EXHIBIT 5.1
OncoGenex Pharmaceuticals, Inc.
1522 217th Place SE, Suite 100
Bothell, Washington 98021
Re: Registration Statement on Form S-8
Ladies and Gentlemen:
We have acted as counsel to OncoGenex Pharmaceuticals, Inc., a Delaware corporation (the
“Company”), in connection with a Registration Statement on Form S-8 relating to the sale by the
Company from time to time of up to 1,108,223 shares of Common Stock, $0.001 par value, of the
Company (the “Shares”), initially issuable and reserved for issuance under the OncoGenex
Pharmaceuticals, Inc. 2010 Performance Incentive Plan (the “Plan”).
We have examined such documents and have reviewed such questions of law as we have considered
necessary and appropriate for the purposes of the opinions set forth below.
In rendering our opinions set forth below, we have assumed the authenticity of all documents
submitted to us as originals, the genuineness of all signatures and the conformity to authentic
originals of all documents submitted to us as copies. We also have assumed the legal capacity for
all purposes relevant hereto of all natural persons and, with respect to all parties to agreements
or instruments relevant hereto other than the Company, that such parties had the requisite power
and authority (corporate or otherwise) to execute, deliver and perform such agreements or
instruments, that such agreements or instruments have been duly authorized by all requisite action
(corporate or otherwise), executed and delivered by such parties and that such agreements or
instruments are the valid, binding and enforceable obligations of such parties. As to questions of
fact material to our opinions, we have relied upon certificates of officers of the Company and of
public officials.
Based on the foregoing, we are of the opinion that the Shares have been duly authorized and,
upon issuance, delivery and payment therefor in accordance with the terms of the Plan, will be
validly issued, fully paid and nonassessable.
Our opinions expressed above are limited to the Delaware General Corporation Law.
We hereby consent to the filing of this opinion as an exhibit to the Registration Statement.
Dated: August 13, 2010
Very truly yours,
DORSEY & WHITNEY LLP
CLD