Recognition and processing of cisplatin- and oxaliplatin-DNA adducts

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Therapeutics

Background:

• Platinum-based chemotherapy agents, such as cisplatin and oxaliplatin, exert their cytotoxic effects primarily through DNA adduct formation.
• Despite forming similar types of DNA adducts at identical sites, cisplatin and oxaliplatin adducts are differentially recognized by cellular proteins, influencing their distinct clinical profiles.
• This differential recognition is hypothesized to contribute to variations in cytotoxicity and tumor spectrum between cisplatin and oxaliplatin.

Purpose of the Study:

• To investigate the kinetic mechanisms of translesion synthesis (TLS) past cisplatin- and oxaliplatin-induced DNA adducts by specific DNA polymerases.
• To elucidate the role of DNA polymerase eta (pol eta) in the bypass of platinum-DNA adducts and its contribution to mutagenicity.
• To explore the structural basis for the differential recognition of cisplatin and oxaliplatin adducts by cellular proteins.

Main Methods:

• Detailed kinetic analysis of dNTP incorporation during translesion synthesis past GG adducts formed by cisplatin and oxaliplatin.
• In vitro assessment of DNA polymerase beta (pol beta) and DNA polymerase eta (pol eta) activity and fidelity.
• Comparison of cisplatin-induced mutation frequencies in human fibroblast cell lines with and without functional pol eta.
• Solution structure determination of the oxaliplatin-GG adduct.

Main Results:

• Both pol beta and pol eta exhibit higher efficiency in catalyzing TLS past oxaliplatin-GG adducts compared to cisplatin-GG adducts.
• Pol eta demonstrates efficient and accurate TLS past oxaliplatin-GG adducts, similar to its activity with cyclobutane TT dimers, suggesting a role in error-free bypass.
• Experimental data confirm pol eta's involvement in error-free bypass of cisplatin adducts in vivo.
• The solution structure of the oxaliplatin-GG adduct reveals significant conformational differences compared to the cisplatin-GG adduct, explaining differential protein recognition.

Conclusions:

• Differential recognition of platinum-DNA adducts by cellular proteins, particularly mismatch repair and damage-recognition proteins, is driven by distinct adduct conformations.
• DNA polymerase eta plays a crucial role in the efficient and potentially error-free bypass of platinum-DNA adducts, contributing to lower mutagenicity of oxaliplatin.
• Structural disparities between cisplatin- and oxaliplatin-GG adducts provide a mechanistic basis for their differential cellular processing and subsequent biological outcomes.