UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

(Rule 13d-102)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO RULES 13d-1(b), (c), AND (d) AND AMENDMENTS THERETO FILED

PURSUANT TO RULE 13d-2(b)

(Amendment No. 5)¹

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

1              The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

(1) Includes 1,291,166 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below) held by BVF. The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed that all the Series B Preferred held by BVF would be converted.

Excludes 668,000 shares of Common Stock currently issuable upon the conversion of certain Series C Preferred (as defined below) held by BVF due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes 1,215,000 shares of Common Stock currently issuable upon the conversion of certain Series D Preferred (as defined below) held by BVF due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Includes 316,000 shares of Common Stock currently issuable upon the conversion of certain Series B Preferred (as defined below) held by BVF2. The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed only certain Series B Preferred held by BVF2 would be converted, and the remaining Series B Preferred held by BVF2 would not be converted, as the conversion of the Series B Preferred held by BVF2 to acquire 316,000 shares of Common Stock bring the Reporting Persons to the aggregate 9.98% limitation. As such, BVF2 holds Series B Preferred to acquire approximately 429,166 additional shares of Common Stock, which are excluded from the table above as a result of the 9.98% limitation.

Excludes 574,000 shares of Common Stock currently issuable upon the conversion certain Series C Preferred (as defined below) held by BVF2 due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes 871,000 shares of Common Stock currently issuable upon the conversion of certain Series D Preferred (as defined below) held by BVF2 due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Excludes 236,833 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below) held by Trading Fund OS. The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed that the Series B Preferred held by BVF would be converted and only certain of the Series B Preferred held by BVF2 would be converted, and the remaining Series B Preferred held by BVF2 and Trading Fund OS would not be converted.

Excludes 155,000 shares of Common Stock currently issuable upon the conversion certain Series C Preferred (as defined below) held by Trading Fund OS due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes 229,000 shares of Common Stock currently issuable upon the conversion of certain Series D Preferred (as defined below) held by Trading Fund OS due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Excludes 236,833 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below) held by Trading Fund OS. The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed only certain Series B Preferred held by BVF would be converted, and the remaining Series B Preferred held by BVF2 and Trading Fund OS would not be converted.

Excludes 155,000 shares of Common Stock currently issuable upon the conversion certain Series C Preferred (as defined below) held by Trading Fund OS due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes 229,000 shares of Common Stock currently issuable upon the conversion of certain Series D Preferred (as defined below) held by Trading Fund OS due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Includes 1,607,166 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below). The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed that all of the Series B Preferred held by BVF and certain Series B Preferred held by BVF2 would be converted and the remaining Series B Preferred held by BVF2 and Trading Fund OS would not be converted, as the conversion of the Series B Preferred held by BVF and the certain Series B Preferred held by BVF2 to acquire 1,291,166 and 316,000 shares of Common Stock, respectively, bring the Reporting Persons to the aggregate 9.98% limitation.

Excludes (i) 668,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred (as defined below) held by BVF, (ii) 574,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by BVF2, (iii) 155,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by Trading Fund OS, and (iv) 161,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes (i) 1,215,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred (as defined below) held by BVF, (ii) 871,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by BVF2, (iii) 229,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by Trading Fund OS, and (iv) 185,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Includes 1,607,166 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below). The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed that all of the Series B Preferred held by BVF and certain Series B Preferred held by BVF2 would be converted and the remaining Series B Preferred held by BVF2 and Trading Fund OS would not be converted, as the conversion of the Series B Preferred held by BVF and the certain Series B Preferred held by BVF2 to acquire 1,291,166 and 316,000 shares of Common Stock, respectively, bring the Reporting Persons to the aggregate 9.98% limitation.

Excludes (i) 668,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred (as defined below) held by BVF, (ii) 574,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by BVF2, (iii) 155,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by Trading Fund OS, and (iv) 161,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes (i) 1,215,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred (as defined below) held by BVF, (ii) 871,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by BVF2, (iii) 229,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by Trading Fund OS, and (iv) 185,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

(1) Includes 1,607,166 shares of Common Stock currently issuable upon the conversion of Series B Preferred (as defined below). The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding. In providing beneficial ownership described herein, the Reporting Persons have assumed that all of the Series B Preferred held by BVF and certain Series B Preferred held by BVF2 would be converted and the remaining Series B Preferred held by BVF2 and Trading Fund OS would not be converted, as the conversion of the Series B Preferred held by BVF and the certain Series B Preferred held by BVF2 to acquire 1,291,166 and 316,000 shares of Common Stock, respectively, bring the Reporting Persons to the aggregate 9.98% limitation.

Excludes (i) 668,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred (as defined below) held by BVF, (ii) 574,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by BVF2, (iii) 155,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held by Trading Fund OS, and (iv) 161,000 shares of Common Stock currently issuable upon the conversion of Series C Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

Excludes (i) 1,215,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred (as defined below) held by BVF, (ii) 871,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by BVF2, (iii) 229,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held by Trading Fund OS, and (iv) 185,000 shares of Common Stock currently issuable upon the conversion of Series D Preferred held within the Partners Managed Accounts, due to the 9.98% limitation. The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, more than 9.98% of the number of shares of Common Stock then issued and outstanding.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred or the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

See Item 4(a) for a full description of the Reporting Person’s beneficial ownership.

Sunesis Pharmaceuticals, Inc., a Delaware corporation (the “Issuer”).

395 Oyster Point Boulevard, Suite 400

South San Francisco, California 94080

Biotechnology Value Fund, L.P. (“BVF”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Biotechnology Value Fund II, L.P. (“BVF2”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Biotechnology Value Trading Fund OS LP (“Trading Fund OS”)

PO Box 309 Ugland House

Grand Cayman, KY1-1104

Cayman Islands

Citizenship: Cayman Islands

BVF Partners OS Ltd. (“Partners OS”)

PO Box 309 Ugland House

Grand Cayman, KY1-1104

Cayman Islands

Citizenship: Cayman Islands

BVF Partners L.P. (“Partners”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

BVF Inc.

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Mark N. Lampert (“Mr. Lampert”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: United States

Each of the foregoing is referred to as a “Reporting Person” and collectively as the “Reporting Persons.”

Common Stock, $0.0001 par value per share (the “Common Stock”)

867328 70 0

As of the close of business on December 31, 2018, the Reporting Persons held 13,639 Series B Preferred shares convertible for an aggregate of approximately 2,273,166 shares of Common Stock (the “Series B Preferred”). The Series B Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Securities Exchange Act of 1934 (the “Exchange Act”), more than 9.98% of the number of shares of Common Stock then issued and outstanding. As of the close of business on December 31, 2018, the Series B Preferred conversion limitation described in the prior sentence limits the aggregate conversion of Series B Preferred by the Reporting Persons to 1,607,166 out of the 2,273,166 shares of Common Stock underlying the Series B Preferred owned by the Reporting Persons in the aggregate. In providing beneficial ownership described herein, the Reporting Persons have assumed that Series B Preferred held by BVF and certain Series B Preferred held by BVF2 to acquire 1,291,166 and 316,000 shares of Common Stock, respectively, would be converted, which would bring the Reporting Persons to the aggregate 9.98% limitation, and the remaining Series B Preferred to acquire 666,000 shares of Common Stock owned by the Reporting Persons in the aggregate would not be converted due to the 9.98% limitation.

As of the close of business on December 31, 2018, the Reporting Persons held 1,558 Series C Preferred shares convertible for an aggregate of approximately 1,558,000 shares of Common Stock (the “Series C Preferred”). The Series C Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Exchange Act, more than 9.98% of the number of shares of Common Stock then issued and outstanding. As of the close of business on December 31, 2018, the Series C Preferred conversion limitation described in the prior sentence limits the aggregate conversion of Series C Preferred by the Reporting Persons to 0 out of the 1,558,000 shares of Common Stock underlying the Series C Preferred owned by the Reporting Persons in the aggregate.

As of the close of business on December 31, 2018, the Reporting Persons held 2,500 Series D Preferred shares convertible for an aggregate of approximately 2,500,000 shares of Common Stock (the “Series D Preferred”). The Series D Preferred may not be converted if, after such conversion, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) of the Exchange Act, more than 9.98% of the number of shares of Common Stock then issued and outstanding. As of the close of business on December 31, 2018, the Series D Preferred conversion limitation described in the prior sentence limits the aggregate conversion of Series D Preferred by the Reporting Persons to 0 out of the 2,500,000 shares of Common Stock underlying the Series D Preferred owned by the Reporting Persons in the aggregate.

The Reporting Persons may choose to convert the Series B Preferred, the Series C Preferred and the Series D Preferred in other amounts among the Reporting Persons, while continuing to comply with the aggregate 9.98% limitation.

As of the close of business on December 31, 2018 (i) BVF beneficially owned 2,140,172 shares of Common Stock, including 1,291,166 shares of Common Stock issuable upon the conversion of Series B Preferred Stock held by it, and excluding 668,000 shares of Common Stock issuable upon the conversion of Series C Preferred held by it and 1,215,000 shares of Common Stock issuable upon the conversion of Series D Preferred held by it; (ii) BVF2 beneficially owned 1,276,934 shares of Common Stock, including 316,000 shares of Common Stock issuable upon the conversion of certain Series B preferred Stock held by it, and excluding 429,166 of certain Series B Preferred Stock held by it, 574,000 shares of Common Stock issuable upon the conversion of Series C Preferred held by it and 871,000 shares of Common Stock issuable upon the conversion of Series D Preferred held by it; and (iii) Trading Fund OS beneficially owned 47,429 shares of Common Stock, excluding 236,833 shares of Common Stock issuable upon the conversion of Series B Preferred Stock held by it, 155,000 shares of Common Stock issuable upon the conversion of Series C Preferred held by it and 229,000 shares of Common Stock issuable upon the conversion of Series D Preferred held by it.

Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 47,429 shares of Common Stock beneficially owned by Trading Fund OS.

Partners, as the general partner of BVF, BVF2, the investment manager of Trading Fund OS, and the sole member of Partners OS, may be deemed to beneficially own the 3,895,026 shares of Common Stock beneficially owned in the aggregate by BVF, BVF2, Trading Fund OS, and certain Partners managed accounts (the “Partners Managed Accounts”), including 430,491 shares of Common Stock held in the Partners Managed Accounts, excluding 161,000 shares of Common Stock issuable upon the conversion of Series C Preferred held within the Partners Managed Accounts and 185,000 shares of Common Stock issuable upon the conversion of Series D Preferred held within the Partners Managed Accounts.

BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 3,895,026 shares of Common Stock beneficially owned by Partners.

Mr. Lampert, as a director and officer of BVF Inc., may be deemed to beneficially own the 3,895,026 shares of Common Stock beneficially owned by BVF Inc.

The foregoing should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of any shares of Common Stock owned by another Reporting Person. Partners OS disclaims beneficial ownership of the shares of Common Stock beneficially owned by Trading Fund OS. Each of Partners, BVF Inc. and Mr. Lampert disclaims beneficial ownership of the shares of Common Stock beneficially owned by BVF, BVF2, Trading Fund OS, and the Partners Managed Accounts, and the filing of this statement shall not be construed as an admission that any such person or entity is the beneficial owner of any such securities.

The following percentages are based on a denominator that is the sum of: (a) 37,421,509 shares of Common Stock outstanding as of October 31, 2018 as disclosed in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 5, 2018 and (b) and certain or all of the 1,607,166 shares of Common Stock that may be acquired upon the conversion of certain Series B Preferred, as applicable.

As of the close of business on December 31, 2018 (i) BVF beneficially owned approximately 5.5% of the outstanding shares of Common Stock, (ii) BVF2 beneficially approximately 3.4% of the outstanding shares of Common Stock, (iii) Trading Fund OS beneficially owned less than 1% of the outstanding shares of Common Stock (iv) Partners OS may be deemed to beneficially own less than 1% of the outstanding shares of Common Stock, and (v) each of Partners, BVF Inc. and Mr. Lampert may be deemed to beneficially own approximately 9.98% of the outstanding shares of Common Stock (approximately 1.2% of which is held in the Partners Managed Accounts).

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

Not Applicable.

Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the shares of Common Stock beneficially owned by BVF, BVF2, Trading Fund OS, and the Partners Managed Accounts.

Not Applicable.

See Exhibit 99.1 to the Schedule 13G filed with the Securities and Exchange Commission on February 16, 2016.

Not Applicable.

By signing below each of the undersigned certifies that, to the best of its 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.

SIGNATURE

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: February 14, 2019