Conjugation of cell-penetrating peptides to parathyroid hormone affects its structure, potency, and transepithelial permeation

Bioconjug Chem. 2015 Mar 18;26(3):477-88. doi: 10.1021/bc5005763. Epub 2015 Mar 4.


Delivery of therapeutic peptides and proteins by the use of cell-penetrating peptides (CPPs) as carriers has been suggested as a feasible strategy. The aim of the present study was to investigate the effect of conjugating a series of well-known CPPs to the biologically active part of parathyroid hormone, i.e., PTH(1-34), and to evaluate the effect with regard to secondary structure, potency in Saos-2 cells, immunogenicity, safety, as well as the transepithelial permeation across monolayers by using the Caco-2 cell culture model. Further, co-administration of CPP and PTH(1-34) as an alternative to covalent conjugation was compared with regard to the transepithelial permeation. CPP-conjugated PTH(1-34) fusion peptides were successfully expressed in Escherichia coli and purified from inclusion bodies. No clear correlation between the degree of secondary structure of the CPP-conjugated PTH(1-34) fusion peptides and their potency was found, albeit a general decrease in permeation was observed for both N- and C-terminally CPP-conjugated PTH(1-34) as compared to native PTH(1-34). However, attachment of CPP to the N-terminus significantly increased permeation across Caco-2 cell monolayers as compared to the corresponding C-terminally CPP-conjugated PTH(1-34). In addition, the nonaarginine sequence proved to be the only CPP capable of increasing permeation when conjugated to PTH(1-34) as compared to co-administration of CPP and PTH(1-34). This enhancement effect was, however, associated with an unacceptably low level of cell viability. In conclusion, covalent conjugation of CPPs to PTH(1-34) influenced the secondary structure, potency, and transepithelial permeation efficiency of the resulting conjugate, and hence this approach appears not to be favorable as compared to co-administration when optimizing CPP-mediated permeation of PTH(1-34) across an intestinal epithelium.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caco-2 Cells
  • Cell Membrane Permeability / drug effects*
  • Cell Membrane Permeability / physiology
  • Cell Survival / drug effects
  • Cell Survival / physiology
  • Cell-Penetrating Peptides / chemistry*
  • Cell-Penetrating Peptides / metabolism
  • Cell-Penetrating Peptides / pharmacology
  • Cells, Cultured
  • Humans
  • Mice
  • Mice, Inbred C57BL
  • Parathyroid Hormone / chemistry*
  • Parathyroid Hormone / metabolism
  • Parathyroid Hormone / pharmacology


  • Cell-Penetrating Peptides
  • Parathyroid Hormone