What Happened to the U.S. Drug Developer After Insider Buying Worth Billions Following a Turnaround?

Prothena Corporation plc (NASDAQ: PRTA) swung to a net profit of $32.7 million (approximately KRW 46 billion) in the first quarter of 2026, reversing its prior losses. The turnaround was driven by a $50 million (about KRW 70 billion) milestone payment from Novo Nordisk for the ongoing Phase 3 trial of coramitug, an investigational therapy for ATTR cardiomyopathy, along with reductions in R&D and SG&A expenses. The company also sharply lowered its projected net cash outflow from operating and investing activities for the full year to $18 million–$23 million and now expects to end the year with cash and cash equivalents of about $273 million (roughly KRW 460 billion). Prothena has authorized up to $100 million (around KRW 140 billion) for share repurchases and has already bought back approximately $7.3 million (about KRW 10 billion) of its stock through the first quarter.

On May 22 and June 2, board member William P. Scully personally acquired about 150,000 shares of Prothena stock on the open market, investing an additional $1.45 million (around KRW 2 billion) and significantly increasing his direct ownership. These discretionary insider purchases—not routine or automated trades—have drawn investor interest in light of the company’s improved results and ongoing share repurchase program.

Investor enthusiasm has also been fueled by the achievement of the Phase 3 milestone with Novo Nordisk and the U.S. FDA’s Fast Track designation for coramitug, underscoring the commercial potential of Prothena’s ATTR cardiomyopathy candidate. As of June 3, the company’s market capitalization stood at approximately $465 million (about KRW 650 billion).

Headquartered in Dublin, Ireland, Prothena is a late-stage clinical biotech company specializing in protein-misfolding therapies. Its pipeline includes prasinezumab for Parkinson’s disease, the anti-amyloid antibody BMS-986446 (PRX005) for Alzheimer’s disease, and two candidates for ATTR amyloidosis—coramitug and PRX019. Prothena advances its clinical and commercialization programs through partnerships with global pharmaceutical firms such as Novo Nordisk, Roche and Bristol Myers Squibb. As is typical in the late-stage biotech sector, future clinical readouts and milestone payments remain key drivers of the company’s valuation and stock price dynamics.