There's a difference between a human trying to break into drug labs and changing experimental results vs a machine in that the machine can do it much easier today.
Of course a human could deliberately prompt it to, but they could do that for any other malicious purpose too. The major disincentive there is that the human will face legal punishment if caught, not anything technical.
Most speculatively, one could imagine a world where so many rogue AI agents were running that one just happened to notice the drug candidate from news coverage and took the initiative. I think that would be technically possible, but so generally destructive that political pressure would put a stop to it on a timescale shorter than a clinical trial.