Studies of Hematologic Malignancies by PNA Technology

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The project goal is a robust assay for detecting episomal or genome- integrated oncoviral DNAs in hematologic malignancies. Considering a limited amount of viral DNA, both high specificity and high sensitivity of DNA diagnostics are required. To reach high specificity, a synthetic DNA mimic, peptide nucleic acid (PNA), will be used for sequence- selective formation of PD-loops in double-stranded (ds) DNA targets. High sensitivity will be provided by rolling-circle amplification (RCA), a powerful contamination-immune isothermal method. Large multiplexing capacity intrinsic in RCA enables mutation-insensitive parallel detection of different oncoviruses. EBV and HHV-8 herpesviruses and HTLV-1 retrovirus will be prototype oncoviruses. Their genomes have PD-loop forming sites (PD-sites) that are unique and very constant. These features make PD-sites promising viral markers, which have never been used before in DNA diagnostics. The assay to be developed includes three steps. First, an oligonucleotide probe hybridizes to dsDNA through PD-loops with subsequent probe circularization. This step, assisted by viral-specific PNA openers, is mostly responsible for the overall specificity of the assay. Secondly, the RCA hyperamplification of circular probes at a single temperature yields the dsDNA product in which the original PD-site repeats more than million times. This step will provide requisite sensitivity. Finally, thus multiply copied PD-sites will be selectively exposed by PNA openers and fluorescently detected with molecular beacons. The last step provides a convenient detection and additionally secures the specificity of the assay. Choice of various PD-sites as markers, together with multiplex RCA and multicolor beacons, will ensure reliable diagnosis of several specific oncoviruses. In Phase I, proof-of-principle experiments will be performed on a model system comparable to Phase II samples. The goal is to detect, after initial optimization, the PD-site in a hundred-fold molar excess over 1 mu g of human DNA. These studies will prove that episomal oncoviruses can be characterized in acute blood infections. In Phase II, the assay will be developed for detecting oncoviruses in cell lines and clinical samples with different viral loads. Detection of selected oncoviral marker PD- sites will be optimized using plasmid models to further increase the sensitivity on the excessive human DNA background. The yield and the specificity of the circular probe assembly will be optimized for different configurations of PD-loops. RCA will be optimized using various DNA polymerases and amplification strategies. Optimal conditions and constructions of beacons in terms of their hybridization kinetics with PD-sites will be thoroughly searched. As a result, detection of less than one oncovirus per human genome is projected, which will be tested on DNA samples from oncoviral-infected cell lines and, finally, on clinical specimens. The success in the project will yield a fluorescent assay for a reliable and highly sensitive isothermal diagnosis of oncoviruses in lymphomas/leukemias. It will allow fool roof characterization of malignant samples by detecting viral DNA in a very low number of copies like in case of provirus.