Activation of human telomerase reverse transcriptase expression by some new symmetrical bis-substituted derivatives of the anthraquinone

Recognition of human telomeric G-quadruplex DNA by 1,5-disubstituted diethyl-amido anthraquinone derivative in different ion environments causing thermal stabilization and apoptosis

Ligand binding to G-quadruplex (G4) structures at human telomeric DNA ends promotes thermal stabilization, disrupting the interaction of the telomerase enzyme, which is found active in 80-85% of cancers and serves as a molecular marker. Anthraquinone compounds are well-known G-quadruplex (G4) binders that inhibit telomerase and induce apoptosis in cancer cells. Our current investigation is based on 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione, a derivative of anthraquinone and its binding characterization with two different human telomeric DNA structures, wHTel26 and HTel22, in the effect of K+ and Na+ by using an array of biophysical, calorimetry, molecular docking and cell viability assay techniques. Binding constants (Kb) in the range of ∼105-107 M-1 and stoichiometries of 1:1, 2:1 & 4:1 were obtained from the absorbance, fluorescence, and circular dichroism study. Remarkable hypochromism (55, 97%) and ∼17 nm shift in absorbance, fluorescence quenching (95, 97%), the unaltered value of fluorescence lifetime, restoration of Circular Dichroism bands, absence of ICD band, indicated the external groove binding/binding somewhere at loops. This is also evident in molecular docking results, the ligand binds to groove forming base (G4, G5, G24, T25) and in the vicinity to TTA loop (G14, G15, T17) bases of wHTel26 and HTel22, respectively. Thermal stabilization induced by ligand was found greater in Na+ ion (27.5 °C) than (19.1 °C) in K+ ion. Ligand caused cell toxicity in MCF-7 cancer cell lines with an IC50 value of ∼8.4 µM. The above findings suggest the ligand, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione could be a potent anticancer drug candidate and has great therapeutic implications.Binding of disubstituted amido anthraquinone derivative, 1,5-bis[3-(diethylamino)propionamido]anthracene-9,10-dione to human telomere HTel22 antiparallel conformation induced thermal stabilization.Communicated by Ramaswamy H. Sarma.

Journey of anthraquinones as anticancer agents - a systematic review of recent literature

Anthraquinones are privileged chemical scaffolds that have been used for centuries in various therapeutic applications. The anthraquinone moiety forms the core of various anticancer agents. However, the emergence of drug-resistant cancers warrants the development of new anticancer agents. The research endeavours towards new anthraquinone-based compounds are increasing rapidly in recent years. They are used as a core chemical template to achieve structural modifications, resulting in the development of new anthraquinone-based compounds as promising anticancer agents. Mechanistically, most of the anthraquinone-based compounds inhibit cancer progression by targeting essential cellular proteins. Herein, we review new anthraquinone analogues that have been developed in recent years as anticancer agents. This includes a systematic review of the recent literature (2005-2021) on anthraquinone-based compounds in cell-based models and key target proteins such as kinases, topoisomerases, telomerases, matrix metalloproteinases and G-quadruplexes involved in the viability of cancer cells. In addition to this, the developments in PEG-based delivery of anthraquinones and the toxicity aspects of anthraquinone derivatives are also discussed. The review dispenses a compact background knowledge to understanding anthraquinones for future research on the expansion of anticancer therapeutics.

In vivo Pharmacokinetic and Anticancer Studies of HH-N25, a Selective Inhibitor of Topoisomerase I, and Hormonal Signaling for Treating Breast Cancer

PURPOSE

Breast cancer is the most frequently diagnosed cancer globally, and the leading cause of cancer-associated mortality among women. The efficacy of most clinical chemotherapies is often limited by poor pharmacokinetics and the development of drug resistance by tumors. In a continuing effort to explore small molecules as alternative therapies, we herein evaluated the therapeutic potential of HH-N25, a novel nitrogen-substituted anthra[1,2-c][1,2,5]thiadiazole-6,11-dione derivative.

METHODS

We evaluated the in vivo pharmacokinetic properties and maximum tolerated dose (MTD) of HH-N25 in rats. We also characterized the compound for in vitro and in vivo anticancer activities and its inhibitory effects against DNA topoisomerases and hormonal signaling in breast cancer. Furthermore, we used molecular docking to analyse the ligand-receptor interactions between the compound and the targets.

RESULTS

The maximum serum concentration (Cmax), half-life (t1/2 beta), mean residence time (MRT), oral clearance (CL/f), and apparent volume of distribution (VD/f) of HH-N25 were 1446.67 ± 312.05 ng/mL, 4.51 ± 0.27 h, 2.56 ± 0.16 h, 8.32 ± 1.45 mL/kg/h, and 1.26 ± 0.15 mL/kg, respectively, after single-dose iv administration at 3 mg/kg body weight. HH-N25 had potent anticancer activity against a panel of human breast cancer cell lines with 50% inhibitory concentrations (IC50) ranging 0.045±0.01~4.21±0.05 µM. The drug also demonstrated marked in vivo anticancer activity at a tolerated dose and prolonged the survival duration of mice without unacceptable toxicities based on body weight changes in human tumor xenograft models. In addition, HH-N25 exhibited a dose-dependent inhibition of topoisomerase I and ligand-mediated activities of progesterone and androgen receptors.

CONCLUSION

HH-N25 represents a new molecular entity that selective suppressed TOP1 and hormonal signaling, and shows potent antitumor activities in human breast cancer cells in vitro and in vivo. HH-N25 thus represents a promising anticancer agent that warrants further preclinical and clinical exploration.

Targeting telomerase for its advent in cancer therapeutics

Telomerase has emerged as an important primary target in anticancer therapy. It is a distinctive reverse transcriptase enzyme, which extends the length of telomere at the 3' chromosomal end, and uses telomerase reverse transcriptase (TERT) and telomerase RNA template-containing domains. Telomerase has a vital role and is a contributing factor in human health, mainly affecting cell aging and cell proliferation. Due to its unique feature, it ensures unrestricted cell proliferation in malignancy and plays a major role in cancer disease. The development of telomerase inhibitors with increased specificity and better pharmacokinetics is being considered to design and develop newer potent anticancer agents. Use of natural and synthetic compounds for the inhibition of telomerase activity can lead to an opening of new vistas in cancer treatment. This review details about the telomerase biochemistry, use of natural and synthetic compounds; vaccines and oncolytic virus in therapy that suppress the telomerase activity. We have discussed structure-activity relationships of various natural and synthetic telomerase inhibitors to help medicinal chemists and chemical biology researchers with a ready reference and updated status of their clinical trials. Suppression of human TERT (hTERT) activity through inhibition of hTERT promoter is an important approach for telomerase inhibition.

Anthraquinone: a promising scaffold for the discovery and development of therapeutic agents in cancer therapy

Cancer, characterized by uncontrolled malignant neoplasm, is a leading cause of death in both advanced and emerging countries. Although, ample drugs are accessible in the market to intervene with tumor progression, none are totally effective and safe. Natural anthraquinone (AQ) equivalents such as emodin, aloe-emodin, alchemix and many synthetic analogs extend their antitumor activity on different targets including telomerase, topoisomerases, kinases, matrix metalloproteinases, DNA and different phases of cell lines. Nano drug delivery strategies are advanced tools which deliver drugs into tumor cells with minimum drug leakage to normal cells. This review delineates the way AQ derivatives are binding on these targets by abolishing tumor cells to produce anticancer activity and purview of nanoformulations related to AQ analogs.

Specific stabilization of promoter G-Quadruplex DNA by 2,6-disubstituted amidoanthracene-9,10-dione based dimeric distamycin analogues and their selective cancer cell cytotoxicity

We have designed and synthesized anthraquinone containing compounds which have oligopyrrole side chains of varying lengths. These compounds stabilized the G-quadruplex DNA formed in the promoter regions of c-MYC oncogenes selectively over the duplex DNA. These observations were recorded using UV-vis spectroscopic titrations, fluorescence measurements and circular dichroism (CD) spectral titrations. The potency of the compounds to stabilize the G4 DNA has been shown from the thermal denaturation experiments. The compound interacts with c-MYC G-quadruplex DNA through stacking mode as obtained from ethidium bromide displacement assay, cyclic voltammetric titration, and docking experiments. Molecular modeling studies suggested that the stacking of the anthraquinone moiety over the G-tetrad of the G4 structures are responsible for the stability of such quadruplex secondary structure. Furthermore, polymerase stop assay also supported the formation of stable G4 structures in the presence of the above-mentioned compounds. The compounds have shown selective cancer cell (HeLa and HEK293T) cytotoxicity over normal cells (NIH3T3 and HDFa) under in vitro conditions as determined from MTT based cell viability assay. Apoptosis was found to be the mechanistic pathway underlying the cancer cell cytotoxicity as obtained from Annexin V-FITC and PI dual staining assay which was further substantiated by nuclear morphological changes as observed by AO/EB dual staining assay. Cellular morphological changes, as well as nuclear condensation and fragmentation upon treatment with these compounds, were observed under bright field and confocal microscopy.

Novel Quinoline-based Ir(III) Complexes Exhibit High Antitumor Activity in Vitro and in Vivo

Eight novel Ir(III) complexes listed as [Ir(H-P)₂(P)]PF₆ (PyP-Ir), [Ir(H-P)₂(dMP)]PF₆ (PydMP-Ir), [Ir(H-P)₂(MP)]PF₆ (PyMP-Ir), [Ir(H-P)₂(tMP)]PF₆ (PytMP-Ir), [Ir(MPy)₂(P)]PF₆ (MPyP-Ir), [Ir(MPy)₂(dMP)]PF₆ (MPydMP-Ir), [Ir(MPy)₂(MP)]PF₆ (MPyMP-Ir), [Ir(MPy)₂((tMP)]PF₆ (MPytMP-Ir) with 2-phenylpyri-dine (H-P) and 3-methyl-2-phenylpyridine (MPy) as ancillary ligands and pyrido-[3,2-a]-pyrido[1',2':1,2]imidazo[4,5-c]phenazine (P), 12,13-dimethyl pyrido-[3,2-a]-pyrido[1',2':1,2]-imidazo-[4,5-c]-phenazine (dMP), 2-methylpyrido [3,2-a]-pyrido-[1',2':1,2]-imidazo-[4,5-c]-phenazine (MP), and 2,12,13-trimethylpyrido-[3,2-a]-pyrido-[1',2':1,2]-imidazo-[4,5-c]-phenazine (tMP) as main ligands, respectively, were designed and synthesized to fully characterize and explore the effect of their toxicity on cancer cells. Cytotoxic mechanism studies demonstrated that the eight Ir(III) complexes exhibited highly potent antitumor activity selectively against cancer cell lines NCI-H460, T-24, and HeLa, and no activity against HL-7702, a noncancerous cell line. Among the eight Ir(III) complexes, MPytMP-Ir exhibited the highest cytotoxicity with an IC₅₀ = 5.05 ± 0.22 nM against NCI-H460 cells. The antitumor activity of MPytMP-Ir in vitro could be contributed to the steric or electronic effect of the methyl groups, which induced telomerase inhibition and damaged mitochondria in NCI-H460 cells. More importantly, MPytMP-Ir displayed a superior inhibitory effect on NCI-H460 xenograft in vivo than cisplatin. Our work demonstrates that MPytMP-Ir could potentially be developed as a novel potent Ir-based antitumor drug.

A prospect of cell immortalization combined with matrix microenvironmental optimization strategy for tissue engineering and regeneration

Cellular senescence is a major hurdle for primary cell-based tissue engineering and regenerative medicine. Telomere erosion, oxidative stress, the expression of oncogenes and the loss of tumor suppressor genes all may account for the cellular senescence process with the involvement of various signaling pathways. To establish immortalized cell lines for research and clinical use, strategies have been applied including internal genomic or external matrix microenvironment modification. Considering the potential risks of malignant transformation and tumorigenesis of genetic manipulation, environmental modification methods, especially the decellularized cell-deposited extracellular matrix (dECM)-based preconditioning strategy, appear to be promising for tissue engineering-aimed cell immortalization. Due to few review articles focusing on this topic, this review provides a summary of cell senescence and immortalization and discusses advantages and limitations of tissue engineering and regeneration with the use of immortalized cells as well as a potential rejuvenation strategy through combination with the dECM approach.

Discovery of (4-bromophenyl)(3-hydroxy-4-methoxyphenyl)methanone through upregulating hTERT induces cell apoptosis and ERS

Dominant-negative mutants of telomerase hTERT were demonstrated to have selective effects in tumor cells. However, no any effective and highly selective hTERT inhibitor has been developed so far. We focused on developing new hTERT modulators and synthesized a small molecular compound, named (4-bromophenyl)(3-hydroxy-4-methoxyphenyl)methanone. Our in vitro studies found that title compound showed high inhibitory activity against telomerase, had high antiproliferative capacity on SMMC-7721 cells with IC₅₀ value 88 nm, and had no obvious toxic effect on human normal hepatocyte cells with IC₅₀ value 10 μM. Our in vivo studies showed that this compound significantly inhibited tumor growth in xenograft tumor models. The further molecular mechanisms of title compound inhibition SMMC-7721 cell proliferation by modulating hTERT were explored; the results showed that endoplasmic reticulum stress (ERS) through ER over response (EOR) activates the expression of hTERT, and then induces ERS, which is believed to be intricately associated with oxidative stress and mitochondrial dysfunction, resulting in apoptotic cell death, thereby modulating the expression of downstream signaling molecules including CHOP (CAAT/enhancer-binding protein homologous protein)) and mitochondrion pathway of apoptosis, leading to inhibition of cell proliferation.

Discovery and optimization of selective inhibitors of protein arginine methyltransferase 5 by docking-based virtual screening

A series of highly selective and potent inhibitors against PRMT5 have been achieved using virtual screening and medicinal chemistry approaches.

Dihydropyrazole derivatives as telomerase inhibitors: Structure-based design, synthesis, SAR and anticancer evaluation in vitro and in vivo

It is of our interest to generate and identify novel compounds with regulation telomerase for cancer therapy. In order to carry out more rational design, based on structure-based drug design, several series of N-substituted-dihydropyrazole derivatives, totally 78 compounds as potential human telomerase inhibitors were designed and synthesized. The results demonstrated that some compounds had potent anticancer activity against four tumor cell lines, and showed good selectivity on tumor cells over somatic cells. By the modified TRAP assay, compound 13i exhibited the most potent inhibitory activity against telomerase with an IC50 value of 0.98 μM. In vivo evaluation results indicated that compound 13i could inhibit growth of S180 and HepG2 tumor-bearing mice, and it also significantly enhanced the survival rate of EAC tumor-bearing mice. The further results in vivo confirmed that it could significantly improve pathological changes of N,N-diethylnitrosamine (DEN)-induced rat hepatic tumor. These data support further studies to assess rational design of more efficient telomerase inhibitors in the future.

Combined spectral experiment and theoretical calculation to study the interaction of 1,4-dihydroxyanthraquinone for metal ions in solution

The interaction between 1,4-dihydroxyanthraquinone (1,4-DHA) and metal ions was studied by UV-Visible and fluorescence spectroscopies in solution. Time-dependent density functional theory calculations confirmed complex structures. The investigation results showed 1,4-DHA can selectively respond some metal ions and can be monitored by UV-Vis, fluorescence spectra and naked-eye. So 1,4-DHA has a potential application in the design of metal ions probe. More, as typical metal ions, Hg(2+) and Er(3+), their reaction abilities for 1,4-DHA were studied in detailed. Experimental results showed they have better response for 1,4-DHA. And theoretical calculation concluded that Er(3+) easily reacts with 1,4-DHA over Hg(2+) attributed to the low reaction energy of Er(3+)-1,4-DHA than Hg(2+)-1,4-DHA.

Craniofacial bone tissue engineering

There are numerous conditions, such as trauma, cancer, congenital malformations, and progressive deforming skeletal diseases, that can compromise the function and architectonics of bones of craniofacial region. The need to develop new approaches for treatment of these disorders arises from the fact that conventional therapeutic strategies face many obstacles and limitations. The use of tissue engineering in regeneration of craniofacial bone structures is a very promising possibility and a great challenge for researchers and practitioners. Developments in stem cell biology and engineering have led to the discovery of different stem cell populations and biodegradable materials with suitable properties. This review summarizes the current achievements in tissue engineering of craniofacial bone, temporomandibular joint, and periodontal ligament.

Structure-based design, synthesis and evaluation of novel anthra[1,2-d]imidazole-6,11-dione derivatives as telomerase inhibitors and potential for cancer polypharmacology

A series of anthra[1,2-d]imidazole-6,11-dione derivatives were synthesized and evaluated for telomerase inhibition, hTERT expression and suppression of cancer cell growth in vitro. All of the compounds tested, except for compounds 4, 7, 16, 24, 27 and 28 were selected by the NCI screening system. Among them, compounds 16, 39, and 40 repressed hTERT expression without greatly affecting cell growth, suggesting for the selectivity toward hTERT expression. Taken together, our findings indicated that the analysis of cytotoxicity and telomerase inhibition might provide information applicable for further developing potential telomerase and polypharmacological targeting strategy.

New anthraquinone derivatives as inhibitors of the HIV-1 reverse transcriptase-associated ribonuclease H function

BACKGROUND

The degradative activity of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), termed ribonuclease H (RNase H), which hydrolyzes the RNA component of the heteroduplex RNA:DNA replication intermediate, is an excellent target for drug discovery. Anthraquinones (AQs) and their derivatives, which are common secondary metabolites occurring in bacteria, fungi, lichens and a large number of families in higher plants, have been reported to have several biological activities including that of inhibiting HIV-1 RT activities in biochemical assays.

METHODS

We have assayed new AQ derivatives on HIV-1 RNase H activities in biochemical assays.

RESULTS

Six series of new AQ derivatives with various substituents at positions 1, 2, 3 and 4 of the AQ ring were tested, and new analogs able to inhibit HIV-1 RT-associated RNase H activity in the low micromolar range were found.

CONCLUSIONS

Our results demonstrate that AQ derivatives are promising anti-RNase H inhibitors.

Design, synthesis and biological evaluation of heterocyclic azoles derivatives containing pyrazine moiety as potential telomerase inhibitors

Three series of novel heterocyclic azoles derivatives containing pyrazine (5a-5k, 8a-8k and 11a-11k) have been designed, synthesized, structurally determined, and their biological activities were evaluated as potential telomerase inhibitors. Among the oxadiazole derivatives, compound 5c showed the most potent biological activity against SW1116 cancer cell line (IC(50)=2.46 μM against SW1116 and IC(50)=3.55 μM for telomerase). Compound 8h performed the best in the thiadiazole derivatives (IC(50)=0.78 μM against HEPG2 and IC(50)=1.24 μM for telomerase), which was comparable to the positive control. While compound 11f showed the most potent biological activity (IC(50)=4.12 μM against SW1116 and IC(50)=15.03 μM for telomerase) among the triazole derivatives. Docking simulation by positioning compounds 5c, 8h and 11f into the telomerase structure active site was performed to explore the possible binding model. The results of apoptosis demonstrated that compound 8h possessed good antitumor activity against HEPG2 cancer cell line. Therefore, compound 8h with potent inhibitory activity in tumor growth inhibition may be a potential antitumor agent against HEPG2 cancer cell. Therefore, the introduction of oxadiazole, thiadiazole and triazole structures reinforced the combination of our compounds and the receptor, resulting in progress of bioactivity.

B1, a novel topoisomerase II inhibitor, induces apoptosis and cell cycle G1 arrest in lung adenocarcinoma A549 cells

In our previous studies, we demonstrated that 2,6-bis-(2-chloroacetamido) anthraquinone (B1) showed a highly significant cytotoxic effect. However, its influence in the cell cycle and apoptotic induction effects has not been investigated yet. Here we report the antiproliferative effect of B1, for which IC50 values were 0.57 μmol/l for lung cancer A549 cells, 0.63 μmol/l for colon cancer HT-29 cells, and 0.53 μmol/l for breast cancer MCF-7 cells. DNA topoisomerase II (Topo II), an essential enzyme in DNA synthesis and meiotic division, is highly expressed in cancer cells. Some currently used clinical anticancer drugs (doxorubicin and mitoxantrone) targeting Topo II are very effective antineoplastic agents. B1, sharing the basic structure of known Topo II inhibitors, demonstrated a significant inhibitory effect on Topo II bioactivity. In A549 cells, B1 increased apoptotic cell population with induction of Fas, Bax, and cleaved poly(ADP-ribose) polymerase and by reduction of Bcl-2 expression. Moreover, cell cycle analysis indicated that B1 induced G1 phase arrest through modulation of G1 cell cycle regulatory proteins, such as the downregulation of cyclin D1 and upregulation of Cip/p21, Kip1/p27, and p53. Thus, our study suggests that B1, with the ability to inhibit Topo II activity and cause cell cycle G1 arrest and apoptosis, has potential as a novel anticancer agent.

The use of hTERT-immortalized cells in tissue engineering

The use of human telomerase reverse transcriptase (hTERT)-immortalized cells in tissue engineering protocols is a potentially important application of telomere biology. Several human cell types have been created that overexpress the hTERT gene with enhanced telomerase activity, extended life span and maintained or even improved functional activities. Furthermore, some studies have employed the telomerized cells in tissue engineering protocols with very good results. However, high telomerase activity allows extensive cell proliferation that may be associated with genomic instability and risk for cell transformation. Thus, safety issues should be studied carefully before using the telomerized tissues in the clinic. Alternatively, the development of conditional or intermittent telomerase activation protocols is needed.

3-Allyl-1-{[3-(4-nitro-phen-yl)-4,5-dihydro-1,3-oxazol-5-yl]meth-yl}-1H-anthra[1,2-d]imidazole-2,6,11(3H)-trione

The mol­ecular structure of the title compound, C₂₈H₂₀N₄O₆, consists of three fused six-membered rings (A,B,C) and one five-membered ring (D). The latter is linked to an isoxazole ring (E) via a methyl­ene unit. A 4-nitro-phenyl substituent (F) is attached to the isoxazole. The fused five and six-membered rings (C,D) are almost coplanar with an r.m.s. deviation of 0.0345 Å and make a dihedral angle of 9.40 (8)° with ring A. The isoxazole and 4-nitro-phenyl rings (E,F) are also almost coplanar with the imidazole and the fused adjacent ring (C,D), forming a dihedral angle of 11.4 (6)°. The crystal packing displays inter­molecular C—H⋯O hydrogen bonding. An intra­molecular C—H⋯O inter­action also occurs.

Alizarine derivatives as new dual inhibitors of the HIV-1 reverse transcriptase-associated DNA polymerase and RNase H activities effective also on the RNase H activity of non-nucleoside resistant reverse transcriptases

HIV-1 reverse transcriptase (RT) has two associated activities, DNA polymerase and RNase H, both essential for viral replication and validated drug targets. Although all RT inhibitors approved for therapy target DNA polymerase activity, the search for new RT inhibitors that target the RNase H function and are possibly active on RTs resistant to the known non-nucleoside inhibitors (NNRTI) is a viable approach for anti-HIV drug development. In this study, several alizarine derivatives were synthesized and tested for both HIV-1 RT-associated activities. Alizarine analogues K-49 and KNA-53 showed IC(50) values for both RT-associated functions of ∼ 10 μm. When tested on the K103N RT, both derivatives inhibited the RT-associated functions equally, whereas when tested on the Y181C RT, KNA-53 inhibited the RNase H function and was inactive on the polymerase function. Mechanism of action studies showed that these derivatives do not intercalate into DNA and do not chelate the divalent cofactor Mg(2+) . Kinetic studies demonstrated that they are noncompetitive inhibitors, they do not bind to the RNase H active site or to the classical NNRTI binding pocket, even though efavirenz binding negatively influenced K-49/KNA-53 binding and vice versa. This behavior suggested that the alizarine derivatives binding site might be close to the NNRTI binding pocket. Docking experiments and molecular dynamic simulation confirmed the experimental data and the ability of these compounds to occupy a binding pocket close to the NNRTI site.

NSC746364, NSC746365, and NSC746366: the spectra of cytotoxicity and molecular correlates of response to telomerase activity

NSC746364, NSC746365, and NSC746366 are structurally novel 2,7-diamidoanthraquinone derivatives compared with other clinically used anticancer agents and have exhibited a unique multilog differential pattern of activity in our earlier studies. To systematically evaluate their potential anticancer activity, three selected compounds were tested for their cytotoxicity in vitro against 60 human cancer lines in the National Cancer Institute's anticancer drug screen as well as for dose response curves and telomerase activity. Cell growth was analyzed by the MTT assay, with differences between dose-response curves analyzed nonparametrically. Telomerase activity was detected by a modified version of the PCR-based assay and telomere repeat amplification protocol assay. To elucidate the structure-activity relationships and in-vitro anticancer activity, we correlated their activity profile [GI(50), total growth inhibition (TGI), and LC(50)] in the screening system and also their effects on telomerase activity, human telomerase reverse transcriptase expression, cell proliferations, and cytotoxicity. As a result we found that NSC746364, NSC746365, and NSC746366 have potent activity with 50% net growth inhibition conferred by 0.23-16.0 micromol/l (2.08 micromol/l mean); 0.78-15.9 micromol/l (2.57 micromol/l mean); 1.38-63.1 micromol/l (3.89 micromol/l mean), respectively. Sensitive cell lines exhibit TGI and 50% lethality to NSC746364, exhibited an LC(50) with as little as 2.82 micromol/l and TGI with as little as 0.95 micromol/l; NSC746365, exhibited an LC(50) with as little as 3.30 micromol/l, and TGI with as little as 1.65 micromol/l; NSC746366, exhibited an LC(50) with as little as 8.80 micromol/l; and TGI with as little as 4.06 micromol/l, respectively. Results of the study extend the initial in-vitro observation reported in the data above and confirm the importance of anticancer activity and telomerase inhibition. The unique molecular characterization, cytotoxicity, and telomerase activity profiles warrant further investigation and indicate a potential novel mechanism of anticancer action involved.

Establishing cell-based reporter systems for the analysis of hTERT expression

Telomeres are the protective structures at the end of eukaryotic chromosomes. Telomerase is a ribonucleoprotein that contains both an RNA and a protein component for the maintenance of telomere length. Telomerase activity is detected in the majority of malignant tumors, but not in normal somatic cells, suggesting that telomerase reactivation is a crucial step in cell immortality and carcinogenesis. The mechanism of how telomerase is activated during tumorigenesis remains unclear. However, the expression of the human telomerase reverse transcriptase (hTERT) gene, which encodes the catalytic protein subunit of human telomerase, has been shown to be the major determining factor. To gain insight into the mechanisms regulating hTERT expression and to facilitate the screening of agents that affect hTERT expression, we have established cell-based systems for monitoring hTERT expression. We linked the hTERT promoter to two different reporter genes encoding green fluorescence protein (GFP) and secreted alkaline phosphatase (SEAP), respectively. These constructs were then transfected into H1299 and hTERT-BJ1 cells. Stable clones harboring these DNA constructs were isolated. In these cells, hTERT expression can be monitored through the quantification of GFP or SEAP activity on an automatic plate reader. Using these systems, we have identified several small molecule compounds that affect the expression of telomerase.

Synthesis and Human Telomerase Inhibition of a Series of Regioisomeric Disubstituted Amidoanthraquinones

Telomerase is the enzymatic activity that maintains the ends of eukaryotic chromosomes. Telomerase activity is detected in most tumor cells whereas it is low or undetectable in most normal somatic cells. Expression of the telomerase catalytic component, the human telomerase reverse transcriptase (hTERT), is believed to be controlled primarily at the level of transcription. Because of this selective expression property of telomerase, it has been touted as a specific target for antitumor chemotherapeutics. However, a concern for the applicability of telomerase inhibitors is that they require a long lag time for telomeres to be shortened to critical length before cancer cells stop proliferating. Here we investigate telomerase inhibitory, cytotoxicity and the hTERT repressing effects on a number of synthesized 2,6-diamidoanthraquinones and 1,5-diamidoanthraquinones as compared to their disubstituted homologues. We found that several of the 1,5-diamidoanthraquinones and 2,6-diamidoanthraquinones inhibited telomerase activity effectively with IC50 at the sub-micro to micro molar range and caused acute cytotoxicity to cancer cells with EC50 similar or better than that of mitoxantrone. Particularly, 2,6-diamidoanthraquinone with 2-ethylaminoacetamido side chains 33, even though not affecting cell proliferation, showed to be endowed with a strong telomerase effect, probably related to a marked stabilization of the G-quadruplex-binding structure. The results suggested that these compounds caused multiple effects to cancer cells. More significantly, they overcome the long lag period problem of classical telomerase inhibitors that they are also potent cytotoxic agents. These results greatly expand the potential of tricyclic anthraquinone pharmacophore in preventive and/or curative therapy.

Synthesis and antitumor evaluation of symmetrical 1,5-diamidoanthraquinone derivatives as compared to their disubstituted homologues

A series of symmetrical 1,5-diamidoanthraquinone derivatives with potentially bioreducible groups has been synthesized and their cytostatic activity against the panel of various cancer cell lines in vitro has been studied. Preliminary structure-activity relationships were established. The results indicated that compounds 5 and 18 exhibited significant potent cytotoxicity at 1.24-1.75 microM for Hepa G2 cell line; compounds 5, 16, and 18 exhibited cytotoxicity at 0.14-1.82 microM for 2.2.15 cell line as determined by XTT colorimetric assay. Two structurally related compounds, mitoxantrone and adriamycin, were tested in parallel as positive controls. In addition, it was found that compounds 5 and 18 were a more potent and specific human hepatoma cell line than mitoxantrone and showed comparable activity to adriamycin. Among them, compound 18 was the most potent for 2.2.15 cells. We have demonstrated that the anthraquinone moiety is essential for activity and that less sterically hindered substituents contribute to enhanced in vitro efficacy. Implications for amidoanthraquinone cytotoxicity as potential anticancer agents are discussed. We further delineate the nature of the pharmacophore for this class of compounds, which provides a rational basis for the structure-activity relationships.

Telomerase activity is not a key determinant of sensitivity to standard cytotoxic drugs in human esophageal carcinoma cell lines

The aim of the present study was to investigate if basal telomerase activity levels may predict sensitivity to cytotoxic drugs in a panel of human esophageal carcinoma cell lines. The TRAPeze telomerase detection assay was used to investigate telomerase activity in the cell lines. Cytotoxic drug sensitivity for 20 standard cytotoxic agents was assessed using the fluorometric microculture cytotoxicity assay (FMCA). Telomerase activity was detected in all cell lines with a broad range of activity levels. Drug sensitivity also varied considerably between the cell lines. Except for a P value towards a correlation between mitoxantrone and telomerase activity (P=0.054), no statistically significant correlation was found between telomerase activity levels and sensitivity to investigated drugs, including key drugs such as cisplatin (P=0.9), 5-fluorouracil (P=0.8) and doxorubicin (P=0.54). We therefore conclude that basal telomerase activity level is not a key determinant of sensitivity to standard cytotoxic drugs in esophageal carcinoma cell lines.

Synthesis and antitumor activity of 1,8-diaminoanthraquinone derivatives

Continuing our ongoing studies on cytotoxic substances, a series of regioisomeric disubstituted aminoanthraquinone (DAAQ) derivatives have been synthesized as cytotoxic activity based on a proposed bioactive amino conformation. To assess the biological activity of amino-substitution in the side-chains of anthraquinone located at positions 1 and 8 of the anthraquinone ring system. The aim of the study was to determine if members of the anthraquinone family could be used as adjuncts to increase the growth inhibiting effect of anticancer agents in rat glioma C6 cells, human hepatoma G2 cells and 2.2.15 cells. In vitro cytotoxicity data is reported for the compounds and some indications of structure--activity relationships have been discerned. A number of compounds were found to have good cytotoxicity against proliferation in these three cell lines. This has led to the discovery some of the DAAQ as a conformationally constrained structure possessing anticancer properties that displays cytotoxicity for these above cell lines and is being investigated further.

The tea polyphenols EGCG and EGC repress mRNA expression of human telomerase reverse transcriptase (hTERT) in carcinoma cells

Tea polyphenols have inhibitive effects for carcinogenesis. A reporter system controlled by hTERT promoter was constructed to evaluate the effects of tea polyphenols, (-)-epigallocatechin-3-gallate (EGCG) and (-)-epigallocatechin (EGC) on the repression of hTERT transcription. The hTERT promoter activity was selectively repressed by 20-40 microM EGCG and EGC in a dose- and time-dependent manner. Real-time RT-PCR confirmed that the endogenous hTERT mRNA level was decreased in H1299, OECM-1 and SAS cells treated with EGCG or EGC. Our results identified the repression activities of EGCG and EGC toward telomerase expression that might be linked to inhibition of carcinoma cell growth. This cell-based reporter system is useful for screening drugs targeting hTERT repression.

Telomere and telomerase as targets for anti-cancer and regeneration therapies

Telomerase is a ribonucleoprotein that directs the synthesis of telomeric sequence. It is detected in majority of malignant tumors, but not in most normal somatic cells. Because telomerase plays a critical role in cell immortality and tumor formation, it has been one of the targets for anti-cancer and regeneration drug development. In this review, we will discuss therapeutic approaches based mainly on small molecules that have been developed to inhibit telomerase activity, modulate telomerase expression, and telomerase directed gene therapy.

Synthesis and structure–activity correlations of the cytotoxic bifunctional 1,4-diamidoanthraquinone derivatives

Anthraquinone-based compounds are attractive target for the design of new anticancer drugs. We have previously described a series of 1,5- and 1,4-difunctionalized anthraquinones, which exhibit different spectra of potency, together with human telomerase evaluation. The present study details the preparation of further, distinct series of regioisomeric difunctionalized amidoanthraquinone and examines their in vitro cytotoxicity in C6, Hepa G2, and 2.2.15 cell lines. Two structurally related compounds, mitoxantrone and adriamycin, were tested in parallel as positive controls. The structure-activity relationships indicated amido substitution may lead to a different mechanism of cytotoxicity. Compounds, which have -(CH2)n- side chains terminating in basic groups such as aminoalkyl-substituted, showed cytotoxic activity in several cell lines. The exact mode of intercalative binding may be dictated by the positional placement of substituent side chains. Implications for amidoanthraquinone cytotoxicity as potential anticancer agents are discussed. In addition, we further delineate the nature of the pharmacophore for this class of compounds, which provides a rational basis for the structure-activity relationships.

Small-Molecule Anthracene-Induced Cytotoxicity and Induction of Apoptosis through Generation of Reactive Oxygen Species

A series of anthracene derivatives have been synthesized, and their potential individual cytotoxicity was evaluated using Jurkat T cells and peripheral blood mononuclear cells (PBMCs) in vitro. These compounds, except for 2l, showed less cytotoxicity in PBMCs than mitoxantrone. We also analyzed the antiproliferative activity of these derivatives using the annexin V/propidium iodide assay. These synthetic compounds induced apoptosis, thus leading to antitumor effects. Compounds 2b, 2e, 2f, 2g, 2h, 2i, 2j, and mitoxantrone produced dose-dependent cytotoxicity, while the antiproliferative activity of the anthracene pharmacophore was retained in Jurkat T cells base on the detection of DNA degradation and membrane unpacking. These clearly indicate a correlation between cytotoxicity and antitumor activity. Unlike mitoxantrone, cytotoxic properties were observed, as documented by the reactivity of these novel compounds against Jurkat T cells and PBMCs as normal cells, respectively. Various concentrations of 2b, 2e, 2f, 2g, 2h, 2i, and 2j preparations also inhibited Jurkat T cell proliferation and induced apoptosis of Jurkat T cells, potentially confirmed through the detection of DNA degradation and membrane unpacking. In the present report we also investigated the antiinflammatory activity against phorbol-12-myristate-13-acetate induced superoxide anion production, a marker for an inflammatory mediator produced by neutrophils, with IC(50) (microM) values of 2b, 2h, 2l, and 2o of 4.28+/-0.89, 3.31+/-0.88, 4.38+/-0.25, and 5.45+/-1.78, respectively. These results suggest that, in addition to the specific chromosomal aberrations and cell death, elevated apoptosis could also be a marker for exposure to anthracene derivatives.