Induction of glutathione-dependent DNA double-strand breaks by the novel anticancer drug brostallicin.

Brostallicin is a DNA minor groove binder in phase II clinical trials. Here, we show that brostallicin induces gamma-H2AX nuclear foci that colocalize with 53BP1 and are dependent on glutathione, as shown by inhibition of those gamma-H2AX foci by l-buthionine sulfoximine. To differentiate brostallicin from the clinically approved minor groove binder trabectedin (ecteinascidin 743), we tested whether the brostallicin-induced gamma-H2AX and antiproliferative responses were dependent on nucleotide excision repair and found that, unlike trabectedin, they are not. Additionally, brostallicin retained activity in the trabectedin-resistant HCT116-ER5 cell line. Induction of gamma-H2AX foci by brostallicin was partially dependent on the repair nuclease Mre11. Pretreatment with aphidicolin partially reduced brostallicin-induced gamma-H2AX foci, suggesting that brostallicin induces both replication-associated and replication-independent DNA damage. Replication-associated DNA damage was further shown by the colocalization of gamma-H2AX foci with replication foci and by the rapid inhibition of DNA synthesis and accumulation of cells in S phase in response to brostallicin. In addition, brostallicin was able to induce lower intensity gamma-H2AX foci in human circulating lymphocytes. Together, our results indicate that brostallicin induces DNA double-strand breaks and suggest gamma-H2AX as a pharmacodynamic biomarker for brostallicin.