Not sure I understand your point...are you questioning targeted gene therapies in general or Ariad's ALK inhibitor specifically? As far as your comment that "the idea that there is a whole class of compounds whose path through the clinic is well predicted by in vitro or mouse models seems, well, rather optimistic", well, welcome to the 21st century.
Take CML, for example, which is caused by the BCR-ABL gene. The ABL gene is a signalling molecule and plays an important role in cell proliferation, however, in CML patients the ABL gene is always active and causes the continuous production of cml cells. It is this activity (and the various mutations that may result) which drugs like ponatinib are designed to target and, in general, if they work in vitro there is a much higher likelihood that they will also work in the clinic (as compared to drugs that do not target a specific gene or protein).
