DA-125, a novel derivative of
adriamycin, is known for its anti-
cancer activity. In this study, the inhibitory mechanism of
DA-125 on topoisomerase was investigated in the simian virus 40 (SV40) replicating
CV-1 cell by studying the SV40 DNA replication intermediates and
DNA-topoisomerase complexes.
DNA-
protein complexes that were formed in the
drug-treated cells were quantitated by using a glass filter assay. SV40 DNA replication intermediates that were accumulated in the
drug-treated
CV-1 cell were analyzed in a high resolution gel.
DA-125 did not accumulate B-dimers of SV40 DNA replication intermediates which were found in the
adriamycin-treated
CV-1 cells.
DA-125 induced a dose-dependent formation of the
DNA-
protein complexes, while
adriamycin did not. When
adriamycin and
etoposide (
VP16) were added to the SV40-infected cells at the same time,
adriamycin blocked the formation of the
DNA-
protein complexes induced by
VP16 in a dose-dependent manner. However,
DA-125 blocked the formation of the
DNA-
protein complexes induced by
VP16 up to the maximum level of the
DNA-
protein complexes that were induced by
DA-125 alone.
Adriamycin and
DA-125 did not inhibit the formation of the
DNA-
protein complexes that were caused by
camptothecin, a known
topoisomerase I poison.
DA-125 is bifunctional in inhibiting
topoisomerase II because it simultaneously has the properties of the
topoisomerase II poison and the
DNA intercalator. As a
topoisomerase II poison,
DA-125 alone induced dose-dependent formation of the
DNA-
protein complexes. However, as
a DNA intercalator, it quantitatively inhibited the formation of the
DNA-
protein complexes induced by a strong
topoisomerase II poison VP16. Furthermore considering that the levels of the
DNA-
protein complex induced by
VP16 were decreased by
DA-125 in terms of the
topoisomerase II poison, we suggest that
DA-125 has a higher affinity to the
drug-binding sites of
DNA than
VP16 has.