Synthesis and liposome encapsulation of a novel ¹⁸F-conjugate of ω-conotoxin GVIA for the potential imaging of N-type Ca²⁺ channels in the brain by positron emission tomography

ω-Conotoxin GVIA is a potent, irreversible antagonist of N-type voltage gated Ca²⁺ channels. A radiofluorinated analogue of GVIA could be useful in assessing regional synaptic density of the brain, in vivo, using positron emission tomography. N-hydroxy succinimidyl 4-[ ¹⁸F]fluorobenzoate was employed to site-specifically label GVIA, preserving native binding affinity. The tracer was characterized with MALDI-TOF mass spectrometry and colorimetric protein assay. Radiochemical decay-corrected yield of the lysine-24 labeled analogue of [¹⁸F]GVIA was 5%. Specific activity of this species was determined to be 1.2 × 10⁵ Ci/mmol. Encapsulation of the tracer in sulfatide containing liposomes, a potential method for enhancing blood-brain penetrance, was accomplished with 40% efficiency.