Study of binding interaction of Capecitabine with human serum albumin using spectroscopic and molecular dynamics simulation approach

5-Fluorouracil (5-FU) has known a key anticancer drug that played an important role in the treatment of breast and gastrointestinal cancers, in either monotherapy or combination therapy with various cytotoxic drugs [1]. Capecitabine (CAP) is an orally administered prodrug of 5-FU, which make it a convenience option for self-administration. It is readly passes intact through the intestinal mucosa and is ultimately converted to 5-FU especially in tumor cells. This selectivity is achieved by the enzyme thymidine phosphorylase (TP), as a final conversion of capecitabine to 5-FU, that is more active in tumor cells compared with normal tissues [3]. Nowadays, binding of a drug to the plasma proteins play an important role in pharmacokinetics and pharmacodynamics. HSA as the most abundant protein in human blood plasma has the ability to bind reversibly a wide variety of drugs with higher affinity compared to other transport proteins. Drug-HSA interaction improves the drug solubility, decreases its toxicity and protects the drug s elimination from the human body [4]. This work reports a detailed study on the interactions between CAP and HAS by employing, molecular dynamics (MD) simulation, fluorescence, and absorption methods. MD simulation was performed on the CAP-HSA complex to investigate the stability of docked conformation and to study the binding interactions in detail. MD simulation was done with the NAMD 2.9 program using the CHARMM 22 force field. The capecitabine structure was parameterized to generate topology and parameter by using the swissparam server. Before the production run, the system was energy minimized and equilibrated using 1000 steps of steepest descent algorithm and subsequently 1000 steps of conjugate gradient algorithm. The system was subjected to MD simulation for 15 ns. The RMSD value of protein backbone with simulation time was assessed in order to explore the dynamic stability of the complex. The RMSD of CAP and CAP–HSA complex reach equilibration and oscillates around in average value after 2 ns simulation time. The average RMSD value of HSA and HAS-CAP complex from a 2–15 ns trajectory are 3.107 ± 0.05 nm and 2.773± 0.03 nm respectively. Moreover, the quenching mechanism associated with the CAP–HSA interaction was determined by performing fluorescence measurements at different temperatures. As shown in Table 1 the value of Ksv for CAP-HSA decrease with increasing temperature, suggesting that CAP quenches the intensity of HSA through a static process. The thermodynamic parameters ΔH°, ΔG°, and ΔS° were calculated, in which the negative ΔG° suggested that the binding of cytarabine to HSA was spontaneous, moreover the negative ΔS° and negative ΔH° revealed that van der Waals force and hydrogen bonds were the major forces to stabilize the protein-cytarabine (1:1) complex.