Evidence that activation of nuclear factor-κB is essential for the cytotoxic effects of doxorubicin and its analogues

Several reports within the last 5 years have suggested that nuclear factor (NF)-κB activation suppresses apoptosis through expression of anti-apoptotic genes. In the present report, we provide evidence from four independent lines that NF-κB activation is required for the cytotoxic effects of doxorubicin. We used doxorubicin and its structural analogues WP631 and WP744, to demonstrate that anthracyclines activate NF-κB, and this activation is essential for apoptosis in myeloid (KBM-5) and lymphoid (Jurkat) cells. All three anthracyclines had cytotoxic effects against KBM-5 cells; analogue WP744, was most potent, with an IC₅₀ of 0.5μM, and doxorubicin was least active, with an IC₅₀ of 2μM. We observed maximum NF-κB activation at 1μM with WP744 and at 50μM with doxorubicin and WP631, and this activation correlated with the IκBα degradation. Because the anthracycline analogue (WP744), most active as a cytotoxic agent, was also most active in inducing NF-κB activation and the latter preceded the cytotoxic effects, suggests that NF-κB activation may mediate cytotoxicity. Second, receptor-interacting protein-deficient cells, which did not respond to doxorubicin-induced NF-κB activation, were also protected from the cytotoxic effects of all the three anthracyclines. Third, suppression of NF-κB activation by pyrrolidine dithiocarbamate, also suppressed the cytotoxic effects of anthracyclines. Fourth, suppression of NF-κB activation by NEMO-binding domain peptide, also suppressed the cytotoxic effects of the drug. Overall our results clearly demonstrate that NF-κB activation and IκBα degradation are early events activated by doxorubicin and its analogues and that they play a critical pro-apoptotic role.