Nature of Business	12 Months Ended
Dec. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business Nature of Operations Cyclerion Therapeutics, Inc. (“Cyclerion”, the “Company” or “we”) became an independent public company on April 1, 2019 after Ironwood Pharmaceuticals, Inc. completed a tax-free spin-off of their sGC business. Cyclerion is focused on building a new pipeline with therapeutics to treat certain neuropsychiatric diseases. Cyclerion has prioritized an individualized therapy for treatment resistant depression (“TRD”) as its foundational product candidate and has entered into a non-binding option to license agreement for the intellectual property associated with this product. With the large unmet medical need in TRD, the clinical development stage of this asset, and the strong commercial opportunity, the Company believes that this product is well suited to be its foundation moving forward for Cyclerion. The Company is currently developing an integrated development and commercial strategy in TRD. Cyclerion has one employee as of December 31, 2024. At inception, Cyclerion was a biopharmaceutical company focused on the treatment of serious diseases with novel soluble guanylate cyclase (“sGC”) stimulators in both the central nervous system (“CNS”) and the periphery. The Company’s strategy changed and Cyclerion's sGC assets have either been sold, out-licensed or has plans to be out-licensed to a third party. The Company’s prior strategy to conduct research and development on sGC stimulators has been discontinued and Cyclerion does not intend to internally pursue research and development or commercialization with any sGC asset. The Company is leveraging its legacy sGC stimulator assets to generate revenues which, in the near-term will be used to implement its strategic building plan in TRD. Praliciguat is an orally administered, once-daily systemic sGC stimulator. On June 3, 2021, Cyclerion entered into a license agreement with Akebia Therapeutics Inc. (“Akebia”) relating to the exclusive worldwide license to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing praliciguat and other related products and forms thereof enumerated in such agreement. On December 13, 2024, Cyclerion announced that Cyclerion and Akebia have re-negotiated a mutually beneficial amendment to their exclusive license agreement for praliciguat, a systemic sGC stimulator. Under this new license amendment, Cyclerion will receive $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and an additional payment of $0.5 million is due in September 2025. In addition, Akebia is responsible for all intellectual property expenses associated with praliciguat. The Company is eligible to receive additional milestone cash payments of up to approximately $558.5 million in total potential future development, regulatory, and commercialization milestone payments for praliciguat. In exchange for a reduction in certain development milestone payments, Cyclerion is eligible to receive certain higher-tiered sales-based royalties ranging from mid-single-digits to twenty percent. In 2021, Akebia paid a $3.0 million upfront payment to the Company upon signing of the license agreement. Olinciguat is a Phase 2, orally administered, once-daily, vascular sGC stimulator. On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee has an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024. The Optionee may exercise the Option on or before February 22, 2025, which may be extended for an additional two-month period for an additional fee of $25,000 (the “Option Period”). If the Optionee exercises the Option during the Option Period, the Optionee and the Company shall promptly commence negotiations of the definitive license agreement. The terms of the license agreement will be negotiated in good faith within a period not to exceed 90 days after the date of exercise of the Option. If the parties cannot reach agreement, all rights revert to the Company. In addition, the Optionee has agreed to reimburse the Company for certain patent expenses incurred during the Option period. Zagociguat is a clinical-stage CNS-penetrant sGC stimulator that has shown rapid improvement in cerebral blood flow, functional brain connectivity, brain response to visual stimulus, cognitive performance, and biomarkers associated mitochondrial function and inflammation in clinical studies. CY3018 is a CNS-targeted sGC stimulator that preferentially localizes to the brain and has a pharmacology profile that suggests its potential for the treatment of neuropsychiatric diseases and disorders. On July 28, 2023, the Company sold Zagociguat and CY3018 to Tisento Therapeutics, Inc. (“Tisento”), a newly formed private company focused on their development, in exchange for $8.0 million in cash consideration, $2.4 million as reimbursement for certain operating expenses related to zagociguat and CY3018 for the period between signing and closing of the transaction, and 10% of all of Tisento’s parent’s outstanding equity securities. See “Asset Purchase Agreement” and “Note 4” below. Cyclerion GmbH, a wholly owned subsidiary, was incorporated in Zug, Switzerland on May 3, 2019. The functional currency is the Swiss franc. Cyclerion GmbH was liquidated and de-registered in May 2024. Cyclerion Securities Corporation, a wholly owned subsidiary, was incorporated in Massachusetts on November 15, 2019 and was granted securities corporation status in Massachusetts. Stock Purchase Agreement In March 2023, the Company entered into a stock purchase agreement with the Company's former Chief Executive Officer (the “CEO”) pursuant to which he invested $5 million in cash for 225,000 shares of common stock and 351,037 shares of Series A Convertible Preferred Stock of the Company at a price of $8.68 per share (after giving effect to the 1-for-20 reverse stock split the Company implemented on May 15, 2023). The Series A Convertible Preferred Stock is convertible into shares of the Company's common stock on a one-to-one basis. The closing of the equity investment took place on May 19, 2023, and (to comply with Nasdaq listing requirements) the Company's shareholders approved such convertibility on July 19, 2023. Asset Purchase Agreement On May 11, 2023, the Company entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”) with an investor group that included the former CEO, JW Celtics Investment Corp and JW Cycle Inc. which subsequently changed their names to Tisento Therapeutics Holdings Inc. (“Tisento Parent”) and Tisento. Upon the closing on July 28, 2023, of the transactions contemplated by the Asset Purchase Agreement, the Company sold to Tisento specified assets relating to the Company’s zagociguat and CY3018 programs (the "Transferred Assets") and Tisento assumed certain liabilities relating thereto, including, but not limited to (i) liabilities, costs and expenses arising after the date of the Asset Purchase Agreement relating to the employment of certain Cyclerion employees and the conduct of certain preclinical and clinical trial activities prior to the closing of the transactions contemplated by the Asset Purchase Agreement, and (ii) liabilities relating to such assets to the extent relating to the period after the closing of the transaction. In consideration for such sale and assumption, at such closing the Company received proceeds of $8.0 million as cash consideration, $2.4 million as reimbursement for certain operating expenses related to such assets for the period between signing and closing of the Asset Purchase Agreement, and shares of common stock of Tisento Parent comprising 10% of the then issued and outstanding equity securities of Tisento Parent immediately following such closing, subject to certain protections against dilution. Reverse Stock Split On May 15, 2023, the Company filed Articles of Amendment to the Company's Restated Articles of Organization with the Secretary of Commonwealth of Massachusetts to effect a 1-for-20 reverse stock split of the Company's issued and outstanding shares of common stock. The reverse stock split was reflected on the Nasdaq Capital Market beginning with the opening of trading on May 16, 2023. All share amounts and per share amounts disclosed in this Annual Report on Form 10-K have been adjusted retroactively to reflect the reverse stock split for all periods presented. At-the-Market Offering On September 3, 2020, the Company entered into a Sales Agreement (the “Sales Agreement”) with Jefferies LLC (“Jefferies”) with respect to an at-the-market offering (the “ATM Offering”) under the 2020 Shelf. Under the ATM Offering, the Company could offer and sell, from time to time at its sole discretion, shares of its common stock, having an aggregate offering price of up to $50.0 million through Jefferies as its sales agent. The Company agreed to pay Jefferies cash commissions of 3.0 percent of the gross proceeds of sales of common stock which could be sold under the Sales Agreement. No shares of common stock have been issued or sold under the ATM Offering in 2023. The 2020 Shelf expired in July 31, 2023. Due to the current market value of our publicly traded common stock held by non-affiliates, our ability to raise future funding though a shelf offering will be limited to the value of one-third of our public float until such time as the public float exceeds $75 million. Basis of Presentation The consolidated financial statements and the related disclosures have been prepared in accordance with U.S. generally accepted accounting principles. In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the fiscal years presented. The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion Securities Corporation and Cyclerion GmbH which was dissolved in May 2024. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying consolidated financial statements. Going Concern At each reporting period, in accordance with Accounting Standards Codification ("ASC") 205-40, Going Concern, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash and cash equivalent balances. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future partnerships, equity or debt issuances, certain cost reduction measures and the potential milestones from the Akebia agreement cannot be considered probable at this time because these plans are not entirely within the Company’s control and/or have not been approved by the Board of Directors as of the date of these consolidated financial statements. The Company expects that its cash and cash equivalents as of December 31, 2024, will be sufficient to fund operations through mid-2025, however the Company will need to obtain additional funding to sustain operations as it expects to continue to generate operating losses for the foreseeable future. The Company's expectation to generate negative operating cash flows in the future and the need for additional funding to support its planned operations, raise substantial doubt regarding the Company’s ability to continue as a going concern. Management's plans to alleviate the conditions that raise substantial doubt include reduced spending, and the pursuit of additional capital. Management has concluded the likelihood that its plan to successfully obtain sufficient funding, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Cyclerion Therapeutics, Inc. (“Cyclerion”, the “Company” or “we”) became an independent public company on April 1, 2019 after Ironwood Pharmaceuticals, Inc. completed a tax-free spin-off of their sGC business. Cyclerion is focused on building a new pipeline with therapeutics to treat certain neuropsychiatric diseases. Cyclerion has prioritized an individualized therapy for treatment resistant depression (“TRD”) as its foundational product candidate and has entered into a non-binding option to license agreement for the intellectual property associated with this product. With the large unmet medical need in TRD, the clinical development stage of this asset, and the strong commercial opportunity, the Company believes that this product is well suited to be its foundation moving forward for Cyclerion. The Company is currently developing an integrated development and commercial strategy in TRD. Cyclerion has one employee as of December 31, 2024.

At inception, Cyclerion was a biopharmaceutical company focused on the treatment of serious diseases with novel soluble guanylate cyclase (“sGC”) stimulators in both the central nervous system (“CNS”) and the periphery. The Company’s strategy changed and Cyclerion's sGC assets have either been sold, out-licensed or has plans to be out-licensed to a third party. The Company’s prior strategy to conduct research and development on sGC stimulators has been discontinued and Cyclerion does not intend to internally pursue research and development or commercialization with any sGC asset. The Company is leveraging its legacy sGC stimulator assets to generate revenues which, in the near-term will be used to implement its strategic building plan in TRD.

Praliciguat is an orally administered, once-daily systemic sGC stimulator. On June 3, 2021, Cyclerion entered into a license agreement with Akebia Therapeutics Inc. (“Akebia”) relating to the exclusive worldwide license to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing praliciguat and other related products and forms thereof enumerated in such agreement.

On December 13, 2024, Cyclerion announced that Cyclerion and Akebia have re-negotiated a mutually beneficial amendment to their exclusive license agreement for praliciguat, a systemic sGC stimulator. Under this new license amendment, Cyclerion will receive $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and an additional payment of $0.5 million is due in September 2025. In addition, Akebia is responsible for all intellectual property expenses associated with praliciguat. The Company is eligible to receive additional milestone cash payments of up to approximately $558.5 million in total potential future development, regulatory, and commercialization milestone payments for praliciguat. In exchange for a reduction in certain development milestone payments, Cyclerion is eligible to receive certain higher-tiered sales-based royalties ranging from mid-single-digits to twenty percent. In 2021, Akebia paid a $3.0 million upfront payment to the Company upon signing of the license agreement.

Olinciguat is a Phase 2, orally administered, once-daily, vascular sGC stimulator. On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee has an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024. The Optionee may exercise the Option on or before February 22, 2025, which may be extended for an additional two-month period for an additional fee of $25,000 (the “Option Period”). If the Optionee exercises the Option during the Option Period, the Optionee and the Company shall promptly commence negotiations of the definitive license agreement. The terms of the license agreement will be negotiated in good faith within a period not to exceed 90 days after the date of exercise of the Option. If the parties cannot reach agreement, all rights revert to the Company. In addition, the Optionee has agreed to reimburse the Company for certain patent expenses incurred during the Option period.

Zagociguat is a clinical-stage CNS-penetrant sGC stimulator that has shown rapid improvement in cerebral blood flow, functional brain connectivity, brain response to visual stimulus, cognitive performance, and biomarkers

associated mitochondrial function and inflammation in clinical studies. CY3018 is a CNS-targeted sGC stimulator that preferentially localizes to the brain and has a pharmacology profile that suggests its potential for the treatment of neuropsychiatric diseases and disorders. On July 28, 2023, the Company sold Zagociguat and CY3018 to Tisento Therapeutics, Inc. (“Tisento”), a newly formed private company focused on their development, in exchange for $8.0 million in cash consideration, $2.4 million as reimbursement for certain operating expenses related to zagociguat and CY3018 for the period between signing and closing of the transaction, and 10% of all of Tisento’s parent’s outstanding equity securities. See “Asset Purchase Agreement” and “Note 4” below.

Cyclerion GmbH, a wholly owned subsidiary, was incorporated in Zug, Switzerland on May 3, 2019. The functional currency is the Swiss franc. Cyclerion GmbH was liquidated and de-registered in May 2024.

Cyclerion Securities Corporation, a wholly owned subsidiary, was incorporated in Massachusetts on November 15, 2019 and was granted securities corporation status in Massachusetts.

In March 2023, the Company entered into a stock purchase agreement with the Company's former Chief Executive Officer (the “CEO”) pursuant to which he invested $5 million in cash for 225,000 shares of common stock and 351,037 shares of Series A Convertible Preferred Stock of the Company at a price of $8.68 per share (after giving effect to the 1-for-20 reverse stock split the Company implemented on May 15, 2023). The Series A Convertible Preferred Stock is convertible into shares of the Company's common stock on a one-to-one basis. The closing of the equity investment took place on May 19, 2023, and (to comply with Nasdaq listing requirements) the Company's shareholders approved such convertibility on July 19, 2023.

On May 11, 2023, the Company entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”) with an investor group that included the former CEO, JW Celtics Investment Corp and JW Cycle Inc. which subsequently changed their names to Tisento Therapeutics Holdings Inc. (“Tisento Parent”) and Tisento. Upon the closing on July 28, 2023, of the transactions contemplated by the Asset Purchase Agreement, the Company sold to Tisento specified assets relating to the Company’s zagociguat and CY3018 programs (the "Transferred Assets") and Tisento assumed certain liabilities relating thereto, including, but not limited to (i) liabilities, costs and expenses arising after the date of the Asset Purchase Agreement relating to the employment of certain Cyclerion employees and the conduct of certain preclinical and clinical trial activities prior to the closing of the transactions contemplated by the Asset Purchase Agreement, and (ii) liabilities relating to such assets to the extent relating to the period after the closing of the transaction. In consideration for such sale and assumption, at such closing the Company received proceeds of $8.0 million as cash consideration, $2.4 million as reimbursement for certain operating expenses related to such assets for the period between signing and closing of the Asset Purchase Agreement, and shares of common stock of Tisento Parent comprising 10% of the then issued and outstanding equity securities of Tisento Parent immediately following such closing, subject to certain protections against dilution.

On May 15, 2023, the Company filed Articles of Amendment to the Company's Restated Articles of Organization with the Secretary of Commonwealth of Massachusetts to effect a 1-for-20 reverse stock split of the Company's issued and outstanding shares of common stock. The reverse stock split was reflected on the Nasdaq Capital Market beginning with the opening of trading on May 16, 2023. All share amounts and per share amounts disclosed in this Annual Report on Form 10-K have been adjusted retroactively to reflect the reverse stock split for all periods presented.

On September 3, 2020, the Company entered into a Sales Agreement (the “Sales Agreement”) with Jefferies LLC (“Jefferies”) with respect to an at-the-market offering (the “ATM Offering”) under the 2020 Shelf. Under the ATM Offering, the Company could offer and sell, from time to time at its sole discretion, shares of its common stock, having an aggregate offering price of up to $50.0 million through Jefferies as its sales agent. The

Company agreed to pay Jefferies cash commissions of 3.0 percent of the gross proceeds of sales of common stock which could be sold under the Sales Agreement. No shares of common stock have been issued or sold under the ATM Offering in 2023. The 2020 Shelf expired in July 31, 2023. Due to the current market value of our publicly traded common stock held by non-affiliates, our ability to raise future funding though a shelf offering will be limited to the value of one-third of our public float until such time as the public float exceeds $75 million.

Basis of Presentation

The consolidated financial statements and the related disclosures have been prepared in accordance with U.S. generally accepted accounting principles. In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the fiscal years presented.

The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion Securities Corporation and Cyclerion GmbH which was dissolved in May 2024. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying consolidated financial statements.

At each reporting period, in accordance with Accounting Standards Codification ("ASC") 205-40, Going Concern, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash and cash equivalent balances. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern.

This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future partnerships, equity or debt issuances, certain cost reduction measures and the potential milestones from the Akebia agreement cannot be considered probable at this time because these plans are not entirely within the Company’s control and/or have not been approved by the Board of Directors as of the date of these consolidated financial statements.

The Company expects that its cash and cash equivalents as of December 31, 2024, will be sufficient to fund operations through mid-2025, however the Company will need to obtain additional funding to sustain operations as it expects to continue to generate operating losses for the foreseeable future. The Company's expectation to generate negative operating cash flows in the future and the need for additional funding to support its planned operations, raise substantial doubt regarding the Company’s ability to continue as a going concern. Management's plans to alleviate the conditions that raise substantial doubt include reduced spending, and the pursuit of additional capital. Management has concluded the likelihood that its plan to successfully obtain sufficient funding, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.