• Visualizing the invisible: New fluoresce

    From ScienceDaily@1:317/3 to All on Friday, March 04, 2022 21:30:34
    Visualizing the invisible: New fluorescent DNA label reveals nanoscopic
    cancer features

    Date:
    March 4, 2022
    Source:
    University of Pittsburgh
    Summary:
    Researchers have developed a new fluorescent label that gives a
    clearer picture of how DNA architecture is disrupted in cancer
    cells. The findings could improve cancer diagnoses for patients
    and classification of future cancer risk.



    FULL STORY ========================================================================== Researchers have developed a new fluorescent label that gives a clearer
    picture of how DNA architecture is disrupted in cancer cells. The findings could improve cancer diagnoses for patients and classification of future
    cancer risk.


    ========================================================================== Published today in Science Advances, the study found that the DNA-binding
    dye performed well in processed clinical tissue samples and generated high-quality images via superresolution fluorescence microscopy.

    "My lab is focused on developing microscopy techniques to visualize the invisible," said senior author Yang Liu, Ph.D., associate professor of
    medicine and bioengineering at the University of Pittsburgh. "We are
    one of the first groups to explore the capabilities of superresolution microscopy in the clinical realm. Previously, we improved its throughput
    and robustness for analysis of clinical cancer samples. Now, we have a DNA
    dye that is easy to use, which solves another big problem in bringing this technology to patient care." Inside the cell's nucleus, DNA strands are
    wound around proteins like beads on a string. Pathologists routinely use traditional light microscopes to visualize disruption to this DNA-protein complex, or chromatin, as a marker of cancer or precancerous lesions.

    "Although we know that chromatin is changed at the molecular scale
    during cancer development, we haven't been able to clearly see what
    those changes are.

    This has bothered me for more than 10 years," said Liu, who is also a
    member of the UPMC Hillman Cancer Center. "To improve cancer diagnosis,
    we need tools to visualize nuclear structure at much greater resolution."
    In 2014, the Nobel Prize-winning invention of superresolution fluorescence microscopy was a major step towards making Liu's vision reality. A
    molecule of interest is labelled with a special fluorescent dye that
    flashes on and off like a blinking star. Unlike traditional fluorescence microscopy, which uses labels that glow constantly, this approach involves switching on only a subset of the labels at each moment. When several
    images are overlayed, the complete picture can be reconstructed --
    at a much higher resolution than previously possible.



    ========================================================================== Until now, the problem was that fluorescent dyes didn't work well on DNA
    or in processed clinical cancer samples. So, Liu and her team formulated
    a new label called Hoechst-Cy5 by combining the DNA-binding molecule Cy5
    and a fluorescent dye called Hoechst with ideal blinking properties for superresolution microscopy.

    After showing that the new label produced higher resolution images than
    other dyes, the researchers compared colorectal tissue from normal, precancerous and cancerous lesions. In normal cells, chromatin is densely packed, especially at the edges of the nucleus. Condensed DNA glows
    brightly because a higher density of labels emits a stronger signal,
    while loosely packed chromatin produces a dimmer signal.

    The images show that as cancer progresses, chromatin becomes less
    densely packed, and the compact structure at the nuclear border is
    severely disrupted.

    While these findings indicate that the new label can distinguish
    normal tissue from precancerous and cancerous lesions, Liu said that superresolution microscopy is unlikely to replace traditional microscopes
    for such routine clinical diagnoses. Instead, this technology could
    shine in risk stratification.

    "Early-stage lesions can have very different clinical outcomes," said Liu.

    "Some people develop cancer very quickly, and others stay at the precursor stage for a long time. Stratifying cancer risk is a major challenge
    in cancer prevention." To see if chromatin structure could hold clues
    about future cancer risk, Liu and her team evaluated patients with Lynch syndrome, a heritable condition that increases the risk of several cancer types, including colon cancer. They looked at non-cancerous colorectal
    tissue from healthy people without Lynch syndrome and Lynch patients
    with or without a personal history of cancer.



    ==========================================================================
    The differences were striking. In Lynch patients who previously
    had colon cancer, chromatin was much less condensed than in healthy
    samples, suggesting that chromatin disruption could be an early sign
    of cancer development -- even in tissue that looks completely normal
    to pathologists.

    For Lynch patients without a personal history of cancer, some will go
    on to develop cancer, while others will not.

    "We see a much larger spread in this group, which is very interesting,"
    said Liu. "Some patients resemble healthy controls, and some are closer
    to Lynch patients who previously had cancer. We think that patients with
    more open chromatin are those who are more likely to develop cancer. We
    need to follow these patients over time to measure outcomes, but we're
    pretty excited that chromatin disruption in normal cells could potentially predict cancer risk." In future work, Liu and her team are interested in examining chromatin structure in endometrial tissue from Lynch patients,
    who also have elevated risk of endometrial cancer. The researchers also received funding recently to look at sputum samples from smokers for
    early detection of lung cancer.

    Other authors who contributed to this study were Jianquan Xu, Ph.D.,
    Xuejiao Sun, M.S., Hongqiang Ma, Ph.D., Rhonda M. Brand, Ph.D., Douglas Hartman, M.D., and Randall E. Brand, M.D., all of Pitt; and Mingfeng Bai, Ph.D., and Kwangho Kim, Ph.D., both of Vanderbilt University.

    This work was funded by the National Institutes of Health (R01CA254112, R33CA225494 and R01CA232593).

    ========================================================================== Story Source: Materials provided by University_of_Pittsburgh. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Jianquan Xu, Xuejiao Sun, Kwangho Kim, Rhonda M. Brand, Douglas
    Hartman,
    Hongqiang Ma, Randall E. Brand, Mingfeng Bai, Yang
    Liu. Ultrastructural visualization of chromatin in cancer
    pathogenesis using a simple small- molecule fluorescent
    probe. Science Advances, 2022; 8 (9) DOI: 10.1126/ sciadv.abm8293 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220304144643.htm

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