove.

Melphalan flufenamide is an Anticancer medication used to treat multiple Myeloma: A Review

Melphalan Flufenamide is a peptide-drug conjugate composed of a peptide conjugated, via an aminopeptidase-targeting linkage, to the alkylating agent melphalan, with potential antineoplastic and anti-angiogenic activities. Upon administration, the highly lipophilic melphalan flufenamide penetrates cell membranes and enters cells. In aminopeptidase-positive tumor cells, melphalan flufenamide is hydrolyzed by peptidases to release the hydrophilic alkylating agent melphalan. This results in the specific release and accumulation of melphalan in aminopeptidase-positive tumor cells. Melphalan alkylates DNA at the N7 position of guanine residues and induces DNA intra- and inter-strand cross-linkages. This results in the inhibition of DNA and RNA synthesis and the induction of apoptosis, thereby inhibiting tumor cell proliferation. Peptidases are overexpressed by certain cancer cells. The administration of melphalan flufenamide allows for enhanced efficacy and reduced toxicity compared to melphalan.1,2,3