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

Karenitecin, a topoisomerase I inhibitor, exhibits potent anti-cancer properties by effectively inhibiting the growth of various human colon cancer cell lines, including COLO205, COLO320, LS174T, SW1398, and WiDr, demonstrated by IC50 values of 2.4 nM, 1.5 nM, 1.6 nM, 2.9 nM, and 3.2 nM, respectively[2]. Furthermore, it not only induces DNA damage in A253 cells at concentrations of 0.01, 0.07, and 0.7 μM but also elevates the levels of cyclin E and cdk2 proteins at 0.07 and 0.7 μM. Significant cell growth inhibition in A253 cells is achieved with IC10, IC50, and IC90 values of 0.01, 0.07, and 0.7 μM after a 2-hour treatment. Additionally, at low concentrations, Karenitecin significantly augments cyclin B/cdc2-associated kinase activity, whereas it slightly diminishes this activity at higher concentrations[1].

Karenitecin (1.0 mg/kg daily × 5 i.p.) significantly reduces growth in both parental Pgp-negative xenografts and Pgp-positive xenografts[2]. It demonstrates a maximum growth inhibition of 61% in COLO320 cells and 54% in COLO205 colon cancer cells following i.p. administration at a dosage of 1 mg/kg in mice.