Etoposide stabilizes a covalent topoisomerase II-cleaved DNA intermediate complex in the catalytic cycle of the enzyme, leading to genomic instability and cell death (2, 3).

The 3 largest subunits forming the catalytic core are encoded by mitochondrial DNA while the other smaller subunits, including COX IV, are nuclear-encoded.

AIM: to study the effects of shikonin on the catalytic activity of DNA topoisomerase I and apoptosis of K562 leukemia cells.