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).

1. Name and Address of Reporting Person* ORBIMED ADVISORS LLC (Last) (First) (Middle) 601 LEXINGTON AVENUE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol AMBIT BIOSCIENCES CORP [ AMBI ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 05/22/2013
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X 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, $0.001 par value per share	05/22/2013		P		21,100	A	$6.861(1)	1,464,322	I	See Footnotes(5)(6)(8)
Common Stock, $0.001 par value per share	05/22/2013		P		200	A	$6.861(2)	13,947	I	See Footnotes(7)(8)
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)(8)
Common Stock, $0.001 par value per share	05/23/2013		P		120	A	$6.9893(4)	14,067	I	See Footnotes(7)(8)

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

1. Name and Address of Reporting Person* ORBIMED ADVISORS LLC (Last) (First) (Middle) 601 LEXINGTON AVENUE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* OrbiMed Capital GP III LLC (Last) (First) (Middle) 601 LEXINGTON AVENUE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ISALY SAMUEL D (Last) (First) (Middle) 601 LEXINGTON AVENUE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

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.

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.

8. This report on Form 4 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.

Remarks:

	/s/ Samuel D. Isaly	05/24/2013
	** 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).
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