title: 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.
abstract: 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.
authors.affiliation: Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Cookson
authors.forename: Fangping
authors.initials: F
authors.lastname: Dai
authors.forename: Victoria
authors.initials: V
authors.lastname: Smith
authors.forename: Robert A
authors.initials: RA
authors.lastname: Heald
authors.forename: Charles A
authors.initials: CA
authors.lastname: Laughton
authors.forename: Malcolm F G
authors.initials: MF
authors.lastname: Stevens
authors.forename: Angelika M
authors.initials: AM
authors.lastname: Burger
mesh_terms: D000166:Acridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004247:DNA; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors*; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054856:G-Quadruplexes; D006801:Humans; D010599:Pharmacokinetics; D019098:Telomerase / Q000037:antagonists & inhibitors*; D016615:Telomere / Q000648:ultrastructure*
chemical_list: C438609:3,11-difluoro-6,8,13-trimethyl-8H-quino(4,3,2-kl)acridinium; D000166:Acridines; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004247:DNA; D019098:Telomerase