Spectroscopy and dynamics of topotecan anti-cancer drug comprised within cyclodextrins

Drug-Induced Conformational Dynamics of P-Glycoprotein Underlies the Transport of Camptothecin Analogs

P-glycoprotein (Pgp) plays a pivotal role in drug bioavailability and multi-drug resistance development. Understanding the protein's activity and designing effective drugs require insight into the mechanisms underlying Pgp-mediated transport of xenobiotics. In this study, we investigated the drug-induced conformational changes in Pgp and adopted a conformationally-gated model to elucidate the Pgp-mediated transport of camptothecin analogs (CPTs). While Pgp displays a wide range of conformations, we simplified it into three model states: 'open-inward', 'open-outward', and 'intermediate'. Utilizing acrylamide quenching of Pgp fluorescence as a tool to examine the protein's tertiary structure, we observed that topotecan (TPT), SN-38, and irinotecan (IRT) induced distinct conformational shifts in the protein. TPT caused a substantial shift akin to AMPPNP, suggesting ATP-independent 'open-outward' conformation. IRT and SN-38 had relatively moderate effects on the conformation of Pgp. Experimental atomic force microscopy (AFM) imaging supports these findings. Further, the rate of ATPase hydrolysis was correlated with ligand-induced Pgp conformational changes. We hypothesize that the separation between the nucleotide-binding domains (NBDs) creates a conformational barrier for substrate transport. Substrates that reduce the conformational barrier, like TPT, are better transported. The affinity for ATP extracted from Pgp-mediated ATP hydrolysis kinetics curves for TPT was about 2-fold and 3-fold higher than SN-38 and IRT, respectively. On the contrary, the dissociation constants (KD) determined by fluorescence quenching for these drugs were not significantly different. Saturation transfer double difference (STDD) NMR of TPT and IRT with Pgp revealed that similar functional groups of the CPTs are accountable for Pgp-CPTs interactions. Efforts aimed at modifying these functional groups, guided by available structure-activity relationship data for CPTs and DNA-Topoisomerase-I complexes, could pave the way for the development of more potent next-generation CPTs.

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.

Lactone Stabilized by Crosslinked Cyclodextrin Metal-Organic Frameworks to Improve Local Bioavailability of Topotecan in Lung Cancer

The protection of unstable anticancer molecules and their delivery to lesions are challenging issues in cancer treatment. Topotecan (TPT), a classic cytotoxic drug, is widely used for treating refractory lung cancer. However, the therapeutic effects of TPT are jeopardized by its active lactone form that is intrinsically hydrolyzed in physiological fluids, resulting in low bioavailability. Herein, the TPT-loaded crosslinked cyclodextrin metal-organic framework (TPT@CL-MOF) was engineered to improve the local bioavailability of TPT for the treatment of lung cancer. CL-MOF exhibited the efficient loading (12.3 wt%) of TPT with sustained release characteristics. In particular the formulation offered excellent protection in vitro against hydrolysis and increased the half-life of TPT from approximately 0.93 h to 22.05 h, which can be attributed to the host-guest interaction between cyclodextrin and TPT, as confirmed by molecular docking. The TPT@CL-MOF could effectively kill the cancer cells and inhibit the migration and invasion of B16F10 cells in vitro. Moreover, TPT@CL-MOF was efficiently distributed in the lungs after intravenous administration. In an in vivo study using a B16F10 pulmonary metastatic tumor model, TPT@CL-MOF significantly reduced the number and size of metastatic lung nodules at a reduced low dose by five times, and no noticeable side effects were observed. Therefore, this study provides a possible alternative therapy for the treatment of lung cancer with the camptothecin family drugs or other unstable therapeutically significant molecules.

Efficient incorporation and protection of lansoprazole in cyclodextrin metal-organic frameworks

Lansoprazole (LPZ) is an acid pump inhibitor, which readily degrades upon acidic or basic conditions and under heating. We investigated here LPZ stability upon incorporation in particles made of cyclodextrin metal-organic frameworks (CD-MOFs). LPZ loaded CD-MOFs were successfully synthesized, reaching high LPZ payloads of 23.2 ± 2.1 wt%, which correspond to a molar ratio of 1:1 between LPZ and γ-CD. The homogeneity of LPZ loaded CD-MOFs in terms of component distribution was confirmed by elemental mapping by STEM-EDX. Both CTAB, the surfactant used in the CD-MOFs synthesis, and LPZ compete for their inclusion in the CD cavities. CTAB allowed obtaining regular cubic particles of around 5 µm with 15 wt% residual CTAB amounts. When LPZ was incorporated, the residual CTAB amount was less than 0.1 wt%, suggesting a higher affinity of LPZ for the CDs than CTAB. These findings were confirmed by molecular simulations. Vibrational circular dichroism studies confirmed the LPZ incorporation inside the CDs. Solid-state NMR showed that LPZ was located in the CDs and that it remained intact even after three years storage. Remarkably, the CD-MOFs matrix protected the drug upon thermal decomposition. This study highlights the interest of CD-MOFs for the incorporation and protection of LPZ.

Expulsion of a potent cancer-cell photosensitizer from its micelle-bound state using β-cyclodextrin: A tenable model for efficient drug release

The present study delves into the interaction of a potent cancer-cell photosensitizer Norharmane (NHM) with non-ionic triblock copolymer P123, followed by the assessment of the stability of the formed complex in the presence of β-cyclodextrin (β-CD). Spectroscopic results unveil the modulation of the prototropic equilibrium of NHM within the constrained microheterogeneous medium of the copolymer micelle to be favoured towards the neutral species of NHM over the cationic counterpart; which has been aptly rationalized invoking the key role of hydrophobic interaction in the association process and is further reinforced from steady-state and time-resolved spectroscopic measurements. The micropolarity of the probe-binding site has been evaluated by the archetypal E_T(30) analysis revealing that the cationic probe remains in the corona region of the micelle instead of penetrating deeper into the micellar core. Moreover, the effect of β-CD on the stability of the NHM-bound P123 aggregates has also been investigated, revealing that β-CD can be used as a potential host for the release of the micelle-encapsulated drug through an inclusion complex formation with the P123 monomers. The result is expected to be of potential interest from medical perspective owing to the context of efficient drug release at their potential sites.

Controlling anticancer drug mediated G-quadruplex formation and stabilization by a molecular container

Controlling of ligand mediated G-quadruplex DNA (GQ-DNA) formation and stabilization is an important and challenging aspect due to its active involvement in many biologically important processes such as DNA replication, transcription, etc. Here, we have demonstrated that topotecan (TPT), a potential anticancer drug, can instigate the formation and stabilization of GQ-DNA (H24 → GQ-DNA) in the absence of Na⁺/K⁺ ions via circular dichroism, fluorescence, NMR, UV melting and molecular dynamics (MD) simulation studies. The primary binding mode of TPT to GQ was found to be stacking at the terminal rather than binding to the groove. We have also reverted this conformational transition (GQ-DNA → H24) using a molecular container, cucurbit[7]uril (CB7), by means of the translocation of the drug (TPT) from GQ-DNA to its nanocavity. Importantly, we have carried out the detection of these conformational transitions using the fluorescence color switch of the drug, which is more direct and simple than some of the other methods that involve sophisticated and complex detection techniques.

Inclusion of an Anthracene-based Fluorophore within Molecular Containers: A Comparative Study of the Cucurbituril and Cyclodextrin Host Families

In this paper, the binding interaction of a promising chloride channel blocker, 9-methyl anthroate (9-MA), with two different classes of molecular containers, β-cyclodextrins (β-CD and methyl-β-CD) and cucurbit[7]uril, having comparable cavity dimensions, has been thoroughly demonstrated via inspection of the modulation of the excited-state properties of the emissive molecule. Spectral data suggest that CB7 encapsulates the probe more efficiently in a 1:2 fashion, whereas the efficacies of β-CDs are relatively less and the corresponding stoichiometry is 1:1. Interestingly, despite being thermodynamically much more favorable than the probe-β-CD complexation equilibria, the fraction of probe-CB7 complex formed is appreciably smaller with respect to that of probe-β-CD complexes. This apparent inconsistency has been addressed via the proposition that since the formation of a 1:2 complex is entropically disadvantageous, it is anticipated that the activation barrier of the corresponding reaction is reasonably high, and thus only a small fraction of the reactants are able to surpass the energy barrier to form the products. This proposition has been thoroughly corroborated by fluorescence lifetime measurements at different temperatures.

A “Ship in a Bottle” Strategy To Load a Hydrophilic Anticancer Drug in Porous Metal Organic Framework Nanoparticles: Efficient Encapsulation, Matrix Stabilization, and Photodelivery

An essential challenge in the development of nanosized metal organic framework (nanoMOF) materials in biomedicine is to develop a strategy to stabilize their supramolecular structure in biological media while being able to control drug encapsulation and release. We have developed a method to efficiently encapsulate topotecan (TPT, 1), an important cytotoxic drug, in biodegradable nanoMOFs. Once inside the pores, 1 monomers aggregate in a "ship in a bottle" fashion, thus filling practically all of the nanoMOFs' available free volume and stabilizing their crystalline supramolecular structures. Highly efficient results have been found with the human pancreatic cell line PANC1, in contrast with free 1. We also demonstrate that one- and two-photon light irradiation emerges as a highly promising strategy to promote stimuli-dependent 1 release from the nanoMOFs, hence opening new standpoints for further developments in triggered drug delivery.