SN 38, DNA topoisomerase I inhibitor

補足情報

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Topoisomerase I also known as DNA topoisomerase I or Topo I is an important enzyme in the unwinding of the DNA double helix during processes such as replication and transcription. This enzyme has a molecular mass of approximately 91 kDa and functions by creating transient single-strand breaks in the DNA allowing relaxation of supercoils. Topoisomerase I is widely expressed in both proliferating and non-proliferating cells with higher levels seen in tissues with rapid cell division like the gastrointestinal tract and some immune cells.

Biological function summary

Topoisomerase I plays a significant role in the modulation of DNA topology ensuring proper chromosomal functions during cellular proliferation. It serves as a single polypeptide and does not require a companion for its activity unlike other topoisomerases that may function in complexes. The enzyme’s ability to relieve torsional stress in DNA is essential for maintaining genomic stability and facilitating the smooth progression of the replication fork.

Pathways

Topoisomerase I is vital for DNA replication and transcription processes. It works in concert with other proteins such as helicases and ligases to ensure efficient unwinding and rewinding of DNA strands. The enzyme participates in the DNA damage response pathway where it interacts with proteins like PARP1 to coordinate repair processes. Its action is important in both the S phase of the cell cycle where DNA synthesis occurs and in the G0 phase where cells are in a quiescent state.

Topoisomerase I is heavily implicated in oncogenesis with significant associations to colorectal and ovarian cancers. Its heightened activity can lead to genomic instability a hallmark of cancer development. The enzyme also relates to chemotherapeutic resistance where mutations in topoisomerase I lead to reduced drug efficacy. Furthermore inhibitors targeting topoisomerase I such as camptothecin-based drugs exploit its role in cancer aiming to induce DNA damage selectively in rapidly dividing cells. Connections to other proteins like BRCA1 are apparent in these pathways as they both contribute to the DNA repair processes in cells.