The five nucleobases - adenine, thymine, guanine, cytosine and uracil - and their derivatives are compounds of great physiological importance. They are structural components of nucleic acids and many substances such as nucleotides and nucleosides.

Due to increased proliferation of cancer cells production and degradation of nucleic acids is much faster in the oncological patients than in the healthy individuals resulting in elevated concentration of nucleobase derivatives in urine. Therefore, these substances, primarily modified nucleosides, may be used as urinary biomarkers to diagnose many pathologies, e.g. severe combined immunodeficiency (SCID), fetal alcohol spectrum disorders (FASD), and many types of cancer, including breast, kidney, uterus, prostate, large intestine, lungs, liver, brain, and blood (leukemia). The level of modified urinary nucleosides also correlates with the progress of cancer. Nucleobase-containing compounds can be also biomarkers of metabolic processes. For example, adenosine triphosphate (ATP) and other adenine-containing compounds play a significant role in the regulation of coronary blood flow, metabolism of heart, and other functions which maintain the homeostasis of the cardiovascular system. ATP is a sensitive biomarker of myocardial ischemia and may be used for monitoring the therapeutic effects of drugs.

Goals of the research

The major difficulty in the application of nucleobases and their derivatives as biomarkers is their identification and quantification which is due to their variety, low concentration and complexity of the composition of body fluids. The selective adsorption of nucleosides (based on the nucleobase they contain) from the fluid (e.g. from urine) and the application of a sufficiently sensitive sensor could greatly simplify the analysis of the samples. The goal of the research was therefore to develop materials enabling both selective adsorption and sensing of the nucleobase derivatives. To achieve selective adsorption of the compounds containing adenine as cancer biomarkers we applied the molecularly imprinted polymers (MIPs) functionalized with thymine so that they could selectively complex adenine, which constitutes a part of the structure of the analyzed compound. This complexation results from the formation of two hydrogen bonds between thymine and adenine, which complementary bases (Watson-Crick pairing). On the other hand, for sensing the adenine-containing compounds fluorescent CdTe quantum dots (QDs) functionalized with thymine were devised with the assumption that the interaction between thymine on the surface of QDs with adenyl group of the compound affected the intensity of QD fluorescence.

 

Results of the research

We have synthesized a series of polymers containing thymine moieties, which formed hydrogen bonds with adenine. This interaction, which is also present in the structure of nucleic acids, is very selective, i.e., the interactions of thymine with other nucleobases are much weaker. Thus, thymine-containing polymers were able to selectively complex and thereby adsorb adenine and its derivatives such as ATP, adenosine, 2’‐deoxyadenosine (2'-dA), and 5’-Deoxy-5’-methylthioadenosine (MTA). To enhance the selective adsorption of adenine the polymers were molecularly imprinted with adenine as a template taking advantage of the fact that thymine, except for its ability to bind adenine, also has a unique property to undergo dimerization when irradiated with UV light (ca. 360 nm). Therefore, irradiation of the thymylated polymer resulted in thymine photodimerization and consequently to the crosslinking of the polymer. If the irradiation of the polymer was performed in the presence of complexed adenine or its derivative as a template, a polymeric matrix was formed (photo)imprinted with adenine (compound). Upon removal of the template, the polymeric matrix could selectively adsorb adenine (derivatives). To increase the surface of the matrix the polymers were supported onto silicagel microspheres (about 700 µm in diameter). The hybrid adsorbents thus obtained could selectively adsorb ATP (in the presence of other nucleotides), adenosine (in the presence of other nucleosides)

Collaboration

Prof.Em. Yotaro Morishima, Fukui University of Technology, Fukui, Japan

Prof. Shin-Ichi Yusa, University of Hyogo, Department of Applied Chemistry, Graduate School of Engineering, Kobe, Japan