Telomestatin, a novel telomerase inhibitor from Streptomyces anulatus

YM-216391, a Novel Cytotoxic Cyclic Peptide from Streptomyces nobilis

YM-216391, a novel cyclic peptide, was isolated from the cultured mycelium of Streptomyces nobilis JCM 4274. It was purified by solvent extraction, silica gel and ODS flash column chromatographies, followed by preparative HPLC. YM-216391 dose-dependently inhibited the growth of human cervical cancer HeLa S3 cells with an IC50 value of 14nM. YM-216391 also showed potent cytotoxic activity against a human cancer cell line panel.

YM-216391, a Novel Cytotoxic Cyclic Peptide from Streptomyces nobilis

YM-216391, a novel cytotoxic cyclic peptide, has been isolated from the cultured mycelium of Streptomyces nobilis JCM 4274. The planar structure of YM-216391 was assigned on the basis of 1D and 2D NMR spectroscopic techniques. The absolute configuration of the amino acid residues in YM-216391 was determined by Marfey's analysis and chiral HPLC analysis of its acid hydrolysate.

Synthesis and establishment of stereochemistry of the unusual polyoxazole-thiazole based cyclopeptide YM-216391 isolated from Streptomyces nobilis

A concise total synthesis of the unusual oxazole-based cyclopeptide structure YM-216391, which also establishes the stereochemistry of the natural product i.e. 1, is described.

Evaluation of by disubstituted acridone derivatives as telomerase inhibitors: the importance of G-quadruplex binding

The synthesis and evaluation of a group of 2,6-, 2,7- and 3,6-bis-aminoalkylamido acridones are reported, which show a similar level of activity against telomerase in vitro compared to their acridine counterparts. Computer modelling and calculations of relative binding energies suggest an equivalent binding mode to human intramolecular G-quadruplex DNA, but with significantly reduced affinity, as a result of the limited delocalisation of the acridone chromophore compared to the acridine system. Thermal melting studies on acridone and acridine quadruplex complexes using a FRET approach support these predictions. Long-term cell proliferation studies at sub-cytotoxic doses with two representative acridones using the SKOV3 cell line, show that neither compound produces growth arrest, in contrast with the effects produced by the tri-substituted acridine compound BRACO-19. It is concluded that telomerase inhibitory activity is a necessary though by itself insufficient property in order for cellular growth arrest to occur at sub-toxic concentrations, and that tight quadruplex binding is also required.

Porphyrin Derivatives for Telomere Binding and Telomerase Inhibition

The capacity of G-quadruplex ligands to stabilize four-stranded DNA makes them able to inhibit telomerase, which is involved in tumour cell proliferation. A series of cationic metalloporphyrin derivatives was prepared by making variations on a meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin skeleton (TMPyP). The DNA binding properties of nickel(II) and manganese(III) porphyrins were studied by surface plasmon resonance, and the capacity of the nickel porphyrins to inhibit telomerase was tested in a TRAP assay. The nature of the metal influences the kinetics (the process is faster for Ni than for Mn) and the mode of interaction (stacking or external binding). The chemical alterations did not lead to increased telomerase inhibition. The best selectivity for G-quadruplex DNA was observed for Mn-TMPyP, which has a tenfold preference for quadruplex over duplex.

Telomerase inhibition and cell growth arrest after telomestatin treatment in multiple myeloma

PURPOSE

The aim of this study was to test the efficacy of telomestatin, an intramolecular G-quadruplex intercalating drug with specificity for telomeric sequences, as a potential therapeutic agent for multiple myeloma.

EXPERIMENTAL DESIGN

We treated ARD, ARP, and MM1S myeloma cells with various concentrations of telomestatin for 7 days and evaluated for telomerase activity. Myeloma cells were treated with the minimal effective telomestatin concentration for 3-5 weeks. Every 7(th) day the fraction of live cells was determined by trypan blue exclusion, aliquots of cells were removed for various molecular assays, and the remaining cells were replated at the same cell number and at the same concentration of telomestatin. Telomere length, apoptosis, and gene expression changes were monitored as described in detail in "Materials and Methods."

RESULTS

Telomestatin treatment led to inhibition of telomerase activity, reduction in telomere length, and apoptotic cell death in ARD, MM1S, and ARP myeloma cells. Gene expression profile after 1 and 7 days of telomestatin treatment revealed >/==" BORDER="0">2-fold change in only 6 (0.027%) and 51 (0.23%) of 33,000 genes surveyed, respectively. No changes were seen in expression of genes involved in cell cycle, apoptosis, DNA repair, or recombination.

CONCLUSIONS

These results demonstrate that telomestatin exerts its antiproliferative and proapoptotic effects in myeloma cells via inhibition of telomerase and subsequent reduction in telomere length. We conclude that telomerase is an important potential therapeutic target for multiple myeloma therapy, and G-quadruplex interacting agents with specificity for binding to telomeric sequences can be important agents for additional evaluation.

Interaction of Telomestatin with the Telomeric Single-strand Overhang

The extremities of chromosomes end in a G-rich single-stranded overhang that has been implicated in the onset of the replicative senescence. The repeated sequence forming a G-overhang is able to adopt a peculiar four-stranded DNA structure in vitro called a G-quadruplex, which is a poor substrate for telomerase. Small molecule ligands that selectively stabilize the telomeric G-quadruplex induce telomere shortening and a delayed growth arrest. Here we show that the G-quadruplex ligand telomestatin has a dramatic effect on the conformation of intracellular G-overhangs. Competition experiments indicate that telomestatin strongly binds in vitro and in vivo to the telomeric overhang and impairs its single-stranded conformation. Long-term treatment of cells with telomestatin greatly reduces the G-overhang size, as evidenced by specific hybridization or telomeric oligonucleotide ligation assay experiments, with a concomitant delayed loss of cell viability. In vivo protection experiments using dimethyl sulfate also indicate that telomestatin treatment alters the dimethyl sulfate effect on G-overhangs, a result compatible with the formation of a local quadruplex structure at telomeric overhang. Altogether these experiments strongly support the hypothesis that the telomeric G-overhang is an intracellular target for the action of telomestatin.

Polyketide and Nonribosomal Peptide Antibiotics: Modularity and Versatility

Polyketide (PK) and nonribosomal peptides (NRP), constructed on multimodular enzymatic assembly lines, often attain the conformations that establish biological activity by cyclization constraints introduced by tailoring enzymes. The dedicated tailoring enzymes are encoded by genes clustered with the assembly line genes for coordinated regulation. NRP heterocyclizations to thiazoles and oxazoles can occur on the elongating framework of acyl-S enzyme intermediates, whereas tandem cyclic PK polyether formation of furans and pyrans can be initiated by post-assembly line epoxidases. Macrocyclizations of NRP, PK, and hybrid NRP-PK scaffolds occur in assembly line chain termination steps. Post-assembly line cascades of enzymatic oxidations also create cross-linked and cyclized architectures that generate the mature scaffolds of natural product antibiotics. The modularity of the natural product assembly lines and permissivity of tailoring enzymes offer prospects for reprogramming to create novel antibiotics with optimized properties.

Telomerase downregulation induced by the G-quadruplex ligand 12459 in A549 cells is mediated by hTERT RNA alternative splicing

Ligand 12459, a potent G-quadruplex-interacting agent that belongs to the triazine series, was previously shown to downregulate telomerase activity in the human A549 lung carcinoma cell line. We show here that the downregulation of telomerase activity is caused by an alteration of the hTERT splicing pattern induced by 12459, i.e. an almost complete disappearance of the active (+alpha,+beta) transcript and an over-expression of the inactive -beta transcript. Spliced intron 6 forming the -beta hTERT transcript contained several tracks of G-rich sequences able to form G-quadruplexes. By using a specific PCR-stop assay, we show that 12459 is able to stabilize the formation of these G-quadruplex structures. A549 cell line clones selected for resistance to 12459 have been analyzed for their hTERT splicing pattern. Resistant clones are able to maintain the active hTERT transcript under 12459 treatment, suggesting the appearance of mechanisms able to bypass the 12459-induced splicing alterations. In contrast to 12459, telomestatin and BRACO19, two other G-quadruplex-interacting agents, have no effect on the hTERT splicing pattern in A549 cells, are cytotoxic against the A549-resistant clones and display a lower efficiency to stabilize hTERT G-quadruplexes. These results lead us to propose that 12459 impairs the splicing machinery of hTERT through stabilization of quadruplexes located in the hTERT intron 6. Differences of selectivity between 12459, BRACO19 and telomestatin for these hTERT quadruplexes may be important to explain their respective activity and inactivity against hTERT splicing.

Resistance to the short term antiproliferative activity of the G-quadruplex ligand 12459 is associated with telomerase overexpression and telomere capping alteration

Ligands that stabilize the telomeric G-rich single-stranded DNA overhang into G-quadruplex can be considered as potential antitumor agents that block telomere replication. Ligand 12459, a potent G-quadruplex ligand that belongs to the triazine series, has been previously shown to induce both telomere shortening and apoptosis in the human A549 cell line as a function of its concentration and time exposure. We show here that A549 clones obtained after mutagenesis and selected for resistance to the short term effect of ligand 12459 frequently displayed hTERT transcript overexpression (2-6-fold). Overexpression of hTERT was also characterized in two resistant clones (JFD10 and JFD18) as an increase in telomerase activity, leading to an increase in telomere length. An increased frequency of anaphase bridges was also detected in JFD10 and JFD18, suggesting an alteration of telomere capping functions. Transfection of either hTERT or DN-hTERT cDNAs into A549 cells did not confer resistance or hypersensitivity to the short term effect of ligand 12459, indicating that telomerase expression is not the main determinant of the antiproliferative effect of ligand 12459. In contrast, transfection of DN-hTERT cDNA into resistant JFD18 cells restored sensitivity to apoptotic concentrations of ligand 12459, suggesting that telomerase does participate in the resistance to this G-quadruplex ligand. This work provides evidence that telomerase activity is not the main target for the 12459 G-quadruplex ligand but that hTERT functions contribute to the resistance phenotype to this class of agents.

Telomere inhibition and telomere disruption as processes for drug targeting

The components and cofactors of the holoenzyme telomerase and its substrate telomeric DNA are attractive targets for anticancer agents that act by inhibiting the activity of telomerase. This review outlines recent advances in telomerase inhibition that have been achieved using antisense oligonucleotides and ribozymes that target the telomerase mRNA or its hTR RNA template. Although these are potent catalytic inhibitors of telomerase, they are challenging to implement in the clinic due to their delayed effectiveness. Drugs that directly bind to the telomeres, the complex structures that are associated at the telomeric ends, and stabilize secondary DNA structures such as G-quadruplexes are also potent inhibitors of telomerase. Special focus is given here to the telomeres, the biological machinery that works in tandem with telomerase to elongate telomeres, the causes of telomere disruption or dysfunction, and the consequences of disruption/dysfunction on the activity and design of anticancer agents.

Activity of a novel G-quadruplex-interactive telomerase inhibitor, telomestatin (SOT-095), against human leukemia cells: involvement of ATM-dependent DNA damage response pathways

The telomerase complex is responsible for telomere maintenance and represents a promising neoplasia therapeutic target. In order to determine whether G-quadruplex-interactive telomerase inhibitor, telomestatin (SOT-095), might have effects on telomere dynamics and to evaluate the clinical utility, we assessed the effects of telomestatin on BCR-ABL-positive human leukemia cells. We found that treatment with telomestatin reproducibly inhibited telomerase activity in the BCR-ABL-positive leukemic cell lines OM9;22 and K562, resulting in telomere shortening. Inhibition of telomerase activity by telomestatin disrupts telomere maintenance and ultimately results in telomere dysfunction. Telomestatin completely suppressed the plating efficiency of K562 cells at 1 microM; however, telomestatin had less effects on BFU-Es and CFU-GMs colony formation from normal bone marrow CD34-positive cells. Enhanced chemosensitivity toward imatinib and chemotherapeutic agents was also observed in telomestatin-treated K562 cells. Further, the combination of telomestatin plus imatinib more effectively inhibited hematopoietic colony formation by primary human chronic myelogenous leukemia cells. Last, telomestatin induced the activation of ATM and Chk2, and subsequently increased the expression of p21(CIP1) and p27(KIP1). These results demonstrate that telomere dysfunction induced by telomestatin activates the ATM-dependent DNA damage response. We conclude that telomerase inhibitors combined with the use of imatinib and other chemotherapeutic agents may be very useful for the treatment of human leukemia.

A novel platinum compound inhibits telomerase activity in vitro and reduces telomere length in a human hepatoma cell line

Telomerase activity is detectable in most human tumors but not in most normal somatic cells or tissues. Telomerase inhibition has, therefore, been proposed as a novel and potentially selective strategy for antitumor therapy. In the present study, we found that platinum compounds, including cisplatin [cis-diamminedichloro-platinum (II)], strongly inhibited the activity of partially purified rat telomerase. Among the agents tested, 2,3-dibromosuccinato [2-(methylaminomethyl)pyridine]platinum (II) (compound E) exhibited the strongest inhibition, with an median inhibitory concentration (IC(50)) of 0.8 micro M. The mode of inhibition was noncompetitive with either dNTPs or TS (first) primer, with K(i) values estimated to be 2.3 or 3.9 micro M for varied TS primer or dNTPs, respectively. Notably, cisplatin also inhibited the telomerase activity, with an IC(50) of 2.0 micro M. Again, the mode of inhibition was noncompetitive, with K(i) values estimated as 7.3 or 8.1 micro M. Preincubation of TS primer with compound E did not affect the telomerase inhibition, whereas preincubation with cisplatin caused remarkable enhancement. Treatment of a human hepatoma cell line HepG2 with a low concentration of compound E gradually reduced the telomere length, indicating that this compound was able to inhibit telomerase in living cells as well as in vitro.

Interactions of cryptolepine and neocryptolepine with unusual DNA structures

Cryptolepine, the main alkaloid present in the roots of Cryptolepis sanguinolenta, presents a large spectrum of biological properties. It has been reported to behave like a DNA intercalator with a preference for GC-rich sequences. In this study, dialysis competition assay and mass spectrometry experiments were used to determine the affinity of cryptolepine and neocryptolepine for DNA structures among duplexes, triplexes, quadruplexes and single strands. Our data confirm that cryptolepine and neocryptolepine prefer GC over AT-rich duplex sequences, but also recognize triplex and quadruplex structures. These compounds are weak telomerase inhibitors and exhibit a significant preference for triplexes over quadruplexes or duplexes.

Telomerase inhibition enhances apoptosis in human acute leukemia cells: possibility of antitelomerase therapy

Telomerase is a ribonucleoprotein enzyme that maintains protective structures at the ends of eukaryotic chromosomes. We examined the impact of telomerase inhibition by the dominant-negative human catalytic subunit of telomerase (DN-hTERT) on the biological features of acute leukemia. We introduced vectors encoding dominant- negative (DN)-hTERT, wild-type (WT)-hTERT, or a control vector expressing only a drug-resistant marker into a telomerase-positive human acute lymphoblastic leukemia cell line, HAL-01. Expression of DN-hTERT dramatically inhibited telomerase activity, leading to apoptotic cell death. Mutant telomerase expression also enhanced daunorubicin-induced apoptosis. Nude mice (n=5 per group) received subcutanous implants of HAL-01 cells expressing the control vector or DN-hTERT or WT-hTERT. Implantation of HAL-01 cells expressing control vector (n=5) rapidly produced tumors, whereas implantation of those expressing DN-hTERT (n=5) did not. Thus, telomerase inhibition both growth of HAL-01 cells in vitro and tumorigenic capacity in vivo. Furthermore, the G-quadruplex-interactive telomerase-specific inhibitor, telomestatin, shortened the telomere length and induced apoptosis in freshly isolated primary acute leukemia cells. These results suggest that antitelomerase therapy may be useful in some acute leukemias in combination with antileukemic agents such as daunorubicin.

Synthesis of 6-formyl-pyridine-2-carboxylate derivatives and their telomerase inhibitory activities

Twenty-one pyridine-2-carboxylate derivatives were prepared by the coupling of 6-formyl-2-carboxylic acid with the corresponding phenol, thiophenol, and aniline, substituted with various functional groups. Among them, the 3,4-dichlorothiophenol ester (9p) showed the highest in vitro telomerase inhibitory activity and quite significant in vivo tumor suppression activity.

Antitumour polycyclic acridines. Palladium(0) mediated syntheses of quino[4,3,2-kl]acridines bearing peripheral substituents as potential telomere maintenance inhibitors

Pd(0) mediated couplings between substituted 2-(pivaloylamino)benzeneboronic acids and 3,6-disubstituted-10-methylacridones 13 bearing a bromo or trifluoromethylsulfonyloxy substituent in the 1-position yield intermediate 1-arylacridones 16 which can be can be cyclised to new 8-methylquino[4,3,2-kl]acridines 17 with phosphorus oxychloride or 6 M HCI in EtOH. Heck reactions between triflate-substituted substrates 17 and acrylic acid derivatives afforded quinoacridines with unsaturated side-chains in the 6-position. Alkylboranes, prepared by interaction of 9-borabicyclo[3,3,1]nonane (9-BBN) and allyl acetate or N-allyltrifluoroacetamide, participated in Suzuki-Miyaura reactions with chloro-substituted 8-methylquinoacridines to form derivatives bearing functionalised propyl groups in the 6- and 10-positions. Representative 8-methylquinoacridines were methylated with methyl iodide to yield telomerase-inhibitory 8,13-dimethylquinoacridinium iodides 24.

Inhibition of telomerase activity by a distamycin derivative: effects on cell proliferation and induction of apoptosis in human cancer cells

In this study, we evaluated the potential of the distamycin derivative MEN 10716 as a telomerase inhibitor. Exposure of human melanoma cell extracts to MEN 10716 induced a dose-dependent inhibition of telomerase activity, with an IC50 of 24+/-3 microM. When intact JR8 melanoma cells were chronically exposed to the drug (200 microM every other day for 50 days), a marked inhibition (>80%) of the enzyme's catalytic activity was consistently observed starting from day 1. At later points in time, MEN 10716 inhibited melanoma cell proliferation and induced apoptosis. Cells surviving MEN 10716 exposure were characterised by a higher melanin content and a greater expression of p16(INK4A) protein than control cells. The effects of MEN 10716 were subsequently evaluated in different tumour cell systems. In particular, even in the H460 non-small cell lung cancer cell line, chronic exposure of the cells to the drug (100 microM every other day for 50 days) induced a consistent inhibition (>85%) of telomerase activity, a reduction of cell proliferation potential, and apoptosis. Conversely, MEN 10716 treatment did not appreciably inhibit cell proliferation in the U2-OS telomerase-negative human osteogenic sarcoma cell line. Interestingly, no variation in the mean telomere length was observed in MEN 10716-treated JR8 melanoma cells, whereas an appreciable increase in the mean telomere length was found in H460 lung cancer cells after drug exposure. Overall, the results of the study indicate that MEN 10716 is a possible telomerase inhibitor and suggest that abrogation of telomerase activity can affect cell proliferation even through pathways that are not dependent on telomere erosion.

Telomere maintenance as a target for anticancer drug discovery

Maintenance of telomeres--specialized complexes that protect the ends of chromosomes--is undertaken by the enzyme complex telomerase, which is a key factor that is activated in more than 80% of cancer cells that have been examined so far, but is absent in most normal cells. So, targeting telomere-maintenance mechanisms could potentially half tumour growth across a broad spectrum of tumour types, with little cytotoxic effect outside tumours. Here, we describe the current understanding of telomere biology, and the application of this knowledge to the development of anticancer drugs.

A G-quadruplex-interactive potent small-molecule inhibitor of telomerase exhibiting in vitro and in vivo antitumor activity

The telomerase complex is responsible for telomere maintenance and represents a promising cancer therapeutic target. We describe herein the antitelomerase and antitumor properties of a small-molecule compound designed by computer modeling to interact with and stabilize human G-quadruplex DNA, a structure that may form with telomeric DNA, thereby inhibiting access to telomerase. The 3,6,9-trisubstituted acridine 9-[4-(N,N-dimethylamino)phenylamino]-3,6-bis(3-pyrrolodinopropionamido) acridine (BRACO19) represents one of the most potent cell-free inhibitors of human telomerase yet described (50% inhibitory concentration of 115 +/- 18 nM). Moreover, in contrast to G-quadruplex interactive agents described previously, BRACO19 did not cause nonspecific acute cytotoxicity at similar concentrations to those required to completely inhibit telomerase activity. There exists a 90-fold differential (mean 50% inhibitory concentration for acute cell kill across seven human tumor cell lines of 10.6 +/- 0.7 microM). The exposure of 21NT human breast cancer cells, which possess relatively short telomeres, to nonacute cytotoxic concentrations of BRACO19 (2 microM) resulted in a marked reduction in cell growth after only 15 days. This was concomitant with a reduction in intracellular telomerase activity and onset of senescence as indicated by an increase in the number of beta-galactosidase positive-staining cells. Intraperitoneal administration of nontoxic doses of BRACO19 (2 mg/kg) to mice bearing advanced stage A431 human vulval carcinoma subcutaneous xenografts and previously treated with paclitaxel induced a significant increase in antitumor effect compared with that observed with paclitaxel alone. BRACO19 thus represents the first of a "second generation" of G-quadruplex-mediated telomerase/telomere-interactive compounds. It possesses nanomolar potency against telomerase but low nonspecific cytotoxicity, growth inhibitory effects, and induction of senescence in a human breast cancer cell line and, moreover, significant antitumor activity in vivo when administered post paclitaxel to mice bearing a human tumor xenograft carcinoma.

Telomestatin, a potent telomerase inhibitor that interacts quite specifically with the human telomeric intramolecular g-quadruplex

Telomestatin is a natural product isolated from Streptomyces anulatus 3533-SV4 and has been shown to be a very potent telomerase inhibitor. The structural similarity between telomestatin and a G-tetrad suggested to us that the telomerase inhibition might be due to its ability either to facilitate the formation of or trap out preformed G-quadruplex structures, and thereby sequester single-stranded d[T(2)AG(3)](n) primer molecules required for telomerase activity. Significantly, telomestatin appears to be a more potent inhibitor of telomerase (5 nM) than any of the previously described G-quadruplex-interactive molecules. In this communication we provide the first experimental evidence that telomestatin selectively facilitates the formation of or stabilizes intramolecular G-quadruplexes, in particular, that produced from the human telomeric sequence d[T(2)AG(3)](4). A simulated annealing (SA) docking approach was used to study the binding interactions of telomestatin with the intramolecular antiparallel G-quadruplex structure. Each intramolecular G-quadruplex molecule was found to bind two telomestatin molecules (unpublished results). A 2:1 model for the telomestatin bound in the external stacking mode in an energy minimized complex with the human telomeric basket-type G-quadruplex was constructed. Our observation that a G-quadruplex-interactive molecule without significant groove interactions is able to reorient in a G-quadruplex structure proints to the importance of core interaction with an asymmetric G-quadruplex structure in producing selective binding. Furthermore, the G-quadruplex interactions of telomestatin are more selective for the intramolecular structure in contrast to other G-quadruplex-interactive agents, such as TMPyP4.

G-quadruplexes as therapeutic targets

The ends of chromosomes (telomeres) consist of tandem repeats of guanine-rich sequences. In eukaryotics, telomeric DNA is single stranded for the final few hundred bases. These single-stranded sequences can fold into a variety of four-stranded structures (quadruplexes) held together by quartets of hydrogen-bonded guanine bases. The reverse transcriptase enzyme telomerase is responsible for maintaining telomeric DNA length in over 85% of cancer cells by catalyzing the synthesis of further telomeric repeats. Its substrate is the single-stranded 3'-telomeric end. Inhibition of telomere maintenance can be achieved by stabilization of a quadruplex structure for the telomere end. A variety of small molecules have been devised to achieve this, ranging from anthraquinones to porphyrins, acridines, and complex polycyclic systems. Structural and mechanistic aspects of these quadruplex complexes are reviewed here, together with a discussion of the issues of selectivity/potency for quadruplex DNAs vs duplex DNA.

Natural and pharmacological regulation of telomerase

The extremities of eukaryotic chromosomes are called telomeres. They have a structure unlike the bulk of the chromosome, which allows the cell DNA repair machinery to distinguish them from 'broken' DNA ends. But these specialised structures present a problem when it comes to replicating the DNA. Indeed, telomeric DNA progressively erodes with each round of cell division in cells that do not express telomerase, a specialised reverse transcriptase necessary to fully duplicate the telomeric DNA. Telomerase is expressed in tumour cells but not in most somatic cells and thus telomeres and telomerase may be proposed as attractive targets for the discovery of new anticancer agents.

Telomerase: diagnostics, cancer therapeutics and tissue engineering

The enzyme telomerase has a key role in controlling the lifespan of human cells. It is absent from most somatic tissues but is reactivated in more than 85% of cancers, making the enzyme ideal as a marker of cancer cells and as a therapeutic target. In the context of normal human cells, the enzyme can extend cellular lifespan without causing cancer-associated changes or altering phenotypic properties. This capability could solve a major obstacle in the use of normal human cells for tissue engineering, that is, the induction of cellular senescence.

Solid-Phase synthesis of a library constructed of aromatic phosphate, long alkyl chains and tryptophane components, and identification of potent dipeptide telomerase inhibitors

Telomerase inhibitors are expected as a new candidate of therapeutic agents for cancer. Recently, we have found novel inhibitors based on the bisindole skeleton. In this study, solid-phase synthesis was applied to construct a library of inhibitors having aromatic phosphate, long alkyl chain and tryptophane components, from which a D,D-ditryptophane derivative has been identified as a new potent telomerase inhibitor with IC(50) values of 0.3 microM. A hypothetical binding model for the new inhibitors has been proposed based on the structure-activity relationship.