Recent development of selective inhibitors targeting the HDAC6 as anti-cancer drugs: Structure, function and design.

HDAC6, a member of the histone deacetylase family, mainly is a cytosolic protein and regulates cell growth by acting on non-histone substrates, such as α -tubulin, cortactin, heat shock protein HSP90, programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1), that are closely related to the proliferation, invasion, immune escape and angiogenesis of cancer tissues. The approved drugs targeting the HDACs are all pan-inhibitors and have many side effects due to their lack of selectivity. Therefore, development of selective inhibitors of HDAC6 has attracted much attention in the field of cancer therapy. In this review, we will summarize the relationship between HDAC6 and cancer, and discuss the design strategies of HDAC6 inhibitors for cancer treatment in recent years.

Design, synthesis, and biological evaluation of novel N-Benzyl piperidine derivatives as potent HDAC/AChE inhibitors for Alzheimer's disease.

The multitarget-directed ligands approach represents a potential strategy to provide effective treatments for Alzheimer's disease (AD) given its multifactorial pathology. Herein, a series of N-benzyl piperidine derivatives were designed, synthesized, and biologically characterized for dual inhibitions of histone deacetylase (HDAC) and acetylcholinesterase (AChE). Among the compounds tested, d5 and d10 exhibited dual enzyme inhibitions (d5: HDACIC50 = 0.17 µM, AChEIC50 = 6.89 µM, d10: HDACIC50 = 0.45 µM, AChEIC50 = 3.22 µM), and both compounds showed activities on scavenging free radical, metal chelating, and inhibiting Aß aggregations. More importantly, both compounds exhibited promising neuroprotective activities in PC-12 cells and good AChE selectivity. Collectively, the multifunctional profiles of compound d5 and d10 encourage further optimization and exploration to develop more potent analogues as potential treatments for AD.

Design, synthesis and biological evaluation of phenyl vinyl sulfone based NLRP3 inflammasome inhibitors.

As the vital component of innate immune system, the NLRP3 inflammasome is implicated in the onset and progression of a variety of inflammatory diseases and has emerged as an attractive drug target. Herein a series of novel phenyl vinyl sulfone based NLRP3 inflammasome inhibitors were designed, synthesized and biologically characterized. The most potent two hits 7a and 5b showed inhibition on the NLRP3 inflammasome with the IC50 of 1.83 ± 0.28 µM and 0.91 ± 0.06 µM, respectively. Further characterization confirmed their inhibition of NLRP3-mediated IL-1ß release in vivo. Collectively, our findings encourage further research of more potent inhibitors based on this chemical scaffold.

Recent advances of small molecule JNK3 inhibitors for Alzheimer's disease.

C-Jun N-terminal kinase (JNK) is a member of mitogen-activated protein kinases (MAPKs) family, with three isoforms, JNK1, JNK2 and JNK3. Alzheimer's disease (AD) is a neurological disorder and the most common type of dementia. Two well-established AD pathologies are the deposition of Aß amyloid plaques and neurofibrillary tangles caused by Tau hyperphosphorylation. JNK3 is involved in forming amyloid Aß and neurofibrillary tangles, suggesting that JNK3 may represent a target to develop treatments for AD. Therefore, this review will discuss the roles of JNK3 in the pathogenesis and treatment of AD, and the latest progress in the development of JNK3 inhibitors.

A branched small molecule-drug conjugate nanomedicine strategy for the targeted HCC chemotherapy.

Off-target toxicity is one of the main challenges faced by anticancer chemotherapeutics. For tumor targeted and precision chemotherapy, we take the advantages of the ligand directed tumor active targeting of small molecule drug conjugates (SMDCs) and the passive tumor targeting of nanoparticles via the enhanced penetration and retention (EPR) effects, put forward a branched small molecule drug conjugate (BSMDC) nanomedicine design concept. In a proof of concept, we used pentaerythritol as the branched moiety, galactosamine (GalN) as the hepatocellular carcinoma (HCC) directing ligands, PTX as a payload, and a stearoyl moiety as the amphiphilic property adjusting group, designed and synthesized BSMDC 1 and prepared its NPs. In cellular level, the BSMDC 1 NPs targeted asialoglycoprotein receptor (ASGPR)-overexpressing HepG2 cells, were effectively taken up in the cells and released in tumor microenvironments, inhibited the HepG2 cell proliferation, arrested HepG2 cell in G2/M phase and induced tumor cell apoptosis. In HepG2 xenograft nude mice, the BSMDC 1 NPs were high specific to target the tumor and demonstrated a higher antitumor efficiency than BSMDC 1, having no apparent influences on mice body weights and major organs, supporting our BSMDC nanomedicine design concept. Therefore, this new strategy may find applications for cancer targeted and precision chemotherapy.

Synthesis and biological evaluation of selective histone deacetylase 6 inhibitors as multifunctional agents against Alzheimer's disease.

Histone deacetylase 6 (HDAC6) is a potential target for Alzheimer's disease (AD). In this study, a series of novel phenothiazine-, memantine-, and 1,2,3,4-tetrahydro-γ-carboline-based HDAC6 inhibitors with a variety of linker moieties were designed and synthesized. As a hydrochloride salt, the phenothiazine-based hydroxamic acid W5 with a pyridyl-containing linker motif was identified as a high potent and selective HDAC6 inhibitor. It inhibited HDAC6 with an IC50 of 2.54 nM and was more than 290- to 3300-fold selective over other HDAC isoforms. In SH-SY5Y cells, W5 dose-dependently increased the acetylated α-tubulin levels and reduced the hyperphosphorylated tau proteins at Ser396. As an effective metal chelator, W5 inhibited Cu2+-induced Aß1-42 aggregation and disaggregated Cu2+-Aß1-42 oligomers, and showed protective effects on the SH-SY5Y cells against Aß1-42- as well as Cu2+-Aß1-42 induced cell damages, serving as a potential ligand to target AD metal dyshomeostasis. Moreover, W5 promoted the differentiated neuronal neurite outgrowth, increased the mRNA expression of the recognized neurogenesis markers, GAP43, N-myc, and MAP-2. Therefore, W5 might be a good lead for the development of novel HDAC6 inhibitors targeting multi-facets of AD.

SAR Investigation and Discovery of Water-Soluble 1-Methyl-1,4-dihydroindeno[1,2-c]pyrazoles as Potent Tubulin Polymerization Inhibitors.

Taking the previously discovered 1-methyl-1,4-dihydroindeno[1,2c]pyrazol derivative LL01 as a lead, systematic structural modifications were made at the phenolic 6- and 7-positions and the aniline at the 3-position of the indenopyrazole core to investigate the SARs and to improve water solubility. Among the designed indenopyrazoles ID01-ID33, a series of potent MTAs were identified. As the hydrochloride salt(s), ID09 and ID33 showed excellent aqueous solubility and favorable Log P value and displayed noteworthily low nanomolar potency against a variety of tumor cells, including those taxol-resistant ones. They inhibited tubulin polymerization, disrupted cellular microtubule networks by targeting the colchicine site, and promoted HepG2 cell cycle arrest and cell apoptosis. In the HepG2 xenograft mouse model, ID09 and ID33 effectively inhibited tumor growth at an oral dose of 25 mg/kg. At an intravenous (iv) injection dose of 10 mg/kg every other day, ID09 suppressed tumor growth by 68% without obvious toxicity.

Design, synthesis and biological evaluation of dual-function inhibitors targeting NMDAR and HDAC for Alzheimer's disease.

Histone deacetylases (HDACs) have been indicated important roles in neurodegenerative disorders including Alzheimer's disease (AD). Herein, a series of novel compounds that contain a memantine moiety were designed to target HDACs and N-methyl-d-aspartate receptor (NMDAR) which are related to the treatment of AD. Biological characterization established that compound 9d exhibited a balanced inhibitory activity on NMDAR and HDACs. This compound is relatively selective to HDAC6 with IC50 of 0.18 µM and also maintains comparable activity on NMDAR (Ki = 0.59 µM) as memantine. Functionally, treatment with 9d increased the level of AcTubulin in MV4-11 cells and rescued PC-12 cells from H2O2-induced cytotoxicity with EC50 of 0.94 µM. Studies in mice also demonstrated that compound 9d efficiently penetrates the blood brain barrier to reach the brain tissue. Collectively, the results strongly encourage further development of 9d as a potential therapeutic agent for AD.

Tacrine-hydroxamate derivatives as multitarget-directed ligands for the treatment of Alzheimer's disease: Design, synthesis, and biological evaluation.

In order to develop multitarget-directed ligands as potential treatments for Alzheimer's disease, twenty-eight new tacrine-hydroxamate derivatives were designed, synthesized, and biologically evaluated. As expected, most of the compounds exhibited inhibitory activities against cholinesterases (ChEs) and histone deacetylase (HDACs). Among the tested compounds, A10 showed not only potent and selective inhibition on AChE at sub-nanomolar potency (AChEIC50 = 0.12 nM, BChEIC50 = 361.52 nM) but also potent inhibition on HDAC (IC50 = 0.23 nM). Moreover, A10 exhibited inhibitory activity on Aß1-42 self-aggregation as well as disaggregation activity on pre-formed Aß fibrils. Furthermore, A10 exhibited antioxidant activity and metal chelating properties. Further mechanistic studies demonstrated that A10 is a pan-inhibitor of HDACs and a mixed-type inhibitor for AChE. It shown that A10 is a BBB penetrant by online prediction. Taken together, the results indicate that A10 can serve as a lead compound to develop promising candidate analogs as AD therapeutics.

Tubulin colchicine site binding agent LL01 displays potent antitumor efficiency both in vitro and in vivo with suitable drug-like properties.

Through rational drug design, we previously identified an indenoprazole derivative, 2-(6-ethoxy-3-(3-ethoxyphenylamino)-1-methyl-1,4-dihydroindeno[1,2-c]pyrazol-7-yloxy)acetamide (LL01), as a potent tubulin polymerization inhibitor targeting the tubulin colchicine binding site. In this study, we further demonstrated that LL01 was not a P-gp substrate. It potently inhibited the growth of a variety of tumor cells, including those with multidrug resistance, with GI50 values in the low nanomole ranges. In vitro liver microsome stability assay, LL01 was modest stable in the liver microsomes of human, mouse and rat, but was fast metabolized in dog. After single oral administration of LL01 at a dose of 10 mg/kg in SD male rats, LL01 showed acceptable PK properties with a mean bioavailability of 41%. In human HepG2 hepatoma xenograft, at the oral doses of 25 mg/kg/day and 12.5 mg/kg/day, LL01 inhibited the tumor growth by 61.27%, and 43.74%, respectively, which is much better than the positive drug sorafenib (29.45%; 30 mg/kg/day). Therefore, LL01 might be a potential drug candidate for further investigation for hepatocellular carcinoma therapy.

Development of small molecule inhibitors targeting NLRP3 inflammasome pathway for inflammatory diseases.

NLRP3 (Nod-like receptor protein 3) belongs to the NOD-like receptor family, which is activated by pathogen and damage-associated signals to form a multimeric protein complex, known as the NLRP3 inflammasome. NLRP3 inflammasome activation leads to release of proinflammatory cytokines IL-1ß and IL-18, thus inducing pyroptosis, a programmed cell death mechanism. Dysregulation of the NLRP3 inflammasome pathway is closely related to the development of many human diseases, such as neuroinflammation, metabolic inflammation, and immune inflammation. Emerging studies have suggested NLRP3 inflammasome as a potential drug-target for inflammatory diseases. Several small molecules have recently been identified to target the NLRP3 inflammasome pathway directly or indirectly and alleviate related disease pathology. This review summarizes recent evolving landscape of small molecule inhibitor development targeting the NLRP3 inflammasome pathway.

Glycyrrhetinic acid-modified graphene oxide mediated siRNA delivery for enhanced liver-cancer targeting therapy.

Graphene oxide (GO) has attracted huge attention in biomedical field in recent years. However, limited attempts have been invested in utilizing GO on active targeted delivery for gene therapy in liver cancer treatments. Glycyrrhetinic acid (GA) has been reported to be widely used as a targeting ligand to functionalize nanomaterials to treat hepatocellular carcinoma. In this article, GA is employed as a liver targeting ligand to construct GA, polyethylene glycol (PEG), polyamidoamine dendrimer (Dendrimer) and nano-graphene oxide (NGO) conjugate (GA-PEG-NGO-Dendrimer, GPND) for siRNA delivery for the first time. As we expected, GPND exhibited excellent stability, low toxicity, negligible hemolytic activity and remarkably high transfection efficiency in vitro. We also found effective VEGFa gene silencing in both mRNA and protein level in HepG2 cells. Notably, siRNA efficiently gathered in liver tumor tissues by the delivery of GPND, and eventually the growth of tumor tissues were inhibited with enhanced targeting capability and no obvious pathological changes. Moreover, histopathological results preliminarily support the high in vivo safety of GPND/anti-VEGFa siRNA nanocomplex. Collectively, GPND/siRNA nanocomplex, with high safety, targeting and transfection as well as prolonged half-life, is a promising nanomedicine and may provide a new direction for highly-specific targeted gene therapy.

Design, synthesis and activity evaluation of indole-based double - Branched HDAC1 inhibitors.

Histone deacetylases inhibitors (HDACIs) represents effective treatments for cancer. In continuing our efforts to develop novel and potent HDACIs, a series of N-hydroxycinnamamide-based HDACIs with aromatic ring and various aliphatic linker have been successfully designed and synthesized. Biological evaluations established that compounds 4h, 4i, 4j, 4l, 4r showed superior inhibition on histone deacetylase and antiproliferative activity in some solid tumor cell lines [HeLa, SK-N-BE(2), PC-3] compared to the known inhibitor SAHA. Among these analogs, 4l exhibited selectivity to HDAC1.

Synthesis and evaluation of novel GSK-3ß inhibitors as multifunctional agents against Alzheimer's disease.

To target the multi-facets of Alzheimer's disease (AD), a series of novel GSK-3ß inhibitors containing the 2,3-diaminopyridine moiety were designed and synthesized. The amide derivatives 5a-f showed moderate potency against GSK-3ß with weak Cu2+, Zn2+ and Al3+ chelating ability. The imine derivatives 9a, 9b and 9e were potent GSK-3ß inhibitors and selective Cu2+and Al3+ chelators. The 1,2-diamine derivatives 10a-e were strong metal-chelators, but decreased or lost their GSK-3ß inhibitory potency. In vitro, compounds 9a, 9b and 9e, especially 9b, exhibited good Cu2+-induced Aß aggregation inhibition, Cu2+-Aß complex disaggregation, ROS formation inhibition, and antioxidant activities. In cells, compounds 9a, 9b and 9e can inhibit tau protein phosphorylation and protect neuro cells against Cu2+-Aß1-42 and H2O2-induced cell damage. Furthermore, compound 9b was predicted to have the ability to pass the BBB with drug likeness properties. Therefore, compound 9b might be a good lead for the development of novel GSK-3ß inhibitors targeting multi-facets of AD.

Advances on graphene-based nanomaterials for biomedical applications.

Graphene-based nanomaterials, such as graphene oxide and reduced graphene oxide, have been attracting increasing attention in the field of biology and biomedicine over the past few years. Incorporation of these novel materials with drug, gene, photosensitizer and other cargos to construct novel delivery systems has witnessed rapid advance on the basis of their large surface area, distinct surface properties, excellent biocompatibility and pH sensitivity. Moreover, the inherent photothermal effect of these appealing materials enables them with the ability of killing targeting cells via a physical mechanism. Recently, more attentions have been attached to tissue engineering, including bone, neural, cardiac, cartilage, musculoskeletal, and skin/adipose tissue engineering, due to the outstanding mechanical strength, stiffness, electrical conductivity, various two-dimensional (2D) and three-dimensional (3D) morphologies of graphene-based nanomaterials. Herein, emerging applications of these nanomaterials in bio-imaging, drug/gene delivery, phototherapy, multimodality therapy and tissue engineering were comprehensively reviewed. Inevitably, the burgeon of this kind of novel materials leads to the endeavor to consider their safety so that this issue has been deeply discussed and summarized in our review. We hope that this review offers an overall understanding of these nanomaterials for later in-depth investigations.

Development of Bruton's Tyrosine Kinase Inhibitors for Rheumatoid Arthritis.

Rheumatoid Arthritis (RA) is a chronic autoimmune disease and becomes one of the major causes of disability and work force loss. The presence of abnormal B cell and autoantibodies produced by most RA patients, primarily ACPA and RF, indicate that the function of B cell was involved in the development of RA disease. Accordingly, the drug targeting B cell has become a hot spot in the treatment of RA. Studies have shown that Bruton's tyrosine kinase (BTK) is involved in the regulation of B cell proliferation and activation process. Some small molecule BTK inhibitors have shown excellent inhibition in biological activity analysis and animal models. Therefore, this review will briefly introduce BTK and its role in cell signaling and overview recent progress of BTK inhibitors for RA treatment.

Structure optimization and preliminary bioactivity evaluation of N-hydroxybenzamide-based HDAC inhibitors with Y-shaped cap.

Histone deacetylase inhibitors (HDACIs) are effective small molecules in the treatment of human cancers. In our continuing efforts to develop novel N-hydroxyterephthalamide-based HDACIs, herein we report the design and development of a new class of N-hydroxybenzamide-based HDACIs. In this new class of analogs, we inserted an ethylene moiety in the linker and used indole as a part of the Y-shaped cap group. Biological characterization identified compounds 4o, 4p, 4q and 4t to show improved HDAC inhibition, while no isoform selectivity for HDACs was observed. These compounds also exhibited improved anti-proliferative activity against multiple cancer cell lines when compared to their parent compound and positive control SAHA.

Development and Characterization of a Hydroxyl-Sulfonamide Analogue, 5-Chloro-N-[2-(4-hydroxysulfamoyl-phenyl)-ethyl]-2-methoxy-benzamide, as a Novel NLRP3 Inflammasome Inhibitor for Potential Treatment of Multiple Sclerosis.

In our efforts to develop novel small-molecule inhibitors for the NOD-like receptor family pyrin-domain-containing 3 (NLRP3) inflammasome as potential disease-modifying agents to treat neurological disorders including multiple sclerosis (MS), a hydroxyl sulfonamide analogue JC-171 has been rationally designed and biologically characterized both in vitro and in vivo. Our studies established that JC-171 dose dependently inhibited LPS/ATP-induced interleukin-1ß (IL-1ß) release from J774A.1 macrophages with an IC50 of 8.45 ± 1.56 µM. Selective inhibition of the NLRP3 inflammasome induced IL-1ß release by this compound was also confirmed using mouse bone-marrow-derived macrophages and LPS-challenged mice in vivo. Furthermore, immunoprecipitation study revealed that JC-171 interfered with NLRP3/ASC interaction induced by LPS/ATP stimulation. More importantly, JC-171 treatment delayed the progression and reduced the severity of experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, in both prophylactic and therapeutic settings. This coincided with blocking of IL-1ß production and a pathogenic Th17 response. Collectively, these results suggest that JC-171 is a selective NLRP3 inflammasome inhibitor with biological activity in vivo, thus strongly encouraging further development of this lead compound as a potential therapeutic agent for human MS.

Design, synthesis and tumor cell growth inhibitory activity of 3-nitro-2H-cheromene derivatives as histone deacetylaes inhibitors.

As a continuous research for the discovery of coumarin-based targeted anticancer agents, we designed and synthesized a series of novel histone deacetylases (HDAC) inhibitors using the 8-ethoxy-3-nitro-2H-chromene as the surface binding or cap group, linear dicarboxylic acid or ω-amino acid moiety with different length as the linking motif, ortho-aminoanilides, amides or α-aminoamides as the zinc binding group and the internal cavity motifs. Most of these 3-nitro-2H-chromene derivatives exhibited good growth inhibitory activity against K562, A549, MCF-7, PC3 and Hela cells and were more potent than the reference drug SAHA and MS-275. At the concentration of 10µM, the ortho-aminoanilide series and the d-Phe derived α-aminoamide derivatives 16a and 16b displayed more potent activity toward HADC1 over HADC2, and only moderate to weak activity over HADC6. In contrast, the amide ZBG analogues, 12a and 12b, 14 and 15, were only moderate HDAC6 inhibitors, but more selective over HDAC1 and HDAC2. The ortho-aminoanilides 9b, 9c, 10b, 10c, 11b, and the α-aminoamides 16a and 16b were potent HADC1 inhibitors with the IC50 values in the nanomolar ranges. The ortho-aminoanilides 10b and10c with a phenyl internal cavity motif were more potent than MS-275 as HADC1 inhibitors and more selective over HADC2.

Selective HDAC inhibitors with potent oral activity against leukemia and colorectal cancer: Design, structure-activity relationship and anti-tumor activity study.

Previously, we reported the discovery of a series of N-hydroxycinnamamide-based HDAC inhibitors, among which compound 11y exhibited high HDAC1/3 selectivity. In this current study, structural derivatization of 11y led to a new series of benzamide based HDAC inhibitors. Most of the compounds exhibited high HDACs inhibitory potency. Compound 11a (with 4-methoxybenzoyl as N-substituent in the cap and 4-(aminomethyl) benzoyl as the linker group) exhibited selectivity against HDAC1 to some extent, and showed potent antiproliferative activity against several tumor cell lines. In vivo studies revealed that compound 11a displayed potent oral antitumor activity in both hematological tumor cell U937 xenograft model and solid tumor cell HCT116 xenograft model with no obvious toxicity. Further modification of benzamide 3, 11a and 19 afforded new thienyl and phenyl compounds (50a, 50b, 63a, 63b and 63c) with dramatic HDAC1 and HDAC2 dual selectivity, and the fluorine containing compound 56, with moderate HDAC3 selectivity.