1,3,5-Triazine inhibitors of histone deacetylases: synthesis and biological activity

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

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

Design, Synthesis, and Biological Evaluation of Novel Thiazolyl Substituted Bis-pyrazole Oxime Derivatives with Potent Antitumor Activities by Selectively Inducing Apoptosis and ROS in Cancer Cells

BACKGROUND

A large number of pyrazole derivatives have different biological activities such as anticancer, antimicrobial, anti-inflammatory, analgesic and antiepileptic activity. Among them, pyrazole oximes have attracted much attention due to their potential pharmacological activities, particularly anticancer activities.

OBJECTIVE

Our goal is to synthesize novel thiazolyl substituted bis-pyrazole oxime derivatives with potent antitumor activities by selectively inducing apoptosis and Reactive Oxygen Species (ROS) accumulation in cancer cells.

METHODS

Eighteen bis-pyrazole oximes were synthesized by conjugating thiazolyl substituted pyrazoles with pyrazoxime. The target compounds were characterized by 1HNMR, 13C NMR, and HRMS, and screened for their antiproliferative activity against four cancer cells in MTT assay. The most potent compound was examined for its inhibitory effect and ROS accumulation in both cancer cells HCT116 and normal intestinal epithelial cells CCD841. Finally, the most potent compound was further evaluated for its apoptotic induction by flow cytometry analysis and immunoblot analysis of apoptosis-related proteins and DNA damage proteins.

RESULTS

Most compounds displayed potent antiproliferative activity against four cancer cell lines in vitro, displaying potencies superior to 5-FU. In particular, the most potent compound 13l selectively inhibited proliferation of colorectal cancer HCT116 cells but not normal colon CCD841 cells. Furthermore, compound 13l also selectively promoted intracellular ROS accumulation in HCT116 which was involved in 13l inhibition of cancer cell proliferation and induction of cell apoptosis. Finally, compound 13l also dose-dependently induced cancer cell apoptosis by regulating apoptotic and DNA damage related proteins expressions.

CONCLUSION

Our synthetic bis-pyrazole oxime derivatives possess potent antitumor activities by selectively inducing apoptosis and ROS accumulation in cancer cells, which may hold great promise as therapeutic agents for the treatment of human cancers.

Synthesis and PI3 Kinase Inhibition Activity of Some Novel Trisubstituted Morpholinopyrimidines

A number of new substituted morpholinopyrimidines were prepared utilizing sequential nucleophilic aromatic substitution and cross-coupling reactions. One of the disubstituted pyrimidines was converted into two trisubstituted compounds which were screened as PI3K inhibitors relative to the well-characterized PI3K inhibitor ZSTK474, and were found to be 1.5⁻3-times more potent. A leucine linker was attached to the most active inhibitor since it would remain on any peptide-containing prodrug after cleavage by prostate-specific antigen, and it did not prevent inhibition of AKT phosphorylation and hence the inhibition of PI3K by the modified inhibitor.

Synthesis and PI 3-Kinase Inhibition Activity of Some Novel 2,4,6-Trisubstituted 1,3,5-Triazines

A number of new trisubstituted triazine phosphatidylinositol 3-kinase (PI3K) inhibitors were prepared via a three-step procedure utilizing sequential nucleophilic aromatic substitution and cross-coupling reactions. All were screened as PI3K inhibitors relative to the well-characterized PI3K inhibitor, ZSTK474. The most active inhibitors prepared here were 2–4 times more potent than ZSTK474. A leucine linker was attached to the most active inhibitor since it would remain on any peptide-containing prodrug after cleavage by a prostate-specific antigen, and it did not prevent inhibition of protein kinase B (Akt) phosphorylation, and hence, the inhibition of PI3K by the modified inhibitor.

5-(4,6-Dimorpholino-1,3,5-triazin-2-yl)-4-(trifluoromethyl)pyridin-2-amine (PQR309), a Potent, Brain-Penetrant, Orally Bioavailable, Pan-Class I PI3K/mTOR Inhibitor as Clinical Candidate in Oncology

Phosphoinositide 3-kinase (PI3K) is deregulated in a wide variety of human tumors and triggers activation of protein kinase B (PKB/Akt) and mammalian target of rapamycin (mTOR). Here we describe the preclinical characterization of compound 1 (PQR309, bimiralisib), a potent 4,6-dimorpholino-1,3,5-triazine-based pan-class I PI3K inhibitor, which targets mTOR kinase in a balanced fashion at higher concentrations. No off-target interactions were detected for 1 in a wide panel of protein kinase, enzyme, and receptor ligand assays. Moreover, 1 did not bind tubulin, which was observed for the structurally related 4 (BKM120, buparlisib). Compound 1 is orally available, crosses the blood-brain barrier, and displayed favorable pharmacokinetic parameters in mice, rats, and dogs. Compound 1 demonstrated efficiency in inhibiting proliferation in tumor cell lines and a rat xenograft model. This, together with the compound's safety profile, identifies 1 as a clinical candidate with a broad application range in oncology, including treatment of brain tumors or CNS metastasis. Compound 1 is currently in phase II clinical trials for advanced solid tumors and refractory lymphoma.

Design and Synthesis of C3-Substituted β-Carboline-Based Histone Deacetylase Inhibitors with Potent Antitumor Activities

A series of hydroxamic acid histone deacetylase (HDAC) inhibitors in which the β-carboline motif has been incorporated were designed and synthesized. The effect of substitution at the C3 amide on HDAC inhibition and antiproliferative activities was investigated. Most of these compounds were found to display significant HDAC inhibitory effects and good antiproliferative activity, with IC₅₀ values in the low-micromolar range. In particular, the HDAC inhibition IC₅₀ value of N-(2-(dimethylamino)ethyl)-N-(4-(hydroxylcarbamoyl)benzyl)-1-(4-methoxyphenyl)-9H-pyrido[3,4-b]indole-3-carboxamide (9 h) is five-fold lower than that of suberoylanilide hydroxamic acid (SAHA, vorinostat). Furthermore, 9 h was found to increase the acetylation of histone H3 and α-tubulin, and to induce DNA damage as evidenced by hypochromism and enhanced phosphorylation of histone H2AX. Compound 9 h inhibits Stat3, Akt, and ERK signaling, important cell-growth-promoting pathways that are aberrantly activated in most cancers. Finally, 9 h showed reasonable solubility and permeability in Caco-2 cells. Our findings suggest that these novel β-carboline-based HDAC inhibitors may hold great promise as therapeutic agents for the treatment of human cancers.

Development of novel β-carboline-based hydroxamate derivatives as HDAC inhibitors with DNA damage and apoptosis inducing abilities

A series of novel β-carboline-based hydroxamate derivatives (8a-n) as HDAC inhibitors have been designed and synthesized. Most of these compounds displayed potent histone deacetylase inhibitory effects and good antiproliferative activity with IC₅₀s in the low micromolar range. One of the most potent compounds (8k) showed the strongest inhibition of the proliferation of human hepatocellular carcinoma (HCC) cells in vitro, with IC₅₀ values lower than that of the currently approved HDAC inhibitor SAHA. Compound 8k also increased acetylation of histone H3 and α-tubulin, consistent with its potent HDAC inhibition. Importantly, 8k induced hypochromism by electrostatic interactions with CT-DNA, suggesting potential induction of DNA damage. Finally, 8k significantly induced HepG2 cell apoptosis by regulating apoptotic relative proteins expression. Together, our findings suggest that these novel β-carboline-based hydroxamate derivatives may provide a new framework for the discovery of novel antitumor agents for the intervention of human carcinoma cells.

Design, synthesis and biological evaluation of hybrids of β-carboline and salicylic acid as potential anticancer and apoptosis inducing agents

A novel series of hybrids (7a-l, 8a-l) from β-carboline and salicylic acid (SA) were designed and synthesized, and their in vitro biological activities were evaluated. Most of the hybrids displayed potent antiproliferative activity against five cancer cell lines in vitro, showing potencies superior to 5-FU and harmine. In particular, compound 8h selectively inhibited proliferation of liver cancer SMMC-7721 cells but not normal liver LO2 cells, and displayed greater inhibitory selectivity than intermediate 5h and SA. 8h also induced cancer cell apoptosis in an Annexin V-FITC/propidium iodide flow cytometry assay, and triggered the mitochondrial/caspase apoptosis by decreasing mitochondrial membrane potential which was associated with up-regulation of Bax, down-regulation of Bcl-2 and activation levels of the caspase cascade in a concentration-dependent manner. Our findings suggest that the β-carboline/SA hybrids may hold greater promise as therapeutic agents for the intervention of human cancers.