Ariceum Therapeutics Data at the 2025 European Association of Nuclear Medicine Annual Congress Further Supports the Advancement of 225Ac-SSO110 for Extensive Stage Small Cell Lung Cancer and Merkel Cell Carcinoma

Oral presentation by Dr Zan highlighted novel Phase 1/2 SANTANA-225 study design of 225Ac-SSO110 in patients with ES-SCLC or MCC

225Ac-SSO110 achieves superior pharmacokinetics with minimal re-distribution of Actinium-225 daughter isotopes and 100% survival in preclinical studies

Initial safety data from SANTANA-225 expected in 2026

BERLIN, Oct. 09, 2025 (GLOBE NEWSWIRE) -- Ariceum Therapeutics (Ariceum), a targeted radiotherapeutics company dedicated to setting new standards in cancer care, today highlighted two oral presentations showcasing the SANTANA-225 Phase 1/2 clinical trial design and preclinical data supporting 225Ac-SSO110’s differentiated profile as a targeted alpha radioligand therapy for somatostatin receptor 2 (SSTR2) positive malignancies at the 38^th Annual Congress of the European Association of Nuclear Medicine (EANM25), held from October 4 - 8, 2025 in Barcelona, Spain.

“These oral presentations demonstrate Ariceum’s commitment to leading innovation in targeted radiotherapeutics,” said Germo Gericke, MD, Chief Medical Officer of Ariceum Therapeutics. “For the first time, we are presenting data showing minimal in-vivo redistribution of daughter radionuclides with 225Ac-SSO110, a non-internalizing SSTR2 antagonist, an important advance in our understanding of targeted alpha therapy. In parallel, our SANTANA-225 study showcases an innovative, first-in-class approach for patients with ES-SCLC and MCC. With the SANTANA-225 initial safety readout expected in 2026 and preliminary efficacy in 2027, we remain committed to setting new standards in both research and patient care for diseases with high unmet needs.”

Details of the Presentations:

Title: SANTANA-225: A multicentre, open-label, Phase I/II study investigating the safety, tolerability, and preliminary efficacy of 225Ac-SSO110 in participants with extensive stage small cell lung cancer (ES-SCLC) or Merkel cell carcinoma (MCC) receiving Standard of Care (SoC); Presentation # OP-780

This presentation, presented by Dr. Elcin Zan, Cleveland Clinic, highlighted the design of Ariceum’s SANTANA-225 Phase 1/2 clinical trial (NCT06939036) evaluating 225Ac-SSO110 for the treatment of first line (1L) maintenance ES-SCLC or 1L MCC. This global, open-label study will assess the safety, tolerability, preliminary efficacy, and recommended Phase 2 dose of 225Ac-SSO110 in patients receiving immune checkpoint inhibitor (CPI) therapy. The clinical trial is expected to enroll approximately 20 patients in the dose escalation phase of the study followed by additional optional expansion cohorts of 15 patients per indication. 225Ac-SSO110 is the first SSTR2-targeting antagonist labelled with Actinium-225 to undergo human trials in combination with CPI therapy.

Title:Improved Tumour Targeting and Efficacy with Comparable Daughter Redistribution of 225Ac-SSO110 versus 225Ac-DOTA-TATE in a Preclinical SCLC Model; Presentation # OP-658

A second oral presentation at EANM25 showcased the superior pharmacokinetic profile of 225Ac-SSO110 versus 225Ac-DOTA-TATE, demonstrating comparable biodistribution to the internalizing agonist, alongside enhanced tumor uptake and a favorable therapeutic index.

The Company evaluated the biodistribution of Actinium-225 (Ac-225) and its daughter radionuclides, including Bismuth-213 (Bi-213), after injection of Actinium-225-labeled SSO110, a non-internalizing SSTR2 antagonist, or the internalizing SSTR2 agonist DOTA-TATE in an ES-SCLC xenograft model. Bismuth-213 plays a critical role in therapeutic assessment as the longest half-life alpha-emitting daughter of Actinium-225. Its localization and retention within target tissue are key determinants of both safety and efficacy in targeted alpha therapies.

The study results demonstrate that 225Ac-SSO110’s differentiated binding profile enables superior tumor uptake and retention, compared with 225Ac-DOTA-TATE. Importantly, 225Ac-SSO110 exhibited similar retention of daughter radionuclides as the internalizing agonist 225Ac-DOTA-TATE and a more favorable therapeutic index. The short blood circulation half-life of 225Ac-SSO110 helps limit systemic redistribution of daughter radionuclides, reducing the potential off-target exposure. Both treatments were well-tolerated with no histopathological abnormalities observed. In prior studies 225Ac-SSO110 has achieved complete tumor remissions after a single injection of 30 kBq, whereas 225Ac-DOTA-TATE failed to control tumor growth with the same injected activity.

These results reinforce the therapeutic potential of 225Ac-SSO110 as a next-generation alpha-emitting radioligand therapy for SSTR2-positive tumors, such as ES-SCLC and MCC.

Abstracts are available in the EANM25 Abstracts Book and the complete presentations can be accessed on the EANM 2025 congress website.

About Ariceum Therapeutics
Ariceum Therapeutics is a clinical-stage oncology company dedicated to redefining the future of care through targeted radiotherapeutics for patients with aggressive and hard-to-treat cancers. The company’s lead program, 225Ac-SSO110, a novel antagonist of the somatostatin type 2 receptor (SSTR2) with best-in-class potential, is currently being investigated in the Phase 1/2 SANTANA-225 study as the first maintenance radiotherapy for extensive stage small cell lung cancer (ES-SCLC) and Merkel Cell Carcinoma (MCC) – two diseases with limited options and poor prognosis. Ariceum is also developing ATT001, a novel radiolabeled I-123 PARP inhibitor designed to deliver subcellular precision radiotherapy to aggressive solid tumors.

Headquartered in Berlin, Ariceum operates across Germany, Switzerland, Australia, the United Kingdom, and the United States. The company is supported by leading global life sciences investors, including EQT Life Sciences, HealthCap, Pureos Bioventures, Andera Partners, and Earlybird Venture Capital.

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