Milena Sobczak
Polish Academy of Sciences
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Featured researches published by Milena Sobczak.
Nucleic Acids Research | 2015
Elzbieta Sochacka; Roman H. Szczepanowski; Marek Cypryk; Milena Sobczak; Magdalena Janicka; Karina Kraszewska; Paulina Bartos; Anna Chwialkowska; Barbara Nawrot
2-Thiouracil-containing nucleosides are essential modified units of natural and synthetic nucleic acids. In particular, the 5-substituted-2-thiouridines (S2Us) present in tRNA play an important role in tuning the translation process through codon–anticodon interactions. The enhanced thermodynamic stability of S2U-containing RNA duplexes and the preferred S2U-A versus S2U-G base pairing are appreciated characteristics of S2U-modified molecular probes. Recently, we have demonstrated that 2-thiouridine (alone or within an RNA chain) is predominantly transformed under oxidative stress conditions to 4-pyrimidinone riboside (H2U) and not to uridine. Due to the important biological functions and various biotechnological applications for sulfur-containing nucleic acids, we compared the thermodynamic stabilities of duplexes containing desulfured products with those of 2-thiouracil-modified RNA and DNA duplexes. Differential scanning calorimetry experiments and theoretical calculations demonstrate that upon 2-thiouracil desulfuration to 4-pyrimidinone, the preferred base pairing of S2U with adenosine is lost, with preferred base pairing with guanosine observed instead. Therefore, biological processes and in vitro assays in which oxidative desulfuration of 2-thiouracil-containing components occurs may be altered. Moreover, we propose that the H2U-G base pair is a suitable model for investigation of the preferred recognition of 3′-G-ending versus A-ending codons by tRNA wobble nucleosides, which may adopt a 4-pyrimidinone-type structural motif.
Bioconjugate Chemistry | 2013
Alina Kwiatkowska; Milena Sobczak; Barbara Mikołajczyk; Slawomir Janczak; Agnieszka B. Olejniczak; Marek Sochacki; Barbara Nawrot
RNA interference (RNAi) technology provides a powerful, yet selective, molecular tool to reduce the expression of genes in eukaryotic cells. Despite the success associated with the effective use of siRNA duplexes for gene silencing, there is a need to improve their properties. These properties, related mainly to migration through the cell membranes, stability of siRNA in vivo, and specificity of their silencing activity, can be improved by chemical modifications of siRNA backbone. In this study, we examined the physicochemical and biological properties of siRNA duplexes targeted against BACE1 gene modified at various positions with a lipophilic boron cluster (C2B10H11, CB). The lipophilicity and resistance to enzymatic degradation of the modified oligomers was higher than the unmodified counterparts. As measured in a dual fluorescence assay (BACE1-GFP/RFP), the carboranyl siRNAs (CB-siRNAs) were as active as the parent nonmodified duplexes and their toxicity toward HeLa cells was also similar. The helical structure of CB-siRNAs remained unchanged upon boron cluster introduction, as determined by CD and UV melting experiments.
New Journal of Chemistry | 2010
Malgorzata Sierant; Milena Sobczak; Magdalena Janicka; Alina Paduszynska; Danuta Piotrzkowska
The use of synthetic short interfering RNAs (siRNAs) is currently a method of choice to manipulate gene expression in mammalian cells. Efforts aimed at improving siRNA biological activity, including increased silencing properties, higher substrate specificity and cellular stability, lower cytotoxicity, and improved target delivery, have been made through the introduction of various chemical modifications into the siRNA strands. In these studies, we present the synthesis of oligoribonucleotides with the single replacement of a cytidine unit for 2′,2′-difluoro-2′-deoxycytidine (gemcitabine, dFdC) and the use of them in a series of siRNAs for gene silencing experiments. The dFdC modifications are located in six different positions of the antisense strand, which are crucial for siRNA silencing activity. The results indicate a position-dependent tolerance for the dFdC modification. Gemcitabine units present in the “seed region”, at positions 1 or 8, resulted in only a ∼15% silencing activity in the corresponding duplexes. The dFdC unit at position 10 virtually switched off the silencing activity (below 10%), while the dFdC unit at the positions 2, 4 or 5 produced duplexes of silencing potential comparable to that of the non-modified duplex (70% silencing). The dFdC modification had little impact on the structure of the siRNA duplexes, as determined by circular dichroism analysis, while melting experiments showed their lower thermal stability.
Molecules | 2017
Damian Kaniowski; Katarzyna Ebenryter-Olbińska; Milena Sobczak; Blazej A. Wojtczak; Slawomir Janczak; Zbigniew J. Leśnikowski; Barbara Nawrot
Boron cluster-modified therapeutic nucleic acids with improved properties are of interest in gene therapy and in cancer boron neutron capture therapy (BNCT). High metallacarborane-loaded antisense oligonucleotides (ASOs) targeting epidermal growth factor receptor (EGFR) were synthesized through post-synthetic Cu (I)-assisted “click” conjugation of alkyne-modified DNA-oligonucleotides with a boron cluster alkyl azide component. The obtained oligomers exhibited increased lipophilicity compared to their non-modified precursors, while their binding affinity to complementary DNA and RNA strands was slightly decreased. Multiple metallacarborane residues present in the oligonucleotide chain, each containing 18 B-H groups, enabled the use of IR spectroscopy as a convenient analytical method for these oligomers based on the diagnostic B-H signal at 2400–2650 cm−1. The silencing activity of boron cluster-modified ASOs used at higher concentrations was similar to that of unmodified oligonucleotides. The screened ASOs, when used in low concentrations (up to 50 μM), exhibited pro-oxidative properties by inducing ROS production and an increase in mitochondrial activities in HeLa cells. In contrast, when used at higher concentrations, the ASOs exhibited anti-oxidative properties by lowering ROS species levels. In the HeLa cells (tested in the MTT assay) treated (without lipofectamine) or transfected with the screened compounds, the mitochondrial activity remained equal to the control level or only slightly changed (±30%). These findings may be useful in the design of dual-action boron cluster-modified therapeutic nucleic acids with combined antisense and anti-oxidant properties.
Bioorganic & Medicinal Chemistry Letters | 2015
Anna Chwialkowska; Ewelina Wielgus; Grazyna Leszczynska; Milena Sobczak; Barbara Mikołajczyk; Elzbieta Sochacka; Barbara Nawrot
An efficient approach for the desulfuration of C5-substituted 2-thiouridines (R5S2U) bound in the RNA chain exclusively to 4-pyrimidinone nucleoside (R5H2U)-containing RNA products is proposed. This post-synthetic transformation avoids the preparation of a suitably protected H2U phosphoramidite, which otherwise would be necessary for solid-phase synthesis of the modified RNA. Optimization of the desulfuration, which included reaction stoichiometry, time and temperature, allowed to transform a set of ten R5S2U-RNAs into their R5H2U-RNA congeners in ca. 90% yield.
Nucleosides, Nucleotides & Nucleic Acids | 2017
Rafał Dolot; Milena Sobczak; Barbara Mikołajczyk; Barbara Nawrot
ABSTRACT A 52-nucleotide DNA/2′-OMe-RNA oligomer mimicking 10–23 DNAzyme in the complex with its substrate was synthesized, purified and crystallized by the hanging-drop method using 0.8 M sodium potassium tartrate as a precipitant. A data set to 1.21 Å resolution was collected from a monocrystal at 100 K using synchrotron radiation on a beamline BL14.1 at BESSY. The crystal belonged to the P21 group with unit-cell a = 49.42, b = 24.69, c = 50.23, β = 118.48.
ChemBioChem | 2018
Malgorzata Sierant; Katarzyna Kulik; Elzbieta Sochacka; Rafał Szewczyk; Milena Sobczak; Barbara Nawrot
The 5‐substituted 2‐thiouridines (R5S2Us) present in the first (wobble) position of the anticodon of transfer RNAs (tRNAs) contribute to accuracy in reading mRNA codons and tuning protein synthesis. Previously, we showed that, under oxidative stress conditions in vitro, R5S2Us were sensitive to hydrogen peroxide (H2O2) and that their oxidative desulfuration produced 5‐substituted uridines (R5Us) and 4‐pyrimidinone nucleosides (R5H2Us) at a ratio that depended on the pH and an R5 substituent. Here, we demonstrate that the desulfuration of 2‐thiouridines, either alone or within an RNA/tRNA chain, is catalyzed by cytochrome c (cyt c). Its kinetics are similar to those of Fenton‐type catalytic 2‐thiouridine (S2U) desulfuration. Cyt c/H2O2‐ and FeII‐mediated reactions deliver predominantly 4‐pyrimidinone nucleoside (H2U)‐type products. The pathway of the cyt c/H2O2‐peroxidase‐mediated S2U→H2U transformation through uridine sulfenic (U‐SOH), sulfinic (U‐SO2H), and sulfonic (U‐SO3H) intermediates is confirmed by LC–MS. The cyt c/H2O2‐mediated oxidative damage of S2U‐tRNA may have biological relevance through alteration of the cellular functions of transfer RNA.
Current Organic Chemistry | 2008
Barbara Nawrot; Kinga Widera; Milena Sobczak; Marzena Wojcik; Wojciech J. Stec
Chemical Communications | 2011
Elzbieta Sochacka; Karina Kraszewska; Marek Sochacki; Milena Sobczak; Magdalena Janicka; Barbara Nawrot
Organic and Biomolecular Chemistry | 2015
Anna Maciaszek; Agnieszka Krakowiak; Magdalena Janicka; Agnieszka Tomaszewska-Antczak; Milena Sobczak; Barbara Mikołajczyk; Piotr Guga