Novel bioactive and stable neurotensin peptide analogues capable of delivering radiopharmaceuticals and molecular beacons to tumors

Samuel Achilefu, Ananthacari Srinivasan, Michelle A. Schmidt, Hermo N. Jimenez, Joseph E. Bugaj, Jack L. Erion

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

The prevalence of neurotensin receptor (NTR) in several human tumors makes it an attractive target for the delivery of cytotoxic drugs and imaging agents. Native neurotensin (NT) is a tridecapeptide that binds to NTR and induces tumor growth. Unfortunately, NT has a short plasma half-life, which hinders its use for in vivo biomedical applications. Numerous reports suggest that Arg(8)-Arg(9) and Tyr(11)-Ile(12) amide bonds are particularly susceptible to degradation by proteolytic enzymes. Predicated on this observation, we substituted Arg(8), Arg(9), and Ile(12) amino acids with the corresponding commercially available mimics. These surrogate amino acids are amenable to standard Fmoc peptide synthesis strategy, and the resulting compounds are stable in biological media for > 4 h and bind to NTR with high affinity. Furthermore, conjugating DTPA to the new peptides and subsequent labeling with 111In-DTPA for nuclear imaging or fluorescein for optical imaging did not diminish the NTR binding affinities of the peptides. In vivo biodistribution of a representative 111In-DTPA-NT peptide analogue in SCID mice bearing NTR-positive human adenocarcinoma (HT29) xenograft shows that the compound was primarily retained in tumor tissue (2.2% ID/g) and the kidneys (4.8% ID/g) at 4 h postinjection. Coinjection of cold NT and the radiolabeled NT peptide analogue inhibited the tumor but not the kidney uptake, demonstrating that retention of the radiolabeled compound in tumor tissue was mediated by NTR specific uptake while it accumulates in the kidneys by a nonspecific mechanism. These findings show that the new NT peptide analogues are robust and can deliver imaging agents to NTR-positive tumors such as pancreatic cancer.

Original languageEnglish
Pages (from-to)3403-3411
Number of pages9
JournalJournal of Medicinal Chemistry
Volume46
Issue number15
DOIs
StatePublished - Jul 17 2003

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