Shattuck Labs to Present Additional Data from the Phase 1B Dose Expansion Clinical Trial of SL-172154 with Azacitidine (AZA) in Frontline Higher-Risk Myelodysplastic Syndromes (HR-MDS) and TP53 mutant (TP53m) Acute Myeloid Leukemia (AML) Patients at the Eu

Shattuck Labs, Inc. (Shattuck) (Nasdaq: STTK), a clinical-stage biotechnology company pioneering the development of bifunctional fusion proteins as a new class of biologic medicine for the treatment of patients with cancer and autoimmune disease, today announced the presentation of additional data from the Phase 1B dose expansion clinical trial of SL-172154 with AZA in frontline HR-MDS and TP53m AML patients. These data will be featured in a poster presentation at the EHA 2024 Congress, being held June 13-16, 2024, both virtually and in Madrid, Spain.

“We are rapidly progressing in our clinical development of SL-172154. After completing initial enrollment in the fourth quarter of 2023, we elected to expand both the frontline HR-MDS and TP53m AML cohorts this year,” said Dr. Lini Pandite, MBChB, M.B.A., Chief Medical Officer of Shattuck. “The complete response rate in HR-MDS increased by the February 1st data cutoff, and the ORR increased in the TP53m AML cohort. This is encouraging because many patients were still early in their course of treatment. With the next planned data cutoff in the late second quarter of 2024, we are well positioned to provide an update at the EHA Annual Congress. We believe these data will further underscore the therapeutic potential of SL-172154 for patients with previously untreated HR-MDS and TP53m AML.”

The full abstract (#P773) is accessible on the EHA Congress portal, and additional details are provided below.

• Title: Phase 1B Study of SL-172154, a Bi-functional Fusion Protein Targeting CD47 and CD40, with Azacitidine in Previously Untreated Acute Myeloid Leukemia and Higher-Risk Myelodysplastic Syndromes
• Presenter: Dr. Amer Zeidan
• Format: Poster Presentation
• Date and Time: June 14th at 18:00 CEST

Key Takeaways from Phase 1B Trial of SL-172154 in Frontline HR-MDS and TP53m AMLKey takeaways: Interim efficacy as of February 1, 2024 observed for SL-172154 in combination with AZA in frontline HR-MDS and TP53m AML. EHA poster presentation to include additional data from the next planned cutoff in the second quarter of 2024.

• HR-MDS: In 23 evaluable patients (20 had TP53m, 21 had complex karyotype, and seven had therapy-related MDS), the objective response rate (ORR) was 65%.
  • Nine patients achieved a CR within 16 weeks as the median time to CR. None of the patients with CR progressed as of the data cutoff.
  • 16 patients were still undergoing treatment.
• TP53m AML: In 14 evaluable patients (11 of whom had secondary AML) the ORR was 36%. A total of 21 patients will be included in the final pre-conference data cutoff.
  • Two patients achieved a CR, the median time to CR was 8.7 weeks. Another patient achieved a CR with incomplete hematologic recovery (CRi) and two patients achieved a partial response (PR). None of the responders progressed as of the data cutoff.
  • Four responders (one CR, one CRi, two PR) were taken to hematopoietic cell transplantation (HCT)
  • Six patients were still undergoing treatment, including one patient in CR.
• Median duration of response and overall survival has not been reached in both HR-MDS and TP53m AML as of the data cutoff date.

Safety: SL-172154 had an acceptable safety profile: Infusion-related reactions (IRRs) were the most common SL-172154 related treatment-emergent adverse events (TEAEs).

• IRR was reported in 18 patients (46%); all were Grade 1 and 2 except for two Grade 3 events. Other SL-172154 related TEAEs (>=10%) were fatigue in five patients (13%) and hypokalemia in four patients (10%).
• Cytokine release syndrome was reported in two patients with HR-MDS (Grade 2 and Grade 3, respectively).
• 11 patients (28%) experienced at least one Grade 3/4 SL-172154 related TEAE, with fatigue, febrile neutropenia, and IRR as the most common (in two patients each).
• Two patients had drug discontinuation that were possibly related to SL-172154: one patient had a Grade 4 event of myocardial infarction, and one patient had a Grade 5 event of cardiac arrest. Both patients had a history of significant cardiovascular disease, adverse risk factors and other comorbidities.

About SL-172154SL-172154 (SIRPα-Fc-CD40L) is an investigational ARC® fusion protein designed to simultaneously inhibit the CD47/SIRPα checkpoint interaction and activate the CD40 costimulatory receptor to bolster an anti-tumor immune response in patients with advanced cancer. Multiple Phase 1 clinical trials are ongoing for patients with platinum-resistant ovarian cancer (NCT04406623, NCT05483933) and patients with AML and HR-MDS (NCT05275439).

About Shattuck Labs, Inc.Shattuck Labs, Inc. (Nasdaq: STTK) is a clinical-stage biotechnology company pioneering the development of bi-functional fusion proteins as a new class of biologic medicine for the treatment of patients with cancer and autoimmune disease. Compounds derived from Shattuck’s proprietary Agonist Redirected Checkpoint (ARC®) platform are designed to simultaneously inhibit checkpoint molecules and activate costimulatory molecules with a single therapeutic. The company’s lead SL-172154 (SIRPα-Fc-CD40L) program, which is designed to block the CD47 immune checkpoint and simultaneously agonize the CD40 pathway, is being evaluated in multiple Phase 1 trials. Shattuck has offices in both Austin, Texas and Durham, North Carolina. For more information, please visit: www.ShattuckLabs.com.

Forward-Looking StatementsCertain statements in this press release may constitute “forward-looking statements” within the meaning of the federal securities laws, including, but not limited to, statements regarding: future presentations of clinical data; clinical development plans and strategies for SL-172154; timing of anticipated clinical data; future plans for Shattuck’s pipeline; and Shattuck’s strategies. Words such as “anticipate,” “may,” “might,” “will,” “objective,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “design,” “estimate,” “predict,” “potential,” “develop,” “plan” or the negative of these terms, and similar expressions, or statements regarding intent, belief, or current expectations, are forward-looking statements. While the company believes these forward-looking statements are reasonable, undue reliance should not be placed on any such forward-looking statements, which are based on information available to the company on the date of this release. These forward-looking statements are based upon current estimates and assumptions and are subject to various risks and uncertainties (including, without limitation, those set forth in Shattuck’s filings with the U.S. Securities and Exchange Commission (SEC)), many of which are beyond the company’s control and subject to change. Actual results could be materially different. Risks and uncertainties which could cause such outcomes to change include: global macroeconomic conditions and related volatility; expectations regarding the initiation, progress, and expected results of Shattuck’s preclinical studies, clinical trials and research and development programs; expectations regarding the timing, completion and outcome of the company’s clinical trials; the unpredictable relationship between preclinical study results and clinical study results; the timing or likelihood of regulatory filings and approvals; liquidity and capital resources and other risks and uncertainties identified in Shattuck’s Annual Report on Form 10-K for the year ended December 31, 2023 and subsequent disclosure documents filed with the SEC. Shattuck claims the protection of the Safe Harbor contained in the Private Securities Litigation Reform Act of 1995 for forward-looking statements. Shattuck expressly disclaims any obligation to update or alter any statements whether as a result of new information, future events or otherwise, except as required by law.

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Investor & Media Contact: Conor RichardsonVice President of Investor RelationsShattuck Labs, [e-mail]