336 research outputs found
Editorial [Hot Topic: Metal Containing Complexes with Anticancer Properties (Guest Editors: A. Nazarov & C. Hartinger)]
No full textHalf-sandwich Anticancer Organometallics Derived from Triazolyl-imidazolium Ligands: From Different Coordination Modes to Heterobimetallic Compounds
No full textTo overcome the adverse effects and narrow pharmacological spectrum of traditional platinum anticancer agents, a large variety of metallodrugs have been investigated in the search for the next generation cancer therapeutics. Half-sandwich metal complexes are a class of compounds that have portrayed promising anticancer activity. Imidazole is an essential building block of molecules in medicinal chemistry, which is commonly featured in many biologically active compounds. The versatile heterocyclic scaffold enables the design and development of ligand systems suitable for metal coordination. Thionation of the C2 carbon or the alkylation of the endocyclic nitrogen atoms leads to the formation of N-heterocyclic thiones (NHTs) and N-heterocyclic carbene (NHC) ligand precursors, respectively, which were both investigated for their anticancer properties upon coordination to transition metals.
An extensive series of asymmetric NHT and NHC compounds derived from an imidazolium scaffold was developed, in which one of the endocyclic nitrogen atoms was alkylated with a methyl or methylpyridyl group, while the other has a pendant triazolyl moiety functionalised with a benzyl or methylferrocene group. The heterocyclic compounds functioned as mono- or multidentate ligand systems generating half-sandwich organometallic complexes of RuII, OsII, RhIII, and IrIII. When the pro-ligands were coordinated to metal centres, the resultant complexes formed pockets that hydrogen bond with the counterion. These pockets were established by the protons of the ligand near the metal centre.
Cytotoxicity assays revealed that the ligand precursors showed only moderate to low anticancer activity. Coordination to metal centres resulted in compounds with a varied degree of improvements in cytotoxicity. NHT complexes generally displayed low to moderate cytotoxicity, with the Ir derivative being moderately cytotoxic and accumulating in the cytoplasm of cancer cells. Conversion into the analogous Ir(NHC) derivatives did not result in significant enhancement in cytotoxicity. The low potency of the Ru- and Os(NHC) derivatives was accounted for by their slow to no reactivity with biological molecules. Replacement of the benzyl group with ferrocene significantly improved the cytotoxicity of the compounds and promoted the generation of reactive oxygen species (ROS) in cancer cells. Alternative coordination modes were investigated with the methylpyridine-derived NHC precursors, which resulted in the unexpected formation of bi- and tridentately coordinated Os and Rh complexes. However, the improvement in cytotoxicity was not as pronounced compared to ferrocene-functionalisation. The investigation of various ligand modifications and coordination modes laid the foundation for the determination of structure-(re)activity relationships of these classes of complexes featuring different imidazole-derived ligands
The serum protein binding of pharmacologically active gallium(III) compounds assessed by hyphenated CE-MS techniques
No full textConjugation Strategies of the Anticancer Ruthenium Complex Plecstatin-1 to Tumour-targeting Peptides using Cleavable and Non-cleavable Linkers
No full textPeptide-drug conjugates (PDCs) have multifaceted applications and here they were explored as
potential chemotherapeutic agents based on the plecstatin compound class. These metal complexes
feature a pyridinecarbothioamide ligand (PCA) were explored as the payload in PDCs as they exhibit
potent anticancer activity. In this doctoral thesis, derivatives of the lead Ru complex plecstatin-1 were
synthesised which contained a functional handle for conjugation to peptides and to create metal-peptide
conjugates (MPCs) which can selectively deliver the plecstatin payload to cancer cells.
To obtain the desired MPCs several strategies were explored. The monodentate chlorido ligand of
plecstatin-1 was substituted for N-heterocycle and N-heterocyclic carbene (NHC) ligands as potential
conjugation handles. However, the Ru–N-heterocycle bond was too labile and resulted in dissociation
of the Ru(arene)(PCA) moiety from the peptides and the NHC-functionalised plecstatin complexes did
not yield the desired Ru complexes.
Alternatively, the η⁶ -arene ligand of plecstatin-1 was explored for functionalisation with a handle for
peptide conjugation by substituting it with L-phenylalanine (Phe) and p-methylbenzylamine.
Incorporation of the phenylalanine-derived plecstatin complex into peptides showed reduced stability
resulting in numerous side products, low yields and poor purity of the MPCs. The p-methylbenzylamine
functionalised plecstatin complexes were successfully conjugated to TAT, neurotensin (NT) and plectintargeting peptides (PTP) via a succinyl linker. The antiproliferative activity of the MPCs was significantly
reduced compared to the unconjugated Ru complex which, however, is common for many PDCs.
In attempts to improve the anticancer activity of the MPCs, the cathepsin B-activatable ValCitPABA
cleavable linker was installed into NT- and PTP-based MPCs. Unfortunately, the incubation of the MPCs
with cathepsin B did not result in the cleavage of the linker and therefore the metal complex was not
released. Consequently, they exhibited minor antiproliferative activity in in vitro anticancer activity
assays.
The developed methodology provides the foundations towards the preparation of novel approaches
towards MPCs. It facilitates the incorporation of metal piano-stool complexes into peptides as payloads
with cleavable and non-cleavable linkers. The functionalisation of the η⁶ -arene ligand allows for
conjugation of piano-stool metal complexes to other targeting vectors or biomolecules to improve their
biological properties
Ferrocene-derived Heterobimetallic Supramolecular Architectures: Synthesis, Guest Encapsulation and Stimulus-Responsive Studies
No full textMetallosupramolecular architectures are increasing in popularity due to their range of applications and ease of self-assembly. Many are able to readily change their shape and/or function in response to external stimuli and have the ability to encapsulate guest molecules within their internal cavities. As the majority of studies into homometallic stimuli-responsive supramolecular systems has focused on total disassembly of the architecture, this provided an opportunity to explore reversible partial disassembly and reassembly by which the entire host structure remains intact. As such, this project was centred on fashioning reversible stimulus-initiated heterobimetallic supramolecular structures whereby the structures would undergo partial disassembly when an external stimulus is applied and reassemble when the stimulus is removed.
Heterobimetallic [PdmLn]x+ complexes bearing symmetrical ferrocene-derived ligands through the formation of Pd–pyridyl bonds have been designed to allow for disassembly and reassembly. The formation of a series of PdL, PdL2 or Pd2L4 structures was possible through controlling the substitution pattern of the coordinating pyridyl rings. Cleavage of the relatively labile Pd–Npyridyl donor bonds, and subsequent disassembly of the supramolecular structure, was achieved through competitive ligand binding with N,N’-dimethylaminopyridine or a Cl- source to form PdCl42-. Triggering complex reassembly was successful for several complexes upon the addition of H+ or Ag+. Guest binding studies revealed interactions with several compounds with the anionic guests p-toluenesulfonate and octyl sulfate, and their binding constants were calculated based on 1H NMR spectroscopy experiments. Alternatively, dis- and reassembling structures can be obtained by introducing heteroditopic ligand systems. A ruthenium(II) heterobimetallic supramolecular structure bearing a non-symmetrically functionalised ferrocenyl ligand was designed to respond to the exposure and removal of light. Ru(II) complexes are well known for their ability to undergo photo-induced ligand ejection, in particular Ru–N bonds. The Ru(II) moiety was attached through a stable Ru–NHC (N-heterocyclic carbene) coordination bond on one arm of the ferrocenyl ligand and a more labile coordination to a pyridyl-triazole group on the other. While the final complex proved challenging to purify for light-responsiveness and guest binding studies, the synthetic routes towards the formation of the target ferrocenyl ligands and Ru(II) complexes are described in detail
Heterobimetallic Supramolecular Architectures: Guest Binding Abilities and Interactions with Biomolecules
No full textIn recent decades, metallosupramolecular architectures (MSAs) have garnered interest for applications in catalysis, molecular storage, as drug delivery vectors or as drugs themselves. For example, M2L3-type architectures have been heavily investigated for their interactions with both canonical and non-canonical DNA constructs. Many MSAs, such as M2L4 cages, also feature internal cavities which make them suitable hosts to encapsulate guest molecules. With implementation of stimulus-responsive units, disassembly or other mechanisms can facilitate release of these guests.
Heterometallic MM′L3 structures are few and far between in the literature. To address this, a three-armed ligand system based on the PICTREN scaffold was designed. An M2L3-like MM′L pseudo-mesocate was obtained in a one-pot reaction from a tris-amino Co(PICTREN) precursor, bpyald and FeCl2. DNA binding studies revealed its DNA binding ability, albeit at slower rates compared to a structurally related DNA-binding helicate. In antiproliferative activity studies, IC50 values in the range of 17–26 μM in human cancer cell lines were found. The lower activity compared to the known DNA-binding helicate was attributed to differences in DNA binding and was comparable to that of Fe(bpy)3.
Often the cavity formed by M2L3-type structures is not appropriately sized to house guests. It can, however, be tuned in M2L4-type structures and many examples are known that host small molecules. In this regard, heterometallic MM′L4 MSAs were designed based on octahedral Ru or square planar Pt motifs (M = Pd, M’ = Pt or RuCl2) and investigated for their guest binding abilities. The heterometallic MSAs were prepared from bridging ligands that could act as H bond donors or acceptors or allowed hydrophobic interactions with guests. Positive charges contributed by the metal centres facilitated electrostatic interactions with anionic molecules which were disrupted to some extent by the endo-chlorido ligands of the octahedral Ru complexes. Their stimulus-responsive disassembly and reassembly enabled for some examples the reversibly release of guest molecules. Guest binding was found to be dependent on the complementary properties of the guest to the host in terms of charge, hydrophobicity, size and H bonding properties. This work represents the first example of the introduction of octahedral metal centres in heterodimetallic M2L4-type supramolecular architectures
Bridging Metals and Peptides: Introducing selectivity to transition metal complexes towards targeted cancer therapy
No full textMetal-based anticancer agents are a prominent feature in chemotherapeutics. Ruthenium complexes show increasing popularity over traditional platinum-based drugs to explore more selective and less toxic treatment options. Depending on the ligand of choice, organometallic compounds have are promising against primary tumours or metastases and “piano-stool” complexes of the general formula [MII/III(arene/Cp*(X)(Y)(Z)] have demonstrated to be particularly efficacious against primary tumours or metastases. The hydrophobic ring system gives the complex the ability to transverse through cell membranes into the cell, while the X, Y, and Z legs of the piano stool may be mono- or multidentate ligand systems such as bioactive moieties or anionic leaving groups, tunable for specific activity.
In this doctoral thesis, a library of metal-based N-heterocyclic carbene (NHC) complexes was synthesised based upon the piano-stool scaffold and characterised in terms of their chemical structure and their biological activity against different human cancer cell lines, showing moderate anticancer activity. Thioredoxin reductase (TrxR) inhibition studies showed unexpected potent inhibition was exhibited by the two Rh derivatives in the library, which will hopefully lead to the development of a generation of new compounds.
To introduce selectivity to piano-stool complexes and thereby reduce toxicity, a novel solid phase strategy was adopted to effect carbene activation on solid resin support, involving the conjugation of Ru(NHC) complexes to peptides utilising the carbene ligand system in the Ru(NHC) complex as the anchor. Selective conjugation was performed at different locations on the peptide backbone to compare synthetic accessibility as well as structure-activity relationship. All compounds were readily synthesised and purified, affording the products in high yields. The peptide conjugates synthesised in this manner were found to be stable to peptide isolation and purification, opening the door for many opportunities in the field of bioorganometallic chemistry.
The novel strategy was then applied to Os-, Rh-, and Ir(NHC) complexes. Choosing a peptide capable of targeting cell compartments and conjugating it to the different transition metal centres to compare accessibility and reproducibility of the conjugation strategy and comparing structure-activity relationships. The compounds were tested for antiproliferative activity in human cancer cell lines but were shown to be not cytotoxic. Despite a lack of cytotoxic activity, the work highlights a new and very useful tool in hand to further develop metallodrugs with targeting capabilities
Application of Advanced Bioanalytical Techniques to Studies of Oxaliplatin Chemotherapy
No full textOxaliplatin is a platinum anticancer drug approved for medical use in treating gastrointestinal
cancers. Organic cation transporters (OCTs) may contribute to the tissue accumulation and
unwanted toxicities of oxaliplatin.
The overall aim of this thesis was to develop new bioanalytical methodologies for studies of
oxaliplatin chemotherapy when given with OCT inhibitors (cimetidine or ergothioneine) for
modulating oxaliplatin toxicities.
To quantify intact oxaliplatin in human plasma, an ultraperformance liquid chromatographyinductively coupled plasma mass spectrometry bioanalytical method was developed and
validated. This improved method detected intact oxaliplatin at a retention time of 1.1 minutes
at concentrations 10 nM in 1 µL of methanol-deproteinised human plasma. To quantify
ergothioneine in cell lysates, a high-performance liquid chromatography-ultraviolet
bioanalytical method was established. These bioanalytical methods were applied to studies of
mechanisms whereby ergothioneine reduces platinum accumulation in HEK293-rOCTN1 and
HEK293-MOCK cells during oxaliplatin exposure, which identified two mechanisms: 1)
ergothioneine inhibition of OCTN1-dependent uptake of oxaliplatin, and 2) ligand
displacement reactions between ergothioneine and oxaliplatin in extracellular fluids forming
positively-charged Pt(diaminocyclohexane)-ergothioneine conjugates with reduced capacity
for cellular uptake. In an analysis of a clinical pharmacokinetic dataset, linear equations were
established for estimating area-under-the-plasma-concentration-versus-time-curve (AUC)
from end-of-infusion plasma concentrations of intact oxaliplatin (AUC = 2.231*end-ofinfusion plasma concentration) and free platinum (AUC = 2.335*end-of-infusion plasma
concentration). Together with other techniques, these AUC estimation methods were applied
to a preliminary blinded analysis of samples from patients (n=15) treated on the CITRON
clinical trial, which aimed to demonstrate whether cimetidine alters oxaliplatin
pharmacokinetics. Within-subject ratios of end-of-infusion plasma concentration and AUC of
intact oxaliplatin and free platinum, when oxaliplatin was given with cimetidine or placebo,
were close to one (mean ratios, 1.06-1.07) with 95% confidence intervals overlapping with
one, suggesting that cimetidine does not alter the pharmacokinetics of oxaliplatin in cancer
patients.
In conclusion, an improved bioanalytical method for the quantification of intact oxaliplatin in
human plasma was developed and validated. Together with other techniques, this method was
applied to studies of the clinical pharmacology of oxaliplatin focusing on its use with the OCT
inhibitors, cimetidine and ergothioneine, for modulating oxaliplatin toxicities
Mono- and multidentate anthracenyl-functionalised NHC organometallics: Surprising reactivity and anticancer activity
No full textMetal-based compounds featuring bioactive ligands have been widely used in a variety
of treatments such as chemotherapeutics. One of the notable ligand classes are Nheterocyclic
carbenes (NHCs) which can coordinate to a metal centre forming
anticancer metal–NHC complexes. To track them in cells, metal–NHC complexes can
be functionalised with a fluorescent moiety as an attractive design feature. For this
purpose, pro-carbenes featuring anthracenyl groups were prepared to form metal–
NHC compounds with the methyl-, pyridyl- or triazolyl-functionalised NHC ligand
potentially acting as mono- or bidentate ligands.
An extensive series of MII/III(cym/Cp*)(NHC) complexes (M = Ru, Os, Rh, Ir) was
synthesised and characterised. Some of the reactions of the pro-carbenes with
[Rh(Cp*)Cl2]2 resulted in the formation of unexpected structures. Intramolecular C–C
bond formation between the Cp* and anthracenyl groups with additional auxiliary
interactions between the Rh centre and anthracenyl moieties was observed, which
yielded polydentate ligands, i.e., hepta- and nonadentate ligand systems. The reaction
mechanism involves formation of a tetramethylfulvene complex via deprotonation of a
Cp* methyl group followed by metallocycloaddition and extraction of a chlorido ligand.
Some Rh–C interactions were extremely weak and could be easily displaced by
stronger electron donors such as 1,3,5-triaza-7-phosphaadamantane (pta). The
anticancer activity of the compounds in terms of in vitro cytotoxic activity against
different human cancer cell lines and cell morphology was investigated. The
complexes with monodentate NHC ligands were found to be cytotoxic with 50%
inhibitory concentrations (IC50) values in the low micromolar range, while the
complexes with C,N-chelating ligands and the Rh complexes with its nonadentately
coordinated ligand were found to exhibit greater activity with a slight decrease in the
IC50 values. The anticancer activity studies of the compounds were complemented by
experiments on the interactions of selected complexes with biomolecules amino acids
and DNA to identify biomolecular interaction potential. The reactions with the small
biomolecules proceeded quickly and resulted in the formation of adducts by
undergoing chlorido ligand exchange. A protein crystallographic study on the
interaction with hen egg white lysozyme revealed that the complex bound to L-aspartic
acid along with dissociation of the p-cymene ligand. These properties of the complexes
make them possible candidates for further development of anticancer drugs
Physicochemical properties of whey protein hydrolysates and their applications in infant formula
No full textWhey protein hydrolysates (WPHs) play a pivotal role in infant formula development,
offering enhanced functionality and nutritional benefits. WPHs produced using various
enzymes were characterised and applied in infant formula model emulsions. This study
aimed to fill the gaps in the current knowledge of the production and properties of
WPHs, as well as the properties of their application in infant formulas.
Real-time hydrolysis of whey protein isolate by bromelain was monitored using in-flow
small-angle X-ray scattering (SAXS). Whey protein molecules were measured with an
average size of ~ 20 Å. During hydrolysis, structural transformations including the
conversion of globular whey protein isolate molecules into Gaussian polypeptides were
examined. SAXS is a powerful tool to track protein hydrolysis dynamics and study
structural modifications.
WPHs produced via bromelain hydrolysis were investigated to stabilise infant formula
model emulsions. WPHs with lower degrees of hydrolysis (< 10%) exhibited superior
emulsion stabilisation, smaller oil droplet sizes, decreased viscosity and improved
storage stability. The proteins/peptides (10 – 15 kDa) in WPHs could be adsorbed on
the oil droplets and stabilise emulsions.
Different WPHs prepared using various enzymes (trypsin, pepsin, bromelain, papain
and flavourzyme) and their role in stabilising infant formula model emulsions were
investigated. Unique peptide sequences with high expression on interfacial
proteins/peptides in WPHs were identified, which strongly depended on their chain
length (10 – 20), molecular weight, higher net charge, higher isoelectric point and
amphipathy (positive hydrophobicity). These descriptions would offer insights for
WPHs tailored in infant formula development.
A novel technique, ultrasound pre-treatment, was used to assist with enzymatic
hydrolysis of whey protein using different enzymes (trypsin, pepsin, bromelain and
papain). The synergy enhanced hydrolysis efficiency, modified protein structures, and
improved functional properties, as well as effectively reduced allergenicity of βlactoglobulin in intact whey protein. These findings were strongly associated with
enzyme specificity. The enhancement of ultrasound-assisted enzymatic hydrolysis
would be considered to apply in infant formula. Overall, the understanding of WPHs
and their potential application in infant formula development would offer insights into
optimising infant formula formulations
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