STOCK TITAN
  1. Home
  2. Sec-filings
  3. RNA
  4. [Form 4] Avidity Biosciences, Inc. Insider Trading Activity

Mosbrooker executes 10b5-1 sales at $44.06 avg after $9.05 option exercise

Filing Impact
(Very High)
Filing Sentiment
(Very Negative)
Form Type
4

Rhea-AI Filing Summary

Eric Mosbrooker, Chief Commercial Officer of Avidity Biosciences (RNA), reported option exercise and share sales on 08/06/2025. He exercised 124,687 stock options at an exercise price of $9.05, generating 124,687 common shares. Those shares and additional holdings were sold in multiple transactions under a Rule 10b5-1 trading plan adopted on September 11, 2024 at a weighted-average sale price of $44.0626 (range $40.54–$45.44).

The Form 4 shows total reported sales of 130,807 shares (124,687 + 6,120) and a reported direct beneficial ownership in common stock of 55,000 shares following the transactions. The filing also reports 190,313 derivative securities beneficially owned following the transactions and discloses an option vesting schedule of 1/48th monthly beginning January 1, 2024.

Positive

  • Sales executed under a Rule 10b5-1 trading plan adopted on September 11, 2024, reducing timing concerns.
  • Weighted-average sale price and price range disclosed ($44.0626; $40.54–$45.44), providing transparent pricing detail.
  • Option exercise details and vesting schedule disclosed (exercise price $9.05; vesting 1/48th monthly from Jan 1, 2024).

Negative

  • Significant insider disposals reported: total reported shares sold on 08/06/2025 equal 130,807 (124,687 + 6,120).
  • Direct common-stock ownership reduced to 55,000 shares following the reported transactions, per the Form 4.
  • Large number of derivative securities remain outstanding: 190,313 derivative securities reported beneficially owned after the transactions.

Insights

TL;DR: Reporting person exercised 124,687 options and sold 130,807 shares under a prearranged 10b5-1 plan; ownership materially changed.

The Form 4 documents an option exercise at a $9.05 strike for 124,687 shares on 08/06/2025, followed by multiple sales under a Rule 10b5-1 plan at a weighted-average price of $44.0626 (range $40.54–$45.44). The net effect is a reported direct common-stock position of 55,000 shares and 190,313 derivative securities beneficially owned post-transactions. These are explicit, material insider transactions; the 10b5-1 disclosure is important for assessing timing and intent, and the exact prices and quantities allow straightforward calculation of proceeds and changes in direct holdings.

TL;DR: Transactions were executed pursuant to a pre-established 10b5-1 plan; filings fully disclose quantities, prices, and vesting terms.

The filing includes explicit disclosure that the sales were effected under a Rule 10b5-1 plan adopted on September 11, 2024, which provides an affirmative defense for prearranged trading. The Form 4 also details the option vesting schedule (1/48th monthly from January 1, 2024) and reports post-transaction beneficial ownership figures for both common stock and derivative securities. For governance review, the filing supplies the necessary transaction chronology, price range, and resultant holdings.

Insider Mosbrooker Eric
Role Chief Commercial Officer
Sold 130,807 shs ($5.76M)
Type Security Shares Price Value
Exercise Stock Option (Right to Buy) 124,687 $0.00 --
Exercise Common Stock 124,687 $9.05 $1.13M
Sale Common Stock 124,687 $44.0626 $5.49M
Sale Common Stock 6,120 $44.0626 $270K
Holdings After Transaction: Stock Option (Right to Buy) — 190,313 shares (Direct); Common Stock — 185,807 shares (Direct)
Footnotes (1)
  1. The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan previously adopted by the Reporting Person on September 11, 2024. This represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $40.54 to $45.44. The Reporting Person undertakes to provide the Issuer, any securityholder of the Issuer, or the Staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. 1/48th of the total number of shares subject to the option shall vest on each monthly anniversary of January 1, 2024 (the "Vesting Commencement Date"), subject to the Reporting Person's continuous service to the Issuer on each such vesting date, so that the options shall be fully vested on the fourth anniversary of the Vesting Commencement Date.
Form 4 Insider Transactions: What Each Field Means →
SEC Form 4
FORM 4 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number: 3235-0287
Estimated average burden
hours per response: 0.5
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
X
 Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.
1. Name and Address of Reporting Person*
Mosbrooker Eric
(Last) (First) (Middle)
C/O AVIDITY BIOSCIENCES, INC.
10578 SCIENCE CENTER DRIVE, SUITE 125
(Street)
SAN DIEGO CA 92121
(City) (State) (Zip)
2. Issuer Name and Ticker or Trading Symbol
Avidity Biosciences, Inc. [ RNA ] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
Director 10% Owner
X Officer (give title below) Other (specify below)
Chief Commercial Officer
3. Date of Earliest Transaction (Month/Day/Year)
08/06/2025
4. If Amendment, Date of Original Filed (Month/Day/Year)
 6. Individual or Joint/Group Filing (Check Applicable Line)
X Form filed by One Reporting Person
Form filed by More than One Reporting Person
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 08/06/2025 M(1) 124,687 A $9.05 185,807 D
Common Stock 08/06/2025 S(1) 124,687 D $44.0626(2) 61,120 D
Common Stock 08/06/2025 S(1) 6,120 D $44.0626(2) 55,000 D
Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 6. Date Exercisable and Expiration Date (Month/Day/Year) 7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (Right to Buy) $9.05 08/06/2025 M 124,687 (3) 12/31/2033 Common Stock 124,687 $0 190,313 D
Explanation of Responses:
1. The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan previously adopted by the Reporting Person on September 11, 2024.
2. This represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $40.54 to $45.44. The Reporting Person undertakes to provide the Issuer, any securityholder of the Issuer, or the Staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
3. 1/48th of the total number of shares subject to the option shall vest on each monthly anniversary of January 1, 2024 (the "Vesting Commencement Date"), subject to the Reporting Person's continuous service to the Issuer on each such vesting date, so that the options shall be fully vested on the fourth anniversary of the Vesting Commencement Date.
Remarks:
/s/ John B. Moriarty, Jr., J.D., Attorney-in-Fact 08/08/2025
** Signature of Reporting Person Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

Source: View Original Filing on SEC EDGAR

FAQ

What transactions did Eric Mosbrooker (RNA) report on the Form 4?

The Form 4 reports an exercise of 124,687 stock options at an exercise price of $9.05 on 08/06/2025 and multiple sales totaling 130,807 shares executed under a Rule 10b5-1 plan.

At what price were the shares sold in Mosbrooker's RNA Form 4?

The sales were executed at a weighted-average price of $44.0626, with individual sale prices ranging from $40.54 to $45.44.

How many shares does Mosbrooker own after the transactions (RNA)?

The Form 4 reports a direct beneficial ownership in common stock of 55,000 shares following the reported transactions.

Were the sales part of a prearranged trading plan (RNA)?

Yes. The Form 4 states the sales were effected pursuant to a Rule 10b5-1 trading plan adopted on September 11, 2024.

What option vesting schedule is disclosed in the Form 4 for RNA?

The filing discloses that 1/48th of the total options vest monthly beginning on January 1, 2024, with full vesting on the fourth anniversary of that date.