Alexander V. Chudinov

Fluorescence Data Analysis on Gel-Based Biochips

A series of biochip readers developed for gel-based biochips includes three imaging models and a novel nonimaging biochip scanner. The imaging readers, ranging from a research-grade versatile reader to a simple portable one, use wide-field objectives and 12-bit digital large-coupled device cameras for parallel addressing of multiple array elements. This feature is valuable for monitoring the kinetics of sample interaction with immobilized probes. Depending on the model and the label used, the sensitivity of these readers approaches 0.3 amol of a labeled sample per gel element. In the selective scanner, both the spot size of the excitation laser beam and the detector field of view match the size of the biochip array elements so that the whole row of the array can be read in a single scan. The portable version reads 50-mm long, 150-element, one-dimensional arrays in 5 s. With a dynamic range of 4000:1, a sensitivity of 1-5 amol of a labeled sample per gel element, and a data format facilitating online processing, the scanner is an attractive, inexpensive solution for biomedical diagnostics. Fluorophores for sample labeling were compared experimentally in terms of detection sensitivity, influence on duplex stability, and suitability for multilabel analysis and thermodynamic studies. Texas Red and tetracarboxyphenylporphyn proved to be the best choice for two-wavelength analysis using the imaging readers.

Rapid genotyping of common deficient thiopurine S-methyltransferase alleles using the DNA-microchip technique

Thiopurine drugs are metabolized, in part, by S-methylation catalyzed by thiopurine S-methyltransferase (TPMT). Patients with very low or undetectable TPMT activity are at high risk of severe, potentially fatal hematopoietic toxicity when they are treated with standard doses of thiopurines. As human TPMT activity is controlled by a common genetic polymorphism, it is an excellent candidate for the clinical application of pharmacogenetics. Here, we report a new molecular approach developed to detect point mutations in the TPMT gene that cause the loss of TPMT activity. A fluorescently labeled amplified DNA is hybridized with oligonucleotide DNA probes immobilized in gel pads on a biochip. The specially designed TPMT biochip can recognize six point mutations in the TPMT gene and seven corresponding alleles associated with TPMT deficiency: TPMT*2; TPMT*3A, TPMT*3B, TPMT*3C, TPMT*3D, TPMT*7, and TPMT*8. The effectiveness of the protocol was tested by genotyping 58 samples of known genotype. The results showed 100% concordance between the biochip-based approach and the established PCR protocol. The genotyping procedure is fast, reliable and can be used for rapid screening of inactivating mutations in the TPMT gene. The study also provides the first data on the frequency of common TPMT variant alleles in the Russian population, based on a biochip analysis of 700 samples. TPMT gene mutations were identified in 44 subjects; genotype *1/*3A was most frequent.

Development of a Biochip for Analyzing Polymorphism of the Biotransformation Genes

Large-scale population studies, diagnosis of genetic predisposition to a broad range of multifactorial diseases, and screening of polymorphic loci associated with individual drug resistance need efficient, accurate, and rapid techniques for identifying many mutations. One of the most promising techniques is hybridization on an oligonucleotide microarray (biochip). The efficiency of this method in assessing genetic polymorphism was demonstrated using an example of mutations in CYP1A1, CYP2D6, GSTM1, GSTT1, NAT2, CYP2C9, CYP2C19, and MTHFR. The biochip constructed provides a convenient tool for pharmacogenetic research.

Gel-based microarrays in clinical diagnostics in Russia

Immobilization of molecular probes in 3D hydrogel elements provides some essential advantages compared with conventional flat surfaces. In this article, an integrated technology based on the use of low-density microarrays comprised of hemispherical gel elements, developed at the Engelhardt Institute of Molecular Biology (Moscow, Russia) for various applications will be reviewed. The structure of the gel can be adapted for immobilization of virtually any biological molecules in a natural hydrophilic environment. The discrimination between matching and mismatching duplexes of nucleic acids in these conditions is more reliable than on conventional flat surfaces, minimizing the number of elements needed to detect specific sequences. Protein molecules immobilized in hydrogel-based biochips better preserve their biological properties. As described in this article, such biochips were successfully applied for laboratory diagnostics in a wide variety of clinical conditions involving the identification of bacterial and viral pathogens, cancer-related mutations and protein tumor markers.

Targeting duplex DNA with chimeric α,β-triplex-forming oligonucleotides

Triplex-directed DNA recognition is strictly limited by polypurine sequences. In an attempt to address this problem with synthetic biology tools, we designed a panel of short chimeric α,β-triplex-forming oligonucleotides (TFOs) and studied their interaction with fluorescently labelled duplex hairpins using various techniques. The hybridization of hairpin with an array of chimeric probes suggests that recognition of double-stranded DNA follows complicated rules combining reversed Hoogsteen and non-canonical homologous hydrogen bonding. In the presence of magnesium ions, chimeric TFOs are able to form highly stable α,β-triplexes, as indicated by native gel-electrophoresis, on-array thermal denaturation and fluorescence-quenching experiments. CD spectra of chimeric triplexes exhibited features typically observed for anti-parallel purine triplexes with a GA or GT third strand. The high potential of chimeric α,β-TFOs in targeting double-stranded DNA was demonstrated in the EcoRI endonuclease protection assay. In this paper, we report, for the first time, the recognition of base pair inversions in a duplex by chimeric TFOs containing α-thymidine and α-deoxyguanosine.

Alginate gel biochip for real-time monitoring of intracellular processes in bacterial and yeast cells

A method was developed for producing cell biochips on the basis of calcium alginate. Cell immobilization in microvolumes of nontoxic alginate gel under mild conditions extended the range of testable micro-organisms. The possibility of studying the intracellular processes with alginate gel biochips was demonstrated in model experiments with Escherichia coli, Bordetella bronchiseptica, and Saccharomyces cerevisiae. Cell biochips proved to be suitable for simultaneous monitoring of nucleic acid and protein syntheses with two fluorescent dyes. The effect of chloramphenicol on nucleic acid synthesis was studied with five bacterial strains. Inducible synthesis of the green fluorescence protein (EGFP) in E. coli cells was monitored with the use of biochips. The level of EGFP synthesis correlated with the inductor concentration in the medium.

Simple and Stereoselective Preparation of an 4‐(Aminomethyl)‐1,2,3‐triazolyl Nucleoside Phosphoramidite

A simple and stereoselective synthesis of a protected 4‐(aminomethyl)‐1‐(2‐deoxy‐β‐D‐ribofuranosyl)‐1,2,3‐triazole cyanoethyl phosphoramidite was developed for the modification of synthetic oligonucleotides. The configuration of the 1,2,3‐triazolyl moiety with respect to the deoxyribose was unambiguously determined in ROESY experiments. The aminomethyl group of the triazolyl nucleotide was fully functional in labelling reactions. Furthermore, the hybridization behavior of 5′ triazole‐terminated oligonucleotide was similar to that of 5′ aminohexyl‐terminated oligomer with the same sequence. Internal modifications of the oligonucleotide strands resulted in significant decrease of duplex stability.

Gel-based oligonucleotide microarray approach to analyze protein–ssDNA binding specificity

Gel-based oligonucleotide microarray approach was developed for quantitative profiling of binding affinity of a protein to single-stranded DNA (ssDNA). To demonstrate additional capabilities of this method, we analyzed the binding specificity of ribonuclease (RNase) binase from Bacillus intermedius (EC 3.1.27.3) to ssDNA using generic hexamer oligodeoxyribonucleotide microchip. Single-stranded octamer oligonucleotides were immobilized within 3D hemispherical gel pads. The octanucleotides in individual pads 5′-{N}N1N2N3N4N5N6{N}-3′ consisted of a fixed hexamer motif N1N2N3N4N5N6 in the middle and variable parts {N} at the ends, where {N} represent A, C, G and T in equal proportions. The chip has 4096 pads with a complete set of hexamer sequences. The affinity was determined by measuring dissociation of the RNase–ssDNA complexes with the temperature increasing from 0°C to 50°C in quasi-equilibrium conditions. RNase binase showed the highest sequence-specificity of binding to motifs 5′-NNG(A/T/C)GNN-3′ with the order of preference: GAG > GTG > GCG. High specificity towards G(A/T/C)G triplets was also confirmed by measuring fluorescent anisotropy of complexes of binase with selected oligodeoxyribonucleotides in solution. The affinity of RNase binase to other 3-nt sequences was also ranked. These results demonstrate the applicability of the method and provide the ground for further investigations of nonenzymatic functions of RNases.

Kinetic effects on signal normalization in oligonucleotide microchips with labeled immobilized probes.

Abstract Among various factors affecting operation of oligonucleotide microchips, the variations in concentration and in homogeneous distribution of immobilized probes over the cells are one of the most important. The labeling of immobilized probes ensures the complete current monitoring on the probe distribution and is reliable and convenient. Using hydrogel-based oligonucleotide microchips, the applicability of Cy3-labeled immobilized probes for quality control and signal normalization after hybridization with Cy5-labeled target DNA was investigated. This study showed that proper signal normalization should be different in thermodynamic conditions and in transient regime with hybridization far from saturation. This kinetic effect holds for both hydrogel-based and surface oligonucleotide microchips. Besides proving basic features, the technique was assessed on a sampling batch of 50 microchips developed for identifying mutations responsible for rifampicin and isoniazid resistance of Mycobacterium tuberculosis.

Microarray with LNA-probes for genotyping of polymorphic variants of Gilbert’s syndrome gene UGT1A1(TA)n

Abstract Background: Gilbert’s syndrome is a common metabolic dysfunction characterized by elevated levels of unconjugated bilirubin in the bloodstream. This condition is usually caused by additional (TA) insertions in a promoter region of the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene, which instead of the sequence А(TА)6TАА contains А(TА)7TАА. While the condition itself is benign, it presents elevated risk for patients treated with irinotecan, a common chemotherapy drug. Methods: The technique is based on hybridization analysis of a pre-amplified segment of the UGT1A1 gene promoter performed on a microarray. Specific probes containing locked nucleic acids (LNA) were designed and immobilized on the microarray to provide accurate identification. Results: A microarray has been developed to identify both common and rare variants of UGT1A1(TA)n polymorphisms. In total, 108 individuals were genotyped. Out of these, 47 (43.5%) had homozygous wild-type genotypes (TA)6/(TA)6; 41(38%) were heterozygotes (TA)6/(TA)7; and 18 (16.7%) – homozygotes (TA)7/(TA)7. In two cases (1.8%), rare genotypes (TA)5/(TA)7and (TA)5/(TA)6were found. The results were in full agreement with the sequencing. In addition, synthetic fragments corresponding to all human allelic variants [(TA)5, (TA)6, (TA)7, (TA)8] were successfully tested. Conclusions: The developed microarray-based approach for identification of polymorphic variants of the UGT1A1 gene is a promising and reliable diagnostic tool that can be successfully implemented in clinical practice.