Batracylin (NSC 320846), a dual inhibitor of DNA topoisomerases I and II induces histone gamma-H2AX as a biomarker of DNA damage.
Batracylin (8-aminoisoindolo [1,2-b]quinazolin-10(12H)-one; NSC320846) is an investigational clinical anticancer agent. Previous animal studies showed activity against solid tumors and Adriamycin-resistant leukemia. We initially sought to test the proposed Top2-mediated DNA cleavage activity of batracylin and identify potential biomarkers for activity. COMPARE analysis in the NCI-60 cell lines showed batracylin activity to be most closely related to the class of Top2 inhibitors. The 50% growth inhibition (GI50) value for batracylin in HT29 colon carcinoma cells was 10 micromol/L. DNA-protein cross-links, consistent with Top2 targeting, were measured by alkaline elution. DNA single-strand breaks were also detected and found to be protein associated. However, only a weak induction of DNA double-strand breaks was observed. Because batracylin induced almost exclusively DNA single-strand breaks, we tested batracylin as a Top1 inhibitor. Batracylin exhibited both Top1- and Top2alpha/beta-mediated DNA cleavage in vitro and in cells. The phosphorylation of histone (gamma-H2AX) was tested to measure the extent of DNA damage. Kinetics of gamma-H2AX "foci" showed early activation with low micromol/L concentrations, thus presenting a useful early biomarker of DNA damage. The half-life of gamma-H2AX signal reversal after drug removal was consistent with reversal of DNA-protein cross-links. The persistence of the DNA-protein complexes induced by batracylin was markedly longer than by etoposide or camptothecin. The phosphorylated DNA damage-responsive kinase, ataxia telangiectasia mutated, was also found activated at sites of gamma-H2AX. The cell cycle checkpoint kinase, Chk2, was only weakly phosphorylated. Thus, batracylin is a dual Top1 and Top2 inhibitor and gamma-H2AX could be considered a biomarker in the ongoing clinical trials.
Rao
V Ashutosh
VA
Laboratory of Molecular Pharmacology and Developmental Therapeutics Program, National Cancer Institute, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
Agama
Keli
K
Holbeck
Susan
S
Pommier
Yves
Y
D014408:Biomarkers, Tumor / Q000096:biosynthesis / Q000378:metabolism; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D053904:DNA Breaks, Single-Stranded; D004249:DNA Damage; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D045325:HCT116 Cells; D019073:HT29 Cells; D006657:Histones / Q000096:biosynthesis* / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D011799:Quinazolines / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors
D014408:Biomarkers, Tumor; D004791:Enzyme Inhibitors; C468783:H2AX protein, human; D006657:Histones; D011799:Quinazolines; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; C057924:batracylin