An innovative viewpoint on how the chemotherapeutic drug affects essential enzymes that promote the development of cancer cells is presented by a recent study at Cornell University.
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The research, carried out in Michelle Wang’s laboratory at the College of Arts and Sciences, will deepen our knowledge of various cancer inhibitors as well as the chemotherapeutic drug impact on DNA.
The paper, Etoposide Promotes DNA Loop Trapping and Barrier Formation by Topoisomerase II appeared in Nature Chemical Biology on January 30. Tung Le, a research specialist, and Meiling Wu, a postdoctoral researcher, are the co-lead authors.
Michelle Wang is a researcher for the Howard Hughes Medical Institute and the James Gilbert White Distinguished Professor of the Physical Sciences.
The team’s techniques will also enable the development of delicate screening tools for the identification of pharmacological mechanisms that can improve patient care.
Image Source – Victor Segura Ibarra and Rita Serda/National Cancer Institute via Flickr, CC BY-NC
Chemotherapeutic Drug Impact: Etoposide and DNA
Etoposide has been used as a reliable chemotherapeutic for treating various cancers for 40 years. Etoposide works by inhibiting Type IIA eukaryotic topoisomerases, also referred to as topo IIs, which are essential for cancer cell replication.
The main benefit of etoposide is its ability to stabilise DNA double-strand breaks before they are repaired, which stops cancer cells from proliferating. The specifics of how etoposide interacts with the structure of DNA are still unclear.
The lengthy, tangled, helical-coiled strands of DNA are at the centre of that replication process. These strands must be untangled, rotated, and replicated by motor proteins for cancer to spread.
Topo IIs are perfect for the task. By cutting the supercoiled DNA, quickly inserting another DNA strand through the middle of it, and then sewing the cut DNA back together, they pull the DNA loose. The body performs all of that without harming the delicate genetic structure of the DNA, which is a remarkable biological feat that occurs approximately 300 billion times per day.
Three topos IIs—yeast topoisomerase II, human topoisomerase II alpha, and human topoisomerase II beta—provided by collaborators led by professor James Berger of Johns Hopkins University were used by Wang’s lab to observe the effects of etoposide on each.
Wang stated that typically, they ponder about the best way to study the molecular processes that occur in DNA. To comprehend how those enzymes function, Wang continued, they want to mimic what might be occurring in the cell. The DNA is pulled or exerted force against by motor proteins. Therefore, they felt, what if they use a force and observe what happens.
According to Wang, it is very difficult for people to understand DNA topology conceptually and in terms of torsional mechanical properties. Wang further stated that there were not many ways to research it.
However, the researchers just so happen to have the ideal equipment. They’ve been working on creating the right tools for the last 20 years, which is why they have them now. These resources and this issue just so happened to coincide at this precise moment.
Chemotherapeutic Drug Impact: Tweezers
The first step was to demonstrate how etoposide compacts, releases, and breaks DNA as well as how it creates DNA loops using optical tweezers. Everyone was taken aback by this loop-trapping behaviour. It revealed an etoposide effect that was not previously known by scientists. It suggests that etoposide might encourage topo II to significantly change DNA topology and structure in vivo.
The team then mimicked the motor removal of a bound protein by using optical tweezers. It unzips double-stranded DNA into two single strands for mapping protein interactions with the DNA in high resolution. The results imply that etoposide could change topo II into a potent inhibitor of the machinery involved in DNA processing.
In their third method, which is a variation of magnetic tweezers, they twisted DNA with a bound topo II and observed the topo II slowly unwind the DNA. They discovered that Etoposide, the chemotherapeutic drug that was added, staggered this pattern and introduced pauses that corresponded to the trapping of supercoiled loops.
The researchers now have a quantitative system for characterizing how other topoisomerase medications behave by capturing the various ways etoposide enhances these actions and interferes with topo II function.
According to Wang, it gives comprehensive ways to study many different topoisomerases and other drugs by providing a set of ideal tools.
