Ownership Submission
FORM 3
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  ORBIMED ADVISORS LLC
2. Date of Event Requiring Statement (Month/Day/Year)
05/15/2013
3. Issuer Name and Ticker or Trading Symbol
AMBIT BIOSCIENCES CORP [AMBI]
(Last)
(First)
(Middle)
601 LEXINGTON AVENUE, 54TH FLOOR
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

NEW YORK, NY 10022
6. Individual or Joint/Group Filing(Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)
2. Amount of Securities Beneficially Owned
(Instr. 4)
3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)
4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Common Stock, $0.001 par value per share 307 (1)
I
See Footnotes (2) (3) (5)
Common Stock, $0.001 par value per share 2 (1)
I
See Footnotes (4) (5)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)
2. Date Exercisable and Expiration Date
(Month/Day/Year)
3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)
4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)
6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Series E Preferred Stock   (6)   (6) Common Stock 367,315 $ (6) I See Footnotes (2) (3) (5)
Series E Preferred Stock   (6)   (6) Common Stock 3,498 $ (6) I See Footnotes (4) (5)
Series D-2 Preferred Stock   (7)   (7) Common Stock 219,863 $ (7) I See Footnotes (2) (3) (5)
Series D-2 Preferred Stock   (7)   (7) Common Stock 2,094 $ (7) I See Footnotes (4) (5)
Series D Preferred Stock   (8)   (8) Common Stock 181,689 $ (8) I See Footnotes (2) (3) (5)
Series D Preferred Stock   (8)   (8) Common Stock 1,730 $ (8) I See Footnotes (4) (5)
Series D-2 Preferred Stock Warrants (Right to Buy) 05/18/2011 05/18/2021 Common Stock 57,217 (1) $ 0.024 I See Footnotes (2) (3) (5)
Series D-2 Preferred Stock Warrants (Right to Buy) 05/18/2011 05/18/2021 Common Stock 544 (1) $ 0.024 I See Footnotes (4) (5)
Common Stock Warrants (Right to Buy) 10/26/2012 10/26/2022 Common Stock 559,441 (1) $ 0.24 I See Footnotes (2) (3) (5)
Common Stock Warrants (Right to Buy) 10/26/2012 10/26/2022 Common Stock 5,328 (1) $ 0.24 I See Footnotes (4) (5)
Common Stock Warrants (Right to Buy) 12/11/2012 09/29/2020 Common Stock 1,848 (1) $ 36.96 I See Footnotes (2) (3) (5)
Common Stock Warrants (Right to Buy) 12/11/2012 09/29/2020 Common Stock 17 (1) $ 36.96 I See Footnotes (4) (5)
Common Stock Warrants (Right to Buy) 12/11/2012 06/05/2019 Common Stock 8,540 (1) $ 21.84 I See Footnotes (2) (3) (5)
Common Stock Warrants (Right to Buy) 12/11/2012 06/05/2019 Common Stock 81 (1) $ 21.84 I See Footnotes (4) (5)

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
ORBIMED ADVISORS LLC
601 LEXINGTON AVENUE, 54TH FLOOR
NEW YORK, NY 10022
    X    
OrbiMed Capital GP III LLC
601 LEXINGTON AVENUE, 54TH FLOOR
NEW YORK, NY 10022
    X    
ISALY SAMUEL D
601 LEXINGTON AVENUE, 54TH FLOOR
NEW YORK, NY 10022
    X    

Signatures

/s/ Samuel D. Isaly 05/15/2013
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(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).
(1) Reflects a 1-for-24 reverse split of the Issuer's common stock effected on April 24, 2013.
(2) These shares of Series E convertible preferred stock, shares of Series D convertible preferred stock, shares of Series D-2 convertible preferred stock, shares of Common Stock, warrants to purchase Series D-2 convertible preferred stock and warrants to purchase Common Stock are held of record by OrbiMed Private Investments III, LP ("OPI") and may be deemed to be indirectly beneficially owned by OrbiMed Capital GP III LLC ("Capital"), OrbiMed Advisors LLC ("Advisors") and Samuel D. Isaly ("Isaly"). Capital is the sole general partner of OPI. Advisors, a registered adviser under the Investment Advisers Act of 1940, as amended, is the sole managing member of Capital. By virtue of such relationships, Capital and Advisors may be deemed to have voting and investment power with respect to the securities held by OPI noted above.
(3) Isaly, a natural person, may also be deemed to have voting and investment power with respect to the securities held by OPI noted above in his capacity as the managing member of, and holder of a controlling interest, in Advisors. As a result, each of Capital, Advisors and Isaly may be deemed to have beneficial ownership of the securities held by OPI.
(4) These shares of Series E convertible preferred stock, shares of Series D convertible preferred stock, shares of Series D-2 convertible preferred stock, shares of Common Stock, warrants to purchase Series D-2 convertible preferred stock and warrants to purchase Common Stock are held of record by OrbiMed Associates III, LP ("Associates") and may be deemed to be indirectly beneficially owned by Advisors and Isaly. Advisors is the sole general partner of Associates. Isaly is the managing member of, and holder of a controlling interest in, Advisors. By virtue of such relationships, Advisors and Isaly may be deemed to have voting and investment power with respect to the securities held by Associates noted above. As a result, each of Advisors and Isaly may be deemed to have beneficial ownership of the securities held by Associates.
(5) This report on Form 3 is jointly filed by Capital, Advisors and Isaly. Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its or his pecuniary interest therein, if any. The Reporting Persons have designated a representative, currently David P. Bonita, an employee of Advisors, to serve on the Issuer's board of directors. This report shall not be deemed an admission that the Reporting Persons are beneficial owners for the purpose of Section 16 of the Exchange Act, or for any other purpose.
(6) The Series E Preferred Stock has no expiration date and is convertible at any time at the option of the holder and will automatically convert upon the closing of the Issuer's initial public offering, at a conversion ratio of 1 share of Common Stock for every 24 shares of Series E Preferred Stock, for no additional consideration.
(7) The Series D-2 Preferred Stock has no expiration date and is convertible at any time at the option of the holder and will automatically convert upon the closing of the Issuer's initial public offering, at a conversion ratio of 1 share of Common Stock for every 24 shares of Series D-2 Preferred Stock, for no additional consideration.
(8) The Series D Preferred Stock has no expiration date and is convertible at any time at the option of the holder and will automatically convert upon the closing of the Issuer's initial public offering, at a conversion ratio of 1 share of Common Stock for every 24 shares of Series D Preferred Stock, for no additional consideration.

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