INTRODUCTION:BAY 2287411 [227Th-anetumab corixetan; mesothelin-targeting antibody-chelator conjugate (MSLN-TTC)] is a targeted alpha therapy consisting of a fully human mesothelin-targeting monoclonal antibody conjugated with a 3,2-hydroxypyridinone (3,2-HOPO) chelator radiolabeled with the alpha particle-emitting radionuclide thorium-227. This phase I study determined the safety, pharmacokinetics, and antitumor activity of MSLN-TTC in mesothelin-expressing mesothelioma and serous ovarian cancer.
METHODS:MSLN-TTC was administered i.v. 1.5, 2.5, or 3.5 MBq of thorium-227 and with a total antibody dose of 10, 30, 50, or 150 mg every 6 weeks to 36 patients included in the intention-to-treat population. Adverse events, tumor response according to RECIST 1.1 and mRECIST criteria, and progression-free survival were determined. Tumor mesothelin expression was assessed retrospectively.
RESULTS:In dose escalation, 35 patients (30 with malignant pleural mesothelioma) received MSLN-TTC across three thorium-227 dose levels and four total antibody doses. No dose-limiting toxicities were observed, and the maximum tolerated dose was not reached due to treatment discontinuations following 45.7% of the patients developing neutralizing antibodies. The most common treatment-emergent adverse events of any grade were fatigue (10/36, 27.8%), decreased lymphocyte count (7/36, 19.4%), nausea (7/36, 19.4%), anemia (6/36, 16.7%), and infusion-related reaction (6/36, 16.7%). The disease control rate was 34.3%, including 12 stable diseases (12/36, 34.3%). No complete or partial responses were observed. The median progression-free survival was 70 days (95% confidence interval 29-161 days).
CONCLUSIONS:MSLN-TTC showed good tolerability, but the maximum tolerated dose could not be determined due to discontinuations after antidrug antibody formation. Stable disease was observed in 12 out of 36 patients.