Characterization of drug-binding levels to serum albumin using a wavelength modulation surface plasmon resonance sensor

The drug binding to serum albumin is an area of intense research in evaluating drug candidates. A simple method based on a wavelength modulation surface plasmon resonance (SPR) sensor was developed for determination of the interaction for a drug and serum albumin. Seven kinds of drugs with different molecular masses and affinities were studied to illustrate the benefits of the wavelength modulation SPR sensor. With a known concentration of a drug, the percentage of the drug binding to human serum albumin (HSA) or bovine serum albumin (BSA) was then determined. The %bound values determined with a SPR sensor were compared with those obtained by other methods. In addition, the reproducibility and stability of the serum albumin immobilized on the sensor surface were studied under the experiment conditions. This method provides detailed information on affinities of the drug binding to serum albumin. The equilibrium constants of reactions for the HSA and penicillin V K, cefoperazone, cefotaximum natricum, oxacillin, amoxicillin, enoxacin, and norfloxacin, were 72.2 ± 3.0, 134 ± 21, 166 ± 25, 261 ± 63, 575 ± 38, 641 ± 36, and 980 ± 16 μmol L−1, respectively, while the equilibrium constants of reactions for the same seven drugs were 112 ± 3.0, 134 ± 19, 161 ± 23, 261 ± 18, 580 ± 85, 558 ± 19, and 675 ± 31 μmol L−1, respectively. The binding percentages range from 90.0 ± 2.2% to 40.8 ± 5.2% for drugs binding HAS, and from 85.9 ± 1.2% to 50.4 ± 2.8% for drugs binding BSA. These results illustrate how the wavelength modulation SPR sensor can be applied to the study of interaction of the small molecular drugs and serum albumin in real time.