Enzymatic synthesis of 13N-β-nicotinamide adenine dinucleotide

Nitrogen-13-labelled β-nicotinamide adenine dinucleotide (13N-NAD) is an interesting new compound for positron emission tomography. A semi-automatic production method is developed that yields a solution of 13N-NAD of radiopharmaceutical quality, suitable for human intravenous administration. The 13N-NAD is prepared enzymatically in one step from cyclotron-produced 13NH3 and nicotinic acid adenine dinucleotide (deamido-NAD). The enzyme NAD synthetase (E.C. 6.3.1.5), catalysing this reaction, is extracted and purified from Escherichia coli. The purified enzyme is immobilized by glutaraldehyde coupling to γ-aminopropylsilane-coated porous glass beads. The enzyme-loaded glass beads are packed in a column. The kinetic properties of the column are optimized. For synthetizing 13N-NAD, the mixture of co-factors and substrates, containing 13NH3, is pumped over the enzyme column. The unreacted 13NH3 is separated from 13N-NAD by on-line passage over a cation exchanger. After passing over a millipore filter, a sterile solution of radiochemically pure 13N-NAD is obtained, containing 70 mCi in 10 mL. The total synthesis time is 10 minutes. The specific activity is about 120 mCi/μmol at EOB. Quality control includes sterility and pyrogen tests, HPLC and HPTLC analysis. (author)