Crosstalk between repair pathways elicits double-strand breaks in alkylated DNA and implications for the action of temozolomide

Crosstalk between repair pathways elicits double-strand breaks in alkylated DNA and implications for the action of temozolomide

Blog Article

Temozolomide (TMZ), a DNA methylating agent, is the primary chemotherapeutic drug used in glioblastoma treatment.TMZ induces mostly N-alkylation Air Conditioner Invertor Module adducts (N7-methylguanine and N3-methyladenine) and some O6-methylguanine (O6mG) adducts.Current models propose that during DNA replication, thymine is incorporated across from O6mG, promoting a futile cycle of mismatch repair (MMR) that leads to DNA double-strand breaks (DSBs).

To revisit the mechanism of O6mG processing, we reacted plasmid DNA with N-methyl-N-nitrosourea (MNU), a temozolomide mimic, and incubated it in Xenopus egg-derived extracts.We have shown that in this system, MMR proteins are enriched on MNU-treated DNA and we observed robust, MMR-dependent, repair synthesis.Our evidence also suggests that MMR, initiated at O6mG:C sites, is strongly stimulated in cis by repair processing of other lesions, such as N-alkylation adducts.

Importantly, MNU-treated plasmids CR-33 display DSBs in extracts, the frequency of which increases linearly with the square of alkylation dose.We suggest that DSBs result from two independent repair processes, one involving MMR at O6mG:C sites and the other involving base excision repair acting at a nearby N-alkylation adduct.We propose a new, replication-independent mechanism of action of TMZ, which operates in addition to the well-studied cell cycle-dependent mode of action.