the insider selling makes sense because they know that GSK is not interested until after the drug is approved and selling enough to make a reasonable economic case. The insiders know that by the time the drug is on the market (and that could take several years because the FDA may not approve on the first time through because of the failed secondary endpoints) they will have a whole new batch of options as well as vesting of previous options.

So the insiders know what the situation is and they are acting because they know that GSK won't pay for the other half of benlysta for a while (and could be a long while given the failed secondary endpoints)