A major Cell paper has uncovered a completely new layer of DNA repair biology: cells use selective autophagy and lysosomes to process and remove Topoisomerase I cleavage complexes (TOP1cc)—the toxic DNA–protein crosslinks created during normal replication and when cells are exposed to TOP1-targeting drugs like camptothecin.
According to the Cell article (2024), researchers discovered that:
Lysosomes actively degrade TOP1cc in vertebrate cells, providing a previously unknown repair pathway that protects genome stability.
This mechanism operates at clinically relevant, low doses of CPT, not the high doses traditionally used to study proteasomal TOP1cc turnover.
TEX264 acts as the autophagy receptor for TOP1cc, detecting trapped complexes at replication forks and mediating their delivery to lysosomes through p97 and ATR-dependent signaling.
The nuclear envelope transiently remodels to allow TOP1cc export from the nucleus to the lysosome—a remarkable trafficking event visualized through live-cell and cryo-EM imaging.
Autophagy-driven TOP1cc clearance is essential for cell survival, directly influencing clinical sensitivity to TOP1-targeted chemotherapeutics.
In short: Topoisomerase I cleavage complexes aren’t just repaired—they’re trafficked, recognized, and selectively destroyed through a dedicated autophagy pathway.
This discovery changes our understanding of TOP1 pharmacology and opens a path toward therapeutics that modulate TOP1cc turnover.
Why This Matters for TopoGEN and Cutting-Edge Anti-Cancer Research
This new biology—TOP1cc recognition, export, and lysosomal destruction—cannot be studied or exploited without sensitive, quantitative tools that detect TOP1cc directly in cells.
And that is exactly what TopoGEN provides.
TopoGEN’s ICE Assay (In Vivo Complex of Enzyme) is the essential tool that enables research like this.
The Cell study relies heavily on detecting TOP1cc (e.g., immunofluorescence and RADAR-like assays), and future investigations into autophagy, TEX264 signaling, and chemotherapeutic sensitivity require accurate measurement of trapped TOP1–DNA complexes at the cellular level.
TopoGEN’s Human TOP1 ICE Assay Kit allows researchers to:
Directly quantify covalent TOP1–DNA complexes
Compare TOP1cc formation under low-dose vs high-dose CPT (critical in this paper)
Examine how TEX264, ATR, p97, MRE11, or autophagy inhibitors shift the balance between proteasomal and lysosomal repair
Evaluate new catalytic inhibitors, drug combinations, or autophagy-modulating co-therapies
This new model of dual-pathway TOP1cc repair (lysosome vs proteasome) makes the ICE assay more important than ever.