Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:PL directly binds to and inhibits the antioxidant enzyme glutathione S-transferase π (GSTP1) resulting in a decrease in glutathione levels and subsequent promotion of cancer-selective cell death by increasing the ROS levels (3).
Category: