Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Aim:

Cell-penetrating peptides (CPP) derived from the native peptide hormone human calcitonin (hCT) represent a high potential drug delivery system for in vivo intracellular targeting of diagnostic and therapeutic compounds. Cell penetration of hCT-derived substances was verified in vitro, however, the knowledge about CPP in vivo distribution and metabolism is very limited. Therefore we studied the in vivo radiopharmacology of Ga-68 radiolabeled DOTA modified, hCT-derived CPP in rats using small animal PET (1).

Methods:

Three hCT-derived peptides (hCT(9-32), LGTYTQDFNKFHTFPQTAIGVGAPNH2; [f_12,16]-hCT(9-32), LGTfTQDfNKFHTFPQTAIGVGAP-NH2; random (rd)-hCT(9-32), FLTAGQNTIQTPVKTGGHFPFADY-NH2) were at the N-terminus modified with DOTA. The internalization of the stabilized peptide, biodistribution and kinetics of the radiolabeled Ga-68-DOTA-hCT(9-32) or Ga-68-DOTA-[f_12,16]-hCT(9-32) or Ga-68-DOTA-rd-hCT(9-32) were studied with small animal PET. The arterial blood at different time points, and urine were analyzed for radio-metabolites.

Results:

Ga-68-DOTA-[f_12,16]-hCT(9-32) was in vitro internalized. In vivo the radio-peptides were eliminated mainly by the renal system, more than 50% of the injected dose was found at 60 min after injection in the urine, only small amounts of the activity were detected in the intestine. The general activity retention in the body was low, except the kidneys. The blood clearance of the original peptides reached terminal half-lifes of Ga-68-DOTA-hCT(9-32) 15.9 min, Ga-68-DOTA-[f_12,16]-hCT(9-32) 20.9 min, Ga-68-DOTA-rd-hCT(9-32) 15.8 min; the relative AUC in comparison to Ga-68-DOTA-hCT(9-32) were 100%, 170%, and 51%, respectively. The patterns of metabolic cleavage in the arterial blood were different. The Ga-68-DOTA-[f_12,16]-hCT(9-32) was metabolized to three radio-metabolites after 30 min, the other radiopeptides were degraded to more than five radioactive metabolites.

Conclusion:

It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex. The blood clearance and the elimination of the Ga-68-DOTA-peptides were relatively high and should be decreased by structural changes to enhance the tissue uptake of this drug carrier system.

References:

(1) Neundorf I, Rennert R, et Bergmann R, Bioconjug Chem. 2008 Aug;19(8):1596-603.