Which drug? As in the anti-cancer drugs that I hope one day to use? Well I’m thinking of things like dis-platin which bind across DNA and prevent it from splitting, which is a really important part of the replication process. If DNA can’t split then a cell will die. This means it’s essentially a poison that attacks all cells. So if you could deliver it to just the tumour, and not to all the cells in the body, people would stand a much better chance of survuving chemotherapy.