Abstract C76: Oxazole-containing macrocyles as selective G-quadruplex stabilizers
Authors: LaVoie Edmond J. , Kim Young Ah , Satyanarayana Mavurapu , Rzuczek Suzanna G. , Pilch Daniel S. , Tsai Yuan-Chin , Qi Haiyan , Lin Chao-Pao , Liu Angela , Liu Leroy F. , Rice Joseph E. 
Published: June 2012

Guanine-rich nucleic acid sequences are known to adopt G-quadruplex structures that are stabilized by the formation of guanine tetrads. Compounds that can stabilize G-quadruplex are known to exhibit cytotoxicity against tumor cells in culture and antitumor activity in mice with human tumor xenografts. Telomestatin, a naturally occurring macrocycle isolated from Streptomyces anulatus, is among the more specific G-quadruplex stabilizers, binding with high specificity to G-quadruplex DNA with no detectable binding to either duplex or single-stranded DNA. Telomestatin has been shown to induce apoptosis of tumor cells in culture and exhibit antitumor activity in mice. The discovery of telomestatin has prompted further studies of other macrocyclic polyoxazoles that can selectively stabilize G-quadruplex DNA and RNA. Recently the synthesis of the macrocyclic hexaoxazole HXDV was reported by our laboratory. HXDV is a 24-membered macrocycle that stabilizes G-quadruplexes. Despite its less complex structure, HXDV is extraordinarily selective at stabilizing G-quadruplex versus duplex DNA, and is at least as potent as telomestatin as a cytotoxic agent. It has been determined that HXDV binds to a 24mer model human telomeric G-quadruplex with a stoichiometry of 2:1 via a terminal capping mode of interaction. Surprisingly, HXDV was found to exhibit anti-proliferative activity against many tumor cells independently of their telomerase status and induces strong apoptosis within 16 hours of treatment. HXDV also inhibited the progression of the cell cycle, resulting in accumulation of cells at the G2/M phase of the cell cycle. Interestingly, these studies revealed that cells were arrested at the M, rather than the G phase of the cell cycle. Unlike tubulin inhibitors, which also arrest cells at M phase, HXDV reduces the expression level of the key M phase regulator Aurora A kinase. In the aggregate, these data suggest that HXDV is a novel M phase blocker, with a possible mode of action distinct from tubulin inhibitors. Both telomestatin and HXDV have limited aqueous solubility. Replacement of one or both isopropyl groups of HXDV with an aminoalkyl side chain alters its phyiscochemical properties and enhances aqueous solubility. We also report herein the synthesis, biophysical evaluation of G-quadruplex stabilization and selectivity, and cytotoxicity data for more than twenty 24-membered macrocyclic polyoxazoles that have either one or two alkylamino side chains varying in length from 2–4 methylene units. One of these derivatives exhibits significant antitumor activity with IC50 values that range from 25 to 70 nM towards human tumor cells. As the citrate salt, the solubility of some of these alkylamino derivatives increased dramatically permitting in vivo studies to evaluation their toxicity and maximum tolerated dose in mice.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C76.