Endemic Alkanna cappadocica was used to isolate novel antitumor molecules from Turkish landscapes in our previous studies. In this study, deoxyalkannin (ALCAP1), β,β-dimethylacrylalkannin (ALCAP2), acetylalkannin (ALCAP3), and
alkannin (ALCAP4) as well as the novel isolated compounds 5-methoxydeoxyalkannin (ALCAP5), 8-methoxydeoxyalkannin (ALCAP6), 5-methoxyacetylalkannin (ALCAP7), 5-methoxy-β,β-dimethylacrylalkannin (ALCAP8) were characterized. The
topoisomerase I (
topo I) inhibitory activity of ALCAPs was investigated using in vitro plasmid relaxation assay and found that ALCAP2, 3, 4 and 7 were potent inhibitors at 2-6μM concentrations. Further, DNA damage response to ALCAP treatments was also studied by measuring the H2AX((S139)) and ATM((S1981)) phosphorylations. ALCAP2, 7 and 8 induced the DNA damage and apoptosis, consistently resulted in PARP cleavage at nanomolar concentrations in K562
leukemia cells. Moreover, when the
free radical (ROS) generating capacity of the compounds was studied by 2',7'-dichlorofluorescein-diacetate assay using flow cytometry, we found that a known
antioxidant N-acetyl-
cysteine almost completely abrogated the H2AX((S139)) phosphorylations and the
caspase 3 cleavage and activation. Thus, γH2AX((S139)) foci formation remained higher than the control, and an increase in CHK2((T68)) phosphorylation was observed by ALCAP2 and 7 treatments suggested that, these compounds can be potential
therapeutics against
tumor cell growth because of their unique
DNA damaging abilities additional to
enzyme inhibition similar to those of
doxorubicin.