Lead-212
A radioactive metal that, once inside the body, turns itself into a much more damaging particle-emitter over the following hours. It is being explored as a way to deliver strong, short-range radiation without needing the rarer isotopes used in similar treatments.
Overview
Lead-212 is itself a beta emitter, but it functions in practice as an in vivo generator of alpha radiation: it decays (half-life 10.64 hours) to bismuth-212 (half-life about 61 minutes), which then decays either directly by alpha emission (to thallium-208) or by a further beta decay to the pure alpha emitter polonium-212. A member of the thorium-232/232U decay series, 212Pb is drawn from generators loaded with its longer-lived parents radium-224 (half-life 3.63 days) or thorium-228 (half-life about 1.9 years).
Its 10.6-hour half-life is long enough to synthesise and ship a labelled radiopharmaceutical but short enough to limit prolonged radiation exposure, and it uses conventional chelation chemistry (unlike some other alpha emitters). 212Pb-DOTAMTATE (AlphaMedix) and other 212Pb-labelled somatostatin and PSMA-targeting agents are in early clinical trials.
Unlike actinium-225, the feedstock chain for 212Pb (natural thorium-232/uranium-232 decay) is not considered scarce: Perspective Therapeutics states its proprietary 224Ra/212Pb generator system and a long-term US DOE supply contract for 228Th could support over 100,000 doses per year, and Orano Med, RadioMedix/Thor Medical and others are commercialising 228Th-based 212Pb generators. Some reviews describe 212Pb supply as having moved from a major constraint to a largely solved production problem, though clinical-scale, GMP-qualified generator throughput is still being industrialised.
- β− 0.57 MeV (to 212Bi)
- in vivo daughter 212Bi decays 35.9% by α to 208Tl, 64.1% by β− to 212Po
- 212Po α 8.78 MeV (from 212Bi decay)
- DOTAM
- DOTAMTATE-type macrocycles
Theranostic partners
- Gallium-68 · A radioactive metal with a one-hour lifetime that is eluted from a shielded generator or made on a cyclotron and attached to a molecule that finds tumours, giving a PET scan the same day.
An alpha-particle version of neuroendocrine radioligand therapy that produced responses in over half of patients who had never had PRRT, with FDA Breakthrough designation.
A drug that homes to the scaffolding cells tumours build around themselves, carrying a radioactive metal that fires alpha particles over a very short range. A matching scan version shows first whether a patient's tumour has the target.
A drug that targets a marker on neuroendocrine tumour cells is being tested with two versions of a radioactive metal: one lets doctors see where the tumour is on a scan, and the other delivers a strong, short-range dose of radiation to kill the tumour cells.
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