Drug-selected cell line panels for evaluation of the pharmacokinetic consequences of multidrug resistance proteins

Soloxolone N-3-(Dimethylamino)propylamide Restores Drug Sensitivity of Tumor Cells with Multidrug-Resistant Phenotype via Inhibition of P-Glycoprotein Efflux Function

Multidrug resistance (MDR) remains a significant challenge in cancer therapy, primarily due to the overexpression of transmembrane drug transporters, with P-glycoprotein (P-gp) being a central focus. Consequently, the development of P-gp inhibitors has emerged as a promising strategy to combat MDR. Given the P-gp targeting potential of soloxolone amides previously predicted by us by an absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis, the aim of the current study was to experimentally verify their P-gp inhibitory and MDR reversing activities in vitro. Screening of soloxolone amides as modulators of P-gp using molecular docking and cellular P-gp substrate efflux assays revealed the ability of compound 4 bearing a N-3-(dimethylamino)propylamide group to interact with the active site of P-gp and inhibit its transport function. Blind and site-specific molecular docking accompanied by a kinetic assay showed that 4 directly binds to the P-gp transmembrane domain with a binding energy similar to that of zosuquidar, a third-generation P-gp inhibitor (ΔG = -10.3 kcal/mol). In vitro assays confirmed that compound 4 enhanced the uptake of Rhodamine 123 (Rho123) and doxorubicin (DOX) by the P-gp-overexpressing human cervical carcinoma KB-8-5 (by 10.2- and 1.5-fold, respectively (p < 0.05, unpaired t-test)) and murine lymphosarcoma RLS40 (by 15.6- and 1.75-fold, respectively (p < 0.05, unpaired t-test)) cells at non-toxic concentrations. In these cell models, 4 showed comparable or slightly higher activity than the reference inhibitor verapamil (VPM), with the most pronounced effect of the hit compound in Rho123-loaded RLS40 cells, where 4 was 2-fold more effective than VPM. Moreover, 4 synergistically restored the sensitivity of KB-8-5 cells to the cytotoxic effect of DOX, demonstrating MDR reversal activity. Based on the data obtained, 4 can be considered as a drug candidate to combat the P-gp-mediated MDR of tumor cells and semisynthetic triterpenoids, with amide moieties in general representing a promising scaffold for the development of novel therapeutics for tumors with low susceptibility to antineoplastic agents.

Synthesis and Biological Properties of Ferrocenyl and Organic Methotrexate Derivatives

Synthesis and biological activity of two series of modified side chain methotrexate (MTX) derivatives are presented, one with a ferrocenyl moiety inserted between the pteroyl and glutamate portions of the molecule and the other with glutamate substituted for short chain amino acids. Ferrocenyl derivatives of MTX turned out to be rather moderate inhibitors of dihydrofolate reductase (DHFR) although molecular modeling suggested more effective interactions between these compounds and the target enzyme. More interestingly, ferrocene-decorated MTX derivatives were able to impede the proliferation of four murine and human cell lines as well as their methotrexate-resistant counterparts, overcoming the multidrug resistance (MDR) barrier. They were also able to directly interact with Abcc1, an MDR protein. Of the amino acid pteroyl conjugates, the γ-aminobutyric acid derivative was an efficient inhibitor of DHFR but had no effect on cell proliferation in the concentration range studied while a taurine conjugate was a poor DHFR inhibitor but able to affect cell viability. We postulate that modification of the methotrexate side chain may be an efficient strategy to overcome efflux-dependent methotrexate resistance.

Fluorescence-Guided Spatial Drug Screening in 3D Colorectal Cancer Spheroids

The limited recapitulation of critical cancer features in 2D cultures causes poor translatability of preclinical results from in vitro assays to in vivo tumor models. This contributes to slow drug development with a low success rate. 3D cultures better recapitulate the tumor microenvironment, enabling more accurate predictions when screening drug candidates and improving the development of chemotherapeutics. Platinum (Pt) (IV) compounds are promising prodrugs designed to reduce the severe systemic toxicity of widely used Food and Drug Administration (FDA)-approved Pt(II) drugs such as cisplatin. Here, this work presents spatiotemporal evaluations in 3D colorectal cancer (CRC) spheroids of mitochondria-targeting Pt(IV) complexes. CRC spheroids provide a greater pathophysiological recapitulation of in vivo tumors than 2D cultures by a marked upregulation of the ABCG2 chemoresistance marker expression. Furthermore, new 3D-staining protocols are introduced to evaluate the real-time decrease in mitochondria membrane potential (ΔΨ) in CRC spheroids, and a Pt-sensing dye to quantify the Pt mitochondrial accumulation. Finally, this work demonstrates a correlation between in vitro results and the efficacy of the compounds in vivo. Overall, the CRC spheroids represent a fast and cost-effective model to assess the behavior of Pt compounds in vitro and predict their translational potential in CRC treatment.

Oncostatin M reverses ABCG2-mediated mitoxantrone resistance

Mitoxantrone resistant variant of SW620 line was developed, characterized and subsequently used as a model system to determine oncostatin M ability to modulate MDR phenomenon. The selection regimen allowed for overexpression of ABCG2 and ABCB1 both at the RNA and protein level, which was further confirmed by functional assays. Oncostatin M supplementation resulted in partial reversal of MDR phenotype by decreasing overexpression of ABCG2 demonstrating for the first time the ability of this cytokine for selective down-regulation of one of MDR proteins.

Development of Half-Sandwich Ru, Os, Rh, and Ir Complexes Bearing the Pyridine-2-ylmethanimine Bidentate Ligand Derived from 7-Chloroquinazolin-4(3H)-one with Enhanced Antiproliferative Activity

Kinesin spindle protein (KSP) inhibitors are one of the most promising anticancer agents developed in recent years. Herein, we report the synthesis of ispinesib-core pyridine derivative conjugates, which are potent KSP inhibitors, with half-sandwich complexes of ruthenium, osmium, rhodium, and iridium. Conjugation of 7-chloroquinazolin-4(3H)-one with the pyridine-2-ylmethylimine group and the organometallic moiety resulted in up to a 36-fold increased cytotoxicity with IC50 values in the micromolar and nanomolar range also toward drug-resistant cells. All studied conjugates increased the percentage of cells in the G2/M phase, simultaneously decreasing the number of cells in the G1/G0 phase, suggesting mitotic arrest. Additionally, ruthenium derivatives were able to generate reactive oxygen species (ROS); however, no significant influence of the organometallic moiety on KSP inhibition was observed, which suggests that conjugation of a KSP inhibitor with the organometallic moiety modulates its mechanism of action.

Design, Synthesis, and Evaluation of Biological Activity of Ferrocene-Ispinesib Hybrids: Impact of a Ferrocenyl Group on the Antiproliferative and Kinesin Spindle Protein Inhibitory Activity

With the aim to combine more than one biologically-active component in a single molecule, derivatives of ispinesib and its (S) analogue were prepared that featured ferrocenyl moieties or bulky organic substituents. Inspired by the strong kinesin spindle protein (KSP) inhibitory activity of ispinesib, the compounds were investigated for their antiproliferative activity. Among these compounds, several derivatives demonstrated significantly higher antiproliferative activity than ispinesib with nanomolar IC50 values against cell lines. Further evaluation indicated that the antiproliferative activity is not directly correlated with their KSP inhibitory activity while docking suggested that several of the derivatives may bind in a manner similar to ispinesib. In order to investigate the mode of action further, cell cycle analysis and reactive oxygen species formation were investigated. The improved antiproliferative activity of the most active compounds may be assigned to synergic effects of various factors such as KSP inhibitory activity due to the ispinesib core and ability to generate ROS and induce mitotic arrest.

Metallofullerenols in biomedical applications

Metallofullerenols (MFs) are functionalized endohedral fullerenes connecting at least three levels of organization of matter: atomic, molecular, and supramolecular, resulting in their unique activity at the nanoscale. Biomedical applications of MFs started from gadolinium-containing contrasting agents, but today their potential medical applications go far beyond diagnostics and magnetic resonance imaging. In many cases, preclinical studies have shown a great therapeutic value of MFs, and here we provide an overview of interactions of MFs with high-energy radiation and with reactive oxygen species generated during radiation as a ground for potential applications in modern therapy of cancer patients. We also present the current knowledge on interactions of MFs with proteins and with other components of cells and tissues. Due to their antioxidant properties, as well as their ability to regulate the expression of genes involved in apoptosis, angiogenesis, and stimulation of the immune response, MFs can contribute to inhibition of tumor growth and protection of normal cells. MFs with enclosed gadolinium act as inhibitors of tumor growth in targeted therapy along with imaging techniques, but we hope that the data gathered in this review will help to accelerate further progress in the implementation of MFs, also the ones containing rare earth metals other than gadolinium, in a broad range of bioapplications covering not only diagnostics and bioimaging but also radiation therapy and cancer treatment by not-cytotoxic agents.

Impact of the ferrocenyl group on cytotoxicity and KSP inhibitory activity of ferrocenyl monastrol conjugates

The incorporation of the ferrocenyl moiety into a bioactive molecule may significantly alter the activity of the resulting conjugate. By applying this strategy, we designed ferrocenyl analogs of monastrol - the first low molecular weight kinesin spindle protein (KSP) inhibitor. The obtained compounds showed low micromolar antiproliferative activity towards a panel of sensitive and ABC-overexpressing cancer cells. Most cytotoxic compounds exhibited also higher KSP modulatory activity and ability for ROS generation compared to monastrol. The increased bioactivity of the studied compounds can be attributed to the presence of the ferrocenyl group.

Synthesis and Biological Activity of Ferrocenyl and Ruthenocenyl Analogues of Etoposide: Discovery of a Novel Dual Inhibitor of Topoisomerase II Activity and Tubulin Polymerization

Two series of the ferrocenyl and ruthenocenyl analogues of etoposide bearing 1,2,3-triazolyl or aminoalkyl linker were synthesized and evaluated for their cytotoxic properties, influence on the cell cycle, ability to induce tubulin polymerization, and inhibition of topoisomerase II activity. We found that the replacement of the etoposide carbohydrate moiety with a metallocenyl group led to organometallic conjugates exhibiting differentiated antiproliferative activity. Biological studies demonstrated that two ferrocenylalkylamino conjugates were notably more active than etoposide, with submicromolar or low-micromolar IC₅₀ values towards SW620, etoposide-resistant SW620E, and methotrexate-resistant SW620M cancer cell lines. Moreover, the simplest ferrocenylmethylamino conjugate exerted dual inhibitory action against tubulin polymerization and topoisomerase II activity while other studied compounds affected only topoisomerase II activity.

Metal-Dependent Cytotoxic and Kinesin Spindle Protein Inhibitory Activity of Ru, Os, Rh, and Ir Half-Sandwich Complexes of Ispinesib-Derived Ligands

Ispinesib is a potent inhibitor of kinesin spindle protein (KSP), which has been identified as a promising target for antimitotic anticancer drugs. Herein, we report the synthesis of half-sandwich complexes of Ru, Os, Rh, and Ir bearing the ispinesib-derived N,N-bidentate ligands (R)- and (S)-2-(1-amino-2-methylpropyl)-3-benzyl-7-chloroquinazolin-4(3H)-one and studies on their chemical and biological properties. Using the enantiomerically pure (R)- and (S)-forms of the ligand, depending on the organometallic moiety, either the S_M,R or R_M,S diastereomers, respectively, were observed in the molecular structures of the Ru- and Os(cym) (cym = η⁶-p-cymene) compounds, whereas the R_M,R or S_M,S diastereomers were found for the Rh- and Ir(Cp*) (Cp* = η⁵-pentamethylcyclopentadienyl) derivatives. However, density functional theory (DFT) calculations suggest that the energy difference between the diastereomers is very small, and therefore a mixture of both will be present in solution. The organometallics exhibited varying antiproliferative activity in a series of human cancer cell lines, with the complexes featuring the (R)-enantiomer of the ligand being more potent than the (S)-configured counterparts. Notably, the Rh and Ir complexes demonstrated high KSP inhibitory activity, even at 1 nM concentration, which was independent of the chirality of the ligand, whereas the Ru and especially the Os derivatives were much less active.

Microtubule-Targeting 7-Deazahypoxanthines Derived from Marine Alkaloid Rigidins: Exploration of the N3 and N9 Positions and Interaction with Multidrug-Resistance Proteins

Our laboratories have been investigating synthetic analogues of marine alkaloid rigidins that possess promising anticancer activities. These analogues, based on the 7-deazahypoxanthine skeleton, are available in one- or two-step synthetic sequences and exert cytotoxicity by disrupting microtubule dynamics in cancer cells. In the present work we extended the available structure-activity relationship (SAR) data to N3- and N9-substituted derivatives. Although N3 substitution results in loss of activity, the N9-substituted compounds retain nanomolar antiproliferative activities and the anti-tubulin mode of action of the original unsubstituted compounds. Furthermore, our results also demonstrate that multidrug-resistance (MDR) proteins do not confer resistance to both N9-unsubstituted and -substituted compounds. It was found that sublines overexpressing ABCG2, ABCC1, and ABCB1 proteins are as responsive to the rigidin analogues as their parental cell lines. Thus, the study reported herein provides further impetus to investigate the rigidin-inspired 7-deazahypoxanthines as promising anticancer agents.

iTRAQ-based proteomic profiling of Pycnoporus sanguineus in response to co-existed tetrabromobisphenol A (TBBPA) and hexavalent chromium

In current study, we investigated the changes of proteome profiles of Pycnoporus sanguineus after a single exposure of Cr(VI), TBBPA and a combined exposure of TBBPA and Cr(VI), with the goal of illuminating the cellular mechanisms involved in the interactions of co-existed TBBPA and Cr(VI) with the cells of P. sanguineus at the protein level. The results revealed that some ATP-binding cassette (ABC) transporters were obviously induced by these pollutants to accelerate the transportation, transformation and detoxification of TBBPA and Cr(VI). Cr(VI) could inhibit the bioremoval of its organic co-pollutants TBBPA through suppressing the expression of several key proteins related to the metabolism of TBBPA by P. sanguineus, including two cytochrome P450s, pentachlorophenol 4-monooxygenase and glutathione S-transferases. Furthermore, Cr(VI) possibly reduced the cell vitality and growth of P. sanguineus by enhancing the expression of imidazole glycerol phosphate synthase as well as by decreasing the abundances of proteins associated with the intracellular metabolic processes, such as the tricarboxylic acid cycle, purine metabolism and glutathione biosynthesis, thereby adversely affecting the biotransformation of TBBPA. Cr(VI) also inhibited the expression of peptidyl prolyl cis/trans isomerases, thus causing the damage of cell membrane integrity. In addition, some important proteins participated in the resistance to Cr(VI) toxicity were observed to up-regulate, including heat shock proteins, 26S proteasome, peroxiredoxins and three critical proteins implicated in S-adenosyl methionine synthesis, which contributed to reducing the hazard of Cr(VI) to P. sanguineus. The results of this study provide novel insights into the physiological responses and molecular mechanism of white rot fungi P. sanguineus to the stress of concomitant TBBPA and Cr(VI).

Selection and characterization of a human ovarian cancer cell line resistant to auranofin

The anti-arthritic drug auranofin exerts also potent antitumour activity in in vitro and in vivo models, whose mechanisms are not yet well defined. From an auranofin-sensitive human ovarian cancer cell line A2780, a highly resistant (>20-fold) subline (A2780/AF-R) was developed and characterized. Marked reduction of gold accumulation occurred in auranofin-resistant A2780 cells. Also, moderately higher thioredoxin reductase activity in A2780/AF-R cells was observed while no changes in intracellular glutathione content occurred. Resistance to auranofin was associated with a low level of cross-resistance to some investigational gold compounds as well as to oxaliplatin and other anticancer drugs with different mode of action (i.e. melphalan, vinblastine, doxorubicin, etoposide, and paclitaxel). Reduced gold accumulation was associated to substantial gene expression changes in various influx (e.g. SLC22A1, SLC47A1, SLCO1B1) and efflux (e.g. ABCB1, ABCC2, ABCC3) transporters. The expression levels of selected proteins (i.e. SLC22A1, SLC47A1, P-gp) were also changed accordingly. These data provide evidence that multiple drug transporters may act as mediators of transport of auranofin and other gold compounds in cancer cells. Further investigation into the molecular mechanisms mediating transport of auranofin and new gold complexes in view of their potential clinical application in the treatment of cancer is warranted.

Synthesis and in vitro Biological Evaluation of Ferrocenyl Side-Chain-Functionalized Paclitaxel Derivatives

Taxanes, including paclitaxel, are widely used in cancer therapy. In an attempt to overcome some of the disadvantages entailed with taxane chemotherapy, we devised the synthesis of ferrocenyl-functionalized paclitaxel derivatives and studied their biological properties. The cytotoxic activity was measured with a panel of human cancer cell lines of various tissue origin, including multidrug-resistant lines. A structure-activity study of paclitaxel ferrocenylation revealed the N-benzoyl-ferrocenyl-substituted derivative to be the most cytotoxic. In contrast, substitution of the 3'-phenyl group of paclitaxel with a ferrocenyl moiety led to less potent antiproliferative compounds. However, these agents were able to overcome multidrug resistance, as they were virtually unrecognized by ABCB1, a major cellular exporter of taxanes. Interestingly, the redox properties of these ferrocenyl derivatives appear to play a less important role in their mode of action, as there was no correlation between intracellular redox activity and cytotoxicity/cell-cycle distribution. The antiproliferative activity of ferrocenyl taxanes strongly depends on the substitution position, and good tubulin polymerization inducers, as confirmed by molecular docking, were usually more cytotoxic, whereas compounds with stronger pro-oxidative properties exhibited lower antiproliferative activity.

Anticancer Activity of Stilbene-Based Derivatives

Stilbene is an abundant structural scaffold in nature, and stilbene-based compounds have been widely reported for their biological activity. Notably, (E)-resveratrol and its natural stilbene-containing derivatives have been extensively investigated as cardioprotective, potent antioxidant, anti-inflammatory, and anticancer agents. Starting from its potent chemotherapeutic activity against a wide variety of cancers, the stilbene scaffold has been subject to synthetic manipulations with the aim of obtaining new analogues with improved anticancer activity and better bioavailability. Within the last decade, the majority of new synthetic stilbene derivatives have demonstrated significant anticancer activity against a large number of cancer cell lines, depending on the type and position of substituents on the stilbene skeleton. This review focuses on the structure-activity relationship of the key compounds containing a stilbene scaffold and describes how the structural modifications affect their anticancer activity.

Synthesis and evaluation of biological properties of ferrocenyl–podophyllotoxin conjugates

Ferrocenyl–podophyllotoxin conjugates have been synthesised and their antiproliferative activity, influence on cell cycle, and interactions with tubulin were evaluated.