The company working on these drugs is Vertex. The following details a drug specifically for the G551D mutation and the hope for VX-809 for DD508...
"These results are quite exciting because no current therapies can target the actual genetic defect that causes CF. The fact that these results are apparent in different measures of CF indicate that the drug is having a direct effect on the CFTR protein.
It is important to note that these results are preliminary and much longer studies on additional patients need to be done before any definite conclusions can be made. Additionally, the G551D mutation affects just 4% of patients with CF, so this drug would not be beneficial to a majority of CF patients. However, there is some more tentative good news in that Vertex is developing an additional drug specifically for the most common defect, delta F508. This mutation results in a defect in the way the CFTR protein is folded, resulting in the protein getting stuck in the endoplasmic reticulum so that it never even makes it to the cell membrane. The new drug in development, VX-809, may be able to free up the CFTR protein so that the channel can make it to the cell membrane and pass chloride ions. Phase 1a clinical studies have begun on VX-809. Hopefully the results from these studies will be as positive as those from VX-770."