Insight into the Course of the Ferrier Rearrangement Used to Obtain Untypical Diosgenyl Saponins.

The Ferrier rearrangement was utilized to obtain 2,3-unsaturated diosgenyl glycosides. This reaction proceeded with high stereoselectivity, yielding mostly saponins with an α configuration (hexoses) or predominantly with a ß configuration (pentoses). The diversity of the glycals used and the glycosides obtained enabled a deep discussion of the Ferrier rearrangement mechanism. The mechanism was supported by DFT calculations concerning the intermediate ions. It was concluded that the vinylogous anomeric effect may influence the reactivity of the glycals. Two possible Ferrier rearrangement intermediates, dioxolenium and allyloxycarbenium ions, were hypothesized to exist in thermodynamic equilibrium that shifted toward the former. The allyloxycarbenium ion participates in the final rearrangement step and determines the reaction regioselectivity. Furthermore, the conformational stability of the 2,3-unsaturated pyranose ring determines the stereoselectivity of the reaction. Factors influencing this stability, as well as the NMR data enabling recognition of the 0H5 and 5H0 conformations, were identified. Chemoselective hydrogenation of 2,3-unsaturated diosgenyl glycosides provided a series of 2,3-dideoxy analogues. The anticancer, hemolytic, and antibacterial activities of the synthesized saponins are presented alongside a discussion of the structure-activity relationships.

Exploring the Antitumor Efficacy of N-Heterocyclic Nitrilotriacetate Oxidovanadium(IV) Salts on Prostate and Breast Cancer Cells.

The crystal structures of two newly synthesized nitrilotriacetate oxidovanadium(IV) salts, namely [QH][VO(nta)(H2O)](H2O)2 (I) and [(acr)H][VO(nta)(H2O)](H2O)2 (II), were determined. Additionally, the cytotoxic effects of four N-heterocyclic nitrilotriacetate oxidovanadium(IV) salts-1,10-phenanthrolinium, [(phen)H][VO(nta)(H2O)](H2O)0.5 (III), 2,2'-bipyridinium [(bpy)H][VO(nta)(H2O)](H2O) (IV), and two newly synthesized compounds (I) and (II)-were evaluated against prostate cancer (PC3) and breast cancer (MCF-7) cells. All the compounds exhibited strong cytotoxic effects on cancer cells and normal cells (HaCaT human keratinocytes). The structure-activity relationship analysis revealed that the number and arrangement of conjugated aromatic rings in the counterion had an impact on the antitumor effect. The compound (III), the 1,10-phenanthrolinium analogue, exhibited the greatest activity, whereas the acridinium salt (II), with a different arrangement of three conjugated aromatic rings, showed the lowest toxicity. The increased concentrations of the compounds resulted in alterations to the cell cycle distribution with different effects in MCF-7 and PC3 cells. In MCF-7 cells, compounds I and II were observed to block the G2/M phase, while compounds III and IV were found to arrest the cell cycle in the G0/G1 phase. In PC3 cells, all compounds increased the rates of cells in the G0/G1 phase.

Intramolecular Proton Transfer in the Radical Anion of Cytidine Monophosphate Sheds Light on the Sensitivities of Dry vs Wet DNA to Electron Attachment-Induced Damage.

Single-strand breaks (SSBs) induced via electron attachment were previously observed in dry DNA under ultrahigh vacuum (UHV), while hydrated electrons were found not able to induce this DNA damage in an aqueous solution. To explain these findings, crossed electron-molecular beam (CEMB) and anion photoelectron spectroscopy (aPES) experiments coupled to density functional theory (DFT) modeling were used to demonstrate the fundamental importance of proton transfer (PT) in radical anions formed via electron attachment. Three molecular systems were investigated: 5'-monophosphate of 2'-deoxycytidine (dCMPH), where PT in the electron adduct is feasible, and two ethylated derivatives, 5'-diethylphosphate and 3',5'-tetraethyldiphosphate of 2'-deoxycytidine, where PT is blocked due to substitution of labile protons with the ethyl residues. CEMB and aPES experiments confirmed the cleavage of the C3'/C5'-O bond as the main dissociation channel related to electron attachment in the ethylated derivatives. In the case of dCMPH, however, electron attachment (in the aPES experiments) yielded its parent (intact) radical anion, dCMPH-, suggesting that its dissociation was inhibited. The aPES-measured vertical detachment energy of the dCMPH- was found to be 3.27 eV, which agreed with its B3LYP/6-31++G(d,p)-calculated value and implied that electron-induced proton transfer (EIPT) had occurred during electron attachment to the dCMPH model nucleotide. In other words, EIPT, subduing dissociation, appeared to be somewhat protective against SSB. While EIPT is facilitated in solution compared to the dry environment, the above findings are consistent with the stability of DNA against hydrated electron-induced SSB in solution versus free electron-induced SSB formation in dry DNA.

Lipidation of Naturally Occurring α-Helical Antimicrobial Peptides as a Promising Strategy for Drug Design.

In this paper, we describe the chemical synthesis, preliminary evaluation of antimicrobial properties and mechanisms of action of a novel group of lipidated derivatives of three naturally occurring α-helical antimicrobial peptides, LL-I (VNWKKVLGKIIKVAK-NH2), LK6 (IKKILSKILLKKL-NH2), ATRA-1 (KRFKKFFKKLK-NH2). The obtained results showed that biological properties of the final compounds were defined both by the length of the fatty acid and by the structural and physico-chemical properties of the initial peptide. We consider C8-C12 length of the hydrocarbon chain as the optimal for antimicrobial activity improvement. However, the most active analogues exerted relatively high cytotoxicity toward keratinocytes, with the exception of the ATRA-1 derivatives, which had a higher selectivity for microbial cells. The ATRA-1 derivatives had relatively low cytotoxicity against healthy human keratinocytes but high cytotoxicity against human breast cancer cells. Taking into account that ATRA-1 analogues carry the highest positive net charge, it can be assumed that this feature contributes to cell selectivity. As expected, the studied lipopeptides showed a strong tendency to self-assembly into fibrils and/or elongated and spherical micelles, with the least cytotoxic ATRA-1 derivatives forming apparently smaller assemblies. The results of the study also confirmed that the bacterial cell membrane is the target for the studied compounds.

Influence of Hypoxia on Radiosensitization of Cancer Cells by 5-Bromo-2'-deoxyuridine.

Radiotherapy is a crucial cancer treatment, but its outcome is still far from satisfactory. One of the reasons that cancer cells show resistance to ionizing radiation is hypoxia, defined as a low level of oxygenation, which is typical for solid tumors. In the hypoxic environment, cancer cells are 2-3 times more resistant to ionizing radiation than normoxic cells. To overcome this important impediment, radiosensitizers should be introduced to cancer therapy. When modified with an electrophilic substituent, nucleosides may undergo efficient dissociative electron attachment (DEA) that leaves behind nucleoside radicals, which, in secondary reactions, are able to induce DNA damage, leading to cancer cell death. We report the radiosensitizing effect of one of the best-known DEA-type radiosensitizers-5-bromo-2'-deoxyuridine (BrdU)-on breast (MCF-7) and prostate (PC3) cancer cells under both normoxia and hypoxia. MCF-7 and PC3 cells were treated with BrdU to investigate the effect of hypoxia on cell proliferation, incorporation into DNA and radiosensitivity. While the oxygen concentration did not significantly affect the efficiency of BrdU incorporation into DNA or the proliferation of tumor cells, the radiosensitizing effect of BrdU on hypoxic cells was more evident than on normoxic cells. Further mechanistic studies performed with the use of flow cytometry showed that under hypoxia, BrdU increased the level of histone H2A.X phosphorylation after X-ray exposure to a greater extent than under normal oxygenation conditions. These results confirm that the formation of double-strand breaks in hypoxic BrdU-treated cancer cells is more efficient. In addition, by performing stationary radiolysis of BrdU solution in the presence of an ●OH radical scavenger, we compared the degree of its electron-induced degradation under aerobic and anaerobic conditions. It was determined that radiodegradation under anaerobic conditions was almost twice as high as that under aerobic conditions.

Design, synthesis and biological evaluation of betulin-3-yl 2-amino-2-deoxy-ß-d-glycopyranosides.

Betulin is a natural pentacyclic triterpenoid, possessing a lupane-structure, with a wide range of pharmacological activities. Its weak hydrosolubility hinders the biological activity of the compound and its derivatives. To circumvent this problem, we synthesized and tested in vitro three d-glycosaminosides of betulin. The structure of betulin was modified by incorporation of 2-amino-2-deoxy-d-gluco- and -d-galactopyranosyl moieties to its C-3 position. So far betulinyl glycosides containing these amino-sugars have not been reported in the literature. The structure of the studied derivatives was confirmed by 1H and 13C NMR spectroscopy as well as mass spectrometry. The 28-O-acetylbetulin-3-yl 2-amino-2-deoxy-ß-d-glucopyranoside and betulin-3-yl 2-amino-2-deoxy-ß-d-gluco- and ß-d-galactopyranoside were tested against the human pathogenic fungi and Gram-positive and Gram-negative bacteria. Moreover, the MTT assay of their cytotoxicity was performed on the MCF-7 breast cancer cell line and on the HDFa, human dermal fibroblasts. The Ames test on mutagenic properties completed our biological assays.

A Pentapeptide with Tyrosine Moiety as Fluorescent Chemosensor for Selective Nanomolar-Level Detection of Copper(II) Ions.

Herein, we have investigated principally with the use of UV and fluorescence (steady-state and time-resolved) spectroscopy the interactions between selected pentapeptides with tyrosine residue (EYHHQ, EHYHQ, EHHQY, and KYHHE) and various metal ions (Cu2+, Mn2+, Co2+, Ni2+, Zn2+, Cr3+, Cd2+, Ag+, Pb2+, Sr2+, Ba2+, Ca2+, Mg2+, Al3+, Fe2+, and Ga3+) in order to establish the relationship between the position of a tyrosine residue in the peptide sequence and the metal ion-binding properties. Among the peptides studied, EHYHQ was evaluated as an efficient and selective ligand for developing a chemosensor for the detection of copper(II) ions. While significant fluorescence emission quenching was observed for that peptide in the presence of Cu2+ cations, other metal cations used at the same and at considerably higher concentrations caused a negligible change of the fluorescence emission spectrum, indicating a high selectivity of EHYHQ for Cu2+ ions. Under optimum conditions, fluorescence intensity was inversely proportional to the concentration of Cu2+ ions. The limit of detection of Cu2+ ions with the use of EHYHQ was determined at the level of 26.6 nM. The binding stoichiometry of the complexes of the studied peptides with Cu2+ ions was evaluated spectrophotometrically and fluorimetrically (as in the case of EHYHQ confirmed by mass spectrometry) and found to be 1:2 (Cu2+-peptide) for all the investigated systems. Furthermore, the stability constant (K) values of these complexes were determined. The reversibility of the proposed Cu2+ ions sensor was confirmed, the pH range where the sensor acts was determined, while its analytical performance was compared with some other reported recently fluorescent sensors. The mechanism of the interactions between EHYHQ and Cu2+ was proposed on the basis of NMR spectroscopy investigations.

5-(N-Trifluoromethylcarboxy)aminouracil as a Potential DNA Radiosensitizer and Its Radiochemical Conversion into N-Uracil-5-yloxamic Acid.

Hypoxia-a hallmark of solid tumors-dramatically impairs radiotherapy, one of the most common anticancer modalities. The adverse effect of the low-oxygen state can be eliminated by the concomitant use of a hypoxic cell radiosensitizer. In the present paper, we show that 5-(N-trifluoromethylcarboxy) aminouracil (CF3CONHU) can be considered as an effective radiosensitizer of DNA damage, working under hypoxia. The title compound was synthesized in the reaction of 5-aminouracil and trifluoroacetic anhydride in trifluoroacetic acid. Then, an aqueous and deoxygenated solution of the HPLC purified compound containing tert-butanol as a hydroxyl radical scavenger was irradiated with X-rays. Radiodegradation in a 26.67 ± 0.31% yield resulted in only one major product-N-uracil-5-yloxamic acid. The mechanism that is possibly responsible for the formation of the observed radioproduct has been elucidated with the use of DFT calculations. The cytotoxic test against the PC3 prostate cancer cell line and HDFa human dermal fibroblasts confirmed the low cytotoxicity of CF3CONHU. Finally, a clonogenic assay and flow cytometric analysis of histone H2A.X phosphorylation proved the radiosensitization in vitro.

5-Iodo-4-thio-2'-Deoxyuridine as a Sensitizer of X-ray Induced Cancer Cell Killing.

Nucleosides, especially pyrimidines modified in the C5-position, can act as radiosensitizers via a mechanism that involves their enzymatic triphosphorylation, incorporation into DNA, and a subsequent dissociative electron attachment (DEA) process. In this paper, we report 5-iodo-4-thio-2'-deoxyuridine (ISdU) as a compound that can effectively lead to ionizing radiation (IR)-induced cellular death, which is proven by a clonogenic assay. The test revealed that the survival of cells, pre-treated with 10 or 100 µM solution of ISdU and exposed to 0.5 Gy of IR, was reduced from 78.4% (for non-treated culture) to 67.7% and to 59.8%, respectively. For a somewhat higher dose of 1 Gy, the surviving fraction was reduced from 68.2% to 54.9% and to 40.8% for incubation with 10 or 100 µM ISdU, respectively. The cytometric analysis of histone H2A.X phosphorylation showed that the radiosensitizing effect of ISdU was associated, at least in part, with the formation of double-strand breaks. Moreover, the cytotoxic test against the MCF-7 breast cancer cell line and human dermal fibroblasts (HDFa line) confirmed low cytotoxic activity of ISdU. Based on the results of steady state radiolysis of ISdU with a dose of 140 Gy and quantum chemical calculations explaining the origin of the MS detected radioproducts, the molecular mechanism of sensitization by ISdU was proposed. In conclusion, we found ISdU to be a potential radiosensitizer that could improve anticancer radiotherapy.

Dihydroxy-Substituted Coumarins as Fluorescent Probes for Nanomolar-Level Detection of the 4-Amino-TEMPO Spin Label.

This paper reports on dihydroxycoumarins as fluorescent probes suitable for the detection and determination of the nitroxide radical, namely 4-amino-TEMPO. Since 4-amino-TEMPO is used as a spin label for the detection of various radicals and damage caused by these species, its determination under physiological conditions might help us to understand the mechanism of the oxidative stress. Among different coumarins studied, only dihydroxy-substituted derivatives show high sensitivity, specificity, and selectivity for the nitroxide radical. In this assay, dihydroxy-substituted coumarins under the action of 4-amino-TEMPO show a very fast and significant increase in fluorescence intensity and lifetime. Among them 6,7-dihydroxycoumarin (esculetin) exhibits the strongest fluorescence enhancement (up to 40 times), with an estimated limit of detection equal to 16.7 nM-a significantly lower value when compared with UV-Vis or electron paramagnetic resonance (EPR) spectroscopy. The method is characterized by an easy procedure of sample preparation and very short time of analysis. The mechanism of the interaction between 6,7-dihydroxycoumarin and 4-amino-TEMPO has been examined with the use of a series of complementary techniques, such as steady-state and time-resolved fluorescence spectroscopy, UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy, potentiometric titration, and high-performance liquid chromatography. It has been proven that the only route of the reaction in the system studied is a proton transfer from the molecule of esculetin to the amino group of the nitroxide. Biological studies performed on prostate cancer cells, breast cancer cells, and normal skin fibroblasts revealed significant anticancer properties of 6,7-dihydroxycoumarin, which caused a considerable decrease in the viability and number of cancer cells, and affected their morphology, contrary to normal fibroblasts. Furthermore, the experiment performed on prostate cancer cells showed that fluorescence emission of esculetin is closely related to intracellular pH-the higher pH, the higher observed fluorescence intensity (in accordance with a chemical experiment). On the other hand, the studies performed in different pH levels revealed that when pH of the solution increases, the observed fluorescence intensity enhancement under the action of 4-amino-TEMPO decreases (better sensing properties of esculetin towards the nitroxide in lower pH).

Why Does the Type of Halogen Atom Matter for the Radiosensitizing Properties of 5-Halogen Substituted 4-Thio-2'-Deoxyuridines?

Radiosensitizing properties of substituted uridines are of great importance for radiotherapy. Very recently, we confirmed 5-iodo-4-thio-2'-deoxyuridine (ISdU) as an efficient agent, increasing the extent of tumor cell killing with ionizing radiation. To our surprise, a similar derivative of 4-thio-2'-deoxyuridine, 5-bromo-4-thio-2'-deoxyuridine (BrSdU), does not show radiosensitizing properties at all. In order to explain this remarkable difference, we carried out a radiolytic (stationary and pulse) and quantum chemical studies, which allowed the pathways to all radioproducts to be rationalized. In contrast to ISdU solutions, where radiolysis leads to 4-thio-2'-deoxyuridine and its dimer, no dissociative electron attachment (DEA) products were observed for BrSdU. This observation seems to explain the lack of radiosensitizing properties of BrSdU since the efficient formation of the uridine-5-yl radical, induced by electron attachment to the modified nucleoside, is suggested to be an indispensable attribute of radiosensitizing uridines. A larger activation barrier for DEA in BrSdU, as compared to ISdU, is probably responsible for the closure of DEA channel in the former system. Indeed, besides DEA, the XSdU anions may undergo competitive protonation, which makes the release of X- kinetically forbidden.

5-Bromo-2'-deoxycytidine-a potential DNA photosensitizer.

A double-stranded oligonucleotide, 80 base pairs in length, was multiply labeled with 5-bromo-2'-deoxycytidine (BrdC) using polymerase chain reaction (PCR). The modified oligonucleotide was irradiated with 300 nm photons and its damage was assayed by employing DHPLC, LC-MS and denaturing polyacrylamide gel electrophoresis (PAGE). Two types of damage were demonstrated, namely, single strand breaks (SSBs) and intrastrand cross-links (ICLs); the ICLs were in the form of d(G^C) and d(C^C) dimers. The former species are probably formed due to photoinduced electron transfer between the photoexcited BrdC and the ground state 2'-deoxyguanosine (dG), whereas the latter is a result of a cycloaddition reaction. Since SSBs and ICLs are potentially lethal to the cell, BrdC could be considered as a nucleoside with possible clinical applications.

5-Thiocyanato-2'-deoxyuridine as a possible radiosensitizer: electron-induced formation of uracil-C5-thiyl radical and its dimerization.

In this work, we have synthesized 5-thiocyanato-2'-deoxyuridine (SCNdU) along with the C6-deuterated nucleobase 5-thiocyanatouracil (6-D-SCNU) and studied their reactions with radiation-produced electrons. ESR spectra in γ-irradiated nitrogen-saturated frozen homogeneous solutions (7.5 M LiCl in H2O or D2O) of these compounds show that electron-induced S-CN bond cleavage occurs to form a thiyl radical (dU-5-S˙ or 6-D-U-5-S˙) and CN(-)via the initial π-anion radical (SCNdU˙(-)) intermediate in which the excess electron is on the uracil base. HPLC and LC-MS/MS studies of γ-irradiated N2-saturated aqueous solutions of SCNdU in the presence of sodium formate as a OH-radical scavenger at ambient temperature show the formation of the dU-5S-5S-dU dimer in preference to dU by about 10 to 1 ratio. This shows that both possible routes of electron-induced bond cleavage (dUC5-SCN and S-CN) in SCNdU˙(-) and dU-5-S˙ formation are preferred for the production of the σ-type uracilyl radical (dU˙) by 10 fold. DFT/M06-2x/6-31++G(d,p) calculations employing the polarizable continuum model (PCM) for aqueous solutions show that dU-5-S˙ and CN(-) formation was thermodynamically favored by over 15 kcal mol(-1) (ΔG) compared to dU˙ and SCN(-) production. The activation barriers for C5-S and S-CN bond cleavage in SCNdU˙(-) amount to 8.7 and 4.0 kcal mol(-1), respectively, favoring dU-5-S˙ and CN(-) formation. These results support the experimental observation of S-CN bond cleavage by electron addition to SCNdU that results in the formation of dU-5-S˙ and the subsequent dU-5S-5S-dU dimer. This establishes SCNdU as a potential radiosensitizer that could cause intra- and inter-strand crosslinking as well as DNA-protein crosslinking via S-S dimer formation.

Surprising Radiolytic Stability of 8-Thiomethyladenine in an Aqueous Solution.

8-Thiomethyladenine (ASCH3), a potentially radiosensitizing modified nucleobase, has been synthesized in a reaction between 8-thioadenine and methyl iodide. Despite favorable dissociative electron attachment (DEA) characteristics, the radiolysis of an aqueous solution of ASCH3 with a dose of X-ray amounting to as much as 300 Gy leads to no effects. Nevertheless, crossed electron-molecule beam experiments in the gas phase on ASCH3 confirm the theoretical findings regarding the stability of its radical anion, namely, the most abundant reaction channel is related to the dissociation of the S-CH3 bond in the respective anion. Furthermore, electron-induced degradation of ASCH3 has been observed in aprotic acetonitrile, which is strong evidence for the involvement of proton transfer (PT) in stabilizing the radical anion in an aqueous solution. These findings demonstrate that PT in water can be the main player in deciding the radiosensitizing properties of modified nucleobases/nucleosides.

Why 6-Iodouridine Cannot Be Used as a Radiosensitizer of DNA Damage? Computational and Experimental Studies.

Previous density functional theory (DFT) studies on 6-brominated pyrimidine nucleosides suggest that 6-iodo-2'-deoxyuridine (6IdU) should act as a better radiosensitizer than its 5-iodosubstituted 2'-deoxyuridine analogue. In this work, we show that 6IdU is unstable in an aqueous solution. Indeed, a complete disappearance of the 6IdU signal was observed during its isolation by reversed-phase high-performance liquid chromatography (RP-HPLC). As indicated by the thermodynamic characteristics for the SN1-type hydrolysis of 6IdU obtained at the CAM-B3LYP/DGDZVP++ level and the polarizable continuum model (PCM) of water, 6-iodouracil (6IU) was already released quantitatively at ambient temperatures. The simulation of the hydrolysis kinetics demonstrated that a thermodynamic equilibrium was reached within seconds for the title compound. To assess the reliability of the calculations carried out, we synthesized 6-iodouridine (6IUrd), which was, unlike 6IdU, sufficiently stable in an aqueous solution at room temperature. The activation barrier for the N-glycosidic bond dissociation in 6IUrd was estimated experimentally using an Arrhenius plot. The stabilities in water calculated for 6IdU, 6IUrd, and 5-iodo-2'-deoxyuridine (5IdU) could be explained by the electronic and steric effects of the 2'-hydroxy group present in the ribose moiety. Our studies highlight the issue of the hydrolytic stability of potentially radiosensitizing nucleotides which, besides having favorable dissociative electron attachment (DEA) characteristics, must be stable in water to have any practical application.

Implications of albumin in cell culture media on the biological action of vanadates(V).

In this article, the implications of binding competition of vanadates(V) with dodecyl sulfates for bovine serum albumin on cytotoxicity of vanadium(V) species against prostate cancer cells have been investigated. The pH- and SDS-dependent vanadate(V)-BSA interactions were observed. At pH 5, there is only one site capable of binding ten vanadates(V) ions (logK(ITC)1 = 4.96 ± 0.06; ΔH(ITC)1 = -1.04 ± 0.03 kcal mol-1), whereas at pH 7 two distinctive binding sites on protein were found, saturated with two and seven V(V) ions, respectively (logK(ITC)1 = 6.11 ± 0.06; ΔH(ITC)1 = 0.78 ± 0.12 kcal mol-1; logK(ITC)2 = 4.80 ± 0.02; ΔH(ITC)2 = - 4.95 ± 0.14 kcal mol-1). SDS influences the stoichiometry and the stability of the resulting V(V)-BSA complexes. Finally, the cytotoxicity of vanadates(V) against prostate cancer cells (PC3 line) was examined in the presence and absence of SDS in the culture medium. In the case of a 24-h incubation with 100 µM vanadate(V), a ca. 20 % reduction in viability of PC3 cells was observed in the presence of SDS. However, in other considered cases (various concentrations and time of incubation) SDS does not affect the dose-dependent action of vanadates(V) on the investigated prostate cancer cells.

Radiosensitization of PC3 Prostate Cancer Cells by 5-Thiocyanato-2'-deoxyuridine.

PURPOSE: The radiosensitizing properties of uracil analogs modified in the C5 position are very interesting in the context of their effectiveness and safety in radiation therapy. Recently, radiation chemical studies have confirmed that 5-thiocyanato-2'-deoxyuridine (SCNdU) undergoes dissociation induced by an excess electron attachment and established this nucleoside as a potential radiosensitizer. In this paper, we verify the sensitizing properties of SCNdU at the cellular level and prove that it can effectively enhance ionizing radiation-induced cellular death. METHODS AND MATERIALS: Prostate cancer cells were treated with SCNdU and irradiated with X rays. The cytotoxicity of SCNdU was determined by MTT test. Cell proliferation was assessed using a clonogenic assay. Cell cycle analyses, DNA damage, and cell death analyses were performed by flow cytometry. RESULTS: SCNdU treatment significantly suppressed the proliferation and increased the radiosensitivity of prostate cancer cells. The radiosensitizing effect expressed by the dose enhancement factor is equal to 1.69. Simultaneous exposure of cells to SCNdU and radiation causes an increase in the fraction of the most radiosensitive G2/M phase, enhancement of the histone H2A.X phosphorylation level, and apoptosis induction. Finally, SCNdU turned out to be marginally cytotoxic in the absence of ionizing radiation. CONCLUSIONS: Our findings indicate that SCNdU treatment enhances the radiosensitivity of prostate cancer cells in a manner associated with the cell cycle regulation, double strand formation, and a slight induction of apoptosis.

2,6-diaminopurine promotes repair of DNA lesions under prebiotic conditions.

High-yielding and selective prebiotic syntheses of RNA and DNA nucleotides involve UV irradiation to promote the key reaction steps and eradicate biologically irrelevant isomers. While these syntheses were likely enabled by UV-rich prebiotic environment, UV-induced formation of photodamages in polymeric nucleic acids, such as cyclobutane pyrimidine dimers (CPDs), remains the key unresolved issue for the origins of RNA and DNA on Earth. Here, we demonstrate that substitution of adenine with 2,6-diaminopurine enables repair of CPDs with yields reaching 92%. This substantial self-repairing activity originates from excellent electron donating properties of 2,6-diaminopurine in nucleic acid strands. We also show that the deoxyribonucleosides of 2,6-diaminopurine and adenine can be formed under the same prebiotic conditions. Considering that 2,6-diaminopurine was previously shown to increase the rate of nonenzymatic RNA replication, this nucleobase could have played critical roles in the formation of functional and photostable RNA/DNA oligomers in UV-rich prebiotic environments.

Uracil-5-yl O-Sulfamate: An Illusive Radiosensitizer. Pitfalls in Modeling the Radiosensitizing Derivatives of Nucleobases.

Efficient radiotherapy requires the concomitant use of ionizing radiation (IR) and a radiosensitizer. In the present work uracil-5-yl O-sulfamate (SU) is tested against its radiosensitizing potential. The compound possesses appropriate dissociative electron attachment (DEA) characteristics calculated at the M06-2X/6-31++G(d,p) level. Crossed electron-molecular beam experiments in the gas phase demonstrate that SU undergoes efficient DEA processes, and the single C-O or S-O bond dissociations account for the majority of fragments induced by electron attachment. Most DEAs proceed already for electrons with kinetic energies of ∼0 eV, which is supported by the exothermic thresholds calculated at the M06-2X/aug-cc-pVTZ level. However, in water solution under reductive conditions and physiological pH, SU does not undergo radiolysis, which demonstrates the crucial influence of aqueous environment on the radiosensitizing properties of modified nucleosides.

5-Selenocyanato and 5-trifluoromethanesulfonyl derivatives of 2'-deoxyuridine: synthesis, radiation and computational chemistry as well as cytotoxicity.

5-Selenocyanato-2'-deoxyuridine (SeCNdU) and 5-trifluoromethanesulfonyl-2'-deoxyuridine (OTfdU) have been synthesized and their structures have been confirmed with NMR and MS methods. Both compounds undergo dissociative electron attachment (DEA) when irradiated with X-rays in an aqueous solution containing a hydroxyl radical scavenger. The DEA yield of SeCNdU significantly exceeds that of 5-bromo-2'-deoxyuridine (BrdU), remaining in good agreement with the computationally revealed profile of electron-induced degradation. The radiolysis products indicate, in line with theoretical predictions, Se-CN bond dissociation as the main reaction channel. On the other hand, the DEA yield for OTfdU is slightly lower than the degradation yield measured for BrdU, despite the fact that the calculated driving force for the electron-induced OTfdU dissociation substantially overpasses the thermodynamic stimulus for BrdU degradation. Moreover, the calculated DEA profile suggests that the electron attachment induced formation of 5-hydroxy-2'-deoxyuridine (OHdU) from OTfdU, while 2'-deoxyuridine (dU) is mainly observed experimentally. We explained this discrepancy in terms of the increased acidity of OTfdU resulting in efficient deprotonation of the N3 atom, which brings about the domination of the OTfdU(N3-H)- anion in the equilibrium mixture. As a consequence, electron addition chiefly leads to the radical dianion, OTfdU(N3-H)˙2-, which easily protonates at the C5 site. As a result, the C5-O rather than O-S bond undergoes dissociation, leading to dU, observed experimentally. A negligible cytotoxicity of the studied compounds toward the MCF-7 cell line at the concentrations used for cell labelling calls for further studies aiming at the clinical use of the proposed derivatives.