Amrubicin

As an anthracycline, amrubicin has antimitotic and cytotoxic activity through a variety of mechanisms of action. Amrubicin is found to form complexes with DNA via intercalation between base pairs, and it inhibits topoisomerase II enzyme activity by stabilizing the DNA-topoisomerase II complex, which prevents the re-ligation portion of the ligation-religation reaction that topoisomerase II normally catalyzes.

Topoisomerase II is an enzyme located in the nucleus that regulates DNA structure through double-strand breakage and re-ligation, therefore modulating DNA replication and transcription. Inhibition of the enzyme leads to inhibition of DNA replication and halt cell growth with an arrest of the cell cycle occurring at the G2/M phase. The mechanism by which amrubicin inhibits DNA topoisomerase II is believed to be through stabilization of the cleavable DNA–topo II complex, ending in re-ligation failure and DNA strand breakage.

DNA damage triggers activation of caspase-3 and -7 and cleavage of the enzyme PARP (Poly ADP ribose polymerase), leading to apoptosis and a loss of mitochondrial membrane potential. Amrubicin, like all anthracyclines, intercalates into DNA and produces reactive oxygen free radicals via interaction with NADPH, which causes cell damage.

Compared with doxorubicin, another member of the anthracycline drug class, amrubicin binds DNA with a 7-fold lower affinity and therefore, higher concentrations of amrubicin are necessary to promote DNA unwinding.