In vivo DNA-protein cross-linking by cis- and trans-diamminedichloroplatinum(II)

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Platinum-based chemotherapy agents are widely used in cancer treatment.
• Understanding the molecular mechanisms of platinum drug action, including DNA-protein interactions, is crucial for optimizing therapy.
• Novikoff hepatoma is a relevant model for studying drug-induced cellular changes.

Purpose of the Study:

• To investigate the formation and repair of DNA-protein cross-links induced by cisplatin (cis-DDP) and transplatin (trans-DDP) in a rat hepatoma model.
• To identify the specific proteins involved in these cross-links.
• To compare the kinetics of cross-link formation and repair between cis-DDP and trans-DDP.

Main Methods:

• Administration of cis-diamminedichloroplatinum(II) (cis-DDP) and trans-diamminedichloroplatinum(II) (trans-DDP) to Novikoff hepatoma-bearing rats.
• Detection of DNA-protein cross-links using antisera against dehistonized chromatin, nuclear matrix, and cytoskeletal preparations.
• Time-course analysis of cross-link formation and repair up to 72 hours post-injection.
• Identification of cross-linked proteins using molecular weight markers.

Main Results:

• Both cis-DDP and trans-DDP induced time-dependent DNA-protein cross-links in Novikoff hepatoma cells.
• cis-DDP-induced cross-links increased up to 24 hours and were repaired by 72 hours.
• trans-DDP induced cross-links more rapidly but were repaired faster (within 48 hours at equitoxic dose, and even faster at equimolar dose).
• Key proteins cross-linked to DNA by both platinum compounds were identified as Novikoff hepatoma cytokeratins (Mr 39,000, 49,000, 56,000) and an additional protein (Mr approximately 68,000).

Conclusions:

• Cisplatin and transplatin effectively form DNA-protein cross-links in vivo, involving specific cytokeratin proteins.
• The kinetics of DNA-protein cross-link formation and repair differ between cis-DDP and trans-DDP.
• These findings provide insights into the molecular interactions of platinum drugs and their repair mechanisms in cancer cells.