Practice question

Sequential application of EdU labeling followed by doxorubicin treatment represents strategy to track and preferentially eliminate newly dividing cells. EdU pulse marks cells traversing S phase with alkyne-modified nucleotide that persists in DNA of daughter cells, identifiable via click chemistry fluorescent azide. When doxorubicin subsequently administered, antineoplastic action via topoisomerase II trapping and generation of reactive oxygen species is most pronounced in actively cycling population where chromatin decondensed, replication forks active, and topoisomerase IIalpha expression high to resolve supercoiling. EdU-positive cells, already in cycle, exhibit heightened susceptibility because modified DNA may stabilize cleavage complexes and replication stress synergizes with doxorubicin induced double-strand breaks activating p53 apoptosis. Quiescent, terminally differentiated, or already dead cells lacking DNA synthesis incorporate minimal EdU and have low topoisomerase activity, escaping immediate toxicity. Click detection of residual EdU after therapy quantifies surviving proliferative fraction, allowing evaluation of chemotherapeutic efficacy and persistence of cancer stem-like cells resistant to conventional agents in tumor models.