Cell surface-directed interaction of anthracyclines leads to cytotoxicity and nuclear factor kappaB activation but not apoptosis signaling.

Anthracyclines are, above all, DNA intercalators, which induce genetic damage leading to cell death. However, increasing evidence firmly suggests that the underlying mechanism for anthracycline cytotoxicity is the induction of apoptosis through intracellular-mediated signaling pathways. Whether drug/DNA interaction is necessary for such apoptosis signaling is unknown. We investigated the cellular effects of the anthracyclines daunorubicin (DNR) and doxorubicin (DOX) using the myeloid leukemia cell line U937. By comparing free drug against agarose bead-immobilized drug iDNR and iDOX (which cannot accumulate within the cell), we observed that whereas both free and immobilized anthracyclines were cytotoxic, only the former induced apoptosis; the latter induced necrosis. Indeed, we did not observe ceramide generation, neutral sphingomyelinase activation, poly (ADP-ribose) polymerase cleavage, or other apoptotic events with iDNR or iDOX. However, both free and immobilized drug were similarly capable of triggering nuclear factor kappaB activation. These observations demonstrate that whereas activation of certain cellular signaling pathways can be achieved solely through membrane interaction, apoptosis signaling requires anthracycline internalization. These results also show that the initiation of cell survival pathways (illustrated by nuclear factor kappaB activation) is independent of intracellular drug/target interaction.