Evaluation of pharmacokinetics, safety, and efficacy of [²¹¹At] meta-astatobenzylguanidine ([²¹¹At] MABG) in patients with pheochromocytoma or paraganglioma (PPGL): A study protocol

Abstract

Background: Pheochromocytoma, or paraganglioma (PPGL), is a tumor that arises from catecholamine-producing chromaffin cells of the adrenal medulla or paraganglion. Systemic therapy, such as the combination of cyclophosphamide, vincristine, and dacarbazine or therapeutic radiopharmaceuticals such as [¹³¹I] meta-iodobenzylguanidine (MIBG), may be administered in cases of locally advanced tumors or distant metastases. However, the current therapies are limited in terms of efficacy and implementation. [²¹¹At] meta-astatobenzylguanidine (MABG) is an alpha-emitting radionuclide-labeled ligand that has demonstrated remarkable tumor-reducing effects in preclinical studies, and is expected to have a high therapeutic effect on pheochromocytoma cells.

Methods: We are currently conducting an investigator-initiated first-in-human clinical trial to evaluate the pharmacokinetics, safety, and efficacy of [²¹¹At] MABG. Patients with locally unresectable or metastatic PPGL refractory to standard therapy and scintigraphically positive [¹²³I] MIBG aggregation are being recruited, and a 3 + 3 dose escalation design was adopted. The initial dose of [²¹¹At] MABG is 0.65 MBq/kg, with a dose escalation in a 1:2:4 ratio in each cohort. Dose-limiting toxicity is observed for 6 weeks after a single bolus dose of [²¹¹At] MABG, and the patients are observed for 3 months to explore safety and efficacy profiles. The primary endpoint is dose-limiting toxicity to determine both maximum tolerated and recommended doses. The secondary endpoints include radiopharmacokinetics, urinary radioactive excretion rate, urinary catecholamine response rate, objective response rate, progression free survival, [¹²³I] MIBG scintigraphy on reducing tumor accumulation, and quality of life.