SIRT Inhibitors Induce Cell Death and p53 Acetylation through Targeting Both SIRT1 and SIRT2

Abstract

SIRT proteins play an important role in the survival and drug resistance of tumor cells, especially during chemotherapy. In this study, we investigated the potency, specificity, and cellular targets of three SIRT inhibitors, Sirtinol, Salermide, and EX527. Cell proliferative and cell cycle analyses showed that Sirtinol and Salermide, but not EX527, were effective in inducing cell death at concentrations of 50 μmol/L or over in MCF-7 cells. Instead, EX527 caused cell cycle arrest at G 1 at comparable concentrations. In vitro SIRT assays using a p53 peptide substrate showed that all three compounds are potent SIRT1/2 inhibitors, with EX527 having the highest inhibitory activity for SIRT1. Computational docking analysis showed that Sirtinol and Salermide have high degrees of selectivity for SIRT1/2, whereas EX527 has high specificity for SIRT1 but not SIRT2. Consistently, Sirtinol and Salermide, but not EX527, treatment resulted in the in vivo acetylation of the SIRT1/2 target p53 and SIRT2 target tubulin in MCF-7 cells, suggesting that EX527 is ineffective in inhibiting SIRT2 and that p53 mediates the cytotoxic function of Sirtinol and Salermide. Studies using breast carcinoma cell lines and p53-deficient mouse fibroblasts confirmed that p53 is essential for the Sirtinol and Salermideinduced apoptosis. Further, we showed using small interfering RNA that silencing both SIRTs, but not SIRT1 and SIRT2 individually, can induce cell death in MCF-7 cells. Together, our results identify the specificity and cellular targets of these novel inhibitors and suggest that SIRT inhibitors require combined targeting of both SIRT1 and SIRT2 to induce p53 acetylation and cell death. Mol Cancer Ther; 9(4); 844-55. ©2010 AACR.

Antitumor Effect of SIRT1 Inhibition in Human HCC Tumor Models In Vitro and In Vivo

“…SIRT1 is not a specific target of cambinol, it also inhibits SIRT2 NAD-dependent deacetylase activity in vitro with IC 50 values of 56 and 59 mmol/L, respectively (33). Although it has been previously shown that combined SIRT1 and SIRT2 inhibition induces cell death, we observed a cytostatic as opposed to a cytotoxic effect in cells treated with cambinol (35).…”

“…Lentivirus production, titer determination, and transduction were carried out as previously described (35). A detailed description can be found in the Supplementary Materials and Methods.…”

Association of SIRT1 and HMGA1 expression in non-small cell lung cancer

“…HMGA1 also counteracts p53 transcriptional activity by relocalizing the nuclear p53 proapoptotic activator HIPK2 to the cytoplasm, thereby inhibiting the apoptotic function of p53 (32). SIRT1 is able to promote cell survival or inhibit apoptosis by deacetylating p53 (50,51). Deacetylation of the p53 protein promotes its accumulation during the stress response, and is required for p53-induced apoptosis and arrest of cell growth (52,53).…”

FOXO3a and Posttranslational Modifications Mediate Glucocorticoid Sensitivity in B-ALL

“…Specifically, p300/CBP has been shown to mediate the FOXO3a acetylation on Lys-242, Lys-245, and Lys-262 residues, whereas SIRT1, 2, and 6 have been shown to target FOXO3a for deacetylation (22,(42)(43)(44)(45). Western blot analysis showed that dexamethasone treatment upregulated CBP/p300 and downregulated SIRT1, 2, and 6 expression in the drug-sensitive RS4;11 and SUP-B15 cells (Fig.…”

“…To this end, we treated both the drug-sensitive RS4;11 and -resistant REH cells with 1 mmol/L of dexamethasone and a range of concentrations (0-100 mmol/L) of EX-527 (a SIRT1 inhibitor; ref. 44), PDF-170 (a SIRT2 inhibitor; ref. 46), and Sirtinol (a pan-SIRT1/ 2/6 inhibitor; ref.…”