Design and synthesis of novel Flavone-based histone deacetylase inhibitors antagonizing activation of STAT3 in breast cancer

Isoflavone Derivatives as Potential Anticancer Agents: Synthesis and Bioactivity Studies

Isoflavones are phenolic natural compounds with a C6C3C6 framework. They possess a plethora of biological activities that are associated with putative benefits to human health. In particular, the cancer chemopreventive and chemotherapeutic potential of isoflavones has attracted the interest of researchers. Several isoflavone derivatives have been synthesised and probed for their anticancer activities. The isoflavone analogues are mainly synthesised by molecular hybridisation and other strategies that enable diversification through early or late-stage functionalisation of A-, B- and C-rings of the isoflavones. This has resulted in the discovery of isoflavone analogues with improved antiproliferative activities against several cancer cells and different mechanisms of action. In this review, the synthesis of isoflavone derivatives and their anticancer activity studies are discussed.

Design, synthesis, and biological evaluation of novel 5,7,4'-trimethoxyflavone sulfonamide-based derivatives as highly potent inhibitors of LRPPRC/STAT3/CDK1

Leucine-rich pentatricopeptide repeat-containing protein (LRPPRC), signal transducer and activator of transcription 3 (STAT3), and cyclin-dependent kinase 1 (CDK1) are promising therapeutic targets for cancer treatment. However, there is a lack of effective inhibitors of LRPPRC, STAT3, and CDK1 in clinic. Our previous study has proved that 5,7,4'-Trimethoxyflavone (TMF) is a novel inhibitor of LRPPRC/STAT3/CDK1. However, the extraction rate of TMF from Tangerine Peel is quite low, and the doses of TMF in cells and mice are rather high. Herein, structural modifications of TMF have led to two series of TMF derivatives including sulfonamide substituted at 3'-position (7a-m) and 3',8-position (11a-m). Among all compounds, 7e, 7k, 11e, and 11g exhibited as effective, broad-spectrum, and potent anticancer agents in vitro. Moreover, 7e, 7k, 11e, and 11g showed better antitumor effects than TMF and clinical used chemotherapy drug capecitabine in vivo with no obvious toxicity. Mechanism studies showed that 11g could bind to LRPPRC, STAT3, and CDK1 to disassociate the LRPPRC-JAK2-STAT3 and JAK2-STAT3-CDK1 complexes, resulting in suppression of JAK2/STAT3 signaling pathway. These findings suggest that 11g may serve as a leading compound for cancer therapy as a triple-target (LRPPRC, STAT3, and CDK1) inhibitor.

Prospects for breast cancer immunotherapy using microRNAs and transposable elements as objects

One of the directions in treatment of chemoresistant breast cancer (BC) may include new methods of activating the immune response against tumor cells. Clinically used checkpoint inhibition using antibodies to PD-1 and PD-L1 works in some patients, but the lack of biomarkers means number of respondents is low. The possibility of combining this method with chemotherapy is limited by an increased risk of toxic liver damage, development of immune-related pneumonitis, and thyroid dysfunction. This article includes introduction into the clinic of new methods of immunotherapy for BC, among which epigenetic activation of retroelements, double-stranded transcripts of which stimulate the interferon response against the tumor, is promising. For this purpose, inhibitors of DNA methyltransferase*, histone deacetylase* and histone methyltransferase* are used (* subtitles in the main text). Their antitumor effect is also mediated by removal of repressive epigenetic marks from tumor suppressor genes. However, numerous studies have proven the role of retroelements in the carcinogenesis of various malignant neoplasms, including BC. Moreover, endogenous retroviruses HERV-K and LINE1 retrotransposons are planned to be used as diagnostic biomarkers for BC. Therefore, a rational approach to using viral mimicry in antitumor therapy of BC may be the simultaneous suppression of specific retrotransposons (drivers for carcinogenesis) using reverse transcriptase inhibitors and silencing of specific transposons involved in carcinogenesis using complementary microRNAs. To determine possible pathways of influence in this direction, 35 specific transposon-derived microRNAs* changes in BC were identified, which can become guides for targeted therapy of BC.

Research progress of multi-target HDAC inhibitors blocking the BRD4-LIFR-JAK1-STAT3 signaling pathway in the treatment of cancer

Histone deacetylase inhibitors (HDACis) show beneficial effects on different hematological malignancy subtypes. However, their impacts on treating solid tumors are still limited due to diverse resistance mechanisms. Recent studies have found that the feedback activation of BRD4-LIFR-JAK1-STAT3 pathway after HDACi incubation is a vital mechanism inducing resistance of specific solid tumor cells to HDACis. This review summarizes the recent development of multi-target HDACis that can concurrently block BRD4-LIFR-JAK1-STAT3 pathway. Moreover, our findings hope to shed novel lights on developing novel multi-target HDACis with reduced BRD4-LIFR-JAK1-STAT3-mediated drug resistance in some tumors.

Recent developments of hydroxamic acid hybrids as potential anti-breast cancer agents

Histone deacetylase inhibitors not only possess favorable effects on modulating tumor microenvironment and host immune cells but also can reactivate the genes silenced due to deacetylation and chromatin condensation. Hydroxamic acid hybrids as promising histone deacetylase inhibitors have the potential to address drug resistance and reduce severe side effects associated with a single drug molecule due to their capacity to simultaneously modulate multiple targets in cancer cells. Accordingly, rational design of hydroxamic acid hybrids may provide valuable therapeutic interventions for the treatment of breast cancer. This review aimed to provide insights into the in vitro and in vivo anti-breast cancer therapeutic potential of hydroxamic acid hybrids, together with their mechanisms of action and structure-activity relationships, covering articles published from 2020 to the present.

Hydroxamic acid hybrids: Histone deacetylase inhibitors with anticancer therapeutic potency

Histone deacetylases (HDACs), a class of enzymes responsible for the removal of acetyl functional groups from the lysine residues in the amino-terminal tails of core histones, play a critical role in the modulation of chromatin architecture and the regulation of gene expression. Dysregulation of HDAC expression has been closely associated with the development of various cancers. Histone deacetylase inhibitors (HDACis) could regulate diverse cellular pathways, cause cell cycle arrest, and promote programmed cell death, making them promising avenues for cancer therapy with potent efficacy and favorable toxicity profiles. Hybrid molecules incorporating two or more pharmacophores in one single molecule, have the potential to simultaneously inhibit two distinct cancer targets, potentially overcome drug resistance and minimize drug-drug interactions. Notably, hydroxamic acid hybrids, exemplified by fimepinostat and tinostamustine as potential HDACis, could exert the anticancer effects through induction of apoptosis, differentiation, and growth arrest in cancer cells, representing useful scaffolds for the discovery of novel HDACis. The purpose of this review is to summarize the current scenario of hydroxamic acid hybrids as HDACis with anticancer therapeutic potential developed since 2020 to facilitate further rational exploitation of more effective candidates.

Technologies of targeting histone deacetylase in drug discovery: Current progress and emerging prospects

Histone deacetylases (HDACs) catalyze the hydrolysis of acetyl-l-lysine side chains in histones and non-histones, which are key to epigenetic regulation in humans. Targeting HDACs has emerged as a promising strategy for treating various types of cancer, including myeloma and hematologic malignancies. At present, numerous small molecule inhibitors targeting HDACs are actively being investigated in clinical trials. Despite their potential efficacy in cancer treatment, HDAC inhibitors suffer from multi-directional selectivity and preclinical resistance issues. Hence, developing novel inhibitors based on cutting-edge medicinal chemistry techniques is essential to overcome these limitations and improve clinical outcomes. This manuscript presents an extensive overview of the properties and biological functions of HDACs in cancer, provides an overview of the current state of development and limitations of clinical HDAC inhibitors, and analyzes a range of innovative medicinal chemistry techniques that are applied. These techniques include selective inhibitors, dual-target inhibitors, proteolysis targeting chimeras, and protein-protein interaction inhibitors.

Novel flavonoid 1,3,4-oxadiazole derivatives ameliorate MPTP-induced Parkinson's disease via Nrf2/NF-κB signaling pathway

Parkinson's disease (PD) is a progressive neurodegenerative disorder with a complex etiology. Neuroinflammation and oxidative stress are important factors driving the progression of PD. It has been reported that 1,3,4-oxadiazole and flavone derivatives have numerous biological functions, especially in the aspect of anti-inflammatory and antioxidant. Based on the strategy of pharmacodynamic combination, we introduced 1,3,4-oxadiazole moiety into the flavonoid backbone, designed and synthesized a series of novel flavonoid 1,3,4-oxadiazole derivatives. Further, we evaluated their toxicity, anti-inflammatory and antioxidant activities using BV2 microglia. Following a comprehensive analysis, compound F12 showed the best pharmacological activity. In vivo, we induced the classical PD animal model by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into C57/BL6J mice. Our results showed that compound F12 ameliorated MPTP-induced dysfunction in mice. Further, compound F12 reduced oxidative stress by promoting the nucleation of nuclear factor erythroid 2-related factor 2 (Nrf2) and decreased the inflammatory response by inhibiting the nuclear translocation of nuclear factor-κB (NF-κB) in vivo and in vitro. Meanwhile, compound F12 inhibited the mitochondrial apoptotic pathway to rescue microglia inflammation-mediated loss of dopaminergic neurons. In conclusion, compound F12 reduced oxidative stress and inflammation and could be as a potential agent for PD treatment.

Research progress of STAT3-based dual inhibitors for cancer therapy

Signal transducer and activator of transcription 3 (STAT3), a transcription factor, regulates gene levels that are associated with cell survival, cell cycle, and immune reaction. It is correlated with the grade of malignancy and the development of various cancers and targeting STAT3 protein is a potentially promising therapeutic strategy for tumors. Over the past 20 years, various compounds have been found to directly inhibit STAT3 activity via different strategies. However, numerous difficulties exist in the development of STAT3 inhibitors, such as serious toxic effects, poor therapeutic effects, and intrinsic and acquired drug resistance. STAT3 inhibitors synergistically suppress cancer development with additional anti-tumor drugs, such as indoleamine 2,3-dioxygenase 1 inhibitors (IDO1i), histone deacetylase inhibitors (HDACi), DNA inhibitors, pro-tumorigenic cytokine inhibitors (PTCi), NF-κB inhibitors, and tubulin inhibitors. Therefore, individual molecule- based dual-target inhibitors can be the candidate alternative or complementary treatment to overcome the disadvantages of just STAT3 or other targets as a monotherapy. In this review, we discuss the theoretical basis for formulating STAT3-based dual-target inhibitors and also summarize their structure-activity relationships (SARs).

Synthesis and Structure-Activity Analysis of Icaritin Derivatives as Potential Tumor Growth Inhibitors of Hepatocellular Carcinoma Cells

The prenylated flavonoid icaritin (ICT, 1), a new drug for treating advanced hepatocellular carcinoma (HCC), was selected as a template to develop more potent inhibitors. An initial semisynthetic modification of ICT was performed to obtain a structure-activity relationship (SAR), which indicated that the cytotoxicity is enhanced by OH-3 rhamnosylation and that OH-7 is an important modification site. Based on the results of the SAR study, 46 N-containing ICT derivatives were synthesized and evaluated as the anti-HCC inhibitors. The results showed that most of the derivatives produced inhibited three HCC cell lines used (Hep3B, HepG2 and SMMC-7721). The modification strategy was validated by 3D-QSAR, which provided information for the further design and optimization of ICT. The most potent compound, 11c, exhibited IC₅₀ values of 7.6 and 3.1 μM against HepG2 and SMMC-7721 cells, respectively, which were more potent than those of ICT and sorafenib, respectively. Further mechanistic studies indicated that 11c caused arrest at the G₀/G₁ phase in the cell cycle and induced cell apoptosis in HepG2 and SMMC-7721 cells.

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.

Medicinal chemistry updates of novel HDACs inhibitors (2020 to present)

Epigentic enzymes histone deacetylases (HDACs) catalyze the removal of acetyl groups from the ε-N-acetylated lysine residues of various protein substrates including both histone and non-histone proteins. Different HDACs have distinct biological functions and are recruited to specific regions of the genome. Due to their important biological functions, HDACs have been validated in clinics for anticancer therapy, and are being explored for potential treatment of several other diseases such as Alzheimer disease (AD), metabolic disease, viral infection, and multiple sclerosis, etc. Besides five approved drugs, there are more than thirty HDACs inhibitors currently being investigated in clinical trials. Centering on the advances of drug discovery programs in this field since 2020, this review discusses HDACs inhibitors from the aspects of the structure-based rational design, isoform selectivity, pharmacology, and toxicology of the compounds of interest. The hope is to provide the medicinal chemistry community with up-to-date information and to accelerate the drug discovery programs in this area.

From natural products to HDAC inhibitors: An overview of drug discovery and design strategy

Histone deacetylases (HDACs) play a key role in the homeostasis of protein acetylation in histones and have recently emerged as a therapeutic target for numerous diseases. The inhibition of HDACs may block angiogenesis, arrest cell growth, and lead to differentiation and apoptosis in tumour cells. Thus, HDAC inhibitors (HDACi) have received increasing attention and many of which are developed from natural sources. In the past few decades, naturally occurring HDACi have been identified to have potent anticancer activities, some of which have demonstrated promising therapeutic effects on haematological malignancies. In this review, we summarized the discovery and modification of HDAC inhibitors from natural sources, novel drug design that uses natural products as parent nuclei, and dual target design strategies that combine HDAC with non-HDAC targets.

A novel epigenetic drug conjugating flavonoid and HDAC inhibitor confers to suppression of acute myeloid leukemogenesis

Epigenetic dysregulation has long been identified as a key driver of leukemogenesis in acute myeloid leukemia (AML). However, epigenetic drugs such as histone deacetylase inhibitors (HDACi) targeting epigenetic alterations in AML have obtained only limited clinical efficiency without clear mechanism. Fortunately, we screened out a novel epigenetic agent named Apigenin-Vorinostat-Conjugate (AVC), which provides us a possibility to handle the heterogenous malignancy. Its inhibition on HDACs was presented by HDACs expression, enzyme activity, and histone acetylation level. Its efficacy against AML was detected by cell viability assay and tumor progression of AML mouse model. Apoptosis is the major way causing cell death. We found AVC efficiently suppresses leukemogenesis whereas sparing the normal human cells. Kasumi-1 cells are at least twenty-fold higher sensitive to AVC (IC50=0.024μM) than vorinostat (IC50=0.513μM) and Ara-C (IC50=0.4366μM). Furthermore, it can efficiently regress the tumorigenesis in AML mouse model while keeping the pivotal organs safe, demonstrating a feasibility and favorable safety profile in treatment of AML. Collectively, these pre-clinical data suggest a promising potential utilizing flavonoid-HDACi-conjugate as a next-generation epigenetic drug for clinical therapy against AML.

Total Synthesis of Mulberry Diels-Alder-Type Adducts Kuwanons G and H

Mulberry Diels-Alder-type adducts (MDAAs) are a group of rare natural polyphenols biosynthetically derived from [4 + 2]-cycloaddition of chalcones and dehydroprenylphenols. In this study, kuwanons G (1) and H (2), two bioactive MDAAs with unique dehydroprenylflavonoid dienes, were totally synthesized for the first time in a biomimetic manner. The key features of the convergent route include the use of the Baker-Venkataraman rearrangement, alkylation of β-diketone, intramolecular cyclization, and Suzuki-Miyaura coupling to achieve the subunit diene.

Discovery and synthesis of rocaglaol derivatives inducing apoptosis in HCT116 cells via suppression of MAPK signaling pathway

Six rocaglaol derivatives were isolated from Dysoxylum gotadhora, and those compounds showed good cytotoxic activity with IC₅₀ values ranging from 10 to 350 ng/mL against five different cancer cells. Obviously, further total synthesis of rocaglaol derivatives for medical chemistry study is of great significance. Then, twenty six rocaglaol derivatives including 25 new compounds were designed, synthesized, and evaluated for their cytotoxic activities against three human cancer cell lines: human colon cancer cells (HCT116), colorectal cancer stem cells (P6C), and human red leukocyte leukemia cells (HEL), using MTT assay. Most of derivatives showed good cytotoxic activities, with the lowest IC₅₀ being 3.2 nM for HEL cells, which was 169 times stronger than that of the positive control (doxorubicin). Further mechanism study indicated that 11k could significantly suppress MAPK pathway in HCT116 cells, which may responsible for induction of apoptosis and cell cycle arrest.