Chinook Therapeutics (KDNY) DEFA14A Additional proxy soliciting materials

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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☐ Preliminary Proxy Statement

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☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to §240.14a-12

CHINOOK THERAPEUTICS, INC.

(Name of Registrant as Specified In Its Charter)

N/A

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Your Vote Counts! CHINOOK THERAPEUTICS, INC. 2023 Annual Meeting Vote by June 08, 2023 11:59 PM ET CHINOOK THERAPEUTICS, INC. 400 FAIRVIEW AVE. NORTH 1 9TH FLOOR SEATTLE, WA 98109 148,294 322,224 OF 2 Ricky Campana P.O. Box 123456 Suite 500 30# 51 Mercedes Way Edgewood, NY 11717 FLASHID-JOB# You invested in CHINOOK THERAPEUTICS, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on June 09, 2023. Get informed before you vote View the Notice & of Proxy oxy Statement, Annual Report, Report, , Stockholder Letter online OR you can receive a free paper or email copy of the, material(s) by requesting prior , to May 26, 2023. If you would like to request a copy of the material(s) for this and/or future stockholder 67890 meetings, online youOR may you (1)can visitreceive www. ProxyVote. a free paper com, copy (2)of call voting 1-800-579-1639 material(s) by orequesting (3) send an prior email to <matcutoff>. to sendmaterial@proxyvote. If u w u like com. to If sending request an copy email, of please the voting include material(s), your control you number may (1) (indicated visit www. below) ProxyVote. in the com, subject (2) line. call 1-800-579-1639 Unless requested, or you (3) will send notan otherwise email to sendmaterial@proxyvote. receive a paper or email copy. com. If sending an email, please include your control number (indicated below) in the subject line. For complete information and to vote, visit www.ProxyVote.com Control # XXXX XXXX XXXX XXXX Smartphone users Vote Virtually at the Meeting* Point your camera here and June 09, 2023 vote without entering a 9:00 AM PDT control number Virtually at: www.virtualshareholdermeeting.com/KDNY2023 *Please check the meeting materials for any special requirements for meeting attendance.

Vote at www.ProxyVote.com Control # XXXX THIS IS NOT A VOTABLE BALLOT SHARE CLASSES REPRESENTED FOR VOTING THE COMPANY NAME INC. - COMMON ASDFGHJKL 123456789.1234 THE COMPANY NAME INC. - CLASS A This is an overview of the proposals being presented at the COMPANY NAME INC. - CLASS Bupcoming stockholder shareholder meeting.. Please follow the instructions on THE COMPANY NAME INC. - CLASS C 123456789.1234 THE COMPANY NAME INC. - CLASS D 1the reverse side to vote these important matters. THE COMPANY NAME INC. - CLASS E.1234 THE COMPANY NAME INC. - CLASS F 123456789.1234 THE COMPANY NAME INC. - 401 K Voting Items Board Recommends 1. Election of Directors Nominees: For 01) Michelle Griffin 02) Eric Dobmeier 2. Ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting For firm for the fiscal year ending December 31, 2023. 3. Advisory vote on the compensation of the Company’s named executive officers. For 4. Approval of the Company’s Amended and Restated Certificate of Incorporation. For 5. Approval of the Company’s Amended and Restated 2015 Equity Incentive Plan. For NOTE: Such other business as may properly come before the meeting or any adjournment thereof. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. FLASHID-JOB#