Vorinostat-induced autophagy switches from a death-promoting to a cytoprotective signal to drive acquired resistance

D Dupéré-Richer,V Ménasché,T H Nielsen,F Pettersson,M Kinal,W H Miller,S Del Rincon

doi:10.1038/cddis.2012.210

D Dupéré-Richer, V Ménasché + Show 5 more

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https://doi.org/10.1038/cddis.2012.210

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Abstract

Histone deacetylase inhibitors (HDACi) have shown promising activity against hematological malignancies in clinical trials and have led to the approval of vorinostat for the treatment of cutaneous T-cell lymphoma. However, de novo or acquired resistance to HDACi therapy is inevitable, and their molecular mechanisms are still unclear. To gain insight into HDACi resistance, we developed vorinostat-resistant clones from the hematological cell lines U937 and SUDHL6. Although cross-resistant to some but not all HDACi, the resistant cell lines exhibit dramatically increased sensitivity toward chloroquine, an inhibitor of autophagy. Consistent with this, resistant cells growing in vorinostat show increased autophagy. Inhibition of autophagy in vorinostat-resistant U937 cells by knockdown of Beclin-1 or Lamp-2 (lysosome-associated membrane protein 2) restores sensitivity to vorinostat. Interestingly, autophagy is also activated in parental U937 cells by de novo treatment with vorinostat. However, in contrast to the resistant cells, inhibition of autophagy decreases sensitivity to vorinostat. These results indicate that autophagy can switch from a proapoptotic signal to a prosurvival function driving acquired resistance. Moreover, inducers of autophagy (such as mammalian target of rapamycin inhibitors) synergize with vorinostat to induce cell death in parental cells, whereas the resistant cells remain insensitive. These data highlight the complexity of the design of combination strategies using modulators of autophagy and HDACi for the treatment of hematological malignancies.

Highlights

HDACs catalyze the removal of acetyl groups from both histone and non-histone proteins
The U937-B8 subline is continuously maintained in 2 mM vorinostat to preserve the resistant phenotype, where it proliferates without evidence of apoptosis
Consistent with our hypothesis, we found that following downregulation of Beclin-1 by short hairpin RNA, vorinostat toxicity in U937 cells was decreased (Figure 6a, left panel)

Summary

Introduction

HDACs catalyze the removal of acetyl groups from both histone and non-histone proteins. The antitumor action of HDACi was initially correlated with the reactivation of tumor suppressor genes potentially silenced in tumor cells through epigenetic mechanisms.[2] Choudhary et al.[3] identified 1750 proteins acetylated by vorinostat that regulate various pathways. Proposed mechanisms of resistance to HDACi include increased antioxidant capacity of the cell,[8,10,11] alteration of the drug target,[12,13] deregulation of proapoptotic and prosurvival gene expression[14,15] and induction or suppression of autophagy.[16]. The role of autophagy in anticancer therapy is still under debate.[17] some studies suggest that autophagy may function as a stress response helping to promote cell survival, others show that increased autophagy leads to apoptosis.[18]. We show that activation of autophagy promotes apoptosis in vorinostat-treated U937 parental cells, while even greater activation of autophagy in vorinostat-resistant clones is necessary to protect the cells from apoptosis and maintain the resistant phenotype

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