EcoR1 Capital, LLC, Oleg Nodelman and EcoR1 Capital Fund Qualified, L.P. report beneficial ownership of Mereo BioPharma Group plc Ordinary Shares. EcoR1 and Nodelman each report beneficial ownership of 5,000,000 Ordinary Shares, while the Qualified Fund reports 4,732,750 Ordinary Shares, each representing 0.6% of the outstanding class based on 798,093,044 Ordinary Shares outstanding as of May 11, 2026. The position is held through American Depositary Shares, with 1,000,000 ADS representing 5,000,000 Ordinary Shares and 946,550 ADS representing 4,732,750 Ordinary Shares. The filers state the holdings are not for the purpose of changing or influencing control of Mereo BioPharma and disclaim group status and beneficial ownership beyond their pecuniary interest.
Positive
None.
Negative
None.
Key Figures
EcoR1 beneficial ownership:5,000,000 Ordinary SharesOleg Nodelman beneficial ownership:5,000,000 Ordinary SharesQualified Fund beneficial ownership:4,732,750 Ordinary Shares+4 more
Qualified Fund beneficial ownership4,732,750 Ordinary SharesEcoR1 Capital Fund Qualified, L.P. beneficially owned 4,732,750 Ordinary Shares
Ownership percentage per filer0.6%EcoR1, Oleg Nodelman and Qualified Fund each reported 0.6% of the class
Shares outstanding baseline798,093,044 Ordinary SharesOrdinary Shares outstanding as of May 11, 2026, used for percentage calculation
EcoR1 ADS holdings1,000,000 American Depositary SharesHeld by EcoR1, each ADS representing 5 Ordinary Shares (total 5,000,000)
Qualified Fund ADS holdings946,550 American Depositary SharesHeld by Qualified Fund, each ADS representing 5 Ordinary Shares (total 4,732,750)
Key Terms
American Depositary Shares, beneficial owner, pecuniary interest, shared voting power, +1 more
5 terms
American Depositary Sharesfinancial
"These Ordinary Shares are held through 1,000,000 American Depositary Shares of the Issuer"
American depositary shares (ADSs) are a way for investors in the United States to buy shares of foreign companies without dealing with international markets directly. They represent ownership in a foreign company's stock and are traded on U.S. stock exchanges, making it easier for American investors to buy, sell, and own parts of companies from around the world.
beneficial ownerfinancial
"it disclaims that it is, a beneficial owner, as defined in Rule 13d-3"
A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.
pecuniary interestfinancial
"disclaims beneficial ownership of the securities reported herein except to the extent of that person's pecuniary interest"
shared voting powerfinancial
"Shared Voting Power 5,000,000.00"
Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.
shared dispositive powerfinancial
"Shared Dispositive Power 5,000,000.00"
FAQ
What ownership stake in MREO does EcoR1 Capital report?
EcoR1 Capital and Oleg Nodelman each report beneficial ownership of 5,000,000 Ordinary Shares of Mereo BioPharma, equal to 0.6% of the outstanding class, based on 798,093,044 Ordinary Shares outstanding as of May 11, 2026.
How many MREO shares does EcoR1 Capital Fund Qualified, L.P. own?
EcoR1 Capital Fund Qualified, L.P. reports beneficial ownership of 4,732,750 Ordinary Shares of Mereo BioPharma, corresponding to 0.6% of the outstanding class. These shares are held through 946,550 American Depositary Shares, each ADS representing 5 Ordinary Shares.
How are EcoR1’s MREO holdings structured through ADSs?
EcoR1’s reported MREO position is held via American Depositary Shares, with 1,000,000 ADS representing 5,000,000 Ordinary Shares, and the Qualified Fund holding 946,550 ADS representing 4,732,750 Ordinary Shares, at a ratio of 1 ADS to 5 Ordinary Shares.
Is EcoR1’s ownership in MREO considered passive or for control purposes?
The reporting persons certify the MREO securities were not acquired and are not held for the purpose of changing or influencing control of Mereo BioPharma and are not held in connection with any such control-related transaction, aside from potential nomination activities described.
Why does the Schedule 13G/A show only 0.6% ownership for MREO?
Each reporting person lists 0.6% of the class based on 798,093,044 Ordinary Shares outstanding as of May 11, 2026. They also state they own 5 percent or less of the class, which aligns with the passive Schedule 13G filing status.
What voting and dispositive power do EcoR1 filers have over MREO shares?
Each reporting person reports 0 shares with sole voting or dispositive power and shared voting and dispositive power over their reported holdings (EcoR1 and Nodelman: 5,000,000 shares; Qualified Fund: 4,732,750 shares), reflecting shared control arrangements.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 2)
Mereo BioPharma Group plc
(Name of Issuer)
Ordinary Shares
(Title of Class of Securities)
589492107
(CUSIP Number)
06/30/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
589492107
1
Names of Reporting Persons
EcoR1 Capital, LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
5,000,000.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
5,000,000.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,000,000.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
.6 %
12
Type of Reporting Person (See Instructions)
IA, OO
Comment for Type of Reporting Person: These Ordinary Shares are held through 1,000,000 American Depositary Shares of the Issuer, each representing 5 Ordinary Shares. Percentage calculated based on 798,093,044 Ordinary Shares outstanding on May 11, 2026, as reported in the Form 10-Q filed by the Issuer for the quarterly period ended March 31, 2026.
SCHEDULE 13G
CUSIP Number(s):
589492107
1
Names of Reporting Persons
Oleg Nodelman
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
5,000,000.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
5,000,000.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,000,000.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
.6 %
12
Type of Reporting Person (See Instructions)
HC, IN
Comment for Type of Reporting Person: These Ordinary Shares are held through 1,000,000 American Depositary Shares of the Issuer, each representing 5 Ordinary Shares. Percentage calculated based on 798,093,044 Ordinary Shares outstanding on May 11, 2026, as reported in the Form 10-Q filed by the Issuer for the quarterly period ended March 31, 2026.
SCHEDULE 13G
CUSIP Number(s):
589492107
1
Names of Reporting Persons
EcoR1 Capital Fund Qualified, L.P.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
4,732,750.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
4,732,750.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
4,732,750.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
.6 %
12
Type of Reporting Person (See Instructions)
PN
Comment for Type of Reporting Person: These Ordinary Shares are held through 946,550 American Depositary Shares of the Issuer, each representing 5 Ordinary Shares. Percentage calculated based on 798,093,044 Ordinary Shares outstanding on May 11, 2026, as reported in the Form 10-Q filed by the Issuer for the quarterly period ended March 31, 2026.
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Mereo BioPharma Group plc
(b)
Address of issuer's principal executive offices:
ONE CAVENDISH PLACE, FOURTH FLOOR, LONDON, United Kingdom, W1G 0QF
Item 2.
(a)
Name of person filing:
EcoR1 Capital, LLC, a Delaware limited liability company ("EcoR1")
EcoR1 Capital Fund Qualified, L.P., a Delaware limited partnership ("Qualified Fund")
Oleg Nodelman
Qualified Fund is filing this statement jointly with the other reporting persons, but not as a member of a group, and it expressly disclaims membership in a group. In addition, the filing of this Schedule 13G on behalf of Qualified Fund should not be construed as an admission that it is, and it disclaims that it is, a beneficial owner, as defined in Rule 13d-3 under the Act, of any securities covered by this Schedule 13G. Each reporting person also disclaims beneficial ownership of the securities reported herein except to the extent of that person's pecuniary interest therein.
(b)
Address or principal business office or, if none, residence:
357 Tehama Street #3
San Francisco, CA 94103
(c)
Citizenship:
See Item 4 of the cover sheet for each reporting person.
(d)
Title of class of securities:
Ordinary Shares
(e)
CUSIP No.:
589492107
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
If a group has filed this schedule pursuant to §240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit stating the identity and Item 3 classification of each member of the group. If a group has filed this schedule pursuant to §240.13d-1(c) or §240.13d-1(d), attach an exhibit stating the identity of each member of the group.
EcoR1 is the general partner and investment adviser of investment funds, including Qualified Fund. Mr. Nodelman is the control person of EcoR1.
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
EcoR1 Capital, LLC
Signature:
/s/ Oleg Nodelman
Name/Title:
Manager
Date:
08/14/2026
Oleg Nodelman
Signature:
/s/ Oleg Nodelman
Name/Title:
Reporting person
Date:
08/14/2026
EcoR1 Capital Fund Qualified, L.P.
Signature:
/s/ Oleg Nodelman
Name/Title:
Manager of the General Partner, EcoR1 Capital, LLC
Date:
08/14/2026
Exhibit Information
EXHIBIT 99 - AGREEMENT REGARDING JOINT FILING OF STATEMENT ON SCHEDULE 13D OR 13G
