Synthesis and initial biological evaluation of new mimics of the LXR-modulator 22(S)-hydroxycholesterol.

The generic, synthetic oxysterol 22(S)-hydroxycholesterol (22SHC) has shown antagonistic effects towards liver X receptor (LXR) in vitro and promising effects on plasma triacylglycerol level and body weight-gain in animal studies. On the contrary, the endogenic LXR agonist 22(R)-hydroxycholesterol (22RHC) and synthetic LXR agonists convincingly have shown agonistic effects on genes involved in lipogenesis, and inhibitory effects on cell proliferation in vitro and in vivo. We hypothesized that the carbon side chain containing the hydroxyl group at the 22-position was a pharmacophore affecting these opposite effects on LXR. This prompted us to initiate a rational drug design incorporating the 22-hydroxylated 20-27 cholesterol moiety into cholesterol-mimicking building blocks. The two enantiomers of the 22-hydroxylated 20-27 cholesterol moiety were synthesized with an excellent enantiomeric excess and the stereochemistry are supported by X-ray crystallography. Molecular modelling of the new compounds showed promising LXR selectivity (LXRß over LXRα) and initial in vitro biological evaluation in human myotubes showed that compound 16b had agonistic effects on the gene expression of SCD1 and increased lipogenesis.

Synthesis and initial in vitro biological evaluation of two new zinc-chelating compounds: comparison with TPEN and PAC-1.

The lipophilic, cell-penetrating zinc chelator N,N,N',N',-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN, 1) and the zinc chelating procaspase-activating compound PAC-1 (2) both have been reported to induce apoptosis in various cell types. The relationship between apoptosis-inducing ability and zinc affinity (Kd), have been investigated with two new model compounds, ZnA-DPA (3) and ZnA-Pyr (4), and compared to that of TPEN and PAC-1. The zinc-chelating o-hydroxybenzylidene moiety in PAC-1 was replaced with a 2,2'-dipicoylamine (DPA) unit (ZnA-DPA, 3) and a 4-pyridoxyl unit (ZnA-Pyr, 4), rendering an order of zinc affinity TPEN>ZnA-Pyr>ZnA-DPA>PAC-1. The compounds were incubated with the rat pheochromocytoma cell line PC12 and cell death was measured in combination with ZnSO4, a caspase-3 inhibitor, or a ROS scavenger. The model compounds ZnA-DPA (3) and ZnA-Pyr (4) induced cell death at higher concentrations as compared to PAC-1 and TPEN, reflecting differences in lipophilicity and thereby cell-penetrating ability. Addition of ZnSO4 reduced cell death induced by ZnA-Pyr (4) more than for ZnA-DPA (3). The ability to induce cell death could be reversed for all compounds using a caspase-3-inhibitor, and most so for TPEN (1) and ZnA-Pyr (4). Reactive oxygen species (ROS), as monitored using dihydro-rhodamine (DHR), were involved in cell death induced by all compounds. These results indicate that the Zn-chelators ZnA-DPA (3) and ZnA-Pyr (4) exercise their apoptosis-inducing effect by mechanisms similar to TPEN (1) and PAC-1 (2), by chelation of zinc, caspase-3 activation, and ROS production.