Abstract A29: Bcl-2 overexpression provides short-term resistance to doxorubicin-DNA adducts but does not protect against longer-term treatments in HL-60 cells.

Abstract

Abstract The anthracycline anticancer agent doxorubicin functions primarily as a topoisomerase II inhibitor but forms more cytotoxic DNA adducts in the presence of formaldehyde. For this reason, the efficacy of doxorubicin can be greatly enhanced with the co-administration of formaldehyde-releasing prodrugs such as AN-9. The combination of doxorubicin with AN-9 results in DNA adduct formation and synergistic apoptosis in HL-60 leukemic cells after 6 hr. Under the same conditions HL-60 cells overexpressing the anti-apoptotic protein Bcl-2 (HL-60/Bcl-2 cells) are completely resistant to doxorubicin/AN-9 treatments. This resistance can be overcome with the use of the small molecule Bcl-2/Bcl-xL/BCL-W inhibitor ABT-737. While it appears that Bcl-2 overexpression confers resistance and thus may limit the therapeutic potential of doxorubicin-DNA adduct forming treatments, this is shown to be only a short-term effect. The use of a DNA adduct forming doxorubicin-formaldehyde conjugate, doxazolidine, produced similar results to the doxorubicin/AN-9 combination with HL-60/Bcl-2 cells being resistant to the drug after 4 hr treatment. This resistance was maintained up to 12 hr treatment, however, after 18 hr the HL-60/Bcl-2 cells started to display classical hallmarks of apoptosis including DNA fragmentation, and chromatin condensation which increased over time (18–36 hr). These results suggest that the Bcl-2 protection is only short-lived and that over time the resistance is overcome and the cells die via classical apoptosis. The exact mechanisms involved in overcoming this resistance in HL-60/Bcl-2 cells are currently being investigated and may involve changes in expression of Bcl-2 family proteins, or Bcl-2 interactions with pro-apoptotic proteins which tip the balance in favour of apoptosis. These findings imply that the damage caused by these DNA adduct forming compounds may be sufficient to overcome Bcl-2 mediated resistance observed in tumors in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A29.