Ac225 RTX-2358Actinium Therapy for Late-stage Aggressive Sarcomas

Inclusion Criteria:

• 18 years of age or older.
• History of relapsed or refractory soft tissue sarcoma.

1. Histological confirmation of sarcoma at any point since diagnosis
2. At least 1 prior treatment regimen

• Measurable disease as per RECIST (v1.1) for soft tissue sarcoma that is also positive on FAPi PET/CT or PET/MRI scan.
• ECOG performance status of 0 or 1.
• Adequate Organ reserve and renal function as evidenced by:

1. Neutrophil count ≥ 1200 µL without granulocyte colony stimulating factor
2. Platelet count ≥ 100,000 µL
3. Hemoglobin ≥ 8 g/dL
4. Total bilirubin level ≤ 1.5 × upper limit of normal (ULN).
5. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN.
6. Calculated creatinine clearance ≥ 60 mL/min. 6. Coagulation parameters (prothrombin time, international normalized ratio and activated partial thromboplastin time) ≤ 1.5 × ULN 7. All patients (males and females of childbearing potential) must agree to practice 2 forms of highly effective contraceptive precautions to prevent pregnancy from the time consent is signed and throughout the trial.

8\. The patient or the patient's legal representative must be willing and able to provide written informed consent.

Exclusion Criteria:

• History of whole pelvic irradiation or lung irradiation.
• History of radioligand therapy.
• Treatment within 14 days prior to first administration with:

1. Palliative surgery or external beam radiation.
2. Approved anticancer therapy including chemotherapy or immunotherapy.
3. Any investigational therapy.
4. Any major surgery (e.g., requiring general anesthesia).

• Patients who are scheduled for external beam radiation therapy or radioligand therapy during the study period.
• Congestive heart failure > Class II New York Heart Association Functional Classification, current pericarditis, myocardial infarction within 6 months, or symptomatic coronary artery disease.
• Patients with uncontrollable incontinence.
• Unstable or clinically significant concurrent medical condition that would, in the opinion of the Investigator, jeopardize the safety of a patient and/or their compliance with the protocol.
• Active infection requiring systemic antibacterial/antibiotic, antifungal, or antiviral therapy. Chronic antiviral therapy for stable viral disease can be included.
• History of active fibrotic condition.
• Any active malignancy other than sarcoma that requires treatment.
• Stable brain metastasis is allowed but documented untreated metastases to brain or meninges are excluded.
• Currently pregnant or lactating.
• Known allergy to any of the study drugs or their excipients.
• Inability or unwillingness to comply with any of the required imaging studies or study assessments.
• History of pneumonitis, interstitial lung disease, chronic obstructive pulmonary disease (COPD) or other inflammatory/fibrotic pulmonary condition.