Local, Targeted Therapy With Alpha Emitter [225Ac]Ac-DOTA-SP (TAT) In Newly Diagnosed Glioma (WHO G3-G4)

1. Background Brain tumors account for approximately 1.35% of all cancers and are responsible for 2.2% of cancer-related deaths. Gliomas are the most common primary brain tumors and, depending on age group, represent 40%-90% of central nervous system tumors. The incidence of malignant gliomas is estimated at 0.5-2 cases per 100,000 persons per year. These tumors occur more frequently in men, most often in the fifth and sixth decades of life. In Poland, approximately 1,300 patients are diagnosed with gliomas annually, including about 600 with malignant disease.

Current standard treatment consists of surgery, radiotherapy, and chemotherapy. Nevertheless, prognosis remains poor, with median survival ranging from 1 to 3 years depending on tumor type. Despite treatment, disease progression commonly occurs, and chemotherapy provides only a modest extension of survival. These limitations underscore the need for novel therapeutic strategies.

Given the infiltrative nature of gliomas, an effective treatment should diffuse throughout the tumor and selectively bind to neoplastic cells. Peptide-based targeted therapy appears particularly promising in this context. Many tumors express membrane receptors at high levels, allowing the use of radioisotope-labeled peptides for diagnosis and therapy. This approach is already applied in selected lymphomas and neuroendocrine tumors.

In gliomas, particularly WHO grade II-IV, increased expression of neurokinin-1 (NK-1) receptors has been observed. Substance P, the natural ligand for NK-1 receptors, demonstrates rapid diffusion and binding to glioma cells. A derivative of substance P developed at the Institute of Nuclear Medicine, University Hospital Basel, showed that more than 95% of gliomas exhibit elevated NK-1 receptor expression, confirming its potential for targeted therapy.

Substance P may be labeled with beta-emitting isotopes such as 90Y and 177Lu. However, due to their longer tissue range, these isotopes may pose a risk to adjacent critical brain structures. This limitation prompted interest in alpha emitters such as 213Bi and 225Ac, which have high energy but very short tissue penetration.

Within the project "Use of Radioisotope-Labeled Substance P in Treating Patients with Brain Tumors" (KB/204/A/201), local treatment with alpha-emitter-labeled substance P was administered in patients with recurrent glioma. Treatment with \[213Bi\]Bi-DOTA-SP was well tolerated and not associated with clinically significant adverse effects. Median progression-free survival (PFS) was 2.7 months, median overall survival (OS) after recurrence was 10.9 months, and median OS from diagnosis was 23.6 months.

Because of the short half-life of 213Bi (46 minutes), subsequent studies focused on 225Ac. In a dose-escalation study of \[225Ac\]Ac-DOTA-SP at activities of 10, 20, and 30 MBq, treatment was also well tolerated. The maximum tolerated dose was determined to be 20 MBq. Median OS from diagnosis was 35 months, median OS from recurrence was 13.2 months, and median PFS from treatment initiation was 2.4 months.

On the basis of these encouraging findings, the present project proposes radioisotope therapy beginning 2 months after standard treatment in patients with newly diagnosed WHO grade G3-G4 glioma, with the aim of assessing whether \[225Ac\]Ac-DOTA-SP improves survival and delays disease progression. 2. Main Objective To evaluate the efficacy of local targeted therapy with the alpha-emitter-labeled neuropeptide \[225Ac\]Ac-DOTA-SP, administered using the forced diffusion method, in patients with newly diagnosed WHO grade G3-G4 glioma after first-line treatment.

Secondary Objective To assess the safety of local targeted therapy with \[225Ac\]Ac-DOTA-SP. 3. Study Design This is an interventional, investigator-initiated study without a control group. 225Ac will be supplied through a cooperation agreement between the Medical University of Warsaw (WUM) and the Institute for Transuranium Elements in Karlsruhe. The sponsoring institution is the Medical University of Warsaw (WUM). 4. Study Procedures

1. Qualification Visit A screening visit will include collection of medical history and review of prior diagnostics and treatment. Relevant medical documentation, including imaging studies (CT and/or MRI), must be provided. The study physician will explain the protocol and answer any questions. 2. Reoperation and Catheter Placement

* \[68Ga\]Ga-PSMA PET/CT will be performed to determine the site for biopsy and catheter placement. * Tumor resection with biopsy, or biopsy alone, will be performed. * Catheters will be placed, with up to three catheters permitted for lesions larger than 2 cm. * This procedure will be carried out in the Departments of Neurosurgery at either the University Clinical Centre (UCK) or the National Oncology Institute (NIO) and will require several days of hospitalization. 3. Local Treatment with \[225Ac\]Ac-DOTA-SP

* Treatment may begin no earlier than 2 months after completion of radiotherapy. * Chemotherapy may continue according to the treating oncologist's recommendation. * Catheter patency will be assessed approximately one week before the planned treatment. * Local administration of 5 MBq of 68Ga in a volume of 1-3 ml will be followed by PET/CT imaging 30 minutes later. 4. Therapy Administration Patients may receive up to four cycles of \[225Ac\]Ac-DOTA-SP. 5. Radiopharmaceutical preparation:

* Labeling will be performed in the Nuclear Medicine Department at WUM. * 68Ga is available from the department's registered 68Ge/68Ga generator. * The radiopharmacy team is qualified and experienced in 68Ga labeling. * 225Ac will be supplied under the cooperation agreement with the Institute for Transuranium Elements in Karlsruhe. * Quality control will be performed to confirm labeling efficiency and radiopharmaceutical purity. * If labeling efficiency is below 90%, the product will not be administered.

Therapeutic administration: * Administered activity of \[225Ac\]Ac-DOTA-SP: 20 MBq * Volume: 10%-20% of the resection cavity volume * Maximum total amount of substance P: 200 μg combined for 68Ga and 225Ac formulations

Pre-treatment medication: * 250 ml of 15% mannitol * 500 ml of 0.9% NaCl * 8 mg dexamethasone intravenously * These will be administered 20-30 minutes prior to treatment

Post-administration imaging and monitoring: * Immediate brain imaging after administration of \[225Ac\]Ac-DOTA-SP with 5-10 MBq of \[68Ga\]Ga-DOTA-SP * Saline infusion via pump at 0.5 ml/hour for 2-4 hours * Repeat brain imaging 2-4 hours after administration, followed by whole-body scanning * Blood and urine testing at 1, 2, 4, and 24 hours after treatment

SPECT/CT assessment of distribution: * SPECT/CT imaging will be performed at 4 hours and 24 hours after administration * Imaging will follow a quantitative protocol developed at the Nuclear Medicine Department of UCK, based on phantom studies * The protocol includes approximately 30 minutes of SPECT acquisition using multiple energy windows and about 3 minutes of low-dose CT for attenuation correction and anatomical localization Treatment will be conducted at UCK during neurosurgical hospitalization. Based on prior experience, hospitalization has typically lasted 3 days. Previous treatment experience showed good tolerability, with transient facial flushing being the only reported side effect, and seizures occurring in some patients who had a history of seizures before therapy. For this reason, patients will remain hospitalized for 24 hours after therapy in the Department of Neurosurgery (UCK).

If treatment is poorly tolerated, it will not be continued. Steroid therapy will be initiated if not already in place, and seizures will be managed according to standard anticonvulsant protocols.

Monitoring Before Each Subsequent Cycle and 2-4 Weeks After Administration * Hematology * AST, ALT * Sodium, potassium * Creatinine, urea * CRP * INR * D-dimers * Karnofsky Performance Status (KPS) * Barthel Index * Assessment of adverse events Follow-Up * MRI with contrast will be performed every 2 months to assess treatment efficacy and approximately 2 weeks before each administration of \[225Ac\]Ac-DOTA-SP. * Follow-up visits, including telemedicine if needed, will be conducted every 2 months during the first 18 months, or more frequently if clinically indicated. * After 18 months, follow-up will occur every 3 months or more often as required. 6. Discontinuation of Therapy

Therapy will be discontinued in the event of: * serious adverse events * concomitant illness preventing further treatment * disease progression * withdrawal of consent by the patient * changes in the patient's condition that, in the investigator's opinion, preclude continued treatment The investigator may also withdraw a patient for safety reasons if unforeseen circumstances arise. 5. Sample Size The target sample size is 25 patients. To account for possible dropout, up to 35 patients may be enrolled. Participants will be recruited from the neurosurgical departments of UCK and NIO. 6. Study Endpoints Primary Endpoint

Progression-free survival (PFS), defined as the time to progression based on: * Clinical progression: deterioration in Karnofsky Performance Status, worsening neurological function, or need for initiation/increase of corticosteroids by more than 50% * Radiological progression on MRI: local progression within 4 cm of the margin of the primary lesion after resection, appearance of a new lesion, or increase in lesion size by more than 25% between consecutive imaging studies Radiation necrosis will be considered in the differential diagnosis, with MRI perfusion and/or biopsy performed as needed.

Secondary Endpoints * Overall survival (OS) from the date of diagnosis * Safety assessment of the treatment 7. Expected Benefits The study is intended to evaluate the efficacy and safety of \[225Ac\]Ac-DOTA-SP as an adjunct to standard therapy. It is anticipated that this approach may prolong survival and delay disease progression compared with currently available treatment methods. 8. Risks and Discomforts Based on current experience, treatment with \[225Ac\]Ac-DOTA-SP has not been associated with clinically significant adverse effects. The most frequently reported adverse event has been seizures, although these were present before treatment in all affected patients. No clinically significant abnormalities have been observed in laboratory tests.

At present, there is no conclusive scientific evidence that the local radioactivity used in this treatment increases the risk of secondary malignancy or hereditary defects. However, efficacy as supplementary treatment after standard therapy has not yet been definitively established. 9. Study Duration The estimated duration of the study is 3 years. Patients who remain alive at the end of the study will continue to be followed until death is reported. 10. Biological Material During reoperation and catheter placement, tissue will be collected for histopathological and genetic analyses in accordance with standard clinical procedures. 11. Data Anonymization No directly identifiable patient data will be stored with the medical data used for analysis. All data will be analyzed anonymously, with each patient assigned an individual study number corresponding to the anonymization list.

• 2. Number of patients experiencing radiological progression (as defined below) [Срок оценки: From enrollment to 18 months]
• 3. Number of patients experiencing local radiological progression (as defined below) [Срок оценки: From enrollment to 18 months]