Prothena (PRTA) 10% Owner Scully William P Buys $835K of Stock

William Scully, a 10% owner of Prothena Corporation plc (NasdaqGS: PRTA), bought 100,000 shares on October 13, 2026, for $8.35 each. This purchase totaled $835,480, reflecting Scully's ongoing confidence in the biotech firm.

Inside Scully's Trade

Scully's latest acquisition adds to his already significant stake in Prothena. Just before this transaction, he had increased his holdings multiple times in September, including a purchase of 100,000 shares at $8.43 on September 18 and several other significant buys, totaling over 362,000 shares that month. His recent activity shows a strong commitment to the company as it nears its next earnings report.

Other Institutional Activity in Prothena

Several other institutional investors have also been adjusting their positions in Prothena. FMR, LLC reduced its stake by 351,881 shares, bringing its total to 7,199,218 shares valued at about $60.11 million. Meanwhile, Blackrock Inc. increased its holdings by 223,846 shares, ending with 4,867,955 shares worth approximately $40.65 million. State Street Corporation added 454,958 shares, totaling 2,393,424 shares valued at around $19.99 million. Acadian Asset Management also grew its position by 463,043 shares, holding 2,010,645 shares worth about $16.79 million.

Prothena Corporation plc Stock Down 0.1%

As of October 16, 2026, Prothena's stock recently traded around $8.49. This is just above its recent price range, which may indicate some optimism from investors ahead of the company's upcoming earnings announcement. The shares have seen significant activity, especially with Scully's recent purchases, which could suggest confidence in the biotech's future.

Recent Earnings

Prothena reported a trailing twelve-month revenue of $54.53 million, but it has faced challenges with a net margin of -80.7%. The company is set to announce its next earnings on November 5, 2026, which could provide further insights into its financial performance.

Insider Buying and Selling at Prothena Corporation plc

In addition to Scully's recent purchase, he engaged in multiple transactions in September. On September 28, he bought 103,500 shares at $8.60, totaling $889,872. The next day, he acquired 162,000 shares at $8.68 for $1.41 million. On October 2, he added another 100,000 shares at $8.57, worth $857,240. These transactions reflect Scully's substantial investment in Prothena, showing his belief in the company's potential.

About Prothena Corporation

Prothena Corporation plc is a late-stage clinical biotechnology company based in Dublin, Ireland. It focuses on discovering and developing therapies for diseases caused by protein dysregulation. Its pipeline includes Prasinezumab, a monoclonal antibody currently in Phase 3 trials for treating Parkinson's disease and other related disorders.

Bottom Line

Investors will be watching Prothena closely as it approaches its earnings date on November 5, 2026. Scully's recent trades indicate a strong belief in the company, and further developments in its clinical trials and financial results will be key points to monitor.