Proteostasis Plunges On Weak Data From Cystic Fibrosis Study

Shares of Proteostasis Therapeutics, Inc. (NASDAQ:PTI) plunged 67.8% on Mar 25, after it announced data from a dose-selecting phase I study evaluating its triple combination candidate in patients with cystic fibrosis (“CF”).

Data showed that statistically significant improvement in percent predicted FEV1 (ppFEV1), a measurement of lung function, at day 14 was achieved in the study cohort with the higher dose of the company’s cystic fibrosis transmembrane conductance regulator (“CFTR”) corrector. However, the improvement was much lower than that achieved by triple combinations of Vertex Pharmaceuticals (NASDAQ:VRTX) in late-stage clinical studies in CF.

Data from clinical studies have shown that two triplet combinations of Vertex achieved improvement in ppFEV1 from baseline in the range of 13-14% in CF patients.

Shares of Proteostasis have decreased 59.6% so far this year against the industry’s 8.1% growth.

The phase I study evaluated two separate triplet combination of a CFTR corrector (PTI-801), a CFTR potentiator (PTI-808) and a CFTR amplifier (PTI-428) in two cohorts in patients. Patients were administered 30 mg of PTI-428 in combination with either 200 mg of PTI-801 and 300 mg of PTI-808 or 600 mg of PTI-801 and 150 mg of PTI-808.

Data from the study showed that patients receiving 600mg of PTI-801 achieved an improvement of 5% in ppFEV1 at day 14 compared to baseline, which is considered statistically significant. However, data suggests that the improvement in ppFEV1 can increase with the rise in duration of treatment for both the arms.

Proteostasis is planning to advance the combination in phase II development with the optimal dose as there was no plateau in ppFEV1 improvement at day 14. The company believes that longer duration studies are likely to increase ppFEV1 improvement from baseline. The company is anticipating phase III development to start in mid-2020.

Meanwhile, data from two add-on studies evaluating PTI-801 or PTI-428 in patients receiving Symdeko showed improvement in average sweat chloride levels. Patient population also include Orkambi-intolerant patients. Although improvement in ppFEV1 was not of statistical significance, it showed potential of PTI-801 as CF treatment. These data suggest opportunity for Proteostasis products in patients non-responsive to Vertex’s products.

Data readouts expected in 2019-end or early 2020 are anticipated to provide clarity on the progress of Proteostasis’ triplet combination.

However, stiff competition prevails in the CF market with Vertex’s strong hold and several other companies developing their CF pipeline including Eloxx Pharmaceuticals (NASDAQ:ELOX) , Corbus Pharmaceuticals and Catabasis Pharmaceuticals (NASDAQ:CATB) .

Zacks Rank

Proteostasis currently carries a Zacks Rank #3 (Hold). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.

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