Ariceum Therapeutics Doses First Patient In SANTANA-225 Phase 1/2 Trial Of 225Ac-SSO110 For Extensive Stage Small Cell Lung Cancer And Merkel Cell Carcinoma

Ariceum Therapeutics (Ariceum), a company focused on targeted radiotherapeutics and advancing standards in cancer care, announced that the first patient has been dosed in the SANTANA-225 Phase 1/2 clinical trial of 225Ac-SSO110. The trial evaluates this therapy in patients with extensive stage small cell lung cancer (ES-SCLC) and Merkel Cell Carcinoma (MCC). 225Ac-SSO110 is a potentially first- and best-in-class Actinium-225-labelled antagonist of the somatostatin type 2 receptor (SSTR2), which is highly overexpressed in neuroendocrine tumors compared to healthy tissue, making it an ideal target for radioligand therapy (RLT).

The SANTANA-225 study (NCT06939036) is a global, open-label Phase 1/2 trial designed to assess the safety, tolerability, preliminary efficacy, and recommended Phase 2 dose of 225Ac-SSO110. The trial will enroll approximately 20 patients in a dose escalation phase, followed by expansion cohorts. Patients eligible for the study include those with ES-SCLC who have received first-line checkpoint inhibitor (CPI) therapy and MCC patients treated with first-line CPI therapy. In February 2025, 225Ac-SSO110 received Orphan Drug Designation (ODD) from the U.S. Food and Drug Administration for the treatment of ES-SCLC.

Germo Gericke, MD, Chief Medical Officer of Ariceum Therapeutics, highlighted the importance of this milestone: “RLTs are redefining precision oncology by enabling targeted delivery of radiation directly to tumor cells while minimizing exposure to healthy tissue. 225Ac-SSO110 is the first SSTR2 antagonist RLT in clinical development, designed to deliver higher doses of alpha radiation directly to patients’ tumors while maintaining a favorable safety profile for individuals with neuroendocrine cancers, including ES-SCLC and MCC. Dosing the first patient in the SANTANA-225 trial is a significant step for our lead program and an important milestone towards addressing urgent patient needs in these aggressive cancers. We expect to report initial safety data from the SANTANA-225 trial in 2026, which may support expansion into additional neuroendocrine tumor indications and further validate the differentiated mechanism of action of 225Ac-SSO110.”

ES-SCLC is a highly aggressive form of lung cancer with very limited treatment options. Approximately two-thirds of patients are diagnosed at an advanced stage with metastases, resulting in poor outcomes and a five-year survival rate of only 5-10%. MCC is a rare and aggressive skin cancer with similarly low survival rates in patients who do not respond to first-line CPI therapy. Both cancers are neuroendocrine tumors that often express SSTR2, making them promising initial indications for SSTR2-targeted therapy.

225Ac-SSO110 is the first SSTR2-targeting antagonist radiolabeled with Actinium-225 to enter human trials in combination with CPI for these neuroendocrine tumor indications. This program addresses high unmet medical needs in ES-SCLC and MCC while laying the groundwork for potential expansion into other SSTR2-expressing cancers, reflecting Ariceum’s commitment to advancing innovative therapies for aggressive malignancies.