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Developing novel hCT derived cell-penetrating peptides with improved metabolic stability
Authors:Robert Rennert  Annette G. Beck-Sickinger
Affiliation:Institute of Biochemistry, Faculty of Biosciences, Pharmacy and Psychology, University of Leipzig, Brüderstr. 34, D-04103 Leipzig, Germany
Abstract:
Many promising therapeutics are currently awaiting their clinical application. Due to their low capability of cell membrane crossing, these compounds do not reach their site of action. One way to overcome this problem might be the fusion of these agents to cell-penetrating peptides (CPP), which are able to shuttle various cargoes across cellular membranes. One disadvantage in using CPP in drug delivery is their low metabolic stability. The aim of our work was to increase the proteolytic resistance of the CPP hCT(9-32), a truncated C-terminal fragment of human calcitonin. Thus, we synthesised six modified N-terminally carboxyfluorescein labelled hCT(9-32) derivatives by replacing positions 12 and/or 16 of hCT(9-32) with either N-methylphenylalanine or d-phenylalanine, respectively. By using confocal laser scanning microscopy we showed that the modifications did neither affect the peptide internalisation efficiency in HeLa nor HEK 293T cells. The metabolic stability of the peptides was investigated in human blood plasma and HEK 293T cell culture supernatant. To analyse the degradation patterns, we used RP-HPLC and MALDI-TOF mass spectrometry. However, we found for all of the new derivatives high metabolic stabilities. In blood plasma, the half-lives for five of the six peptides increased compared to unmodified hCT(9-32). The degradation patterns showed a distinct stabilisation in the N-terminal part of the modified peptides, in the C-terminal part, we found some cleavage to a minor extent. Furthermore, we studied the conformation of the peptides by CD spectroscopy and demonstrated that they possess no cell toxicity. Since our metabolically more stable compounds are still able to pass the cell membrane they provide powerful tools as drug delivery vectors.
Keywords:CD, circular dichroism   CF, carboxyfluorescein   CLSM, confocal laser scanning microscopy   CPP, cell-penetrating peptide   DIC, diisopropylcarbodiimide   HATU, O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate   hCT, human calcitonin   HOBt, 1-hydroxybenzotriazole   MALDI-TOF, matrix assisted laser desorption ionisation-time of flight   MS, mass spectrometry   RP-HPLC, reversed phase - high performance liquid chromatography   SPPS, solid phase peptide synthesis   TBTU, O-(benzotriazol-1-yl)1,1,3,3-tetramethyluronium tetrafluoroborate   TFA, trifluoroacetic acid   TFE, trifluoroethanole   XTT, 2,3-bis(methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide
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