title: Interaction of [D-Trp6, Des-Gly10] LHRH ethylamide and hydroxy propyl beta-cyclodextrin (HPbetaCD): thermodynamics of interaction and protection from degradation by alpha-chymotrypsin.
abstract: OBJECTIVE
  The purpose of this study is to investigate the mechanisms and thermodynamics of the interaction between hydroxypropyl beta-cyclodextrin (HPdetaCD) and [D-Trp6, des-Gly10] LHRH ethylamide (deslorelin), a peptide drug.
  
  
  METHODS
  We used UV and fluorescence spectroscopy to study the interaction of HPbetaCD and deslorelin. Circular dichroism was used to study the conformational changes induced in deslorelin upon interaction with HP beta CD. The thermodynamics of the interaction of deslorelin and HPbetaCD was studied using isothermal titration calorimetry (ITC). We also determined the effect of HPbetaCD on the degradation of deslorelin by alpha-chymotrypsin.
  
  
  RESULTS
  UV and fluorescence spectroscopy indicated that HPbetaD induced a change in polarity of the environment surrounding the chromophores of deslorelin. Wavelength selective fluorescence indicated an increase in the fluorescence polarization of deslorelin with an increase in excitation wavelength in the presence of HPbetaCD suggesting that tryptophan is present in a media of reduced mobility. Circular dichroism studies indicated that HPbetaCD stabilizes the conformation of deslorelin. In addition, ITC indicated an exothermic reaction between deslorelin and HPbetaCD with a low enthalpy of binding of approximately -600 cal/mol and a binding affinity of approximately -1.25 x 10(2) M-1. Finally, the rate of degradation of deslorelin by alpha-chymotrypsin was decreased by 33% in the presence of HPbetaCD.
  
  
  CONCLUSIONS
  These results indicate that there is an interaction between HPbetaCD and deslorelin, which involves the inclusion of aromatic amino acids of deslorelin into the hydrophobic cavity of the cyclodextrin. This inclusion, providing steric hindrance, may be one of the mechanisms by which HPbetaCD reduces enzymatic hydrolysis of deslorelin.
authors.affiliation: Department of Pharmaceutical Sciences, 986025 University of Nebraska Medical Center, Omaha, NE 68198-6025, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Koushik
authors.forename: N
authors.initials: N
authors.lastname: Bandi
authors.forename: U B
authors.initials: UB
authors.lastname: Kompella
mesh_terms: D000073738:2-Hydroxypropyl-beta-cyclodextrin; D024322:Amino Acids, Aromatic / Q000737:chemistry; D002918:Chymotrypsin / Q000032:analysis / Q000737:chemistry*; D003505:Cyclodextrins / Q000032:analysis / Q000737:chemistry*; D004347:Drug Interactions; D004355:Drug Stability; D005079:Excipients / Q000032:analysis / Q000737:chemistry; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence / Q000379:methods; D013816:Thermodynamics; D017329:Triptorelin Pamoate / Q000031:analogs & derivatives; D047391:alpha-Cyclodextrins; D047392:beta-Cyclodextrins
chemical_list: D024322:Amino Acids, Aromatic; D003505:Cyclodextrins; D005079:Excipients; D047391:alpha-Cyclodextrins; D047392:beta-Cyclodextrins; C479658:hydroxypropyl-alpha-cyclodextrin; D017329:Triptorelin Pamoate; D000073738:2-Hydroxypropyl-beta-cyclodextrin; D007987:Gonadotropin-Releasing Hormone; D002918:Chymotrypsin; C117608:alpha-chymotrypsin; C066438:deslorelin