Exhibit 5.1
DORSEY & WHITNEY LLP
October 19, 2010
OncoGenex Pharmaceuticals, Inc.
1522 217th Place SE, Suite 100
Bothell, Washington 98021
Re: Securities Registered under Registration Statement on Form S-3
Ladies and Gentlemen:
Reference is made to our opinion letter dated June 26, 2009 and included as Exhibit 5.1 to the
Registration Statement on Form S-3 (the “Registration Statement”) filed on June 26, 2009, as
amended on July 13, 2009, by OncoGenex Pharmaceuticals, Inc., a Delaware corporation (the
“Company”), with the Securities and Exchange Commission (the “SEC”) under the Securities Act of
1933, as amended (the “Securities Act”), for the registration of, among other things, shares of
common stock, $0.001 par value per share (the “Common Stock”) and warrants to purchase Common
Stock. The Registration Statement was declared effective by the SEC on July 17, 2009. We are
delivering this supplemental opinion letter in connection with the preliminary and final prospectus
supplements (the “Prospectus Supplements”) filed on October 18, 2010 and October 19, 2010,
respectively, by the Company with the SEC pursuant to Rule 424 under the Securities Act. The
Prospectus Supplements relate to the offering by the Company pursuant to the Registration Statement
of up to 3,174,602 shares of Common Stock (the “Shares”), Warrants to purchase up to 1,587,301
shares of Common Stock and the shares of Common Stock issuable upon exercise of the Warrants (the
“Warrant Shares”). We understand that the Shares, the Warrants and the Warrant Shares are to be
offered and sold in the manner described in the Prospectus Supplements.
We have reviewed such documents and made such examination of law as we have deemed appropriate
to give the opinions expressed below. We have relied, without independent verification, on
certificates of public officials and, as to matters of fact material to the opinions set forth
below, on certificates of officers of the Company.
The opinion expressed below is limited to the Delaware General Corporation Law (which includes
applicable provisions of the Delaware Constitution and reported judicial decisions interpreting the
Delaware General Corporation Law and the Delaware Constitution).
Based on the foregoing, we are of the opinion that the Shares, Warrants and Warrant Shares
have been duly authorized and, upon issuance and delivery of the Shares and Warrants against
payment therefor in accordance with the terms of the Underwriting Agreement and issuance, delivery
and payment for the Warrant Shares in accordance with the terms of the Warrants, such Shares,
Warrants and Warrant Shares, respectively, will be validly issued, fully paid and non-assessable.
We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration
Statement and to the references to our firm under the caption “Legal Matters” in the Registration
Statement. In giving our consent, we do not admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.
Very truly yours,
DORSEY & WHITNEY LLP
/s/ Dorsey & Whitney LLP