Watch out for the Proteostasis triple data later this year


Proteostasis’s massive 448% share rise yesterday on news that its cystic fibrosis (CF) doublet looks at least as good as Vertex’s combinations Orkambi and Symdeko looks a little overdone. The data covers just 14 patients treated with PTI-801/PTI-808 for 14 days, and only five were in the sole dose group to show a benefit over placebo, who received 300mg of each molecule. Still, the company claimed a dose response – this will be put to the test when data from patients given the high dose of 400mg/300mg appear in early 2019. Investors seem to believe the data so far validate Proteostasis’s plan to move forward with a triplet that includes another agent, CF-428, data on which is expected by the end of the year. Still, Proteostasis could find it tough to compete with Vertex Pharmaceuticals, which has set a high bar for efficacy with its own triplets, which are also further ahead in the clinic. One explanation for Proteostasis’s huge rise is that many investors held short positions ahead of these data and needed to cover them, leading to a “short squeeze” that bid prices up. Shares fell back 22% in early trading today. A fundraising seems likely, as Proteostasis had $63m in cash at June 30.

Comparing CFTR modulator trials in F508del homozygous patients
    Change vs placebo
  Company Sweat chloride (mmol/l) ppFEV1 (%)
Orkambi (lumacaftor-ivacaftor)* Vertex -11 +4.2
Symdeko (tezacaftor-ivacaftor)** Vertex -10.1 +6.8
PTI-801/PTI-808*** Proteostasis -11.6 +6.6
VX-659-tezacaftor-ivacaftor Vertex -39.2 +9.7
VX-445-tezacaftor-ivacaftor Vertex -38.8 +11
*Day 56, dose-ranging study; **Week 24, pivotal trial; ***Day 14, 300mg/300mg dose, ph I trial; Day 29, ph II trials.
Source: Company presentations; NEJM articles: VX-659–Tezacaftor–Ivacaftor in Patients with Cystic Fibrosis and One or Two Phe508del Alleles; VX-445–Tezacaftor–Ivacaftor in Patients with Cystic Fibrosis and One or Two Phe508del Alleles.

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