A New Strategy for Detection and Development of Tractable Telomerase Inhibitors

Abstract

Despite intense academic and industrial efforts and innumerable in vitro and cell studies, no small-molecule telomerase inhibitors have emerged as drugs. Insufficient understanding of enzyme structure and mechanisms of interdiction coupled with the substantial complexities presented by its dimeric composition have stalled all progress toward small-molecule therapeutics. Here we challenge the assumption that human telomerase provides the best platform for inhibitor development by probing a monomeric Tetrahymena telomerase with six tool compounds. We find BIBR-1532 (2) and MST-312 (5) inhibit only human telomerase, whereas β-R (1), THyF (3), TMPyP4 (6), and EGCG (4) inhibit both enzymes. Our study demonstrates that some small-molecule scaffolds can be easily surveyed with in vitro studies using Tetrahymena telomerase, a finding that could lead to more tractable inhibitors with a greater potential for development given the more precise insights that can be gleaned from this more easily expressed and assayed monomeric enzyme.

Microenvironmental Regulation of Telomerase Isoforms in Human Embryonic Stem Cells

“…The species differences in the lack of TERT may be attributed to differing naive and primed pluripotent states; however, previous studies have demonstrated that human and mice cells differ in their telomere signaling pathways [90]. Although the specific mechanism(s) of telomerase inhibition for the synthetic tea catechin (TI-IX) is not known, treatment of cells with TI-IX results in both acute telomere uncappingmediated cell cycle arrest and long-term telomere erosion [91] that may be mediated by its effects on DNA substrate binding of telomerase [56]. However, many catechols do exhibit antioxidant and/or oxidant properties [92], so TI-IX effects through alteration in cellular redox status cannot be ruled out in our study.…”

“…Telomerase inhibitor IX (TI-IX; Calbiochem) is a cellpermeable, bis-catechol containing m-phenylenediamide compound (MST-312) that inhibits telomerase activity [55,56]. Telomerase inhibitor III (TI-III; Calbiochem) is a cell-permeable, hexameric phosphorothioate oligonucleotide (PS-ODN) compound that acts as a telomere mimic resulting in inhibition of telomerase activity [57].…”

“…To build on our data that demonstrate that TERT protein abundance is significantly altered independent of telomerase activity in hESCs grown under different O 2 microenvironments, we investigated the potential for additional role(s) of telomerase in hESCs. To undertake this, we utilized the small-molecule telomerase inhibitors TI-IX and TI-III that have different modes of telomerase inhibition [55][56][57].…”

“…Preliminary experimentation and literature sourced concentrations previously used on human cells that effectively inhibited telomerase activity [55][56][57] indicated that TI-IX and TI-III inhibitors were most effective at nontoxic doses of 20 and 5 mM, respectively, in hESCs cultured in high-and low-O 2 conditions (Figs. 4B and 5B and Supplementary Figs.…”

Telomerase Inhibition Studies of Novel Spiroketal-Containing Rubromycin Derivatives

“…Recent studies by the Pettus group has provided further mechanistic insight into the role of b-rubromycin in telomerase inhibition and identified the spiroketal scaffold to be the best lead inhibitor. [8] Biological assay results for the parent compound, g-rubromycin together with our synthetic analogues are reported herein.…”