TriplatinNC is a highly positively charged, substitution-inert derivative of the phase II clinical anticancer
drug,
BBR3464. Such substitution-inert complexes form a distinct subset of polynuclear
platinum complexes (PPCs) interacting with
DNA and other biomolecules through noncovalent interactions. Rapid cellular entry is facilitated via interaction with cell surface glycosoaminoglycans and is a mechanism unique to PPCs. Nanoscale secondary ion mass spectrometry (nanoSIMS) showed rapid distribution within cytoplasmic and nucleolar compartments, but not the nucleus. In this article, the downstream effects of nucleolar localization are described. In human colon
carcinoma cells, HCT116, the production rate of 47S
rRNA precursor transcripts was dramatically reduced as an early event after
drug treatment. Transcriptional inhibition of rRNA was followed by a robust G1 arrest, and activation of apoptotic
proteins caspase-8, -9, and -3 and PARP-1 in a p53-independent manner. Using cell synchronization and flow cytometry, it was determined that cells treated while in G1 arrest immediately, but cells treated in S or G2 successfully complete mitosis. Twenty-four hours
after treatment, the majority of cells finally arrest in G1, but nearly one-third contained highly compacted
DNA; a distinct
biological feature that cannot be associated with mitosis, senescence, or apoptosis. This unique effect mirrored the efficient condensation of
tRNA and
DNA in cell-free systems. The combination of
DNA compaction and apoptosis by
TriplatinNC treatment conferred striking activity in
platinum-resistant and/or p53 mutant or null cell lines. Taken together, our results support that the
biological activity of
TriplatinNC reflects reduced metabolic deactivation (substitution-inert compound not reactive to
sulfur nucleophiles), high cellular accumulation, and novel consequences of high-affinity noncovalent
DNA binding, producing a new profile and a further shift in the structure-activity paradigms for antitumor complexes.