[ ²¹² Pb]VMT-α-NET therapy in somatostatin receptor 2 (SSTR2) expressing neuroendocrine tumors (NETs): Dose-limiting toxicity (DLT) observation participants after 1 year follow-up and preliminary report for expansion participants.

3005 Background: [ 212 Pb]VMT-α-NET, a next generation 212 Pb-based, SSTR2-targeted alpha-particle radiopharmaceutical therapy (RPT), was designed to achieve superior biodistribution via optimized tumor uptake and retention and rapid renal clearance. Results reported here are from the Phase 1/2a first-in-human study [NCT05636618]. Methods: Safety, pharmacokinetics, dosimetry and efficacy using RECIST v1.1 were investigated in the treatment of participants with [ 212 Pb]VMT-α-NET who had SSTR2-expressing, well-differentiated adult NETs of any grade. Participants received ≥1 prior therapy. No prior peptide receptor radionuclide therapy was allowed. The trial has multiple dose cohorts including 92.5 MBq (2.5 mCi, cohort 1) and 185 MBq (5 mCi, cohort 2) of administered activity based on a Bayesian modified toxicity probability interval (mTPI-2) design. Up to 8 participants per cohort were treated with 4 doses of [ 212 Pb]VMT-α-NET for DLT observation. Cohort 2 enrollment was expanded to further define the safety and efficacy profile at this dose level. Results: Nine (9) gastroenteropancreatic NET participants were enrolled into cohorts 1 and 2 for DLT observation. The ninth of these participants was enrolled more than 1 year prior to presentation of these data. Among these participants at the time of abstract submission, no DLTs were observed, and there were no grade 4, 5 or serious adverse events (SAEs). Specifically, no renal insufficiency or dysphagia were observed. Hematologic AEs were low grade and few in number. No treatment discontinuations due to AE occurred. Three (3) of the 7 cohort 2 participants enrolled for DLT observation achieved investigator-assessed partial responses (PRs). Two PRs were unconfirmed at the time of abstract submission. Durable progression-free survival (PFS) was consistently observed. More than 15 additional participants were enrolled in the cohort 2 expansion. Preliminary data for these patients will be reported at the congress. Conclusions: [ 212 Pb]VMT-α-NET is a well-tolerated, next generation RPT showing signs of clinical activity at early dose-levels in this phase 1/2a study. Based on these clinical data, further dose-escalation and development of this promising therapy are warranted. Clinical trial information: NCT05636618 .