Transplatin
is an inactive platinum drug; however, a number of analogues, such
as trans-EE and trans-PtTz, demonstrate
promising antitumor activity in vitro and in vivo. Although the ultimate target is nuclear DNA, increasing
evidence indicate that proteins also play important roles in the display
of antitumor activity. The linker histone H1 is situated by the portal
between the unwrapped DNA and the nucleosome core. Our recent study
revealed that H1 can readily react with cisplatin, and the adducts
tend to form ternary complexes with DNA. In this work, we have investigated
the reaction of histone H1 with two antitumor-active trans-oriented complexes, trans-EE and trans-PtTz, and the effect of H1 upon the platination of DNA. The results
show that trans-platinum drugs are much more reactive
than cisplatin toward H1. Interestingly, in addition to the expected
bidentate adducts (by displacement of the two labile chlorido ligands),
also a tridentate adduct can be formed by displacement of one nonlabile
carrier ligand of trans-EE or trans-PtTz. The trans-Pt/H1 adducts can then react with
DNA and generate protein–Pt–DNA ternary complexes. Additionally,
platinum can be transferred from trans-Pt/H1 adducts
to DNA, generating binary trans-Pt/DNA complexes.
Such a transfer of the platinum agent to DNA was not observed in the
reaction of cisplatin. Furthermore, the detailed investigation carried
out on a model peptide indicates that H1 promotes the DNA platination
by trans-EE, while it reduces that
of trans-PtTz and cisplatin. These results suggest
that H1 can play a key role in the DNA platination and modulate the
efficacy of different platinum agents.