Assessment of the complexation degree of camptothecin derivatives and cyclodextrins using spectroscopic and separative methodologies

Robust Inclusion Complex of Topotecan Comprised within a Rhodamine-Labeled β-Cyclodextrin: Competing Proton and Energy Transfer Processes

Monitoring the biological fate of medicaments within the environments of cancer cells is an important challenge which is nowadays the object of intensive studies. In this regard, rhodamine-based supramolecular systems are one of the most suitable probes used in drug delivery thanks to their high emission quantum yield and sensitivity to the environment which helps to track the medicament in real time. In this work, we used steady-state and time-resolved spectroscopy techniques to investigate the dynamics of the anticancer drug, topotecan (TPT), in water (pH ~6.2) in the presence of a rhodamine-labeled methylated β-cyclodextrin (RB-RM-βCD). A stable complex of 1:1 stoichiometry is formed with a K_eq value of ~4 × 10⁴ M^-1 at room temperature. The fluorescence signal of the caged TPT is reduced due to: (1) the CD confinement effect; and (2) a Förster resonance energy transfer (FRET) process from the trapped drug to the RB-RM-βCD occurring in ~43 ps with 40% efficiency. These findings provide additional knowledge about the spectroscopic and photodynamic interactions between drugs and fluorescent functionalized CDs, and may lead to the design of new fluorescent CD-based host-guest nanosystems with efficient FRET to be used in bioimaging for drug delivery monitoring.

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

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.

Discovery of 7-Methyl-10-Hydroxyhomocamptothecins with 1,2,3-Triazole Moiety as Potent Topoisomerase I Inhibitors

Homocamptothecin is emerging as an important topoisomerase I inhibitor originating in natural product camptothecin. We report the modifications and SAR of homocamptothecin on position C10 to develop potent topoisomerase I inhibitors for anticancer drug discovery. Based on click chemistry, twenty-one 1,2,3-triazole-substituted homocamptothecin derivatives were readily synthesized in two steps. For A549, cycloalkyl- and alkyl-substituted compounds 6j, 6l, and 6o revealed highly antiproliferative inhibitory activities with IC50 value of 30, 30, and 50 nm, respectively. In addition, cyclopropyl 6j exhibited greater Topo I inhibitory activity than 20(S)-Camptothecin, which indicated suitability for further drug development.

Spectrofluorimetric determination of SN-38, a promising new anti-tumor agent, in the presence and absence of organized media

This study focuses on the spectrofluorimetric behavior of the camptothecin derivative 7-ethyl-10-hydroxycamptothecin (SN-38) alone and in the presence of organized media and also on its potential analytical applications. SN-38 displays native fluorescence in both lactone and carboxylate form, which has been the base for development of two spectrofluorimetric methods, one for the lactone form (acidic media) and another for the carboxylate form (basic media). In an attempt to improve the understanding of SN-38, its interaction with several cyclodextrins and surfactants has been studied using spectrofluorimetry. Consequently, the optimal working conditions for the determination of SN-38 have been established in both the presence and the absence of organized media. The proposed methods were applied to human urine, using liquid-liquid extraction for clean-up of the samples, with satisfactory recoveries. No interference of the urine matrix was observed.