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Johannes Jacob Pieter Kastelein

CIK 2000389 · Chief Scientific Officer · last filed 2026-08-25

Johannes Jacob Pieter Kastelein is a Chief Scientific Officer who has filed 18 SEC Form 4 insider transactions across 2 companies since 2024. The most recent filing, for NAMS, was dated Aug 25, 2026. Across all open-market trades the lifetime net is −$20.8M, making them a net seller over the disclosed history. Current disclosed insider exposure totals $4.6M across reported positions.

"Disclosed insider exposure" sums this person's most-recently-reported share counts across each company they're an insider in, multiplied by the current underlying price. It is not net worth — it misses retail holdings, private investments, real estate, index funds, and any company where the person isn't an SEC-reporting insider. For informational purposes only.

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Disclosed Exposure

$4.61M

Companies

2

Total Filings

18

Lifetime Open-Market Net

-$20.83M

Filer Profile

Reported Address
C/O NEWAMSTERDAM PHARMA COMPANY N.V.
GOOIMEER 2-35
NAARDEN, P7 1411 DC
Profile details as reported on the filer's SEC submissions — for individual insiders the address is often in care of the issuer. Related filers are identified from jointly filed SEC submissions and shared reported addresses. View filings on SEC EDGAR.

Holdings By Company

Latest on-record share count from this person's most recent non-derivative Form 4 transaction in each company. Disclosed exposure = shares × current underlying price.
Symbol Role Shares Price Disclosed Exposure Lifetime OM Net Filings Latest Filed
NAMS Chief Scientific Officer 122,802 $22.80 $2.80M -$3.36M 1 2026-08-25
NAMSW Chief Scientific Officer 153,591 $11.78 $1.81M -$17.46M 10 2026-03-09

Recent Filings

18 filings
Insider activity across all companies, newest first. Form 4 rows are post-trade confirmations (buys, sells, grants, exercises). Notice (144) rows are pre-trade notices of intent to sell restricted or control stock under Rule 144 — they may not all execute. Compare adjacent dates to see which notices became actual sales.
Filed Symbol Action Net Shares Net $ Link
2026-08-25 NAMS Notice (144/A) −250,000 -$6.97M EDGAR
2026-08-25 NAMS Mixed — -$3.36M EDGAR
2026-08-24 NAMS Notice (144) −125,000 -$3.48M EDGAR
2026-03-09 NAMSW Mixed — -$9.09M EDGAR
2026-03-05 NAMS Notice (144) −300,000 -$9.35M EDGAR
2026-02-24 NAMSW Sell (S) −45,481 -$1.61M EDGAR
2026-02-20 NAMS Notice (144) −45,481 -$1.58M EDGAR
2026-01-07 NAMSW Mixed +19,500 -$199.5K EDGAR
2026-01-05 NAMS Notice (144) −6,000 -$199.5K EDGAR
2025-08-25 NAMS Notice (144) −100,000 -$2.50M EDGAR
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Form 4 codes: P = open-market purchase · S = open-market sale · A = grant/award · M = option exercise · F = tax withholding at vest · G = bona-fide gift · D = disposition to issuer · J = other (see filing footnote). Only P / S codes carry directional signal.
Notice (144 / 144/A): Form 144 is a notice of intent to sell restricted/control stock under Rule 144, filed before the sale; 144/A is an amendment. Many notices are pre-scheduled under Rule 10b5-1 plans. A Form 4 with code S typically follows within a few days when the planned sale executes; missing follow-up Form 4s suggest the notice was cancelled or modified.