Combination Therapy With Histone Deacetylase Inhibitors (HDACi) for the Treatment of Cancer: Achieving the Full Therapeutic Potential of HDACi

Synthesis and HDAC1 inhibitory activity of a novel series of coumarin-based amide derivatives for treatment of cancer

Background: Histone deacetylases (HDACs) play a vital role in the epigenetic regulation of transcription and expression. HDAC1 overexpression is seen in many cancers. Methodology: The authors synthesized and evaluated 27 novel coumarin-based amide derivatives for HDAC1 inhibitory activity. The compounds were screened at the US National Cancer Institute, and 5k and 5u were selected for five-dose assays. Compound 5k showed GI50 values of 0.294 and 0.264 μM against MOLT-4 and LOX-IMVI, respectively; whereas 5u had GI50 values of 0.189 and 0.263 μM, respectively. Both derivatives showed better activity than entinostat and suberoylanilide hydroxamic acid. Compound 5k exhibited an IC50 value of 1.00 μM on ACHN cells. Conclusion: Coumarin derivatives exhibited promising HDAC1 inhibitory potential and warrant future development as anticancer agents.

A review of the therapeutic potential of histone deacetylase inhibitors in rhabdomyosarcoma

This review aims to summarize the putative role of histone deacetylases (HDACs) in rhabdomyosarcoma (RMS) and the effects of HDAC inhibitors (HDACi) on RMS by elucidating and highlighting known oncogenic pathways, mechanisms of resistance, and the synergistic potential of histone deacetylase inhibitors. We searched two databases (PubMed and Google Scholar) for the keywords "Rhabdomyosarcoma, histone deacetylase, histone deacetylase inhibitors." We excluded three publications that did not permit access to the full text to review and those that focus exclusively on pleiomorphic RMS in adults. Forty-seven papers met the inclusion criteria. This review highlights that HDACi induce cytotoxicity, cell-cycle arrest, and oxidative stress in RMS cells. Ultimately, HDACi have been shown to increase apoptosis and the cessation of embryonal and alveolar RMS proliferation in vivo and in vitro, both synergistically and on its own. HDACi contain potent therapeutic potential against RMS. This review discusses the significant findings and the biological mechanisms behind the anti-cancer effects of HDACi. Additionally, this review highlights important clinical trials assessing the efficacy of HDACi in sarcomas.

Platinum(IV) combo prodrugs containing cyclohexane-1R,2R-diamine, valproic acid, and perillic acid as a multiaction chemotherapeutic platform for colon cancer

The complex [PtCl2(cyclohexane-1R,2R-diamine)] has been combined in a Pt(IV) molecule with two different bioactive molecules (i.e., the histone deacetylase inhibitor 2-propylpentanoic acid or valproic acid, VPA, and the potential antimetastatic molecule 4-isopropenylcyclohexene-1-carboxylic acid or perillic acid, PA) in order to obtain a set of multiaction or multitarget antiproliferative agents. In addition to traditional thermal synthetic procedures, microwave-assisted heating was used to speed up their preparation. All Pt(IV) complexes showed antiproliferative activity on four human colon cancer cell lines (namely HCT116, HCT8, RKO and HT29) in the nanomolar range, considerably better than those of [PtCl2(cyclohexane-1R,2R-diamine)], VPA, PA, and the reference drug oxaliplatin. The synthesized complexes showed pro-apoptotic and pro-necrotic effects and the ability to induce cell cycle alterations. Moreover, the downregulation of histone deacetylase activity, leading to an increase in histone H3 and H4 levels, and the antimigratory activity, indicated by the reduction of the levels of matrix metalloproteinases MMP2 and MMP9, demonstrated the multiaction nature of the complexes, which showed biological properties similar to or better than those of VPA and PA, but at lower concentrations, probably due to the lipophilicity of the combo molecule that increases the intracellular concentration of the single components (i.e., [PtCl2(cyclohexane-1R,2R-diamine)], VPA and PA).

Novel epigenetic molecular therapies for imprinting disorders

Genomic imprinting disorders are caused by the disruption of genomic imprinting processes leading to a deficit or increase of an active allele. Their unique molecular mechanisms underlying imprinted genes offer an opportunity to investigate epigenetic-based therapy for reactivation of an inactive allele or reduction of an active allele. Current treatments are based on managing symptoms, not targeting the molecular mechanisms underlying imprinting disorders. Here, we highlight molecular approaches of therapeutic candidates in preclinical and clinical studies for individual imprinting disorders. These include the significant progress of discovery and testing of small molecules, antisense oligonucleotides, and CRISPR mediated genome editing approaches as new therapeutic strategies. We discuss the significant challenges of translating these promising therapies from the preclinical stage to the clinic, especially for genome editing based approaches.

Repurposing of triamterene as a histone deacetylase inhibitor to overcome cisplatin resistance in lung cancer treatment

PURPOSE

Cisplatin is the core chemotherapeutic drug used for first-line treatment of advanced non-small cell lung cancer (NSCLC). However, drug resistance is severely hindering its clinical efficacy. This study investigated the circumvention of cisplatin resistance by repurposing non-oncology drugs with putative histone deacetylase (HDAC) inhibitory effect.

METHODS

A few clinically approved drugs were identified by a computational drug repurposing tool called "DRUGSURV" and evaluated for HDAC inhibition. Triamterene, originally indicated as a diuretic, was chosen for further investigation in pairs of parental and cisplatin-resistant NSCLC cell lines. Sulforhodamine B assay was used to evaluate cell proliferation. Western blot analysis was performed to examine histone acetylation. Flow cytometry was used to examine apoptosis and cell cycle effects. Chromatin immunoprecipitation was conducted to investigate the interaction of transcription factors to the promoter of genes regulating cisplatin uptake and cell cycle progression. The circumvention of cisplatin resistance by triamterene was further verified in a patient-derived tumor xenograft (PDX) from a cisplatin-refractory NSCLC patient.

RESULTS

Triamterene was found to inhibit HDACs. It was shown to enhance cellular cisplatin accumulation and potentiate cisplatin-induced cell cycle arrest, DNA damage, and apoptosis. Mechanistically, triamterene was found to induce histone acetylation in chromatin, thereby reducing the association of HDAC1 but promoting the interaction of Sp1 with the gene promoter of hCTR1 and p21. Triamterene was further shown to potentiate the anti-cancer effect of cisplatin in cisplatin-resistant PDX in vivo.

CONCLUSION

The findings advocate further clinical evaluation of the repurposing use of triamterene to overcome cisplatin resistance.

Tackling FGFR3-driven bladder cancer with a promising synergistic FGFR/HDAC targeted therapy

Bladder cancer (BC) is one of the most prevalent malignancies worldwide and FGFR3 alterations are particularly common in BC. Despite approval of erdafitinib, durable responses for FGFR inhibitors are still uncommon and most patients relapse to metastatic disease. Given the necessity to discover more efficient therapies for BC, herein, we sought to explore promising synergistic combinations for BC with FGFR3 fusions. Our studies confirmed the synergy between FGFR and HDAC inhibitors in vitro and demonstrated its benefits in vivo. Mechanistic studies revealed that quisinostat can downregulate FGFR3 expression by suppressing FGFR3 translation. Additionally, quisinostat can also sensitize BC cells to erdafitinib by downregulating HDGF. Furthermore, the synergy was also confirmed in BC cells with FGFR3 S249C. This study discovers a new avenue for treatment of FGFR3-driven BC and uncovers new mechanistic insights. These preclinical studies pave the way for a direct translation of this combination to early phase clinical trials.

A landscape of response to drug combinations in non-small cell lung cancer

Combination of anti-cancer drugs is broadly seen as way to overcome the often-limited efficacy of single agents. The design and testing of combinations are however very challenging. Here we present a uniquely large dataset screening over 5000 targeted agent combinations across 81 non-small cell lung cancer cell lines. Our analysis reveals a profound heterogeneity of response across the tumor models. Notably, combinations very rarely result in a strong gain in efficacy over the range of response observable with single agents. Importantly, gain of activity over single agents is more often seen when co-targeting functionally proximal genes, offering a strategy for designing more efficient combinations. Because combinatorial effect is strongly context specific, tumor specificity should be achievable. The resource provided, together with an additional validation screen sheds light on major challenges and opportunities in building efficacious combinations against cancer and provides an opportunity for training computational models for synergy prediction.

Synthesis and bioevaluation of novel stilbene-based derivatives as tubulin/HDAC dual-target inhibitors with potent antitumor activities in vitro and in vivo

A series of novel stilbene-based derivatives were designed and synthesized as tubulin/HDAC dual-target inhibitors. Among forty-three target compounds, compound II-19k not only exhibited considerable antiproliferative activity in the hematological cell line K562 with IC₅₀ value of 0.003 μM, but also effectively inhibited the growth of various solid tumor cell lines with IC₅₀ values ranging from 0.005 to 0.036 μM. The mechanism studies demonstrated that II-19k could inhibit microtubules and HDACs at the cellular level, block cell cycle arrest at G2 phase, induce cell apoptosis, and reduce solid tumor cells metastasis. What's more, the vascular disrupting effects of compound II-19k were more pronounced than the combined administration of parent compound 8 and HDAC inhibitor SAHA. The in vivo antitumor assay of II-19k also showed the superiority of dual-target inhibition of tubulin and HDAC. II-19k significantly suppressed the tumor volume and effectively reduced tumor weight by 73.12% without apparent toxicity. Overall, the promising bioactivities of II-19k make it valuable for further development as an antitumor agent.

Design, synthesis, and biological evaluation of novel HDAC inhibitors with a 3-(benzazol-2-yl)quinoxaline framework

A series of novel histone deacetylase (HDAC) inhibitors derived from 3-(benzazol-2-yl)quinoxaline derivatives were designed and synthesized by a pharmacophore fusion strategy. In vitro results showed that most of the synthesized compounds exhibited good anti-proliferative activity. Among them, compound 10c showed the most potent cytotoxicity, especially in HCT-116 cells with an IC50 value of 0.91 μM much superior to Vorinostat (5.66 μM). 10c was also found to induce cell apoptosis, arrest the cell cycle at G2/M phase, induce the generation of reactive oxygen species and inhibit cell invasion and migration in HCT-116 cells. Further studies revealed that 10c could up-regulate the acetylation levels of H3 and α-tubulin, exhibit significant Topo I inhibition and induce the release of related apoptotic biomarkers. These results highlight the great potential of 10c to become a promising anti-cancer HDAC inhibitor.

Discovery of novel, potent, and orally bioavailable HDACs inhibitors with LSD1 inhibitory activity for the treatment of solid tumors

Histone deacetylases (HDACs) and lysine-specific demethylase 1 (LSD1) are attractive targets for epigenetic cancer therapy. There is an intimate interplay between the two enzymes. HDACs inhibitors have shown synergistic anticancer effects in combination with LSD1 inhibitors in several types of cancer. Herein, we describe the discovery of compound 5e, a highly potent HDACs inhibitor (HDAC1/2/6/8; IC₅₀ = 2.07/4.71/2.40/107 nM) with anti-LSD1 potency (IC₅₀ = 1.34 μM). Compound 5e exhibited marked antiproliferative activity in several cancer cell lines. 5e effectively induced mitochondrial apoptosis with G2/M phase arrest, inhibiting cell migration and invasion in MGC-803 and HCT-116 cancer cells. It also showed good liver microsomal stability and acceptable pharmacokinetic parameters in SD rats. More importantly, orally administered compound 5e demonstrated higher in vivo antitumor efficacy than SAHA in the MGC-803 (TGI = 71.5%) and HCT-116 (TGI = 57.6%) xenograft tumor models accompanied by good tolerability. This study provides a novel lead compound with dual inhibitory activity against HDACs and LSD1 to further develop epigenetic drugs for solid tumor therapy. Further optimization is needed to improve the LSD1 activity to achieve dual inhibitors with balanced potency on LSD1 and HDACs.

The impact of histone deacetylase inhibitors on immune cells and implications for cancer therapy

Many cancers possess the ability to suppress the immune response to malignant cells, thus facilitating tumour growth and invasion, and this has fuelled research to reverse these mechanisms and re-activate the immune system with consequent important therapeutic benefit. One such approach is to use histone deacetylase inhibitors (HDACi), a novel class of targeted therapies, which manipulate the immune response to cancer through epigenetic modification. Four HDACi have recently been approved for clinical use in malignancies including multiple myeloma and T-cell lymphoma. Most research in this context has focussed on HDACi and tumour cells, however, little is known about their impact on the cells of the immune system. Additionally, HDACi have been shown to impact the mechanisms by which other anti-cancer therapies exert their effects by, for example, increasing accessibility to exposed DNA through chromatin relaxation, impairing DNA damage repair pathways and increasing immune checkpoint receptor expression. This review details the effects of HDACi on immune cells, highlights the variability in these effects depending on experimental design, and provides an overview of clinical trials investigating the combination of HDACi with chemotherapy, radiotherapy, immunotherapy and multimodal regimens.

Vorinostat decrease M2 macrophage polarization through ARID1A6488delG/HDAC6/IL-10 signaling pathway in endometriosis-associated ovarian carcinoma

Endometriosis is a common disease in women and may be one of the factors that induces malignant epithelial ovarian tumors. Previous studies suggested that endometriosis is related to ARID1A mutation mediating the expression of HDAC6, but the detailed pathogenic mechanism is still unclear. First, we collected endometriosis-associated ovarian carcinoma (EAOC) clinical samples and examined the expression of HDAC6. Our results found that the high HDAC6 expression group was positively correlated with EAOC histology (P = 0.015), stage (P < 0.000), and tumor size (P < 0.000) and inversely correlated with survival (P < 0.000). We also found that ARID1A^6488delG/HDAC6 induced M2 polarization of macrophages through IL-10. In addition, the HDAC inhibitor (HDACi) vorinostat inhibited cell growth and blocked the effect of HDAC6. Tomographic microscopy was used to monitor the live cell morphology of these treated cells, and we found that vorinostat treatment resulted in substantial cell apoptosis by 3 h 42 min. Next, we established a transgenic mouse model of EAOC and found that vorinostat significantly reduced the size of ovarian tumors by inhibiting M2 macrophage polarization in mice. Together, these data demonstrate that the signaling pathway of E4F1/ARID1A^6488delG/HDAC6/GATA3 mediates macrophage polarization and provides a novel immune cell-associated therapeutic strategy targeting IL-10 in EAOC.

Chidamide, a novel histone deacetylase inhibitor, inhibits laryngeal cancer progression in vitro and in vivo

Although surgery is an important treatment for laryngeal cancer, surgery has a significant negative impact on the quality of life of patients, and many patients have poor tolerance to surgery. Therefore, alternative chemotherapeutic drugs are an important research hotspot. Chidamide is a histone deacetylase inhibitor that selectively inhibits the expression of type I and IIb histone deacetylases (1, 2, 3 and 10). It has a significant anticancer effect on a variety of solid tumours. This study verified the inhibitory effect of chidamide on laryngeal carcinoma. We conducted a variety of cellular and animal experiments to explore how chidamide inhibits the development of laryngeal cancer. The results showed that chidamide had significant antitumour activity against laryngeal carcinoma cells and xenografts and could induce cell apoptosis, ferroptosis and pyroptosis. This study provides a potential option for the treatment of laryngeal cancer.

Antiandrogen-Equipped Histone Deacetylase Inhibitors Selectively Inhibit Androgen Receptor (AR) and AR-Splice Variant (AR-SV) in Castration-Resistant Prostate Cancer (CRPC)

Background: Epigenetic modification influences androgen receptor (AR) activation, often resulting in prostate cancer (PCa) development and progression. Silencing histone-modifying enzymes (histone deacetylases-HDACs) either genetically or pharmacologically suppresses PCa proliferation in preclinical models of PCa; however, results from clinical studies were not encouraging. Similarly, PCa patients eventually become resistant to androgen ablation therapy (ADT). Our goal is to develop dual-acting small molecules comprising antiandrogen and HDAC-inhibiting moieties that may overcome the resistance of ADT and effectively suppress the growth of castration-resistant prostate cancer (CRPC). Methods: Several rationally designed antiandrogen-equipped HDAC inhibitors (HDACi) were synthesized, and their efficacy on CRPC growth was examined both in vitro and in vivo. Results: While screening our newly developed small molecules, we observed that SBI-46 significantly inhibited the proliferation of AR+ CRPC cells but not AR- CRPC and normal immortalized prostate epithelial cells (RWPE1) or normal kidney cells (HEK-293 and VERO). Molecular analysis confirmed that SBI-46 downregulated the expressions of both AR+ and AR-splice variants (AR-SVs) in CRPC cells. Further studies revealed the downregulation of AR downstream (PSA) events in CRPC cells. The oral administration of SBI-46 abrogated the growth of C4-2B and 22Rv1 CRPC xenograft tumors that express AR or both AR and AR-SV in xenotransplanted nude mice models. Further, immunohistochemical analysis confirmed that SBI-46 inhibits AR signaling in xenografted tumor tissues. Conclusion: These results demonstrate that SBI-46 is a potent agent that inhibits preclinical models of CRPC by downregulating the expressions of both AR and AR-SV. Furthermore, these results suggest that SBI-46 may be a potent compound for treating CRPC.

Apolipoprotein E induces pathogenic senescent-like myeloid cells in prostate cancer

Tumor cells promote the recruitment of immunosuppressive neutrophils, a subset of myeloid cells driving immune suppression, tumor proliferation, and treatment resistance. Physiologically, neutrophils are known to have a short half-life. Here, we report the identification of a subset of neutrophils that have upregulated expression of cellular senescence markers and persist in the tumor microenvironment. Senescent-like neutrophils express the triggering receptor expressed on myeloid cells 2 (TREM2) and are more immunosuppressive and tumor-promoting than canonical immunosuppressive neutrophils. Genetic and pharmacological elimination of senescent-like neutrophils decreases tumor progression in different mouse models of prostate cancer. Mechanistically, we have found that apolipoprotein E (APOE) secreted by prostate tumor cells binds TREM2 on neutrophils, promoting their senescence. APOE and TREM2 expression increases in prostate cancers and correlates with poor prognosis. Collectively, these results reveal an alternative mechanism of tumor immune evasion and support the development of immune senolytics targeting senescent-like neutrophils for cancer therapy.

Thymoquinone, piperine, and sorafenib combinations attenuate liver and breast cancers progression: epigenetic and molecular docking approaches

BACKGROUND

Traditional herbal medicine has been used for centuries to cure many pathological disorders, including cancer. Thymoquinone (TQ) and piperine (PIP) are major bioactive constituents of the black seed (Nigella sativa) and black pepper (Piper nigrum), respectively. The current study aimed to explore the potential chemo-modulatory effects, mechanisms of action, molecular targets, and binding interactions after TQ and PIP treatments and their combination with sorafenib (SOR) against human triple-negative breast cancer (MDA-MB-231) and liver cancer (HepG2) cells.

METHODS

We determined drug cytotoxicity by MTT assay, cell cycle, and death mechanism by flow cytometry. Besides, the potential effect of TQ, PIP, and SOR treatment on genome methylation and acetylation by determination of DNA methyltransferase (DNMT3B), histone deacetylase (HDAC3) and miRNA-29c expression levels. Finally, a molecular docking study was performed to propose potential mechanisms of action and binding affinity of TQ, PIP, and SOR with DNMT3B and HDAC3.

RESULTS

Collectively, our data show that combinations of TQ and/or PIP with SOR have significantly enhanced the SOR anti-proliferative and cytotoxic effects depending on the dose and cell line by enhancing G2/M phase arrest, inducing apoptosis, downregulation of DNMT3B and HDAC3 expression and upregulation of the tumor suppressor, miRNA-29c. Finally, the molecular docking study has identified strong interactions between SOR, PIP, and TQ with DNMT3B and HDAC3, inhibiting their normal oncogenic activities and leading to growth arrest and cell death.

CONCLUSION

This study reported TQ and PIP as enhancers of the antiproliferative and cytotoxic effects of SOR and addressed the mechanisms, and identified molecular targets involved in their action.

VRK1 Kinase Activity Modulating Histone H4K16 Acetylation Inhibited by SIRT2 and VRK-IN-1

The accessibility of DNA to different cellular functions requires a dynamic regulation of chromatin organization that is mediated by different epigenetic modifications, which regulate chromatin accessibility and degree of compaction. These epigenetic modifications, particularly the acetylation of histone H4 in lysine 14 (H4K16ac), determine the degree of chromatin accessibility to different nuclear functions, as well as to DNA damage drugs. H4K16ac is regulated by the balance between two alternative histone modifications, acetylation and deacetylation, which are mediated by acetylases and deacetylases. Tip60/KAT5 acetylates, and SIRT2 deacetylates histone H4K16. However, the balance between these two epigenetic enzymes is unknown. VRK1 regulates the level of H4K16 acetylation by activating Tip60. We have shown that the VRK1 and SIRT2 are able to form a stable protein complex. For this work, we used in vitro interaction, pull-down and in vitro kinase assays. In cells, their interaction and colocalization were detected by immunoprecipitation and immunofluorescence. The kinase activity of VRK1 is inhibited by a direct interaction of its N-terminal kinase domain with SIRT2 in vitro. This interaction causes a loss of H4K16ac similarly to the effect of a novel VRK1 inhibitor (VRK-IN-1) or VRK1 depletion. The use of specific SIRT2 inhibitors in lung adenocarcinoma cells induces H4K16ac, contrary to the novel VRK-IN-1 inhibitor, which prevents H4K16ac and a correct DNA damage response. Therefore, the inhibition of SIRT2 can cooperate with VRK1 in the accessibility of drugs to chromatin in response to DNA damage caused by doxorubicin.

HAND2 Assists MYCN Enhancer Invasion to Regulate a Noradrenergic Neuroblastoma Phenotype

Noradrenergic neuroblastoma is characterized by a core transcriptional regulatory circuitry (CRC) comprised of transcription factors (TF) such as PHOX2B, HAND2, and GATA3, which form a network with MYCN. At normal physiologic levels, MYCN mainly binds to promoters but when aberrantly upregulated as in neuroblastoma, MYCN also binds to enhancers. Here, we investigated how MYCN invades enhancers and whether CRC TFs play a role in this process. HAND2 was found to regulate chromatin accessibility and to assist MYCN binding to enhancers. Moreover, HAND2 cooperated with MYCN to compete with nucleosomes to regulate global gene transcription. The cooperative interaction between MYCN and HAND2 could be targeted with an Aurora A kinase inhibitor plus a histone deacetylase inhibitor, resulting in potent downregulation of both MYCN and the CRC TFs and suppression of MYCN-amplified neuroblastoma tumor growth. This study identifies cooperation between MYCN and HAND2 in neuroblastoma and demonstrates that simultaneously targeting MYCN and CRC TFs is an effective way to treat this aggressive pediatric tumor.

SIGNIFICANCE

HAND2 and MYCN compete with nucleosomes to regulate global gene transcription and to drive a malignant neuroblastoma phenotype.

Select HDAC Inhibitors Enhance Osteolysis and Bone Metastasis Outgrowth but Can Be Mitigated With Bisphosphonate Therapy

Breast cancer has a high predilection for spreading to bone with approximately 70% of patients who succumb to disease harboring bone disseminated tumor cells. Despite this high prevalence, treatments for bone metastatic breast cancer predominantly manage morbidities, including pain and hypercalcemia, rather than reducing bone metastasis incidence or growth. Histone deacetylase inhibitors (HDACi), including panobinostat, entinostat, and valproic acid, typically slow primary tumor progression and are currently in clinical trials for the treatment of many cancers, including primary and metastatic breast cancer, but their effects on bone metastatic disease have not been examined in preclinical models. We report that treatment with the HDACi panobinostat, but not entinostat or valproic acid, significantly reduced trabecular bone volume in tumor-naïve mice, consistent with previous reports of HDACi-induced bone loss. Surprisingly, treatment with entinostat or panobinostat, but not valproic acid, increased tumor burden and incidence in an experimental model of breast cancer bone metastasis. In vitro, multiple HDACi stimulated expression of pro-osteolytic genes in breast tumor cells, suggesting this may be a mechanism by which HDACi fuel tumor growth. In support of this, combination therapy of panobinostat or entinostat with the antiresorptive bisphosphonate zoledronic acid prevented bone metastatic progression; however, the addition of zoledronic acid to panobinostat therapy failed to fully correct panobinostat-induced bone loss. Together these data demonstrate that select HDACi fuel bone metastatic growth and provide potential mechanistic and therapeutic avenues to offset these effects. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Epigenetic Regulations in Mammalian Cells: Roles and Profiling Techniques

The genome is almost identical in all the cells of the body. However, the functions and morphologies of each cell are different, and the factors that determine them are the genes and proteins expressed in the cells. Over the past decades, studies on epigenetic information, such as DNA methylation, histone modifications, chromatin accessibility, and chromatin conformation have shown that these properties play a fundamental role in gene regulation. Furthermore, various diseases such as cancer have been found to be associated with epigenetic mechanisms. In this study, we summarized the biological properties of epigenetics and single-cell epigenomic profiling techniques, and discussed future challenges in the field of epigenetics.

Targeting Epigenetic Changes Mediated by Members of the SMYD Family of Lysine Methyltransferases

A comprehensive understanding of the mechanisms involved in epigenetic changes in gene expression is essential to the clinical management of diseases linked to the SMYD family of lysine methyltransferases. The five known SMYD enzymes catalyze the transfer of donor methyl groups from S-adenosylmethionine (SAM) to specific lysines on histones and non-histone substrates. SMYDs family members have distinct tissue distributions and tissue-specific functions, including regulation of development, cell differentiation, and embryogenesis. Diseases associated with SMYDs include the repressed transcription of SMYD1 genes needed for the formation of ion channels in the heart leading to heart failure, SMYD2 overexpression in esophageal squamous cell carcinoma (ESCC) or p53-related cancers, and poor prognosis associated with SMYD3 overexpression in more than 14 types of cancer including breast cancer, colon cancer, prostate cancer, lung cancer, and pancreatic cancer. Given the importance of epigenetics in various pathologies, the development of epigenetic inhibitors has attracted considerable attention from the pharmaceutical industry. The pharmacologic development of the inhibitors involves the identification of molecules regulating both functional SMYD SET (Suppressor of variegation, Enhancer of Zeste, Trithorax) and MYND (Myeloid-Nervy-DEAF1) domains, a process facilitated by available X-ray structures for SMYD1, SMYD2, and SMYD3. Important leads for potential pharmaceutical agents have been reported for SMYD2 and SMYD3 enzymes, and six epigenetic inhibitors have been developed for drugs used to treat myelodysplastic syndrome (Vidaza, Dacogen), cutaneous T-cell lymphoma (Zoinza, Isrodax), and peripheral T-cell lymphoma (Beleodag, Epidaza). The recently demonstrated reversal of SMYD histone methylation suggests that reversing the epigenetic effects of SMYDs in cancerous tissues may be a desirable target for pharmacological development.

Epigenetic reprogramming in cancer: From diagnosis to treatment

Disruption of the epigenetic program of gene expression is a hallmark of cancer that initiates and propagates tumorigenesis. Altered DNA methylation, histone modifications and ncRNAs expression are a feature of cancer cells. The dynamic epigenetic changes during oncogenic transformation are related to tumor heterogeneity, unlimited self-renewal and multi-lineage differentiation. This stem cell-like state or the aberrant reprogramming of cancer stem cells is the major challenge in treatment and drug resistance. Given the reversible nature of epigenetic modifications, the ability to restore the cancer epigenome through the inhibition of the epigenetic modifiers is a promising therapy for cancer treatment, either as a monotherapy or in combination with other anticancer therapies, including immunotherapies. Herein, we highlighted the main epigenetic alterations, their potential as a biomarker for early diagnosis and the epigenetic therapies approved for cancer treatment.

A convergent fabrication of pH and redox dual-responsive hybrids of mesoporous silica nanoparticles for the treatment of breast cancer

Mesoporous silica nanoparticle (MSN), sodium hyaluronate (SH), silk fibroin (SS), and oxidized sodium carboxymethyl cellulose (O-CMC) hybrids were used to develop an intelligent drug delivery platform that may be employed for pH and redox-responsive bi-drug administration. The first drug, cytarabine (Cyt), was loaded with amino-functionalized mesoporous silica (MSN-NH₂) encased by the hydrogel of cystamine (Cys) and SH cross-linked by amide bonds. Hydrophobic doxorubicin (DOX) was co-loaded with Cyt/MSN-NH₂/SA in the hydrogel of SS and O-CMC in the Cyt- loaded hydrogel. Dual-responsive drug delivery may be achieved by encapsulating SS and O-CMC in a hydrogel, including Cyt/MSN-NH₂/SA/DOX/SS/O-CMC, which has acyl hydrazone bonds (-HC = N) and disulfide bond (-S-S-) exchange reaction with glutathione (GSH). Compared to hydrogels encapsulating only one drug (Cyt or DOX), cell survival analysis revealed that the newly fabricated hydrogels have significantly greater chemotherapeutic efficacy. The cell proliferation of the fabricated nanoparticles was examined in MCF-7 and MDA-MB-231 cells, which indicates that the nanoparticles effectively kill the cancer cells without affecting non-cancerous cells. Further, we effectively investigated the morphological changes, and various biochemical staining methods examined nuclear fragmentation/condensation. Furthermore, the biosafety of the nanoparticles was investigated by the in vivo animal model, which reveals that they remarkably enhanced the safety profile in various organs. These outcomes demonstrated that this nanoparticle platform was a promising beneficial agent for improving breast cancer treatment.

Perspectives on the future of urothelial carcinoma therapy: chemotherapy and beyond

INTRODUCTION

Despite recent developments in the landscape of urothelial carcinoma (UC) treatment, platinum combination chemotherapy still remains a milestone. Recently immunotherapeutic agents have gained ever-growing attractivity, particularly in the metastatic setting. Novel chemotherapeutic strategies and agents, such as antibody-drug conjugates (ADCs), and powerful combination regimens have been developed to overcome the resistance of most UC to current therapies.

AREAS COVERED

Herein, we review the current standard-of-care chemotherapy, the development of ADCs, the rationale for combining therapy regimens with chemotherapy in current trials, and future directions in UC management.

EXPERT OPINION

Immunotherapy has prompted a revolution in the treatment paradigm of UC. However, only a few patients experience a long-term response when treated with single-agent immunotherapies. Combination treatments are necessary to bypass resistance mechanisms and broaden the clinical utility of current options. Current evidence supports the intensification of standard-of-care chemotherapy with maintenance immunotherapy. However, the optimal sequence, combination, and duration must be determined to achieve individual longevity with acceptable health-related quality of life. In that regard, ADCs appear as a promising alternative for single and combination strategies in UC, as they specifically target the tumor cells, thereby, theoretically improving treatment efficacy and avoiding extensive off-target toxicities.

Epigenetically programmed resistance to chemo- and immuno-therapies

Resistance to cancer treatments remains a major barrier in developing cancer cures. While promising combination chemotherapy treatments and novel immunotherapies have improved patient outcomes, resistance to these treatments remains poorly understood. New insights into the dysregulation of the epigenome show how it promotes tumor growth and resistance to therapy. By altering control of gene expression, tumor cells can evade immune cell recognition, ignore apoptotic cues, and reverse DNA damage induced by chemotherapies. In this chapter, we summarize the data on epigenetic remodeling during cancer progression and treatment that enable cancer cell survival and describe how these epigenetic changes are being targeted clinically to overcome resistance.

Anticancer effects of the HDAC inhibitor, 3β,6β‑dihydroxyurs‑12‑en‑27‑oic acid, in MCF‑7 breast cancer cells via the inhibition of Akt/mTOR pathways

Astilbe chinensis (A. chinensis) is a perennial herb that is used to treat chronic bronchitis and pain. The anticancer activity of 3β,6β‑dihydroxyurs‑12‑en‑27‑oic acid (ACT‑3), a major component isolated from A. chinensis, has not yet been investigated in detail. The purpose of the present study was to investigate the histone deacetylase (HDAC) inhibitory and anticancer activities of ACT‑3 compared with suberoylanilide hydroxamic acid (SAHA) in MCF‑7 human breast cancer cells. The purity of ACT‑3 was determined using high‑performance liquid chromatography. In the present study, the effects of ACT‑3 on anticancer effects of MCF‑7 cells were determined by measuring the level of apoptotic cell death and cell cycle regulator using flow cytometry analysis and western blot analysis, respectively. The effects of ACT‑3 on HDAC enzyme activity were measured using assay kits. ACT‑3 and SAHA increased the levels of acetylated histone H3 and reduced the levels of HDAC1 and HDAC3 in MCF‑7 cells. ACT‑3 significantly decreased the cell viability in a concentration‑dependent manner and induced different morphological changes at high concentrations. ACT‑3 and SAHA significantly inhibited the colony formation in MCF‑7 cells. ACT‑3 inhibited total HDAC activity in a dose‑dependent manner. ACT‑3 significantly reduced the expression levels of cyclin D1 and cyclin‑dependent kinase 4, and upregulated the expression levels of p21^WAF1 and p53. A significant increase in the G1 phase cell population was observed in MCF‑7 cells and ACT‑3 induced apoptosis by reducing the ratio of B‑cell lymphoma‑2 (Bcl‑2)/Bcl‑2‑associated X (Bax) and releasing cleaved caspase 9. Additionally, ACT‑3 significantly increased autophagic cell death by inhibiting the serine‑threonine kinase/mammalian target of the rapamycin pathway. Autophagy induction was confirmed via acridine orange staining. ACT‑3 significantly increased the pERK1/2 and p21 in MCF‑7 cells. Thus, the activated ERK pathway played an important role in cell cycle arrest and apoptosis via ERK‑dependent induction of p21 in MCF‑7 cells. These data indicated that ACT‑3 can be used as a promising anticancer agent to overcome the limitations and reduce the side effects of conventional anticancer drugs.

Progress of small molecules for targeted protein degradation: PROTACs and other technologies

Recent years have witnessed the rapid development of targeted protein degradation (TPD), especially proteolysis targeting chimeras. These degraders have manifested many advantages over small molecule inhibitors. To date, a huge number of degraders have been excavated against over 70 disease-related targets. In particular, degraders against estrogen receptor and androgen receptor have crowded into phase II clinical trial. TPD technologies largely expand the scope of druggable targets, and provide powerful tools for addressing intractable problems that can not be tackled by traditional small molecule inhibitors. In this review, we mainly focus on the structures and biological activities of small molecule degraders as well as the elucidation of mechanisms of emerging TPD technologies. We also propose the challenges that exist in the TPD field at present.

Determining Potency of Inhibitors Targeting Histone Deacetylase 6 by Quantification of Acetylated Tubulin in Cells

During the preclinical development of small molecule inhibitors, compounds or compound libraries are typically first screened using purified target enzymes in vitro to select candidates with high potency. In the later stages of the development, however, functional cell-based assays may provide biologically more relevant data. In this chapter, we describe a detailed protocol for determining the potency of inhibitors targeting human histone deacetylase 6 in complex cellular environments. Cells are first treated with a dilution series of tested compounds, cell lysates separated by SDS-PAGE, and electrotransferred to a blotting membrane. The inhibitor potency is then determined indirectly by quantifying the levels of acetylated tubulin as a surrogate readout.

Epigenetic Priming and Development of New Combination Therapy Approaches

Muscle-invasive urothelial carcinoma of the bladder (MIBC) has been treated with cisplatin-based chemotherapy for over 30 years. With the advent of immune checkpoint inhibitors, antibody drug conjugates and FGFR3 inhibitors new therapeutic options have been approved for patients with urothelial carcinoma (UC) and are still under investigation regarding association between patients' response and recently defined molecular subtypes. Unfortunately, similar to chemotherapy, only a fraction of UC patients responds to these new treatment approaches. Thus, either further new efficacious therapeutic options for treatment of individual subtypes or new approaches to overcome treatment resistance and to increase patients' response to standard of care treatment are needed.Epigenetic modifications of DNA and chromatin are known to mediate cellular plasticity or treatment resistance, and the responsible epigenetic regulators are frequently mutated or aberrantly expressed in UC. Thus, these enzymes provide targets for novel drug combination therapies to "episensitize" toward approved standard therapies by epigenetic priming. In general, these epigenetic regulators comprise writers and erasers like DNA methyltransferases and DNA demethylases (for DNA methylation), histone methyltransferases and histone demethylases (for histone methylation), as well as acetyl transferases and histone deacetylases (for histone and nonhistone acetylation). Such modifications, e.g., acetyl groups, are recognized by further epigenetic reader proteins, e.g., like the bromodomain and extra-terminal domain (BET) family proteins that often interact in multi-protein complexes and finally regulate chromatin conformation and transcriptional activity.Concurringly, epigenetic regulators target a plethora of cellular functions. Their pharmaceutical inhibitors often inhibit enzymatic activity of more than one isoenzyme or may have further noncanonical cytotoxic effects. Thus, analysis of their functions in UC pathogenesis as well as of the antineoplastic capacity of corresponding inhibitors alone or in combination with other approved drugs should follow a multidimensional approach. Here, we present our standard approach to analyze cellular effects of new epigenetic inhibitors on UC cells alone to define their potency and to conclude on putative reasonable combination therapy partners. We further describe our approach to identify efficacious synergistic combination therapies (e.g., with cisplatin or PARP inhibitors) that may have reduced normal toxicity through dose reduction, which can then be further analyzed in animal experiments. This approach may also serve as prototype for the preclinical evaluation of other epigenetic treatment approaches.

Histone deacetylase inhibitors as sanguine epitherapeutics against the deadliest lung cancer

The back-breaking resistance mechanisms generated by lung cancer cells against epidermal growth factor receptor (EGFR), KRAS and Janus kinase 2 (JAK2) directed therapies strongly prioritizes the requirement of novel therapies which are perfectly tolerated, potentially cytotoxic and can reinstate the drug-sensitivity in lung cancer cells. Enzymatic proteins modifying the post-translational modifications of nucleosome-integrated histone substrates are appearing as current targets for defeating various malignancies. Histone deacetylases (HDACs) are hyperexpressed in diverse lung cancer types. Blocking the active pocket of these acetylation erasers through HDAC inhibitors (HDACi) has come out as an optimistic therapeutic recourse for annihilating lung cancer. This article in the beginning gives an overview about lung cancer statistics and predominant lung cancer types. Succeeding this, compendium about conventional therapies and their serious drawbacks has been provided. Then, connection of uncommon expression of classical HDACs in lung cancer onset and expansion has been detailed. Moreover, keeping the main theme in view this article deeply discusses HDACi in the context of aggressive lung cancer as single agents and spotlights various molecular targets suppressed or induced by these inhibitors for engendering cytotoxic effect. Most particularly, the raised pharmacological effects achieved on using these inhibitors in concerted form with other therapeutic molecules and the cancer-linked pathways altered by this procedure are described. The positive direction towards further heightening of efficacy and the pressing requirement of exhaustive clinical assessment has been proposed as a new focus point.

Analysis of HDACi-Coupled Nanoparticles: Opportunities and Challenges

Systemic administration of histone deacetylase inhibitors (HDACi), like valproic acid (VPA), is often associated with rapid drug metabolization and untargeted tissue distribution. This requires high-dose application that can lead to unintended side effects. Hence, drug carrier systems such as nanoparticles (NPs) are developed to circumvent these disadvantages by enhancing serum half-life as well as organ specificity.This chapter gives a summary of the biological characterization of HDACi-coupled NPs in vitro, including investigation of cellular uptake, biocompatibility, as well as intracellular drug release and activity. Suitable methods, opportunities, and challenges will be discussed to provide general guidelines for the analysis of HDACi drug carrier systems with a special focus on recently developed cellulose-based VPA-coupled NPs.

BMX, a specific HDAC8 inhibitor, with TMZ for advanced CRC therapy: a novel synergic effect to elicit p53-, β-catenin- and MGMT-dependent apoptotic cell death

BACKGROUND

Despite advances in treatment, patients with refractory colorectal cancer (CRC) still have poor long-term survival, so there is a need for more effective therapeutic options.

METHODS

To evaluate the HDAC8 inhibition efficacy as a CRC treatment, we examined the effects of various HDAC8 inhibitors (HDAC8i), including BMX (NBM-T-L-BMX-OS01) in combination with temozolomide (TMZ) or other standard CRC drugs on p53 mutated HT29 cells, as well as wild-type p53 HCT116 and RKO cells.

RESULTS

We showed that HDAC8i with TMZ cotreatment resulted in HT29 arrest in the S and G2/M phase, whereas HCT116 and RKO arrest in the G0/G1 phase was accompanied by high sub-G1. Subsequently, this combination approach upregulated p53-mediated MGMT inhibition, leading to apoptosis. Furthermore, we observed the cotreatment also enabled triggering of cell senescence and decreased expression of stem cell biomarkers. Mechanistically, we found down-expression levels of β-catenin, cyclin D1 and c-Myc via GSK3β/β-catenin signaling. Intriguingly, autophagy also contributes to cell death under the opposite status of β-catenin/p62 axis, suggesting that there exists a negative feedback regulation between Wnt/β-catenin and autophagy. Consistently, the Gene Set Enrichment Analysis (GSEA) indicated both apoptotic and autophagy biomarkers in HT29 and RKO were upregulated after treating with BMX.

CONCLUSIONS

BMX may act as a HDAC8 eraser and in combination with reframed-TMZ generates a remarkable synergic effect, providing a novel therapeutic target for various CRCs. Video Abstract.

HDAC6 Inhibition Alleviates Ischemia- and Cisplatin-Induced Acute Kidney Injury by Promoting Autophagy

Histone deacetylase (HDAC) 6 exists exclusively in cytoplasm and deacetylates cytoplasmic proteins such as α-tubulin. HDAC6 dysfunction is associated with several pathological conditions in renal disorders, including UUO-induced fibrotic kidneys and rhabdomyolysis-induced nephropathy. However, the role of HDAC6 in ischemic acute kidney injury (AKI) and the mechanism by which HDAC6 inhibition protects tubular cells after AKI remain unclear. In the present study, we observed that HDAC6 was markedly activated in kidneys subjected to ischemia- and cisplatin (cis)-induced AKI treatment. Pharmacological inhibition of HDAC6 alleviated renal impairment and renal tubular damage after ischemia and cisplatin treatment. HDAC6 dysfunction was associated with decreased acetylation of α-tubulin at the residue of lysine 40 and autophagy. HDAC6 inhibition preserved acetyl-α-tubulin-enhanced autophagy flux in AKI and cultured tubular cells. Genetic ablation of the renal tubular (RT) Atg7 gene or pharmacological inhibition of autophagy suppressed the protective effects of HDAC6. Taken together, our study indicates that HDAC6 contributes to ischemia- and cisplatin-induced AKI by inhibiting autophagy and the acetylation of α-tubulin. These results suggest that HDAC6 could be a potential target for ischemic and nephrotoxic AKI.

Targeting the epigenome in malignant melanoma: Facts, challenges and therapeutic promises

Malignant melanoma is the most lethal type of skin cancer with high rates of mortality. Although current treatment options provide a short-clinical benefit, acquired-drug resistance highlights the low 5-year survival rate among patients with advanced stage of the disease. In parallel, the involvement of an aberrant epigenetic landscape, (e.g., alterations in DNA methylation patterns, histone modifications marks and expression of non-coding RNAs), in addition to the genetic background, has been also associated with the onset and progression of melanoma. In this review article, we report on current therapeutic options in melanoma treatment with a focus on distinct epigenetic alterations and how their reversal, by specific drug compounds, can restore a normal phenotype. In particular, we concentrate on how single and/or combinatorial therapeutic approaches have utilized epigenetic drug compounds in being effective against malignant melanoma. Finally, the role of deregulated epigenetic mechanisms in promoting drug resistance to targeted therapies and immune checkpoint inhibitors is presented leading to the development of newly synthesized and/or improved drug compounds capable of targeting the epigenome of malignant melanoma.

Targeting epigenetic regulators for inflammation: Mechanisms and intervention therapy

Emerging evidence indicates that resolution of inflammation is a critical and dynamic endogenous process for host tissues defending against external invasive pathogens or internal tissue injury. It has long been known that autoimmune diseases and chronic inflammatory disorders are characterized by dysregulated immune responses, leading to excessive and uncontrol tissue inflammation. The dysregulation of epigenetic alterations including DNA methylation, posttranslational modifications to histone proteins, and noncoding RNA expression has been implicated in a host of inflammatory disorders and the immune system. The inflammatory response is considered as a critical trigger of epigenetic alterations that in turn intercede inflammatory actions. Thus, understanding the molecular mechanism that dictates the outcome of targeting epigenetic regulators for inflammatory disease is required for inflammation resolution. In this article, we elucidate the critical role of the nuclear factor‐κB signaling pathway, JAK/STAT signaling pathway, and the NLRP3 inflammasome in chronic inflammatory diseases. And we formulate the relationship between inflammation, coronavirus disease 2019, and human cancers. Additionally, we review the mechanism of epigenetic modifications involved in inflammation and innate immune cells. All that matters is that we propose and discuss the rejuvenation potential of interventions that target epigenetic regulators and regulatory mechanisms for chronic inflammation‐associated diseases to improve therapeutic outcomes.

Development of Fluorinated Peptoid-Based Histone Deacetylase (HDAC) Inhibitors for Therapy-Resistant Acute Leukemia

Using a microwave-assisted protocol, we synthesized 16 peptoid-capped HDAC inhibitors (HDACi) with fluorinated linkers and identified two hit compounds. In biochemical and cellular assays, 10h stood out as a potent unselective HDACi with remarkable cytotoxic potential against different therapy-resistant leukemia cell lines. 10h demonstrated prominent antileukemic activity with low cytotoxic activity toward healthy cells. Moreover, 10h exhibited synergistic interactions with the DNA methyltransferase inhibitor decitabine in AML cell lines. The comparison of crystal structures of HDAC6 complexes with 10h and its nonfluorinated counterpart revealed a similar occupation of the L1 loop pocket but slight differences in zinc coordination. The substitution pattern of the acyl residue turned out to be crucial in terms of isoform selectivity. The introduction of an isopropyl group onto the phenyl ring provided the highly HDAC6-selective inhibitor 10p, which demonstrated moderate synergy with decitabine and exceeded the HDAC6 selectivity of tubastatin A.

Transcription factors TEAD2 and E2A globally repress acetyl-CoA synthesis to promote tumorigenesis

Acetyl-coenzyme A (acetyl-CoA) plays an important role in metabolism, gene expression, signaling, and other cellular processes via transfer of its acetyl group to proteins and metabolites. However, the synthesis and usage of acetyl-CoA in disease states such as cancer are poorly characterized. Here, we investigated global acetyl-CoA synthesis and protein acetylation in a mouse model and patient samples of hepatocellular carcinoma (HCC). Unexpectedly, we found that acetyl-CoA levels are decreased in HCC due to transcriptional downregulation of all six acetyl-CoA biosynthesis pathways. This led to hypo-acetylation specifically of non-histone proteins, including many enzymes in metabolic pathways. Importantly, repression of acetyl-CoA synthesis promoted oncogenic dedifferentiation and proliferation. Mechanistically, acetyl-CoA synthesis was repressed by the transcription factors TEAD2 and E2A, previously unknown to control acetyl-CoA synthesis. Knockdown of TEAD2 and E2A restored acetyl-CoA levels and inhibited tumor growth. Our findings causally link transcriptional reprogramming of acetyl-CoA metabolism, dedifferentiation, and cancer.

Impact of Histone Modifications and Their Therapeutic Targeting in Hematological Malignancies

Hematologic malignancies are a large and heterogeneous group of neoplasms characterized by complex pathogenetic mechanisms. The abnormal regulation of epigenetic mechanisms and specifically, histone modifications, has been demonstrated to play a central role in hematological cancer pathogenesis and progression. A variety of epigenetic enzymes that affect the state of histones have been detected as deregulated, being either over- or underexpressed, which induces changes in chromatin compaction and, subsequently, affects gene expression. Recent advances in the field of epigenetics have revealed novel therapeutic targets, with many epigenetic drugs being investigated in clinical trials. The present review focuses on the biological impact of histone modifications in the pathogenesis of hematologic malignancies, describing a wide range of therapeutic agents that have been discovered to target these alterations and are currently under investigation in clinical trials.

A phase I/II study of ivaltinostat combined with gemcitabine and erlotinib in patients with untreated locally advanced or metastatic pancreatic adenocarcinoma

This phase I/II study evaluated the safety and efficacy of a new histone deacetylase (HDAC) inhibitor, ivaltinostat, in combination with gemcitabine and erlotinib for advanced pancreatic ductal adenocarcinoma (PDAC). Patients diagnosed with unresectable, histologically confirmed PDAC who had not undergone previous therapy were eligible. Phase I had a 3 + 3 dose escalation design to determine the maximum tolerable dose (MTD) of ivaltinostat (intravenously on days 1, 8 and 15) with gemcitabine (1000 mg/m2 intravenously on days 1, 8 and 15) and erlotinib (100 mg/day, orally) for a 28-day cycle. In phase II, patients received a six-cycle treatment with the MTD of ivaltinostat determined in phase I. The primary endpoint was the objective response rate (ORR). Secondary endpoints included overall survival (OS), disease control rate (DCR) and progression-free survival (PFS). The MTD of ivaltinostat for the phase II trial was determined to be 250 mg/m2 . In phase II, 24 patients were enrolled. The median OS and PFS were 8.6 (95% confidence interval [CI]: 5.3-11.2) and 5.3 months (95% CI: 3.7-5.8). Of the 16 patients evaluated for response, ORR and DCR were 25.0% and 93.8% with a median OS/PFS of 10.8 (95% CI: 8.3-16.7)/5.8 (95% CI: 4.6-6.7) months. Correlative studies showed that mutation burden detected by cfDNA and specific blood markers such as TIMP1, pro-MMP10, PECAM1, proMMP-2 and IGFBP1 were associated with clinical outcomes. Although the result of a small study, a combination of ivaltinostat, gemcitabine and erlotinib appeared to be a potential treatment option for advanced PDAC.

Research on the progress of Traditional Chinese medicine components and preparations on histone deacetylase inhibitors - Like effects in the course of disease treatment

ETHNOPHARMACOLOGICAL RELEVANCE

During the treatment of diseases, histone deacetylases (HDAC) may have side effects such as strong immune inhibition and drug resistance, which may lead to damage of heart, liver and kidney. Traditional Chinese medicine (TCM) is a valuable and unique resource in China, which has good efficacy and safety. At present, it has been found that Chinese herbal compounds and active ingredients can effectively inhibit the expression of HDAC. Moreover, pharmacological studies have shown that these TCMs have shown therapeutic effects in the treatment of cancer, cardiovascular and cerebrovascular diseases, orthopedic diseases and skin diseases.

AIM OF THE REVIEW

This article reviews the mechanism of action of HDAC, and introduces the epigenetic correlation between TCM and HDAC. We expounded the histone deacetylase inhibitor (HDACi)-like inhibitory effect and clinical application of natural drugs, and summarized the research progress of TCM on HDAC in recent years.

MATERIALS AND METHODS

We collected relevant information published before March 2022 by searching the literature in various online databases such as PubMed, CNKI, Wanfang Database, Elsevier, Web of Science and China Biomedical Database. Search terms include "HDAC" or "HDACi", as well as "herb" or "herbal ingredient".

RESULTS

A large number of studies have proved that many TCMs and their chemical components have the effect of inhibiting HDAC activity, which is highly selective, acts on different HDAC subtypes, and plays a certain therapeutic effect in cancer, cardiovascular and cerebrovascular diseases, orthopedic diseases, skin diseases and other diseases by inhibiting the process of HDAC.

DISCUSSION AND CONCLUSIONS

The review of this paper is helpful to understand and excavate the active components of TCM, further explore the role of plant drugs with HDACi-like effect in diseases, and provide ideas for the development of new HDACi.

Targeting the acetylation signaling pathway in cancer therapy

Acetylation represents one of the major post-translational protein modifications, which introduces an acetyl functional group into amino acids such as the lysine residue to yield an acetate ester bond, neutralizing its positive charge. Regulation of protein functions by acetylation occurs in multiple ways, such as affecting protein stability, activity, localization, and interaction with other proteins or DNA. It has been well documented that the recruitment of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to the transcriptional machinery can modulate histone acetylation status, which is directly involved in the dynamic regulation of genes controlling cell proliferation and division. Dysregulation of gene expression is involved in tumorigenesis and aberrant activation of histone deacetylases has been reported in several types of cancer. Moreover, there is growing body of evidence showing that acetylation is widely involved in non-histone proteins to impact their roles in various cellular processes including tumorigenesis. As such, small molecular compounds inhibiting HAT or HDAC enzymatic activities have been developed and investigated for therapeutic purpose. Here we review the recent progress in our understanding of protein acetylation and discuss the therapeutic potential of targeting the acetylation signaling pathway in cancer.

Exploring epigenetic reprogramming during central nervous system infection

Epigenetics involves the study of various modes of adaptable transcriptional regulation, contributing to cell identity, characteristics, and function. During central nervous system (CNS) infection, epigenetic mechanisms can exert pronounced control over the maturation and antimicrobial properties of nearly every immune cell type. Epigenetics is a relatively new field, with the first mention of these marks proposed only a half-century ago and a substantial body of immunological epigenetic research emerging only in the last few decades. Here, we review the best-characterized epigenetic marks and their functions as well as illustrate how various immune cell populations responding to CNS infection utilize these marks to organize their activation state and inflammatory processes. We also discuss the metabolic and clinical implications of epigenetic marks and the rapidly expanding set of tools available to researchers that are enabling elucidation of increasingly detailed genetic regulatory pathways. These considerations paint an intricate picture of inflammatory regulation, where epigenetic marks influence genetic, signaling, and environmental elements to orchestrate a tailored immunological response to the threat at hand, cementing epigenetics as an important player in immunity.

Therapy Resistant Gastroenteropancreatic Neuroendocrine Tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are a heterogenous group of malignancies originating from neuroendocrine cells of the gastrointestinal tract, the incidence of which has been increasing for several decades. While there has been significant progress in the development of therapeutic options for patients with advanced or metastatic disease, these remain limited both in quantity and durability of benefit. This review examines the latest research elucidating the mechanisms of both up-front resistance and the eventual development of resistance to the primary systemic therapeutic options including somatostatin analogues, peptide receptor radionuclide therapy with lutetium Lu 177 dotatate, everolimus, sunitinib, and temozolomide-based chemotherapy. Further, potential strategies for overcoming these mechanisms of resistance are reviewed in addition to a comprehensive review of ongoing and planned clinical trials addressing this important challenge.

LncRNA SNHG1 regulates neuroblastoma cell fate via interactions with HDAC1/2

The small nucleolar RNA host gene 1 (SNHG1) is a novel oncogenic long non-coding RNA (lncRNA) aberrantly expressed in different tumor types. We previously found highly expressed SNHG1 was associated with poor prognosis and MYCN status in neuroblastoma (NB). However, the molecular mechanisms of SNHG1 in NB are still unclear. Here, we disrupted endogenous SNHG1 in the MYCN-amplified NB cell line SK-N-BE(2)C using the CRISPR/Cas9 system and demonstrated the proliferation and colony formation ability of SNHG1-knowndown cells were suppressed. The transcriptome analysis and functional assays of SNHG1-knockdown cells revealed SNHG1 was involved in various biological processes including cell growth, migration, apoptosis, cell cycle, and reactive oxygen species (ROS). Interestingly, the expression of core regulatory circuitry (CRC) transcription factors in MYCN-amplified NB, including PHOX2B, HAND2, GATA3, ISL1, TBX1, and MYCN, were decreased in SNHG1-knockdown cells. The chromatin-immunoprecipitation sequencing (ChIP-seq) and transposase-accessible chromatin using sequencing (ATAC-seq) analyses showed that chromatin status of these CRC members was altered, which might stem from interactions between SNHG1 and HDAC1/2. These findings demonstrate that SNHG1 plays a crucial role in maintaining NB identity via chromatin regulation and reveal the function of the lncRNA SNHG1 in NB.

Mechanisms of tumor resistance to immune checkpoint blockade and combination strategies to overcome resistance

Immune checkpoint blockade (ICB) has rapidly transformed the treatment paradigm for various cancer types. Multiple single or combinations of ICB treatments have been approved by the US Food and Drug Administration, providing more options for patients with advanced cancer. However, most patients could not benefit from these immunotherapies due to primary and acquired drug resistance. Thus, a better understanding of the mechanisms of ICB resistance is urgently needed to improve clinical outcomes. Here, we focused on the changes in the biological functions of CD8⁺ T cells to elucidate the underlying resistance mechanisms of ICB therapies and summarized the advanced coping strategies to increase ICB efficacy. Combinational ICB approaches and individualized immunotherapies require further in-depth investigation to facilitate longer-lasting efficacy and a more excellent safety of ICB in a broader range of patients.

Sensitivity towards HDAC inhibition is associated with RTK/MAPK pathway activation in gastric cancer

Gastric cancer ranks the fifth most common and third leading cause of cancer-related deaths worldwide. Alterations in the RTK/MAPK, WNT, cell adhesion, TP53, TGFβ, NOTCH, and NFκB signaling pathways could be identified as main oncogenic drivers. A combination of altered pathways can be associated with molecular subtypes of gastric cancer. In order to generate model systems to study the impact of different pathway alterations in a defined genetic background, we generated three murine organoid models: a RAS-activated (Kras^G12D , Tp53^R172H ), a WNT-activated (Apc^fl/fl , Tp53^R172H ), and a diffuse (Cdh1^fl/fl , Apc^fl/fl ) model. These organoid models were morphologically and phenotypically diverse, differed in proteome expression signatures and possessed individual drug sensitivities. A differential vulnerability to RTK/MAPK pathway interference based on the different mitogenic drivers and according to the level of dependence on the pathway could be uncovered. Furthermore, an association between RTK/MAPK pathway activity and susceptibility to HDAC inhibition was observed. This finding was further validated in patient-derived organoids from gastric adenocarcinoma, thus identifying a novel treatment approach for RTK/MAPK pathway altered gastric cancer patients.

The emerging roles of HDACs and their therapeutic implications in cancer

Deregulation of protein post-translational modifications is intensively involved in the etiology of diseases, including degenerative diseases, inflammatory injuries, and cancers. Acetylation is one of the most common post-translational modifications of proteins, and the acetylation levels are controlled by two mutually antagonistic enzyme families, histone acetyl transferases (HATs) and histone deacetylases (HDACs). HATs loosen the chromatin structure by neutralizing the positive charge of lysine residues of histones; whereas HDACs deacetylate certain histones, thus inhibiting gene transcription. Compared with HATs, HDACs have been more intensively studied, particularly regarding their clinical significance. HDACs extensively participate in the regulation of proliferation, migration, angiogenesis, immune escape, and therapeutic resistance of cancer cells, thus emerging as critical targets for clinical cancer therapy. Compared to HATs, inhibitors of HDAC have been clinically used for cancer treatment. Here, we enumerate and integratethe mechanisms of HDAC family members in tumorigenesis and cancer progression, and address the new and exciting therapeutic implications of single or combined HDAC inhibitor (HDACi) treatment.