Design and Synthesis of Janus Kinase 2 (JAK2) and Histone Deacetlyase (HDAC) Bispecific Inhibitors Based on Pacritinib and Evidence of Dual Pathway Inhibition in Hematological Cell Lines

Advances in dual-targeting inhibitors of HDAC6 for cancer treatment

Histone Deacetylase 6 (HDAC6) is an essential regulator of histone acetylation processes, exerting influence on a multitude of cellular functions such as cell motility, endocytosis, autophagy, apoptosis, and protein trafficking through its deacetylation activity. The significant implications of HDAC6 in diseases such as cancer, neurodegenerative disorders, and immune disorders have motivated extensive investigation into the development of specific inhibitors targeting this enzyme for therapeutic purposes. Single targeting drugs carry the risk of inducing drug resistance, thus prompting exploration of dual targeting therapy which offers the potential to impact multiple signaling pathways simultaneously, thereby lowering the likelihood of resistance development. While pharmacological studies have exhibited promise in combined therapy involving HDAC6, challenges related to potential drug interactions exist. In response to these challenges, researchers are investigating HDAC6 hybrid molecules which enable the concomitant targeting of HDAC6 and other key proteins, thus enhancing treatment efficacy while mitigating side effects and reducing the risk of resistance compared to traditional combination therapies. The published design strategies for dual targeting inhibitors of HDAC6 are summarized and discussed in this review. This will provide some valuable insights into more novel HDAC6 dual targeting inhibitors to meet the urgent need for innovative therapies in oncology and other related fields.

Small molecule inhibitors targeting heat shock protein 90: An updated review

As a molecular chaperone, heat shock protein 90 (HSP90) plays important roles in the folding, stabilization, activation, and degradation of over 500 client proteins, and is extensively involved in cell signaling, proliferation, and survival. Thus, it has emerged as an important target in a variety of diseases, including cancer, neurodegenerative diseases, and viral infections. Therefore, targeted inhibition of HSP90 provides a valuable and promising therapeutic strategy for the treatment of HSP90-related diseases. This review aims to systematically summarize the progress of research on HSP90 inhibitors in the last five years, focusing on their structural features, design strategies, and biological activities. It will refer to the natural products and their derivatives (including novobiocin derivatives, deguelin derivatives, quinone derivatives, and terpenoid derivatives), and to synthetic small molecules (including resorcinol derivatives, pyrazoles derivatives, triazole derivatives, pyrimidine derivatives, benzamide derivatives, benzothiazole derivatives, and benzofuran derivatives). In addition, the major HSP90 small-molecule inhibitors that have moved into clinical trials to date are also presented here.

Emerging therapeutic strategies in cancer therapy by HDAC inhibition as the chemotherapeutic potent and epigenetic regulator

In developing new cancer medications, attention has been focused on novel epigenetic medicines called histone deacetylase (HDAC) inhibitors. Our understanding of cancer behavior is being advanced by research on epigenetics, which also supplies new targets for improving the effectiveness of cancer therapy. Most recently published patents emphasize HDAC selective drugs and multitarget HDAC inhibitors. Though significant progress has been made in emerging HDAC selective antagonists, it is urgently necessary to find new HDAC blockers with novel zinc-binding analogues to avoid the undesirable pharmacological characteristics of hydroxamic acid. HDAC antagonists have lately been explored as a novel approach to treating various diseases, including cancer. The complicated terrain of HDAC inhibitor development is summarized in this article, starting with a discussion of the many HDAC isotypes and their involvement in cancer biology, followed by a discussion of the mechanisms of action of HDAC inhibitors, their current level of development, effect of miRNA, and their combination with immunotherapeutic.

Novel dual inhibitors of PARP and HDAC induce intratumoral STING-mediated antitumor immunity in triple-negative breast cancer

PARP inhibitors and HDAC inhibitors have been approved for the clinical treatment of malignancies, but acquired resistance of or limited effects on solid tumors with a single agent remain as challenges. Bioinformatics analyses and a combination of experiments had demonstrated the synergistic effects of PARP and HDAC inhibitors in triple-negative breast cancer. A series of novel dual PARP and HDAC inhibitors were rationally designed and synthesized, and these molecules exhibited high enzyme inhibition activity with excellent antitumor effects in vitro and in vivo. Mechanistically, dual PARP and HDAC inhibitors induced BRCAness to restore synthetic lethality and promoted cytosolic DNA accumulation, which further activates the cGAS-STING pathway and produces proinflammatory chemokines through type I IFN-mediated JAK-STAT pathway. Moreover, these inhibitors promoted neoantigen generation, upregulated antigen presentation genes and PD-L1, and enhanced antitumor immunity when combined with immune checkpoint blockade therapy. These results indicated that novel dual PARP and HDAC inhibitors have antitumor immunomodulatory functions in triple-negative breast cancer. Novel dual PARP and HDAC inhibitors induce BRCAness to restore synthetic lethality, activating tumoral IFN signaling via the cGAS-STING pathway and inducing cytokine production, promoting neoantigen generation and presentation to enhance the immune response.

Role of Histone Deacetylase 6 and Histone Deacetylase 6 Inhibition in Colorectal Cancer

Histone deacetylase 6 (HDAC6), by deacetylation of multiple substrates and association with interacting proteins, regulates many physiological processes that are involved in cancer development and invasiveness such as cell proliferation, apoptosis, motility, epithelial to mesenchymal transition, and angiogenesis. Due to its ability to remove misfolded proteins, induce autophagy, and regulate unfolded protein response, HDAC6 plays a protective role in responses to stress and enables tumor cell survival. The scope of this review is to discuss the roles of HDCA6 and its implications for the therapy of colorectal cancer (CRC). As HDAC6 is overexpressed in CRC, correlates with poor disease prognosis, and is not essential for normal mammalian development, it represents a good therapeutic target. Selective inhibition of HDAC6 impairs growth and progression without inducing major adverse events in experimental animals. In CRC, HDAC6 inhibitors have shown the potential to reduce tumor progression and enhance the therapeutic effect of other drugs. As HDAC6 is involved in the regulation of immune responses, HDAC6 inhibitors have shown the potential to improve antitumor immunity by increasing the immunogenicity of tumor cells, augmenting immune cell activity, and alleviating immunosuppression in the tumor microenvironment. Therefore, HDAC6 inhibitors may represent promising candidates to improve the effect of and overcome resistance to immunotherapy.

Harnessing pyrimidine as a building block for histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are well-established multifaceted bioactive agents against tumors and neurodegenerative disorders. Pyrimidine and its fused and substituted derivatives were employed as a surface recognition moiety of HDAC inhibitors. De facto, the literature was loaded with different success stories of pyrimidine-based HDAC inhibitors that garnered much interest. Provoked by our continuous interest in HDAC inhibitors, we summarized and elaborated on the successful harnessing of the pyrimidine scaffold in this regard. Furthermore, we dissect our perspective that may guide medicinal chemists for an effective future design of more active chemotherapeutic agents with potential clinical applications.

Discovery of C-5 Pyrazole-Substituted Pyrrolopyridine Derivatives as Potent and Selective Inhibitors for Janus Kinase 1

Developing selective inhibitors for Janus kinase 1 (JAK1) is a significant focus for improving the efficacy and alleviating the adverse effects in treating immune-inflammatory diseases. Herein, we report the discovery of a series of C-5 pyrazole-modified pyrrolopyrimidine derivatives as JAK1-selective inhibitors. The potential hydrogen bond between the pyrazole group and E966 in JAK1 is the key point that enhances JAK1 selectivity. These compounds exhibit 10- to 20-fold JAK1 selectivity over JAK2 in enzyme assays. Compound 12b also exhibits excellent JAK1 selectivity in Ba/F3-TEL-JAK cellular assays. Metabolism studies and the results of the hair growth model in mice indicate that compound 12b may be a viable lead compound for the development of highly JAK1-selective inhibitors for immune and inflammatory diseases.

Epigenetic regulation in hematopoiesis and its implications in the targeted therapy of hematologic malignancies

Hematologic malignancies are one of the most common cancers, and the incidence has been rising in recent decades. The clinical and molecular features of hematologic malignancies are highly heterogenous, and some hematologic malignancies are incurable, challenging the treatment, and prognosis of the patients. However, hematopoiesis and oncogenesis of hematologic malignancies are profoundly affected by epigenetic regulation. Studies have found that methylation-related mutations, abnormal methylation profiles of DNA, and abnormal histone deacetylase expression are recurrent in leukemia and lymphoma. Furthermore, the hypomethylating agents and histone deacetylase inhibitors are effective to treat acute myeloid leukemia and T-cell lymphomas, indicating that epigenetic regulation is indispensable to hematologic oncogenesis. Epigenetic regulation mainly includes DNA modifications, histone modifications, and noncoding RNA-mediated targeting, and regulates various DNA-based processes. This review presents the role of writers, readers, and erasers of DNA methylation and histone methylation, and acetylation in hematologic malignancies. In addition, this review provides the influence of microRNAs and long noncoding RNAs on hematologic malignancies. Furthermore, the implication of epigenetic regulation in targeted treatment is discussed. This review comprehensively presents the change and function of each epigenetic regulator in normal and oncogenic hematopoiesis and provides innovative epigenetic-targeted treatment in clinical practice.

Pharmacological Modulation of the Crosstalk between Aberrant Janus Kinase Signaling and Epigenetic Modifiers of the Histone Deacetylase Family to Treat Cancer

Hyperactivated Janus kinase (JAK) signaling is an appreciated drug target in human cancers. Numerous mutant JAK molecules as well as inherent and acquired drug resistance mechanisms limit the efficacy of JAK inhibitors (JAKi). There is accumulating evidence that epigenetic mechanisms control JAK-dependent signaling cascades. Like JAKs, epigenetic modifiers of the histone deacetylase (HDAC) family regulate the growth and development of cells and are often dysregulated in cancer cells. The notion that inhibitors of histone deacetylases (HDACi) abrogate oncogenic JAK-dependent signaling cascades illustrates an intricate crosstalk between JAKs and HDACs. Here, we summarize how structurally divergent, broad-acting as well as isoenzyme-specific HDACi, hybrid fusion pharmacophores containing JAKi and HDACi, and proteolysis targeting chimeras for JAKs inactivate the four JAK proteins JAK1, JAK2, JAK3, and tyrosine kinase-2. These agents suppress aberrant JAK activity through specific transcription-dependent processes and mechanisms that alter the phosphorylation and stability of JAKs. Pharmacological inhibition of HDACs abrogates allosteric activation of JAKs, overcomes limitations of ATP-competitive type 1 and type 2 JAKi, and interacts favorably with JAKi. Since such findings were collected in cultured cells, experimental animals, and cancer patients, we condense preclinical and translational relevance. We also discuss how future research on acetylation-dependent mechanisms that regulate JAKs might allow the rational design of improved treatments for cancer patients. SIGNIFICANCE STATEMENT: Reversible lysine-ɛ-N acetylation and deacetylation cycles control phosphorylation-dependent Janus kinase-signal transducer and activator of transcription signaling. The intricate crosstalk between these fundamental molecular mechanisms provides opportunities for pharmacological intervention strategies with modern small molecule inhibitors. This could help patients suffering from cancer.

Discovery of selective HDAC6 inhibitors capped by flavonoid or flavonoid-analogous moieties as anti-cancer therapeutics simultaneously harboring anti-proliferative and immunomodulatory activities

Specific HDAC6 inhibitors (HDAC6is) simultaneously harboring anti-proliferative and immunomodulatory properties may prohibit tumor progression via intrinsic and immune driven effects. Herein, built upon the structurally novel lead TFH-7, structure-activity relationship study culminated in the identification of azaflavone-capped compound 20, which exhibited comparable HDAC6 inhibitory activity (IC₅₀ = 8.5 nM) to that of Tubastatin A, a highly selective HDAC6i, as well as favorable subtype specificity. Importantly, concurrent with its impressive anti-proliferative efficacy against several solid tumor cell lines, 20 remarkably alleviated the transduction of immune-related STAT3 signaling and attenuated the expression of immunosuppressive checkpoint PD-L1 at submicromolar concentration, highlighting the immunomodulatory properties. Moreover, consistent with its favorable subtype selectivity, 20 displayed low cytotoxicity against normal human umbilical vein endothelial cells, revealing a promising safety profile. Following the intravenous administration, it demonstrated acceptable elimination half-life and exposure in Sprague-Dawley rats. Hence, the extensive functional investigation or structural modification of 20 is valuable.

Discovery of spirooxindole-derived small-molecule compounds as novel HDAC/MDM2 dual inhibitors and investigation of their anticancer activity

Simultaneous inhibition of more than one target is considered to be a novel strategy in cancer therapy. Owing to the importance of histone deacetylases (HDACs) and p53-murine double minute 2 (MDM2) interaction in tumor development and their synergistic effects, a series of MDM2/HDAC bifunctional small-molecule inhibitors were rationally designed and synthesized by incorporating an HDAC pharmacophore into spirooxindole skeletons. These compounds exhibited good inhibitory activities against both targets. In particular, compound 11b was demonstrated to be most potent for MDM2 and HDAC, reaching the enzyme inhibition of 68% and 79%, respectively. Compound 11b also showed efficient antiproliferative activity towards MCF-7 cells with better potency than the reference drug SAHA and Nutlin-3. Furthermore, western blot analysis revealed that compound 11b increased the expression of p53 and Ac-H4 in MCF-7 cells in a dose-dependent manner. Our results indicate that dual inhibition of HDAC and MDM2 may provide a novel and efficient strategy for the discovery of antitumor drug in the future.

Dual-target Janus kinase (JAK) inhibitors: Comprehensive review on the JAK-based strategies for treating solid or hematological malignancies and immune-related diseases

Janus kinases (JAKs) are the non-receptor tyrosine kinases covering JAK1, JAK2, JAK3, and TYK2 which regulate signal transductions of hematopoietic cytokines and growth factors to play essential roles in cell growth, survival, and development. Dysregulated JAK activity leading to a constitutively activated signal transducers and activators of transcription (STAT) is strongly associated with immune-related diseases and cancers. Targeting JAK to interfere the signaling of JAK/STAT pathway has achieved quite success in the treatment of these diseases. However, inadequate clinical response and serious adverse events come along by the treatment of monotherapy of JAK inhibitors. With better and deeper understanding of JAK/STAT pathway in the pathogenesis of diseases, researchers start to show huge interest in combining inhibition of JAK and other oncogenic targets to realize a broader regulation on pathological processes to block disease development and progression, which has hastened extensive research of dual JAK inhibitors over the past decades. Until now, studies of dual JAK inhibitors have added BTK, SYK, FLT3, HDAC, Src, and Aurora kinases to the overall inhibitory profile and demonstrated significant advantage and superiority over single-target inhibitors. In this review, we elucidated the possible mechanism of synergic effects caused by dual JAK inhibitors and briefly describe the development of these agents.

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.

Targeting Histone Deacetylases: Opportunities for Cancer Treatment and Chemoprevention

The dysregulation of gene expression is a critical event involved in all steps of tumorigenesis. Aberrant histone and non-histone acetylation modifications of gene expression due to the abnormal activation of histone deacetylases (HDAC) have been reported in hematologic and solid types of cancer. In this sense, the cancer-associated epigenetic alterations are promising targets for anticancer therapy and chemoprevention. HDAC inhibitors (HDACi) induce histone hyperacetylation within target proteins, altering cell cycle and proliferation, cell differentiation, and the regulation of cell death programs. Over the last three decades, an increasing number of synthetic and naturally derived compounds, such as dietary-derived products, have been demonstrated to act as HDACi and have provided biological and molecular insights with regard to the role of HDAC in cancer. The first part of this review is focused on the biological roles of the Zinc-dependent HDAC family in malignant diseases. Accordingly, the small-molecules and natural products such as HDACi are described in terms of cancer therapy and chemoprevention. Furthermore, structural considerations are included to improve the HDACi selectivity and combinatory potential with other specific targeting agents in bifunctional inhibitors and proteolysis targeting chimeras. Additionally, clinical trials that combine HDACi with current therapies are discussed, which may open new avenues in terms of the feasibility of HDACi’s future clinical applications in precision cancer therapies.

Quinazoline-based hydroxamic acid derivatives as dual histone methylation and deacetylation inhibitors for potential anticancer agents

Cancer is a common malignant disease with complex signaling networks, which means it is unmanageable to cancer therapy by using single classical targeted drug. Recently, dual- or multitarget drugs have emerged as a promising option for cancer therapies. Although many multifunctional compounds targeting HDAC have been validated, as far as we know, there is no molecule targeting GLP and HDAC synchronously. In the present work, we designed and synthesized a series of quinazoline-based hydroxamic acid derivatives as dual GLP and HDAC inhibitors. These hybrid compounds showed potent enzymatic inhibitory activities against GLP and HDAC1/6 with IC₅₀ values in the nanomolar range of less than 190 nM. Furthermore, most of our compounds displayed significant broad spectrum cytotoxic activities apart from D3 and D8 against all the tested cancer cells with IC₅₀ values less than 50 μM. D1, D6 and D7 showed more potent cytotoxic activities than D2, D4 and D5 in those cancer cells. Especially, compound D7 showed potent inhibitory potency activity against both GLP and HDAC1/6 with IC₅₀ values of 1.3, 89, 13 nM. Besides, D7 exhibited the most potent antiproliferative activity against all the tested cancer cells. Further evaluations indicated that D7 could inhibit the methylation and deacetylation of H3K9 on protein level. Moreover, D7 could induce cancer cell apoptosis, G0/G1 cell cycle arrest, and partly block migration and invasion. All these thorough evaluations warranted D7 as a promising lead compound worth further optimization and development for cancer therapy.

Discovery of Dual CDK6/PIM1 Inhibitors with a Novel Structure, High Potency, and Favorable Druggability for the Treatment of Acute Myeloid Leukemia

Nowadays, the simultaneous inhibition of two or more pathways plays an increasingly important role in cancer treatment due to the complex and diverse pathogenesis of cancer, and the combination of the cyclin-dependent kinase 6 (CDK6) inhibitor and PIM1 inhibitor was found to generate synergistic effects in acute myeloid leukemia (AML) treatment. Therefore, we discovered a novel lead 1 targeting CDK6/PIM1 via pharmacophore-based and structure-based virtual screening, synthesized five different series of new derivates, and obtained a potent and balanced dual CDK6/PIM1 inhibitor 51, which showed high kinase selectivity. Meanwhile, 51 displayed an excellent safety profile and great pharmacokinetic properties. Furthermore, 51 displayed stronger potency in reducing the burden of AML than palbociclib and SMI-4a in vivo. In summary, we offered a new direction for AML treatment and provided a great lead compound for AML preclinical studies.

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.

Indirubin Derivatives as Dual Inhibitors Targeting Cyclin-Dependent Kinase and Histone Deacetylase for Treating Cancer

To utilize the unique scaffold of a natural product indirubin, we herein adopted the strategy of combined pharmacophores to design and synthesize a series of novel indirubin derivatives as dual inhibitors against cyclin-dependent kinase (CDK) and histone deacetylase (HDAC). Among them, the lead compound 8b with remarkable CDK2/4/6 and HDAC6 inhibitory activity of IC₅₀ = 60.9 ± 2.9, 276 ± 22.3, 27.2 ± 4.2, and 128.6 ± 0.4 nM, respectively, can efficiently induce apoptosis and S-phase arrest in several cancer cell lines. In particular, compound 8b can prevent the proliferation of a non-small-cell lung cancer cell line (A549) through the Mcl-1/XIAP/PARP axis, in agreement with the unique modes of action of the combined agents of HDAC inhibitors and CDK inhibitors. In an A549 xerograph model, compound 8b showed significant antitumor efficacy correlated with its dual inhibition. Our data demonstrated that compound 8b as a single agent could be a promising drug candidate for cancer therapy in combination with CDK and HDAC inhibitors.

Double-edged Swords: Diaryl pyrazoline thiazolidinediones synchronously targeting cancer epigenetics and angiogenesis

In the present study, two novel series of compounds incorporating naphthyl and pyridyl linker were synthesized and biological assays revealed 5-((6-(2-(5-(2-chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethoxy) naphthalene-2-yl)methylene)thiazolidine-2,4-dione (14b) as the most potent dual inhibitors of vascular endothelial growth factors receptor-2 (VEGFR-2) and histone deacetylase 4 (HDAC4). Compounds 13b, 14b, 17f, and 21f were found to stabilize HDAC4; where, pyridyl linker swords were endowed with higher stabilization effects than naphthyl linker. Also, 13b and 14b showed best inhibitory activity on VEGFR-2 as compared to others. Compound 14b was most potent as evident by in-vitro and in-vivo biological assessments. It displayed anti-angiogenic potential by inhibiting endothelial cell proliferation, migration, tube formation and also suppressed new capillary formation in the growing chick chorioallantoic membranes (CAMs). It showed selectivity and potency towards HDAC4 as compared to other HDAC isoforms. Compound 14b (25 mg/kg, i.p.) also indicated exceptional antitumor efficacy on in-vivo animal xenograft model of human colorectal adenocarcinoma (HT-29). The mechanism of action of 14b was also confirmed by western blot.

Rational Multitargeted Drug Design Strategy from the Perspective of a Medicinal Chemist

The development of multitarget-directed ligands (MTDLs) has become a widely focused research topic, but rational design remains as an enormous challenge. This paper reviews and discusses the design strategy of incorporating the second activity into an existing single-active ligand. If the binding sites of both targets share similar endogenous substrates, MTDLs can be designed by merging two lead compounds with similar functional groups. If the binding sites are large or adjacent to the solution, two key pharmacophores can be fused directly. If the binding regions are small and deep inside the proteins, the linked-pharmacophore strategy might be the only way. The added pharmacophores of second targets should not affect the binding mode of the original ones. Moreover, the inhibitory activities of the two targets need to be adjusted to achieve an optimal ratio.

Small molecules in targeted cancer therapy: advances, challenges, and future perspectives

Due to the advantages in efficacy and safety compared with traditional chemotherapy drugs, targeted therapeutic drugs have become mainstream cancer treatments. Since the first tyrosine kinase inhibitor imatinib was approved to enter the market by the US Food and Drug Administration (FDA) in 2001, an increasing number of small-molecule targeted drugs have been developed for the treatment of malignancies. By December 2020, 89 small-molecule targeted antitumor drugs have been approved by the US FDA and the National Medical Products Administration (NMPA) of China. Despite great progress, small-molecule targeted anti-cancer drugs still face many challenges, such as a low response rate and drug resistance. To better promote the development of targeted anti-cancer drugs, we conducted a comprehensive review of small-molecule targeted anti-cancer drugs according to the target classification. We present all the approved drugs as well as important drug candidates in clinical trials for each target, discuss the current challenges, and provide insights and perspectives for the research and development of anti-cancer drugs.

Thiazolidinedione "Magic Bullets" Simultaneously Targeting PPARγ and HDACs: Design, Synthesis, and Investigations of their In Vitro and In Vivo Antitumor Effects

Monotargeting anticancer agents suffer from resistance and target nonspecificity concerns, which can be tackled with a multitargeting approach. The combined treatment with HDAC inhibitors and PPARγ agonists has displayed potential antitumor effects. Based on these observations, this work involves design and synthesis of molecules that can simultaneously target PPARγ and HDAC. Several out of 25 compounds inhibited HDAC4, and six compounds acted as dual-targeting agents. Compound 7i was the most potent, with activity toward PPARγ EC50 = 0.245 μM and HDAC4 IC50 = 1.1 μM. Additionally, compounds 7c and 7i were cytotoxic to CCRF-CEM cells (CC50 = 2.8 and 9.6 μM, respectively), induced apoptosis, and caused DNA fragmentation. Furthermore, compound 7c modulated the expression of c-Myc, cleaved caspase-3, and caused in vivo tumor regression in CCRF-CEM tumor xenografts. Thus, this study provides a basis for the rational design of dual/multitargeting agents that could be developed further as anticancer therapeutics.

Discovery of STAT3 and Histone Deacetylase (HDAC) Dual-Pathway Inhibitors for the Treatment of Solid Cancer

Nowadays, simultaneous inhibition of multiple targets through drug combination is an important anticancer strategy owing to the complex mechanism behind tumorigenesis. Recent studies have demonstrated that the inhibition of histone deacetylases (HDACs) will lead to compensated activation of a notorious cancer-related drug target, signal transducer and activator of transcription 3 (STAT3), in breast cancer through a cascade, which probably limits the anti-proliferation effect of HDAC inhibitors in solid tumors. By incorporating the pharmacophore of the HDAC inhibitor SAHA (vorinostat) into the STAT3 inhibitor pterostilbene, a series of potent pterostilbene hydroxamic acid derivatives with dual-target inhibition activity were synthesized. An excellent hydroxamate derivate, compound 14, inhibited STAT3 (K_D = 33 nM) and HDAC (IC₅₀ = 23.15 nM) with robust potency in vitro. Compound 14 also showed potent anti-proliferation ability in vivo and in vitro. Our study provides the first STAT3 and HDAC dual-target inhibitor for further exploration.

Bioinformatic analysis linking genomic defects to chemosensitivity and mechanism of action

A joint analysis of the NCI60 small molecule screening data, their genetically defective genes, and mechanisms of action (MOA) of FDA approved cancer drugs screened in the NCI60 is proposed for identifying links between chemosensitivity, genomic defects and MOA. Self-Organizing-Maps (SOMs) are used to organize the chemosensitivity data. Student's t-tests are used to identify SOM clusters with enhanced chemosensitivity for tumor cell lines with versus without genetically defective genes. Fisher's exact and chi-square tests are used to reveal instances where defective gene to chemosensitivity associations have enriched MOAs. The results of this analysis find a relatively small set of defective genes, inclusive of ABL1, AXL, BRAF, CDC25A, CDKN2A, IGF1R, KRAS, MECOM, MMP1, MYC, NOTCH1, NRAS, PIK3CG, PTK2, RPTOR, SPTBN1, STAT2, TNKS and ZHX2, as possible candidates for roles in chemosensitivity for compound MOAs that target primarily, but not exclusively, kinases, nucleic acid synthesis, protein synthesis, apoptosis and tubulin. These results find exploitable instances of enhanced chemosensitivity of compound MOA's for selected defective genes. Collectively these findings will advance the interpretation of pre-clinical screening data as well as contribute towards the goals of cancer drug discovery, development decision making, and explanation of drug mechanisms.

Discovery of imidazopyrrolopyridines derivatives as novel and selective inhibitors of JAK2

Herein, we describe the design, synthesis, and structure-activity relationships of a series of imidazopyrrolopyridines derivatives that selectively inhibit Janus kinase 2 (JAK2). These screening cascades revealed that 6k was a preferred compound, with IC₅₀ values of 10 nM for JAK2. Moreover, 6k was a selective JAK2 inhibitor with 19-fold, >30-fold and >30-fold selectivity over JAK1, JAK3 and TYK2 respectively. In cytokine-stimulated cell-based assays, 6k exhibited a higher JAK2 selectivity over JAK1 isoforms. Indeed, at a dose of 20 mg/kg compound 6k, pSTAT3 and pSTAT5 expression was reduced to levels comparable to those of control animals untreated with GM-CSF. Additionally, 6k showed a relatively good bioavailability (F = 38%), a suitable half-life time (T_1/2 = 1.9 h), a satisfactory metabolic stability, suggesting that 6k might be a promising inhibitor of JAK2 for further development research for the treatment of MPNs.

Multicomponent synthesis and anti-proliferative screening of biaryl triazole-containing cyclophanes

We report a practical two-step approach involving a Ugi 4-CR/ azide-alkyne cycloaddition for the synthesis of biaryl-containing cyclophanes. The series represents an extension of our previously reported macrocycles as an effort to enhance the anti-proliferative activity of this scaffold. In this variant, we incorporate a biphenyl moiety in the framework, thus enhancing the macrocycle size, lipophilicity, and structural diversity. Macrocycles were tested against different cell lines, being more cytotoxic against prostate (PC-3 and DU-145) and breast (MCF-7) tumor cells. Gratifyingly, the most active compound showed a significative enhancement of PC-3 growth inhibition with respect to our previous series, reaffirming the potential anti-proliferative activity of this kind of cyclophanes.

Discovery of Novel Pyrrolo[2,3-d]pyrimidine-based Derivatives as Potent JAK/HDAC Dual Inhibitors for the Treatment of Refractory Solid Tumors

It remains a big challenge to develop HDAC inhibitors effective for solid tumors. Previous studies have suggested that the feedback activation of JAK-STAT3 pathway represents a key mechanism leading to resistance to HDAC inhibitors in breast cancer, suggesting the therapeutic promise of JAK/HDAC dual inhibitors. In this work, we discovered a series of pyrrolo[2,3-d]pyrimidine-based derivatives as potent JAK and HDAC dual inhibitors. Especially, compounds 15d and 15h potently inhibited JAK1/2/3 and HDAC1/6 and displayed antiproliferative and proapoptotic activities in triple-negative breast cancer cell lines. Besides, compounds 15d and 15h also diminished the activation of LIFR-JAK-STAT signaling triggered by tumor-associated fibroblasts, which suggests that these compounds could potentially overcome the drug resistance caused by the tumor microenvironment. More importantly, compound 15d effectively inhibited the tumor growth in MDA-MB-231 xenograft tumor model. Overall, this work provides valuable leads and novel antitumor mechanisms for the treatment of the SAHA-resistant triple-negative breast cancers.

Recent Advances in Multi-target Drugs Targeting Protein Kinases and Histone Deacetylases in Cancer Therapy

Protein Kinase Inhibitors (PKIs) and Histone Deacetylase Inhibitors (HDACIs) are two important classes of anticancer agents and have provided a variety of small molecule drugs for the treatment of various types of human cancers. However, malignant tumors are of a multifactorial nature that can hardly be "cured" by targeting a single target, and treatment of cancers hence requires modulation of multiple biological targets to restore the physiological balance and generate sufficient therapeutic efficacy. Multi-target drugs have attracted great interest because of their advantages in the treatment of complex cancers by simultaneously targeting multiple signaling pathways and possibly leading to synergistic effects. Synergistic effects have been observed in the combination of kinase inhibitors, such as imatinib, dasatinib, or sorafenib, with an array of HDACIs including vorinostat, romidepsin, or panobinostat. A considerable number of multi-target agents based on PKIs and HDACIs have been developed. In this review, we summarize the recent literature on the development of multi-target kinase-HDAC inhibitors and provide our view on the challenges and future directions on this topic.

An update on the emerging approaches for histone deacetylase (HDAC) inhibitor drug discovery and future perspectives

INTRODUCTION

HDACs catalyze the removal of acetyl groups from the ε-N-acetylated lysine residues of various protein substrates including both histone and nonhistone proteins. Different HDACs have distinct biological functions and are recruited to specific regions of the genome. HDAC inhibitors have attracted much attention in recent decades; indeed, there have been more than thirty HDAC inhibitors investigated in clinic trials with five approvals being achieved.

AREAS COVERED

This review covers the emerging approaches for HDAC inhibitor drug discovery from the past five years and includes discussion of structure-based rational design, isoform selectivity, and dual mechanism/multi-targeting. Chemical structures in addition to the in vitro and in vivo inhibiting activity of these compounds have also been discussed.

EXPERT OPINION

The exact role and biological functions of HDACs is still under investigation with a variety of HDAC inhibitors having been designed and evaluated. HDAC inhibitors have shown promise in treating cancer, AD, metabolic disease, viral infection, and multiple sclerosis, but there is still a lot of room for clinical improvement. In the future, more efforts should be put into (i) HDAC isoform identification (ii) the optimization of selectivity, activity, and pharmacokinetics; and (iii) unconventional approaches for discovering different effective scaffolds and pharmacophores.

A Review of Progress in Histone Deacetylase 6 Inhibitors Research: Structural Specificity and Functional Diversity

Histone deacetylases (HDACs) are essential for maintaining homeostasis by catalyzing histone deacetylation. Aberrant expression of HDACs is associated with various human diseases. Although HDAC inhibitors are used as effective chemotherapeutic agents in clinical practice, their applications remain limited due to associated side effects induced by weak isoform selectivity. HDAC6 displays unique structure and cellular localization as well as diverse substrates and exhibits a wider range of biological functions than other isoforms. HDAC6 inhibitors have been effectively used to treat cancers, neurodegenerative diseases, and autoimmune disorders without exerting significant toxic effects. Progress has been made in defining the crystal structures of HDAC6 catalytic domains which has influenced the structure-based drug design of HDAC6 inhibitors. This review summarizes recent literature on HDAC6 inhibitors with particular reference to structural specificity and functional diversity. It may provide up-to-date guidance for the development of HDAC6 inhibitors and perspectives for optimization of therapeutic applications.

Shifting the paradigm in treating multi-factorial diseases: polypharmacological co-inhibitors of HDAC6

Multi-factorial diseases are illnesses that exploit multiple cellular processes, or stages within one process, and thus highly targeted therapies often succumb to the disease, losing efficacy as resistance sets in. Combination therapies have become a mainstay to battle these diseases, however these regimens are plagued with caveats. An emerging avenue to treat multi-factorial diseases is polypharmacology, wherein a single drug is rationally designed to bind multiple targets, and is widely touted to be superior to combination therapy by inherently addressing the latter's shortcomings, which include poor patient compliance, narrow therapeutic windows and spiraling healthcare costs. Through its roles in intracellular trafficking, cell motility, mitosis, protein folding and as a back-up to the proteasome pathway, HDAC6 has rapidly become an exciting new target for therapeutics, particularly in the discovery of new drugs to treat Alzheimer's disease and cancer. Herein, we describe recent efforts to marry together HDAC pharmacophores, with a particular emphasis on HDAC6 selectivity, with those of other targets towards the discovery of potent therapeutics to treat these evasive diseases. Such polypharmacological agents may supercede combination therapies through inherent synergism, permitting reduced dosing, wider therapeutic windows and improved compliance.

Anticancer properties of chimeric HDAC and kinase inhibitors

Histone deacetylases (HDACs) are epigenetic regulators of chromatin condensation and decondensation and exert effects on the proliferation and spread of cancer. Thus, HDAC enzymes are promising drug targets for the treatment of cancer. Some HDAC inhibitors such as the hydroxamic acid derivatives vorinostat or panobinostat were already approved for the treatment of hematologic cancer diseases, and are under intensive investigation for their use in solid tumors. But there are also drawbacks of the clinical application of HDAC inhibitors like intrinsic or acquired drug resistance and, thus, new HDAC inhibitors with improved activities are sought for. Kinase inhibitors are very promising anticancer drugs and often showed synergistic anticancer effects in combination with HDAC inhibitors. Several hybrid molecules with HDAC and kinase inhibitory structural motifs were disclosed with even improved anticancer activities when compared with co-application of HDAC and receptor tyrosine kinase inhibitors. Chimeric inhibitors with HDAC inhibitory activities exert a rapidly growing field of research and only in this year several new dual HDAC/kinase inhibitors were disclosed. This review briefly summarizes the status and future perspective of the most advanced and promising dual HDAC/kinase inhibitors and their potential as anticancer drug candidates.

HDAC-Bax Multiple Ligands Enhance Bax-Dependent Apoptosis in HeLa Cells

Inspired by the synergistic effect of BTSA1 (a Bax activator) and SAHA (a histone deacetylase (HDAC) inhibitor) in HeLa cell growth suppression, a series of novel HDAC-Bax multiple ligands were designed rationally. Compound 23, which possesses similar HDAC inhibitory activity relative to SAHA and Bax affinity comparable to BTSA1, exhibits a superior growth suppression against HeLa cells, and its antiproliferative activities are 15-fold and 3-fold higher than BTSA1 and SAHA, respectively. The better antiproliferative activity and lower cytotoxicity of compound 23 indicated that our HDAC-Bax multiple ligand design strategy achieved success. Further studies suggested that compound 23 could enhance Bax-dependent apoptosis by upregulating Bax, followed by inducing the conformational activation of Bax. To our knowledge, we first report HDAC-Bax multiple ligands and demonstrate a new paradigm for the treatment of solid tumors by enhancing Bax-dependent apoptosis.

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.

Recent advances in small molecular modulators targeting histone deacetylase 6

Histone deacetylase 6 (HDAC6) is a unique isozyme in the HDAC family with various distinguished characters. HDAC6 is predominantly localized in the cytoplasm and has several specific nonhistone substrates, such as α-tubulin, cortactin, Hsp90, tau and peroxiredoxins. Accumulating evidence reveals that targeting HDAC6 may serve as a promising therapeutic strategy for the treatment of cancers, neurological disorders and immune diseases, making the development of HDAC6 inhibitors particularly attractive. Recently, multitarget drug design and proteolysis targeting chimera technology have also been applied in the discovery of novel small molecular modulators targeting HDAC6. In this review, we briefly describe the structural features and biological functions of HDAC6 and discuss the recent advances in HDAC6 modulators, including selective inhibitors, chimeric inhibitors and proteolysis targeting chimeras for multiple therapeutic purposes.

Bifunctional HDAC Therapeutics: One Drug to Rule Them All?

Histone deacetylase (HDAC) enzymes play crucial roles in epigenetic gene expression and are an attractive therapeutic target. Five HDAC inhibitors have been approved for cancer treatment to date, however, clinical applications have been limited due to poor single-agent drug efficacy and side effects associated with a lack of HDAC isoform or complex selectivity. An emerging strategy aiming to address these limitations is the development of bifunctional HDAC therapeutics-single molecules comprising a HDAC inhibitor conjugated to another specificity targeting moiety. This review summarises the recent advancements in novel types of dual-targeting HDAC modulators, including proteolysis-targeting chimeras (PROTACs), with a focus on HDAC isoform and complex selectivity, and the future potential of such bifunctional molecules in achieving enhanced drug efficacy and therapeutic benefits in treating disease.

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.

Efficacy of JAK inhibitors in Crohn's Disease

Inhibition of Janus kinases [JAKs] in Crohn's disease [CD] patients has shown conflicting results in clinical trials. Tofacitinib, a pan-JAK inhibitor, showed efficacy in ulcerative colitis [UC] and has been approved for the treatment of patients with moderate to severe UC. In contrast, studies in CD patients were disappointing and the primary end point of clinical remission could not be met in the respective phase II induction and maintenance trials. Subsequently, the clinical development of tofacitinib was discontinued in CD. In contrast, efficacy of filgotinib, a selective JAK1 inhibitor, in CD patients was demonstrated in the randomized, double-blinded, placebo-controlled phase II FITZROY study. Upadacitinib also showed promising results in a phase II trial in moderate to severe CD. Subsequently, phase III programmes in CD have been initiated for both substances, which are still ongoing. Several newer molecules of this class of orally administrated immunosuppressants are being tested in clinical programmes. The concern of side effects of systemic JAK inhibition is addressed by either exclusively intestinal action or higher selectivity [Tyk2 inhibitors]. In general, JAK inhibitors constitute a new promising class of drugs for the treatment of CD.

Dual-Target Inhibitors Based on HDACs: Novel Antitumor Agents for Cancer Therapy

Histone deacetylases (HDACs) play an important role in regulating target gene expression. They have been highlighted as a novel category of anticancer targets, and their inhibition can induce apoptosis, differentiation, and growth arrest in cancer cells. In view of the fact that HDAC inhibitors and other antitumor agents, such as BET inhibitors, topoisomerase inhibitors, and RTK pathway inhibitors, exert a synergistic effect on cellular processes in cancer cells, the combined inhibition of two targets is regarded as a rational strategy to improve the effectiveness of these single-target drugs for cancer treatment. In this review, we discuss the theoretical basis for designing HDAC-involved dual-target drugs and provide insight into the structure-activity relationships of these dual-target agents.

Multi-Targeting Anticancer Agents: Rational Approaches, Synthetic Routes and Structure Activity Relationship

We live in a world with complex diseases such as cancer which cannot be cured with one-compound one-target based therapeutic paradigm. This could be due to the involvement of multiple pathogenic mechanisms. One-compound-various-targets stratagem has become a prevailing research topic in anti-cancer drug discovery. The simultaneous interruption of two or more targets has improved the therapeutic efficacy as compared to the specific targeted based therapy. In this review, six types of dual targeting agents along with some interesting strategies used for their design and synthesis are discussed. Their pharmacology with various types of the molecular interactions within their specific targets has also been described. This assemblage will reveal the recent trends and insights in front of the scientific community working in dual inhibitors and help them in designing the next generation of multi-targeted anti-cancer agents.

Janus kinases (JAKs): The efficient therapeutic targets for autoimmune diseases and myeloproliferative disorders

The Janus kinases or JAKs are a family of intracellular tyrosine kinases that play an essential role in the signaling of numerous cytokines that have been implicated in the pathogenesis of autoimmune diseases and myeloproliferative disorders. JAKs are activated upon ligand induced receptor homo- or heterodimerization, which results in the immediate phosphorylation of tyrosine residues and the phosphotyrosines then serve as docking sites for cytoplasmic signal transducer and activator of transcription (STAT) proteins which become phosphorylated by the JAKs upon recruitment to the receptor complex. The phosphorylated STAT proteins dimerize and travel to the cellular nucleus, where they act as transcription factors. Interfering in the JAK-STAT pathway has yielded the only approved small molecule kinase inhibitors for immunological indications. Numerous medicinal chemistry studies are currently aimed at the design of novel and potent inhibitors for JAKs. Additionally, whether the second-generation inhibitors which possessed selectivity for JAKs are more efficient are under research. This Perspective summarizes the progress in the discovery and development of JAKs inhibitors, including the potential binding site and approaches for identifying small-molecule inhibitors, as well as future therapeutic perspectives in autoimmune diseases and myeloproliferative disorders are also put forward in order to provide reference and rational for the drug discovery of novel and potent JAKs inhibitors.

Histone deacetylase (HDAC) inhibitors in cancer: a patent review (2017-present)

Introduction: Histone deacetylase (HDAC) inhibitors play a crucial role in restoring the balance of acetylation and deacetylation of lysine residues of histones and non-histone proteins, which are applied to treat several diseases including cancer.Area covered: This review covers recent efforts in the synthesis and applications of inhibitors and hybrid inhibitors targeting HDAC from 2017 to 2019.Expert opinion: HDACs are important epigenetic targets and HDAC inhibitors have become important biologically active compounds for the treatment of cancers. Among the recent patents available, most of them place emphasis on HDAC selective inhibitors and multitarget HDAC inhibitors. Although great accomplishments have been achieved in developing HDAC selective inhibitors, there is still an urgent need for discovery of novel HDAC inhibitors with new zinc-binding groups avoiding the unfavorable pharmacokinetics profiles of hydroxamic acid. Apart from cancer therapy, HDAC inhibitors have recently been considered as a new strategy in treating other human diseases, such as alcohol use disorder (AUD), neurological disorders, age-related diseases, and so forth.