Nucleolar Targeting by Platinum: p53-Independent Apoptosis Follows rRNA Inhibition, Cell-Cycle Arrest, and DNA Compaction

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• 作者：Erica J. Peterson ; Vijay R. Menon ; Laura Gatti ; Ralph Kipping ; Dilhara Dewasinghe ; Paola Perego ; Lawrence F. Povirk ; Nicholas P. Farrell
• 刊名：Molecular Pharmaceutics
• 出版年：2015
• 出版时间：January 5, 2015
• 年：2015
• 卷：12
• 期：1
• 页码：287-297
• 全文大小：534K
• ISSN：1543-8392

文摘

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鈥揳ctivity paradigms for antitumor complexes.