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Proteostasis Therapeutics shares tumble on disappointing data for cystic fibrosis triplet therapy

The triplet therapy for cystic fibrosis patients failed to show a significant improvement in the measure of a lung function referred to as ppFEV1
scientist in a lab
The Boston company still expects to kick off Phase 3 studies for its cystic fibrosis therapies by mid-2020

Shares of Proteostasis Therapeutics Inc (NASDAQ:PTI) plunged Monday after the biopharmaceutical company unveiled disappointing Phase 1 data for its triplet therapy for cystic fibrosis patients of PTI-801 (a cystic fibrosis transmembrane conductance regulator corrector), PTI-808 (CFTR potentiator) and PTI-428 (CFTR amplifier).

The results of the triplet therapy failed to show a significant improvement in the measure of patients' lung function referred to as ppFEV1.

READ: Proteostasis Therapeutics shares surge on positive Phase 1 trial data for cystic fibrosis therapy

On top of this, the data also included readouts from separate studies of PTI-801 and PTI-428 as add-on treatments to tezacaftor/ivacaftor therapy in patients with cystic fibrosis.

Patients who received PTI-801 as part of the separate study saw improvement in sweat chloride, but did not show a “statistically significant" improvement in ppFEV1 either after 14 days of treatment.

Investors were left disappointed by the results and sent Proteostasis shares down 63% to $1.48 in afternoon trade Monday.

Before the end of the year, the Boston-based company plans to evaluate optimal doses of PTI-801 and PTI-808 as part of longer studies in cystic fibrosis patients “who are not predisposed to rapid pulmonary decline”.

Proteostasis will also be starting three new Phase 2 studies in cystic fibrosis patients with at least one F508del mutation for its triplet therapy and PTI 801/808 combination therapies.

The company still expects to start Phase 3 studies for its cystic fibrosis therapies by mid-2020.

Proteostasis Therapeutics is developing small molecule therapies to treat cystic fibrosis and other diseases caused by dysfunctional protein processing. 

Contact Ellen Kelleher at [email protected]

-- This story is updated to reflect latest share price movement --



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