title: Surface plasmon resonance and circular dichroism characterization of cucurbitacins binding to serum albumins for early pharmacokinetic profiling.
abstract: Cucurbitacins are a group of tetracyclic triterpenoids, known for centuries for their anti-cancer and anti-inflammatory properties, which are being actively investigated over the past decades in order to elucidate their mechanism of action. In perspective of being used as therapeutic molecules, a pharmacokinetic characterization is crucial to assess the affinity toward blood carrier proteins and extrapolate distribution volumes. Usually, pharmacokinetic data are first collected on animal models and later translated to humans; therefore, an early characterization of the interaction with carrier proteins from different species is highly desirable. In the present study, the interactions of cucurbitacins E and I with human and rat serum albumins (HSA and RSA) were investigated by means of surface plasmon resonance (SPR)-based optical biosensing and circular dichroism (CD) spectroscopy. Active HSA and RSA sensor chip surfaces were prepared through an amine coupling reaction protocol, and the equilibrium dissociation constants (Kd) for the different cucurbitacins-serum albumins complexes were then determined by SPR analysis. Further information on the binding of cucurbitacins to serum albumins was obtained by CD competition experiments with biliverdin, a specific marker binding to subdomain IB of HSA. SPR data unveiled a previously unreported binding event between CucI and HSA; the determined binding affinities of both compounds were slightly higher for RSA with respect to HSA, even though all the compounds can be ranked as high-affinity binders for both carriers. CD analysis showed that the two cucurbitacins modify the binding of biliverdin to serum albumins through opposite allosteric modulation (positive for HSA, negative for RSA), confirming the need for caution in the translation of pharmacokinetic data across species.
authors: Department of Pharmacy and Biotechnology, University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy.
authors: Edoardo
authors: E
authors: Fabini
authors: Department of Physics and Chemistry, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto, CEP 14049-900, Brazil.
authors: Giovana Maria Lanchoti
authors: GM
authors: Fiori
authors: Department of Pharmacy and Biotechnology, University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy.
authors: Daniele
authors: D
authors: Tedesco
authors: Department of Physics and Chemistry, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Ribeirão Preto, CEP 14049-900, Brazil.
authors: Norberto Peporine
authors: NP
authors: Lopes
authors: Department of Pharmacy and Biotechnology, University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy. Electronic address: carlo.bertucci@unibo.it.
authors: Carlo
authors: C
authors: Bertucci
mesh_terms: D000818:Animals; D001665:Binding Sites; D002942:Circular Dichroism / Q000379:methods*; D054728:Cucurbitacins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D051381:Rats; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism*; D020349:Surface Plasmon Resonance / Q000379:methods*
chemical_list: D012709:Serum Albumin; D054728:Cucurbitacins
keywords: Binding affinity; Circular dichroism; Cucurbitacins; Drug binding; SPR optical biosensor; Serum albumins