Antitumor polycyclic acridines. 20. Search for DNA quadruplex binding selectivity in a series of 8,13-dimethylquino[4,3,2-kl]acridinium salts: telomere-targeted agents.

The growth-inhibitory activities of an extensive series of quaternized quino[4,3,2- kl]acridinium salts against tumor cell lines in vitro have been measured and their biological properties interpreted in the light of differential binding to different DNA isoforms. Selectivity for quadruplex DNA binding and stabilization by compounds were explored through an array of methods: UV absorption and fluorescence emission spectroscopy, surface plasmon resonance, and competition dialysis. Quadruplex DNA interaction was further characterized through FRET and DNA polymerase arrest assays. Telomerase inhibition, inferred from the TRAP assay, is attributed to quadruplex stabilization, supported by the strong correlation (R(2) = 0.81) across the series between quadruplex DNA binding affinity and TRAP inhibition potency. Growth inhibition potency in the NCI60 human tumor cell line panel is more marked in compounds with greater DNA duplex binding affinity (R(2) = 0.82). Quantification of relative quadruplex and duplex binding affinity constants puts some of these ligands among the most selective quadruplex DNA interactive agents reported to date.

Antitumor polycyclic acridines. 17. Synthesis and pharmaceutical profiles of pentacyclic acridinium salts designed to destabilize telomeric integrity.

Palladium(0)-mediated Suzuki-Miyaura and Heck transformations have been exploited to provide examples of 8-methylquino[4,3,2-kl]acridines and 8,13-dimethylquino[4,3,2-kl]acridinium iodides bearing bulky saturated (3-acetoxy)propyl or (E)-3-(morpholin-4-yl)-3-oxopropenyl substituents variously in the 3-, 6-, or 10-positions of the pentacyclic nucleus. The pharmacological/pharmaceutical properties of four compounds (4, RHPS4), (5, IH383), (6, RHPS16), and (17, RHPS19) were measured to assess their clinical potential as DNA G-quadruplex-stabilizing/telomerase inhibitory agents. The following properties were measured: stability in tissue culture media in the presence of A549 lung and MCF-7 breast tumor cells, metabolic stability when incubated with rat liver microsomes, and rate of uptake and subcellular location in A549 and MCF-7 cells. Compound 17 was unstable in tissue culture media, failed to achieve nuclear access, and was excluded from further consideration. Of the other agents, 4 exhibited the most favorable pharmaceutical profile: the agent has appropriate stability in the presence of tumor cells and rat liver microsomes and achieves rapid ingress into cell nuclei where the putative molecular target is located.

Pharmacodynamics of the G-quadruplex-stabilizing telomerase inhibitor 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate (RHPS4) in vitro: activity in human tumor cells correlates with telomere length and can be enhanced, or antagonized, with cytotoxic agents.

Telomeric integrity is required to maintain the replicative ability of cancer cells and is a target for the G-quadruplex-stabilizing drug 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate (RHPS4). We report a senescent-like growth arrest in MCF-7 breast cancer cells, within 14 to 17 days, and a reduction in telomere length (from 5.2 kilobases (kb) to 4.7 and 4.3 kb after 17 days of treatment at 0.5 and 1 microM, respectively). These effects occurred at noncytotoxic drug concentrations (doses < 1 microM over a 14-day exposure) compatible with long-term drug dosing. The telomere length of cancer cells influences their sensitivity to growth inhibition by RHPS4: mutant (mt) human telomerase reverse transcriptase (hTERT)-expressing MCF-7 cells [short telomere restriction fragment (TRF) length, 1.9 kb; IC50, 0.2 microM] were 10 times more sensitive to RHPS4 compared with wild-type (wt) hTERT-expressing, vector-transfected control cells (longer TRF-length 5.2 kb; IC50 2 microM) in the 5 day SRB assay. This relationship was corroborated in a panel of 36 human tumor xenografts grown in vitro showing a positive correlation between telomere length and growth inhibitory potency of RHPS4 (15-day clonogenic assay, r = 0.75). These observations are consistent with loss of the protective capping status of telomeres mediated by RHPS4 G-quadruplex-stabilization, thus leading to greater susceptibility of cells with shorter telomeres. In combination studies, paclitaxel (Taxol), doxorubicin (Adriamycin), and the experimental therapeutic agent 17-(allylamino)-17-demethoxygeldanamycin, which inhibits the 90-kDa heat shock protein, conferred enhanced sensitivity in RHPS4 treated MCF-7 cells, whereas the DNA-interactive temozolomide and cisplatin antagonized the action of RHPS4. Our results support the combined use of certain classes of cytotoxic anticancer agents with RHPS4 to enhance potential clinical benefit.