PRTA SEC Filing News — Prothena Corporation plc

Latest SEC filings for Prothena Corporation plc (PRTA) explained in plain English. Covers insider buying and selling (Form 4), proposed insider sales (Form 144), material company events (8-K), and quarterly & annual reports (10-Q / 10-K). StrongBuyAnalytics provides navigation and brief excerpts or summaries; original filings remain at the SEC/source links and were authored by their filers, not StrongBuyAnalytics. Filing dates shown are source dates. Coverage and detection can be delayed or incomplete because of SEC availability, amendments, parsing, caching, or outages. Latest source filing date shown: 2026-10-15.

Prothena Corporation plc, a late-stage clinical biotechnology company, focuses on discovery and development of novel therapies to treat diseases caused by protein dysregulation. Its product pipeline includes Prasinezumab, an investigational humanized monoclonal antibody which is in Phase 3 clinical trial for the treatment of parkinson's disease and other synucleinopathies. The company also develops Coramitug, an investigational antibody, which is in Phase 3 clinical trial for the treatment of tr…
Sector: Healthcare Industry: Biotechnology Market Cap: $435.3M CIK: 1559053
20
Total Filings
9
Bullish Classifications
0
Bearish Classifications
17
Insider Transactions
2
Material Events (8-K)
1
Periodic Reports
Rule-based classifications for PRTA currently lean bullish. Of the 20 displayed SEC filing records, 9 carry bullish classifications versus 0 bearish classifications. These labels summarize filing attributes; they are not recommendations, probabilities, or evidence of future price direction. There were 17 insider transactions (Form 4) in this period.
PRTA Filing Activity Snapshot 2026-07-30 — 2026-10-15
Insider Transactions (Form 4)
9 buys vs 0 sells
Net insider buying in this period — more purchases than sales reported.
Largest Form 144 Filing
$1.82M
SCULLY WILLIAM P (10% Owner) · 2026-10-09
215,000 shares · Form 4
Insider Transactions 17 · Forms 3, 4 and 5

A Form 4 is filed within two business days of a company insider — an officer, a director, or a holder of more than ten percent of the stock — changing their position in the shares. All 17 filings in this group are Form 4s for Prothena Corporation plc.

The difficulty with reading these filings as a group is that a single form type covers transactions that mean entirely different things. An executive spending their own money to buy stock and an executive having shares withheld to pay tax on a vesting grant both appear as a Form 4. Every filing below is therefore tagged with the nature of the underlying transaction, taken from the transaction code reported on the form itself.

Across the 17 insider filings shown, the breakdown is 9 open-market purchase, 6 option exercise and 2 gift. 9 of them involved a discretionary open-market trade; the rest are compensation and administrative mechanics.

What each transaction type means

Open-market purchase ×9
The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.
Option exercise ×6
The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.
Gift ×2
Shares were transferred as a gift, typically for estate or charitable planning. No sale into the market took place.
Form 4 Open-market purchase Insider Buying 2026-10-15

PRTA insider SCULLY WILLIAM P (10% Owner) bought 110,000 shares (~$920.0K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 110,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 100,000 $8.35 $835.5K
P Open-market purchase 10,000 $8.46 $84.6K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 110,000 Est. Value: $920.0K
Form 4 Open-market purchase Insider Buying 2026-10-09

PRTA insider SCULLY WILLIAM P (10% Owner) bought 215,000 shares (~$1.82M)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 215,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 125,000 $8.40 $1.05M
P Open-market purchase 90,000 $8.57 $770.9K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 215,000 Est. Value: $1.82M
Form 4 Open-market purchase Insider Buying 2026-10-06

PRTA insider SCULLY WILLIAM P (10% Owner) bought 100,000 shares (~$857.2K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 100,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 100,000 $8.57 $857.2K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 100,000 Est. Value: $857.2K
Form 4 Open-market purchase Insider Buying 2026-09-30

PRTA insider SCULLY WILLIAM P (10% Owner) bought 162,000 shares (~$1.41M)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 162,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 162,000 $8.68 $1.41M
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 162,000 Est. Value: $1.41M
Form 4 Open-market purchase Insider Buying 2026-09-29

PRTA insider SCULLY WILLIAM P (10% Owner) bought 103,500 shares (~$889.9K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 103,500 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 103,500 $8.60 $889.9K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 103,500 Est. Value: $889.9K
Form 4 Open-market purchase Insider Buying 2026-09-21

PRTA insider SCULLY WILLIAM P (10% Owner) bought 100,000 shares (~$843.5K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 100,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 100,000 $8.43 $843.5K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 100,000 Est. Value: $843.5K
Form 4 Open-market purchase Insider Buying 2026-09-03

PRTA insider SCULLY WILLIAM P (10% Owner) bought 27,000 shares (~$255.7K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 27,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 27,000 $9.47 $255.7K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 27,000 Est. Value: $255.7K
Form 4 Open-market purchase Insider Buying 2026-08-21

PRTA insider SCULLY WILLIAM P (10% Owner) bought 50,000 shares (~$439.4K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 50,000 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 50,000 $8.79 $439.4K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 50,000 Est. Value: $439.4K
Form 4 Gift Tax / Compensation Filing 2026-08-18

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

SCULLY WILLIAM P (10% Owner) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were transferred as a gift, typically for estate or charitable planning. No sale into the market took place.

Transactions reported on this filing
Code Nature Shares Price Value
G Gift 336,000 — —
G Gift 627,553 — —
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 963,553
Form 4 Gift Tax / Compensation Filing 2026-08-11

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

SCULLY WILLIAM P (10% Owner) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were transferred as a gift, typically for estate or charitable planning. No sale into the market took place.

Transactions reported on this filing
Code Nature Shares Price Value
G Gift 251,553 — —
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 251,553
Form 4 Open-market purchase Insider Buying 2026-08-10

PRTA insider SCULLY WILLIAM P (10% Owner) bought 37,500 shares (~$323.2K)

SCULLY WILLIAM P, listed as 10% Owner at PROTHENA CORP PUBLIC LTD CO, reported an open-market purchase of 37,500 PRTA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 34,000 $8.62 $293.1K
P Open-market purchase 3,500 $8.62 $30.2K
Filing: Form 4 (Insider Transaction) Insider: SCULLY WILLIAM P (10% Owner) Shares: 37,500 Est. Value: $323.2K
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Zago Wagner M. (Chief Scientific Officer) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 51,000 — —
D Disposition to issuer 51,000 $8.56 $436.6K
M Option exercise derivative · Restricted Stock Units 51,000 — —
Filing: Form 4 (Insider Transaction) Insider: Zago Wagner M. (Chief Scientific Officer) Shares: 102,000
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Walker Karin L (Chief Accounting Officer) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 15,000 — —
D Disposition to issuer 15,000 $8.56 $128.4K
M Option exercise derivative · Restricted Stock Units 15,000 — —
Filing: Form 4 (Insider Transaction) Insider: Walker Karin L (Chief Accounting Officer) Shares: 30,000
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Swanson Chad J. (Chief Development Officer) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 51,000 — —
D Disposition to issuer 40,800 $8.56 $349.2K
F Tax withholding on vested shares 3,467 $8.56 $29.7K
M Option exercise derivative · Restricted Stock Units 51,000 — —
Filing: Form 4 (Insider Transaction) Insider: Swanson Chad J. (Chief Development Officer) Shares: 95,267
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Smith Brandon S. (Chief Operating Officer) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 78,000 — —
D Disposition to issuer 78,000 $8.56 $667.7K
M Option exercise derivative · Restricted Stock Units 78,000 — —
Filing: Form 4 (Insider Transaction) Insider: Smith Brandon S. (Chief Operating Officer) Shares: 156,000
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Nguyen Tran (Chief Strategy Officer and CFO) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 57,000 — —
D Disposition to issuer 57,000 $8.56 $487.9K
M Option exercise derivative · Restricted Stock Units 57,000 — —
Filing: Form 4 (Insider Transaction) Insider: Nguyen Tran (Chief Strategy Officer and CFO) Shares: 114,000
Form 4 Option exercise Tax / Compensation Filing 2026-07-30

PRTA insider Form 4 filed for equity award, exercise, or tax withholding

Kinney Gene G. (Director, President and CEO) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 84,000 — —
D Disposition to issuer 84,000 $8.56 $719.0K
M Option exercise derivative · Restricted Stock Units 84,000 — —
Filing: Form 4 (Insider Transaction) Insider: Kinney Gene G. (Director, President and CEO) Shares: 168,000
Material Events 2 · Form 8-K

An 8-K reports a material event in the window between scheduled reports. There are 2 in this period for Prothena Corporation plc. Each 8-K names the item number it is filed under, and that number is the fastest way to tell a routine disclosure from a consequential one.

Item 2.02 is an earnings release, Item 5.02 is a change of directors or officers, and Item 1.01 or 2.01 covers a material agreement or a completed acquisition. Item 7.01 and Item 8.01 are the general-purpose disclosure items and carry no fixed meaning on their own.

Form 8-K Material Company Update 2026-10-02

PRTA filed 8-K — material company event

PROTHENA CORP PUBLIC LTD CO filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
Form 8-K Material Company Update 2026-08-06

PRTA filed 8-K — material company event

PROTHENA CORP PUBLIC LTD CO filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
Periodic Reports 1 · Forms 10-K and 10-Q

The periodic reports are where the audited and reviewed financial statements live. This period contains 1 quarterly report (10-Q) for Prothena Corporation plc.

The two are not equivalent in weight. A 10-K is audited by an external firm and includes the full risk factor disclosure, business description and management discussion; a 10-Q is unaudited, reviewed rather than examined, and much shorter. When a figure in a quarterly report is later revised, the annual report is usually where the correction appears.

An amended report — 10-K/A or 10-Q/A — restates or corrects something in the original filing, and is worth reading against the version it replaces.

Form 10-Q Quarterly Report 2026-08-06

PRTA filed Quarterly Report (10-Q)

PROTHENA CORP PUBLIC LTD CO filed its quarterly report with the SEC. This report includes unaudited financial statements and management discussion for the quarter.

Filing: 10-Q (Quarterly Report)

How we classify Prothena Corporation plc's filings

Straight from EDGAR

Each displayed record links to an original source document. StrongBuyAnalytics provides navigation and brief excerpts or summaries, not the filing itself. Parsing may omit context or contain errors, so read the original document in full.

Transaction codes, not guesswork

The nature shown on each insider filing comes from the transaction code the filer entered on the form itself — P for an open-market purchase, A for a compensation award, F for shares withheld to pay tax, M for an option exercise. Where one filing contains several codes, the transaction table lists them line by line.

Why the distinction matters

Insider activity is routinely summarised as buying or selling, which flattens together decisions that mean very different things. Shares withheld for tax on a vesting grant are an automatic administrative step; shares bought on the open market are someone committing their own money at the current price.

What this page does not tell you

A filing records what happened, not why. Form 4 does not always disclose whether a sale was executed under a pre-arranged Rule 10b5-1 plan, and no single filing is a basis for a decision on PRTA. Read these alongside the fundamentals rather than in isolation.

Frequently Asked Questions — PRTA SEC Filings

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Publisher, sources & limitations — September 15, 2026. StrongBuyAnalytics provides navigation and brief excerpts or summaries for educational use. Original filings remain at SEC EDGAR or other displayed source links; StrongBuyAnalytics does not author them. Filing dates are source dates, not publication dates for this page. Coverage can be delayed, incomplete, amended, or unavailable because of SEC/source availability, parsing, caching, or outages. Verify every material statement in the original filing.
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