Shares of the autoimmune and rare disease drugmaker Viridian Therapeutics fell over 30% Monday despite positive results for a key prospect for thyroid eye disease that it’s developing as a competitor to Amgen’s Tepezza.
The company said Monday its monoclonal antibody elegrobart met the primary endpoint in a Phase 3 trial in people with active thyroid eye disease. Viridian said it’s on track to submit the drug, which blocks the insulin-like growth factor-1 receptor, or IGF-1R, for regulatory approval next year.
The Phase 3 trial enrolled 132 people with active thyroid eye disease, an autoimmune condition linked to Graves’ disease that can cause redness, double vision and eye bulging, or proptosis. It evaluated subcutaneous injections of the drug in 88 participants while the rest received a placebo. Among those taking elegrobart, half received doses every four weeks or every eight weeks.
After roughly six months, those who received the drug every four weeks saw a meaningful reduction in eye bulging without damage to the other eye at 54%, compared to 18% for those taking placebo, meeting the study’s main goal.
Participants in the four-week dosing group also experienced greater improvements in double vision, at 71%, compared to 32% for those on placebo.
Elegrobart additionally outperformed placebo in the eight-week dosing group, with a reduction in eye bulging at 63% and improvement in double vision at 54%, versus the placebo group’s 18% and 32%, respectively.
Viridian is developing elegrobart and another experimental drug, veligrotug, as potential competitors to Tepezza, the only approved treatment for thyroid eye disease. The company has said its candidates could be more appealing because of a more convenient dosing regimen.
However, Jefferies analyst Faisal Khurshid wrote in a note to clients that the proptosis data “came in below investor expectations,” while the double vision data were harder to interpret and the safety seemed acceptable. Khurshid said he expects “fierce investor debate on commercial feasibility” based on the data.
Elegrobart was generally well-tolerated with low rates of hearing impairment, a common side effect with Tepezza.
Thomas Smith, an analyst at Leerink Partners, wrote in his own note that while the drug met its central goal and “represents the best [subcutaneous drug] data seen to date” in active thyroid eye disease, elegrobart seems less effective compared to veligrotug.
Veligrotug is on track to receive an approval decision from the Food and Drug Administration by June 30 for thyroid eye disease. Delivered via intravenous infusion, it reduced eye bulging in people with chronic thyroid eye disease by 70%.
