I would also point out that demonstrating a long list of failures followed by only several potential successes is par for the course with early drug discovery. It is quite common to test tens of thousands of compounds to find hits, to then lose 90% of those hits from validation, then to take a lead compound that has activity but far too low for it to be a drug candidate (typically you want binding in the micromolar, nanomolar is your goal for a real good drug, and from a lead compound you can expect a couple hundred millimolar at best, unless you are quite lucky).

The lead is then often given to medical chemists who make a couple hundred analogues and you test those to find the best one.

So, this passage speaks to the challenge of early drug discovery in general, not this specific case.