The big way they are figuring out how to repurpose old compounds that fell out of the pipeline is by using biomarkers.

We are now much more equipt at finding biomarkers, generally through gene sequencing. Drugs that failed, often failed because they were applied to an entire population of a disease (ie multiple sclerosis). Now, we can subset the MS population by different biomarkers and test just that small subset for efficacy.

While testing anyone that happens to have MS would show a massive failure rate, testing 5% of the population that has specific biomarkers, we may be able to show a huge increase in efficacy and thus the drug would be approved for MS patients that fit the exact bio marker profile.