Discovery and development of SAHA as an anticancer agent

SOX2 promotes resistance of melanoma with PD-L1 high expression to T-cell-mediated cytotoxicity that can be reversed by SAHA

BACKGROUND

Immune checkpoint inhibitors (ICIs) induce better tumor regression in melanoma with programmed cell death 1 ligand 1 (PD-L1) high expression, but there has been an upsurge of failed responses. In this study, we aimed to explore the additional mechanisms possibly accounting for ICIs resistance and interventional strategies to overcome the resistance in melanoma with PD-L1 high expression.

METHODS

Melanoma xenografts and cytotoxicity assays were used to investigate function of SOX2 in regulating antitumor immunity. The activity of the janus kinase-signal transducer and activator of transcriptions (JAK-STAT) pathway was investigated by western blots, quantitative PCR and luciferase assay. Epigenetic compounds library screen was employed to identify inhibitors that could decrease SOX2 level. The effect of histone deacetylase inhibitor SAHA in antitumor immunity alone or in combination with immunotherapy was also determined in vitro and in vivo. Prognostic impact of SOX2 was analyzed using transcriptional profiles and clinical data download from the Gene Expression Omnibus and The Cancer Genome Atlas repository.

RESULTS

We uncovered a role of SOX2 in attenuating the sensitivity of melanoma cells to CD8+ T-cell killing. Mechanistically, SOX2 inhibited phosphatases suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase non-receptor type 1 (PTPN1) transcription, induced duration activation of the JAK-STAT pathway and thereby overexpression of interferon stimulated genes resistance signature (ISG.RS). By targeting the SOX2-JAK-STAT signaling, SAHA promoted the antitumor efficacy of IFNγ or anti-PD-1 in vitro and in vivo. Moreover, SOX2 was an independent prognostic factor for poor survival and resistant to anti-PD-1 therapy in melanoma with PD-L1 high expression.

CONCLUSIONS

Our data unveiled an additional function of SOX2 causing immune evasion of CD8+ T-cell killing through alleviating the JAK-STAT pathway and ISG.RS expression. We also provided a rationale to explore a novel combination of ICIs with SAHA clinically, especially in melanoma with PD-L1 and SOX2 high expression.

Pharmacological inhibition of HDAC1/3-interacting proteins induced morphological changes, and hindered the cell proliferation and migration of hepatocellular carcinoma cells

Liver diseases are particularly severe health problems, but the options available for preventing and treating them remain limited. Accumulating evidence has shown that there is altered expression of individual histone deacetylase (HDAC) family members in hepatocellular carcinoma cells. In a previous study, we have identified a set of proteins which interact with histone deacetylase 1 and 3 (HDAC1/3) in hepatocellular carcinoma cell lines HepG2 by proteomic approach. This study was designed to investigate the therapeutic potential and expression of HDAC1/3-interacting genes in a human hepatocellular carcinoma cell line (HepG2). Pharmacological and transcriptional inhibition of HDAC1/3 resulted in the suppression of cancer cell proliferation, change of cell morphology, and downregulation of HDAC1/3 genes in HepG2 cells. The pharmacological inhibition also resulted in inhibition of liver cancer cell migration by wound scratch assay. Taken together, the results from this study show that the upregulation of HDAC1/3 in hepatocellular carcinoma resulted in the overexpression of CNOT1, PFDN2/6, and HMG20B, and that these genes could serve as novel molecular targets in liver cancer.

Post-translational lysine ac(et)ylation in health, ageing and disease

The acetylation/acylation (ac(et)ylation) of lysine side chains is a dynamic post-translational modification (PTM) regulating fundamental cellular processes with implications on the organisms' ageing process: metabolism, transcription, translation, cell proliferation, regulation of the cytoskeleton and DNA damage repair. First identified to occur on histones, later studies revealed the presence of lysine ac(et)ylation in organisms of all kingdoms of life, in proteins covering all essential cellular processes. A remarkable finding showed that the NAD⁺-dependent sirtuin deacetylase Sir2 has an impact on replicative lifespan in Saccharomyces cerevisiae suggesting that lysine acetylation has a direct role in the ageing process. Later studies identified sirtuins as mediators for beneficial effects of caloric/dietary restriction on the organisms' health- or lifespan. However, the molecular mechanisms underlying these effects are only incompletely understood. Progress in mass-spectrometry, structural biology, synthetic and semi-synthetic biology deepened our understanding of this PTM. This review summarizes recent developments in the research field. It shows how lysine ac(et)ylation regulates protein function, how it is regulated enzymatically and non-enzymatically, how a dysfunction in this post-translational machinery contributes to disease development. A focus is set on sirtuins and lysine acyltransferases as these are direct sensors and mediators of the cellular metabolic state. Finally, this review highlights technological advances to study lysine ac(et)ylation.

Phase 1/2 Trial of Vorinostat and Radiation and Maintenance Vorinostat in Children with Diffuse Intrinsic Pontine Glioma: A Children's Oncology Group Report

BACKGROUND

A phase 1/2 trial of vorinostat (suberoylanilide hydroxamic acid), an oral histone deacetylase (HDAC) inhibitor, was conducted in children with newly-diagnosed diffuse intrinsic pontine glioma (DIPG) through the Children's Oncology Group (COG) to: 1) determine the recommended phase 2 dose (RP2D) of vorinostat given concurrently with radiation therapy; 2) document the toxicities of continuing vorinostat as maintenance therapy after radiation; and 3) to determine the efficacy of this regimen by comparing the risk of progression or death with an historical model from past COG trials.

METHODS

Vorinostat was given once daily, Monday through Friday, during radiation therapy (54 Gy in 30 fractions), and then continued at 230 mg/m 2 daily for a maximum of twelve 28-day cycles.

RESULTS

Twelve patients enrolled on the phase 1 study; the RP2D of vorinostat given concurrently with radiation was 230 mg/m 2/day, Monday through Friday weekly. The six patients enrolled at the RP2D and an additional 64 patients enrolled onto the phase 2 study contributed to the efficacy assessment. Although vorinostat was well-tolerated, did not interrupt radiation therapy, and was permanently discontinued in only 8.6% of patients due to toxicities, risk for EFS-event was not significantly reduced compared with the target risk derived from historical COG data (p = 0.32; 1-sided). The 1-year EFS was 5.85% (95% CI 1.89 - 13.1%) and 1-year OS was 39.2% (27.8 - 50.5%).

CONCLUSIONS

Vorinostat given concurrently with radiation followed by vorinostat monotherapy was well tolerated in children with newly-diagnosed DIPG but failed to improve outcome.

A phase 2 trial of the histone deacetylase inhibitor panobinostat for graft-versus-host disease prevention

Immunomodulatory properties of histone deacetylase inhibitors represent a reasonable approach for acute graft-versus-host disease (aGVHD) prevention. We report a phase 2 trial evaluating panobinostat (PANO) administered over 26 weeks, starting on day -5 (5 mg orally 3 times a week) with tacrolimus initiated on day -3 plus sirolimus on day -1, with a median patient age of 58 years (range, 19-72 years) (n = 38). Donor source consisted of HLA 8/8-matched donors, related (n = 13) or unrelated (n = 25), using granulocyte colony-stimulating factor-stimulated peripheral blood stem cells. Myeloablative (n = 18) or reduced-intensity (n = 20) conditioning regimens were used for patients with acute myeloid leukemia (n = 17), myelodysplastic syndrome (n = 13), or other malignancies (n = 8). The cumulative incidence of aGVHD II-IV by day 100 was 18.4% (90% confidence interval [CI], 9.4% to 29.9%). Cumulative incidence of chronic GVHD at 1 year was 31.6% (90% CI, 19.5% to 44.3%). Adverse events related to PANO were thrombocytopenia (n = 5), leukopenia (n = 6), gastrointestinal toxicity (n = 3), rash (n = 4), renal failure/peripheral edema (n = 1), and periorbital edema (n = 1). At 1 year, overall survival was 89.5% (90% CI, 81.6% to 98.0%), relapse-free survival was 78.9% (90% CI, 68.8% to 90.6%), nonrelapse mortality was 2.6% (90% CI, 0.3% to 9.9%), and GVHD relapse-free survival was 60.5% (90% CI, 48.8% to 75.1%). PANO hits histone 3 as early as day 15 in CD8, CD4 and T regs. In conclusion, PANO combination met the primary study end point for aGVHD prevention and warrants further testing. This trial was registered at www.clinicaltrials.gov as #NCT02588339.

Ultrasonic Atomizer-Driven Development of Biocompatible and Biodegradable Poly(d,l-lactide-co-glycolide) Nanocarrier-Encapsulated Suberoylanilide Hydroxamic Acid to Combat Brain Cancer

The path to the discovery of anticancer drugs and investigating their potential activity has remained a quest for several decades. Suberoylanilide hydroxamic acid (SAHA), also known as "Vorinostat", is a well-known histone deacetylase inhibitor (HDACi) and has the potential to act as a therapeutic agent against tumorigenesis. Herein, we have fabricated SAHA incorporated into biocompatible and biodegradable poly(d,l-lactide-co-glycolide) PLGA nanoparticles (NPs) using a facile method of ultrasonic atomization and evaluated their anticancer property. We have explored their characteristics using dynamic light scattering (DLS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), encapsulation efficiency, and in vitro drug release and have investigated their efficacy on U87 glioblastoma (GBM) cells. SAHA-PLGA NPs synthesized were of average mean size of 80 ± 23 and 105 ± 6.0 nm observed through cryo-field-emission gun SEM and HR-TEM with a polydispersity index of 0.068 and a ζ-potential value of -13.26 mV. The encapsulation efficiency was 53%, with a sustained in vitro release up to 48 h. The in vitro assessment of SAHA-PLGA NPs for their anticancer activity on U87 GBM cells showed cellular cytotoxicity with an IC₅₀ of 19.91 μM. SAHA-PLGA NP-treated cells also showed suppression in migration with 8.77 μM concentration, and cell growth inhibition was observed in the wound scratch assay for up to 24 h. The cellular uptake studies have been utilized by time-dependent experiments, revealing their cellular internalization. Taking this into account, our present experimental findings indicate that SAHA-PLGA NPs could play a significant role in enhancing the effectiveness and bioavailability and reducing adverse effects of cancer chemotherapy. It also highlights the inherent potential of these biocompatible entities for chemotherapeutic applications in biomedical and pharmaceutics.

Discovery of potent histone deacetylase inhibitors with modified phenanthridine caps

In discovery of novel HDAC inhibitory with anticancer potency, pharmacophores of phenanthridine were introduced to the structure of HDAC inhibitors. Fatty and aromatic linkers were evaluated for their solubility and activity. Both enzyme inhibitory and in vitro antiproliferative (against U937 cells) screening results revealed better activities of compounds with aromatic linker than molecules with fatty linker. Compared with SAHA (IC₅₀ values of 1.34, 0.14, 2.58, 0.67 and 18.17 µM), molecule Fb-4 exhibited 0.87, 0.09, 0.32, 0.34 and 17.37 µM of IC₅₀ values against K562, U266, MCF-7, U937 and HEPG2 cells, respectively. As revealed by cell cycle and apoptotic analysis, induction of G2/M phase arrest and apoptosis plays an important role in the inhibition of MCF-7 cells by Fb-4. Generally, a potent HDAC inhibitor was developed in the present study which could be utilised as a lead compound for further anticancer drug design.

Structural and Drug Targeting Insights on Mutant p53

p53 is a transcription factor with a pivotal role in cell homeostasis and fate. Its impairment is a major event in tumor onset and development. In fact, about half of human cancers bear TP53 mutations that not only halt the normal function of p53, but also may acquire oncogenic gain of functions that favor tumorigenesis. Although considered undruggable for a long time, evidence has proven the capability of many compounds to restore a wild-type (wt)-like function to mutant p53 (mutp53). However, they have not reached the clinic to date. Structural studies have strongly contributed to the knowledge about p53 structure, stability, dynamics, function, and regulation. Importantly, they have afforded relevant insights into wt and mutp53 pharmacology at molecular levels, fostering the design and development of p53-targeted anticancer therapies. Herein, we provide an integrated view of mutp53 regulation, particularly focusing on mutp53 structural traits and on targeting agents capable of its reactivation, including their biological, biochemical and biophysical features. With this, we expect to pave the way for the development of improved small molecules that may advance precision cancer therapy by targeting p53.

Santacruzamate: Compositions, Analogs and Methods of Use: A Patent Evaluation of WO 2014/018913 (A2)

BACKGROUND

Santacruzamate A (SCA) is a natural product isolated from a marine cyanobacterium. Activity test results revealed that SCA is a highly potent HDAC2 inhibitor with an IC₅₀ value of 0.112 nM. The IC₅₀ of SCA in inhibiting cancer cell proliferation is 28.3 μM and 1.3μM on HCT116 and HuT-78 cells, respectively.

OBJECTIVE

To develop HDAC inhibitors with improved activity, SCA analogs were synthesized for the structure-activity relationship (SAR) studies.

METHOD

Various substituted groups were introduced into the zinc binging group, linker, and cap regions of SCA by various chemical synthetic methods.

RESULT

Compared with SCA, the derivatives of SCA did not exhibit improved HDAC2 inhibitory activity. Nevertheless, several molecules such as III-32, III-33, IV-4b, and IV-11 showed improved activity in inhibiting cell proliferation on HCT116 and HuT-78 cells.

CONCLUSION

Collectively, a potent HDAC2 inhibitor SCA was discovered as a lead compound for further development of selective HDAC inhibitors.

The disruption of protein-protein interactions with co-chaperones and client substrates as a strategy towards Hsp90 inhibition

The 90-kiloDalton (kD) heat shock protein (Hsp90) is a ubiquitous, ATP-dependent molecular chaperone whose primary function is to ensure the proper folding of several hundred client protein substrates. Because many of these clients are overexpressed or become mutated during cancer progression, Hsp90 inhibition has been pursued as a potential strategy for cancer as one can target multiple oncoproteins and signaling pathways simultaneously. The first discovered Hsp90 inhibitors, geldanamycin and radicicol, function by competitively binding to Hsp90's N-terminal binding site and inhibiting its ATPase activity. However, most of these N-terminal inhibitors exhibited detrimental activities during clinical evaluation due to induction of the pro-survival heat shock response as well as poor selectivity amongst the four isoforms. Consequently, alternative approaches to Hsp90 inhibition have been pursued and include C-terminal inhibition, isoform-selective inhibition, and the disruption of Hsp90 protein-protein interactions. Since the Hsp90 protein folding cycle requires the assembly of Hsp90 into a large heteroprotein complex, along with various co-chaperones and immunophilins, the development of small molecules that prevent assembly of the complex offers an alternative method of Hsp90 inhibition.

A Chemo-Genomic Approach Identifies Diverse Epigenetic Therapeutic Vulnerabilities in MYCN-Amplified Neuroblastoma

Although a rare disease, neuroblastoma accounts for the highest proportion of childhood cancer deaths. There is a lack of recurrent somatic mutations in neuroblastoma embryonal tumours, suggesting a possible role for epigenetic alterations in driving this cancer. While an increasing number of reports suggest an association of MYCN with epigenetic machinery, the mechanisms of these interactions are poorly understood in the neuroblastoma setting. Utilising chemo-genomic approaches we revealed global MYCN-epigenetic interactions and identified numerous epigenetic proteins as MYCN targets. The epigenetic regulators HDAC2, CBX8 and CBP (CREBBP) were all MYCN target genes and also putative MYCN interactors. MYCN-related epigenetic genes included SMARCs, HDACs, SMYDs, BRDs and CREBBP. Expression levels of the majority of MYCN-related epigenetic genes showed predictive ability for neuroblastoma patient outcome. Furthermore, a compound library screen targeting epigenetic proteins revealed broad susceptibility of neuroblastoma cells to all classes of epigenetic regulators, belonging to families of bromodomains, HDACs, HATs, histone methyltransferases, DNA methyltransferases and lysin demethylases. Ninety-six percent of the compounds reduced MYCN-amplified neuroblastoma cell viability. We show that the C646 (CBP-bromodomain targeting compound) exhibits switch-like temporal and dose response behaviour and is effective at reducing neuroblastoma viability. Responsiveness correlates with MYCN expression, with MYCN-amplified cells being more susceptible to C646 treatment. Thus, exploiting the broad vulnerability of neuroblastoma cells to epigenetic targeting compounds represents an exciting strategy in neuroblastoma treatment, particularly for high-risk MYCN-amplified tumours.

Recent developments in epigenetic cancer therapeutics: clinical advancement and emerging trends

Epigenetic drug discovery field has evidenced significant advancement in the recent times. A plethora of small molecule inhibitors have progressed to clinical stage investigations and are being explored exhaustively to ascertain conclusive benefits in diverse malignancies. Literature precedents indicates that substantial amount of efforts were directed towards the use of epigenetic tools in monotherapy as well as in combination regimens at the clinical level, however, the preclinical/preliminary explorations were inclined towards the identification of prudent approaches that can leverage the anticancer potential of small molecule epigenetic inhibitors as single agents only. This review article presents an update of FDA approved epigenetic drugs along with the epigenetic inhibitors undergoing clinical stage investigations in different cancer types. A detailed discussion of the pragmatic strategies that are expected to steer the progress of the epigenetic therapy through the implementation of emerging approaches such as PROTACS and CRISPR/Cas9 along with logical ways for scaffold fabrication to selectively approach the enzyme isoforms in pursuit of garnering amplified antitumor effects has been covered. In addition, the compilation also presents the rational strategies for the construction of multi-targeting scaffold assemblages employing previously identified pharmacophores as potential alternatives to the combination therapy.

Safety and efficacy of combination of suberoylamilide hydroxyamic acid and mitomycin C in reducing pro-fibrotic changes in human corneal epithelial cells

Corneal haze post refractive surgery is prevented by mitomycin c (MMC) treatment though it can lead to corneal endothelial damage, persistent epithelial defects and necrosis of cells. Suberanilohydroxamic acid (SAHA) however has been proposed to prevent corneal haze without any adverse effects. For clinical application we have investigated the short and long term outcome of cells exposed to SAHA. Human donor cornea, cultured limbal epithelial cells, corneal rims and lenticules were incubated with SAHA and MMC. The cells/tissue was then analyzed by RT-qPCR, immunofluorescence and western blot for markers of apoptosis and fibrosis. The results reveal that short term exposure of SAHA and SAHA + MMC reduced apoptosis levels and increased αSMA expression compared to those treated with MMC. Epithelial cells derived from cultured corneal rim that were incubated with the MMC, SAHA or MMC + SAHA revealed enhanced apoptosis, reduced levels of CK3/CK12, ∆NP63 and COL4A compared to other treatments. In SAHA treated lenticules TGFβ induced fibrosis was reduced. The results imply that MMC treatment for corneal haze has both short term and long term adverse effects on cells and the cellular properties. However, a combinatorial treatment of SAHA + MMC prevents expression of corneal fibrotic markers without causing any adverse effect on cellular properties.

CAP rigidification of MS-275 and chidamide leads to enhanced antiproliferative effects mediated through HDAC1, 2 and tubulin polymerization inhibition

The study focuses on the prudent design and synthesis of anilide type class I HDAC inhibitors employing a functionalized pyrrolo[2,3-d]pyrimidine skeleton as the surface recognition part. Utilization of the bicyclic aromatic ring to fabricate the target compounds was envisioned to confer rigidity to the chemical architecture of MS-275 and chidamide. In-vitro enzymatic and cellular assays led to the identification of compound 7 as a potent inhibitor of HDAC1 and 2 isoform that exerted substantial cell growth inhibitory effects against human breast MDA-MB-231, cervical HeLa, breast MDA-MB-468, colorectal DLD1, and colorectal HCT116 cell lines with an IC₅₀ values of 0.05-0.47 μM, better than MS-275 and chidamide. In addition, the anilide 7 was also endowed with a superior antiproliferative profile than MS275 and chidamide towards the human cutaneous T cell lymphoma (HH and HuT78), leukemia (HL60 and KG-1), and HDACi sensitive/resistant gastric cell lines (YCC11 and YCC3/7). Exhaustive exploration of the construct 7 confirmed it to be a microtubule-targeting agent that could trigger the cell-cycle arrest in mitosis. In pursuit of extracting the benefits of evidenced microtubule-destabilizing activity of the anilide 7, it was further evaluated against non-small-cell lung cancer cell lines as well as the multiple-drug resistant uterine cancer cell line (MES-SA/Dx5) and overwhelmingly positive results in context of inhibitory effects were attained. Furthermore, molecular modelling studies were performed and some key interactions of the anilide 7 with the amino acid residues of the active site of HDAC1 isoform and tubulin were figured out.

A C21-steroidal derivative suppresses T-cell lymphoma in mice by inhibiting SIRT3 via SAP18-SIN3

The SIN3 repressor complex and the NAD-dependent deacetylase SIRT3 control cell growth, and development as well as malignant transformation. Even then, a little known about cross-talks between these two chromatin modifiers or whether their interaction explored therapeutically. Here we describe the identification of a C₂₁-steroidal derivative compound, 3-O-chloroacetyl-gagamine, A671, which potently suppresses the growth of mouse and human T-cell lymphoma and erythroleukemia in vitro and preclinical models. A671 exerts its anti-neoplastic effects by direct interaction with Histone deacetylase complex subunit SAP18, a component of the SIN3 suppressor complex. This interaction stabilizes and activates SAP18, leading to transcriptional suppression of SIRT3, consequently to inhibition of proliferation and cell death. The resistance of cancer cells to A671 correlated with diminished SAP18 activation and sustained SIRT3 expression. These results uncover the SAP18-SIN3-SIRT3 axis that can be pharmacologically targeted by a C₂₁-steroidal agent to suppress T-cell lymphoma and other malignancies.

Gajendran et al. show that a C21-steroidal derivative called A671, 3-O-chloroacetyl-gagamine, suppresses the growth of T-cell lymphoma in mice. They find that A671 activates SAP18 to suppress the transcription of SIRT3, inhibiting cell growth. This study presents a new pharmacological target pathway for T-cell lymphoma.

Therapeutic evaluation of palbociclib and its compatibility with other chemotherapies for primary and recurrent nasopharyngeal carcinoma

BACKGROUND

Recent genomic analyses revealed that druggable molecule targets were only detectable in approximately 6% of patients with nasopharyngeal carcinoma (NPC). However, a dependency on dysregulated CDK4/6-cyclinD1 pathway signaling is an essential event in the pathogenesis of NPC. In this study, we aimed to evaluate the therapeutic efficacy of a specific CDK4/6 inhibitor, palbociclib, and its compatibility with other chemotherapeutic drugs for the treatment of NPC by using newly established xenograft models and cell lines derived from primary, recurrent, and metastatic NPC.

METHODS

We evaluated the efficacies of palbociclib monotherapy and concurrent treatment with palbociclib and cisplatin or suberanilohydroxamic acid (SAHA) in NPC cell lines and xenograft models. RNA sequencing was then used to profile the drug response-related pathways. Palbociclib-resistant NPC cell lines were established to determine the potential use of cisplatin as a second-line treatment after the development of palbociclib resistance. We further examined the efficacy of palbociclib treatment against cisplatin-resistant NPC cells.

RESULTS

In NPC cells, palbociclib monotherapy was confirmed to induce cell cycle arrest in the G1 phase in vitro. Palbociclib monotherapy also had significant inhibitory effects in all six tested NPC tumor models in vivo, as indicated by substantial reductions in the total tumor volumes and in Ki-67 proliferation marker expression. In NPC cells, concurrent palbociclib treatment mitigated the cytotoxic effect of cisplatin in vitro. Notably, concurrent treatment with palbociclib and SAHA synergistically promoted NPC cell death both in vitro and in vivo. This combination also further inhibited tumor growth by inducing autophagy-associated cell death. NPC cell lines with induced palbociclib or cisplatin resistance remained sensitive to treatment with cisplatin or palbociclib, respectively.

CONCLUSIONS

Our study findings provide essential support for the use of palbociclib as an alternative therapy for NPC and increase awareness of the effective timing of palbociclib administration with other chemotherapeutic drugs. Our results provide a foundation for the design of first-in-human clinical trials of palbociclib regimens in patients with NPC.

A G-Quadruplex-Binding Small Molecule and the HDAC Inhibitor SAHA (Vorinostat) Act Synergistically in Gemcitabine-Sensitive and Resistant Pancreatic Cancer Cells

The stabilisation of G-quadruplexes (G4s) by small-molecule compounds is an effective approach for causing cell growth arrest, followed by cell death. Some of these compounds are currently being developed for the treatment of human cancers. We have previously developed a substituted naphthalene diimide G4-binding molecule (CM03) with selective potency for pancreatic cancer cells, including gemcitabine-resistant cells. We report here that CM03 and the histone deacetylase (HDAC) inhibitor SAHA (suberanilohydroxamic acid) have synergistic effects at concentrations close to and below their individual GI₅₀ values, in both gemcitabine-sensitive and resistant pancreatic cancer cell lines. Immunoblot analysis showed elevated levels of γ-H2AX and cleaved PARP proteins upon drug combination treatment, indicating increased levels of DNA damage (double-strand break events: DSBs) and apoptosis induction, respectively. We propose that the mechanism of synergy involves SAHA relaxing condensed chromatin, resulting in higher levels of G4 formation. In turn, CM03 can stabilise a greater number of G4s, leading to the downregulation of more G4-containing genes as well as a higher incidence of DSBs due to torsional strain on DNA and chromatin structure.

Exploring the multiple roles of guardian of the genome: P53

Background

Cells have evolved balanced mechanisms to protect themselves by initiating a specific response to a variety of stress. TheTP53gene, encoding P53 protein, is one of the many widely studied genes in human cells owing to its multifaceted functions and complex dynamics. The tumour-suppressing activity of P53 plays a principal role in the cellular response to stress. The majority of the human cancer cells exhibit the inactivation of the P53 pathway. In this review, we discuss the recent advancements in P53 research with particular focus on the role of P53 in DNA damage responses, apoptosis, autophagy, and cellular metabolism. We also discussed important P53-reactivation strategies that can play a crucial role in cancer therapy and the role of P53 in various diseases.

Main body

We used electronic databases like PubMed and Google Scholar for literature search. In response to a variety of cellular stress such as genotoxic stress, ischemic stress, oncogenic expression, P53 acts as a sensor, and suppresses tumour development by promoting cell death or permanent inhibition of cell proliferation. It controls several genes that play a role in the arrest of the cell cycle, cellular senescence, DNA repair system, and apoptosis. P53 plays a crucial role in supporting DNA repair by arresting the cell cycle to purchase time for the repair system to restore genome stability. Apoptosis is essential for maintaining tissue homeostasis and tumour suppression. P53 can induce apoptosis in a genetically unstable cell by interacting with many pro-apoptotic and anti-apoptotic factors.

Furthermore, P53 can activate autophagy, which also plays a role in tumour suppression. P53 also regulates many metabolic pathways of glucose, lipid, and amino acid metabolism. Thus under mild metabolic stress, P53 contributes to the cell’s ability to adapt to and survive the stress.

Conclusion

These multiple levels of regulation enable P53 to perform diversified roles in many cell responses. Understanding the complete function of P53 is still a work in progress because of the inherent complexity involved in between P53 and its target proteins. Further research is required to unravel the mystery of this Guardian of the genome “TP53”.

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.

Mutant p53 in Cancer Progression and Targeted Therapies

TP53 is the most frequently mutated tumor suppressor gene in human cancer. The majority of mutations of p53 are missense mutations, leading to the expression of the full length p53 mutant proteins. Mutant p53 (Mutp53) proteins not only lose wild-type p53-dependent tumor suppressive functions, but also frequently acquire oncogenic gain-of-functions (GOF) that promote tumorigenesis. In this review, we summarize the recent advances in our understanding of the oncogenic GOF of mutp53 and the potential therapies targeting mutp53 in human cancers. In particular, we discuss the promising drugs that are currently under clinical trials as well as the emerging therapeutic strategies, including CRISPR/Cas9 based genome edition of mutant TP53 allele, small peptide mediated restoration of wild-type p53 function, and immunotherapies that directly eliminate mutp53 expressing tumor cells.

OxymaPure Coupling Reagents: Beyond Solid-Phase Peptide Synthesis

OxymaPure [ethyl 2-cyano-2-(hydroxyimino)acetate] is an exceptional reagent with which to suppress racemization and enhance coupling efficiency during amide bond formation. The tremendous popularity of OxymaPure has led to the development of several Oxyma-based reagents. OxymaPure and its derived reagents are widely used in solid- and solution-phase peptide chemistry. This review summarizes the recent developments and applications of OxymaPure and Oxyma-based reagents in peptide chemistry, in particular in solution-phase chemistry. Moreover, the side reaction associated with OxymaPure is also discussed.

1 Introduction

2 Oxyma-Based Coupling Reagents

2.1 Aminium/Uronium Salts of OxymaPure

2.2 Phosphonium Salts of OxymaPure

2.3 Oxyma-Based Phosphates

2.4 Sulfonate Esters of OxymaPure

2.5 Benzoate Esters of OxymaPure

2.6 Carbonates of OxymaPure Derivatives

3 OxymaPure Derivatives

4 Other Oxime-Based Additives and Coupling Reagents

5 Side Reactions Using OxymaPure Derivatives

6 Conclusion

7 List of Abbreviations

Discovery of N-(2-Amino-4-Fluorophenyl)-4-[bis-(2-Chloroethyl)-Amino]-Benzamide as a Potent HDAC3 Inhibitor

In discovery of HDAC inhibitors with improved activity and selectivity, fluorine substitution was performed on our previously derived lead compound. The synthesized molecules N-(2-amino-4-fluorophenyl)-4-[bis-(2-chloroethyl)-amino]-benzamide (FNA) exhibited class I (HDAC1, 2, and 3) selectivity in the in vitro enzymatic assay and especially potent against HDAC3 activity (IC₅₀: 95.48 nM). The results of in vitro antiproliferative assay indicated that FNA exhibited solid tumor cell inhibitory activities with IC₅₀ value of 1.30 μM against HepG2 cells compared with SAHA (17.25 μM). Moreover, the in vivo xenograft model study revealed that FNA could inhibit tumor growth with tumor growth inhibition (TGI) of 48.89% compared with SAHA (TGI of 48.13%). Further HepG2 cell–based apoptosis and cell cycle studies showed that promotion of apoptosis and G2/M phase arrest make contributions to the antitumor activity of FNA. In addition, drug combination results showed that 0.5 μM of FNA could improve the anticancer activity of taxol and camptothecin. The present studies revealed the potential of FNA utilized as a high potent lead compound for further discovery of isoform selective HDAC inhibitors.

Binding of inhibitors to active-site mutants of CD1, the enigmatic catalytic domain of histone deacetylase 6

The zinc hydrolase histone deacetylase 6 (HDAC6) is unique among vertebrate deacetylases in that it contains two catalytic domains, designated CD1 and CD2. Both domains are fully functional as lysine deacetylases in vitro. However, the in vivo function of only the CD2 domain is well defined, whereas that of the CD1 domain is more enigmatic. Three X-ray crystal structures of HDAC6 CD1-inhibitor complexes are now reported to broaden the understanding of affinity determinants in the active site. Notably, cocrystallization with inhibitors was facilitated by using active-site mutants of zebrafish HDAC6 CD1. The first mutant studied, H82F/F202Y HDAC6 CD1, was designed to mimic the active site of human HDAC6 CD1. The structure of its complex with trichostatin A was generally identical to that with the wild-type zebrafish enzyme. The second mutant studied, K330L HDAC6 CD1, was prepared to mimic the active site of HDAC6 CD2. It has previously been demonstrated that this substitution does not perturb inhibitor binding conformations in HDAC6 CD1; here, this mutant facilitated cocrystallization with derivatives of the cancer chemotherapy drug suberoylanilide hydroxamic acid (SAHA). These crystal structures allow the mapping of inhibitor-binding regions in the outer active-site cleft, where one HDAC isozyme typically differs from another. It is expected that these structures will help to guide the structure-based design of inhibitors with selectivity against HDAC6 CD1, which in turn will enable new chemical biology approaches to probe its cellular function.

The design of a novel near-infrared fluorescent HDAC inhibitor and image of tumor cells

Histone deacetylases (HDACs) have been found to be biomarkers of cancers and the corresponding inhibitors have attracted much attention these years. Herein we reported a near-infrared fluorescent HDAC inhibitor based on vorinostat (SAHA) and a NIR fluorophore. This newly designed inhibitor showed similar inhibitory activity to SAHA against three HDAC isoforms (HDAC1, 3, 6). The western blot assay showed significant difference in compared with the negative group. When used as probe for further kinematic imaging, Probe 1 showed enhanced retention in tumor cells and the potential of HDAC inhibitors in drug delivery was firstly brought out. The cytotoxicity assay showed Probe 1 had some anti-proliferation activities with corresponding IC₅₀ values of 9.20 ± 0.96 μM on Hela cells and 5.91 ± 0.57 μM on MDA-MB-231 cells. These results indicated that Probe 1 could be used as a potential NIR fluorescent in the study of HDAC inhibitors and lead compound for the development of visible drugs.

Recent Progress in Histone Deacetylase Inhibitors as Anticancer Agents

Histone Deacetylase (HDAC) inhibitors are a relatively new class of anti-cancer agents that play important roles in epigenetic or non-epigenetic regulation, inducing death, apoptosis, and cell cycle arrest in cancer cells. Recently, their use has been clinically validated in cancer patients resulting in the approval by the FDA of four HDAC inhibitors, vorinostat, romidepsin, belinostat and panobinostat, used for the treatment of cutaneous/peripheral T-cell lymphoma and multiple myeloma. Many more HDAC inhibitors are at different stages of clinical development for the treatment of hematological malignancies as well as solid tumors. Also, clinical trials of several HDAC inhibitors for use as anti-cancer drugs (alone or in combination with other anti-cancer therapeutics) are ongoing. In the intensifying efforts to discover new, hopefully, more therapeutically efficacious HDAC inhibitors, molecular modelingbased rational drug design has played an important role. In this review, we summarize four major structural classes of HDAC inhibitors (hydroxamic acid derivatives, aminobenzamide, cyclic peptide and short-chain fatty acids) that are in clinical trials and different computer modeling tools available for their structural modifications as a guide to discover additional HDAC inhibitors with greater therapeutic utility.

Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Improves Energetic Status and Cardiomyogenic Differentiation of Human Dilated Myocardium-Derived Primary Mesenchymal Cells

Background. In this study the effect of histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) on the energetic status and cardiomyogenic differentiation of human healthy and dilated myocardium-derived mesenchymal stromal cells (hmMSC) have been investigated. Methods. The hmMSC were isolated from the healthy and dilated post-operation heart biopsies by explant outgrowth method. Cell proliferation, HDAC activity, mitochondrial membrane potential, and level of adenosine triphosphate (ATP) were evaluated. The effect of SAHA on mitochondrial parameters has been investigated also by Seahorse XF analyzer and cardiomyogenic differentiation was confirmed by the expression of transcription factor NK2 Homeobox 5 (Nkx2.5), cardiac troponin T and alpha cardiac actin at gene and protein levels. Results. Dilated myocardium-derived hmMSC had almost 1.5 folds higher HDAC activity compared to the healthy cells and significantly lower mitochondrial membrane potential and ATP level. HDAC class I and II inhibitor SAHA improved energetic status of mitochondria in dilated myocardium-isolated hmMSC and increased expression of cardiac specific proteins during 14 days of exposure of cells to SAHA. Conclusions. HDAC inhibitor SAHA can be a promising therapeutic for dilated cardiomyopathy (DCM). Dilated hmMSC exposed to SAHA improved energetic status and, subsequently, cardiomyogenic differentiation. Data suggest that human dilated myocardium-derived MSC still have cardio tissue regenerative potential, which might be stimulated by HDAC inhibitors.

Polycythemia vera: the current status of preclinical models and therapeutic targets

INTRODUCTION

Polycythemia vera (PV) is the most common myeloproliferative neoplasm (MPN). PV is characterized by erythrocytosis, leukocytosis, thrombocytosis, increased hematocrit, and hemoglobin in the peripheral blood. Splenomegaly and myelofibrosis often occur in PV patients. Almost all PV patients harbor a mutation in the JAK2 gene, mainly represented by the JAK2^V617F point mutation.

AREAS COVERED

This article examines the recent in vitro and in vivo available models of PV and moreover, it offers insights on emerging biomarkers and therapeutic targets. The evidence from mouse models, resembling a PV-like phenotype generated by different technical approaches, is discussed. The authors searched PubMed, books, and clinicaltrials.gov for original and review articles and drugs development status including the terms Myeloproliferative Neoplasms, Polycythemia Vera, erythrocytosis, hematocrit, splenomegaly, bone marrow fibrosis, JAK2^V617F, Hematopoietic Stem Cells, MPN cytoreductive therapy, JAK2 inhibitor, histone deacetylase inhibitor, PV-like phenotype, JAK2^V617F BMT, transgenic JAK2^V617F mouse, JAK2 physiologic promoter.

EXPERT OPINION

Preclinical models of PV are valuable tools for enabling an understanding of the pathophysiology and the molecular mechanisms of the disease. These models provide new biological insights on the contribution of concomitant mutations and the efficacy of novel drugs in a 'more faithful' setting. This may facilitate an enhanced understanding of pathogenetic mechanisms and targeted therapy.

Gallic acid, a phenolic acid, hinders the progression of prostate cancer by inhibition of histone deacetylase 1 and 2 expression

Gallic acid (GA) is known to possess diverse biological activities, including anticancer. Histone deacetylase (HDACs) are controlled by tumor suppressor gene transcription and are overexpressed in various tumors, resulting in tumor development, progression and poor prognosis. This study aims to demonstrate the effect of GA on inhibition of prostate cancer (PCa) progression by modulating the expression of HDAC1 and 2 in PCa cells. To prove our research rationale, we used diverse experimental methods. GA decreased the cell viability of only PCa cell lines and not normal cells (contrary to another HDAC inhibitor, suberoylanilide hydroxamic acid) and also inhibited colony and tumor spheroid formation. Exposure to GA decreased the mitochondrial membrane potential (ΔΨm), increased the number of apoptotic cells and induced DNA fragmentation. Western blot analysis revealed down-regulated expression of HDAC1 and 2, leading to up-regulation of acetyl-p53 expression at the protein level, subsequent to down-regulating the expression of cell-cycle-related genes, i.e., proliferating cell nuclear antigen (PCNA), Cyclin D1 and E1, up-regulating the expression of cell cycle arrest gene p21 and regulating the expression of apoptosis intrinsic pathway-related genes, such as Bax, Bcl-2, cleaved Caspase-3 and poly (ADP-ribose) polymerase 1 in both PCa cell lines. Furthermore, oral administration of GA for 8 weeks on PC-3 cells-derived tumor xenograft mice model decreases the tumor size, damages the tumor structure and down-regulates the expression of HDAC1 and 2 and PCNA in tumor mass, as confirmed by histological analysis. These results indicated that GA may hinder the PCa progression by inhibiting HDAC1 and 2 expression, thereby demonstrating the potential of GA to be used as HDACs inhibitor and anti-PCa therapeutics.

Design and in silico screening of aryl allyl mercaptan analogs as potential histone deacetylases (HDAC) inhibitors

The Zn⁺² HDACIs show promising anticancer activity. Allyl mercaptan (AM), a metastabilzed monomeric form of diallyl disulphide (DADS) shows better HDACI activity. The present work screens a dataset of aryl AM derivatives 1(a-g) for potential HDACI action viain silico models. DFT calculations predicted the geometrical parameters and frontier orbital calculations suggested better chemical reactivity. Negative chemical potential and NBO hyper conjugative interactions predicted their chemical stability. ADME study confirmed favourable drug likeliness. Molecular docked models suggested the formation of coordinate bond between sulphur of allylmercaptan and Zn²⁺ cofactor of HDAC8. Besides, models also predicted the dominance of hydrophobic interactions. The aryl AM analogs docked perfectly with HDAC3 as well. The glide score and S-Zn distance of compounds 1a, 1f and 1g were found to be better than allylmercaptan. Therefore, the designed aryl AM analogs filtered as better HDACIs. These could be further used for design and synthesis of new improved HDACIs.

PIWIL4 Maintains HIV-1 Latency by Enforcing Epigenetically Suppressive Modifications on the 5' Long Terminal Repeat

Although substantial progress has been made in depicting the molecular pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection, the comprehensive mechanism of HIV-1 latency and the most promising therapeutic strategies to effectively reactivate the HIV-1 latent reservoir to achieve a functional cure for AIDS remain to be systematically illuminated. Here, we demonstrated that piwi (P element-induced Wimpy)-like RNA-mediated gene silencing 4 (PIWIL4) played an important role in suppressing HIV-1 transcription and contributed to the latency state in HIV-1-infected cells through its recruitment of various suppressive factors, including heterochromatin protein 1α/β/γ, SETDB1, and HDAC4. The knockdown of PIWIL4 enhanced HIV-1 transcription and reversed HIV-1 latency in both HIV-1 latently infected Jurkat T cells and primary CD4⁺ T lymphocytes and resting CD4⁺ T lymphocytes from HIV-1-infected individuals on suppressive combined antiretroviral therapy (cART). Furthermore, in the absence of PIWIL4, HIV-1 latently infected Jurkat T cells were more sensitive to reactivation with vorinostat (suberoylanilide hydroxamic acid, or SAHA), JQ1, or prostratin. These findings indicated that PIWIL4 promotes HIV-1 latency by imposing repressive marks at the HIV-1 5' long terminal repeat. Thus, the manipulation of PIWIL4 could be a novel strategy for developing promising latency-reversing agents (LRAs).IMPORTANCE HIV-1 latency is systematically modulated by host factors and viral proteins. During this process, the suppression of HIV-1 transcription plays an essential role in promoting HIV-1 latency. In this study, we found that PIWIL4 repressed HIV-1 promoter activity and maintained HIV-1 latency. In particular, we report that PIWIL4 can regulate gene expression through its association with the suppressive activity of HDAC4. Therefore, we have identified a new function for PIWIL4: it is not only a suppressor of endogenous retrotransposons but also plays an important role in inhibiting transcription and leading to latent infection of HIV-1, a well-known exogenous retrovirus. Our results also indicate a novel therapeutic target to reactivate the HIV-1 latent reservoir.

Suppression of histone deacetylases by SAHA relieves bone cancer pain in rats via inhibiting activation of glial cells in spinal dorsal horn and dorsal root ganglia

BACKGROUND

Robust activation of glial cells has been reported to occur particularly during the pathogenesis of bone cancer pain (BCP). Researchers from our group and others have shown that histone deacetylases (HDACs) play a significant role in modulating glia-mediated immune responses; however, it still remains unclear whether HDACs are involved in the activation of glial cells during the development of BCP.

METHODS

BCP model was established by intra-tibia tumor cell inoculation (TCI). The expression levels and distribution sites of histone deacetylases (HDACs) in the spinal dorsal horn and dorsal root ganglia were evaluated by Western blot and immunofluorescent staining, respectively. Suberoylanilide hydroxamic acid (SAHA), a clinically used HDAC inhibitor, was then intraperitoneally and intrathecally injected to rescue the increased expression levels of HDAC1 and HDAC2. The analgesic effects of SAHA administration on BCP were then evaluated by measuring the paw withdrawal thresholds (PWTs). The effects of SAHA on activation of glial cells and expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in the spinal dorsal horn and dorsal root ganglia of TCI rats were further evaluated by immunofluorescent staining and Western blot analysis. Subsequently, the effects of SAHA administration on tumor growth and cancer cell-induced bone destruction were analyzed by hematoxylin and eosin (HE) staining and micro-CT scanning.

RESULTS

TCI caused rapid and long-lasting increased expression of HDAC1/HDAC2 in glial cells of the spinal dorsal horn and dorsal root ganglia. Inhibiting HDACs by SAHA not only reversed TCI-induced upregulation of HDACs but also inhibited the activation of glial cells in the spinal dorsal horn and dorsal root ganglia, and relieved TCI-induced mechanical allodynia. Further, we found that SAHA administration could not prevent cancer infiltration or bone destruction in the tibia, which indicated that the analgesic effects of SAHA were not due to its anti-tumor effects. Moreover, we found that SAHA administration could inhibit GSK3β activity in the spinal dorsal horn and dorsal root ganglia, which might contributed to the relief of BCP.

CONCLUSION

Our findings suggest that HDAC1 and HDAC2 are involved in the glia-mediated neuroinflammation in the spinal dorsal horn and dorsal root ganglia underlying the pathogenesis of BCP, which indicated that inhibiting HDACs by SAHA might be a potential strategy for pain relief of BCP.

Purine/purine isoster based scaffolds as new derivatives of benzamide class of HDAC inhibitors

This study reports the design, synthesis and evaluation of a series of histone deacetylase (HDAC) inhibitors containing purine/purine isoster as a capping group and an N-(2-aminophenyl)-benzamide unit. In vitro cytotoxicity studies reveal that benzamide 14 suppressed the growth of triple-negative breast cancer cells MDA-MB-231 (IC₅₀ = 1.48 μM), MDA-MB-468 (IC₅₀ = 0.65 μM), and liver cancer cells HepG2 (IC₅₀ = 2.44 μM), better than MS-275 (5) and Chidamide (6). Compared to the well-known HDAC inhibitor SAHA, 14 showed a higher toxicity (IC₅₀ = 0.33 μM) in three leukemic cell lines, K-562, KG-1 and THP-1. Moreover, 14 was found to be equally virulent in the HDAC-sensitive and -resistant gastric cell lines, YCC11 and YCC3/7, respectively, indicating the potential of 14 to overcome HDACi resistance. Furthermore, substantial inhibitory effects more pronounced than MS-275 (5) and Chidamide (6) were displayed by 14 towards HDAC1, 2 and 3 isoforms with IC₅₀ values of 0.108, 0.585 and 0.563 μM respectively. Compound 14 also exhibited a potent antitumor efficacy in human MDA-MB-231 breast cancer xenograft mouse model, providing a potential lead for the development of anticancer agents.

Synthesis, Characterization and Biological Evaluation of Novel Dihydropyranoindoles Improving the Anticancer Effects of HDAC Inhibitors

The dihydropyranoindole scaffold was identified as a promising target for improving the anti-cancer activity of HDAC inhibitors from the preliminary screening of a library of compounds. A suitable methodology has been developed for the preparation of novel dihydropyranoindoles via the Hemetsberger indole synthesis using azido-phenylacrylates, derived from the reaction of corresponding alkynyl-benzaldehydes with methyl azidoacetate, followed by thermal cyclization in high boiling solvents. Anti-cancer activity of all the newly synthesized compounds was evaluated against the SH-SY5Y and Kelly neuroblastoma cells as well as the MDA-MB-231 and MCF-7 breast adenocarcinoma cell lines. Biological studies showed that the tetracyclic systems had significant cytotoxic activity at higher concentration against the neuroblastoma cancer cells. More importantly, these systems, at the lower concentration, considerably enhanced the SAHA toxicity. In addition to that, the toxicity of designated systems on the healthy human cells was found to be significantly less than the cancer cells.

Transcriptional Regulation at DSBs: Mechanisms and Consequences

Defective double-strand break (DSB) repair leads to genomic instabilities that may augment carcinogenesis. DSBs trigger transient transcriptional silencing in the vicinity of transcriptionally active genes through multilayered processes instigated by Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), and poly-(ADP-ribose) polymerase 1 (PARP1). Novel factors have been identified that ensure DSB-induced silencing via two distinct pathways: direct inhibition of RNA Polymerase II (Pol II) mediated by negative elongation factor (NELF), and histone code editing by CDYL1 and histone deacetylases (HDACs) that catalyze H3K27me3 and erase lysine crotonylation, respectively. Here, we highlight major advances in understanding the mechanisms underlying transcriptional silencing at DSBs, and discuss its functional implications on repair. Furthermore, we discuss consequential links between DSB-silencing factors and carcinogenesis and discuss the potential of exploiting them for targeted cancer therapy.

Discovery of novel cyclin-dependent kinase (CDK) and histone deacetylase (HDAC) dual inhibitors with potent in vitro and in vivo anticancer activity

In the current study, we reported a series of novel 1-H-pyrazole-3-carboxamide-based inhibitors targeting histone deacetylase (HDAC) and cyclin-dependent kinase (CDK). The representative compounds N-(4-((2-aminophenyl)carbamoyl)benzyl)-4-(2,6-dichlorobenzamido)-1H-pyrazole-3-carboxamide (7c) and N-(4-(2-((2-aminophenyl)amino)-2-oxoethyl)phenyl)-4-(2,6-dichlorobenzamido)-1H-pyrazole-3-carboxamide (14a) with potent antiproliferative activities towards five solid cancer cell lines, showed excellent inhibitory activities against HDAC2 (IC₅₀ = 0.25 and 0.24 nM respectively) and CDK2 (IC₅₀ = 0.30 and 0.56 nM respectively). In addition, compounds 7c and 14a significantly inhibited the migration of A375 and H460 cells. Further studies revealed that compounds 7c and 14a could arrest cell cycle in G2/M phase and promote apoptosis in A375, HCT116, H460 and Hela cells, which was associated with increasing the intracellular reactive oxygen species (ROS) levels. More importantly, compound 7c possessed favorable pharmacokinetic properties with the intraperitoneal bioavailability of 63.6% in ICR mice, and potent in vivo antitumor efficacy in the HCT116 xenograft model. Our study demonstrated that compound 7c provides a promising strategy for the treatment of malignant tumors.

Co-Prodrugs of 7-Ethyl-10-hydroxycamptothecin and Vorinostat with in Vitro Hydrolysis and Anticancer Effects

7-Ethyl-10-hydroxycamptothecin (SN38) and vorinostat (SAHA) are quite promising combination therapy agents applied to the clinical treatment of cancer. In this study, we designed and synthesized a series of novel SN38-SAHA co-prodrugs, which were conjugated by four different amino acids including glycine, alanine, aminobutyric acid, and 6-aminocaproic acid. The hydrolytic reconversion rate to SN38 and SAHA critically depended on the carbon chain length, which were evaluated in PBS (pH 6.0/7.4) and plasma (human/mouse). With decreasing amino acid chain length, the hydrolytic reconversion rate increased gradually. The in vitro cytotoxicity test was evaluated by the sulforhodamine B (SRB) assay on the human lung adenocarcinoma cell line A549 and human colorectal cancer cell line HCT116. With the evaluation of stability and in vitro cytotoxicity, an appropriate linker was found, and the active drug can be released efficiently from compound 3a, which exhibited strong antiproliferative activity in A549 and HCT-116 cell lines correspondingly. These results indicated that the well-designed co-prodrug 3a and this kind of strategy can be a promising approach for anticancer therapy.

CAY10683 and imatinib have synergistic effects in overcoming imatinib resistance via HDAC2 inhibition in chronic myeloid leukemia

Imatinib (IM) is utilized for targeting the BCR-ABL fusion protein and as such, chronic myeloid leukemia (CML) is considered to be a curable disorder for which patients can achieve a long survival. However, 15-20% CML cases end up with IM resistance that will develop into the accelerated stage and eventually the blast crisis, thereby restricting the treatment choices and giving rise to a dismal survival rate. Histone deacetylases (HDACs) have been identified to modulate the oncogene as well as tumor suppressor gene activities, and they play crucial parts in tumorigenesis. It is found recently that IM combined with HDAC inhibitors (HDACi) can serve as a promising means of overcoming IM resistance in CML cases. Santacruzamate A (CAY10683) has been developed as one of the selective and powerful HDACi to resist HDAC2. Therefore, in this study, we aimed to examine whether CAY10683 combined with IM could serve as the candidate antitumor treatment for CML cases with IM resistance. The influences of CAY10683 combined with IM on the cell cycle arrest, apoptosis, and viability of CML cells with IM resistance were investigated, and it was discovered that the combined treatment exerted synergistic effects on managing the IM resistance. Moreover, further studies indicated that CAY10683 combined with IM mainly exerted synergistic effects through inhibiting HDAC2 in K562-R and LAMA84-R cells with IM resistance. Besides, the PI3K/Akt signal transduction pathway was found to mediate the HDAC2 regulation of CML cells with IM resistance. Eventually, it was also discovered, based on the xenograft mouse model, that the combined treatment dramatically suppressed CML proliferation in vivo. To sum up, findings in the current study indicate that CAY10683 combined with IM can be potentially used as the candidate treatment for CML with IM resistance.

Structural Basis of Catalysis and Inhibition of HDAC6 CD1, the Enigmatic Catalytic Domain of Histone Deacetylase 6

Histone deacetylase 6 (HDAC6) is emerging as a target for inhibition in therapeutic strategies aimed at treating cancer, neurodegenerative disease, and other disorders. Among the metal-dependent HDAC isozymes, HDAC6 is unique in that it contains two catalytic domains, CD1 and CD2. CD2 is a tubulin deacetylase and a tau deacetylase, and the development of HDAC6-selective inhibitors has focused exclusively on this domain. In contrast, there is a dearth of structural and functional information regarding CD1, which exhibits much narrower substrate specificity in comparison with CD2. As the first step in addressing the CD1 information gap, we now present X-ray crystal structures of seven inhibitor complexes with wild-type, Y363F, and K330L HDAC6 CD1. These structures broaden our understanding of molecular features that are important for catalysis and inhibitor binding. The active site of HDAC6 CD1 is wider than that of CD2, which is unexpected in view of the narrow substrate specificity of CD1. Amino acid substitutions between HDAC6 CD1 and CD2, as well as conformational differences in conserved residues, define striking differences in active site contours. Catalytic activity measurements with HDAC6 CD1 confirm the preference for peptide substrates containing C-terminal acetyllysine residues. However, these measurements also show that CD1 exhibits weak activity for peptide substrates bearing certain small amino acids on the carboxyl side of the scissile acetyllysine residue. Taken together, these results establish a foundation for understanding the structural basis of HDAC6 CD1 catalysis and inhibition, pointing to possible avenues for the development of HDAC6 CD1-selective inhibitors.

Phase I/II intra-patient dose escalation study of vorinostat in children with relapsed solid tumor, lymphoma, or leukemia

Background

Until today, adult and pediatric clinical trials investigating single-agent or combinatorial HDAC inhibitors including vorinostat in solid tumors have largely failed to demonstrate efficacy. These results may in part be explained by data from preclinical models showing significant activity only at higher concentrations compared to those achieved with current dosing regimens. In the current pediatric trial, we applied an intra-patient dose escalation design.

The purpose of this trial was to determine a safe dose recommendation (SDR) of single-agent vorinostat for intra-patient dose escalation, pharmacokinetic analyses (PK), and activity evaluation in children (3–18 years) with relapsed or therapy-refractory malignancies.

Results

A phase I intra-patient dose (de)escalation was performed until individual maximum tolerated dose (MTD). The starting dose was 180 mg/m²/day with weekly dose escalations of 50 mg/m² until DLT/maximum dose. After MTD determination, patients seamlessly continued in phase II with disease assessments every 3 months. PK and plasma cytokine profiles were determined. Fifty of 52 patients received treatment. n = 27/50 (54%) completed the intra-patient (de)escalation and entered phase II. An SDR of 130 mg/m²/day was determined (maximum, 580 mg/m²/day). n = 46/50 (92%) patients experienced treatment-related AEs which were mostly reversible and included thrombocytopenia, fatigue, nausea, diarrhea, anemia, and vomiting. n = 6/50 (12%) had treatment-related SAEs. No treatment-related deaths occurred. Higher dose levels resulted in higher C_max. Five patients achieved prolonged disease control (> 12 months) and showed a higher C_max (> 270 ng/mL) and MTDs. Best overall response (combining PR and SD, no CR observed) rate in phase II was 6/27 (22%) with a median PFS and OS of 5.3 and 22.4 months. Low levels of baseline cytokine expression were significantly correlated with favorable outcome.

Conclusion

An SDR of 130 mg/m²/day for individual dose escalation was determined. Higher drug exposure was associated with responses and long-term disease stabilization with manageable toxicity. Patients with low expression of plasma cytokine levels at baseline were able to tolerate higher doses of vorinostat and benefited from treatment. Baseline cytokine profile is a promising potential predictive biomarker.

Trial registration

ClinicalTrials.gov, NCT01422499. Registered 24 August 2011,

Cancer Stem Cells: Powerful Targets to Improve Current Anticancer Therapeutics

A frequent observation in several malignancies is the development of resistance to therapy that results in frequent tumor relapse and metastasis. Much of the tumor resistance phenotype comes from its heterogeneity that halts the ability of therapeutic agents to eliminate all cancer cells effectively. Tumor heterogeneity is, in part, controlled by cancer stem cells (CSC). CSC may be considered the reservoir of cancer cells as they exhibit properties of self-renewal and plasticity and the capability of reestablishing a heterogeneous tumor cell population. The endowed resistance mechanisms of CSC are mainly attributed to several factors including cellular quiescence, accumulation of ABC transporters, disruption of apoptosis, epigenetic reprogramming, and metabolism. There is a current need to develop new therapeutic drugs capable of targeting CSC to overcome tumor resistance. Emerging in vitro and in vivo studies strongly support the potential benefits of combination therapies capable of targeting cancer stem cell-targeting agents. Clinical trials are still underway to address the pharmacokinetics, safety, and efficacy of combination treatment. This review will address the main characteristics, therapeutic implications, and perspectives of targeting CSC to improve current anticancer therapeutics.

Histone Deacetylase Inhibitors in Tumor Immunotherapy

BACKGROUND

With an increasing understanding of the antitumor immune response, considerable progress has been made in the field of tumor immunotherapy in the last decade. Inhibition of histone deacetylases represents a new strategy in tumor therapy and histone deacetylase inhibitors have been recently developed and validated as potential antitumor drugs. In addition to the direct antitumor effects, histone deacetylase inhibitors have been found to have the ability to improve tumor recognition by immune cells that may contribute to their antitumor activity. These immunomodolutory effects are desirable, and their in-depth comprehension will facilitate the design of novel regimens with improved clinical efficacy.

OBJECTIVE

Our goal here is to review recent developments in the application of histone deacetylase inhibitors as immune modulators in cancer treatment.

METHODS

Systemic compilation of the relevant literature in this field.

RESULTS & CONCLUSION

In this review, we summarize recent advances in the understanding of how histone deacetylase inhibitors alter immune process and discuss their effects on various cytokines. We also discuss the challenges to optimize the use of these inhibitors as immune modulators in cancer treatment. Information gained from this review will be valuable to this field and may be helpful for designing tumor immunotherapy trials involving histone deacetylase inhibitors.

Crafting Carbazole-Based Vorinostat and Tubastatin-A-like Histone Deacetylase (HDAC) Inhibitors with Potent in Vitro and in Vivo Neuroactive Functions

Small-molecule inhibitors of HDACs (HDACi) induce hyperacetylation of histone and nonhistone proteins and have emerged as potential therapeutic agents in most animal models tested. The established HDACi vorinostat and tubastatin-A alleviate neurodegenerative and behavioral conditions in animal models of neuropsychiatric disorders restoring the neurotrophic milieu. In spite of the neuroactive pharmacological role of HDACi (vorinostat and tubastatin-A), they are limited by efficacy and toxicity. Considering these limitations and concern, we have designed novel compounds 3-11 as potential HDACi based on the strategic crafting of the key pharmacophoric elements of vorinostat and tubastatin-A into architecting a single molecule. The molecules 3-11 were synthesized through a multistep reaction sequence starting from carbazole and were fully characterized by NMR and mass spectral analysis. The novel molecules 3-11 showed remarkable pan HDAC inhibition and the potential to increase the levels of acetyl H3 and acetyl tubulin. In addition, few novel HDAC inhibitors 4-8, 10, and 11 exhibited significant neurite outgrowth-promoting activity with no observable cytotoxic effects, and interestingly, compound 5 has shown comparably more neurite growth than the parent compounds vorinostat and tubastatin-A. Also, compound 5 was evaluated for possible mood-elevating effects in a chronic unpredictable stress model of Zebrafish. It showed potent anxiolytic and antidepressant-like effects in the novel tank test and social interaction test, respectively. Furthermore, the potent in vitro and in vivo neuroactive compound 5 has shown selectivity for class II over class I HDACs. Our results suggest that the novel carbazole-based HDAC inhibitors, crafted with vorinostat and tubastatin-A pharmacophoric moieties, have potent neurite outgrowth activity and potential to be developed as therapeutics to treat depression and related psychiatric disorders.

Design, Synthesis, and Docking Study of Acyl Thiourea Derivatives as Possible Histone Deacetylase Inhibitors with a Novel Zinc Binding Group

Histone deacetylase inhibitors with zinc binding groups often exhibit drawbacks like non-selectivity or toxic effects. Thus, there are continuous efforts to modify the currently available inhibitors or to discover new derivatives to overcome these problems. One approach is to synthesize new compounds with novel zinc binding groups. The present study describes the utilization of acyl thiourea functionality, known to possess the ability to complex with metals, to be a novel zinc binding group incorporated into the designed histone deacetylase inhibitors. N-adipoyl monoanilide thiourea (4) and N-pimeloyl monoanilide thiourea (5) have been synthesized and characterized successfully. They showed inhibition of growth of human colon adenocarcinoma and mouse hepatoblastoma cells with low cytotoxic effect against normal human breast cells. Their binding mode to the active site of several histone deacetylases has been studied by docking and the results gave a preliminary indication that they could be successful histone deacetylase inhibitors.

Epigenetic Drugs for Cancer and microRNAs: A Focus on Histone Deacetylase Inhibitors

Over recent decades, it has become clear that epigenetic abnormalities are involved in the hallmarks of cancer. Histone modifications, such as acetylation, play a crucial role in cancer development and progression, by regulating gene expression, such as for oncogenes or tumor suppressor genes. Therefore, histone deacetylase inhibitors (HDACi) have recently shown efficacy against both hematological and solid cancers. Designed to target histone deacetylases (HDAC), these drugs can modify the expression pattern of numerous genes including those coding for micro-RNAs (miRNA). miRNAs are small non-coding RNAs that regulate gene expression by targeting messenger RNA. Current research has found that miRNAs from a tumor can be investigated in the tumor itself, as well as in patient body fluids. In this review, we summarized current knowledge about HDAC and HDACi in several cancers, and described their impact on miRNA expression. We discuss briefly how circulating miRNAs may be used as biomarkers of HDACi response and used to investigate response to treatment.

Epigenetic Metalloenzymes

Epigenetics controls the expression of genes and is responsible for cellular phenotypes. The fundamental basis of these mechanisms involves in part the post-translational modifications (PTMs) of DNA and proteins, in particular, the nuclear histones. DNA can be methylated or demethylated on cytosine. Histones are marked by several modifications including acetylation and/or methylation, and of particular importance are the covalent modifications of lysine. There exists a balance between addition and removal of these PTMs, leading to three groups of enzymes involved in these processes: the writers adding marks, the erasers removing them, and the readers able to detect these marks and participating in the recruitment of transcription factors. The stimulation or the repression in the expression of genes is thus the result of a subtle equilibrium between all the possibilities coming from the combinations of these PTMs. Indeed, these mechanisms can be deregulated and then participate in the appearance, development and maintenance of various human diseases, including cancers, neurological and metabolic disorders. Some of the key players in epigenetics are metalloenzymes, belonging mostly to the group of erasers: the zinc-dependent histone deacetylases (HDACs), the iron-dependent lysine demethylases of the Jumonji family (JMJ or KDM) and for DNA the iron-dependent ten-eleven-translocation enzymes (TET) responsible for the oxidation of methylcytosine prior to the demethylation of DNA. This review presents these metalloenzymes, their importance in human disease and their inhibitors.