Selisistat (EX 527)

Selisistat (EX 527) exhibits a potently inhibitory effect against SIRT1 deacetylase activity in a concentration-dependent manner with an IC50 of 38 nM, and displays much lower activity against SIRT2 and SIRT3 with IC50 values of 19.6 μM and 48.7 μM, respectively. It does not inhibit SIRT4-7 and class I/II HDAC activity at concentrations up to 100 μM. This compound alone (1 μM) has no detectable effect on the acetylation of p53 lysine 382 in NCI-H460 cells, but significantly increases the amount of acetylated p53 in NCI-H460 cells, human mammary epithelial cells, U-2 OS and MCF-7 cells subjected to genotoxic agents Hydrogen peroxide, which is more effective than that caused by Nicotinamide (5 mM). Surprisingly, it does not result in detectable effects on p53-controled gene expression, cell survival, or cell proliferation. ^[1] It causes a 90% increase in cell number of HCT116 cells after 7 days in the condition of 0.1% serum but not 10% serum, suggesting that SIRT1 is a significant regulator of cell proliferation during growth factor deprivation conditions. ^[2] Additionally, it abrogates resveratrol effects on glucose responses, and prevents resveratrol-induced up-regulation of Glut2, glucokinase, Pdx-1, and Tfam in INS-1E Cells, due to the opposite effect of EX 527 and resveratrol on SIRT1 deacetylase activity. ^[3]

Administration of Selisistat (EX 527; ~10 μg) to rats increases hypothalamic acetyl-p53 levels by inhibiting hypothalamic SIRT1 activity. Co-administration of this compound with ghrelin markedly blunts the orexigenic action of ghrelin by decreasing the pAMPK levels, increasing the ACC levels, and abolishing the higher expression of the transcription factors FoxO1, pCREB, and Bsx and the neuropeptides NPY and AgRP in the hypothalamic arcuate nucleus. ^[4]

• Inhibition of GST-SIRT1 deacetylase activity

  293T cells are transiently transfected with GST-tagged human SIRT1 in the pDEST27 Gateway vector using FuGENE-6. After 48 hours, the cells are lysed with 50 mM Tris, pH 8.0, 120 mM NaCl, 1 mM EDTA, and 0.5% Nonidet P-40, supplemented with Complete Mini protease inhibitor cocktail tablets. GST-SIRT1 is purified from lysates and washed extensively in the above buffer. The deacetylation assay is performed with approximately 30 ng of GST-SIRT1 in the presence of Selisistat (EX 527) (48 pM to 100 μM). Deacetylation is measured using the Fluor de Lys kit using a fluorogenic peptide encompassing residues 379 to 382 of p53, acetylated on lysine 382. The acetylated lysine residue is coupled to an aminomethylcoumarin moiety. The peptide is deacetylated by SIRT1, followed by the addition of a proteolytic developer that releases the fluorescent aminomethylcoumarin. Briefly, enzyme preparations are incubated with 170 μM NAD⁺ and 100 μM p53 fluorogenic peptide for 45 minutes at 37 °C followed by incubation in developer for 15 minutes at 37 °C. Fluorescence is measured by excitation at 360 nm and emission at 460 nm and enzymatic activity is expressed in relative fluorescence units.

• Cell lines

  NCI-H460, MCF-7, U-2 OS and HMEC

• Concentrations

  Dissolved in DMSO, final concentration 1 μM

• Incubation Time

  48 or 72 hours

• Method

  For viability assays, cells are treated with Selisistat (EX 527) for 48 hours. Cell viability is then determined using the Cell Titer-Glo luminescent assay, which measures total ATP level as an index of cell number. Luminescence is measured on a Luminoskan Ascent. For the proliferation assay, 0.5 μCi/mL of [¹⁴C]thymidine is added to the medium immediately after this compound. Plates are counted at 48 hours (HMEC) or 72 hours (NCI-H460, MCF-7, and U-2 OS cells) in a Microbeta liquid scintillation counter. Thymidine incorporated by the cells is detected by proximity to the scintillant in the base of the Cytostar-T tissue culture plate.

• Animal Models

  Male Sprague-Dawley rats

• Dosages

  ~5 μg/rat

• Administration

  Intracerebroventricular injection