Identification of potent histone deacetylase 2 (HDAC2) inhibitors through combined structure and ligand-based designs and molecular modelling approach

Histone deacetylase 2 (HDAC2) is associated with various neuropathic degenerative diseases and is considered a novel target for Alzheimer's disease (AD). Elevated levels of HDAC2 trigger excitatory neurotransmission and reduce synaptic plasticity, synaptic number, and memory formation. In the current study, we identified HDAC2 inhibitors using an integrated structure and ligand-based approaches to drug design. Three pharmacophore models were generated by using different pharmacophoric features and validated using the Enrichment factor (EF), Güner-henry (GH) score, and percentage yield. The model of choice was used to screen a library of Zinc-15 compounds and interfering compounds were eliminated by using drug likeliness and PAINS filtering. Further, docking studies in three stages were carried out to obtain hits with good binding energies and were followed by ADMET studies yielding three virtual hits. The virtual hits, i.e. ZINC000008184553, ZINC0000013641114, and ZINC000032533141, were subjected to molecular dynamics simulation studies. Compound ZINC000008184553, identified as lead, was found to have optimal stability, low toxicity under simulated conditions, and may potentially inhibit HDAC2.Communicated by Ramaswamy H. Sarma.

Rational discovery of dual FLT3/HDAC inhibitors as a potential AML therapy

Acute myeloid leukemia (AML) patients often experience poor therapeutic outcomes and relapse after treatment with single-target drugs, representing the urgent need of new therapies. Simultaneous inhibition of multiple oncogenic signals is a promising strategy for tumor therapy. Previous studies have reported that concomitant inhibition of Fms-like tyrosine kinase 3 (FLT3) and histone deacetylases (HDACs) can significantly improve the therapeutic efficacy for AML. Herein, a series of novel dual FLT3/HDAC inhibitors were developed through a rational structure-based drug design strategy for the first time. Among them, multiple compounds showed potent and equivalent inhibitory activities against FLT3-ITD and HDAC1, with the representative compound 63 selectively inhibiting HDAC class I (HDAC1/2/3/8) and IIB isoforms (HDAC6) related to tumorigenesis, and intensively blocking proliferation of MV4-11 cells. The antiproliferation activity was proven to depend on the dual inhibition of FLT3 and HDAC1. Mechanism assays demonstrated that 63 prohibited both FLT3 and HDAC pathways, induced apoptosis and arrested cell cycle in MV4-11 cells in a dose-dependent manner. In summary, this study validated the therapeutic potential of a kind of dual FLT3/HDAC inhibitors for AML and provided novel compounds for further biological investigation on concomitant inhibition of FLT3/HDAC pathways. Additionally, the structure-based drug design strategy described herein may provide profound enlightenment for developing superior anti-AML drugs.

Potential of histone deacetylase inhibitors in the control and regulation of prostate, breast and ovarian cancer

Histone deacetylases (HDACs) are enzymes that play a role in chromatin remodeling and epigenetics. They belong to a specific category of enzymes that eliminate the acetyl part of the histones’ -N-acetyl lysine, causing the histones to be wrapped compactly around DNA. Numerous biological processes rely on HDACs, including cell proliferation and differentiation, angiogenesis, metastasis, gene regulation, and transcription. Epigenetic changes, specifically increased expression and activity of HDACs, are commonly detected in cancer. As a result, HDACi could be used to develop anticancer drugs. Although preclinical outcomes with HDACs as monotherapy have been promising clinical trials have had mixed results and limited success. In both preclinical and clinical trials, however, combination therapy with different anticancer medicines has proved to have synergistic effects. Furthermore, these combinations improved efficacy, decreased tumor resistance to therapy, and decreased toxicity. In the present review, the detailed modes of action, classification of HDACs, and their correlation with different cancers like prostate, breast, and ovarian cancer were discussed. Further, the different cell signaling pathways and the structure-activity relationship and pharmaco-toxicological properties of the HDACi, and their synergistic effects with other anticancer drugs observed in recent preclinical and clinical studies used in combination therapy were discussed for prostate, breast, and ovarian cancer treatment.

New kinase and HDAC hybrid inhibitors: recent advances and perspectives

Cancer is the second most common cause of death worldwide. It can easily acquire resistance to treatments, demanding new therapeutic strategies, such as simultaneous inhibition of kinase and HDAC enzymes with hybrid inhibitors. Different approaches to this have varied according to their targets, with a few common trends, such as the usage of heterocycle scaffolds for kinase interaction, especially pyrimidine and quinazolines, and hydroxamic acids and benzamides for HDAC inhibition. Besides the hybrid compounds developed focusing on the inhibition tyrosine kinase and receptor tyrosine kinase, many advances have occurred in the development of serine-threonine kinase/HDAC and lipid kinase/HDAC novel compounds. Here, the latest strategies employed in this research area will be reviewed, alongside trends in inhibitor design, and observed gaps will be punctuated.

Molecular hybrids: A five-year survey on structures of multiple targeted hybrids of protein kinase inhibitors for cancer therapy

Protein kinases have grown over the past few years as a crucial target for different cancer types. With the multifactorial nature of cancer, and the fast development of drug resistance for conventional chemotherapeutics, a strategy for designing multi-target agents was suggested to potentially increase drug efficacy, minimize side effects and retain the proper pharmacokinetic properties. Kinase inhibitors were used extensively in such strategy. Different kinase inhibitor agents which target EGFR, VEGFR, c-Met, CDK, PDK and other targets were merged into hybrids with conventional chemotherapeutics such as tubulin polymerization and topoisomerase inhibitors. Other hybrids were designed gathering kinase inhibitors with targeted cancer therapy such as HDAC, PARP, HSP 90 inhibitors. Nitric oxide donor molecules were also merged with kinase inhibitors for cancer therapy. The current review presents the hybrids designed in the past five years discussing their design principles, results and highlights their future perspectives.

Development and therapeutic potential of 2-aminothiazole derivatives in anticancer drug discovery

Currently, the development of anticancer drug resistance is significantly restricted the clinical efficacy of the most commonly prescribed anticancer drug. Malignant disease is widely prevalent and considered to be the major challenges of this century, which concerns the medical community all over the world. Consequently, investigating small molecule antitumor agents, which could decrease drug resistance and reduce unpleasant side effect is more desirable. 2-aminothiazole scaffold has emerged as a promising scaffold in medicinal chemistry and drug discovery research. This nucleus is a fundamental part of some clinically applied anticancer drugs such as dasatinib and alpelisib. Literature survey documented that different 2-aminothiazole analogs exhibited their potent and selective nanomolar inhibitory activity against a wide range of human cancerous cell lines such as breast, leukemia, lung, colon, CNS, melanoma, ovarian, renal, and prostate. In this paper, we have reviewed the progresses and structural modification of 2-aminothiazole to pursuit potent anticancers and also highlighted in vitro activities and in silico studies. The information will useful for future innovation. Representatives of 2-aminothiazole-containing compounds classification.

Comprehensive review for anticancer hybridized multitargeting HDAC inhibitors

Despite the encouraging clinical progress of chemotherapeutic agents in cancer treatment, innovation and development of new effective anticancer candidates still represents a challenging endeavor. With 15 million death every year in 2030 according to the estimates, cancer has increased rising of an alarm as a real crisis for public health and health systems worldwide. Therefore, scientist began to introduce innovative solutions to control the cancer global health problem. One of the promising strategies in this issue is the multitarget or smart hybrids having two or more pharmacophores targeting cancer. These rationalized hybrid molecules have gained great interests in cancer treatment as they are capable to simultaneously inhibit more than cancer pathway or target without drug-drug interactions and with less side effects. A prime important example of these hybrids, the HDAC hybrid inhibitors or referred as multitargeting HDAC inhibitors. The ability of HDAC inhibitors to synergistically improve the efficacy of other anti-cancer drugs and moreover, the ease of HDAC inhibitors cap group modification prompt many medicinal chemists to innovate and develop new generation of HDAC hybrid inhibitors. Notably, and during this short period, there are four HDAC inhibitor hybrids have entered different phases of clinical trials for treatment of different types of blood and solid tumors, namely; CUDC-101, CUDC-907, Tinostamustine, and Domatinostat. This review shed light on the most recent hybrids of HDACIs with one or more other cancer target pharmacophore. The designed multitarget hybrids include topoisomerase inhibitors, kinase inhibitors, nitric oxide releasers, antiandrogens, FLT3 and JAC-2 inhibitors, PDE5-inhibitors, NAMPT-inhibitors, Protease inhibitors, BRD4-inhibitors and other targets. This review may help researchers in development and discovery of new horizons in cancer treatment.

Dual inhibitors of histone deacetylases and other cancer-related targets: A pharmacological perspective

Epigenetic enzymes histone deacetylases (HDACs) are clinically validated anticancer drug targets which have been studied intensively in the past few decades. Although several drugs have been approved in this field, they are still limited to a subset of hematological malignancies (in particular T-cell lymphomas), with therapeutic potential not fully realized and the drug-resistance occurred after a certain period of use. To maximize the therapeutic potential of these classes of anticancer drugs, and to extend their application to solid tumors, numerous combination therapies containing an HDACi and an anticancer agent from other mechanisms are currently ongoing in clinical trials. Recently, dual targeting strategy comprising the HDACs component has emerged as an alternative approach for combination therapies. In this perspective, we intend to gather all HDACs-containing dual inhibitors related to cancer therapy published in literature since 2015, classify them into five categories based on targets' biological functions, and discuss the rationale why dual acting agents should work better than combinatorial therapies using two separate drugs. The article discusses the pharmacological aspects of these dual inhibitors, including in vitro biological activities, pharmacokinetic studies, in vivo efficacy studies, as well as available clinical trials. The review of the current status and advances should provide better analysis for future opportunities and challenges of this field.

Paradigm shift of "classical" HDAC inhibitors to "hybrid" HDAC inhibitors in therapeutic interventions

'Epigenetic' regulation of genes via post-translational modulation of proteins is the current mainstay approach for the disease therapies, particularly explored in the Histone Deacetylase (HDAC) class of enzymes. Mainly sight saw in cancer chemotherapeutics, HDAC inhibitors have also found a promising role in other diseases (neurodegenerative disorders, cardiovascular diseases, and viral infections) and successfully entered in various combination therapies (pre-clinical/clinical stages). The prevalent flexibility in the structural design of HDAC inhibitors makes them easily tuneable to merge with other pharmacophore modules for generating multi-targeted single hybrids as a novel tactic to overcome drawbacks of polypharmacy. Herein, we reviewed the putative role of prevalent HDAC hybrids inhibitors in the current and prospective stage as a translational approach to overcome the limitations of the existing conventional drug candidates (parent molecule) when used either alone (drug resistance, solubility issues, adverse side effects, selectivity profile) or in combination (pharmacokinetic interactions, patient compliance) for treating various diseases.

Discovery of 1,3-Disubstituted 2,5-Diketopiperazine Derivatives as Potent Class I HDACs Inhibitors

Histone deacetylases (HDACs) as attractive targets in many diseases therapies has been studied extensively, and its application in cancer research is the most important. Here, we developed a series of derivatives containing natural 2,5-diketopiperazine (DKP) skeleton. Several compounds exhibited distinct HDAC1 inhibitory activities, in particular 2a (IC₅₀ = 405 nM). The selectivity profile for representative 2a indicated that this series of compounds had a preference for HDAC1-3. Additionally, 2a showed the best growth inhibitory activities against K562 and HL-60 tumor cell line with IC₅₀ values of 4.23 and 4.16 µM, respectively. This work may lay the foundation for developing DKP-based HDAC inhibitors as a potential anticancer agent.

Design, Synthesis and Biological Evaluation of Novel Benzoylimidazole Derivatives as Raf and Histone Deacetylases Dual Inhibitors

In recent studies, combinations of histone deacetylases (HDACs) inhibitor with kinase inhibitor showed additive and synergistic effects. BRaf^V600E as an attractive target in many diseases treatments has been studied extensively. Herein, we present a novel design approach though incorporating the pharmacophores of BRaf^V600E inhibitor and HDACs inhibitor in one molecule. Several synthesized compounds exhibited distinct BRaf^V600E and HDAC1 inhibitory activities. The representative dual Raf/HDAC inhibitor, 7a, showed better antiproliferative activities against A549 and SK-Mel-2 in cellular assay than SAHA and sorafenib, with IC₅₀ values of 9.11 µM and 5.40 µM, respectively. This work may lay the foundation for the further development of dual Raf/HDAC inhibitors as potential anticancer agents.

Synthesis of 2-Amino-5-Carboxamide Thiazole Derivatives via Dehydrative Cyclization of Thiourea Intermediate Resin on Solid Phase

In this study, we synthesized 2-amino-5-carboxamide thiazole derivatives on solid phase. The synthesis of the library starts with the reductive amination of the 4-formyl-3-methoxy phenoxy resin to prevent isomer formation. The dehydrative cyclization of thiourea intermediate resin, which is the key step in the synthetic process, was successfully synthesized using α-bromoketone in the presence of the DMF so as to afford 2-amino-5-carboxylate thiazole resin. The resulting resin is coupled with various amines. Finally, the 2-amino-5-carboxamide thiazole resin was cleaved from the polymer support using a TFA and DCM cocktail. The physicochemical properties of the proposed 2-amino-5-carboxamide thiazole derivatives were calculated and showed potential to be an reasonable oral bioavailability drug properties as determined by Lipinski's Rule.

Design, synthesis, and biological evaluation of AV6 derivatives as novel dual reactivators of latent HIV-1

The “shock and kill” strategy might be a promising therapeutic approach for HIV/AIDS due to the existence of latent viral reservoirs. A major challenge of the “shock and kill” strategy arises from the general lack of clinically effective latency-reversing agents (LRAs). The 2-methylquinoline derivative, antiviral 6 (AV6) has been reported to induce latent HIV-1 expression and act synergistically with a HDAC inhibitor VA to reverse HIV latency. We report herein the design and identification of AV6 analogues which possess the zinc-binding group of HDAC inhibitors and have dual acting mechanism for the reactivation of HIV-1 from latency. Evaluation of compounds for the reactivation of HIV-1 latency identified two excellent active compounds 12c and 12d. Further bioassays revealed that these two compounds reactivated latent HIV-1 through dual mechanism, the inhibition of HDACs and NFAT-required for early HIV-1 gene expression. Additionally, it was found that 12c and 12d could reactivate HIV-1 transcription by releasing P-TEFb from the inactive complex 7SK snRNP. At last, molecular docking identified their orientation and binding interactions at the active site of HDAC2. This experimental data suggests that 12c and 12d can be served as effective HIV-1 LRAs which can be taken up for further studies.

As dual-acting HIV LRAs, compounds 12c and 12d could activate latent HIV-1 via the NFAT-required mechanism and as histone deacetylase (HDAC) inhibitors.

Design, synthesis and biological evaluation of 2,3-dihydroimidazo[1,2-c]quinazoline derivatives as novel phosphatidylinositol 3-kinase and histone deacetylase dual inhibitors

A novel design approach by combination of PI3K and HDAC inhibitory activity in one molecule to produce dual inhibitors.