Induction of senescence in cancer cells by the G‐quadruplex stabilizer, BMVC4, is independent of its telomerase inhibitory activity

Abstract

BACKGROUND AND PURPOSETelomerase is the enzyme responsible for extending G-strand telomeric DNA and represents a promising target for treatment of neoplasia. Inhibition of telomerase can be achieved by stabilization of G-quadruplex DNA structures. Here, we characterize the cellular effects of a novel G-quadruplex stabilizing compound, 3,6-bis(4-methyl-2-vinylpyrazinium iodine) carbazole (BMVC4). EXPERIMENTAL APPROACHThe cellular effects of BMVC4 were characterized in both telomerase-positive and alternative lengthening of telomeres (ALT) cancer cells. The molecular mechanism of how BMVC4 induced senescence is also addressed. KEY RESULTSBMVC4-treated cancer cells showed typical senescence phenotypes. BMVC4 induced senescence in both ALT and telomerase-overexpressing cells, suggesting that telomere shortening through telomerase inhibition might not be the cause for senescence. A large fraction of DNA damage foci was not localized to telomeres in BMVC4-treated cells and BMVC4 suppressed c-myc expression through stabilizing the G-quadruplex structure located at its promoter. These results indicated that the cellular targets of BMVC4 were not limited to telomeres. Further analyses showed that BMVC4 induced DNA breaks and activation of ataxia telangiectasia-mutated mediated DNA damage response pathway. CONCLUSIONS AND IMPLICATIONSBMVC4, a G-quadruplex stabilizer, induced senescence by activation of pathways of response to DNA damage that was independent of its telomerase inhibitory activity. Thus, BMVC4 has the potential to be developed as a chemotherapeutic agent against both telomerase positive and ALT cancer cells. AbbreviationsALT, alternative lengthening of telomeres; ATM, ataxia telangiectasia-mutated; ATR, ATM and Rad3-related; BMVC, 3,6-bis(1-methyl-4-vinylpyridium iodide) carbazole; BMVC4, 3,6-bis(4-methyl-2-vinylpyrazinium iodide) carbazole; hTERT, human telomerase reverse transcriptase; QFS, G-quadruplex forming sequences; SA-b-Gal, senescence-associated (SA) b-galactosidase BJP British Journal of Pharmacology

Inhibition of Cancer Cell Migration and Invasion through Suppressing the Wnt1-mediating Signal Pathway by G-quadruplex Structure Stabilizers

“…3B). Under the BMVC or BMVC4 conditions, no apparent cytotoxic effect was observed for up to 6 days (19,20). These results indicate that G-quadruplex stabilizers could reduce the expression of WNT1.…”

“…On the other hand, c-myc is also a downstream target gene of the Wnt/␤-catenin pathway. Previously we demonstrated that BMVC4 repressed the c-myc expression (19,20). Because a G-quadruplex forming sequence was also identified at the promoter region of c-myc, it is likely that the repressing effect of c-myc by BMVC4 might be through its own G-quadruplex forming sequence directly and through repressing WNT1 expressing indirectly.…”

“…Previously, we characterized two carbazole derivatives, BMVC and BMVC4 ( Fig. 2A), that bound and stabilized the G-quadruplex structures formed by both human telomeric DNA sequences and the quadruplex-forming sequence located at the c-myc promoter (19,20). These two compounds were employed here to determine whether they could bind and stabilize the G-quadruplex structure formed by the G-rich sequence of WNT1 promoter.…”

“…Previously, we have developed two carbazole derivatives, 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC) 4 and 3,6-bis(4-methyl-2-vinylpyrazinium) carbazole diiodide (BMVC4), that bind to G-quadruplex structure formed by telomeric DNA sequences, inhibit telomerase activity, cause telomere shortening, and induce cancer cells into senescence (19,20). The binding of BMVC and BMVC4 to G-quadruplex structures, however, is not limited to telomeres as they also target a quadruplex forming sequence located at the promoter region of c-myc to repress its expression.…”

ALTernative Telomere Maintenance and Cancer

“…In this case, ALT can be viewed as a state of perturbed DNA synthesis. Thus, an armamentarium of DNA synthesis inhibitors, including newly developed PCNA and BLM inhibitors [113,114] and G-quadruplex stabilizing agents [115,116], may exploit vulnerabilities present in ALT cells.…”