ABSTRACT
A recent approach in anticancer chemotherapy envisages telomerase as a potentially useful target. An attractive strategy deals with the development of compounds able to stabilize telomeric DNA in the G-quadruplex folded structure and, among them, a prominent position is found in the perylenes. With the aim to further investigate the role of drug structure, in view of possible pharmaceutical applications, we synthesized a series of compounds related to PIPER, a well-known perylene-based telomerase inhibitor. We modified the number of condensed aromatic rings and introduced different side chains to modulate drug protonation state and extent of self-aggregation. Effective telomerase inhibition was induced by heptacyclic analogues only, some showing a remarkably wide selectivity index with reference to inhibition of Taq polymerase. G-quadruplex stabilization was monitored by circular dichroism and melting experiments. Cell cytotoxicity measurements indicated a poor short-term cell killing ability for the best G-quartet binders. Besides the presence of a planar seven-condensed ring system, the introduction of a cyclic amine in the side chains critically affects the selectivity window.
Subject(s)
Antineoplastic Agents/pharmacology , DNA/drug effects , Enzyme Inhibitors/pharmacology , Perylene/analogs & derivatives , Perylene/pharmacology , Telomerase/antagonists & inhibitors , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/chemistry , Cell Line, Tumor , Cell Proliferation/drug effects , Circular Dichroism , DNA/chemistry , Drug Screening Assays, Antitumor , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/chemistry , Humans , Molecular Structure , Perylene/chemical synthesis , Sensitivity and Specificity , Stereoisomerism , Structure-Activity Relationship , Taq Polymerase/antagonists & inhibitorsABSTRACT
The anthrapyrazoles have entered clinical trials and show significant activity against breast cancer. However, these drugs are cardiotoxic and ineffective in multidrug-resistant (MDR) tumor cells. We have reported previously on the synthesis and antitumor characteristics of the 9-aza-anthrapyrazoles and their lack of cardiotoxicity; unfortunately, the leading candidates are cross-resistant in MDR-expressing cells. The results also indicated that the side arm structures of 9-aza-anthrapyrazole play a critical role in determining the drug resistance in MDR-expressing cells-only compounds that have a tertiary amine on both side arms are not cross-resistant. To further elucidate the biochemical and pharmacological impact of the side arm structures, one of the 9-aza-anthrapyrazole compounds, BBR 3422 [2-(2-aminoethyl)-5-(2-methylaminoethyl)indazolo[4,3-g,h]isoquinoline-6(2H)-one], was selected to be photolabeled with N-hydroxysuccinimidyl-4-azidosalicylic acid (NHS-ASA). In comparison to the parental compound, the photolabeled BBR 3422 was not as cytotoxic or DNA active, but it competed better than the parental compound against azidopine on P-glycoprotein labeling. In addition, confocal microscopic studies showed that BBR 3422 was clustered mainly in the cell nucleus, but its photolabeled analogue was located in the cytoplasm of the human breast cancer cell line MCF-7. Only a trace amount of both compounds was detected in the doxorubicin-derived resistant cell line MCF-7/ADR. The treatment of MCF-7/ADR cells with verapamil increased the intracellular amounts of both compounds.
