Novel cambinol analogs as sirtuin inhibitors: synthesis, biological evaluation, and rationalization of activity

Abstract

The tenovins and cambinol are two classes of sirtuin inhibitor that exhibit antitumor activity in preclinical models. This report describes modifications to the core structure of cambinol, in particular by incorporation of substituents at the N1-position, which lead to increased potency and modified selectivity. These improvements have been rationalized using molecular modeling techniques. The expected functional selectivity in cells was also observed for both a SIRT1 and a SIRT2 selective analog.

Figure 1

(A) Docking solution obtained for N1 substituted analog 6j. The N1-aliphatic carbon chain in 6j is proposed to insert into a narrow lipophilic channel delimited by Phe96, Leu 138, and Ile169. (B) A comparison of the amino acid sequence for the 96-loop in human SIRT1 and SIRT2.

Figure 2

Levels of p53 and acetylated p53 in MCF-7 breast adenocarcinoma cells treated with different concentrations of cambinol (1) and 6b in the presence of etoposide. The black line represents the position of the 51KDa molecular weight marker. Samples were first analyzed with the K382-acetylated p53 antibody and subsequently reloaded and analyzed with the antibody against total p53.

Figure 3

Western blot analysis of the levels of α-tubulin acetylated at K40 and total α-tubulin in H1299 cells treated with increasing concentrations of cambinol (1) and analog 6j. All samples were also treated with trichostatin A, an inhibitor of class I and II HDACs, to reduce the background effect of these deacetylases. The black line represents the position of the 51KDa molecular weight marker. Samples were first analyzed with the K40-acetylated α-tubulin antibody and subsequently reloaded and analyzed with the antibody against total α-tubulin. For a more detailed statistical analysis of this experiment, see Supporting Information Figure S14.

Scheme 1

(A) Synthesis of 1 and 6a–j^a and (B) Structural Comparison of Tenovin-6 and Splitomicin ^a Reagents and conditions: (i) piperidine, ethanol, reflux, 2 h (4a, 86%; 4b, 87%; 4c, 95%); (ii) NaBH₄, pyridine, rt, 2 h (5a, 95%; 5b, 93%; 5c, 76%); 7 was reduced in 95%; (iii) Na, ethanol, thiourea (for 1, 51%; 6b, 43%; 6c, 42%; 6d, 40%) or urea (6a, 20%) or N-methylthiourea (6e, 16%), reflux, 18 h. For substituents in compounds i–xi and 6f, g, h, and j, see Table 1; for compounds xii–xix, R₁ = p-F (xii); m-I (xiii); m-NO₂ (xiv); phenyl ring replaced by 2-furyl (xv); o-Cl (xvi); o-I (xvii); o-NO₂ (xviii); phenyl ring replaced by 2-pyridyl (xix).