Karenitecin (Cositecan) is an inhibitor of topoisomerase I. It has potent anti-cancer activity.

Karenitecin is a topoisomerase I inhibitor, with potent anti-cancer activity. Karenitecin inhibits several human colon cancer cell lines such as COLO205, COLO320, LS174T, SW1398 and WiDr cells, with IC50s of 2.4 nM, 1.5 nM, 1.6 nM, 2.9 nM, and 3.2 nM, respectively[2]. Karenitecin induces DNA damage (0.01, 0.07, and 0.7 μM), and increases cyclin E and cdk2 protein expression in A253 cells (0.07, and 0.7 μM). Karenitecin inhibits cell growth of A253 cells with IC10, IC50, and IC90 values of 0.01, 0.07, and 0.7 μM after 2 h treatment. Karenitecin markedly enhances the cyclin B/cdc2-associated kinase activity at low concentration, but slightly suppresses this kinase activity at higher concentration[1].

Karenitecin (1.0 mg/kg daily × 5 i.p.) significantly suppresses growth inhibition both in the parental Pgp-negative xenografts and in the Pgp-positive xenografts[2]. Karenitecin shows maximum growth inhibition of 61% on COLO320 cells and 54% on COLO205 colon cancer cells via i.p. administration of 1 mg/kg in mice.