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DL-[Carboxyl-¹¹C]tryptophan, a Potential Agent for Pancreatic Imaging; Production and Preclinical Investigations

Oak Ridge Associated Universities and Oak Ridge National Laboratory, Oak Ridge, Tennessee

Correspondence: For reprints contact: Lee C. Washburn, Oak Ridge Associated Universities, P. O. Box 117, Oak Ridge, TN 37830.

ABSTRACT

In animal studies, DL-[carboxyl-¹⁴C]tryptophan [DL-Try(C-14)] showed a high specificity for the pancreas, which suggested the potential of DL-[carboxyl-¹¹C]tryptophan [DL-Try(C-11)] for clinical pancreatic imaging. The blood clearance and tissue uptake of the amino acid were very rapid, and no carrier effect was observed through a dose of 5 mg/kg. None of three transplanted hamster pancreatic adenocarcinomas that we studied showed a selective uptake of DL-Try(C-14) by the tumor, and none of the three enzymatic regimens investigated gave significant enhancement of the pancreatic specificity. Commercial L-Try(C-14) gave slightly better pancreatic specificity than the analogous racemic compound but without enough improvement to warrant attempts at optical resolution. DL-Try(C-11) was synthesized in amounts up to 325 mCi using a rapid, high-temperature, high-pressure modification of the Bücherer-Strecker amino acid synthesis. Yields ranged from 30–60%, and a total of 40 min was required for synthesis and chromatographic purification. DL-Try(C-11) thus appears to have significant potential as a clinical pancreas-imaging agent, particularly when used in conjunction with positron computerized transaxial tomography.