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Debt | 3 Months Ended
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Mar. 31, 2026
Debt Disclosure [Abstract] |
Debt | Debt K2 HealthVentures LLC Loan Agreement On December 16, 2022, the Company entered into a Loan and Security Agreement (the “Original Loan Agreement”) with K2 HealthVentures LLC as a lender, the other lenders party thereto (collectively, the “Lender”), K2 HealthVentures LLC, as administrative agent for Lender (the “Administrative Agent”), and Ankura Trust Company, LLC, as collateral agent for the Lender. Pursuant to the terms of the Original Loan Agreement, the Lender agreed to make available to the Company term loans (each, collectively, the “Term Loan”) in an aggregate principal amount of up to $35.0 million. As of December 31, 2024, the Company had drawn a principal amount of $10.0 million. The Lender’s commitment to make available additional Term Loans under the Original Loan Agreement expired without being drawn on January 1, 2025. The Original Loan Agreement had a Term Loan maturity date of December 1, 2026 (the “Original Term Loan Maturity Date”). On January 13, 2025, the Company entered into an amendment to the Original Loan Agreement (the “Amendment” and the Original Loan Agreement as amended thereby, the “Amended Loan Agreement”) to, among other things, extend the Original Term Loan Maturity Date and increase the maximum available amount of term loans. The Amended Loan Agreement provides for term loans in an aggregate principal amount of up to $75.0 million, consisting of: •a first tranche term loan of $20.0 million; •second tranche term loans of up to $30.0 million in the aggregate available at the Company’s request until December 15, 2025, subject to certain time-based, clinical milestones; and •third tranche term loans of up to $25.0 million in the aggregate available at the Company’s request subject to the Lender’s approval. The Company drew $20.0 million upon entry into the Amendment (approximately $10.0 million of which was used to refinance obligations under the Original Loan Agreement and pay fees and expenses incurred in connection with the Amendment). The second tranche term loan was available until December 15, 2025 based on certain milestones and expired without being drawn. The Amended Loan Agreement has a Term Loan maturity date of January 1, 2029 (the “Amended Term Loan Maturity Date”). The Amended Loan Agreement provides for an interest only period until January 1, 2027, following which the Term Loan shall be repaid in equal monthly payments through the Amended Term Loan Maturity Date. The Term Loan bears interest at (i) a variable per annum cash pay rate equal to the Prime Rate plus 1.45% (subject to a floor of 8.45% per annum) and (ii) a fixed per annum paid-in-kind rate equal to 1.0%. Interest is due and payable monthly in arrears. Upon final payment or prepayment of the Term Loan, the Company is required to pay a final payment equal to 5.95% of the amount borrowed. The Amended Loan Agreement was accounted for as a debt extinguishment, as the new loan was considered substantially different from the original loan. The Company recognized debt issuance costs and discount upon issuance of $2.0 million within Term Loan, non-current on its condensed consolidated balance sheet and recorded a loss on debt extinguishment of $0.7 million, which was recorded within loss on debt extinguishment in its condensed consolidated statement of operations and comprehensive loss for the three mont hs ended March 31, 2025. Fees Under the terms of the Original Loan Agreement, the Company was obligated to pay a final fee equal to 6.25% of the aggregate amount of the term loans funded thereunder (the “Original Exit Fee”) upon the earliest of (i) the Original Term Loan Maturity Date, (ii) the acceleration of the Term Loan, and (iii) the prepayment of the Term Loan. The Company was also obligated to pay the Lender a one-time facility fee of $0.2 million (“Original Facility Fee”) on the initial closing date. The Original Exit Fee of $0.6 million and Original Facility Fee of $0.2 million were recorded as debt discount, and were being accreted using the effective interest method within interest expense in the condensed consolidated statements of operations and comprehensive loss. The Company’s obligation to pay the Original Exit Fee remains outstanding, and the timing for payment thereof was unaffected by, and reaffirmed in connection with, the Amendment, and is recorded in the condensed consolidated balance sheet within Term loan, current as of March 31, 2026 and December 31, 2025. The Company was obligated to pay the Lender a one-time facility fee of $0.3 million upon entry into the Amendment. The Company is also obligated to pay a funding fee on each third tranche term loan in an amount equal to the sum of 0.5% multiplied by the amount of such third tranche term loan, if and when funded. Under the terms of the Amended Loan Agreement, the Company is obligated to pay a final fee equal to 5.95% of the aggregate amount of the Term Loan funded thereunder (the “Amended Exit Fee”) upon the earliest of (i) the Amended Term Loan Maturity Date, (ii) the acceleration of the Term Loan, and (iii) the prepayment of the Term Loan. As of March 31, 2026, the amount owed under the Amended Exit Fee is equal to $1.2 million. The Original Exit Fe e and the Amended Exit Fee have been fully accrued and recorded as debt discount as of the closing date of the Amendment and are being accreted using the effective interest method within interest expense in the consolidated statement of operations and comprehensive loss. The Company has the option to prepay all, but not less than all, of the Term Loan prior to the Amended Term Loan Maturity Date, which would require that the Company pay the Lender a prepayment penalty fee based on a percentage of the outstanding principal balance and the funding date of the individual tranches thereunder. As to each such tranche under the Term Loan, such fee shall be equal to 3% if the payment occurs on or before 24 months after the funding date of such tranche, 2% if the prepayment occurs more than 24 months after, but on or before 36 months after the funding date of such tranche, or 1% if the prepayment occurs more than 36 months after the funding date of such tranche. No prepayment penalty fee is required if the applicable tranche is prepaid within six months prior to the Amended Term Loan Maturity Date or refinanced with the Lender. Other Terms The Company must maintain, at all times, a cash runway of at least 5 months, provided that this covenant will be waived during any period in which the Company’s market capitalization exceeds $700.0 million. The Company’s obligations under the Amended Loan Agreement are secured by a first priority security interest in substantially all of its assets (with an exclusion for intellectual property). The Amended Loan Agreement contains customary represent ations and warranties, and also includes customary events of default, including payment default, breach of covenants, change of control, and material adverse effects. The Amended Loa n Agreement restricts certain activities, such as disposing of the Company’s business or certain assets, incurring additional debt or liens or making payments on other debt, making certain investments and declaring dividends, acquiring or merging with another entity, engaging in transactions with affiliates or encumbering intellectual property, among others. Upon the occurrence of an event of default, a default interest rate of an additional 5% per annum may be applied to the outstanding loan balances, and the Lender may declare all outstanding obligations immediately due and payable and exercise all of its rights and remedies as set forth in the Amended Loan Agreement and u nder applicable law. Warrants In connection with the Original Loan Agreement, the Company issued to the Lender a warrant (the “Original Warrant”), which Original Warrant is exercisable for 35,773 shares of the Company’s common stock and expires on December 15, 2032. In connection with the Amendment, the Original Warrant was amended and restated (the “Amended and Restated Warrant”) to reduce the exercise price from $10.49 to $3.71 per share (the “Exercise Price”). The incremental value associated with this modification was immaterial, and was included as part of the determination of the loss on debt extinguishment, with a corresponding increase in additional paid-in capital during the three months ended March 31, 2025. In connection with the Amendment, the Company issued an additional warrant (the “New Warrant”, together with the Amended and Restated Warrant, the “Warrants”) to purchase a number of shares of the Company’s common stock calculated as follows: (a) (i) 0.025, multiplied by (ii) the aggregate principal amount of the term loans actually funded under the Amended Loan Agreement, divided by (b) the Exercise Price. The New Warrant expires on January 13, 2035 and allows for the purchase of 134,691 shares of the Company’s common stock. If the Company draws down on additional tranches of the Term Loan, the number of shares available for purchase by the Lender under the New Warrant would increase. The Company determined the estimated fair value of the New Warrant at the date of issuance to be $0.5 million, which was included as part of the determination of the loss on debt extinguishment, with a corresponding increase in additional paid-in capital. As of the date of the issuance, significant assumptions include an expected life of 10 years, a risk-free rate of 4.79% and an expected volatility of 89.47%. See Note 10 for additional information regarding the New Warrant. Loan Conversion Feature Under the terms of the Amended Loan Agreement, the Lender may, at its option, elect to convert up to $9.0 million of the then outstanding Term Loan (the “Conversion Amount”) ($4.0 million of which was reflected in the Original Loan Agreement and $5.0 million of which is reflected in the Amended Loan Agreement) into shares of the Company’s common stock (the “Conversion Shares”). The number of shares to be issued upon conversion is determined by dividing (a) the portion of the term loan amount converted, by (b) the Applicable Conversion Price. Applicable Conversion Price means (i) with respect to any conversion of up to $4.0 million of the Conversion Amount, $10.49, and (ii) with respect to any conversion of the remaining $5.0 million of the Conversion Amount, $4.83, in each case subject to certain adjustments set forth in the Amended Loan Agreement. The Company determined that the embedded conversion option is not required to be separated from the Term Loan. The embedded conversion option meets the derivative accounting scope exception since the embedded conversion option is indexed to the Company’s own common stock and qualifies for classification within stockholders’ equity. On November 17, 2025 and March 18, 2026, the Lender elected to convert $4.0 million and $1.0 million, respectively, of its outstanding loan balance into the Company’s common stock. Pursuant to the terms of the Amended Loan Agreement, the conversion price was $4.83 per share, resulting in the issuance of 828,860 and 207,215 shares, respectively. Interest Expense and future repayments The C ompany recorded interest expense at a weighted average rate of 12.35% and 12.94% related to the Loan Agreement for the three months ended March 31, 2026, and 2025, respectively. During the three months ended March 31, 2026, and 2025, the Company recorded interest expense of $0.5 million and $0.6 million, respectively. Future principal debt payments and Exit Fee of the term loan funded as of March 31, 2026 are as follows (in thousands):
2026 (remainder of year) | $ | —
2027 | 6,858
2028 | 7,467
2029 | 675
Total principal payments | 15,000
Exit Fee | 1,815
Deferred interest | 235
Total principal payments and Exit Fee | 17,050
Less: unamortized debt discount | (1,029)
Less: Term loan, current portion | $ | (2,136)
Term loan, non-current | $ | 13,885
The Wellcome Trust Limited Convertible Grant Agreement In July 2024, the Company entered into a convertible loan agreement (the “Convertible Grant Agreement”) with The Wellcome Trust Limited (“Wellcome”). The Convertible Grant Agreement provides for an unsecured convertible loan (the “Convertible Loan”) from Wellcome of up to approximately $11.7 million, payable to Alto in six tranches, of which up to $2.0 million could be funded upon the execution of the Convertible Grant Agreement and the remainder of which will be funded upon the completion of certain milestones as set forth in the Convertible Grant Agreement. As of March 31, 2026, the Company has drawn down the entirety of the $2.0 million execution tranche and will continue to access the loan as needed as the ALTO-100 study in bipolar depression progresses. Interest accrues at an annual rate equal to the Sterling Overnight Index Rate plus 2%, subject to potential adjustment if such annual interest rate equals or exceeds 9% at any time. Proceeds from the Convertible Loan may be used by the Company solely to advance development of ALTO-100 in bipolar depression. The Convertible Grant Agreement also includes customary covenants, representations and warranties, including with respect to the conduct of the Company’s Phase 2b clinical trial evaluating ALTO-100 in patients with bipolar depression and certain information and audit rights of Wellcome in connection therewith, as well as with respect to the Company’s efforts to develop and exploit ALTO-100. At any time after the second anniversary of the effective date of the Convertible Grant Agreement or in connection with an event of default, Wellcome has the right, at its election, to convert some or all of the Convertible Loan into shares of the Company’s common stock at a price per share equal to a 20% discount to the thirty-day volume-weighted average price of Common Stock on the New York Stock Exchange at the date of such conversion. The Convertible Grant Agreement provides that in no event shall the aggregate number of shares of Common Stock issued pursuant to conversion of the Convertible Loan exceed 5,363,326, which is equal to 19.9% of the number of shares of Common Stock outstanding as of the date of the Convertible Grant Agreement. At any time after the fifth anniversary of the effective date of the Convertible Grant Agreement or in connection with an event of default, Wellcome may require repayment of the Convertible Loan in full, together with accrued interest, to the extent not converted as described above. Future principal debt payments of the Convertible Grant Agreement funded as of March 31, 2026 are as follows (in thousands):
2026 (remainder of year) | $ | —
2027 | —
2028 | —
2029 | 2,000
Term loan, non-current | $ | 2,000
The Company assessed the terms and features of the Convertible Grant Agreement and determined that the Company was eligible to elect the fair value option under ASC 825, Financial Instruments. The Convertible Grant Agreement contains various embedded features and the election of the fair value option allowed the Company to bypass analysis of potential embedded derivatives and further analysis of bifurcation of any recognized financial liabilities. Under the fair value option, the financial liability is initially measured at its fair value on the issue date and subsequently remeasured at estimated fair value on a recurring basis at each reporting date. Changes in the fair value of the Convertible Grant Agreement, which include accrued interest, if any, are recorded as a component of other, net or within other comprehensive income (loss) in the condensed consolidated statements of operations and comprehensive loss. The Company has not elected to present interest expense separately from changes in fair value and therefore will not present interest expense associated with the Convertible Grant Agreement. Any changes in fair value caused by instrument-specific credit risk are presented separately in other comprehensive income or loss. The Company determined the initial fair value of the Convertible Grant Agreement using a probability-weighted income approach. Draw downs under the Convertible Grant Agreement were $0.8 million and $1.3 million during the years ended December 31, 2025, and 2024, respectively. The Company remeasured the fair value of the Convertible Grant Agreement as of March 31, 2026 to b e $2.3 million using a probability-weighted income approach. The Company calculated discounted cash flows of the Convertible Grant Agreement using a discount rate of 20.69% and adjusted for the probability of various repayment scenarios. The following table reconciles the change in fair value of the Convertible Grant Agreement during the three months ended March 31, 2026 (in thousands):
Fair value balance as of December 31, 2025 | $ | 2,227
Issuance of new tranches | —
Principal payments | —
Changes in fair value reported in statements of operations | 115
Changes in fair value reported in other comprehensive loss | (7)
Fair value balance as of March 31, 2026 | $ | 2,335 |

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