It makes a pore, and the cell bursts

Once docked, the peptide and HDM-2 assemble into ring-shaped structures in the membrane, which electron microscopy with gold-labelled antibodies showed as layered rings forming the walls of actual pores, roughly one peptide to one HDM-2. A pore in a cell membrane ends the cell's ability to hold its contents and its ion gradients, and it lyses. This is necrosis, a physical bursting, not apoptosis, the orderly self-dismantling that most cancer drugs trigger. The authors named the mechanism poptosis to separate it from both.