# EDGAR Filing Document

**Accession Number:** 0001503802
**File Stem:** 0001193125-25-262581
**Filing Date:** 2025-11
**Character Count:** 94363
**Document Hash:** a2fd6b6379ff5b55209f38d5d3a6c2e9
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-262581.hdr.sgml**: 20251103

**ACCESSION NUMBER**: 0001193125-25-262581

**CONFORMED SUBMISSION TYPE**: S-3

**PUBLIC DOCUMENT COUNT**: 17

**FILED AS OF DATE**: 20251103

**DATE AS OF CHANGE**: 20251103

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Karyopharm Therapeutics Inc.
- **CENTRAL INDEX KEY:** 0001503802
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 263931704
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-3
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-291224
- **FILM NUMBER:** 251444298

**BUSINESS ADDRESS:**
- **STREET 1:** 85 WELLS AVENUE
- **STREET 2:** SECOND FLOOR
- **CITY:** NEWTON
- **STATE:** MA
- **ZIP:** 02459
- **BUSINESS PHONE:** 617-658-0600

**MAIL ADDRESS:**
- **STREET 1:** 85 WELLS AVENUE
- **STREET 2:** SECOND FLOOR
- **CITY:** NEWTON
- **STATE:** MA
- **ZIP:** 02459

##### [**Table of Contents**](#toc)
**As filed with the Securities and Exchange Commission on November 3, 2025** 

**Registration No. 333-** 

**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**Washington, D.C. 20549** 

**FORM S-3** 

**REGISTRATION STATEMENT** 

***UNDER***

***THE SECURITIES ACT OF 1933***

## KARYOPHARM THERAPEUTICS INC.
**(Exact name of registrant as specified in its charter)** 

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| | |
|:---|:---|
| **Delaware** | **26-3931704** |
| **(State or other jurisdiction of<br>incorporation or organization)** | **(I.R.S. Employer<br>Identification Number)** |

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**85 Wells Avenue, 2nd Floor** 

**Newton, MA 02459** 

**(617) 658-0600** 

**(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant's Principal Executive Offices)** 

**Richard Paulson** 

**President and Chief Executive Officer** 

**Karyopharm Therapeutics Inc.** 

**85 Wells Avenue, 2nd Floor** 

**Newton, MA 02459** 

**(617) 658-0600** 

**(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)** 

***Copies to:***

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| | |
|:---|:---|
| **Jason L. Kropp**<br> **Craig Hilts**<br> **Sidley Austin LLP**<br> **60 State Street**<br> **Boston, MA 02109**<br> **Telephone: (617) 223-0300** | **Michael Mano**<br> **Senior Vice President, General Counsel and Secretary**<br> **Karyopharm Therapeutics Inc.**<br> **85 Wells Avenue, 2nd Floor**<br> **Newton, MA 02459**<br> **Telephone: (617) 658-0600** |

---

**Approximate date of commencement of proposed sale to the public**: From time to time after this registration statement becomes effective.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ☐ | Accelerated filer | ☒ |
| Non-accelerated filer | ☐ | Smaller reporting company | ☒ |
|  |  | Emerging growth company | ☐ |

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If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

**This Registration Statement shall hereafter become effective in accordance with the provisions of Section 8(a) of the Securities Act of 1933.** 

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**The information in this prospectus is not complete and may be changed. The selling stockholders named in this prospectus may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and the selling stockholders named in this prospectus are not soliciting offers to buy these securities in any state or other jurisdiction where the offer or sale is not permitted.** 

**Subject to completion, dated November 3, 2025** 

**PROSPECTUS** 

**2,805,688 Shares**![LOGO](g54161g00s01.jpg)

**Common Stock** 

This prospectus relates to the resale from time to time of up to 2,805,688 shares of common stock of Karyopharm Therapeutics Inc. by the selling stockholders listed on page 11, including their donees, pledgees, assignees, transferees or other successors-in-interest, which consist of 1,487,917 outstanding shares of our common stock held by the selling stockholders and 1,317,771 shares of our common stock issuable upon the exercise of outstanding warrants to purchase shares of our common stock held by the selling stockholders (the "Warrants"). We will not receive any proceeds from the sale of the shares offered by this prospectus.

We have agreed, pursuant to a registration rights agreement that we entered into with the selling stockholders, to bear all of the expenses incurred in connection with the registration of these shares. The selling stockholders will pay or assume discounts, commissions, fees of underwriters, selling brokers or dealer managers and similar expenses, if any, incurred for the sale of these shares of our common stock.

The selling stockholders identified in this prospectus, or their donees, pledgees, assignees, transferees or other successors-in-interest, may offer the shares from time to time on terms to be determined at the time of sale through ordinary brokerage transactions or through any other means described in this prospectus under the caption "Plan of Distribution." The shares may be sold at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices. For a list of the selling stockholders, see the section entitled "Selling Stockholders" on page 11 of this prospectus.

We may amend or supplement this prospectus from time to time by filing amendments or supplements as required. You should read the entire prospectus and any amendments or supplements carefully before you make your investment decision.

Our common stock is listed on the Nasdaq Global Select Market under the symbol "KPTI." On October 31, 2025, the last reported closing sale price of our common stock on the Nasdaq Global Select Market was $5.80 per share. You are urged to obtain current market quotations for our common stock.

**Investing in our common stock involves certain risks. See "[Risk Factors](#tx54161_3)" on page 4 of this prospectus, and in the documents incorporated by reference in this prospectus, for a discussion of the factors you should carefully consider before deciding to purchase these securities.** 

**Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.** 

**The date of this prospectus is , 2025.** 

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**TABLE OF CONTENTS** 

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|:---|:---|
|  | **Page** |
|  [ABOUT THIS PROSPECTUS](#tx54161_1) | 1 |
|  [PROSPECTUS SUMMARY](#tx54161_2) | 2 |
|  [RISK FACTORS](#tx54161_3) | 4 |
|  [CAUTIONARY NOTE REGARDING FORWARD-LOOKING INFORMATION AND INDUSTRY DATA](#tx54161_4) | 5 |
|  [USE OF PROCEEDS](#tx54161_5) | 6 |
|  [DESCRIPTION OF CAPITAL STOCK](#tx54161_6) | 7 |
|  [SELLING STOCKHOLDERS](#tx54161_7) | 11 |
|  [PLAN OF DISTRIBUTION](#tx54161_8) | 14 |
|  [LEGAL MATTERS](#tx54161_9) | 16 |
|  [EXPERTS](#tx54161_10) | 16 |
|  [WHERE YOU CAN FIND MORE INFORMATION](#tx54161_11) | 17 |
|  [INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE](#tx54161_12) | 17 |

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**ABOUT THIS PROSPECTUS** 

You should rely only on the information contained or incorporated by reference in this prospectus. We have not and the selling stockholders have not authorized anyone else to provide you with different or additional information from that contained in this prospectus. We take no responsibility for, and can provide no assurance as to the reliability of, any information that others may give. The selling stockholders are offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where offers and sales are permitted. You should assume that the information appearing in this prospectus is accurate only as of the date on the front cover of this prospectus, regardless of the time of delivery of this prospectus or of any sale of common stock. Our business, financial condition, results of operations and prospects may have changed since such date.

Unless the context otherwise indicates, references in this prospectus to "we," "our" and "us" refer, collectively, to Karyopharm Therapeutics Inc., a Delaware corporation, and its consolidated subsidiaries.

We own or have rights to, or have applied for, trademarks, service marks and trade names that we use in connection with the operation of our business, including our corporate name, logos and website names. Other trademarks, service marks and trade names appearing in this prospectus are the property of their respective owners. Solely for convenience, some of the trademarks, service marks and trade names referred to in this prospectus are listed without the <sup>®</sup> and <sup>™</sup> symbols, but we will assert, to the fullest extent under applicable law, our rights to our trademarks, service marks and trade names.

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**PROSPECTUS SUMMARY** 

*This summary highlights, and is qualified in its entirety by, the more detailed information included elsewhere in this prospectus or incorporated by reference in the prospectus. This summary does not contain all of the information that you should consider before investing in our common stock. You should read and carefully consider the entire prospectus, especially the "Risk Factors" section of this prospectus, before deciding to invest in our common stock.* 

**Karyopharm Therapeutics Inc.** 

We are a commercial-stage pharmaceutical company pioneering novel cancer therapies and dedicated to the discovery, development and commercialization of first-in-class drugs directed against nuclear export for the treatment of cancer. Our scientific expertise is based upon an understanding of the regulation of intracellular communication between the nucleus and the cytoplasm. We have discovered and are developing and commercializing novel, small molecule **<u>S</u>**elective **<u>I</u>**nhibitor of **<u>N</u>**uclear **<u>E</u>**xport ("SINE") compounds that inhibit the nuclear export protein exportin 1 ("XPO1"). These SINE compounds represent a new class of drug candidates with a novel mechanism of action that have the potential to treat a variety of diseases with high unmet medical need. Our lead asset, XPOVIO<sup>®</sup> (selinexor), was the first oral XPO1 inhibitor to receive marketing approval, receiving its initial U.S. approval from the U.S. Food and Drug Administration ("FDA") in July 2019.

**Corporate Information** 

We were incorporated under the laws of the State of Delaware in December 2008. Our executive offices are located at 85 Wells Avenue, 2nd Floor, Newton, Massachusetts 02459, and our telephone number is (617) 658-0600. Our website address is www.karyopharm.com. We have included our website address in this prospectus solely as an inactive textual reference.

**Private Placement** 

On October 7, 2025, we entered into a securities purchase agreement for a private placement with the selling stockholders whereby, on October 10, 2025, we issued and sold an aggregate of (i) 1,487,917 shares of our common stock and (ii) accompanying Warrants to purchase up to 1,317,771 shares of our common stock. The price per share and accompanying Warrant was $5.880706 and we received gross proceeds of approximately $8.75 million, before deducing placement agent fees and offering expenses payable by us. The exercise price of the Warrants is $6.64 per share. For a detailed description of the transactions contemplated by the securities purchase agreement with the selling stockholders and the securities issued pursuant thereto, see the section captioned "Selling Stockholders" in this prospectus. We filed the registration statement on Form S-3, of which this prospectus forms a part, to fulfill our contractual obligations under the registration rights agreement entered into concurrently with the securities purchase agreement with the selling stockholders to provide for the resale by the selling stockholders of the shares of common stock as well as the shares of common stock issuable upon exercise of the Warrants offered hereby.

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**THE OFFERING** 

Common stock offered by selling stockholders 2,805,688, consisting of 1,487,917 outstanding shares of our common stock and 1,317,771 shares of our common stock issuable upon the exercise of Warrants.

Use of Proceeds We will not receive any proceeds from the sale of shares in this offering.

Risk factors You should read the "Risk Factors" section of this prospectus beginning on page 4 and the risk factors incorporated by reference in this prospectus for a discussion of factors to consider carefully before deciding to invest in shares of our common stock.

Nasdaq Global Select Market Symbol "KPTI"

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**RISK FACTORS** 

Investing in our common stock involves a high degree of risk. Before deciding whether to invest in our common stock, you should consider carefully the risks and uncertainties described under the section captioned "Risk Factors" contained in our most recent Annual Report on Form 10-K, our most recent Quarterly Report on Form 10-Q and other filings we make with the Securities and Exchange Commission (the "SEC") from time to time, which are incorporated by reference herein in their entirety, together with the other information in this prospectus and in the documents incorporated by reference in this prospectus.

The risks described in our most recent Annual Report on Form 10-K, our most recent Quarterly Report on Form 10-Q and the other filings we make with the SEC incorporated by reference herein are not the only ones facing our company. Additional risks and uncertainties may also impair our business operations. If any of the risks described in our most recent Annual Report on Form 10-K, our most recent Quarterly Report on Form 10-Q and the other filings incorporated by reference herein occurs, our business, financial condition, results of operations and future growth prospects could be harmed. In these circumstances, the market price of our common stock could decline, and you may lose all or part of your investment.

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**CAUTIONARY NOTE REGARDING FORWARD-LOOKING INFORMATION AND INDUSTRY DATA** 

This prospectus and the documents incorporated by reference herein contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), that involve substantial risks and uncertainties. All statements, other than statements of historical fact, contained in this prospectus or incorporated by reference herein, including statements regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management, are forward-looking statements. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "might," "plan," "potential," "predict," "project," "should," "target," "would," and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. You are cautioned that these forward-looking statements are only predictions and are subject to risks, uncertainties and assumptions that are referenced in the section of any accompanying prospectus supplement entitled "Risk Factors." You should also carefully review the risk factors and cautionary statements described in the other documents we file from time to time with the SEC, specifically our most recent Annual Report on Form 10-K, our Quarterly Reports on Form 10-Q and our Current Reports on Form 8-K. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, collaborations, joint ventures or investments that we may make or enter into.

You should read this prospectus and the information incorporated by reference herein completely and with the understanding that our actual future results may be materially different from what we expect. We do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

A statement contained in a document incorporated by reference into this prospectus shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus, any prospectus supplement or in any other subsequently filed document which is also incorporated in this prospectus modifies or replaces such statement. Any statements so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

This prospectus incorporates by reference certain statistical and other industry and market data that we obtained from industry publications and research, surveys and studies conducted by third parties. All of the market data incorporated by reference in this prospectus involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such data. Industry publications and third-party research, surveys and studies generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information.

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**USE OF PROCEEDS** 

We are filing the registration statement of which this prospectus is a part to permit the holders of the shares of our common stock described in the section entitled "Selling Stockholders" to resell such shares. We are not selling any securities under this prospectus and we will not receive any proceeds from the sale of shares of our common stock by the selling stockholders.

The selling stockholders will pay any discounts, commissions, fees of underwriters, selling brokers or dealer managers and expenses incurred by the selling stockholders for brokerage, accounting, tax or legal services or any other expenses incurred by the selling stockholders in disposing of the shares. We will bear all other costs, fees and expenses incurred in effecting the registration of the shares covered by this prospectus, including, without limitation, all registration and filing fees, printing fees, Nasdaq listing fees and fees and expenses of our counsel and our accountants.

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**DESCRIPTION OF CAPITAL STOCK** 

The following description of our capital stock is intended as a summary only and therefore is not a complete description of our capital stock. This description is based upon, and is qualified by reference to, our restated certificate of incorporation, our by-laws, our existing warrants and applicable provisions of Delaware corporate law. You should read our certificate of incorporation and by-laws, which are filed as exhibits to the registration statement of which this prospectus forms a part, for the provisions that are important to you.

Our authorized capital stock consists of 53,333,333 shares of common stock, par value $0.0001 per share, and 5,000,000 shares of preferred stock, $0.0001 par value per share. As of October 30, 2025, 17,050,876 shares of common stock were outstanding, 1,789,241 shares of common stock were issuable upon the exercise of pre-funded warrants with an exercise price of $0.0001 per share, 9,622,478 shares of common stock were issuable upon the exercise of warrants with a weighted average exercise price of $12.50 per share, and no shares of preferred stock were outstanding.

**Common Stock** 

*Annual Meeting.* Annual meetings of our stockholders are held on the date designated in accordance with our by-laws. Written notice must be mailed to each stockholder entitled to vote not less than ten nor more than 60 days before the date of the meeting. The presence in person or by proxy of the holders of record of a majority of our issued and outstanding shares entitled to vote at such meeting constitutes a quorum for the transaction of business at meetings of the stockholders. Special meetings of the stockholders may be called for any purpose by the board of directors, the chairman of the board or the chief executive officer. Except as may be otherwise provided by applicable law, our certificate of incorporation or our by-laws, all elections shall be decided by a plurality, and all other questions shall be decided by a majority, of the votes cast by stockholders entitled to vote thereon at a duly held meeting of stockholders at which a quorum is present.

*Voting Rights*. Each holder of common stock is entitled to one vote for each share held of record on all matters to be voted upon by stockholders.

*Dividends*. Subject to the rights, powers and preferences of any outstanding preferred stock, and except as provided by law or in our certificate of incorporation, dividends may be declared and paid or set aside for payment on the common stock out of legally available assets or funds when and as declared by the board of directors.

*Liquidation and Dissolution*. Subject to the rights, powers and preferences of any outstanding preferred stock, in the event of our liquidation or dissolution, our net assets will be distributed pro rata to the holders of our common stock.

*Other Rights*. Holders of the common stock have no right to:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• convert the stock into any other security;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• have the stock redeemed;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• purchase additional stock; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• maintain their proportionate ownership interest.

The common stock does not have cumulative voting rights. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue. Holders of shares of the common stock are not required to make additional capital contributions.

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*Transfer Agent and Registrar*. Computershare Trust Company, N.A. is transfer agent and registrar for the common stock.

**Preferred Stock** 

We are authorized to issue "blank check" preferred stock, which may be issued in one or more series upon authorization of our board of directors. Our board of directors is authorized to fix the designations, powers, preferences and the relative, participating, optional or other special rights and any qualifications, limitations and restrictions of the shares of each series of preferred stock. The authorized shares of our preferred stock are available for issuance without further action by our stockholders, unless such action is required by applicable law or the rules of any stock exchange on which our securities may be listed. If the approval of our stockholders is not required for the issuance of shares of our preferred stock, our board may determine not to seek stockholder approval.

A series of our preferred stock could, depending on the terms of such series, impede the completion of a merger, tender offer or other takeover attempt. Our board of directors will make any determination to issue preferred shares based upon its judgment as to the best interests of our stockholders. Our directors, in so acting, could issue preferred stock having terms that could discourage an acquisition attempt through which an acquirer may be able to change the composition of our board of directors, including a tender offer or other transaction that some, or a majority, of our stockholders might believe to be in their best interests or in which stockholders might receive a premium for their stock over the then-current market price of the stock.

**Warrants** 

On December 5, 2022, we issued to certain institutional investors, in a private placement offering of securities, warrants to purchase up to 635,703 shares of common stock, which have an exercise price of $95.37 per share. The warrants are exercisable through December 7, 2027. As of October 30, 2025, none of these warrants have been exercised.

On October 10, 2025, we issued to certain institutional investors, in a private placement offering of securities, warrants to purchase up to 1,317,771 shares of common stock, which have an exercise price of $6.64 per share. The warrants are exercisable until the date that is the first to occur of (i) thirty (30) days following the public announcement by the Company of the top-line results from the Phase 3 XPORT-EC-042 clinical trial of selinexor in patients with endometrial cancer or (ii) October 10, 2028. As of October 30, 2025, none of these warrants have been exercised.

On October 10, 2025, we issued to certain institutional investors, pursuant to (i) privately negotiated agreements with (a) a limited number of existing holders of our 3.00% Convertible Senior Notes due 2025, and (b) existing holders of our 9.00% Senior Convertible Notes due 2029 and (ii) fee agreements with (a) investors party to our Sixth Amendment to the Revenue Interest Financing Agreement, dated October 7, 2025 and (b) lenders party to our First Amendment and Waiver to Credit and Guaranty Agreement, dated October 7, 2025, pre-funded warrants to purchase an aggregate of 2,913,136 shares of common stock, which have an exercise price of $0.0001 per share, and newly issued warrants to purchase an aggregate of 7,453,098 shares of common stock, which have an exercise price of $6.64 per share. Warrants to purchase an aggregate of 4,384,681 shares of common stock are exercisable through October 10, 2030 and warrants to purchase an aggregate of 3,068,417 shares of common stock are exercisable through May 13, 2029. As of October 30, 2025, pre-funded warrants to purchase an aggregate of 1,123,895 shares of common stock have been exercised.

On October 10, 2025, we issued to J. Wood Capital Advisors LLC, pursuant to a fee letter, warrants to purchase up to 215,906 shares of common stock, which have an exercise price of $6.64 per share. The warrants are exercisable through October 10, 2030. As of October 30, 2025, none of these warrants have been exercised.

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**Provisions of Our Certificate of Incorporation and By-laws and Delaware Law That May Have Anti-Takeover Effects** 

*Board of Directors*. Our certificate of incorporation and by-laws provide for a board of directors divided as nearly equally as possible into three classes. Each class is elected to a term expiring at the annual meeting of stockholders held in the third year following the year of such election. The number of directors comprising our board of directors is fixed from time to time by the board of directors.

*Removal of Directors by Stockholders*. Our certificate of incorporation and by-laws provide that, subject to the rights of holders of any series of preferred stock, a member of our board of directors may only be removed for cause and only by an affirmative vote of the holders of at least 75% of the outstanding shares entitled to vote on the election of the directors.

*Super-Majority Voting*. The General Corporation Law of the State of Delaware (the "DGCL"), provides generally that the affirmative vote of a majority of the shares entitled to vote on any matter is required to amend a corporation's certificate of incorporation or by-laws, unless a corporation's certificate of incorporation or by-laws, as the case may be, requires a greater percentage. Subject to the rights of holders of any series of preferred stock, our by-laws may be amended or repealed by a majority vote of our board of directors or the affirmative vote of the holders of at least 75% of the votes that all our stockholders would be entitled to cast in any annual election of directors. In addition, the affirmative vote of the holders of at least 75% of the votes that all our stockholders would be entitled to cast in any annual election of directors is required to amend or repeal, or to adopt any provisions inconsistent with, any of the provisions of our certificate of incorporation described under the prior two paragraphs.

*Stockholder Nomination of Directors*. Our by-laws provide that a stockholder must notify us in writing of any stockholder nomination of a director not earlier than 120 days but not later than 90 days prior to the first anniversary of the preceding year's annual meeting; provided, that if the date of the annual meeting is advanced by more than 20 days, or delayed by more than 60 days, from such anniversary date, notice by the stockholder to be timely must be so delivered not earlier than the 120th day prior to the date of such annual meeting and not later than close of business on the later of (x) the 90th day prior to the date of such meeting and (y) the 10th day following the day on which notice of the date of such annual meeting was mailed or public announcement of the date of such annual meeting is first made by us, whichever occurs first.

*No Action By Written Consent*. Our certificate of incorporation and our by-laws provide that our stockholders may not act by written consent and may only act at duly called meetings of stockholders. Our certificate of incorporation and our by-laws also provide that, except as otherwise required by law, special meetings of our stockholders can only be called by our board of directors, chairman of the board or chief executive officer. In addition, our by-laws establish an advance notice procedure for stockholder proposals to be brought before an annual meeting of stockholders, including proposed nominations of candidates for election to our board of directors.

*Issuance of Preferred Stock*. Our board of directors is authorized, without further action by our stockholders, to issue up to 5,000,000 shares of preferred stock in one or more series, and to fix the designations, powers, preferences and the relative, participating, optional or other special rights, and any qualifications, limitations and restrictions of the shares of each series of Preferred Stock. The issuance of preferred stock could impede the completion of a merger, tender offer or other takeover attempt.

*Delaware Business Combination Statute*. We are subject to Section 203 of the DGCL. Subject to certain exceptions, Section 203 prevents a publicly held Delaware corporation from engaging in a "business combination" with any "interested stockholder" for three years following the date that the person became an interested stockholder, unless the interested stockholder attained such status with the approval of the corporation's board of directors or unless the business combination is approved in a prescribed manner or the

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interested stockholder acquired at least 85% of the corporation's outstanding voting stock in the transaction in which it became an interested stockholder. A "business combination" includes, among other things, a merger or consolidation involving us and the "interested stockholder" and the sale of more than 10% of our assets. In general, an "interested stockholder" is any entity or person beneficially owning 15% or more of our outstanding voting stock and any entity or person affiliated with or controlling or controlled by such entity or person.

*Exclusive Forum Selection*. Our by-laws provide that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware (or, if the Court of Chancery of the State of Delaware does not have jurisdiction, the federal district court for the District of Delaware) shall, to the fullest extent permitted by law, be the sole and exclusive forum for: (i) any derivative action or proceeding brought on behalf of the Company, (ii) any action asserting a claim of breach of a fiduciary duty owed by any director, officer, other employee or stockholder of the Company to the Company or the Company's stockholders, (iii) any action asserting a claim arising pursuant to any provision of the General Corporation Law of the State of Delaware or as to which the General Corporation Law of the State of Delaware confers jurisdiction on the Court of Chancery of the State of Delaware, or (iv) any action asserting a claim arising pursuant to any provision of our certificate of incorporation or our by-laws or governed by the internal affairs doctrine; provided, however, that this exclusive forum provision shall not apply to claims arising under the Securities Act or the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction. In addition, unless the Company consents in writing to the selection of an alternative forum, the federal district courts of the United States of America shall, to the fullest extent permitted by law, be the sole and exclusive forum for the resolution of any claims arising under the Securities Act.

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**SELLING STOCKHOLDERS** 

On October 7, 2025, we entered into a securities purchase agreement (the "Purchase Agreement") with certain institutional investors (the "Investors"), pursuant to which we issued and sold in a private placement (the "Private Placement") an aggregate of (i) 1,487,917 shares of our common stock and (ii) accompanying Warrants to purchase up to 1,317,771 additional shares of common stock. The price per share and accompanying Warrant was $5.880706. The exercise price of the Warrants is $6.64 per share. The closing of the issuance and sale of these securities was consummated on October 10, 2025 (the "Private Placement Closing Date"). We received gross proceeds of approximately $8.75 million from the Private Placement, before deducting placement agent fees and offering expenses, and excluding any proceeds that we may receive upon exercise of any Warrants.

The Warrants are exercisable at any time prior to the date that is the first to occur of (i) thirty (30) days following the public announcement by the Company of the top-line results from the Phase 3 XPORT-EC-042 clinical trial of selinexor in patients with endometrial cancer or (ii) October 10, 2028. We cannot predict when or whether any of the selling stockholders will exercise their Warrants.

The Warrants issued in the Private Placement provide that a holder of Warrants does not have the right to exercise any portion of its Warrants if such holder, together with its affiliates, would beneficially own in excess of 4.99% (or, upon the election of the holder, prior to the issuance of the Warrant, 9.99%) of the number of shares of our issued and outstanding common stock or any other class of equity security that is registered pursuant to Section 12 of the Exchange Act (the "Beneficial Ownership Limitation"); provided, however, that each holder may increase or decrease the Beneficial Ownership Limitation by giving notice to the Company, but not to any percentage in excess of 19.99%, and provided that any increase will not be effective until the 61st day after such notice is delivered to us.

In connection with the Private Placement, we entered into a registration rights agreement with the Investors, dated as of October 7, 2025 (the "Registration Rights Agreement"), pursuant to which we agreed to file a registration statement with the SEC covering the resale of the shares of common stock sold in the Private Placement and the shares of common stock underlying the Warrants described above. We agreed to file such registration statement within 45 days following the Private Placement Closing Date. The Registration Rights Agreement includes customary indemnification rights in connection with the registration statement. The registration statement of which this prospectus forms a part has been filed in accordance with the Registration Rights Agreement.

The foregoing summary descriptions of the Purchase Agreement and the Registration Rights Agreement do not purport to be complete and are qualified in their entirety by reference to the full text of such documents, which are filed as exhibits to the registration statement of which this prospectus forms a part, and are incorporated by reference herein.

This prospectus covers the sale or other disposition by the selling stockholders of up to the total number of shares of our common stock that were issued to the Investors pursuant to the Purchase Agreement, plus the total number of shares of our common stock issuable upon exercise of the Warrants issued to the selling stockholders, without giving effect to the Beneficial Ownership Limitation described above. The table below sets forth, to our knowledge, information concerning the beneficial ownership of shares of our common stock held by the selling stockholders as of October 30, 2025. The information in the table below with respect to the selling stockholders has been obtained from the respective selling stockholders. When we refer to the "selling stockholders" in this prospectus, or, if required, a post-effective amendment to the registration statement of which this prospectus is a part, we mean the selling stockholders listed in the table below as offering shares, as well as their respective donees, pledgees, assignees, transferees or other successors-in-interest. Throughout this prospectus, when we refer to the shares of our common stock being registered on behalf of the selling stockholders, we are referring to the shares of our common stock and the shares underlying the Warrants issued to the selling stockholders pursuant to the Purchase Agreement, without giving effect to the Beneficial Ownership Limitation described

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above. The selling stockholders may sell all, some or none of the shares of common stock subject to this prospectus. See "Plan of Distribution" below as it may be supplemented and amended from time to time.

The number of shares of common stock beneficially owned prior to the offering for each selling stockholder includes all shares of our common stock beneficially held by such selling stockholder as of October 30, 2025, which includes (i) all shares of our common stock purchased by such selling stockholder in the Private Placement and (ii) all shares of common stock issuable upon exercise of the Warrants purchased by such selling stockholder in the Private Placement. The percentages of shares owned before and after the offering are based on 17,050,876 shares of common stock outstanding as of October 30, 2025, which includes the outstanding shares of common stock offered by this prospectus but does not include any shares of common stock offered by this prospectus that are issuable pursuant to warrants and are deemed outstanding in the table below because they are beneficially owned by a person.

Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to our common stock. Generally, a person "beneficially owns" shares of our common stock if the person has or shares with others the right to vote those shares or to dispose of them, or if the person has the right to acquire voting or disposition rights within 60 days. In computing the number of shares of our common stock beneficially owned by a person and the percentage ownership of that person, we deemed outstanding shares of common stock issuable upon the exercise of the Warrants held by that selling stockholder described above because all are exercisable within 60 days of October 30, 2025. We did not deem these shares outstanding, however, for the purpose of computing the percentage ownership of any other person. The inclusion of any shares in this table does not constitute an admission of beneficial ownership for any selling stockholder named below.

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| | | | | | |
|:---|:---|:---|:---|:---|:---|
|  | **Shares of<br>Common Stock<br>Beneficially Owned<br>Prior to the Offering** | **Shares of<br>Common Stock<br>Beneficially Owned<br>Prior to the Offering** | **Number of<br>Shares of<br>Common<br>Stock<br>Being<br>Offered(1)** | **Shares of<br>Common Stock<br>to be Beneficially<br>Owned After<br>Offering(2)** | **Shares of<br>Common Stock<br>to be Beneficially<br>Owned After<br>Offering(2)** |
| **Name of Selling Stockholder** | **Number** | **Percentage** | **Number of<br>Shares of<br>Common<br>Stock<br>Being<br>Offered(1)** | **Number** | **Percentage** |
|  Entities advised or subadvised by T. Rowe Price Investment Management, Inc. (3) | 2304242 | 4.99% | 1603250 | 700992 | 4.11% |
|  Entities affiliated with SilverArc Capital Management, LLC (4) | 825403 | 4.84% | 801625 | 23778 | \* |
|  Boxer Capital Master Fund, LP (5) | 240488 | 1.4% | 240488 |  | \* |
|  Cap 1, LLC (6) | 208151 | 1.2% | 160325 | 47826 | \* |

---

\* Less than one percent. 

(1) The number of shares of our Common Stock in the column "Number of Shares of Common Stock Being
Offered" represents all of the shares of our common stock that a selling stockholder may offer and sell from time to time under this prospectus, including shares issuable upon the exercise of Warrants issued in the Private Placement, without
giving effect to the Beneficial Ownership Limitation.

(2) We do not know when or in what amounts the selling stockholders may offer shares for sale. The selling
stockholders might not sell any or might sell all of the shares offered by this prospectus. Because the selling stockholders may offer all or some of the shares pursuant to this offering, and because there are currently no agreements, arrangements
or understandings with respect to the sale of any of the shares, we cannot estimate the number of the shares that will be held by the selling stockholders after completion of the offering. However, for purposes of this table, we have assumed that,
after completion of the offering, none of the shares covered by this prospectus will be held by the selling stockholders, including common stock issuable upon exercise of the Warrants issued in the Private Placement.

(3) The shares reported under "Shares of Common Stock Beneficially Owned Prior to the Offering" consist
of (i) 923,000 shares of common stock and 447,624 shares of common stock issuable upon exercise of Warrants, in each case held by T. Rowe Price Small-Cap Value Fund, Inc., (ii) 585,316 shares of common stock
and 283,029 shares of common stock issuable upon exercise of Warrants, in each case held by T.

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Rowe Price U.S. Small-Cap Value Equity Trust, (iii) 39,347 shares of common stock and 19,200 shares of common stock issuable upon exercise of Warrants, in each case held by T. Rowe Price U.S. Equities Trust and (iv) 3,567 shares of common stock and 3,159 shares of common stock issuable upon exercise of Warrants, in each case held by T. Rowe Price Health Care ETF. TRPIM (as defined below) is prohibited from exercising Warrants, if, as a result of such exercise, TRPIM would beneficially own more than 4.99% of the total number of shares of common stock then issued and outstanding immediately after giving effect to the exercise. As such, the shares reported under "Shares of Common Stock Beneficially Owned Prior to the Offering" give effect to the 4.99% blocker contained in the Warrants. In the absence of the Beneficial Ownership Limitation, TRPIM would be deemed to beneficially own 13.91% of the outstanding shares of common stock. T. Rowe Price Investment Management, Inc. ("TRPIM"), as investment adviser, has dispositive and voting power with respect to the shares held by these funds and accounts. For purposes of the Exchange Act, TRPIM may be deemed to be the beneficial owner of these aforementioned shares of common stock and shares of common stock issuable upon exercise of Warrants; however, TRPIM expressly disclaims that it is, in fact, the beneficial owner of such securities. TRPIM is a wholly owned subsidiary of T. Rowe Price Group, Inc., which is a publicly traded financial services holding company. The principal business address of TRPIM is 1307 Point Street, Baltimore, MD 21231.

(4) The shares reported under "Shares of Common Stock Beneficially Owned Prior to the Offering" consist
of (i) 15,049 shares of common stock and 14,842 shares of common stock issuable upon exercise of Warrants, in each case held by SilverArc Capital Alpha Fund I, L.P. and (ii) 410,070 shares of common stock and 385,442 shares of common stock issuable
upon exercise of Warrants, in each case held by SilverArc Capital Alpha Fund II, L.P. (together, the "SilverArc Funds"). The SilverArc Funds are prohibited from exercising Warrants, if, as a result of such exercise, the SilverArc Funds
would beneficially own more than 4.99% of the total number of shares of common stock then issued and outstanding immediately after giving effect to the exercise. SilverArc Capital Management, LLC is the controlling entity of the SilverArc Funds and
is solely owned by Devesh Gandhi. Mr. Gandhi may be deemed to have shared voting and investment power of the securities managed by SilverArc Capital Management, LLC. Mr. Gandhi disclaims beneficial ownership of such securities, except to
the extent of his pecuniary interest therein. The address of the selling stockholders is 20 Park Plaza, 4th Floor, Boston, MA 02116.

(5) The shares reported under "Shares of Common Stock Beneficially Owned Prior to the Offering" consist
of 127,536 shares of common stock and 112,952 shares of common stock issuable upon exercise of Warrants, in each case held by Boxer Capital Master Fund, LP. The address of the selling stockholder is 12860 El Camino Real, Ste 300 San Diego, CA 92130.

(6) The shares reported under "Shares of Common Stock Beneficially Owned Prior to the Offering" consist
of 132,850 shares of common stock and 75,301 shares of common stock issuable upon exercise of Warrants, in each case held by Cap 1 LLC. The address of the selling stockholder is 207 Sixth Street, West Palm Beach, Florida 33401.

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**PLAN OF DISTRIBUTION** 

The selling stockholders, which as used herein includes donees, pledgees, transferees or other successors-in-interest selling shares of common stock or interests in shares of common stock received after the date of this prospectus from a selling stockholder as a gift, pledge, partnership distribution or other transfer, may, from time to time, sell, transfer or otherwise dispose of any or all of their shares of common stock or interests in shares of common stock on any stock exchange, market or trading facility on which the shares are traded or in private transactions. These dispositions may be at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices.

The selling stockholders may use any one or more of the following methods when disposing of shares or interests therein:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• block trades in which the broker-dealer will attempt to sell the shares as agent, but may position and resell a
portion of the block as principal to facilitate the transaction;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• purchases by a broker-dealer as principal and resale by the broker-dealer for its account;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an exchange distribution in accordance with the rules of the applicable exchange;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• privately negotiated transactions;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• short sales;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• through the writing or settlement of options or other hedging transactions, whether through an options exchange
or otherwise;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• broker-dealers may agree with the selling stockholders to sell a specified number of such shares at a stipulated
price per share;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a combination of any such methods of sale; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any other method permitted by applicable law.

The selling stockholders may, from time to time, pledge or grant a security interest in some or all of the shares of common stock owned by them and, if they default in the performance of their secured obligations, the pledgees or secured parties may offer and sell the shares of common stock, from time to time, under this prospectus, or under an amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act, amending the list of selling stockholders to include the pledgee, transferee or other successors in interest as selling stockholders under this prospectus. The selling stockholders also may transfer the shares of common stock in other circumstances, in which case the transferees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

In connection with the sale of our common stock or interests therein, the selling stockholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the common stock in the course of hedging the positions they assume. The selling stockholders may also sell shares of our common stock short and deliver these securities to close out their short positions, or loan or pledge the common stock to broker-dealers that in turn may sell these securities. The selling stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities which require the delivery to such broker-dealer or other financial institution of shares offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The aggregate proceeds to the selling stockholders from the sale of the common stock offered by them will be the purchase price of the common stock less discounts or commissions, if any. Each of the selling

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stockholders reserves the right to accept and, together with their agents from time to time, to reject, in whole or in part, any proposed purchase of common stock to be made directly or through agents. We will not receive any of the proceeds from the sale of shares of common stock by the selling stockholders. Upon any exercise of the warrants by payment of cash, however, we will receive the exercise price of the warrants in cash.

The selling stockholders also may resell all or a portion of the shares in open market transactions in reliance upon Rule 144 under the Securities Act, provided that they meet the criteria and conform to the requirements of that rule.

The selling stockholders and any underwriters, broker-dealers or agents that participate in the sale of the common stock or interests therein may be "underwriters" within the meaning of Section 2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earn on any resale of the shares may be underwriting discounts and commissions under the Securities Act. Selling stockholders who are "underwriters" within the meaning of Section 2(11) of the Securities Act will be subject to the prospectus delivery requirements of the Securities Act.

To the extent required, the shares of our common stock to be sold, the names of the selling stockholders, the respective purchase prices and public offering prices, the names of any agents, dealers or underwriters, and any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

In order to comply with the securities laws of some states, if applicable, the common stock may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the common stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

We have advised the selling stockholders that the anti-manipulation rules of Regulation M under the Exchange Act, may apply to sales of shares in the market and to the activities of the selling stockholders and their affiliates. In addition, to the extent applicable, we will make copies of this prospectus (as it may be supplemented or amended from time to time) available to the selling stockholders for the purpose of satisfying the prospectus delivery requirements of the Securities Act. The selling stockholders may indemnify any broker-dealer that participates in transactions involving the sale of the shares against certain liabilities, including liabilities arising under the Securities Act.

We have agreed to indemnify the selling stockholders against liabilities, including liabilities under the Securities Act and state securities laws, relating to the registration of the shares offered by this prospectus.

We have agreed with the selling stockholders to use commercially reasonable efforts to cause the registration statement of which this prospectus constitutes a part to remain continuously effective until the earlier of (1) such time as all of the shares covered by this prospectus have been disposed of pursuant to and in accordance with such registration statement or (2) the date on which all of the shares may be sold without restriction pursuant to Rule 144 of the Securities Act.

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**LEGAL MATTERS** 

The validity of the shares of our common stock offered hereby has been passed upon for us by Sidley Austin LLP.

**EXPERTS** 

The consolidated financial statements of Karyopharm Therapeutics Inc. appearing in Karyopharm Therapeutics Inc.'s Annual Report (Form 10-K) for the year ended December 31, 2024, and the effectiveness of Karyopharm Therapeutics Inc.'s internal control over financial reporting as of December 31, 2024, have been audited by Ernst & Young LLP, independent registered public accounting firm, as set forth in their report thereon (which contains an explanatory paragraph describing conditions that raise substantial doubt about the Company's ability to continue as a going concern as described in Note 1 to the consolidated financial statements) appearing elsewhere herein, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

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**WHERE YOU CAN FIND MORE INFORMATION** 

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC's website at http://www.sec.gov. Copies of certain information filed by us with the SEC are also available on our website at www.karyopharm.com. Our website is not a part of this prospectus and the information contained on, or accessible through, our website is not incorporated by reference in this prospectus.

This prospectus is part of a registration statement we filed with the SEC. This prospectus omits some information contained in the registration statement in accordance with SEC rules and regulations. You should review the information and exhibits in the registration statement for further information about us and our consolidated subsidiaries and the securities offered under this prospectus. Statements in this prospectus concerning any document we filed as an exhibit to the registration statement or that we otherwise filed with the SEC are not intended to be comprehensive and are qualified by reference to these filings and the exhibits attached thereto. You should review the complete document to evaluate these statements. You can obtain a copy of the registration statement from the SEC's website.

**INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE** 

The SEC allows us to incorporate by reference in this prospectus much of the information we file with the SEC, which means that we can disclose important information to you by referring you to those publicly available documents. The information that we incorporate by reference in this prospectus is considered to be part of this prospectus. Because we are incorporating by reference future filings with the SEC, this prospectus is continually updated and those future filings may modify or supersede some of the information included or incorporated in this prospectus. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus or in any document previously incorporated by reference have been modified or superseded. This prospectus incorporates by reference the documents listed below (File No. 001-36167) and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus and prior to the sale of all the shares covered by this prospectus, other than those documents or the portions of those documents not deemed to be filed until the offering of the securities under the registration statement is terminated or completed:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025022765/kpti-20241231.htm) for the year ended December 31, 2024, which was filed on February 19, 2025;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• The information included in our definitive proxy statement on [Schedule 14A](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025053511/kpti-20250414.htm) for the 2025 Annual Meeting of Stockholders, which was filed on April 
14, 2025, to the extent incorporated by reference into Part III of the Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025022765/kpti-20241231.htm) for the fiscal year ended December 31, 2024;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Quarterly Reports on Form 10-Q for the quarterly period ended [March 31, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025069231/kpti-20250331.htm) , which was filed on May 12, 2025, for the quarterly period ended [June 30, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025106238/kpti-20250630.htm) , which was
filed on August 11, 2025, and for the quarterly period ended [September 30, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001503802/000119312525261667/kpti-20250930.htm) , which was filed on
November 3, 2025;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Current Reports on Form 8-K filed on [January 2, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025000092/kpti-20250102.htm) , [January 30, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000119312525017223/d893335d8k.htm) , [January 31, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000119312525018385/d914351d8k.htm) , [February 24, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025025640/kpti-20250224.htm) , [May 29, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000095017025079009/kpti-20250528.htm) , [September 11, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000150380225000006/kpti-20250905.htm) , [October 8, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000119312525233983/d940170d8k.htm) (excluding Items 2.02 and 7.01) and [October 14, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1503802/000119312525239015/d81116d8k.htm) ;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• The description of our common stock contained in our Registration Statement on [Form 8-A](http://www.sec.gov/Archives/edgar/data/1503802/000110465913079966/a13-19023_78a12b.htm) filed on November 
1, 2013, as the description therein has been updated and superseded by the description of our capital stock contained in [Exhibit 4.2](http://www.sec.gov/Archives/edgar/data/1503802/000095017025022765/kpti-ex4_2.htm) to our Annual Report
on Form 10-K for the fiscal year ended December 31, 2024, as filed with the SEC on February 19, 2025 including any amendments or reports filed for the purpose of updating such description; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Any other filings we make pursuant to the Exchange Act after the date of filing the registration statement of
which this prospectus is a part and prior to effectiveness of the registration statement.

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You may request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:

Karyopharm Therapeutics Inc.

85 Wells Avenue, 2nd Floor

Newton, MA 02459

Attn: Investor Relations

(617) 658-0600

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**2,805,688 Shares**![LOGO](g54161g00s24.jpg)

**Common Stock** 

**PROSPECTUS** 

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**, 2025** 

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**PART II** 

**INFORMATION NOT REQUIRED IN PROSPECTUS** 

**Item 14.** **Other Expenses of Issuance and Distribution.** <br>

The following table sets forth the various expenses to be incurred in connection with the sale and distribution of the securities being registered hereby, all of which will be borne by Karyopharm Therapeutics Inc. (except any underwriting discounts and commissions and expenses incurred by the selling stockholders for brokerage, accounting, tax or legal services or any other expenses incurred by the selling stockholders in disposing of the shares). All amounts shown are estimates except the SEC registration fee.

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| | |
|:---|:---|
|  SEC registration fee | $2371 |
|  Legal fees and expenses | $50000 |
|  Accounting fees and expenses | $5000 |
|  Printing fees and expenses | $15000 |
|  Miscellaneous fees and expenses | $5000 |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Total expenses | $77371 |

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**Item 15.** **Indemnification of Directors and Officers.** <br>

Section 102(b)(7) of the General Corporation Law of the State of Delaware permits a corporation to eliminate or limit the personal liability of directors or officers of a corporation to the corporation (in the case of directors) or its stockholders (in the case of directors and officers) for monetary damages for any breach of fiduciary duty as a director or officer, except where the director or officer breached his or her duty of loyalty, failed to act in good faith, engaged in intentional misconduct or knowingly violated a law, authorized the payment of a dividend or approved a stock repurchase in violation of Delaware corporate law or obtained an improper personal benefit. Our restated certificate of incorporation provides that, to the fullest extent permitted by the General Corporation Law of the State of Delaware, no director or officer of the registrant shall be personally liable to the registrant (in the case of directors) or its stockholders (in the case of directors and officers) for monetary damages for any breach of fiduciary duty as a director or officer.

Section 145 of the General Corporation Law of the State of Delaware provides that a corporation has the power to indemnify a director, officer, employee, or agent of the corporation, or a person serving at the request of the corporation for another corporation, partnership, joint venture, trust or other enterprise in related capacities against expenses (including attorneys' fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with an action, suit or proceeding to which he was or is or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding by reason of such position, if such person acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the best interests of the corporation, and, in any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful, except that, in the case of actions brought by or in the right of the corporation, no indemnification shall be made with respect to any claim, issue or matter as to which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the Court of Chancery or other adjudicating court determines that, despite the adjudication of liability but in view of all of the circumstances of the case, such person is fairly and reasonably entitled to indemnity for such expenses which the Court of Chancery or such other court shall deem proper.

Our restated certificate of incorporation provides that we will indemnify each person who was or is a party or threatened to be made a party to any threatened, pending or completed action, suit or proceeding whether civil, criminal, administrative or investigative (other than an action by or in the right of us) by reason of the fact that he or she is or was, or has agreed to become, a director or officer, or is or was serving, or has agreed to serve, at our request, as a director, officer, partner, employee or trustee of, or in a similar capacity with, another corporation, partnership, joint venture, trust or other enterprise (including any employee benefit plan) (all such persons being

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##### [**Table of Contents**](#toc)
referred to as an "Indemnitee"), or by reason of any action alleged to have been taken or omitted in such capacity, against all expenses (including attorneys' fees), liabilities, losses, judgments, fines (including excise taxes and penalties arising under the Employee Retirement Income Security Act of 1974), and amounts paid in settlement actually and reasonably incurred in connection with such action, suit or proceeding and any appeal therefrom, if such Indemnitee acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interests, and, with respect to any criminal action or proceeding, he or she had no reasonable cause to believe his or her conduct was unlawful. Our restated certificate of incorporation also provides that we will indemnify any Indemnitee who was or is a party to any threatened, pending, or completed action or suit by or in the right of us to procure a judgment in our favor by reason of the fact that the Indemnitee is or was, or has agreed to become, a director or officer, or is or was serving, or has agreed to serve, at our request, as a director, officer, partner, employee or trustee of, or in a similar capacity with, another corporation, partnership, joint venture, trust or other enterprise (including any employee benefit plan), or by reason of any action alleged to have been taken or omitted in such capacity, against all expenses (including attorneys' fees) and, to the extent permitted by law, amounts paid in settlement actually and reasonably incurred in connection with such action, suit or proceeding, and any appeal therefrom, if the Indemnitee acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interests, except that no indemnification shall be made with respect to any claim, issue or matter as to which such person shall have been adjudged to be liable to us, unless a court determines that, despite such adjudication but in view of all of the circumstances, he or she is entitled to indemnification of such expenses. Notwithstanding the foregoing, to the extent that any Indemnitee has been successful, on the merits or otherwise, he or she will be indemnified by us against all expenses (including attorneys' fees) actually and reasonably incurred in connection therewith. Expenses must be advanced to an Indemnitee under certain circumstances.

We have entered into indemnification agreements with each of our directors. These indemnification agreements may require us, among other things, to indemnify our directors for some expenses, including attorneys' fees, judgments, fines and settlement amounts incurred by a director in any action or proceeding arising out of his or her service as one of our directors, or any of our subsidiaries or any other company or enterprise to which the person provides services at our request.

We maintain a liability insurance policy that covers certain liabilities of directors and officers of our corporation arising out of claims based on acts or omissions in their capacities as directors or officers.

Insofar as the foregoing provisions permit indemnification of directors, executive officers, or persons controlling us for liability arising under the Securities Act, we have been informed that, in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is therefore unenforceable.

**Item 16.** **Exhibits.** <br>

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| | |
|:---|:---|
| **Exhibit<br>No.** | **Description** |
| &nbsp;&nbsp;&nbsp;&nbsp;3.1 | [Restated Certificate of Incorporation of the Registrant, as amended (1)](http://www.sec.gov/Archives/edgar/data/1503802/000095017025069231/kpti-ex3_1.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;3.2 | [Third Amended and Restated By-Laws of the Registrant (2)](http://www.sec.gov/Archives/edgar/data/1503802/000119312522297530/d423713dex31.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.1 | [Form of Warrant to Purchase Common Stock (3)](http://www.sec.gov/Archives/edgar/data/1503802/000119312525239015/d81116dex43.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.2 | [Form of Pre-Funded Warrant to Purchase Common Stock (3)](http://www.sec.gov/Archives/edgar/data/1503802/000119312525239015/d81116dex46.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.3 | [Securities Purchase Agreement, dated October 7, 2025, by and among the Registrant and the other parties thereto (3)](http://www.sec.gov/Archives/edgar/data/1503802/000119312525239015/d81116dex107.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.3 | [Registration Rights Agreement, dated October 7, 2025, by and among the Registrant and the other parties thereto (3)](http://www.sec.gov/Archives/edgar/data/1503802/000119312525239015/d81116dex109.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;5.1 | [Opinion of Sidley Austin LLP](d54161dex51.htm) |
| 23.1 | [Consent of Ernst & Young LLP, independent registered public accounting firm for the Registrant](d54161dex231.htm) |

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##### [**Table of Contents**](#toc)

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| | |
|:---|:---|
| **Exhibit<br>No.** | **Description** |
| 23.2 | [Consent of Sidley Austin LLP (included in Exhibit 5.1)](d54161dex51.htm) |
| 24.1 | [Powers of Attorney (included in the signature pages to the Registration Statement)](d54161ds3.htm#sig) |
| 107 | [Filing Fee Table](d54161dexfilingfees.htm) |

---

(1) Incorporated by reference to the Registrant's Quarterly Report on Form 10-Q (File No. 001-36167) filed with the Securities and Exchange Commission on May 12, 2025.

(2) Incorporated by reference to the Registrant's Current Report on Form 8-K (File No. 001-36167) filed with the Securities and Exchange Commission on December 2, 2022.

(3) Incorporated by reference to the Registrant's Current Report on Form 8-K (File No. 001-36167) filed with the Securities and Exchange Commission on October 14, 2025.

**Item 17.** **Undertakings.** <br>

(a) The undersigned registrant hereby undertakes:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this
registration statement:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933, as amended, or the
Securities Act;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) To reflect in the prospectus any facts or events arising after the effective date of this registration
statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in this registration statement. Notwithstanding the foregoing, any increase or
decrease in the volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form
of prospectus filed with the Securities and Exchange Commission, or the Commission, pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percent change in the maximum aggregate offering price
set forth in the "Calculation of Registration Fee" table in the effective registration statement; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) To include any material information with respect to the plan of distribution not previously disclosed in this
registration statement or any material change to such information in this registration statement;

*provided, however*, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, that are incorporated by reference in this registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of this registration statement.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) That, for the purposes of determining any liability under the Securities Act, each post-effective amendment
shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at the time shall be deemed to be the initial bona fide offering thereof.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) To remove from registration by means of a post-effective amendment any of the securities being registered which
remain unsold at the termination of the offering.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(4) That, for the purpose of determining liability under the Securities Act to any purchaser:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) each prospectus filed by the Registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the
registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

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##### [**Table of Contents**](#toc)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration
statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii) or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act shall be deemed to be part of and
included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule
430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that
prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof; provided, however, that no statement made in a registration statement or prospectus that is part of the registration
statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective
date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(b) The undersigned registrant hereby undertakes that, for purposes of determining any liability under the
Securities Act, each filing of the registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of
the Exchange Act) that is incorporated by reference in this registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

(c) Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors,
officers and controlling persons of the registrant pursuant to the indemnification provisions described herein, or otherwise, the registrant has been advised that in the opinion of the Commission such indemnification is against public policy as
expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its
counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

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##### [**Table of Contents**](#toc)
**SIGNATURES** 

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the city of Newton, Commonwealth of Massachusetts, on November 3, 2025.

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| | |
|:---|:---|
| **KARYOPHARM THERAPEUTICS INC.** | **KARYOPHARM THERAPEUTICS INC.** |
| By: | /s/ Richard Paulson |
| Name: | Richard Paulson |
| Title: | President and Chief Executive Officer |

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##### [**Table of Contents**](#toc)
**SIGNATURES AND POWER OF ATTORNEY** 

We, the undersigned officers and directors of Karyopharm Therapeutics Inc. hereby severally constitute and appoint Richard Paulson, Lori Macomber and Michael Mano, and each of them singly, our true and lawful attorneys with full power to any of them, and to each of them singly, to sign for us and in our names in the capacities indicated below the Registration Statement on Form S-3 filed herewith and any and all amendments (including post-effective amendments) to said Registration Statement, and any registration statement filed pursuant to Rule 462 under the Securities Act of 1933, as amended, in connection with said Registration Statement, and to file or cause to be filed the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, and generally to do all such things in our name and on our behalf in our capacities as officers and directors to enable Karyopharm Therapeutics Inc. to comply with the provisions of the Securities Act of 1933, as amended, and all requirements of the Securities and Exchange Commission, hereby ratifying and confirming all that said attorneys, and each of them, or their substitute or substitutes, shall do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

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| | | |
|:---|:---|:---|
| **Signature** | **Title** | **Date** |
| /s/ Richard Paulson<br> Richard Paulson | President, Chief Executive Officer and Director (Principal Executive Officer) | November 3, 2025 |
| /s/ Lori Macomber<br> Lori Macomber | Chief Financial Officer (Principal Financial Officer) | November 3, 2025 |
| /s/ Kristin Abate<br> Kristin Abate | Chief Accounting Officer (Principal Accounting Officer) | November 3, 2025 |
| /s/ Garen G. Bohlin<br> Garen G. Bohlin | Director | November 3, 2025 |
| /s/ Barry E. Greene<br> Barry E. Greene | Director | November 3, 2025 |
| /s/ Christy J. Oliger<br> Christy J. Oliger | Director | November 3, 2025 |
| /s/ Deepika R. Pakianathan<br> Deepika R. Pakianathan, Ph.D. | Director | November 3, 2025 |
| /s/ Zhen Su<br> Zhen Su, M.D. | Director | November 3, 2025 |
| /s/ Chen Schor<br> Chen Schor | Director | November 3, 2025 |

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## Exhibit 5.1

**Exhibit 5.1** 

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| | |
|:---|:---|
| ![LOGO](g54161g38f75.jpg)  | SIDLEY AUSTIN (NE) LLP<br> 60 STATE STREET, 36TH FLOOR<br> BOSTON, MASSACHUSETTS 02109<br> PHONE: +1 617 223 0300<br> FAX: +1 617 223 0301<br>AMERICA • ASIA PACIFIC • EUROPE |

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November 3, 2025

Karyopharm Therapeutics Inc.

85 Wells Avenue, 2nd Floor

Newton, MA 02459

Re: <u>Registration Statement on Form S-3</u> 

Ladies and Gentlemen:

We refer to the Registration Statement on Form S-3 (the "<u>Registration Statement</u>") being filed by Karyopharm Therapeutics Inc., a Delaware corporation (the "<u>Company</u>"), with the Securities and Exchange Commission on the date hereof, under the Securities Act of 1933, as amended (the "<u>Securities Act</u>"), relating to the registration of up to 2,805,688 shares of the Company's common stock, par value $0.0001 per share (the "<u>Common Stock</u>"), which includes 1,487,917 shares of Common Stock (the "<u>Common Shares</u>") that are issued and outstanding and up to 1,317,771 shares of Common Stock (the "<u>Warrant Shares</u>" and, collectively with the Common Shares, the "<u>Shares</u>") that may be issued upon the exercise of issued and outstanding warrants (the "<u>Warrants</u>"). The Shares may be offered and sold by the selling stockholders named in the Registration Statement.

This opinion letter is being delivered in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

We have examined the Registration Statement, the Certificate of Incorporation, as amended, of the Company filed with the Secretary of State of the State of Delaware, the bylaws, as amended, of the Company, the Warrants and the resolutions adopted by the board of directors of the Company relating to the Registration Statement and the issuance of the Warrants and the Shares by the Company. We have also examined originals, or copies of originals certified to our satisfaction, of such agreements, documents, certificates and statements of the Company and other corporate documents and instruments, and have examined such questions of law, as we have considered relevant and necessary as a basis for this opinion letter. We have assumed the authenticity of all documents submitted to us as originals, the genuineness of all signatures, the legal capacity of all persons and the conformity with the original documents of any copies thereof submitted to us for examination. As to facts relevant to the opinions expressed herein, we have relied without independent investigation or verification upon, and assumed the accuracy and completeness of, certificates, letters and oral and written statements and representations of public officials and officers and other representatives of the Company.

Sidley Austin (NE) LLP is a limited liability partnership doing business as Sidley Austin LLP and practicing in affiliation with other Sidley Austin partnerships.

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![LOGO](g54161g38f75.jpg)

Karyopharm Therapeutics Inc.

November 3, 2025

Based on the foregoing, and subject to the other qualifications and limitations set forth herein, we are of the opinion that:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1. The Common Shares are validly issued, fully paid and non-assessable.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2. The Warrant Shares, when duly issued and delivered in accordance with the terms of the Warrants (including the payment of the applicable exercise price), will be validly issued, fully paid and non-assessable.

In rendering the opinion set forth in paragraph 2 above, we have assumed that at the time of the issuance of any Shares upon exercise of any Warrant there will be a sufficient number of shares of Common Stock authorized and then available for issuance under the Company's certificate of incorporation as in effect at such time.

This opinion letter is limited to the General Corporation Law of the State of Delaware. We express no opinion as to the laws, rules or regulations of any other jurisdiction, including, without limitation, the federal laws of the United States of America or any state securities or blue sky laws.

We hereby consent to the filing of this opinion letter as an exhibit to the Registration Statement and to all references to our Firm included in or made a part of the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act.

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| |
|:---|
| Very truly yours, |
| /s/ Sidley Austin LLP |

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## Exhibit 23.1

**Exhibit 23.1** 

**Consent of Independent Registered Public Accounting Firm** 

We consent to the reference to our firm under the caption "Experts" in the Registration Statement (Form S-3) and related Prospectus of Karyopharm Therapeutics Inc. for the registration of 2,805,688 shares of its common stock and to the incorporation by reference therein of our reports dated February 19, 2025, with respect to the consolidated financial statements of Karyopharm Therapeutics Inc., and the effectiveness of internal control over financial reporting of Karyopharm Therapeutics Inc., included in its Annual Report (Form 10-K) for the year ended December 31, 2024, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Boston, Massachusetts

November 3, 2025

## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

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| |
|:---|
| **Calculation of Filing Fee Tables**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**S-3**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**Karyopharm Therapeutics Inc.**  |

---

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| | | | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|:---|:---|
| | | **Security Type**  | **Security Class Title**  | **Fee Calculation or Carry Forward Rule**  | **Amount Registered**  | **Proposed Maximum Offering Price Per Unit**  | **Maximum Aggregate Offering Price**  | **Fee Rate**  | **Amount of Registration Fee**  |
| **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** |
| Fees to be Paid | 1 | Equity | Common Stock, $0.0001 par value per share | Other | 2805688 | $6.12 | $17170810.56 | 0.0001381 | $2371.29 |
| Fees Previously Paid |  |  |  |  |  |  |  |  |  |
| **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** |
| Carry Forward Securities |  |  |  |  |  |  |  |  |  |
|  |  |  | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: |  | $17170810.56  |  | $2371.29  |
|  |  |  | Total Fees Previously Paid:  | Total Fees Previously Paid:  | Total Fees Previously Paid:  |  |  |  | $0.00  |
|  |  |  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  |  |  |  | $0.00  |
|  |  |  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  |  |  |  | $2371.29  |

---

 **Offering Note** <br>

<sup>1</sup> (1) The shares of common stock will be offered for resale by the selling stockholders pursuant to the prospectus contained in the registration statement to which this exhibit is attached. The registration statement registers the resale of an aggregate of 2,805,688 shares of the Registrant's common stock, which consists of (i) 1,487,917 outstanding shares of common stock and (ii) 1,317,771 shares of common stock issuable upon the exercise of outstanding warrants. Pursuant to Rule 416 under the Securities Act of 1933, as amended (the "Securities Act"), the shares of common stock being registered hereunder include such indeterminate number of shares of common stock as may be issuable upon stock splits, stock dividends, or other distribution, recapitalization or similar events. (2) This estimate is made pursuant to Rule 457(c) of the Securities Act solely for purposes of calculating the registration fee. The price per share and aggregate offering price are based upon the average of the high and low prices of the Registrant's common stock on October 30, 2025, as reported on the Nasdaq Global Select Market.

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| | |
|:---|:---|
| | |
| **Rules 457(b) and 0-11(a)(2)** | **Rules 457(b) and 0-11(a)(2)** |
| Fee Offset Claims | N/A |
| Fee Offset Sources | N/A |
| **Rule 457(p)** | **Rule 457(p)** |
| Fee Offset Claims | N/A |
| Fee Offset Sources | N/A |

---

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| | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|
| | **Security Type**  | **Security Class Title**  | **Amount of Securities Previously Registered**  | **Maximum Aggregate Offering Price of Securities Previously Registered**  | **Form Type**  | **File Number**  | **Initial Effective Date**  |
| N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |

---