EPR studies of intermolecular interactions and competitive binding of drugs in a drug-BSA binding model

Akdogan Y., Emrullahoglu M., Tatlidil D., Ucuncu M., ÇAKAN AKDOĞAN G.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS, no.32, pp.22531-22539, 2016 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Publication Date: 2016
  • Doi Number: 10.1039/c6cp04137j
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.22531-22539
  • Dokuz Eylül University Affiliated: Yes


Understanding intermolecular interactions between drugs and proteins is very important in drug delivery studies. Here, we studied different binding interactions between salicylic acid and bovine serum albumin (BSA) using electron paramagnetic resonance (EPR) spectroscopy. Salicylic acid was labeled with a stable radical (spin label) in order to monitor its mobilized (free) or immobilized (bound to BSA) states. In addition to spin labeled salicylic acid (SL-salicylic acid), its derivatives including SL-benzoic acid, SL-phenol, SL-benzene, SL-cyclohexane and SL-hexane were synthesized to reveal the effects of various drug binding interactions. EPR results of these SL-molecules showed that hydrophobic interaction is the main driving force. Whereas each of the two functional groups (-COOH and -OH) on the benzene ring has a minute but detectable effect on the drug-protein complex formation. In order to investigate the effect of electrostatic interaction on drug binding, cationic BSA (cBSA) was synthesized, altering the negative net charge of BSA to positive. The salicylic acid loading capacity of cBSA is significantly higher compared to that of BSA, indicating the importance of electrostatic interaction in drug binding. Moreover, the competitive binding properties of salicylic acid, ibuprofen and aspirin to BSA were studied. The combined EPR results of SL-salicylic acid/ibuprofen and SL-ibuprofen/salicylic acid showed that ibuprofen is able to replace up to similar to 83% of bound SL-salicylic acid, and salicylic acid can replace only similar to 14% of the bound SL-ibuprofen. This indicates that similar to 97% of all salicylic acid and ibuprofen binding sites are shared. On the other hand, aspirin replaces only similar to 23% of bound SL-salicylic acid, and salicylic acid replaces similar to 50% of bound SL-aspirin, indicating that similar to 73% of all salicylic acid and aspirin binding sites are shared. These results show that EPR spectroscopy in combination with the spin labeling technique is a very powerful method to investigate drug binding dynamics in detail.