G-quadruplex compounds and cis-platin act synergistically to inhibit cancer cell growth in vitro and in vivo.

The ability of two structurally diverse telomeric G-quadruplex-binding compounds to synergise the action of cis-platin has been investigated in two cancer cell lines. One compound is a trisubstituted acridine compound AS1410, a close analogue of BRACO-19, and the other is a non-polycyclic compound synthesised using click chemistry and containing two triazole rings. Both compounds produce growth arrest at sub-cytotoxic concentrations in the two cell lines (MCF7 and A549), with behaviour consistent with telomere targeting mechanisms. Synergistic behaviour was observed in both cell lines with both compounds in combination with cis-platin, but only when the ratio of AS1410:cis-platin is >1. In vivo tumour xenograft studies with the A549 lung cancer model and the trisubstituted acridine compound AS1410 showed only a modest anti-tumour effect when administered alone, but produced rapid and highly significant decreases in tumour volume when administered in combination with cis-platin.

Amide-based prodrugs of spermidine-bridged dinuclear platinum. Synthesis, DNA binding, and biological activity.

The chemistry and biology of acetyl-protected spermidine-bridged dinuclear platinum complexes [{ trans-PtCl(NH 3) 2] 2-mu-NH 2(CH 2) 3N(COR)(CH 2) 4NH 2]X 2 (R = H, X = Cl (1,1/t,t-spermidine, BBR3571); R = CH 3 , X = Cl ( 2); R = CH 2 Cl, X = ClO 4 ( 3); R = CF 3 , X = Cl ( 4)) are compared with their carbamate analogues. The compounds are potential prodrugs for the parent compound 1, a highly potent antitumor agent. At pH 6-8 hydrolysis of the blocking group with the release of the "parent" protonated species follows the order 4 > 3 >> 2. For 4, rate constants for the deprotection increase in this pH range. The DNA binding profile of 4 is similar to the Boc derivative, confirming the central influence of charge on DNA binding properties. The differences in cytotoxicity for the protected compounds in ovarian carcinoma cell lines sensitive and resistant to cisplatin cannot completely be explained by spontaneous release of 1,1/t,t-spermidine at physiological pH. Inherent cytotoxicity and cell line specificity may contribute to the observed behavior. The properties of the compounds present them also as possible "second-generation" analogues of the clinically relevant trinuclear complex [{ trans-PtCl(NH 3) 2} 2-mu- trans-Pt(NH 3) 2(NH 2(CH 2) 6NH 2) 2](NO 3) 4, ( 8, BBR3464).

Structure-based design of benzylamino-acridine compounds as G-quadruplex DNA telomere targeting agents.

The design, synthesis, biophysical and biochemical evaluation is presented of a new series of benzylamino-substituted acridines as G-quadruplex binding telomerase inhibitors. Replacement of the previously reported anilino substituents by benzylamino groups results in enhanced quadruplex interaction, and for one compound, superior telomerase inhibitory activity.

Evidence for the involvement of p38 MAP kinase in the action of the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA).

AIMS: DMXAA (AS1404), a small-molecule vascular disrupting agent that has now completed Phase II clinical trial, induces endothelial cell apoptosis, increased vascular permeability and decreased tumour blood flow in vivo. Its action is incompletely understood and we wished to develop an in vitro system to study its effects. METHODS: Human tumour cell lines developed from aggressive tumours were grown on Matrigel to simulate a tumour microenvironment. Cells were analysed by light microscopy and by gene expression profiling. RESULTS: Several cell lines formed networks when grown on Matrigel and the NZM7 melanoma cell line was chosen for further study. Addition of DMXAA at a clinically achievable concentration (30 microg/mL) prevented network formation, but co-addition of SB203580 (10 microM), a selective inhibitor of p38 MAP kinase, reversed the effect of DMXAA and restored network formation. Analysis of expression genes for endothelial and related functions showed that cells growing on Matrigel expressed a pattern similar to that of NZM7 cells growing as xenografts in vivo but different from that of cells grown on standard tissue culture plates. Addition of DMXAA resulted in the inhibition of expression of several genes including the transcriptional activator Ets1 and matrix metalloproteinase-2 (MMP2), but co-addition of SB203580 did not reverse these effects of DMXAA on gene expression. CONCLUSION: The results suggest that p38 MAP kinase plays an important role in the action of DMXAA and that growth of tumour cells on Matrigel provides a promising model for further studies on the action of this drug.

Discovery and development of anticancer aptamers.

Aptamers, also termed as decoys or "chemical antibodies," represent an emerging class of therapeutics. They are short DNA or RNA oligonucleotides or peptides that assume a specific and stable three-dimensional shape in vivo, thereby providing specific tight binding to protein targets. In some cases and as opposed to antisense oligonucleotides, effects can be mediated against extracellular targets, thereby preventing a need for intracellular transportation. The first aptamer approved for use in man is a RNA-based molecule (Macugen, pegaptanib) that is administered locally (intravitreally) to treat age-related macular degeneration by targeting vascular endothelial growth factor. The most advanced aptamer in the cancer setting is AS1411, formerly known as AGRO100, which is being administered systemically in clinical trials. AS1411 is a 26-mer unmodified guanosine-rich oligonucleotide, which induces growth inhibition in vitro, and has shown activity against human tumor xenografts in vivo. The mechanism underlying its antiproliferative effects in cancer cells seems to involve initial binding to cell surface nucleolin and internalization, leading to an inhibition of DNA replication. In contrast to other unmodified oligonucleotides, AS1411 is relatively stable in serum-containing medium, probably as a result of the formation of dimers and a quartet structure. In a dose escalation phase I study in patients with advanced solid tumors, doses up to 10 mg/kg/d (using a four or seven continuous infusion regime) have been studied. Promising signs of activity have been reported (multiple cases of stable disease and one near complete response in a patient with renal cancer) in the absence of any significant adverse effects. Further trials are ongoing in renal and non-small cell lung cancers. In preclinical studies, additional aptamers have been described against several cancer targets, such as tenascin-C, the transcription factor signal transducer and activator of transcription 3, and antiapoptotic and Ku proteins.

Synthesis and antimelanoma activity of reversed amide analogues of N-acetyl-4-S-cysteaminylphenol.

The melanin biosynthetic pathway from tyrosine is a potential target for combating malignant melanoma. N-Acetyl-4-S-cysteaminylphenol 1 is a previously synthesized analogue of tyrosine that probably acts by this pathway. It interferes with cell growth and proliferation via selective oxidation in melanocytes to an oquinone that can alkylate cellular nucleophiles. We previously synthesized a range of analogues of the original lead compound 1 most of which displayed greater cytotoxicity than 1. Eighteen new analogues with the amide group reversed have now been synthesized and tested for antimelanoma activity. Most of these reverse amides showed greater cytotoxicity than N-acetyl-4-S-cysteaminylphenol towards five representative melanoma cell lines. The highest cytotoxicity was observed for the piperidine and hexamethyleneimine derivatives 7, 8, 12, 13, and 17 and the catechol 18. The most active compound, 7, had cytotoxicity comparable to cisplatin against the five melanoma cell lines. The moderate activity of 7 and 18 against SK-Mel-24 (non-tyrosinase containing) and an ovarian cell line suggests that interference with the melanin pathway may not be the only mode of action of these compounds. Assays of some of the compounds as substrates for tyrosinase showed that the catechol 18 was the best substrate and that the piperidine derivative 7 was the best substrate of the phenolic compounds synthesized.

Rat tumor response to the vascular-disrupting agent 5,6-dimethylxanthenone-4-acetic acid as measured by dynamic contrast-enhanced magnetic resonance imaging, plasma 5-hydroxyindoleacetic acid levels, and tumor necrosis.

The dose-dependent effects of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) on rat GH3 prolactinomas were investigated in vivo. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to assess tumor blood flow/permeability pretreatment and 24 hours posttreatment with 0, 100, 200, or 350 mg/kg DMXAA. DCE-MRI data were analyzed using K(trans) and the integrated area under the gadolinium time curve (IAUGC) as response biomarkers. High-performance liquid chromatography (HPLC) was used to determine the plasma concentration of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) following treatment to provide an index of increased vessel permeability and vascular damage. Finally, tumor necrosis was assessed by grading hematoxylin and eosin-stained sections cut from the same tumors investigated by MRI. Both tumor K(trans) and IAUGC were significantly reduced 24 hours posttreatment with 350 mg/kg DMXAA only, with no evidence of dose response. HPLC demonstrated a significant increase in plasma 5-HIAA 24 hours posttreatment with 200 and 350 mg/kg DMXAA. Histologic analysis revealed some evidence of tumor necrosis following treatment with 100 or 200 mg/kg DMXAA, reaching significance with 350 mg/kg DMXAA. The absence of any reduction in K(trans) or IAUGC following treatment with 200 mg/kg, despite a significant increase in 5-HIAA, raises concerns about the utility of established DCE-MRI biomarkers to assess tumor response to DMXAA.

Enhancement of aqueous solubility and stability employing a trans acetate axis in trans planar amine platinum compounds while maintaining the biological profile.

A general approach to solubilization and possible in vivo activation of the transplatinum geometry is presented. The synthesis and characterization of new water-soluble cytotoxic transplatinum compounds are described. Use of acetate ligands (and carboxylate ligands in general) in trans-[Pt(OAc)(2)(L)(L')] results in significantly enhanced aqueous solubility and chemical stability in comparison to the parent dichlorides. The new compounds are the first cytotoxic transplatinum compounds containing an N(2)O(2) donor set, similar to carboplatin and oxaliplatin.

Synthesis and antimelanoma activity of sterically congested tertiary amide analogues of N-acetyl-4-S-cysteaminylphenol.

Interference with the biosynthetic pathway to melanin may be a useful means for developing new chemotherapeutic drugs to combat malignant melanoma. N-Acetyl-4-S-cysteaminylphenol (1) is an analogue of tyrosine that is involved in the pathway to melanin. It is probably oxidized selectively in melanocytes to an o-quinone that can alkylate thiol groups on important cellular enzymes, resulting in interference with cell growth and proliferation. We previously synthesized a range of more lipophilic analogues of 1 by independently varying the acyl portion and introducing substitution alpha to the nitrogen. Most of the new compounds displayed greater cytotoxicity than the original lead compound 1. We also made a series of tertiary amides that again showed higher cytotoxicity than 1. In this work three new acetamides and two new cyclohexanecarboxamides containing 4-S-cysteaminylphenol were prepared incorporating both substitution alpha to the nitrogen and different substituents on the nitrogen of the amide in each compound to increase lipophilicity and to reduce further the possibility of hydrolysis of the amides. Most of the new tertiary amides showed greater cytotoxicity towards five representative melanoma cell lines than the parent secondary amide. The highest cytotoxicity against these five cell lines with IC50 values of 1-15 nicroM, comparable to cisplatin, was observed for N-[2[(4-hydroxyphenyl)thio]-1,1-dimethylethyl]-N-methylcyclohexanecarboxamide (8c). The IC50 values of 14.5 and 5.4 microM for this compound against SK-Mel-24 (not containing tyrosinase) and an ovarian cell line, respectively, suggest that interference with the melanin pathway may not be the only mode of action of this new compound. The cyclohexanecarboxamides were better substrates for mushroom tyrosinase (EC 1.14.18.1) than the acetamides.

In vitro and in vivo pharmacokinetic-pharmacodynamic relationships for the trisubstituted aminopurine cyclin-dependent kinase inhibitors olomoucine, bohemine and CYC202.

PURPOSE: To investigate pharmacokinetic-pharmacodynamic relationships for the trisubstituted aminopurine cyclin-dependent kinase inhibitors olomoucine, bohemine, and CYC202 (R-roscovitine; seliciclib) in the HCT116 human colon carcinoma model. EXPERIMENTAL DESIGN: The in vitro activity of the agents was determined in a human tumor panel using the sulforhodamine B assay. The concentration and time dependence was established in HCT116 cells. Molecular biomarkers, including RB phosphorylation and cyclin expression, were assessed by Western blotting. Pharmacokinetic properties were characterized in mice following analysis by liquid chromatography-tandem mass spectrometry. Based on these studies, a dosing regimen was developed for CYC202 that allowed therapeutic exposures in the HCT116 tumor xenograft. RESULTS: The antitumor potency of the agents in vitro was in the order olomoucine (IC50, 56 micromol/L) < bohemine (IC50, 27 micromol/L) < CYC202 (IC50, 15 micromol/L), corresponding to their activities as cyclin-dependent kinase inhibitors. Antitumor activity increased with exposure time up to 16 hours. The agents caused inhibition of RB and RNA polymerase II phosphorylation and depletion of cyclins. They exhibited relatively rapid clearance following administration to mice. CYC202 displayed the slowest clearance from plasma and the highest tumor uptake, with oral bioavailability of 86%. Oral dosing of CYC202 gave active concentrations in the tumor, modulation of pharmacodynamic markers, and inhibition of tumor growth. CONCLUSIONS: CYC202 showed therapeutic activity on human cancer cell lines in vitro and on xenografts. Pharmacodynamic markers are altered in vitro and in vivo, consistent with the inhibition of cyclin-dependent kinases. Such markers may be potentially useful in the clinical development of CYC202 and other cyclin-dependent kinase inhibitors.

Emerging drugs for ovarian cancer.

Because most patients presenting with advanced ovarian cancer are not curable by surgery alone, chemotherapy represents an essential component of treatment. The disease may be considered as chemosensitive, as in around three-quarters of patients major (complete) responses are seen to initial treatment with the platinum-containing drugs cisplatin and carboplatin either used alone or in combination with the taxane, paclitaxel. However, only 15-20% of patients experience long-term remission as tumours often become resistant. The probability of achieving a second response depends on the duration of remission after first-line therapy: if this is < 6 months (considered as platinum resistant) second responses are uncommon and usually short-lived; if this is > 6, and especially if > 12 months (platinum sensitive), responses may be seen in about a quarter of patients, to the same drugs as used first line or to drugs such as pegylated liposomal doxorubicin, topotecan and hexamethylmelamine (all three are approved in this setting by the FDA). Gemcitabine, oral etoposide, docetaxel and oxaliplatin also show some activity either in sequential addition to existing approved of first-line therapy (as with gemcitabine) or as second-line therapy. However, there is an urgent unmet clinical need for new drugs capable of prolonging survival either by increasing long-term remission rates and/or duration as first-line treatment or to improve on outcomes of second-line treatment. Strategies currently being exploited in clinical trials include attempts to deliver more killing selectively to tumours (e.g., intraperitoneal administration of cisplatin or radiolabelled monoclonal antibodies), agents designed to target drug resistance mechanisms (e.g., TLK-286 activated by glutathione transferase), agents targeting proteins/receptors shown to be selectively expressed in the disease (e.g., monoclonal antibodies recognising CA-125 or HER1; small molecules targeting HER1 such as gefitinib) and disrupting established tumour vasculature (e.g., 5,6-dimethyl xanthenone 4-acetic acid). At the pre-clinical level, agents being developed to target the phosphatidylinositol 3 kinase/AKT/mTOR pathway, and K-Ras inhibitors, may offer efficacy in the future.

Tumor dose response to the vascular disrupting agent, 5,6-dimethylxanthenone-4-acetic acid, using in vivo magnetic resonance spectroscopy.

PURPOSE: To use (31)P and (1)H magnetic resonance spectroscopy (MRS) to assess changes in tumor metabolic profile in vivo in response to 5,6-dimethylxanthenone-4-acetic acid (DMXAA) with a view to identifying biomarkers associated with tumor dose response. EXPERIMENTAL DESIGN: In vivo (31)P and (1)H MRS measurements of (a) tumor bioenergetics [beta-nucleoside triphosphate/inorganic phosphate (beta-NTP/Pi)], (b) the membrane-associated phosphodiesters and phosphomonoesters (PDE/PME), (c) choline (mmol/L), and (d) lactate/water ratio were made on murine HT29 colon carcinoma xenografts pretreatment and 6 or 24 hours posttreatment with increasing doses of DMXAA. Following in vivo MRS, the tumors were excised and used for high-resolution (31)P and (1)H MRS of extracts to provide validation of the in vivo MRS data, histologic analysis of necrosis, and high-performance liquid chromatography. RESULTS: Both beta-NTP/Pi and PDE/PME decreased in a dose-dependent manner 6 hours posttreatment with DMXAA, with significant decreases in beta-NTP/Pi with 15 mg/kg (P < 0.001) and 21 mg/kg (P < 0.01). A significant decrease in total choline in vivo was found 24 hours posttreatment with 21 mg/kg DMXAA (P < 0.05); this was associated with a significant reduction in the concentration of the membrane degradation products glycerophosphoethanolamine and glycerophosphocholine measured in tissue extracts (P < 0.05). CONCLUSIONS: The reduction in tumor energetics and membrane turnover is consistent with the vascular-disrupting activity of DMXAA. (31)P MRS revealed tumor response to DMXAA at doses below the maximum tolerated dose for mice. Both (31)P and (1)H MRS provide biomarkers of tumor response to DMXAA that could be used in clinical trials.

Overcoming the immortality of tumour cells by telomere and telomerase based cancer therapeutics--current status and future prospects.

A key property of malignant tumours is their immortality or limitless replicative potential. Cell replication is associated with the maintenance of telomeres and in the great majority of cases, through the reactivation of the reverse transcriptase telomerase. Targeting the telomere/telomerase machinery offers a novel and potentially broad-spectrum anticancer therapeutic strategy since telomerase is constitutively overexpressed in the vast majority of human cancers. Telomeres are also critically short in most tumours compared to normal tissues. Strategies that exploit these differences include the direct targeting of components of telomerase: the protein component hTERT or RNA component hTR. Examples of such agents include the small molecule hTERT inhibitor BIBR1532 and GRN163L, a thio-phosphoramidate oligonucleotide targeting the template region of hTR as a "template antagonist". Anti-tumour effects have been observed in both cell lines and, especially for GRN163L, in xenografted human tumours in mice. Effects, however, are largely dependent upon initial telomere length, which can result in a substantial lag before antitumour activity is observed in tumours possessing relatively long telomeres. An alternative approach is to target the telomere itself (Telomere Targeting Agents, TTAs). Several classes of small molecules have been described that induce the G-rich single-stranded overhang of telomeric DNA to fold into 4-stranded G-quadruplex structures. Such folding is incompatible with telomerase function and may induce rapid telomere uncapping. These molecules have shown potent telomerase inhibition in nanomolar concentrations in vitro and the rapid induction of senescence in cancer cells. The trisubstituted acridine based TTA, BRACO19, has demonstrated single agent activity against human tumour xenografts with anti-tumour effects apparent from only 7 days of treatment. In the near future, it is expected that lead examples from both the direct telomerase targeted agents (e.g., GRN163L) and from the distinct class of those targeting telomeres (e.g., AS1410 based on BRACO19) will enter Phase I clinical trial where clinical benefit from this class of novel drugs will be determined.

Mechanisms of tumor vascular shutdown induced by 5,6-dimethylxanthenone-4-acetic acid (DMXAA): Increased tumor vascular permeability.

The novel vascular targeting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) has completed phase 1 clinical trial and has shown tumor antivascular activity in both mice and humans. We have investigated its ability to change tumor vascular permeability, relating it to tumor vascular perfusion and other responses. The murine colon 38 adenocarcinoma was grown in C57Bl wild-type mice and mice lacking expression of either tumor necrosis factor receptor-1 (TNFR1(-/-)) or TNF (TNF-/-). Tumor vascular permeability, as measured by extravasation of albumin-Evans Blue complexes 4 hr after DMXAA treatment, was significantly increased in tumor tissue in C57Bl, TNFR1-/- and TNF-/- mice but not in normal (skin) tissue. Significant linear relationships were found between increased tumor vascular permeability, decreased functioning tumor blood vessels (measured by Hoechst 33342 staining at 4 hr), increased plasma 5-hydroxyindole-3-acetic acid concentrations (as a measure of serotonin release by platelets) and the degree of induced tumor hemorrhagic necrosis. The results support the hypothesis that DMXAA increases tumor vascular permeability both directly and through the induction of other vasoactive mediators, including TNF. DMXAA might be useful clinically to potentiate the vascular permeability of other anticancer modalities such as cytotoxic drugs, antibodies, drug conjugates and gene therapy.

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.

A G-quadruplex telomere targeting agent produces p16-associated senescence and chromosomal fusions in human prostate cancer cells.

The trisubstituted acridine derivative BRACO-19 has been designed to interact with and stabilize the quadruplex DNA structures that can be formed by folding of the single-stranded repeats at the 3' end of human telomeres. We suggest that the BRACO-19 complex inhibits the catalytic function of telomerase in human cancer cells and also destabilizes the telomerase-telomere capping complex so that cells enter senescence. Here, we present evidence showing that the inhibition of cell growth caused by BRACO-19 in DU145 prostate cancer cells occurs more rapidly than would be expected solely by the inhibition of the catalytic function of telomerase, and that senescence is accompanied by an initial up-regulation of the cyclin-dependent kinase inhibitor p21, with subsequent increases in p16(INK4a) expression. We also show that treatment with BRACO-19 causes extensive end-to-end chromosomal fusions, consistent with telomere uncapping.

SJG-136 (NSC 694501), a novel rationally designed DNA minor groove interstrand cross-linking agent with potent and broad spectrum antitumor activity: part 1: cellular pharmacology, in vitro and initial in vivo antitumor activity.

SJG-136 (NSC 694501) is a rationally designed pyrrolobenzodiazepine dimer that binds in the minor groove of DNA. It spans 6 bp with a preference for binding to purine-GATC-pyrimidine sequences. The agent has potent activity in the National Cancer Institute (NCI) anticancer drug screen with 50% net growth inhibition conferred by 0.14 to 320 nmol/L (7.4 nmol/L mean). Sensitive cell lines exhibit total growth inhibition and 50% lethality after treatment with as little as 0.83 and 7.1 nmol/L SJG-136, respectively. COMPARE and molecular target analysis of SJG-136 data versus that of >60,000 compounds tested in the NCI 60 cell line screen shows that, although the agent has similarity to other DNA binding agents, the pattern of activity for SJG-136 does not fit within the clusters of any known agents, suggesting that SJG-136 possesses a distinct mechanism of action. Testing in the NCI standard hollow fiber assay produced prominent growth inhibition in 20 of 24 i.p. and 7 of 24 s.c. test combinations with 5 of 12 cell lines exhibiting cell kill. In addition, SJG-136 produced antitumor activity in mice bearing CH1 and CH1cisR xenografts, a cisplatin-resistant human ovarian tumor model, and also in mice bearing LS174T xenografts, a human colon tumor model. SJG-136 produces DNA interstrand cross-links between two N-2 guanine positions on opposite strands and separated by 2 bp. In human tumor cell lines, the cross-links form rapidly and persist compared with those produced by conventional cross-linking agents such as nitrogen mustards. In mice bearing the LS174T human colon xenograft, DNA interstrand cross-links can be detected in tumor cells using a modification of the single cell gel electrophoresis (comet) assay after administration of a therapeutic dose. Cross-links in the tumor increase with dose and are clearly detectable at 1 hour after i.v. administration. The level of cross-linking persists over a 24-hour period in this tumor in contrast to cross-links produced by conventional cross-linking agents observed over the same time period.

Synthesis and biological evaluation of novel chloroethylaminoanthraquinones with potent cytotoxic activity against cisplatin-resistant tumor cells.

Novel 1- and 1,4-substituted chloroethylaminoanthraquinones with DNA binding and alkylating properties along with their respective hydroxyethylaminoanthraquinone intermediates were synthesized. Selected chloroethylaminoanthraquinones were shown to cross-link DNA and alkylate guanines (at low nM concentration) with a preference for reaction sites containing 5'-PyG. A compound (Alchemix) with the bis-chloroethyl functionality confined to one side chain alkylated but did not cross-link DNA. All the 1,4-disubstituted chloroethylaminoanthraquinones were potently cytotoxic (nM IC(50)s) against cisplatin-resistant ovarian cancer cell lines.

Trisubstituted acridine derivatives as potent and selective telomerase inhibitors.

The synthesis and evaluation for telomerase-inhibitory and quadruplex DNA binding properties of three related series of rationally designed trisubstituted acridine derivatives are described. These are substituted on the acridine ring at the 2,6,9; 2,7,9; and 3,6,9 positions. The ability of several of the most potent compounds to interact with and stabilize an intramolecular G-quadruplex DNA was evaluated by surface plasmon resonance methods, and affinities were found to correlate with potency in a telomerase assay. The interactions of a number of compounds with a parallel quadruplex DNA structure were simulated by molecular modeling methods. The calculated interaction energies were compared with telomerase activity and showed generally consistent correlations between quadruplex affinity and telomerase inhibition. These data support a model for the action of these compounds that involves the stabilization of intermediate quadruplex structures that inhibit the elongation of telomeric DNA by telomerase in tumor cells.