Nuclear DNA binding and inhibition of growth of HeLa cells in culture were
determined after 24 h incubation with the ruthenium anticancer agents cis-[Cl2(NH3)4Ru]Cl
(CCR) and (ImH)trans-[(Im)2Cl4Ru] (ICR) as a function of [Ru], Po2, and added transferrin.
Consistent with the “activation-by-reduction” hypothesis, cytotoxicity and DNA binding for
both complexes increased under reduced oxygen conditions. Consistent with the “transferrin-
transport” hypothesis, inhibition of cell growth also increased with added transferrin for
both complexes. Despite their differences in charge, reduction potentials and substitution
rates, both complexes behaved remarkably similarly indicating a common mechanism of
action for both. Under atmospheric Conditions (Po2 = 159 torr), CCR inhibited HeLa cell
growth with IC50 = 3.5 μM, while that for ICR was 2.0 μM. The binding of both complexes
to DNA (RuDNA/PDNA) correlated with toxicity and was approximately linear in the concentration
of the ruthenium complex in the culture medium, [Ru]. For both complexes, IC50
values decrease and DNA binding increases with decreasing log(Po2). In general, DNA
binding at all oxygen pressures for both complexes is in the range of one Ru per 1000-2000
DNA base pairs at [Ru] = IC50.
