Synthesis, in vitro and structural aspects of cap substituted Suberoylanilide hydroxamic acid analogs as potential inducers of apoptosis in Glioblastoma cancer cells via HDAC /microRNA regulation.

Glioblastoma multiforme (GBM) is a heterogeneous, aggressive brain cancer characterized by chemo-resistance and cancer stemness. Histone deacetylases (HDACs) are a group of enzymes that regulate chromatin epigenetics which were in turn found to be controlled by microRNAs (miRs). The drug employed in chemotherapy for the treatment of GBM is Temozolomide (TMZ). Unfortunately, many GBM patients exhibit chemo-resistance to this drug. Here we have synthesized various Suberoyl anilide hydroxamic acid (SAHA) analogs with many substitutions at the cap site majority of which not yet studied. These SAHA analogs have exhibited profound cytotoxicity at 2 µM, and 4 µM concentrations in GBM cancer cell line U87MG, and 1 µM, and 2 µM concentrations in breast cancer cell line MCF-7. Surprisingly, these analogs have exhibited cytotoxic effects in chronic lymphoid leukemia cells (Raji) at 64 µM, and 128 µM concentrations due to mutated p53. Among all the synthesized analogs 3-Chloro-SAHA, 3-Chloro-4-fluoro SAHA have exhibited effective cytotoxicity in all cancer cells. These potent analogs inhibited HDAC-8 enzyme activity by 2-folds in U87MG, and MCF-7 cell lines and 7-folds decrease in HDAC-8 activity was observed in Raji cell line. These analogs decreased the expression of HDAC-2, HDAC-3 genes and enhanced the expression of p53 tumor suppressor. Interestingly, these compounds decreased the expression of Rictor, the main component of the mTORC2 complex involved cancer cell metabolism. Furthermore, these molecules have decreased oncogenic microRNA expression such as miR-21 and enhanced the expression of tumor suppressor microRNAs such as miR-143. The HDAC binding ability of these molecules was highly significant and have exhibited the ability to cross blood-brain barrier (BBB), and followed the Lipinski rule of five. Thus, these molecules need to be taken up further to clinics for better therapy against GBM either singly or combination therapy.

Streamlined Target Deconvolution Approach Utilizing a Single Photoreactive Chloroalkane Capture Tag.

Identification of physiologically relevant targets for lead compounds emerging from drug discovery screens is often the rate-limiting step toward understanding their mechanism of action and potential for undesired off-target effects. To this end, we developed a streamlined chemical proteomic approach utilizing a single, photoreactive cleavable chloroalkane capture tag, which upon attachment to bioactive compounds facilitates selective isolation of their respective cellular targets for subsequent identification by mass spectrometry. When properly positioned, the tag does not significantly affect compound potency and membrane permeability, allowing for binding interactions with the tethered compound (probe) to be established within intact cells under physiological conditions. Subsequent UV-induced covalent photo-cross-linking "freezes" the interactions between the probe and its cellular targets and prevents their dissociation upon cell lysis. Targets cross-linked to the capture tag are then efficiently enriched through covalent capture onto HaloTag coated beads and subsequent selective chemical release from the solid support. The tag's built-in capability for selective enrichment eliminates the need for ligation of a capture tag, thereby simplifying the workflow and reducing variability introduced through additional operational steps. At the same time, the capacity for adequate cross-linking without structural optimization permits modular assembly of photoreactive chloroalkane probes, which reduces the burden of customized chemistry. Using three model compounds, we demonstrate the capability of this approach to identify known and novel cellular targets, including those with low affinity and/or low abundance as well as membrane targets with several transmembrane domains.

Binding of inhibitors to active-site mutants of CD1, the enigmatic catalytic domain of histone deacetylase 6.

The zinc hydrolase histone deacetylase 6 (HDAC6) is unique among vertebrate deacetylases in that it contains two catalytic domains, designated CD1 and CD2. Both domains are fully functional as lysine deacetylases in vitro. However, the in vivo function of only the CD2 domain is well defined, whereas that of the CD1 domain is more enigmatic. Three X-ray crystal structures of HDAC6 CD1-inhibitor complexes are now reported to broaden the understanding of affinity determinants in the active site. Notably, cocrystallization with inhibitors was facilitated by using active-site mutants of zebrafish HDAC6 CD1. The first mutant studied, H82F/F202Y HDAC6 CD1, was designed to mimic the active site of human HDAC6 CD1. The structure of its complex with trichostatin A was generally identical to that with the wild-type zebrafish enzyme. The second mutant studied, K330L HDAC6 CD1, was prepared to mimic the active site of HDAC6 CD2. It has previously been demonstrated that this substitution does not perturb inhibitor binding conformations in HDAC6 CD1; here, this mutant facilitated cocrystallization with derivatives of the cancer chemotherapy drug suberoylanilide hydroxamic acid (SAHA). These crystal structures allow the mapping of inhibitor-binding regions in the outer active-site cleft, where one HDAC isozyme typically differs from another. It is expected that these structures will help to guide the structure-based design of inhibitors with selectivity against HDAC6 CD1, which in turn will enable new chemical biology approaches to probe its cellular function.

A 18ß-glycyrrhetinic acid conjugate with Vorinostat degrades HDAC3 and HDAC6 with improved antitumor effects.

Semisynthetic 18ß-glycyrrhetinic acid (GA) analogues bearing 1-en-2-cyano-3-oxo substitution on ring A have enhanced antitumor effects with reduced levels of HDAC3 and HDAC6 proteins. Aiming to inhibit both HDAC protein and activity, we developed a hybrid molecule by tethering active GA analogue methyl 2-cyano-3,11-dioxo-18ß-olean-1,12-dien-30-oate (CDODA-Me) and Vorinostat (SAHA). We tested the proper hybrid approaches of GA with hydroxamic acid and turned out that GA conjugated with SAHA by a piperazine linker was the best. The conjugate (15) of CDODA-Me and SAHA linked through a piperazine group was a potent cytotoxic agent against cancer cells with apoptosis induction. Compound 15 was more effective than the simple combination of CDODA-Me and SAHA to induce apoptosis. Mechanistic studies revealed that 15 was less effective than SAHA to inhibit HDAC activity, but was more effective than CDODA-Me to decrease the levels of HDAC3 and HDAC6 proteins with upregulated levels of acetylated H3 and acetylated α-tubulin. Compound 15 represents a new HDAC3 and HDAC6 inhibitor by reducing protein levels.

A nanodelivered Vorinostat derivative is a promising oral compound for the treatment of visceral leishmaniasis.

There is currently no satisfactory treatment for visceral leishmaniasis; the disease is thus in desperate need of novel drugs. The ideal candidate should be effective, safe, affordable, and administered via the oral route. Histone deacetylases (HDACs) are involved in silencing critical regulatory pathways, including pro-apoptotic programs, and represent potential therapeutic targets for pharmacological interventions. O-alkyl hydroxamates have traditionally been considered to exert no effect on mammal HDACs. The aim of this study was to evaluate the effect of MDG, a SAHA derivative of the O-alkyl hydroxamate family with no activity on human histone deacetylase enzymes, on the visceral leishmaniasis causative agents and in a murine model of the disease. The effects of vorinostat, tubacin and valproic acid (well-known mammal HDAC inhibitors) on the parasite were also evaluated. MDG was found to be highly active against Leishmania infantum and L. donovani intracellular amastigotes in vitro but not against the promastigote stage. In contrast, vorinostat, tubacin and valproic acid showed no activity against the parasite. Assays investigating hERG and Cav1.2 channels in vitro found no evidence of MDG-driven cardiotoxicity. MDG showed neither hepatotoxicity nor mutagenicity, nor did it exert activity on cytochrome P450 enzymes. MDG was adsorbed onto gold nanoparticles for the in vivo experiments, performed on infected Balb/c mice. MDG was effective at reducing the parasite load in major target tissues (bone marrow, spleen and liver) in more than 70% at 25 mg/kg through both the oral and intraperitoneal route, proving more active than the reference compounds (meglumine antimoniate, MA) without showing toxicity. In addition, the combination of MDG and MA was very effective.

Design, synthesis, and biological evaluation of histone deacetylase inhibitors possessing glutathione peroxidase-like and antioxidant activities against Alzheimer's disease.

A series of hybrids containing the pharmacophores of the histone deacetylase (HDAC) inhibitor, SAHA, and the antioxidant ebselen were designed and synthesized as multi-target-directed ligands against Alzheimer's disease. An in vitro assay indicated that some of these molecules exhibit potent HDAC inhibitory activity and ebselen-related pharmacological effects. Specifically, the optimal compound 7f was found to be a potent HDAC inhibitor (IC50 = 0.037 µM), possessing rapid hydrogen peroxide scavenging activity and glutathione peroxidase-like activity (ν0 = 150.0 µM min-1) and good free oxygen radical absorbance capacity (value of ORAC: 2.2). Furthermore, compound 7f showed significant protective effects against damage induced by H2O2 and the ability to prevent ROS accumulation in PC12 cells.