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Structural and mechanistic studies of polymerase η bypass of phenanthriplatin DNA damage
Mark T Gregory1, Ga Young Park2, Timothy C Johnstone2
1Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases andThe Johns Hopkins University-National Institutes of Health Graduate Partnership Program, National Institutes of Health, Bethesda, MD 20892; and.
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.
Insights
Phenanthriplatin, a novel platinum compound, inhibits DNA replication and shows distinct activity from cisplatin. It effectively targets cancer cells regardless of Pol η expression, offering potential against cisplatin-resistant tumors.
Area of Science:
- Oncology
- Molecular Biology
- Medicinal Chemistry
Background:
- Platinum-based chemotherapy is crucial for cancer treatment but faces challenges with drug resistance.
- Developing new platinum compounds with distinct mechanisms is vital to overcome resistance.
- Phenanthriplatin (cis-diamminephenanthridinechloroplatinum(II)) is a monofunctional platinum complex with unique activity.
Purpose of the Study:
- To investigate the effects of phenanthriplatin on DNA replication and compare its mechanism with traditional platinum drugs.
- To evaluate phenanthriplatin's efficacy in the context of DNA polymerases, particularly Pol η, involved in DNA repair and resistance.
- To assess phenanthriplatin's potential as a therapeutic agent for cisplatin-resistant cancers.
Main Methods:
- Assessing the inhibition of DNA polymerases (Pol ν, ζ, κ, Klenow fragment) by phenanthriplatin lesions.
- Studying the ability of DNA polymerases to bypass phenanthriplatin adducts, focusing on Pol η.
- Utilizing X-ray crystallography to determine the structural interactions between phenanthriplatin-DNA adducts and Pol η.
- Comparing the toxicity of phenanthriplatin in cells with varying Pol η expression levels (Pol η+ and Pol η-).
Main Results:
- Phenanthriplatin lesions effectively inhibit DNA polymerases ν, ζ, κ, and the Klenow fragment.
- While other polymerases can insert bases opposite phenanthriplatin, only Pol η can efficiently bypass the adduct.
- Structural analysis reveals distinct interactions between phenanthriplatin-DNA and Pol η compared to cisplatin-DNA adducts.
- Phenanthriplatin demonstrates high toxicity in both Pol η-expressing and non-expressing cells, unlike cisplatin and oxaliplatin.
Conclusions:
- Phenanthriplatin's mechanism of inhibiting DNA replication differs from established platinum drugs.
- Its efficacy is independent of Pol η expression, suggesting it can overcome resistance mechanisms associated with this enzyme.
- Phenanthriplatin represents a promising candidate for treating cancers resistant to current platinum-based therapies.
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