A series of xanthenes inhibiting Rad6 function and Rad6-Rad18 interaction in the PCNA ubiquitination cascade

Area of Science:

• Biochemistry
• Molecular Biology
• Medicinal Chemistry

Background:

• Ubiquitination of proliferating cell nuclear antigen (PCNA) is crucial for DNA damage tolerance and translesion DNA synthesis.
• This process involves a cascade including E1 (Uba1), E2 (Rad6), and E3 (Rad18) ubiquitin enzymes.
• Dysregulation of these pathways is implicated in cancer progression.

Purpose of the Study:

• To discover novel small molecules that inhibit PCNA ubiquitination.
• To investigate the mechanism of inhibition, focusing on Rad6 and Rad18 interactions.
• To explore the therapeutic potential of these inhibitors in cancer.

Main Methods:

• Synthesis and screening of a series of xanthene compounds.
• Biochemical assays to assess inhibition of PCNA ubiquitination and Rad6∼ubiquitin thioester formation.
• Analysis of the Rad6-Rad18 interaction using biochemical methods.
• Structure-activity relationship (SAR) studies to identify key structural features for inhibition.

Main Results:

• Identification of xanthen-3-ones as potent inhibitors of PCNA ubiquitination.
• Demonstration that these compounds inhibit Rad6∼ubiquitin thioester formation.
• Discovery that these xanthenes disrupt the Rad6-Rad18 interaction.
• SAR studies elucidated critical chemical features for inhibiting different steps in the cascade.

Conclusions:

• Xanthene derivatives are first-in-class inhibitors of PCNA ubiquitination.
• These compounds serve as valuable chemical probes for studying Rad6 and Rad18 function.
• The inhibition of Rad6-Rad18 interaction represents a novel small-molecule activity.
• These xanthenes hold potential as therapeutic agents for cancer treatment.