**Interaction Characterization of a Tyrosine Kinase Inhibitor Erlotinib with a Model Transport Protein in the Presence of Quercetin: A Drug–Protein and Drug–Drug Interaction Investigation Using Multi-Spectroscopic and Computational Approaches**

**Tanveer A. Wani 1,\* , Mohammed M. Alanazi <sup>1</sup> , Nawaf A. Alsaif <sup>1</sup> , Ahmed H. Bakheit <sup>1</sup> , Seema Zargar <sup>2</sup> , Ommalhasan Mohammed Alsalami <sup>2</sup> and Azmat Ali Khan <sup>1</sup>**


**Citation:** Wani, T.A.; Alanazi, M.M.; Alsaif, N.A.; Bakheit, A.H.; Zargar, S.; Alsalami, O.M.; Khan, A.A. Interaction Characterization of a Tyrosine Kinase Inhibitor Erlotinib with a Model Transport Protein in the Presence of Quercetin: A Drug–Protein and Drug–Drug Interaction Investigation Using Multi-Spectroscopic and Computational Approaches. *Molecules* **2022**, *27*, 1265. https:// doi.org/10.3390/molecules27041265

Academic Editors: Brullo Chiara and Thomas Mavromoustakos

Received: 27 December 2021 Accepted: 11 February 2022 Published: 14 February 2022

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**Abstract:** The interaction between erlotinib (ERL) and bovine serum albumin (BSA) was studied in the presence of quercetin (QUR), a flavonoid with antioxidant properties. Ligands bind to the transport protein BSA resulting in competition between different ligands and displacing a bound ligand, resulting in higher plasma concentrations. Therefore, various spectroscopic experiments were conducted in addition to in silico studies to evaluate the interaction behavior of the BSA-ERL system in the presence and absence of QUR. The quenching curve and binding constants values suggest competition between QUR and ERL to bind to BSA. The binding constant for the BSA-ERL system decreased from 2.07 <sup>×</sup> <sup>10</sup><sup>4</sup> to 0.02 <sup>×</sup> <sup>10</sup><sup>2</sup> in the presence of QUR. The interaction of ERL with BSA at Site II is ruled out based on the site marker studies. The suggested Site on BSA for interaction with ERL is Site I. Stability of the BSA-ERL system was established with molecular dynamic simulation studies for both Site I and Site III interaction. In addition, the analysis can significantly help evaluate the effect of various quercetin-containing foods and supplements during the ERL-treatment regimen. In vitro binding evaluation provides a cheaper alternative approach to investigate ligand-protein interaction before clinical studies.

**Keywords:** erlotinib; bovine serum albumin; fluorescence quenching; binding interaction; quercetin; competition
