Synthesis, radiolabeling and in vivo biodistribution of syn- and anti-^99mTc ACBC BAT as potential tumor imaging agents

Abstract

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Objectives: The non-natural non-metabolized amino acids syn- and anti-1-[N-[(1,1-dimethylethoxy)carbonyl]amino]-3-[N,N’-bis[2-[[(4-methoxyphenyl)methyl]thio]ethyl]-1,2-ethanediamine]-1-cyclobutanecarboxylic acid methyl esters (syn- and anti-ACBC BAT) were synthesized, radiolabeled with ^99mTc, deprotected and evaluated in vivo in SCID mice implanted with human tumor cell lines as potential SPECT tumor imaging agents.

Methods: The synthesis began with syn- and anti- 1-[N-[(1,1-dimethylethoxy)carbonyl]amino]-3-hydroxy-1-cyclobutanecarboxylic acid methyl esters, reported earlier by this group (McConathy, et al, Applied Radiation and Isotopes. 2003, 58, 657-666). The alcohol at C3 was converted to a trifluoromethanesulfonate which was subsequently displaced by N,N’-bis[2-[[(4-methoxyphenyl)methyl]thio]ethyl]-1,2-ethanediamine (BAT) to afford syn- and anti- 1-[N-[(1,1-dimethylethoxy)carbonyl]amino]-3-[N,N’-bis[2-[[(4-methoxyphenyl)methyl]thio]ethyl]-1,2-ethanediamine]-1-cyclobutanecarboxylic acid methyl esters (ACBC BAT) as precursors to the radiolabeling. The individual protected ACBC BAT compounds were dissolved in pH 7 phosphate buffer. A solution of sodium pertechnatate (^99mTc) was added followed by a saturated solution stannous tartrate at 95^oC. The pH of the resulting solution was adjusted to 12 by the addition of 1 N sodium hydroxide. After one hour, the pH of the solution was adjusted to 7 with 1 N hydrochloric acid. The labeled complex was extracted into dichloromethane. Removal of protecting groups was accomplished by reaction with trifluoroacetic acid. Chromatographic purification provided the syn- and anti- ^99mTc ACBC BAT complexes with radiochemical purity over 99% measured by radiometric TLC.

Results: The in vivo tissue distribution of syn- and anti- ^99mTc ACBC BAT were evaluated in SCID mice implanted in the flank with lung (A549), breast (MDA MB468), prostate (DU145), ovarian (SKOV3), and glioma (U87) human cancer cell lines. Syn- and anti- ^99mTc ACBC BAT demonstrated uptake dose/g in the tumors at 120 min p.i.. ,Syn- ^99mTc ACBC BAT showed 1.1%, 1.0%, 0.8%, 0.8%, and 0.6% uptake in A549, MB468, DU145, SKOV3 and U87. Anti- 99mTc ACBC BAT showed 0.9%, 1.0%, 0.5%, 0.6%, and 0.9% uptake in A549, MB468, DU145, SKOV3 and U87.

Conclusions: Both syn- and anti- ^99mTc ACBC BAT were synthesized and radiolabeled in high radiochemical purity. The SCID mice biodistribution assays showed moderate tumor uptake. These results support further SAR studies of syn- and anti- ^99mTc ACBC BAT homologs as potential SPECT imaging agents.

Research Support (if any): Research supported by Nihon Medi-Physics Co., Ltd.