Current trends in the development of histone deacetylase inhibitors: a review of recent patent applications

The Potential Strategies for Overcoming Multidrug Resistance and Reducing Side Effects of Monomer Tubulin Inhibitors for Cancer Therapy

BACKGROUND

Tubulin is an essential target in tumor therapy, and this is attributed to its ability to target MT dynamics and interfere with critical cellular functions, including mitosis, cell signaling, and intracellular trafficking. Several tubulin inhibitors have been approved for clinical application. However, the shortcomings, such as drug resistance and toxic side effects, limit its clinical application. Compared with single-target drugs, multi-target drugs can effectively improve efficacy to reduce side effects and overcome the development of drug resistance. Tubulin protein degraders do not require high concentrations and can be recycled. After degradation, the protein needs to be resynthesized to regain function, which significantly delays the development of drug resistance.

METHODS

Using SciFinder® as a tool, the publications about tubulin-based dual-target inhibitors and tubulin degraders were surveyed with an exclusion of those published as patents.

RESULTS

This study presents the research progress of tubulin-based dual-target inhibitors and tubulin degraders as antitumor agents to provide a reference for developing and applying more efficient drugs for cancer therapy.

CONCLUSION

The multi-target inhibitors and protein degraders have shown a development prospect to overcome multidrug resistance and reduce side effects in the treatment of tumors. Currently, the design of dual-target inhibitors for tubulin needs to be further optimized, and it is worth further clarifying the detailed mechanism of protein degradation.

Dissecting Histone Deacetylase 3 in Multiple Disease Conditions: Selective Inhibition as a Promising Therapeutic Strategy

The acetylation of histone and non-histone proteins has been implicated in several disease states. Modulation of such epigenetic modifications has therefore made histone deacetylases (HDACs) important drug targets. HDAC3, among various class I HDACs, has been signified as a potentially validated target in multiple diseases, namely, cancer, neurodegenerative diseases, diabetes, obesity, cardiovascular disorders, autoimmune diseases, inflammatory diseases, parasitic infections, and HIV. However, only a handful of HDAC3-selective inhibitors have been reported in spite of continuous efforts in design and development of HDAC3-selective inhibitors. In this Perspective, the roles of HDAC3 in various diseases as well as numerous potent and HDAC3-selective inhibitors have been discussed in detail. It will surely open up a new vista in the discovery of newer, more effective, and more selective HDAC3 inhibitors.

Cyclic Tetrapeptides from Nature and Design: A Review of Synthetic Methodologies, Structure, and Function

Small cyclic peptides possess a wide range of biological properties and unique structures that make them attractive to scientists working in a range of areas from medicinal to materials chemistry. However, cyclic tetrapeptides (CTPs), which are important members of this family, are notoriously difficult to synthesize. Various synthetic methodologies have been developed that enable access to natural product CTPs and their rationally designed synthetic analogues having novel molecular structures. These methodologies include the use of reversible protecting groups such as pseudoprolines that restrict conformational freedom, ring contraction strategies, on-resin cyclization approaches, and optimization of coupling reagents and reaction conditions such as temperature and dilution factors. Several fundamental studies have documented the impacts of amino acid configurations, N-alkylation, and steric bulk on both synthetic success and ensuing conformations. Carefully executed retrosynthetic ring dissection and the unique structural features of the linear precursor sequences that result from the ring dissection are crucial for the success of the cyclization step. Other factors that influence the outcome of the cyclization step include reaction temperature, solvent, reagents used as well as dilution levels. The purpose of this review is to highlight the current state of affairs on naturally occurring and rationally designed cyclic tetrapeptides, including strategies investigated for their syntheses in the literature, the conformations adopted by these molecules, and specific examples of their function. Using selected examples from the literature, an in-depth discussion of the synthetic techniques and reaction parameters applied for the successful syntheses of 12-, 13-, and 14-membered natural product CTPs and their novel analogues are presented, with particular focus on the cyclization step. Selected examples of the three-dimensional structures of cyclic tetrapeptides studied by NMR, and X-ray crystallography are also included.

Key actors in cancer therapy: epigenetic modifiers

Epigenetic reprogramming plays a crucial role in the tumorigenicity and maintenance of tumor-specific gene expression that especially occurs through DNA methylation and/or histone modifications. It has well-defined mechanisms. It is known that alterations in the DNA methylation pattern and/or the loss of specific histone acetylation/methylation markers are related to several hallmarks of cancer, such as drug resistance, stemness, epithelial-mesenchymal transition, and metastasis. It has also recently been highlighted that epigenetic alterations are critical for the regulation of the stemlike properties of cancer cells (tumor-initiating cells; cancer stem cells). Cancer stem cells are thought to be responsible for the recurrence of cancer which makes the patient return to the clinic with metastatic tumor tissue. Hence, the dysregulation of epigenetic machinery represents potential new therapeutic targets. Therefore, compounds with epigenetic activities have become crucial for developing new therapy regimens (e.g., antimetastatic agents) in the fight against cancer. Here, we review the epigenetic modifiers that have already been used in the clinic and/or in clinical trials, related preclinical studies in cancer therapy, and the smart combination strategies that target cancer stem cells along with the other cancer cells. The emerging role of epitranscriptome (RNA epigenetic) in cancer therapy has also been included in this review as a new avenue and potential target for the better management of cancer-beneficial epigenetic machinery.

Epigenetics in cancer stem cells

Compelling evidence have demonstrated that bulk tumors can arise from a unique subset of cells commonly termed "cancer stem cells" that has been proposed to be a strong driving force of tumorigenesis and a key mechanism of therapeutic resistance. Recent advances in epigenomics have illuminated key mechanisms by which epigenetic regulation contribute to cancer progression. In this review, we present a discussion of how deregulation of various epigenetic pathways can contribute to cancer initiation and tumorigenesis, particularly with respect to maintenance and survival of cancer stem cells. This information, together with several promising clinical and preclinical trials of epigenetic modulating drugs, offer new possibilities for targeting cancer stem cells as well as improving cancer therapy overall.

Design, synthesis, and antitumor evaluation of histone deacetylase inhibitors with L-phenylglycine scaffold

In our previous research, a novel series of histone deacetylase (HDAC) inhibitors with L-phenylglycine scaffold were designed and synthesized, among which amides D3 and D7 and ureido D18 were far superior to the positive control (suberoylanilide hydroxamic acid [SAHA]) in HDAC inhibition, but were only comparable to SAHA in antiproliferation on tumor cell lines. Herein, further structural derivation of lead compounds D3, D7, and D18 was carried out to improve their cellular activities. Most of our newly synthesized compounds exhibited more potent HDAC inhibitory activities than the positive control SAHA, and several derivatives were even better than their parent compounds. However, compared with SAHA and our lead compounds, only secondary amine series compounds exhibited improved antiproliferative activities, likely due to their appropriate topological polar surface area values and cell permeabilities. In a human histiocytic lymphoma (U937) xenograft model, the most potent secondary amine 9d exhibited similar in vivo antitumor activity to that of SAHA.

Potential Gene Interactions in the Cell Cycles of Gametes, Zygotes, Embryonic Stem Cells and the Development of Cancer

OBJECTIVES

This review is to explore whether potential gene interactions in the cell cycles of gametes, zygotes, and embryonic stem (ES) cells are associated with the development of cancer.

METHODS

MEDPILOT at the Central Library of the University of Cologne, Germany (Zentralbibliothek Köln) that covers 5,800 international medical journals and 4,300 E-journals was used to collect data. The initial searches were done in December 2012 and additional searches in October 2013-May 2015. The search terms included "cancer development," "gene interaction," and "ES cells," and the time period was between 1998 and 2015. A total of 147 articles in English language only were included in this review.

RESULTS

Transgenerational gene translation is implemented in the zygote through interactions of epigenetic isoforms of transcription factors (TFs) from parental gametes, predominantly during the first two zygote cleavages. Pluripotent transcription factors may provide interacting links with mutated genes during zygote-to-ES cell switches. Translation of post-transcriptional carcinogenic genes is implemented by abnormally spliced, tumor-specific isoforms of gene-encoded mRNA/non-coding RNA variants of TFs employing de novo gene synthesis and neofunctionalization. Post-translationally, mutated genes are preserved in pre-neoplastic ES cell subpopulations that can give rise to overt cancer stem cells. Thus, TFs operate as cell/disease-specific epigenetic messengers triggering clinical expression of neoplasms.

CONCLUSION

Potential gene interactions in the cell cycle of gametes, zygotes, and ES cells may play some roles in the development of cancer.

Epigenetic therapy for solid tumors: from bench science to clinical trials

The cancer epigenome is characterized by global DNA methylation and chromatin changes, such as the hypermethylation of specific CpG island promoters. Epigenetic agents like DNA methyltransferase or histone deacetylase inhibitors induce phenotype changes by reactivation of epigenetically silenced tumor suppressor genes. Despite initial promise in hematologic malignancies, epigenetic agents have not shown significant efficacy as monotherapy against solid tumors. Recent trials showed that epigenetic agents exert favorable modifier effects when combined with chemotherapy, hormonal therapy, or other epigenetic agents. Due to the novel nature of their mechanism, it is important to reconsider the optimal patient selection, drug regimen, study design, and outcome measures when pursuing future trials in order to discover the full potential of this new therapeutic modality.

Epigenetic deregulations in chordoma

Chordoma is a rare type of malignant bone tumour arising from remnant notochord and prognosis of patients with it remains poor as its molecular and genetic mechanisms are not well understood. Increasing evidence has demonstrated that epigenetic mechanisms (DNA methylation, histone modification and nucleosome remodelling), play a crucial role in the pathogenesis of many diseases. Aberrant epigenetic patterns are present in patients with chordoma, indicating a potential role for epigenetic mechanisms inthis malignancy. Furthermore, epigenetic alterations may provide novel biomarkers for diagnosis and prognosis as well as therapeutic targets for treatment. In this review, we discuss relevant epigenetic findings associated with chordoma, and their potential application for diagnosis, prognosis and treatment.

Design, synthesis and biological evaluation of colchicine derivatives as novel tubulin and histone deacetylase dual inhibitors

A new class of colchicine derivatives were designed and synthesized as tubulin-HDAC dual inhibitors. Biological evaluations of these hybrids included the inhibitory activity of HDAC, tubulin polymerization analysis, in vitro cell cycle analysis in HCT-116 cells and cytotoxicity against different cancer cell lines. Hybrid 6d behaved as potent HDAC-tubulin dual inhibitor and showed comparable cytotoxicity with colchicine. Compound 11a exhibited powerful tubulin inhibitory activity, moderate anti-HDAC activity and the most potent cytotoxicity (IC50 = 2-105 nM).

Towards selective inhibition of histone deacetylase isoforms: what has been achieved, where we are and what will be next

Histone deacetylases (HDACs) are widely studied targets for the treatment of cancer and other diseases. Up to now, over twenty HDAC inhibitors have entered clinical studies and two of them have already reached the market, namely the hydroxamic acid derivative SAHA (vorinostat, Zolinza) and the cyclic depsipeptide FK228 (romidepsin, Istodax) that have been approved for the treatment of cutaneous T-cell lymphoma (CTCL). A common aspect of the first HDAC inhibitors is the absence of any particular selectivity towards specific isozymes. Some of molecules resulted to be “pan”-HDAC inhibitors, while others are class I selective. In the meantime, the knowledge of HDAC biology has continuously progressed. Key advances in the structural biology of various isozymes, reliable molecular homology models as well as suitable biological assays have provided new tools for drug discovery activities. This Minireview aims at surveying these recent developments as well as the design, synthesis and biological characterization of isoform-selective derivatives.

Design, synthesis and biological evaluation of 4′-demethyl-4-deoxypodophyllotoxin derivatives as novel tubulin and histone deacetylase dual inhibitors

In this study, we have designed and synthesized a class of 4′-demethyl-4-deoxypodophyllotoxin derivatives as tubulin–HDAC dual inhibitors.

The discovery of colchicine-SAHA hybrids as a new class of antitumor agents

A novel class of colchicine-SAHA hybrids were designed and synthesised based on the synergistic antitumor effect of tubulin inhibitors and histone deacetylases (HDAC) inhibitors. To the best of our knowledge, this is the first design of molecules that are dual inhibitors of tubulin and HDAC. Biological evaluations of these compounds included the inhibitory activity of HDAC, in vitro cell cycle analysis in BEL-7402 cells as well as cytotoxicity in five cancer cell lines.