Enhanced Stability and Bioactivity of Natural Anticancer Topoisomerase I Inhibitors through Cyclodextrin Complexation.

Víctor González-Ruiz,J. Carlos Menéndez,Patrycja Michalska,Ana I. Olives,Olmo Martín-Cámara,M. Antonia Martín,Ángel Cores,Rafael León,Víctor Cervera-Carrascón,Karen Orellana

doi:10.3390/pharmaceutics13101609

Abstract

The use of cyclodextrins as drug nano-carrier systems for drug delivery is gaining importance in the pharmaceutical industry due to the interesting pharmacokinetic properties of the resulting inclusion complexes. In the present work, complexes of the anti-cancer alkaloids camptothecin and luotonin A have been prepared with β-cyclodextrin and hydroxypropyl-β-cyclodextrin. These cyclodextrin complexes were characterized by nuclear magnetic resonance spectroscopy (NMR). The variations in the 1H-NMR and 13C-NMR chemical shifts allowed to establish the inclusion modes of the compounds into the cyclodextrin cavities, which were supported by docking and molecular dynamics studies. The efficiency of the complexation was quantified by UV-Vis spectrophotometry and spectrofluorimetry, which showed that the protonation equilibria of camptothecin and luotonin A were drastically hampered upon formation of the inclusion complexes. The stabilization of camptothecin towards hydrolysis inside the cyclodextrin cavity was verified by the quantitation of the active lactone form by reverse phase liquid chromatography fluorimetric detection, both in basic conditions and in the presence of serum albumin. The antitumor activity of luotonin A and camptothecin complexes were studied in several cancer cell lines (breast, lung, hepatic carcinoma, ovarian carcinoma and human neuroblastoma) and an enhanced activity was found compared to the free alkaloids, particularly in the case of hydroxypropyl-β-cyclodextrin derivatives. This result shows that the cyclodextrin inclusion strategy has much potential towards reaching the goal of employing luotonin A or its analogues as stable analogues of camptothecin.

Highlights

Topoisomerase I is a very relevant, relatively unexploited, anticancer target [1,2]
We started our work by examining the changes in the the fluorescence fluorescence spectra spectra of of the the We started our work by examining the changes in alkaloids in the presence of increasing amounts of both cyclodextrins under study, as alkaloids in the presence of increasing amounts of both cyclodextrins under study, asa proof of of their inclusion. Both alkaloids have at least one one basicbasic nitrogen that that can be a proof their inclusion. Both alkaloids have at least nitrogen canprobe tonated under strongly acidic conditions, and it can be reasonably assumed that the protonated under strongly acidic conditions, and it can be reasonably assumed that the more one that is primarily included in the cavmore lipophilic lipophilicneutral neutralform formisisthe the one that is primarily included in cyclodextrin the cyclodextrin ity
Aqueous HCl standardized solutions with 0.1 M, 1.0 M and 10.0 M concentrations were initially assayed as titrating agents; we found that the lower-concentration solutions required high volumes to observe the spectral changes due to the protonation of camptothecin, and for this reason 10.0 M HCl was chosen for subsequent work

Summary

Introduction

Topoisomerase I is a very relevant, relatively unexploited, anticancer target [1,2]. Camptothecin (CPT), an alkaloid from Camptotheca acuminata, was the first anti-cancer compound that was proved to exert topoisomerase I inhibition. This mechanism raised much interest, but the clinical application of camptothecin was hampered. This mechanism raised much interest, but the clinical application of camptothecin was hampered by its poor solubility and itsand lowits chemical stability, which is due to fast hydrolby itswater poor water solubility low chemical stability, which is the duevery to the very fast ysis of the essential lactone ring to the corresponding hydroxy acid [3]. Besides to a lower activity, this ring-opening process is associated to an releading to aanticancer lower anticancer activity, this ring-opening process is associated to increased an increased nal toxicity [4,5,6]

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Results

Conclusion