Abstract 3221: Analysis of the relationship between autophagy and senescence in response to Adriamycin in breast tumor cells

Abstract

Abstract Autophagy is a conservative biological process, which involves the degradation of intracellular components (proteins or organelles) via the fusion of autophagosomes with lysosomes. Autophagy has been reported to have both cytoprotective and cytotoxic actions in response to either chemotherapy or radiation in different tumor model systems. In previous studies (Elmore LW et al., J Biol Chem. 2002 Sep 20; 277(38): 35509-15.), Adriamycin (doxorubicin), one of the primary chemotherapeutic drugs utilized in the treatment of breast cancer, was shown to induce a pronounced senescence response within 72hrs in MCF-7 breast tumor cells (at a clinically relevant concentration of 1μM, with a 2 hr exposure). Interestingly, Adriamycin was also observed to cause a time-dependent increase of autophagy within 72hrs (by acridine orange, Monodansylcadaverine) staining and electron microscopy). The current study was designed to evaluate the relationship between Adriamycin-induced autophagy and senescence in MCF-7 breast tumor cells. The antioxidants, GSH (glutathione) and NAC (N-acetyl cysteine), were previously shown to effectively block Adriamycin-induced senescence (Di X. et al., Biochem Pharmacol. 2009 Apr 1; 77(7):1139-50.). We now demonstrate that both GSH and NAC also effectively abolish Adriamycin-induced autophagy in MCF-7cells (as confirmed by the disappearance of punctuated red fluorescence staining (RFP-LC3) induced by Adriamycin. Unexpectedly, however, the autophagy inhibitors, 3-MA or wortmannin, failed to block Adriamycin-induced senescence (based on β-Gal staining). Another autophagy inhibitor, chloroquine, showed a significant blockade to β-Gal staining, although typical senescence morphology phenotypes, such as cell enlargement and flattening were still observed by phase contrast microscopy. Silencing of the autophagic protein, ATG5, failed to completely block Adriamycin-induced senescence, although the MCF-7/ATG5 knockdown cells showed decreased and delayed β-Gal staining. Taken together, our studies suggest that that autophagy proceeds and may contribute to the development of Adriamycin-induced senescence. The fact that blockade of senescence (by reactive oxygen scavengers) abrogates Adriamycin-induced autophagy further suggests that senescence and autophagy may be collaterally regulated in response to Adriamycin in MCF-7 cells. Both autophagy and senescence may be related to tumor dormancy (Gewirtz DA, Autophagy. 2009 Nov 24; 5(8).). Further studies are in progress to delineate the roles (cytoprotective or cytotoxic) of autophagy and the relationship of autophagy to senescence, tumor dormancy and sensitivity to chemotherapy and radiation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3221.