ProQR surges on CF data on busy day for the field

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ProQR Therapeutics ($PRQR) saw its stock surge on the back of data from a small clinical trial of its cystic fibrosis drug QR-010. The data proved compelling enough to drive shares in ProQR up 38% in premarket trading, although questions about the potential challenger to Vertex’s ($VRTX) crown remain.

Leiden, the Netherlands-based ProQR gave single-stranded RNA antisense oligonucleotide QR-010 to 18 cystic fibrosis patients. Ten of the participants were homozygous for the F508del mutation, while the rest were heterozygous. ProQR thinks QR-010 can restore functional CFTR and stop progression of the disease in patients with at least a copy of the mutation. To date, ProQR has lacked clinical data to back up its belief in the mechanism of action.

The Phase Ib trial is the first step in the ongoing process of delivering such data. ProQR heralded the data as a success--and investors appear to agree--but the results fall short of eradicating all doubts. The company’s optimism is underpinned by the performance of the homozygous cohort. When three participants who didn’t meet certain baseline and post-dose criteria were excluded, QR-010 was associated with -4.1mV change in CFTR-mediated total chloride transport after 26 days.

ProQR set out to show a change of greater than -3.5mV, the value achieved by the 150mg dose of Vertex’s Kalydeco in its Phase II trial. QR-010 hit the target in the homozygous per protocol cohort, but performance in heterozygous patients was less impressive. CFTR-mediated total chloride transport increased 2.2mV among these subjects. The data also lack details of the range of changes experienced by patients in each cohort.

Such details matter given the competitive nature of the market ProQR is trying to break into. Vertex is well established in cystic fibrosis and is looking to cement its dominance by introducing a triple pill combining Kalydeco, VX-661 and a third drug. AbbVie ($ABBV) and its partner Galápagos ($GLPG) are also working on a triple combination, early data from one component of which were presented at the same event as the QR-010 results.

Galápagos gave its potentiator GLPG1837 to seven patients, but the size and short duration of the trial make it hard to assess the potential of the drug. Data from an ongoing trial that gave higher doses of GLPG1837 may provide greater clarity, although at this stage it isn’t clear if the molecule will win a spot in the triple combination. AbbVie and Galápagos moved another potentiator into Phase I earlier this year.