SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(1)

Consists of 871,851 shares owned by F2 Bio Ventures V, L.P. (“F2 V”) and includes 121,396 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 V. The Reporting Person is the sole member ofF2 Bio Ventures GP Ltd (“F2 V GP”), the General Partner of F2 V.

(2)

Consists of (i) 1,794,983 shares owned by F2 Bioscience IV, L.P. (“F2 IV”) and includes 249,932 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV, (ii) 587,500 shares owned by F2 Bioscience VI, L.P. (“F2 VI”) and (iii) 1,557,328 shares owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 III. The Reporting Person is a member of each of F2 IV GP, the General Partner of F2 IV and F2 VI and of F2 Bioscience GP III Ltd., (“F2 III GP”) the General Partner of F2 Bioscience III L.P.

(3)

Consists of (i) 871,851 shares owned by F2 V and includes 121,396 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 V, (ii) 1,794,983 shares owned by F2 IV and includes 249,932 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV, (iii) 587,500 shares owned by F2 VI, and (iv) 1,557,328 shares owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 III. The Reporting Person is the sole member of F2 V GP, the General Partner of F2 V. The Reporting Person is a member of each F2 IV GP, the General Partner of F2 IV and F2 VI, and of F2 III GP, the General Partner of F2 III.

The percentage is calculated based upon 28,938,899 shares of outstanding Common Stock being deemed issued and outstanding, as reported by the Issuer in the Final Prospectus.

Item 2.

Identity and Background

Item 2 is hereby supplemented to add the following:

Prior to June 6, 2014 (the “Effective Date”), certain of the Reporting Persons were parties to a certain agreement (the “Prior Stockholders’ Agreement”) with the other persons referred to on Schedule B attached to this Amendment No. 2 (the “Separately Filing Group Members”), which contained, among other things, certain director election provisions and price-based transfer restrictions on the shares of Common Stock held by Reporting Persons. As a result, certain of the Reporting Persons may have belonged to a “group,” within the meaning of Section 13(d)(3) of the Act, comprised of certain of the Reporting Persons and the Separately Filing Group Members. It is the understanding of the Reporting Persons that the Separately Filing Group Members have filed or are filing separate Amendments to Schedule 13Ds pursuant to Rule 13d-1(k)(2) under the Act. Ownership information of the Separately Filing Group Members is or will be reflected in the separate filings made by the Separately Filing Group Members.

On April 24, 2014, the Issuer, the Reporting Persons and the Separately Filing Group Members entered into a Fifth Amended and Restated Stockholders’ Agreement (the “New Stockholders’ Agreement”), which became effective on the Effective Date and amended and restated in its entirety the Prior Stockholders’ Agreement.  The New Stockholders’ Agreement is attached as Exhibit 10.1 to the Issuer’s Current Report on Form 8-K as filed with the Securities and Exchange Commission on April 30, 2013 and incorporated by reference herein. The New Stockholders’ Agreement eliminated the aforementioned voting agreements and limitations on the sale of the shares of Common Stock held by the Reporting Persons and the Separately Filing Group Members and grants the parties thereto certain resale, demand and piggyback registration rights as set forth therein.  With the termination of such agreements, any group within the meaning of Section 13(d)(3) of the Act that may have been deemed to have been formed among the Reporting Persons and the Separately Filing Group Members has been terminated, effective as of the Effective Date.  Each Reporting Person expressly disclaims membership in any such group and beneficial ownership of any securities beneficially owned by any other Reporting Person (other than as reported herein) or Separately Filing Group Member.  Any further filings with respect to securities of the Issuer, if required, shall be filed by each Reporting Person separately or jointly with their affiliates.

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby supplemented to add the following:

Upon consummation of the IPO, all shares of Preferred Stock of the Issuer held by the Reporting Persons were converted into shares of Common Stock.

In connection with the IPO, the Issuer issued an aggregate of 129,128 shares of Common Stock to the Reporting Persons in satisfaction of accumulated and unpaid dividends on the Preferred Stock.

Schedule C is also amended and incorporated herein to this Item 3 by reference.

Item 4.

Purpose of Transaction

The first paragraph of Item 4 is hereby amended and restated in its entirety as follows:

Each of the Reporting Persons acquired the shares indicated next to the name of such Reporting Person in Schedule C for investment purposes.  Depending on market conditions, its continuing evaluation of the business and prospects of the Issuer and other factors, any or all of the Reporting Persons may dispose of or acquire additional shares of the Issuer in compliance with applicable law.

Item 5.

Interest in Securities of the Issuer

Item 5 is hereby amended and restated in its entirety as follows:

(a)           Aggregate number of securities beneficially owned by each Reporting Person disclosed in Item 2: See Line 11 of the cover sheets.

Percent of Class:  See Line 13 of the cover sheets.  The percentages set forth on the cover sheets for each Reporting Person are calculated based upon 28,938,899 shares of outstanding Common Stock being deemed issued and outstanding, as reported by the Issuer in the Final Prospectus.

(b)                                   Regarding the number of shares as to which such person has:

(i)            sole power to vote or to direct the vote:

See Line 7 of cover sheets.

(ii)           shared power to vote or to direct the vote:

See Line 8 of cover sheets.

(iii)          sole power to dispose or to direct the disposition:

See Line 9 of cover sheets.

(iv)          shared power to dispose or to direct the disposition:

See Line 10 of cover sheets.

(c)           Except as set forth in Item 3 above, none of the Reporting Persons has effected any transaction in the Common Stock during the last 60 days.

(d)           No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, shares beneficially owned by any of the Reporting Persons.

(e)           Not Applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

Item 6 of the Original Schedule 13D is hereby amended and restated in its entirety as follows:

The portion of Item 2 containing the description of the New Stockholders’ Agreement and the termination of the Prior Stockholders’ Agreement and associated termination of any group within the meaning of Section 13(d)(3) of the Act that may have been deemed to have been formed among the parties thereto, and Item 3, are incorporated by reference into this Item 6.

F2 and F2 Capital are party to an Investment Advisory Agreement, dated April 22, 2013, which is attached as Exhibit 6 to the Original Schedule 13D and incorporated by reference herein.

Certain of the Reporting Persons hold warrants to purchase an aggregate of 357,047 shares of Common Stock which are exercisable at the Reporting Person’s option until the expiration date on April 23, 2018 or exercise automatically in the event of a sale of the Issuer.

Item 7.

Material to be Filed as Exhibits.

Item 7 of the Original Schedule 13D is amended and supplemented as follows:

Exhibit
Number

Description

5

Fifth Amended and Restated Stockholders’ Agreement, dated as of April 24, 2014, by and among the Issuer and the stockholders party thereto.*

F2 BIOSCIENCE III L.P.

By: F2 Bioscience IV GP Ltd.,

its general partner

By:

/s/ Morag Law as Attorney-in-Fact under Power of Attorney

Name: Morag Law

Title: Authorised Signatory

F2 BIOSCIENCE GP LTD.

By:

/s/ Morag Law as Attorney-in-Fact under Power of Attorney

Name: Morag Law

Title: Authorised Signatory

F2 CAPITAL LIMITED

By:

/s/ Morag Law as Attorney-in-Fact under Power of Attorney

Name: Morag Law

Title: Authorised Signatory

By:

/s/ Dr. Morana Jovan-Embiricos by Morag Law as Attorney-in-Fact under Power of Attorney

Name: Dr. Morana Jovan-Embiricos

By:

/s/ Katherine Priestley by Morag Law as Attorney-in-Fact under Power of Attorney

Name: Katherine Priestley

NAME

SHARE OWNERSHIP

F2 Bioscience III L.P.

1,914,375 shares of Common Stock which includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock.

F2 Bioscience GP Ltd

1,914,375 shares of Common Stock, consisting of 1,557,328 shares of Common Stock owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV.

Dr. Morana Jovan Embiricos

5,540,037 shares of Common Stock, consisting of (i) 871,851 shares owned by F2 V and includes 121,396 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 V, (ii) 1,794,983 shares owned by F2 IV and includes 249,932 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV, (iii) 587,500 shares owned by F2 VI, and (iv) 1,557,328 shares owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 III.

Katherine Priestley

4,546,790 shares of Common Stock, consisting of (i) 1,794,983 shares owned by F2 IV and includes 249,932 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV, (ii) 587,500 shares owned by F2 VI, and (iii) 1,557,328 shares owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 III.

F2 Capital Limited

5,540,037 shares of Common Stock, consisting of (i) 871,851 shares owned by F2 V and includes 121,396 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 V, (ii) 1,794,983 shares owned by F2 IV and includes 249,932 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 IV, (iii) 587,500 shares owned by F2 VI, and (iv) 1,557,328 shares owned by F2 III and includes 357,047 shares of Common Stock that may be issued upon the exercise of warrants to purchase Common Stock owned by F2 III.