Structural and mechanistic studies of polymerase η bypass of phenanthriplatin DNA damage

Abstract

Platinum drugs are a mainstay of anticancer chemotherapy. Nevertheless, tumors often display inherent or acquired resistance to platinum-based treatments, prompting the search for new compounds that do not exhibit cross-resistance with current therapies. Phenanthriplatin, cis-diamminephenanthridinechloroplatinum(II), is a potent monofunctional platinum complex that displays a spectrum of activity distinct from those of the clinically approved platinum drugs. Inhibition of RNA polymerases by phenanthriplatin lesions has been implicated in its mechanism of action. The present study evaluates the ability of phenanthriplatin lesions to inhibit DNA replication, a function disrupted by traditional platinum drugs. Phenanthriplatin lesions effectively inhibit DNA polymerases ν, ζ, and κ and the Klenow fragment. In contrast to results obtained with DNA damaged by cisplatin, all of these polymerases were capable of inserting a base opposite a phenanthriplatin lesion, but only Pol η, an enzyme efficient in translesion synthesis, was able to fully bypass the adduct, albeit with low efficiency. X-ray structural characterization of Pol η complexed with site-specifically platinated DNA at both the insertion and +1 extension steps reveals that phenanthriplatin on DNA interacts with and inhibits Pol η in a manner distinct from that of cisplatin-DNA adducts. Unlike cisplatin and oxaliplatin, the efficacies of which are influenced by Pol η expression, phenanthriplatin is highly toxic to both Pol η+ and Pol η− cells. Given that increased expression of Pol η is a known mechanism by which cells resist cisplatin treatment, phenanthriplatin may be valuable in the treatment of cancers that are, or can easily become, resistant to cisplatin.cancer therapy | monofunctional platinum drug candidates | pol eta | X-ray crystallography

Third row transition metals for the treatment of cancer

“…These biochemical results were corroborated by an X-ray crystallographic study of pol η stalled at different stages of translesion synthesis. The structural data also confirmed that the orientational preference, observed in the small molecule studies described above [39], was preserved in the macromolecular structures and that the preferred diastereomer is the one responsible for arresting the polymerase [42].…”

Structural Basis for the Inefficient Nucleotide Incorporation Opposite Cisplatin-DNA Lesion by Human DNA Polymerase β

“…Non-hydrolyzable nucleotide analogs such as dUMPNPP (dUTP*) and dAMPCPP have been shown to tightly bind the pol␤ active site (29,30), and the use of these analogs does not significantly alter the active site conformation of a pol␤ ternary complex (29,31). The dNTP* analogs have been used to obtain ternary complex structures of various DNA polymerases (17,32,34,35) including pol in complex with cisplatin-and phenanthriplatin-modified DNA (32,35). Unfortunately, our extensive efforts to crystalize a ternary complex of pol␤ incorporating dCTP* opposite the templating 3Ј-dG of the Pt-GG lesion failed.…”

Roles of Residues Arg-61 and Gln-38 of Human DNA Polymerase η in Bypass of Deoxyguanosine and 7,8-Dihydro-8-oxo-2′-deoxyguanosine

“…Thus, Arg-61 can adopt different conformations during each stage of the catalytic reaction cycle. In addition, the reported structures have also indicated that another highly conserved residue near the active site, Gln-38, may play an important role in stabilizing the template base in the nucleotidyl transfer reaction (10,11,21,30,34,35,37).…”