Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN 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 *
Bonita David P
   2. Issuer Name and Ticker or Trading Symbol
AMBIT BIOSCIENCES CORP [AMBI] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
C/O ORBIMED ADVISORS LLC, 601 LEXINGTON AVENUE, 54TH FLOOR		 3. Date of Earliest Transaction (Month/Day/Year)
05/22/2013
(Street)

NEW YORK, NY 10022		 4. If Amendment, Date 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
(City)
(State)
(Zip)
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, $0.001 par value per share 05/22/2013   P   21,100 A $ 6.861 (1) 1,464,322 I See Footnotes (5) (6)
Common Stock, $0.001 par value per share 05/22/2013   P   200 A $ 6.861 (2) 13,947 I See Footnote (7)
Common Stock, $0.001 par value per share 05/23/2013   P   12,380 A $ 6.9893 (3) 1,476,702 I See Footnotes (5) (6)
Common Stock, $0.001 par value per share 05/23/2013   P   120 A $ 6.9893 (4) 14,067 I See Footnote (7)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 Underlying Securities
(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 of Derivative Security: 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

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
Bonita David P
C/O ORBIMED ADVISORS LLC
601 LEXINGTON AVENUE, 54TH FLOOR
NEW YORK, NY 10022		   X   X    

Signatures

 /s/ David P. Bonita   05/24/2013
**Signature of Reporting Person Date

Explanation of Responses:

* 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).
(1) The shares were purchased by OrbiMed Private Investments III, LP ("OPI") in multiple transactions and the price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $6.70 to $7.00, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission full information regarding the shares purchased at each separate price within the ranges set forth in footnote (1) of this Form 4.
(2) The shares were purchased by OrbiMed Associates III, LP ("Associates") in multiple transactions and the price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $6.70 to $7.00, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission full information regarding the shares purchased at each separate price within the ranges set forth in footnote (2) of this Form 4.
(3) The shares were purchased by OPI in multiple transactions and the price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $6.81 to $7.20, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission full information regarding the shares purchased at each separate price within the ranges set forth in footnote (3) of this Form 4.
(4) The shares were purchased by Associates in multiple transactions and the price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $6.81 to $7.20, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission full information regarding the shares purchased at each separate price within the ranges set forth in footnote (4) of this Form 4.
(5) These securities are held of record by 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.
(6) 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. The Reporting Person is an employee of Advisors and disclaims beneficial ownership over such securities, except to the extent of his pecuniary interest therein, if any.
(7) These securities are held of record by 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. The Reporting Person disclaims beneficial ownership over such securities, except to the extent of his pecuniary interest therein, if any.

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