Bilateral internal carotid artery occlusion with compensatory perfusion in a HIV-infected patient.

SUMMARY: HIV infection occlusive arteriopathies may result in neurological symptoms. We report a case of bilateral complete occlusion of the extracranial portions of the internal carotid arteries in a HIV+ve patient who presented with a syncopal episode due to intraventricular haemorrhage. Compensatory blood flow from the posterior cerebral circulation via the circle of Willis resulted in small telangiectatic vessels arising from the posterior cerebral circulation which probably accounted for this rare haemorrhagic complication of an occlusive arteriopathy.

Potent inhibition of telomerase by small-molecule pentacyclic acridines capable of interacting with G-quadruplexes.

A novel pentacyclic acridine, 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate (RHPS4), has been identified as a potent inhibitor of telomerase in the cell-free telomeric repeat amplification protocol (TRAP). Modeling and biophysical studies suggest that RHPS4 inhibits telomerase through stabilization of four-stranded G-quadruplex structures formed by single-stranded telomeric DNA. In contrast to G-quadruplex interactive telomerase inhibitors described previously, RHPS4 inhibited telomerase at submicromolar levels (50% inhibition in the TRAP assay at 0.33 +/- 0.13 microM). Moreover, RHPS4 exhibited a wide differential between this potent inhibition of telomerase and acute cellular cytotoxicity (mean IC(50) value of 7.02 microM in 4-day growth inhibition assay). RHPS4, when added to 21NT breast cancer cells at nonacute cytotoxic concentrations (200 nM) every 3 to 4 days, induced a marked cessation in cell growth after 15 days. Similar effects were observed using another cell line possessing relatively short telomeres, A431 human vulval carcinoma cells, but not in a human ovarian carcinoma cell line (SKOV-3) possessing relatively long telomeres. In 21NT cells, growth cessation was accompanied by an increase in cells in the G(2)/M phase of the cell cycle, a reduction in cellular telomerase activity, and a lower expression of the hTERT gene. These effects occurred in the absence of a detectable reduction in telomere length as measured by slot blotting. RHPS4 also induced a cessation of growth of GM847 cells that maintain telomeres by a nontelomerase alternative mechanism for lengthening telomeres (ALT) after 15 days. RHPS4 represents a promising G-quadruplex interactive small molecule that is a potent cell-free inhibitor of human telomerase and induces growth inhibitory effects in human tumor cell lines after prolonged (2-week) exposure to nonacute cytotoxic drug concentrations.

A novel inhibitor of human telomerase derived from 10H-indolo[3,2-b]quinoline.

The bis-dimethylaminoethyl derivative of quindoline (10H-indolo[3,2-b]quinoline), an alkaloid from the West African shrub Cryptolepis sanguinolenta, has been synthesised. This has been shown to have modest cytotoxicity, as well as inhibitory activity against the telomerase enzyme. It is hypothesised that the latter activity is due to stabilisation of an intermediate guanine-quadruplex complex, in accordance with computer modelling.

Molecular modeling studies on G-quadruplex complexes of telomerase inhibitors: structure-activity relationships.

Inhibition of the ability of the enzyme telomerase to add telomeric repeats to the end of chromosomes is a novel target for potential anticancer therapy. This paper examines the hypothesis that compounds possessing a planar aromatic chromophore inhibit telomerase via stabilization of, and binding to, a folded guanine quadruplex structure. Two series of telomerase inhibitors have been designed based on the 2,6-disubstituted amidoanthracene-9,10-dione and 3,6-disubstituted acridine chromophores in order to investigate structure-activity relationships between biological activity and substituent group size. The relative binding energies between these compounds and the folded human telomere DNA quadruplex were determined using molecular simulation methods, involving explicitly solvated structures. The results obtained are in excellent agreement with the biological activity as measured in vitro using a modified TRAP assay and in general agreement with the ranking order of binding enthalpies found in isothermal titration calorimetry studies. This broad agreement provides strong support for the hypothesis that guanine quadruplexes are the primary target for telomerase inhibitors with extended planar chromophores.

Human telomerase inhibition by substituted acridine derivatives.

A series of 3,6-disubstituted acridine derivatives have been rationally designed as telomerase inhibitors. They have been designed on the basis that inhibition of telomerase occurs by stabilising G-quadruplex structures formed by the folding of telomeric DNA. The most potent inhibitors have IC50 values against telomerase of between 1.3 and 8 microM, comparable to their cytotoxicity in ovarian cancer cell lines.

2,7-Disubstituted amidofluorenone derivatives as inhibitors of human telomerase.

Telomerase is a major new target for the rational design of novel anticancer agents. We have previously identified anthraquinone-based molecules capable of inhibiting telomerase by stabilizing G-quadruplex structures formed by the folding of telomeric DNA. In the present study we describe the synthesis and biological evaluation of a series of analogous fluorenone-based compounds with the specific aims of, first, determining if the anthraquinone chromophore is a prerequisite for activity and, second, whether the conventional cytotoxicity inherent to anthraquinone-based molecules may be reduced by rational design. This fluorenone series of compounds exhibits a broad range of telomerase inhibitory activity, with the most potent inhibitors displaying levels of activity (8-12 microM) comparable with other classes of G-quadruplex-interactive agents. Comparisons with analogous anthraquinone-based compounds reveal a general reduction in the level of cellular cytotoxicity. Molecular modeling techniques have been used to compare the interaction of fluorenone- and analogous anthraquinone-based inhibitors with a human G-quadruplex structure and to rationalize their observed biological activities.

Design, synthesis and evaluation of human telomerase inhibitors based upon a tetracyclic structural motif.

There is currently significant interest in the development of inhibitors of human telomerase for the treatment of cancer. We describe here the design and synthesis of a new class of mono-substituted small-molecule inhibitors of human telomerase based upon a tetracyclic structural motif. In contrast to the structurally related molecule 9-hydroxyellipticine, recently shown to inhibit telomerase activity in cell cultures but found to be inactive in a cell-free system, we demonstrate direct inhibition of the telomerase enzyme by the tetracyclic compounds in a modified cell-free TRAP assay. The most potent compounds exhibit activity in the low micromolar range and are thus comparable with some of the more active small-molecule telomerase inhibitors based on planar aromatic chromophores, previously described by ourselves and others. These compounds may represent useful leads for the development of more potent inhibitors of human telomerase.

Human telomerase inhibition by regioisomeric disubstituted amidoanthracene-9,10-diones.

Telomerase is an attractive target for the design of new anticancer drugs. We have previously described a series of 1,4- and 2, 6-difunctionalized amidoanthracene-9,10-diones that inhibit human telomerase via stabilization of telomeric G-quadruplex structures. The present study details the preparation of three further, distinct series of regioisomeric difunctionalized amidoanthracene-9,10-diones substituted at the 1,5-, 1,8-, and 2,7-positions, respectively. Their in vitro cytotoxicity and Taq DNA polymerase and human telomerase inhibition properties are reported and compared with those of their 1,4- and 2,6-isomers. Potent telomerase inhibition (telIC50 values 1.3-17.3 microM) is exhibited within each isomeric series. In addition, biophysical and molecular modeling studies have been conducted to examine binding to the target G-quadruplex structure formed by the folding of telomeric DNA. These studies indicate that the isomeric diamidoanthracene-9,10-diones bind to the human telomeric G-quadruplex structure with a stoichiometry of 1:1. Plausible G-quadruplex-ligand complexes have been identified for each isomeric family, with three distinct modes of intercalative binding being proposed. The exact mode of intercalative binding is dictated by the positional placement of substituent side chains. Furthermore, in contrast to previous studies directed toward triplex DNA, it is evident that stringent control over positional attachment of substituents is not a necessity for effective telomerase inhibition.

1,4- and 2,6-disubstituted amidoanthracene-9,10-dione derivatives as inhibitors of human telomerase.

A number of 1,4- and 2,6-difunctionalized amidoanthracene-9, 10-diones have been prepared. We have examined their in vitro cytotoxicity in several tumor cell lines and their ability to inhibit the telomere-addition function of the human telomerase enzyme together with their inhibition of the Taq polymerase enzyme. Compounds with -(CH2)2- side chains terminating in basic groups such as piperidine show inhibition of telomerase at telIC50 levels of 4-11 microM. These are thus among the most potent nonnucleoside telomerase inhibitors reported to date. Cytotoxicity levels in human tumor cell lines were at comparable levels for several compounds. Implications for amidoanthracene-9,10-dione telomerase inhibitors as potential anticancer agents are discussed.