Novel metal chelating molecules with anticancer activity. Striking effect of the imidazole substitution of the histidine-pyridine-histidine system

An insight into recent developments in imidazole based heterocyclic compounds as anticancer agents: Synthesis, SARs, and mechanism of actions

Among all non-communicable diseases, cancer is ranked as the second most common cause of death and is rising constantly. While cancer treatments mainly include radiation therapy, chemotherapy, and surgery; chemotherapy is considered the most commonly employed and effective treatment. Most of the chemotherapeutic agents are azoles based compounds and imidazole is one such insightful azole. The anticancer properties of imidazole-based compounds have been thoroughly explored in recent years and all monosubstituted, disubstituted, trisubstituted, and tetrasubstituted imidazoles have been explored for their anticancer activities. Along with these compounds, other imidazole-based compounds like 1,3-dihydro-2H-imidazole-2-thiones, imidazolones, and poly imidazole compounds have also been explored for their anticancer activities. The activities of these compounds are heavily influenced by their structural resemblance to combretastatin 4A and ABI (2-aryl-4-benzoyl-imidazole). The lead compounds were highly active on breast, gastric, colon, ovarian, cervical, bone marrow, melanoma, prostate, lung, leukemic, neuroblastoma, liver, Ehrlich, melanoma, and pancreatic cancers. The targets of these leads like tubulin, heme oxygenases, VEGF, tyrosine kinases, EGFR, and others have also been explored. The exploration of the anticancer potential of substituted imidazole compounds is the main topic of this review including synthesis, SAR, and mechanism.

Ligand-based design and synthesis of new trityl histamine and trityl cysteamine derivatives as SIRT2 inhibitors for cancer therapy

The relentless pursuit of novel therapeutic agents against cancer has led to the identification of multiple molecular targets, among which Sirtuin 2 (SIRT2) has garnered significant attention. This study presents an extensive SAR study of our reported trityl scaffold-based SIRT2 inhibitors. This study encompasses a range of different medicinal chemistry approaches to improve the activity of the lead compounds TH-3 and STCY1. The rationally designed and synthesized structures were confirmed using NMR and high-resolution mass spectroscopy before performing SIRT2 inhibition assay, NCI60 cytotoxicity test, and cell cycle analysis. Indeed, our strategies afforded hitherto unreported SIRT2 inhibitors with high activity, particularly 2a, 4a, 7c, and 7f. Remarkably, the presence of a lipophilic para substitution on the phenyl group of a freely rotating or a locked trityl moiety enhanced activity SIRT2 inhibition. Concomitantly, the synthesized compounds showed prominent activity against different cancer lines from the NCI60 assay. Of interest, compound 7c stands out as a potent and highly selective antiproliferative agent against leukemia and colon cancer panels. Furthermore, 7c treatment resulted in cell cycle arrest in MCF-7 cells at G2 phase and did not cause in vitro DNA cleavage.

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

Design, Synthesis, and Biological Evaluation of Novel Dihydropyrimidinone Derivatives as Potential Anticancer Agents and Tubulin Polymerization Inhibitors

The severity and prevalence of cancer in modern time are a huge global health burden. Continuous efforts are being made toward the development of newer therapeutic candidates to treat and manage this ailment. The dihydropyrimidinone scaffold is one of the key nuclei that have been highly explored and investigated against cancer. It has the potential to combat the consequences of cancer by interacting with several biological targets. Tubulin polymerization inhibition is one such strategy to prevent the progression of cancer. In the presented work, we have synthesized a series of sixteen dihydropyrimidinone derivatives by following a rational drug design. The synthesized compounds have been characterized by ¹H NMR and ¹³C NMR and were further evaluated for cytotoxic activity against breast cancer cell lines (MCF-7 and MDA-MB-231), lung cancer cell lines (A549), and colon cancer cell lines (HCT-116). Compounds 5D and 5P were found most potent and revealed a better cytotoxic activity compared with the standard drug colchicine. Furthermore, the tubulin polymerization inhibition assay revealed that compound 5D showed better inhibition than colchicines, whereas compound 5P revealed an almost equal inhibition to that of colchicine. Furthermore, to investigate the possible mode of action and binding patterns, compounds 5P and 5D were subjected to molecular docking against tubulin (Protein Data Bank ID: ISA0). The results showed that compounds revealed significant interactions and were well occupied inside the cavity of tubulin. The compounds 5D and 5P may serve as new leads in drug development against cancer.

Structure based design, synthesis, and evaluation of anti-CML activity of the quinolinequinones as LY83583 analogs

Quinone-based small molecules are the promising structures for antiproliferative drug design and can induce apoptosis in cancer cells. Among them, one of the quinolinequinones, named as 6-anilino-5,8-quinolinequinone, LY83583 has the ability to inhibit the growth of cancer cells as an inhibitor of cyclase. The biological potential of all synthesized compounds as the analogs of the identified lead molecule LY83583 that possessed the antiproliferative efficiency was determined. The two series of the LY83583 analogs containing electron-withdrawing or electron-donating group(s) were synthesized and subsequently in vitro evaluated for their cytotoxic activity against K562, Jurkat, MT-2, and HeLa cell lines using MTT assay. All the LY83583 analogs showed antiproliferative activity with good IC₅₀ values (less than positive control imatinib). Four analogs from each series were also selected for the determination of selectivity against human peripheral blood mononuclear cells (PBMCs). The analog AQQ15 showed high potency towards all cancer cell lines with almost similar selectivity of imatinib. In order to get a better insight into cytotoxic effects of the analog AQQ15 in K562 cells, further apoptotic effects due to annexin V/ethidium homodimer III staining, ABL1 kinase inhibition, and DNA cleaving ability were examined. The analog AQQ15 induced apoptotic cell death in K562 cells with 34.6% compared to imatinib (6.5%). This analog showed no considerable ABL1 kinase inhibitory activity but significant DNA cleavage activity indicating DNA fragmentation-induced apoptosis. Besides, molecular docking studies revealed that the analog AQQ15 established proper interactions with the deoxyribose sugar attached with the nucleobases adenine and guanidine respectively, in the minor groove of the double helix of DNA. In silico predicted pharmacokinetic parameters of this analog were found to comply with the standard range making it an efficient anticancer drug candidate for further research.

A New Inhibitor of ADAM17 Composed of a Zinc-Binding Dithiol Moiety and a Specificity Pocket-Binding Appendage

A disintegrin and metalloproteinase 17 (ADAM17) is a zinc-dependent enzyme that catalyzes the cleavage of the extracellular domains of various transmembrane proteins. ADAM17 is regarded as a promising drug target for the suppression of various diseases, including cancer metastasis. We synthesized a new ADAM17 inhibitor, SN-4, composed of a zinc-binding dithiol moiety and an appendage that specifically binds to a pocket of ADAM17. We show that SN-4 inhibits the ability of ADAM17 to cleave tumor necrosis factor α (TNF-α) in vitro. This activity was reduced by the addition of zinc, indicating the importance of the zinc chelating dithiol moiety. Inhibition of TNF-α cleavage by SN-4 in cells was also observed, and with an IC50 of 3.22 µM, SN-4 showed slightly higher activity than the well-studied ADAM17 inhibitor marimastat. Furthermore, SN-4 was shown to inhibit cleavage of CD44 by ADAM17, but not by ADAM10, and to suppress cell invasion. Molecular docking showed good fitting of the specificity pocket-binding group and one SH of SN-4 and hinted at possible means of structural optimization. This study provides clues for the development of potent and selective ADAM17 inhibitors.

HSP70 induction by bleomycin metal core analogs

Induction of heat shock protein 70 (HSP70) is known to be effective against various diseases. We are interested in HSP70 induction capability of an antitumor antibiotic bleomycin which produces oxidative stress by iron chelate formation and oxygen activation in a cell. The HSP70 induction activity of bleomycin and its six metal core analogs was examined, and a compound HPH-1Trt of 10 μM was found to induce this protein in a pheochromocytoma cell line and some T cell and monocytic cell lines. Its mechanism is increase of HSP70 mRNA, but higher concentration of this compound showed toxicity. Two new derivatives were then synthesized, and one of them named DHPH-1Trt was shown to have less toxicity and higher HSP70 induction activity. This study would lead to a clue for new HSP70 inducer clinically used in near future.

Effects of Glycyrrhetic Acid on Human Chronic Myelogenous Leukemia Cells

Objectives

Chronic myelogenous leukemia (CML) is a type of blood cancer that is initially treated with imatinib (first Abl kinase inhibitor). However, some patients with CML develop imatinib resistance. Several new generation drugs have been developed, but do not overcome this problem. Glycyrrhetic acid (GA) is a plant-derived pentacyclic triterpenoid that exhibits multiple pharmacological properties for the treatment of cancers. The current study aimed to investigate the effects of GA on the K562 cell line (Bcr-Abl positive leukemia).

Materials and Methods

The MTT cell proliferation assay was employed to evaluate the cytotoxic effect of GA compared with imatinib (positive control) against leukemia and normal blood cells. For detection of cell death, an apoptotic/necrotic/healthy assay was performed against the K562 cell line. To investigate the kinase inhibitory activity of GA, the Abl1 kinase profiling assay and a molecular docking study were performed.

Results

GA showed Abl kinase inhibitory activity with an IC₅₀ value of 29.2 μM and induced apoptosis in the K562 cell line after 6 h of treatment.

Conclusion

The current findings indicate that this class of plant extract could be a potential candidate for treatment of CML.

Radwan M, E. Ozturk S, Ulusoy NG, Sozer E, E. Ellakwa D, Ocak Z, Can M, F.S. Ali T, I. Abd-Alla H, Yayli N, Tateishi H, Otsuka M, Fujita M. Design, Synthesis and Biological Evaluation of Pentacyclic Triterpene Derivatives: Optimization of Anti-ABL Kinase Activity

Imatinib, an Abelson (ABL) tyrosine kinase inhibitor, is a lead molecular-targeted drug against chronic myelogenous leukemia (CML). To overcome its resistance and adverse effects, new inhibitors of ABL kinase are needed. Our previous study showed that the benzyl ester of gypsogenin (1c), a pentacyclic triterpene, has anti-ABL kinase and a subsequent anti-CML activity. To optimize its activities, benzyl esters of carefully selected triterpenes (PT1-PT6), from different classes comprising oleanane, ursane and lupane, and new substituted benzyl esters of gypsogenin (GP1-GP5) were synthesized. All of the synthesized compounds were purified and charachterized by different spectroscopic methods. Cytotoxicity of the parent triterpenes and the synthesized compounds against CML cell line K562 was examined; revealing three promising compounds PT5, GP2 and GP5 (IC50 5.46, 4.78 and 3.19 μM, respectively). These compounds were shown to inhibit extracellular signal-regulated kinase (ERK) downstream signaling, and induce apoptosis in K562 cells. Among them, PT5 was identified to have in vitro activity (IC50 = 1.44 μM) against ABL1 kinase, about sixfold of 1c, which was justified by molecular docking. The in vitro activities of GP2 and GP5 are less than PT5, hence they were supposed to possess other more mechanisms of cytotoxicity. In general, our design and derivatizations resulted in enhancing the activity against ABL1 kinase and CML cells.

Antiproliferative S-Trityl-l-Cysteine -Derived Compounds as SIRT2 Inhibitors: Repurposing and Solubility Enhancement

S-trityl-l-cysteine (STLC) is a well-recognized lead compound known for its anticancer activity owing to its potent inhibitory effect on human mitotic kinesin Eg5. STLC contains two free terminal amino and carboxyl groups that play pivotal roles in binding to the Eg5 pocket. On the other hand, such a zwitterion structure complicates the clinical development of STLC because of the solubility issues. Masking either of these radicals reduces or abolishes STLC activity against Eg5. We recently identified and characterized a new class of nicotinamide adenine dinucleotide-dependent deacetylase isoform 2 of sirtuin protein (SIRT2) inhibitors that can be utilized as cytotoxic agents based on an S-trityl-l-histidine scaffold. Herein, we propose new STLC-derived compounds that possess pronounced SIRT2 inhibition effects. These derivatives contain modified amino and carboxyl groups, which conferred STLC with SIRT2 bioactivity, representing an explicit repurposing approach. Compounds STC4 and STC11 exhibited half maximal inhibitory concentration values of 10.8 ± 1.9 and 9.5 ± 1.2 μM, respectively, against SIRT2. Additionally, introduction of the derivatizations in this study addressed the solubility limitations of free STLC, presumably due to interruption of the zwitterion structure. Therefore, we could obtain drug-like STLC derivatives that work by a new mechanism of action. The new derivatives were designed, synthesized, and their structure was confirmed using different spectroscopic approaches. In vitro and cellular bioassays with various cancer cell lines and in silico molecular docking and solubility calculations of the synthesized compounds demonstrated that they warrant attention for further refinement of their bioactivity.

New SIRT2 inhibitors: Histidine-based bleomycin spin-off

Bleomycin is considered to exert its antitumor activity via DNA cleavage mediated by activated oxygen generated from the iron complex in its chelator moiety. Spin-offs from this moiety, HPH-1Trt and HPH-2Trt, with anti-cancer activities were recently synthesized. In this paper, we developed inhibitors of nicotinamide adenine dinucleotide-dependent deacetylase isoform 2 of Sirtuin protein (SIRT2), based on HPH-1Trt/HPH-2Trt, and aimed to generate new anti-cancer drugs. HPH-1Trt and HPH-2Trt had in vitro anti-SIRT2 inhibitory activity with 50% inhibitory concentration (IC₅₀) values of 5.5 and 8.8 μM, respectively. A structural portion of HPH-1Trt/HPH-2Trt, a tritylhistidine derivative TH-1, had stronger activity (IC₅₀ = 1.7 μM), and thus, fourteen derivatives of TH-1 were synthesized. Among them, TH-3 had the strongest activity (IC₅₀ = 1.3 μM). Selective binding of TH-3 in the pocket of SIRT2 protein was confirmed with a molecular docking study. Furthermore, TH-3 strongly lowered viability of the breast cancer cell line MCF7 with an IC₅₀ of 0.71 μM. A structure-activity relationship study using cell lines suggested that the mechanism of TH-3 to suppress MCF7 cells involves not only SIRT2 inhibition, but also another function. This compound may be a new candidate anti-cancer drug.

Blockade of TGF-β/Smad signaling by the small compound HPH-15 ameliorates experimental skin fibrosis

Background

Transforming growth factor-β (TGF-β)/Smad signaling is well known to play a critical role in the pathogenesis of systemic sclerosis (SSc). We previously developed an artificial molecule, the histidine-pyridine-histidine ligand derivative HPH-15, which may have an antifibrotic effect. The purpose of the present study was to clarify the effects of this drug in human skin fibroblasts and in a preclinical model of SSc.

Methods

The effects of HPH-15 on expression of extracellular matrix components and TGF-β signaling in human dermal fibroblasts were analyzed. The antifibrotic properties of HPH-15 and its mechanisms were also examined in a bleomycin-induced skin fibrosis mouse model.

Results

HPH-15 suppressed the TGF-β-induced phosphorylation of Smad3 and inhibited the expression of collagen I, fibronectin 1, connective tissue growth factor, and α-smooth muscle actin induced by TGF-β in cultured human skin fibroblasts. In the bleomycin-induced skin fibrosis model, oral administration of HPH-15 protected against the development of skin fibrosis and ameliorated established skin fibrosis. Additionally, HPH-15 suppressed the phosphorylation of Smad3 in various cells, including macrophages in the bleomycin-injected skin. Further, in the treated mice, dermal infiltration of proinflammatory macrophages (CD11b⁺Ly6C^hi) and M2 profibrotic macrophages (CD11b⁺CD204⁺ or CD11b⁺CD206⁺) was significantly decreased during the early and late stages, respectively. HPH-15 treatment resulted in decreased messenger RNA (mRNA) expression of the M2 macrophage markers arginase 1 and Ym-1 in the skin, whereas it inversely augmented expression of Friend leukemia integration 1 and Krüppel-like factor 5 mRNAs, the transcription factors that repress collagen synthesis. No apparent adverse effects of HPH-15 were found during the treatment.

Conclusions

HPH-15 may inhibit skin fibrosis by inhibiting the phosphorylation of Smad3 in dermal fibroblasts and possibly in macrophages. Our results demonstrate several positive qualities of HPH-15, including oral bioavailability, a good safety profile, and therapeutic effectiveness. Thus, this TGF-β/Smad inhibitor is a potential candidate therapeutic for SSc clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1534-y) contains supplementary material, which is available to authorized users.

The First Pentacyclic Triterpenoid Gypsogenin Derivative Exhibiting Anti-ABL1 Kinase and Anti-chronic Myelogenous Leukemia Activities

The discovery of the chimeric tyrosine kinase breakpoint cluster region kinase-Abelson kinase (BCR-ABL)-targeted drug imatinib conceptually changed the treatment of chronic myelogenous leukemia (CML). However, some CML patients show drug resistance to imatinib. To address this issue, some artificial heterocyclic compounds have been identified as BCR-ABL inhibitors. Here we examined whether plant-derived pentacyclic triterpenoid gypsogenin and/or their derivatives show inhibitory activity against BCR-ABL. Among the three derivatives, benzyl 3-hydroxy-23-oxoolean-12-en-28-oate (1c) was found to be the most effective anticancer agent on the CML cell line K562, with an IC₅₀ value of 9.3 µM. In contrast, the IC₅₀ against normal peripheral blood mononuclear cells was 276.0 µM, showing better selectivity than imatinib. Compound 1c had in vitro inhibitory activity against Abelson kinase 1 (ABL1) (IC₅₀=8.7 µM), the kinase component of BCR-ABL. In addition, compound 1c showed a different inhibitory profile against eight kinases compared with imatinib. The interaction between ATP binding site of ABL and 1c was examined by molecular docking study, and the binding mode was different from imatinib and newer generation inhibitors. Furthermore, 1c suppressed signaling downstream of BCR-ABL. This study suggests the possibility that plant extracts may be a source for CML treatment and offer a strategy to overcome drug resistance to known BCR-ABL inhibitors.

Design, Synthesis, and Biological Evaluation of Novel 1,3,4-Thiadiazole Derivatives as Potential Antitumor Agents against Chronic Myelogenous Leukemia: Striking Effect of Nitrothiazole Moiety

In an attempt to develop potent antitumor agents, new 1,3,4-thiadiazole derivatives were synthesized and evaluated for their cytotoxic effects on multiple human cancer cell lines, including the K562 chronic myelogenous leukemia cell line that expresses the Bcr-Abl tyrosine kinase. N-(5-Nitrothiazol-2-yl)-2-((5-((4-(trifluoromethyl)phenyl)amino)-1,3,4-thiadiazol-2-yl)thio)acetamide (2) inhibited the Abl protein kinase with an IC₅₀ value of 7.4 µM and showed selective activity against the Bcr-Abl positive K562 cell line. Furthermore, a Bcr-Abl-compound 2 molecular modelling simulation highlighted the anchoring role of the nitrothiazole moiety in bonding and hydrophobic interaction with the key amino acid residues. These results provide promising starting points for further development of novel kinase inhibitors.