Fluorescence Spectral Properties of the Anticancer Drug Topotecan by Steady-State and Frequency Domain Fluorometry with One-Photon and Multi-Photon Excitation

Elucidation of binding mechanism of dibutyl phthalate on bovine serum albumin by spectroscopic analysis and molecular docking method

Dibutyl phthalate has been illegally used in beverages and directly affects the human health. Herein, the interaction occurred between dibutyl phthalate and bovine serum albumin was studied. The experimental results demonstrated that dibutyl phthalate could bind to bovine serum albumin and statically quench the intrinsic fluorescence of this protein. Circular dichroism measurements proved that the binding of dibutyl phthalate would lead to an obvious decrease of α-helix content in the bovine serum albumin. Molecular docking analysis clarified the fluorescence quenching mechanism, size distribution and zeta potential variation, conformational change of BSA, the site marker competitive fluorescence quenching and the interaction mechanism of dibutyl phthalate to bovine serum albumin. This work provided a useful information for the binding of dibutyl phthalate to protein.

Lysosomal Sequestration Impairs the Activity of the Preclinical FGFR Inhibitor PD173074

Knowledge of intracellular pharmacokinetics of anticancer agents is imperative for understanding drug efficacy as well as intrinsic and acquired cellular resistance mechanisms. However, the factors driving subcellular drug distribution are complex and poorly understood. Here, we describe for the first time the intrinsic fluorescence properties of the fibroblast growth factor receptor inhibitor PD1703074 as well as utilization of this physicochemical feature to investigate intracellular accumulation and compartmentalization of this compound in human lung cancer cells. Cell-free PD173074 fluorescence, intracellular accumulation and distribution were investigated using analytical chemistry and molecular biology approaches. Analyses on a subcellular scale revealed selective drug accumulation in lysosomes. Coincubation with inhibitors of lysosomal acidification strongly enhanced PD173074-mediated fibroblast growth factor receptor (FGFR) inhibition and cytotoxicity. In conclusion, intrinsic fluorescence enables analysis of molecular factors influencing intracellular pharmacokinetics of PD173074. Lysosome-alkalinizing agents might represent candidates for rational combination treatment, preventing cancer cell-intrinsic PD173074 resistance based on lysosomal trapping.

A quantitative characterization of interaction between prion protein with nucleic acids

Binding of recombinant prion protein with small highly structured RNAs, prokaryotic and eukaryotic prion protein mRNA pseudoknots, tRNA and polyA has been studied by the change in fluorescence anisotropy of the intrinsic tryptophan groups of the protein. The affinities of these RNAs to the prion protein and the number of sites where the protein binds to the nucleic acids do not vary appreciably although the RNAs have very different compositions and structures. The binding parameters do not depend upon pH of the solution and show a poor co-operativity. The reactants form larger nucleoprotein complexes at pH 5 compared to that at neutral pH. The electrostatic force between the protein and nucleic acids dominates the binding interaction at neutral pH. In contrast, nucleic acid interaction with the incipient nonpolar groups exposed from the structured region of the prion protein dominates the reaction at pH 5. Prion protein of a particular species forms larger complexes with prion protein mRNA pseudoknots of the same species. The structure of the pseudoknots and not their base sequences probably dominates their interaction with prion protein. Possibilities of the conversion of the prion protein to its infectious form in the cytoplasm by nucleic acids have been discussed.

Fluorescence study of drug-carrier interactions in CTAB/PBS buffer model systems

The well-known cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was used as a model carrier to study drug-carrier interactions with fluorescence probes (5-hexadecanoylaminofluorescein (HAF) and 2,10-bis-(3-aminopropyloxy)dibenzo[a,j]perylene-8,16-dione (NIR 628) by applying ensemble as well as single molecule fluorescence techniques. The impact of the probes on the micelle parameters (critical micelle concentration, average aggregation number, hydrodynamic radius) was investigated under physiological conditions. In the presence of additional electrolytes, such as buffer, the critical micelle concentration decreased by a factor of about 10. In contrast, no influence of the probes on the critical micelle concentration and on average aggregation number was observed. The results show that HAF does not affect the characteristics of CTAB micelles. Analyzing fluorescence correlation spectroscopy data and time-resolved anisotropy decays in terms of the "two-step" in combination with the "wobbling-in-cone" model, it was proven that HAF and NIR 628 are differently associated with the micelles. Based on ensemble and single molecule fluorescence experiments, intra- and intermicellar energy transfer process between the two dyes were probed and characterized.

Utilizing inherent fluorescence of therapeutics to analyze real-time uptake and multi-parametric effector kinetics

The precise detection of pharmaceutical drug uptake and knowledge of a drug's efficacy at the single-cell level is crucial for understanding a compound's performance. Many pharmaceutical drugs, like the model substances Doxorubicin, Mitoxantrone or Irinotecan, have a distinctive natural fluorescence that can be readily exploited for research purposes. Utilizing this respective natural fluorescence, we propose a method analyzing simultaneously in real-time the efficiency, effects and the associated kinetics of compound-uptake and efflux in mammalian cells by flow cytometry. We show that real-time flow cytometric quantification of compound-uptake is reliably measured and that analyzing their respective uptake kinetic provides additional valuable information which can be used for improving drug dosage and delivery. Exploiting the native fluorescence of natural compounds is clearly advantageous compared to the usage of non-related fluorescent uptake-reporter substances, possibly yielding in unphysiological data. Flow cytometric analysis allows live-dye based multi-parametric high-throughput screening of pharmaceutical compound activity, improving cytotoxicity testing by combining several assays into a single, high resolution readout. This approach can be a useful tool identifying potential inhibitors for multiple drug resistance (MDR), representing a major challenge to the targeted treatment of various diseases.

Kinetic modelling of the role of the aldehyde dehydrogenase enzyme and the breast cancer resistance protein in drug resistance and transport

A compartmental model for the in vitro uptake kinetics of the anti-cancer agent topotecan (TPT) has been extended from a previously published model. The extended model describes the drug activity and delivery of the pharmacologically active form to the DNA target as well as the catalysis of the aldehyde dehydrogenase (ALDH) enzyme and the elimination of drug from the cytoplasm via the efflux pump. Verification of the proposed model is achieved using scanning-laser microscopy data from live human breast cancer cells. Before estimating the unknown model parameters from the experimental in vitro data it is essential to determine parameter uniqueness (or otherwise) from this imposed output structure. This is formally performed as a structural identifiability analysis, which demonstrates that all of the unknown model parameters are uniquely determined by the output structure corresponding to the experiment.

Chrysin blocks topotecan-induced apoptosis in Caco-2 cells in spite of inhibition of ABC-transporters

ATP-driven efflux pumps such as phosphoglycoprotein-170 (P-gp), multidrug-resistance-associated protein-2 (MRP-2), or breast cancer resistance protein (BCRP) play a crucial role in limiting the efficacy of tumor pharmacotherapy. Selected flavonoids have been suggested to inhibit individual efflux-transporters and to act therefore as multidrug-resistance reversing agents. In the present study it is shown that the flavonoid chrysin acts as a potent inhibitor of P-gp, MRP-2, and BCRP in Caco-2 colon carcinoma cells. As a consequence, cells accumulated higher rates of the apoptosis-inducing chemotherapeutic topotecan in the presence of chrysin, even though under these conditions the expression of the transporters was markedly increased. Interestingly, in spite of the enhanced cellular drug accumulation the topotecan-induced apoptosis, assessed according to DNA-fragmentation, chromatin condensation, and by determination of sub-G1 peaks using fluorescence-assisted-cell sorting (FACS), was potently inhibited by chrysin. Suggested transport-independent apoptosis inhibiting activities of ATP-binding cassette (ABC)-transporters, such as the inhibition of caspases, were shown to be necessary for the inhibition of topotecan-induced apoptosis and were found to be associated with stabilization of beta-catenin especially in the cytosol. Inhibition of topotecan-induced intracellular acidification, however, was proven not to prevent caspase-activation and apoptosis. In conclusion, our studies show that chrysin in spite of raising the cellular concentrations of topotecan potently inhibits the apoptosis-inducing activities of the anti-tumor drug. Inhibition of caspase-activation was identified as the underlying mechanism and is suggested to be caused by transport-independent functions of ABC-transporters.

ABCG2-associated resistance to Hoechst 33342 and topotecan in a murine cell model with constitutive expression of side population characteristics

Drug resistant tumor "side-populations," enriched in cancer stem cells and identified by reduced accumulation of Hoechst 33342 under ABCG2-mediated efflux, may compromise therapeutic outcome. Side-population cells have predicted resistance to minor groove ligands, including the DNA topoisomerase I poison topotecan. We have used a stable Hoechst 33342-resistant murine L cell system (HoeR415) to study resistance patterns, removing the need for SP isolation before microarray analysis of gene expression and the tracking of cell cycle dynamics and cytotoxicity. The majority of HoeR415 cells displayed a side-population phenotype comparable with that of the side-population resident in the ABCG2 over-expressing A549 lung cancer cell line. Photo-crosslinking showed direct protection against minor groove ligand residence on DNA, driven by ABCG2-mediated efflux and not arising from any binding competition with endogenous polyamines. The covalent minor-groove binding properties of the drug FCE24517 (tallimustine) prevented resistance suggesting a mechanism for overcoming SP-related drug resistance. Hoechst 33342-resistant murine cells showed lower but significant crossresistance to topotecan, again attributable to enhanced ABCG2 expression, enabling cells to evade S-phase arrest. Hoechst 33342/TPT-resistant cells showed limited ancillary gene expression changes that could modify cellular capacity to cope with chronic stress including over-expression of Aldh1a1 and Mgst1, but under-expression of Plk2 and Nnt. There was no evidence to link the putative stem cell marker ALDH1A1 with any augmentation of the TPT resistance phenotype. The study has implications for the patterns of drug resistance arising during tumor repopulation and the basal resistance to minor groove-binding drugs of tumor side-populations.

A coupled drug kinetics-cell cycle model to analyse the response of human cells to intervention by topotecan

A model describing the response of the growth of single human cells in the absence and presence of the anti-cancer agent topotecan (TPT) is presented. The model includes a novel coupling of both the kinetics of TPT and cell cycle responses to the agent. By linking the models in this way, rather than using separate (disjoint) approaches, it is possible to illustrate how the drug perturbs the cell cycle. The model is compared to experimental in vitro cell cycle response data (comprising single cell descriptors for molecular and behavioural events), showing good qualitative agreement for a range of TPT dose levels.

A mathematical model for the in vitro kinetics of the anti-cancer agent topotecan

In this paper a compartmental modelling approach is applied to provide a mathematical description of the activity of the anti-cancer agent topotecan, and delivery to its nuclear DNA target following administration. The activity of topotecan in defined buffers is first modelled using a linear two compartment model that then forms the basis of a cell based model for drug activity in live cell experiments. An identifiability analysis is performed before parameter estimation to ensure that the model output (i.e., continuous, perfect and noise-free data) uniquely determines the parameters. Parameter estimation is performed using experimental data which offers concentrations of active and inactive forms of topotecan from high performance liquid chromatography methods.

Subcellular localization of the camptothecin analogues, topotecan and gimatecan

Lipophilicity of camptothecins derivatives has been reported to improve the stability of the lactone ring and to favor rapid uptake and intracellular accumulation. Recently, a novel series of lipophilic camptothecins substituted at position 7 was developed, and gimatecan (ST1481) was selected for clinical development on the basis of some favorable features, including potent cytotoxicity and the unique feature of the lack of recognition by breast cancer resistance-associated protein (BCRP). In this work the intrinsic fluorescence properties of this compound were exploited to investigate its intracellular disposition in comparison with the water-soluble camptothecin, topotecan (TPT), in HT-29 colon carcinoma cells and in a subline, HT-29/Mit, selected for resistance to mitoxantrone and overexpressing BCRP. The study was performed at single-cell level by means of microspectrofluorometry and fluorescence image analysis. The results indicated a quite different subcellular localization of TPT ST1481, since TPT localized mainly in mitochondria, whereas gimatecan exhibited a lysosomal localization. An increased persistence of DNA damage in gimatecan-treated cells was consistent with the interpretation that lysosomes represent a store of active drug. In contrast to gimatecan, which showed a similar localization in HT-29 cells and in the mitoxantrone-resistant subline, the cellular pharmacokinetic of TPT was markedly influenced by overexpression of BCRP protein in the resistant subline. In conclusion, the present results indicating a quite different behavior of the two camptothecins suggest that, apart from intracellular accumulation, subcellular distribution plays a role in their cytotoxic potency and contributes to their pharmacological features.