PURPOSE: 203/212Pb is a promising theranostic isotope pair for targeted alpha therapy (TAT) of neuroendocrine tumors (NET). VMT-α-NET is a novel SSTR2 targeting peptide that can be labeled with both isotopes. The aim of this work was to perform first clinical investigations of [203/212Pb]Pb-VMT-α-NET regarding imaging, biokinetics, tolerability and response.

METHODS: 12 patients (9 m/3 w; mean age 71, range 60-84) with progressive metastatic GEP-NET grade 1-3 received diagnostic imaging with [203Pb]Pb-VMT-α-NET (4.9 MBq/kg bw) up to 24 h p.i. (whole body & SPECT/CT) and, if eligible, a single dose of [212Pb]Pb-VMT-α-NET therapy (1.2 MBq/kg bw) after exhaustion of all current therapies (including [177Lu]Lu- & [225Ac]Ac-DOTATATE), and post-treatment imaging with [212Pb]Pb-VMT-α-NET up to 24 h p.i. (whole body & SPECT/CT). Clinical and laboratory parameters were monitored. A visual and quantitative comparison was made with [68 Ga]Ga-DOTATATE PET scans before and 3 months after therapy.

RESULTS: No high-grade adverse effects were observed in all patients evaluated with [203Pb]Pb-VMT-α-NET. All patients showed an initial high, but lesion-dependent heterogeneous intratumoral accumulation, comparable to [68 Ga]Ga-DOTATATE PET. Treatment with [212Pb]Pb-VMT-α-NET was also well tolerated by all patients without high-grade or serious adverse side effects. Post-therapeutic PET scans and tumor marker controls showed stable findings in all patients up to 3 months after treatment.

CONCLUSION: Imaging with [203Pb]Pb-VMT-α-NET followed by a single dose of [212Pb]Pb-VMT-α-NET appears to be well tolerated with promising efficacy, even in a heterogenous and heavily pretreated patient population. Further studies are warranted to examine tolerability and efficacy over multiple treatment cycles in larger patient populations.