Enhanced cellular uptake and cytotoxicity studies of organometallic bioconjugates of the NLS peptide in Hep G2 cells

Strategies for the Nuclear Delivery of Metal Complexes to Cancer Cells

The nucleus is an essential organelle for the function of cells. It holds most of the genetic material and plays a crucial role in the regulation of cell growth and proliferation. Since many antitumoral therapies target nucleic acids to induce cell death, tumor-specific nuclear drug delivery could potentiate therapeutic effects and prevent potential off-target side effects on healthy tissue. Due to their great structural variety, good biocompatibility, and unique physico-chemical properties, organometallic complexes and other metal-based compounds have sparked great interest as promising anticancer agents. In this review, strategies for specific nuclear delivery of metal complexes are summarized and discussed to highlight crucial parameters to consider for the design of new metal complexes as anticancer drug candidates. Moreover, the existing opportunities and challenges of tumor-specific, nucleus-targeting metal complexes are emphasized to outline some new perspectives and help in the design of new cancer treatments.

Curious Case of Cobaltocenium Carbaldehyde

Cobaltocenium carbaldehyde (formylcobaltocenium) hexafluoridophosphate, a long sought-after functionalized cobaltocenium salt, is accessible from cobaltocenium carboxylic acid by a three-step synthetic sequence involving (i) chlorination to the acid chloride, (ii) copper-borohydride reduction to the hydroxymethyl derivative, and (iii) Dess-Martin oxidation to the title compound. Due to the strongly electron-withdrawing cationic cobaltocenium moiety, no standard aldehyde reactivity is observed. Instead, nucleophilic addition followed by haloform-type cleavage prevails, thereby ruling out common useful aldehyde derivatization. One-electron reduction of cobaltocenium carbaldehyde hexafluoridophosphate affords the deep-blue, isolable cobaltocene carbaldehyde 19-valence-electron radical whose spin density is located fully at cobalt and not at the formyl carbon atom. ¹H/¹³C NMR, IR, EPR spectroscopy, high-resolution mass spectrometry, cyclic voltammetry, single crystal structure analysis (XRD), and density functional theory are applied to characterize these unusual formyl-cobaltocenium/cobaltocene compounds.

Highlights of New Strategies to Increase the Efficacy of Transition Metal Complexes for Cancer Treatments

Although important progress has been made, cancer still remains a complex disease to treat. Serious side effects, the insurgence of resistance and poor selectivity are some of the problems associated with the classical metal-based anti-cancer therapies currently in clinical use. New treatment approaches are still needed to increase cancer patient survival without cancer recurrence. Herein, we reviewed two promising-at least in our opinion-new strategies to increase the efficacy of transition metal-based complexes. First, we considered the possibility of assembling two biologically active fragments containing different metal centres into the same molecule, thus obtaining a heterobimetallic complex. A critical comparison with the monometallic counterparts was done. The reviewed literature has been divided into two groups: the case of platinum; the case of gold. Secondly, the conjugation of metal-based complexes to a targeting moiety was discussed. Particularly, we highlighted some interesting examples of compounds targeting cancer cell organelles according to a third-order targeting approach, and complexes targeting the whole cancer cell, according to a second-order targeting strategy.

Novel α-tocopherol-ferrocene conjugates for the specific delivery of transgenes in liver cancer cells under high serum conditions

The delivery of therapeutic genes to a specific organ has drawn significant research attention. Among the pool of various delivery vectors, cationic liposomes (non-viral) are potential candidates for delivering therapeutic genes due to their low immunogenic response. Here, we have developed novel ferrocene-conjugated cationic tocopheryl aggregates as non-viral vectors. These formulations can transfer a reporter gene (pGL3; encoded for luciferase protein) specifically to liver cancer cells (HepG2 and Huh7) instead of non-hepatic cancer cells, such as Caco-2 (human colon carcinoma) and HeLa (cervical cancer) cells. The transfection efficiency (TE) of the optimum liposomal formulation is more significant than commercially available Lipofectamine 2000 (L2K). Notably, it retains its TE under high serum conditions (up to 50% FBS). A coupled effect from conjugated ferrocene and tocopherol in the cationic liposomal formulation might be responsible for the cell-specific delivery and higher serum compatibility. Therefore, the present proposed delivery system may provide a platform for further progress in terms of developing hepatotropic gene delivery systems.

The organometallic ferrocene exhibits amplified anti-tumor activity by targeted delivery via highly selective ligands to αvβ3, αvβ6, or α5β1 integrins

High levels of reactive oxygen species (ROS) in tumors have been shown to exert anti-tumor activity, leading to the concept of ROS induction as therapeutic strategy. The organometallic compound ferrocene (Fc) generates ROS through a reversible one-electron oxidation. Incorporation of Fc into a tumor-targeting, bioactive molecule can enhance its therapeutic activity and enable tumor specific delivery. Therefore, we conjugated Fc to five synthetic, Arg-Gly-Asp (RGD)-based integrin binding ligands to enable targeting of the cell adhesion and signaling receptor integrin subtypes αvβ3, α5β1, or αvβ6, which are overexpressed in various, distinct tumors. We designed and synthesized a library of integrin-ligand-ferrocene (ILF) derivatives and showed that ILF conjugates maintained the high integrin affinity and selectivity of their parent ligands. A thorough biological characterization allowed us to identify the two most promising ligands, an αvβ3 (L2b) and an αvβ6 (L3b) targeting ILF, which displayed selective integrin-dependent cell uptake and pronounced ferrocene-mediated anti-tumor effects in vitro, along with increased ROS production and DNA damage. Hence, ILFs are promising candidates for the selective, tumor-targeted delivery of ferrocene to maximize its anti-cancer efficacy and minimize systemic toxicity, thereby improving the therapeutic window of ferrocene compared to currently used non-selective anti-cancer drugs.

Metallo-Polyelectrolytes: Correlating Macromolecular Architectures with Properties and Applications

Since the middle of the 20th century, metallopolymers have represented a standalone subfield with a beneficial combination of functionality from inorganic metal centers and processability from the organic polymeric frameworks. Metallo-polyelectrolytes are a new class of soft materials that showcase fundamentally different properties from neutral polymers due to their intrinsically ionic behaviors. This review describes recent trends in metallo-polyelectrolytes and discusses emerging properties and challenges, as well as future directions from a perspective of macromolecular architectures. The correlations between macromolecular architectures and properties are discussed from copolymer self-assembly, metallo-enzymes for biomedical applications, metallo-peptides for catalysis, crosslinked networks, and metallogels.

Novel anticancer PdII complexes: The effect of the conjugation of transferrin binding peptide and the nature of halogen coordinated on antitumor activity

A series of Pd^II complexes with bis-(2-pyridylmethyl)glycine as a ligand of formula [PdX(bis-(2-pyridylmethyl)glycine)] where X = Cl, Br, I were prepared and the effect of the halogen nature in the antitumor activity of eight tumorigenic and one non-tumorigenic cell line was evaluated. The chloride derivative was further functionalized with a transferrin receptor binding peptide, generating the first Pd^II based metallopeptide. Its antitumor activity was also evaluated. However, among all the complexes, the chloride and iodine parent compounds showed the lowest GI₅₀ values in the panel evaluated, and lowest GI₅₀ than cisplatin in several cell lines. In contrast, the bromine derivative showed higher values of GI₅₀ than chloride and iodine (around 30 - 50 μM). The same trend was observed for the bovine serum albumin binding constant with higher values for iodine, chlorine, and bromine in this order. In aqueous solution, the chloride is exchanged by water while the bromine and iodine are not. DNA was evaluated as a target and showed no significative interaction for all the compounds. The results suggest sulfur-rich proteins and not DNA as a target. This report represents the first Pd^II metallopeptide reported, its evaluation in solution and antitumor activity. This work opens the possibilities for further functionalization of Pd^II complexes and the importance of the halogen coordination in the design of novel metallodrugs.

Nano-Based Systems and Biomacromolecules as Carriers for Metallodrugs in Anticancer Therapy

Since the discovery of cisplatin and its potency in anticancer therapy, the development of metallodrugs has been an active area of research. The large choice of transition metals, oxidation states, coordinating ligands, and different geometries, allows for the design of metal-based agents with unique mechanisms of action. Many metallodrugs, such as titanium, ruthenium, gallium, tin, gold, and copper-based complexes have been found to have anticancer activities. However, biological application of these agents necessitates aqueous solubility and low systemic toxicity. This minireview highlights the emerging strategies to facilitate the in vivo application of metallodrugs, aimed at enhancing their solubility and bioavailability, as well as improving their delivery to tumor tissues. The focus is on encapsulating the metal-based complexes into nanocarriers or coupling to biomacromolecules, generating efficacious anticancer therapies. The delivery systems for complexes of platinum, ruthenium, copper, and iron are discussed with most recent examples.

Enzymatically synthesized poly(amino-co-ester) polyplexes for systemic delivery of pcDNA-miRNA-214 to suppress colorectal cancer liver metastasis

Liver metastases from colorectal cancer (CRC) are the major cause of cancer-related deaths in CRC patients. In our previous study, microRNA-214 (miR-214) was identified in CRC patients as a novel regulator of CRC liver metastasis, which could serve as a therapeutic target to inhibit CRC proliferation and metastasis. In this study, we aim to develop a new CRC treatment strategy based on miR-214 gene therapy using biodegradable non-viral gene vectors. We developed multifunctional quaternary polyplexes that consist of cationic poly(ω-pentadecalactone-co-N-methyldiethyleneamine-co-sebacate) (PPMS) for DNA condensation to form a nano-sized polyplex core, hyaluronic acids (HA) grafted with a poly(ethylene glycol) (PEG) (HA-g-mPEG) shell for polyplex stabilization and targeted delivery, and nuclear localization signal (NLS) peptides for enhanced intracellular transport of pDNA to the nucleus. The results showed that the DNA/NLS/PPMS/HA-g-mPEG quaternary polyplexes could enhance DNA condensation, increase cellular uptake efficiency and decrease cytotoxicity. Most importantly, the quaternary polyplexes showed favorable transfection efficiency both in vitro and in vivo. The colony formation and migration ability were significantly inhibited in HCT116 cells transfected with pcDNA-miR-214 quaternary polyplexes. The up-regulation of miR-214 in HCT116 cells by pre-transfection of polyplexes-miR-214 could remarkably inhibit tumor growth and liver metastases in a xenograft mouse model. Furthermore, systemic administration of miR-214 using this multifunctional vector resulted in dramatic inhibition of liver metastasis without obvious toxicity in CRC xenografted mice. Collectively, systemic delivery of pcDNA-miR-214 by this multifunctional vector could be a powerful and highly specific therapeutic approach in the treatment of CRC liver metastasis.

Chirality in metal-based anticancer agents

Chiral metal-based drugs are currently an interesting and rapidly growing field in anticancer research. Here the different chiral metal-based anticancer agents and the extent to which the chiral resolution affects their biological properties are discussed. This review will aid the design of new potent and efficient chiral metal-based anticancer drugs that exploit the unique properties combined with their potential selectivity toward targeted chiral biomolecules.

Designing metallodrugs with nuclease and protease activity

The accidental discovery of cisplatin some 50 years ago generated renewed interest in metallopharmaceuticals. Beyond cisplatin, many useful metallodrugs have been synthesized for the diagnosis and treatment of various diseases, but toxicity concerns, and the propensity to induce chemoresistance and secondary cancers make it imperative to search for novel metallodrugs that address these limitations. The Amino Terminal Cu(ii) and Ni(ii) (ATCUN) binding motif has emerged as a suitable template to design catalytic metallodrugs with nuclease and protease activities. Unlike their classical counterparts, ATCUN-based metallodrugs exhibit low toxicity, employ novel mechanisms to irreversibly inactivate disease-associated genes or proteins providing in principle, a channel to circumvent the rapid emergence of chemoresistance. The ATCUN motif thus presents novel strategies for the treatment of many diseases including cancers, HIV and infections caused by drug-resistant bacteria at the genetic level. This review discusses their design, mechanisms of action and potential for further development to expand their scope of application.

Cell-Penetrating Peptide Spirolactam Derivative as a Reversible Fluorescent pH Probe for Live Cell Imaging

A colorless and nonfluorescent spirolactam derivative, RhB-R₁₂K, was synthesized by amide condensation between the carboxyl group of rhodamine B (RhB) and the amino group of cell-penetrating peptide (CPP). The fluorescence intensity of RhB-R₁₂K sharply increased as the pH value decreased from 8.0 to 4.9, demonstrating sensitive and reversible response to intracellular pH distribution. This CPP probe was completely water soluble, had low cytotoxicity, was membrane permeable, and was suitable for pH measurement in various organelles by choosing organelle-specific CPP sequences. Interestingly, CPPs acted not only as carriers but also as indispensable parts of fluorophores here. The presence of active groups on the peptides potentially allows for modification with additional dyes to construct multifunctional and ratiometric probes for cell imaging.

Cobaltoceniumethynyl gold(I) as an unusual heterodinuclear bioorganometallic fragment to study the biological properties of alkynyl gold complexes

A cobaltoceniumethynyl gold(i) complex with a triphenylphosphane ligand triggered efficient cytotoxic effects in cancer cells in contrast to a derivative with two cobaltocenium moieties. The complex effectively inhibited the enzyme thioredoxin reductase (TrxR) suggesting this enzyme as a possible biological target. The cellular uptake of both metal fragments of the active complex was studied by atomic absorption spectroscopy and indicated a high biological stability of the complex.

Peptide-mediated vectorization of metal complexes: conjugation strategies and biomedical applications

The rich chemical and structural versatility of transition metal complexes provides numerous novel paths to be pursued in the design of molecules that exert particular chemical or physicochemical effects that could operate over specific biological targets.

Induction of Cytotoxicity in Pyridine Analogues of the Anti-metastatic Ru(III) Complex NAMI-A by Ferrocene Functionalization

A series of novel ferrocene (Fc) functionalized Ru(III) complexes was synthesized and characterized. These compounds are derivatives of the anti-metastatic Ru(III) complex imidazolium [trans-RuCl4(1H-imidazole) (DMSO-S)] (NAMI-A) and are derived from its pyridine analogue (NAMI-Pyr), with direct coupling of Fc to pyridine at the 4 or 3 positions, or at the 4 position via a two-carbon linker, which is either unsaturated (vinyl) or saturated (ethyl). Electron paramagnetic resonance (EPR) and UV-vis spectroscopic studies of the ligand exchange processes of the compounds in phosphate buffered saline (PBS) report similar solution behavior to NAMI-Pyr. However, the complex with Fc substitution at the 3 position of the coordinated pyridine shows greater solution stability, through resistance to the formation of oligomeric species. Further EPR studies of the complexes with human serum albumin (hsA) indicate that the Fc groups enhance noncoordinate interactions with the protein and help to inhibit the formation of protein-coordinated species, suggesting the potential for enhanced bioavailability. Cyclic voltammetry measurements demonstrate that the Fc groups modestly reduce the reduction potential of the Ru(III) center as compared to NAMI-Pyr, while the reduction potentials of the Fc moieties of the four compounds vary by 217 mV, with the longer linkers giving significantly lower values of E1/2. EPR spectra of the compounds with 2-carbon linkers show the formation of a high-spin Fe(III) species (S = 5/2) in PBS with a distinctive signal at g = 4.3, demonstrating oxidation of the Fe(II) ferrocene center and likely reflecting degradation products. Density functional theory calculations and paramagnetic (1)H NMR describe delocalization of spin density onto the ligands and indicate that the vinyl linker could be a potential pathway for electron transfer between the Ru and Fe centers. In the case of the ethyl linker, electron transfer is suggested to occur via an indirect mechanism enabled by the greater flexibility of the ligand. In vitro assays with the SW480 cell line reveal cytotoxicity induced by the ruthenium ferrocenylpyridine complexes that is at least an order of magnitude higher than the unfunctionalized complex, NAMI-Pyr. Furthermore, migration studies with LNCaP cells reveal that Fc functionalization does not reduce the ability of the compounds to inhibit cell motility. Overall, these studies demonstrate that NAMI-A-type compounds can be functionalized with redox-active ligands to produce both cytotoxic and anti-metastatic activity.

Vesicular disruption of lysosomal targeting organometallic polyarginine bioconjugates

Compounds which are able to destabilize the lysosomal membrane have been proposed as interesting candidates for targeted anticancer drugs due to the pronounced lysosomal changes in cancer cells. For this purpose, metallocene derivatives of a cell penetrating polyarginine peptide M–(Arg)9(Phe)2Lys–NH2 (where M = ferrocene carboxylate or ruthenocene carboxylate) were designed and their biological activities were investigated in detail. The ferrocenoyl- and ruthenocenoyl polyarginine bioconjugates were synthesized via Fmoc solid-phase peptide synthesis (SPPS) protocols on a microwave-assisted synthesizer. After HPLC purification >98% purity was observed for all conjugates. Their interaction with supported biomimetic membranes was investigated on a quartz crystal microbalance (QCM) and revealed a very strong binding of the metallocene peptides and their metal-free congeners to an artificial eukaryotic membrane model (DMPC–cholesterol). To demonstrate their antiproliferative utility as cytotoxic compounds for a targeted anticancer drug, cell viability (by the crystal violet assay), apoptosis (flow cytometry, Ann V/PI staining), induction of reactive oxygen species (ROS, by flow cytometry with dihydroethidium staining), and changes in cancer cell metabolism, e.g. respiration and glycolysis, were studied. Our results reveal only a weak toxicity for the metal-free polyarginine peptide, which could be significantly enhanced (to ca. 50 μM against HeLa cells in the best case) by coupling ferrocene or ruthenocene carboxylates to the N-terminus of the peptide. The investigation of the cellular uptake and intracellular localization by fluorescence microscopy revealed an enhanced vesicular disruption by the metallocene bioconjugate compared to the metal-free derivative which could be triggered by light and chemicals. Further studies of apoptosis, respiration, glycolysis and ROS formation reveal the superior characteristics of the metallocene compounds. While most cells remain viable even at 300 μM of the metal free bioconjugate 1, most cells are dead or in late stages of apoptosis at 200 μM of the ruthenocene derivative 3, and at 100 μM of the most active ferrocene derivative 2, however, all show very little sign of necrosis. Also, the metal free compound 1 does not induce ROS formation but both metallocene–polyarginine bioconjugates are clearly associated with enhanced intracellular ROS levels, with levels for the redox-active ferrocene derivative being two times higher than for the structurally very similar but redox-silent ruthenocene derivative. We propose that such metallocene–polyarginine peptides induce lysosomal membrane permeabilization and thereby could be developed towards targeted anticancer drugs.

Development of human bone marrow derived cells lines stably expressing Tet regulated hepatocyte growth factor or fibroblast growth factor 4 gene

AIM: To develop human bone marrow derived cells lines stably expressing Tet regulated hepatocyte growth factor (HGF) or fibroblast growth factor 4 (FGF4) gene.

METHODS: HGF and FGF4 genes were synthesized and then cloned into a lentiviral vector to result in plenti6.3/TO-HGF and plenti6.3/TO-FGF4, respectively. Lenti3.3/TR was transfected into UE7T-13 cells to develop a UE7T-13-TR cell line possessing Tet-on gene swift. Then, plenti6.3/TO-HGF and plenti6.3/TO-FGF4 were used to transfect UE7T-13-TR cell to result in UE7T-13-TR-HGF cell line that could stably express Tet regulated HGF and UE7T-13-TR-FGF4 cell line that could stably express Tet regulated FGF4. The expression of target genes was detected by Q-PCR, and the levels and secretion of proteins were detected by Western blot and ELISA.

RESULTS: We successfully developed UE7T-13-TR-HGF and UE7T-13-TR-FGF4 cell lines. Q-PCR analysis verified that the expression of the HGF gene in UE7T-13-TR-HGF in the presence of Tet was 78-fold higher than that in the absence of Tet, and the fold change for FGF4 was more than 20 thousand folds. Western blot and ELISA analyses verified that HGF and FGF4 proteins could be synthesized and secreted outside the cell membrane.

CONCLUSION: We have successfully developed UE7T-13-TR-HGF and UE7T-13-TR-FGF4 cell lines through lentiviral transfection, which lays a foundation for further study.

Exploring nitrogen ligand diversity in trans-N-heterocyclic carbene-amine platinum complexes: synthesis, characterization, and application to fluorescence

Expand and diversify your Ptfolio: N-Heterocyclic carbene-Pt-pyridine complexes have been used to generate an expanded and diversified set of trans NHC-Pt complexes with various amines, polyamines, hydroxylamines, or hydrazine as ligands. Attachment of a fluorophore moiety has also been successfully achieved.

Solid-phase synthesis of oxaliplatin-TAT peptide bioconjugates

Platinum-based drugs play a crucial role in the fight against cancer. Oxaliplatin, which is used in the treatment of colorectal carcinoma, was the last platinum-based agent to be approved worldwide. However, the efficiency of the therapy is limited for example by a low accumulation of the drug in cancer cells. Cell-penetrating peptides (CPPs) are known to ease the cellular membrane transport and are used as vectors for low-molecular-weight drugs and drug carriers; of them, TAT peptides are the best-studied group. In this work, a TAT-peptide fragment (YGRKKRRQRRR) was for the first time conjugated to a platinum(IV) analog of oxaliplatin as a vehicle for membrane penetration. Solid-phase peptide synthesis and subsequent coupling with the platinum complex afforded mono- and difunctionalized conjugates, which were separated by preparative HPLC and characterized by analytical HPLC, ESI-MS, and (1)H NMR spectroscopy. Both conjugates are active in the low micromolar range in CH1 and SW480 human cancer cells, requiring much lower concentrations than the untargeted analogs for equal effects.

Copper, nickel, and zinc cyclam-amino acid and cyclam-peptide complexes may be synthesized with "click" chemistry and are noncytotoxic

We describe the synthesis of cyclam metal complexes derivatized with amino acids or a tripeptide using a copper(I)-catalyzed Huisgen "click" reaction. The linker triazole formed during the synthesis plays an active coordinating role in the complexes. The reaction conditions do not racemize the amino acid stereocenters. However, a methylene group adjacent to the triazole is susceptible to H/D exchange under ambient conditions, an observation which has potentially important implications for structures involving stereocenters adjacent to triazoles in click-derived structures. The successful incorporation of several amino acids is described, including reactive tryptophan and cysteine side chains. All complexes are formed rapidly upon introduction of the relevant metal salt, including synthetically convenient cases where trifluoroacetate salts of cyclam derivatives are used directly in the metalation. None of the metal complexes displayed any cytotoxicity to mammalian cells, suggesting that the attachment of such complexes to amino acids and peptides does not induce toxicity, further supporting their potential suitability for labeling/imaging studies. One Cu(II)-cyclam-triazole-cysteine disulfide complex displayed moderate activity against MCF-10A breast nontumorigenic epithelial cells.

Metal-containing peptide nucleic acid conjugates

Peptide Nucleic Acids (PNAs) are non-natural DNA/RNA analogues with favourable physico-chemical properties and promising applications. Discovered nearly 20 years ago, PNAs have recently re-gained quite a lot of attention. In this Perspective article, we discuss the latest advances on the preparation and utilisation of PNA monomers and oligomers containing metal complexes. These metal- conjugates have found applications in various research fields such as in the sequence-specific detection of nucleic acids, in the hydrolysis of nucleic acids and peptides, as radioactive probes or as modulators of PNA·DNA hybrid stability, and last but not least as probes for molecular and cell biology.

Metal complex mediated conjugation of peptides to nucleus targeting acridine orange: a modular concept for dual-modality imaging agents

To target the nucleus of specific cells, trifunctional radiopharmaceuticals are required. We have synthesized acridine orange derivatives which comprise an imidazole-2-carbaldehyde function for coordination to the [Re(CO)₃](+) or [(99m)Tc(CO)₃](+) core. Upon coordination, this aldehyde is activated and rapidly forms imines with amines from biological molecules. This metal-mediated imine formation allows for the conjugation of a nuclear targeting portion with a specific cell receptor binding function directly on the metal. With this concept, we have conjugated the acridine orange part to a bombesin peptide directly on the (99m)Tc core and in one step. In addition, a linker containing an integrated disulfide has been coupled to bombesin. LC/MS study showed that the disulfide was reductively cleaved with a 60 min half-life time. This concept enables the combination of a nucleus targeting agent with a specific cell receptor molecule directly on the metal without the need of separate conjugation prior to labeling, thus, a modular approach. High uptake of the BBN conjugate into PC-3 cells was detected by fluorescence microscopy, whereas uptake into B16BL6 cells was negligible.

Direct functionalisation of group 10 N-heterocyclic carbene complexes for diversity enhancement

The synthesis of alkyne-substituted N-heterocyclic carbene complexes of Pd(II) and Pt(II) is reported. Catalyzed 1,3-dipolar cycloaddition with azides has been applied as a modular way of functionalisation of group 10 transition metal NHC complexes to generate potentially new metallodrugs.

New potential anticancer agent of carborane derivatives: selective cellular interaction and activity of ferrocene-substituted dithio-o-carborane conjugates

The large diversity of structures and unique bonding modes of organometallic complexes make them possible to act as promising candidate therapeutic agents. In this study, the new type of ferrocene-substituted dithio-o-carborane conjugates (FcSB1, FcSB2, and FcSBCO) has been synthesized, and their in vitro antineoplastic activities have been explored by means of the electrochemical study, the real time cell electronic sensing (RT-CES) system, and biological assays. The conjugate-cell interactions were first monitored by electrochemistry, and the results show different cell uptake efficiency for FcSB1, FcSB2, and FcSBCO toward target cells. Both the highly hydrophobic ferrocenyl and carboranyl groups render the conjugates able to rapidly enter cells and exert acute cytotoxicity after 4 h incubation in serum-free media. However, FcSB1, FcSB2, and FcSBCO display different inhibition efficiencies toward SMMC-7721 and HepG2 cancer cells via the G(0)/G(1) arrest mechanism in a physiological environment. The anticancer activity is in the order FcSB2 > FcSB1 > FcSBCO, which is parallel to the order of the redox potentials of the ferrocenyl groups in the three complexes. In particular, FcSB1 and FcSB2 display a potent selective inhibition effect on the proliferation of the cancer cell lines SMMC-7721 and HepG2, but almost no effect on the normal cell line, the human embryonic lung fibroblast (HELF) cells. Thus, these results may provide some clues for use of the ferrocene-carborane conjugates in developing anticancer drugs.

Label-free screening of drug-protein interactions by time-resolved Fourier transform infrared spectroscopic assays exemplified by Ras interactions

Time-resolved Fourier transform infrared (FT-IR) spectroscopy can reveal molecular details of protein interactions. Analysis of difference spectra selects the absorptions of respective protein groups involved in an interaction against the background of the whole sample. By comparison of the same difference spectrum with and without a small molecule, one can determine whether the small molecule interferes with the protein or not. Usually a marker band of a specific residue of the protein is monitored. Here, we show three different time-resolved FT-IR assays detecting interactions of potential small molecules for molecular therapy with the GTPase Ras as an example for small GTPase binding proteins. Ras regulates signal transduction processes through a switching mechanism, cycling between an active "on" GTP-bound form and an inactive "off" GDP-bound state. Molecular defects in Ras can impair the ability of Ras and the Ras-RasGAP complex to hydrolyze GTP, contributing to uncontrolled cell growth and cancer. Oncogenic mutated Ras is found in about 30% of all cancer cells. We show in vitro assays, indicating (I) the shift of Ras into its "off" conformation, which inhibits the Ras pathway; (II) down-regulation of Ras signaling by changes in the Ras-Raf effector interaction; and (III) down-regulation of Ras signaling pathway by catalyzing GTP hydrolysis. Since almost all molecules have characteristic marker bands in the infrared, time-resolved FT-IR spectroscopy can be used label-free. No artificial nucleotides that could influence the interaction are needed. Both, sample preparation and evaluation can be automated in order to allow for high-throughput screening.