Telomeres are present at the ends of all eukaryotic chromosomes. Human telomeres play an important role in critical processes underlying genome stability, cancer, and aging, and their importance was recognized via the award of the 2009 Nobel Prize in Physiology or Medicine.The telomeric overhang DNA is also a substrate for telomerase, which elongates telomeric sequence by adding G-rich repeats. Telomerase is activated in 80-90% of human tumors and is low or undetectable in most normal somatic cells. Thus, telomerase or its telomere DNA substrate presents a target with good selectivity for tumor over healthy tissue.
    For a long time, telomeres have been considered to be transcriptionally silent. Very recently, a breaking finding demonstrated that telomere DNA is transcribed into telomeric repeat-containing RNA in mammalian cells. The telomeric RNA, a newly appeared player in telomere biology, may be a key component of telomere machinery that could facilitate new insight into fundamental biological processes such as cancer and aging.

Our researches focus on:
(1) Understanding the structures and functions of human telomere DNA and RNA by chemical approaches
(2) Developing various chemical methods to targeting human telomeres and telomerase for the treatment of cancer

1. Revealing telomere's mysterious by chemical approaches
    Using artificial nucleic acids, we found that human telomric DNA formed a G-quadruplex structure (News story describing this work was highlighted in Chem. & Eng. News, 2006, July 31, American Chemical Society) (Fig. a). Furthermore, we found that long telomere DNA forms a higher-order DNA structure containing consecutive G-quadruplexes by using atomic force microscopy. (Highlighted on Nature Asia as the top one most viewed research highlights, November 16 2009) (Fig. b). Our recent studies also demonstrated that a G-quadruplex can stabilize T-loop telomere structure (Fig. c). We have investigated the local DNA conformations by using the photoreactions of 5-halouracil-containing DNA. It was suggested that the product of 2'-deoxyribonolactone residue is effectively produced only in the antiparallel G-quadruplex (Fig. d).
    We investigated the structural features of human telomere RNA. The NMR showed that human telomere RNA forms a parallel G-quadruplex structure (Fig. e). Furthermore, using a light-switching probe, we found that human telomere RNA forms a parallel G-quadruplex structure in living cells, providing the in vivo evidence for the presence of the G-quadruplex in human (Fig. f). We also demonstrated that a novel U-tetrad is formed at human telomere RNA G-quadruplex (Fig. g). The unique structural feature may provide new targets for efforts directed toward the design of potent and selective RNA G-quadruplex-interacting molecules. These results provide valuable information to allow understanding of the structure and function of human telomere RNA.
    Recently, we developed a simple "click chemistry" method to detect G-quadruplex structure. By using this approach we discovered a DNA-RNA hybrid-type G-quadruplex structure formed from human telomeric DNA and RNA sequences (Fig. h). Furthermore, we demonstrated that formation of such an intermolecular G-quadruplex by telomeric RNA and DNA contributes to telomere end protection.



2. Developing various chemical approaches to targeting human telomeres and telomerase for the treatment of cancer
    Recently, we developed a novel approach toward sequence-specific cleaving human telomeric DNA. EDTP as metal binding group was conjugated to an oligonucleotide DNA. Oligonucleotide probe DNA bearing this kind of metal-affinity group were efficiently recruiting the catalytic species to the target site by G-quadruplex formation and resulting in an efficient cleavage at telomere DNA (Fig. a). To further expand this research, we developed a small 6-mer oligonucleotide with a photo-cross-linking reagent to cause efficient photo-cross-linking to human telomere DNA upon light irradiation. Because the main effect on the target is controllable by switching the light on/off, the small, photocontrolled oligonucleotide can minimize side effects by irradiation of only cancer cells, which alleviates the main problem with present-day anticancer agents. (Fig. b).