Form 4: William P. Scully Increases Stake in Prothena Corp

10% owner William P. Scully acquired 125,000 shares of Prothena Corp at a weighted average price of $8.1698.

Summary

• Reporting person William P. Scully purchased 125,000 ordinary shares of Prothena Corp (PRTA) on June 11, 2026.
• The shares were acquired at a weighted average price of $8.1698 per share, with individual transaction prices ranging from $7.84 to $8.43.
• Following this transaction, Scully's direct beneficial ownership increased to 1,061,000 shares.
• Scully maintains additional indirect ownership of 80,000 shares via Manatee Equity Fund LLC and 52,000 shares held by his spouse.

Sentiment

Score: 8

Explanation: StockSavvy.ai views this as a positive signal, as a 10% owner increasing their position by 125,000 shares demonstrates strong conviction in the company's future.

Positives

• Significant insider accumulation by a 10% owner signals confidence in the company's long-term prospects.
• The purchase of 125,000 shares represents a meaningful increase in the reporting person's direct equity position.

Negatives

• None identified in this filing.

Risks

• Market volatility may impact the value of the acquired shares.
• The reporting person disclaims beneficial ownership of shares held by Manatee Equity Fund LLC except to the extent of his pecuniary interest.

Future Outlook

Not applicable as this is an insider transaction report.

Industry Context

StockSavvy.ai notes that insider buying by major shareholders is generally viewed as a bullish indicator, suggesting that those with the most intimate knowledge of the company believe the stock is undervalued at current levels.

Comparison to Industry Standards

• Insider buying activity is consistent with standard capital allocation strategies for long-term stakeholders in the biotechnology sector.

Related Party Transactions

• The reporting person holds indirect interest in shares via Manatee Equity Fund LLC and shares held by his spouse.

Stakeholder Impact

• Shareholders may interpret this purchase as a vote of confidence from a major investor.

Next Steps

• No future actions or milestones were disclosed in this filing.

Key Dates

Recommendation

While insider buying is a positive signal, it is not a standalone reason to buy; investors should continue to monitor the company's clinical trial progress and financial performance.

Keywords

Prothena, PRTA, Insider Trading, Form 4, William P. Scully, Equity Acquisition