A biophysical and computational study unraveling the molecular interaction mechanism of a new Janus kinase inhibitor Tofacitinib with bovine serum albumin

The interaction of a recently certified kinase inhibitor Tofacitinib (TFB) with bovine serum albumin (BSA) has been studied, by spectroscopic and molecular docking studies. Spectrofluorimetric measurements at 3 different temperatures (288, 298, and 310K) showed that TFB quench the intrinsic fluorescence of BSA upon forming a nonfluorescent complex. The intrinsic fluorescence data showed that TFB binds to BSA with binding constant (K-b) of approximately 10(4)M(-1), affirming a significant affinity of TFB with BSA. The decrease in Stern-Volmer quenching constant with increasing temperature exhibited the static mechanism of quenching. Negative value of G (-6.94 +/- 0.32kcalmol(-1)), H (-7.87 +/- 0.52kcalmol(-1)), and S (-3.14 +/- 0.42calmol(-1)K(-1)) at all 3 temperatures declared the reaction between BSA and TFB to be spontaneous and exothermic. Far-UV circular dichroism spectroscopy results demonstrated an increase in helical content of BSA in the presence of TFB. Moreover, dynamic light scattering measurements showed that TFB resulted into a decrease in the hydrodynamic radii (from 3.6 +/- 0.053 to 2.9 +/- 0.02nm) of BSA. Molecular docking studies confirmed that TFB binds near site II on BSA, hydrogen bonding, and hydrophobic interaction were involved in the BSA-TFB complex formation. The present study characterizing the BSA-TFB interaction could be significant towards gaining an insight into the drug pharmacokinetics and pharmacodynamics and also in the direction of rational drug designing with better competence, against emerging immune-mediated diseases, ie, alopecia and rheumatoid arthritis.