Monitoring metallofulfenamic–bovine serum albumin interactions: a novel method for metallodrug analysis

Abstract

A new methodology for drug/metallodrug detection in an aqueous solution and their interactions with serum albumin are presented. The interactions of metals with flufenamic acid (FFA, a non-steroidal anti-inflammatory drug (NSAID)) were studied by quantum dot assisted laser desorption/ionization mass spectrometry (QALDI-MS) and Fourier transform infrared (FT-IR) spectroscopy. The drug/metallodrug interactions were investigated using many analytical methods such as fluorescence and 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy and matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). QALDI-MS offered a soft ionization of weak interactions in the metallodrugs because there was no disturbance of the non-covalent bonds among the metals with this drug. Fluorescence emission spectra of BSA in the presence of FFA and metalloflufenamic were recorded at an excitation wavelength of 295 nm (tryptophan), and clearly showed that FFA and metalloflufenamic act as quenchers. Quenching of the BSA emission was attributed to changes in the environment of protein fluorophores after the drug and their complexes bind to the backbone of the protein. 3D-fluorescence spectra showed strong interactions in the order of Fe(III)–FFA complex > Cu(II)–FFA complex > FFA according to the quenching of the tryptophan emission fluorophore. FTIR studies confirmed the interactions among FFA, the metallodrug and protein. Successful detection of the high mass protein of BSA, BSA–FFA and the metallodrug–BSA complexes at about 66 kDa could be used to probe their non-covalent interactions based on mass shift or the change observed in these peak profiles.