ABSTRACT
Histone deacetylases (HDACs) are a family of enzymes that play a crucial role in biological process and diseases. In contrast to other isozymes, HDAC8 is uniquely incapable of histone acetylation. In order to delineate its physiological function, we developed HDAC8-selective inhibitors using knowledge-based design combined with structural modeling techniques. Enzyme inhibitory analysis demonstrated that some of the resulting compounds (22 b, 22 d, 22 f, and 22 g) exhibited anti-HDAC8 activity superior to PCI34051, a known HDAC8-specific inhibitor, with IC(50) values in the range of 5-50 nM. Among them, compound 22 d showed antiproliferative effects toward several human lung cancer cell lines (A549, H1299, and CL1-5); it exhibited cytotoxicity against human lung CL1-5 cells similar to that of SAHA yet without significant cytotoxicity for normal IMR-90 cells. Expression profiling of HDAC isoforms in three cancer cell lines indicated that the HDAC8 level in CL1-5 is higher than that in H1299 and CL1-1 cells, a result consistent with the differential cytotoxicity of compound 22 d. These results suggest the effectiveness of our design concept, which may lead to a tool compound for studying the specific role of HDAC8 in cellular biological processes.
Subject(s)
Amides/chemistry , Cinnamates/chemical synthesis , Histone Deacetylase Inhibitors/chemical synthesis , Repressor Proteins/antagonists & inhibitors , Amides/chemical synthesis , Amides/toxicity , Binding Sites , Cell Line, Tumor , Cell Survival/drug effects , Cinnamates/chemistry , Cinnamates/toxicity , Drug Design , Half-Life , HeLa Cells , Histone Deacetylase Inhibitors/chemistry , Histone Deacetylase Inhibitors/toxicity , Histone Deacetylases/metabolism , Humans , Molecular Docking Simulation , Repressor Proteins/metabolismABSTRACT
Lon proteases are a family of ATP-dependent proteases involved in protein quality control, with a unique proteolytic domain and an AAA(+) (ATPases associated with various cellular activities) module accommodated within a single polypeptide chain. They were classified into two types as either the ubiquitous soluble LonA or membrane-inserted archaeal LonB. In addition to the energy-dependent forms, a number of medically and ecologically important groups of bacteria encode a third type of Lon-like proteins in which the conserved proteolytic domain is fused to a large N-terminal fragment lacking canonical AAA(+) motifs. Here we showed that these Lon-like proteases formed a clade distinct from LonA and LonB. Characterization of one such Lon-like protease from Meiothermus taiwanensis indicated that it formed a hexameric assembly with a hollow chamber similar to LonA/B. The enzyme was devoid of ATPase activity but retained an ability to bind symmetrically six nucleotides per hexamer; accordingly, structure-based alignment suggested possible existence of a non-functional AAA-like domain. The enzyme degraded unstructured or unfolded protein and peptide substrates, but not well-folded proteins, in ATP-independent manner. These results highlight a new type of Lon proteases that may be involved in breakdown of excessive damage or unfolded proteins during stress conditions without consumption of energy.
Subject(s)
Protease La/chemistry , Protein Unfolding , Adenosine Triphosphatases/metabolism , Amino Acid Sequence , Deinococcus/enzymology , Enzyme Activation , Hydrolysis , Magnesium/metabolism , Models, Molecular , Molecular Sequence Data , Nucleotides/metabolism , Protease La/classification , Protease La/genetics , Protease La/metabolism , Protein Binding , Protein Conformation , Sequence AlignmentABSTRACT
Our previous studies have demonstrated that osthole, a Chinese herbal compound, could be incorporated into the hydroxycinnamide scaffold of LBH-589, a potent HDAC inhibitor, as an effective hydrophobic cap; the resulting compounds showed significant potency against several HDAC isoforms. Here, we presented a series of osthole derivatives fused with the aliphatic-hydroxamate core of suberoylanilide hydroxamic acid (SAHA), a clinically-approved HDAC inhibitor. Several compounds showed potent activity against nuclear HDACs. Further assays against individual HDAC isoforms revealed that some compounds showed not only SAHA-like activity towards HDAC1, -4 and -6, they inhibited HDAC8 by log difference than SAHA and thus exhibited a broader HDAC inhibition spectrum. Among them, compound 6g showed potent antiproliferative effect on several human cancer cell lines.
