Investigations on the interactions of 5-fluorouracil with bovine serum albumin: Optical spectroscopic and molecular modeling studies Shanmugavel Chinnathambi a , Devadasan Velmurugan b,c , Nobutaka Hanagata d,e , Prakasa Rao Aruna a , Singaravelu Ganesan a,n a Department of Medical Physics, Anna University, Chennai 600025, India b Bioinformatics Infrastructure Facility, University of Madras, Chennai 600025, India c Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Chennai 600025, India d Nanotechnology Innovation Station, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan e Graduate School of Life Science, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0812, Japan article info Article history: Received 7 September 2013 Received in revised form 22 January 2014 Accepted 24 January 2014 Available online 6 February 2014 Keywords: Serum albumin Fluorescence quenching Anisotropy Molecular modeling abstract 5-Fluorouracil is clinically used as antitumor drug to treat many types of cancer, which is made available to the target tissues in conjugation with transport protein serum albumin. 5-Fluorouracil which is low toxic when compared to the other drugs of this family and hence its binding characteristics are therefore of prime interest. The steady state and time resolved fluorescence studies, Fourier transform infrared spectroscopy and circular dichroism studies were employed to explain the mode and the mechanism of interaction of 5FU with BSA. 5-Fluorouracil binding is characterized with one high affinity binding site, with the binding constant of the order of 10 4 . The molecular distance r ( 1.5 nm) between donor (bovine serum abumin) and acceptor (5-fluorouracil) was estimated according to Forster's theory of non- radiative energy transfer. The feature of 5-fluorouracil induced structural changes of bovine serum albumin has been studied in detail by circular dichroism and Fourier transform infrared spectroscopy analysis. The binding dynamics was expounded by synchronous fluorescence spectroscopy, florescence lifetime measurements and molecular modeling elicits that hydrophobic interactions and hydrogen bonding, stabilizes the 5-fluorouracil interaction with BSA. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Cancer patient with advanced stages and those patients who are not eligible for surgery and radiation therapy are treated with chemotherapy. Many of the chemotherapeutic agents are admini- strated intravenously. In order to deliver the drugs to the target selectively, carriers are used. Serum albumins are the major native carrier found in the blood and are involved in the transporting and delivering of exogenous and endogenous materials (fatty acids, nutrients, steroids, and a variety of therapeutic drugs) [1–4]. Further serum helps in maintaining the pH of blood in our body and it is the main contributor to colloidal osmotic blood pressure. It must be noted that the effectiveness of drug solubility, biodis- tribution and their interaction is highly affected by their binding nature and interaction with protein. For example, strong binding can decrease the concentration of free drugs in plasma where as weak binding may lead to poor distribution and short lifetime [5]. This clearly indicates that the binding of drug with protein may alter the pharmacokinetics and cytotoxic effects. Hence the knowl- edge on the interaction of drug with protein is essential to design new drugs and improve the therapeutic efficacy. Bovine serum albumin (BSA) has been used as a model protein to study drug interaction, as it has 76% structural homology with that of human serum albumin (HSA). The protein BSA, with a molecular weight of 66200 Da, having 583 amino acids in a single polypeptide chain, homologous domains (I, II, and III) divided into nine loops (L1–L9) by 17 disulfide bridges. Each domain has two subdomains. BSA contains two tryptophan residues (Trp-134 and Trp-212) that possess intrinsic fluorescence. Trp-212 locates within a hydro- phobic binding pocket in the subdomain IIA and Trp-134, locates on the surface of the domain I [1]. 5-Fluorouracil (5-FU) is an analog of uracil with a fluorine atom at the C-5 position in place of hydrogen (Fig. 1). 5-FU is an antimetabolite. It is used to treat various cancers such as color- ectal, colon, breast, ovarian, liver, head and neck cancers by effectively blocking DNA synthesis through inhibition of thymidy- late synthase and subsequently cell replication [6,7]. Although many improvements in the therapeutic response and patient Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2014.01.063 0022-2313 & 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ91 44 22358685. E-mail addresses: sganesan@annauniv.edu, sganesan_61@yahoo.com (S. Ganesan). Journal of Luminescence 151 (2014) 1–10