The activity of a Ga(III) catecholate complex against Aspergillus fumigatus in conditions mimicking cystic fibrosis lung and inhaled formulations for its pulmonary administration.

Azole-resistant Aspergillus fumigatus (A. fumigatus) is an emerging worldwide pathogen. Pulmonary aspergillosis primarily affects severely immunocompromised patients and is also a particularly critical condition for cystic fibrosis (CF) patients. A recently designed gallium polypyridyl catecholate complex, GaS1, has previously demonstrated in vitro and in vivo antimicrobial activity against Gram-negative bacteria. In the present work GaS1 activity was assessed against A. fumigatus clinical isolates in a novel air-liquid-interface lung infection model, mimicking the conditions found in the CF airways. Furthermore, in this study both a solution for nebulisation and dry powders for inhalation were developed with a view to optimising GaS1 delivery to the lung. The solution for nebulisation was characterised for its osmolality and pH, while the dry powders were characterised by scanning electron microscopy, powder X-ray diffraction, thermal analysis and laser light scattering particle size analysis. The aerodynamic deposition profiles of all formulations were determined using a next generation impactor. GaS1, tested in a concentration range of 0.016-0.5 mg/mL, inhibited the growth of A. fumigatus lung isolates in a complex host-environment-mimicking medium at the non-toxic concentration of 0.063 mg/mL. A marked dose-dependent antifungal activity of GaS1 was also observed in the presence of differentiated human distal lung epithelial cells (NCI-H441) at the air liquid interface, with nearly no fungal growth detected at the macroscopic and microscopic level. A solution for nebulisation and three different dry powder inhaler formulations, prepared by spray-drying GaS1 with different concentrations of L-leucine, displayed suitable aerodynamic characteristics for GaS1 delivery to the lungs, while maintaining excellent antifungal activity. Overall, the results obtained highlight the potential of gallium-polypyridyl catecholate complexes for the management of difficult-to-treat A. fumigatus pulmonary infections.

Quantitative proteomic analysis reveals Ga(III) polypyridyl catecholate complexes disrupt Aspergillus fumigatus mitochondrial function.

Infections caused by the airborne fungal pathogen, Aspergillus fumigatus, are increasing in severity due to growing numbers of immunocompromised individuals and the increasing incidence of antifungal drug resistance, exacerbating treatment challenges. Gallium has proven to be a strong candidate in the fight against microbial pathogens due to its iron-mimicking capability and substitution of Ga(III) in place of Fe(III), disrupting iron-dependent pathways. Since the antimicrobial properties of 2,2'-bipyridine and derivatives have been previously reported, we assessed the in vitro activity and proteomic effects of a recently reported heteroleptic Ga(III) polypyridyl catecholate compound against A. fumigatus. This compound has demonstrated promising growth-inhibition and impact on the A. fumigatus proteome compared to untreated controls. Proteins associated with DNA replication and repair mechanisms along with lipid metabolism and the oxidative stress responses were elevated in abundance compared to control. Crucially, a large number of mitochondrial proteins were reduced in abundance. Respiration is an important source of energy to fuel metabolic processes required for growth, survival and virulence, the disruption of which may be a viable strategy for the treatment of microbial infections.

Click-Capable Phenanthriplatin Derivatives as Tools to Study Pt(II)-Induced Nucleolar Stress.

It is well established that oxaliplatin, one of the three Pt(II) anticancer drugs approved worldwide, and phenanthriplatin, an important preclinical monofunctional Pt(II) anticancer drug, possess a different mode of action from that of cisplatin and carboplatin, namely, the induction of nucleolar stress. The exact mechanisms that lead to Pt-induced nucleolar stress are, however, still poorly understood. As such, studies aimed at better understanding the biological targets of both oxaliplatin and phenanthriplatin are urgently needed to expand our understanding of Pt-induced nucleolar stress and guide the future design of Pt chemotherapeutics. One approach that has seen great success in the past is the use of Pt-click complexes to study the biological targets of Pt drugs. Herein, we report the synthesis and characterization of the first examples of click-capable phenanthriplatin complexes. Furthermore, through monitoring the relocalization of nucleolar proteins, RNA transcription levels, and DNA damage repair biomarker γH2AX, and by investigating their in vitro cytotoxicity, we show that these complexes successfully mimic the cellular responses observed for phenanthriplatin treatment in the same experiments. The click-capable phenanthriplatin derivatives described here expand the existing library of Pt-click complexes. Significantly they are suitable for studying nucleolar stress mechanisms and further elucidating the biological targets of Pt complexes.

First-in-class metallo-PROTAC as an effective degrader of select Pt-binding proteins.

We report the development of the first metallo-PROTAC, specifically a Pt-PROTAC, that can effectively degrade select Pt(II)-binding proteins. The Pt-PROTAC prototype successfully degraded thioredoxin-1 and thioredoxin reductase-1 in multiple myeloma cancer cell lines. Metallo-PROTACs will have important applications in the identification of metal binding proteins and as chemotherapeutic agents.

Comparison of click-capable oxaliplatin and cisplatin derivatives to better understand Pt(ii)-induced nucleolar stress.

Pt(ii) chemotherapeutic complexes have been used as predominant anticancer drugs for nearly fifty years. Currently there are three FDA-approved chemotherapeutic Pt(ii) complexes: cisplatin, carboplatin, and oxaliplatin. Until recently, it was believed that all three complexes induced cellular apoptosis through the DNA damage response pathway. Studies within the last decade, however, suggest that oxaliplatin may instead induce cell death through a unique nucleolar stress pathway. Pt(ii)-induced nucleolar stress is not well understood and further investigation of this pathway may provide both basic knowledge about nucleolar stress as well as insight for more tunable Pt(ii) chemotherapeutics. Through a previous structure-function analysis, it was determined that nucleolar stress induction is highly sensitive to modifications at the 4-position of the 1,2-diaminocyclohexane (DACH) ring of oxaliplatin. Specifically, more flexible and less rigid substituents (methyl, ethyl, propyl) induce nucleolar stress, while more rigid and bulkier substituents (isopropyl, acetamide) do not. These findings suggest that a click-capable functional group can be installed at the 4-position of the DACH ring while still inducing nucleolar stress. Herein, we report novel click-capable azide-modified oxaliplatin mimics that cause nucleolar stress. Through NPM1 relocalization, fibrillarin redistribution, and γH2AX studies, key differences have been identified between previously studied click-capable cisplatin mimics and these novel click-capable oxaliplatin mimics. These complexes provide new tools to identify cellular targets and localization through post-treatment Cu-catalyzed azide-alkyne cycloaddition and may help to better understand Pt(ii)-induced nucleolar stress. To our knowledge, these are the first reported oxaliplatin mimics to include an azide handle, and cis-[(1R,2R,4S) 4-methylazido-1,2-cyclohexanediamine]dichlorido platinum(ii) is the first azide-functionalized oxaliplatin derivative to induce nucleolar stress.

Synthesis, characterisation and antibacterial activity of novel Ga(III) polypyridyl catecholate complexes.

Ga(III) polypyridyl catecholate complexes of type [Ga(bipy)2(O,O)](NO3) or [Ga(phen)2(O,O)](NO3) respectively were readily synthesised on reaction of Ga(NO3)3 in methanol with 1 equivalent of catecholate ligand (2,3-DHBA, 3,4-DHBA, 2,3,4-THBA or CafA) and then 2 equivalents of either bipy or phen. The complexes were characterised in full including by X-ray crystallography, which established that the catecholate ligands coordinate the Ga(III) centres in a bidentate manner via the two deprotonated hydroxy groups. All Ga(III) complexes exhibited good in vitro antibacterial activity against the Gram-negative pathogenic bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. The complexes were inactive against the Gram-positive pathogenic bacteria Staphylococcus aureus including against a methicillin-resistant Staphylococcus aureus strain (MRSA). [Ga(bipy)2(2,3-DHBA-2H)](NO3)·1.5H2O (1) was shown to be non toxic in vivo in larvae of Galleria mellonella at doses up to 2000 µg mL-1 and to offer protection at doses of 100 and 250 µg mL-1 at 48 and 96 h to larvae infected with P. aeruginosa.

A trans-Pt(II) hedgehog pathway inhibitor complex with cytotoxicity towards breast cancer stem cells and triple negative breast cancer cells.

The first example of a Pt complex of GANT61, a hedgehog (Hh) pathway inhibitor is reported. Reaction of cis-[Pt(II)Cl2(dmso)2] with one equivalent of 4-pyridine carboxaldehyde (4-PCA, control ligand) or one equivalent of GANT61 (Hh pathway inhibitor) in acetone at rt for 30 minutes afforded trans-[Pt(II)Cl2(dmso)(4-PCA)] (1) and trans-[Pt(II)Cl2(dmso)(GANT61)] (2) respectively, where 4-PCA and GANT61 are N-donor ligands. The structures of 1 and 2 were fully characterised by elemental analysis, 1H NMR, 13C NMR and IR spectroscopy and X-ray crystallography. 1 and 2 undergo isomerisation from trans- to cis-in solution and therefore the biological activity of 2 is also associated with the cis-configuration. The in vitro cytotoxicity data show that 2 is a potent inhibitor of the growth of breast CSC-depleted HMLER and breast CSC-enriched HMLER-shEcad cells. Furthermore 2 markedly reduced the size and viability and significantly reduced the number of CSC-enriched HMLER-shEcad mammospheres formed. 2 also induced apoptosis with low micromolar IC50 values against two triple negative breast cancer lines, MDA-MB-231 (MDA231) and BT549. 2, which possesses the Hh pathway inhibitor GANT61 as an N donor ligand exhibits far superior anti-CSC activity including in the CSC-enriched mammosphere model and activity against TNBC cells as compared to its control analogue, the trans-Pt(II) 4-PCA complex 1. The trans-Pt GANT61 complex 2 has also been shown to cause DNA damage and inhibit the Hh pathway at the level of GLI.

Advances in the Design and Development of PROTAC-mediated HDAC Degradation.

Due to developments in modern chemistry, previously uundruggable substrates are now targetable thanks to selective degradation using the ubiquitin-proteasomal degradation system. PROteolysis TArgeting Chimeras (PROTACs) are heterobifunctional molecules designed specifically to degrade target proteins. They are of significant interest to industry and academia as they are highly specific and can target previously undruggable target proteins from transcription factors to enzymes. More than 15 degraders are expected to be evaluated in clinical trials by the end of 2021. Herein, we describe recent advances in the design and development of PROTAC-mediated degradation of histone deacetylases (HDACs). PROTAC-mediated degradation of HDACs can offer some significant advantages over direct inhibition, such as the use of substoichiometric doses and the potential to disrupt enzyme-independent HDAC function. We discuss the potential implication of the degradation of HDACs in comparison with HDAC knockout studies. Along with the selection of HDAC inhibitors and E3 ligase ligands for the design of PROTACs. The potential utility of HDAC PROTACs in various disease pathologies from cancer to inflammation to neurodegeneration is driving the interest in this field.

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles.

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

A single microbubble formulation carrying 5-fluorouridine, Irinotecan and oxaliplatin to enable FOLFIRINOX treatment of pancreatic and colon cancer using ultrasound targeted microbubble destruction.

FOLFIRINOX and FOLFOXIRI are combination chemotherapy treatments that incorporate the same drug cocktail (folinic acid, 5-fluorouracil, oxaliplatin and irinotecan) but exploit an altered dosing regimen when used in the management of pancreatic and colorectal cancer, respectively. Both have proven effective in extending life when used to treat patients with metastatic disease but are accompanied by significant adverse effects. To facilitate improved tumour-targeting of this drug combination, an ultrasound responsive microbubble formulation loaded with 5-fluorouridine, irinotecan and oxaliplatin (FIRINOX MB) was developed and its efficacy tested, together with the non-toxic folinic acid, in preclinical murine models of pancreatic and colorectal cancer. A significant improvement in tumour growth delay was observed in both models following ultrasound targeted microbubble destruction (UTMD) mediated FIRINOX treatment with pancreatic tumours 189% and colorectal tumours 82% smaller at the conclusion of the study when compared to animals treated with a standard dose of FOLFIRINOX. Survival prospects were also improved for animals in the UTMD mediated FIRINOX treatment group with an average survival of 22.17 ± 12.19 days (pancreatic) and 44.40 ± 3.85 days (colorectal) compared to standard FOLFIRINOX treatment (15.83 ± 4.17 days(pancreatic) and 37.50 ± 7.72 days (colon)). Notably, this improved efficacy was achieved using FIRINOX MB that contained 5-fluorouricil, irinotecan and oxaliplatin loadings that were 13.44-fold, 9.19-fold and 1.53-fold lower than used for the standard FOLFIRINOX treatment. These results suggest that UTMD enhances delivery of FIRINOX chemotherapy, making it significantly more effective at a substantially lower dose. In addition, the reduced systemic levels of 5-fluorouracil, irinotecan and oxaliplatin should also make the treatment more tolerable and reduce the adverse effects often associated with this treatment.

Quantitative proteomic reveals gallium maltolate induces an iron-limited stress response and reduced quorum-sensing in Pseudomonas aeruginosa.

Gallium-based drugs have been repurposed as antibacterial therapeutic candidates and have shown significant potential as an alternative treatment option against drug resistant pathogens. The activity of gallium (Ga3+) is a result of its chemical similarity to ferric iron (Fe3+) and substitution into iron-dependent pathways. Ga3+ is redox inactive in typical physiological environments and therefore perturbs iron metabolism vital for bacterial growth. Gallium maltolate (GaM) is a well-known water-soluble formulation of gallium, consisting of a central gallium cation coordinated to three maltolate ligands, [Ga(Maltol-1H)3]. This study implemented a label-free quantitative proteomic approach to observe the effect of GaM on the bacterial pathogen, Pseudomonas aeruginosa. The replacement of iron for gallium mimics an iron-limitation response, as shown by increased abundance of proteins associated with iron acquisition and storage. A decreased abundance of proteins associated with quorum-sensing and swarming motility was also identified. These processes are a fundamental component of bacterial virulence and dissemination and hence suggest a potential role for GaM in the treatment of P. aeruginosa infection.

Synthesis and characterisation of Co(iii) complexes of N-formyl hydroxylamines and antibacterial activity of a Co(iii) peptide deformylase inhibitor complex.

The X-ray crystal structure and pKa values of GSK322, a well-known and effective peptide deformylase inhibitor and antibacterial drug candidate, are reported. The first examples of Co(iii) complexes of N-formyl hydroxylamines are reported. Reaction of N-hydroxy-N-phenylformamide (HFA) with [Co(tren)Cl2]Cl and [Co(tpa)Cl2]Cl (where tren = tris(2-aminoethyl)amine, tpa = tris(2-pyridylmethyl)amine) with one equivalent of NaOH in H2O afforded [Co(tren)(HFA-1H)](PF6)1.5Cl0.5 (1) and [Co(tpa)(HFA-1H)]Cl2 (2), respectively. X-ray crystal structures of both complexes revealed that the N-formyl hydroxylamine group acts as a bidentate ligand, coordinating the Co(iii) centres via the carbonyl oxygen and deprotonated hydroxy group (O,O'), a coordination mode typically observed for closely related mono-deprotonated hydroxamic acids. Reaction of the N-formyl hydroxylamine-based GSK322 with [Co(tpa)Cl2]Cl afforded the corresponding Co(iii) chaperone complex of the peptide deformylase inhibitor, [Co(tpa)(GSK322-1H)](PF6)2. GSK322 and [Co(tpa)(GSK322-1H)](PF6)2 exhibited better Gram-positive activity than Gram-negative, where low MICs (1.56-6.25 µM) were determined for S. aureus strains, independent of their antibiotic susceptibility.

Exploiting azide-alkyne click chemistry in the synthesis, tracking and targeting of platinum anticancer complexes.

Click chemistry is fundamentally important to medicinal chemistry and chemical biology. It represents a powerful and versatile tool, which can be exploited to develop novel Pt-based anticancer drugs and to better understand the biological effects of Pt-based anticancer drugs at a cellular level. Innovative azide-alkyne cycloaddition-based approaches are being used to functionalise Pt-based complexes with biomolecules to enhance tumour targeting. Valuable information in relation to the mechanisms of action and resistance of Pt-based drugs is also being revealed through click-based detection, isolation and tracking of Pt drug surrogates in biological and cellular environments. Although less well-explored, inorganic Pt-click reactions enable synthesis of novel (potentially multimetallic) Pt complexes and provide plausible routes to introduce functional groups and monitoring Pt-azido drug localisation.

Ni(II), Pd(II), and Pt(II) Complexes of the Hedgehog Pathway Inhibitor GANT61-D.

GANT61-D is an important hedgehog pathway inhibitor and an interesting ligand candidate for metal coordination. The first examples of metal complexes of the potent hedgehog pathway inhibitor GANT61-D are described. The reaction of Ni(II), Pd(II), and Pt(II) precursors with the hedgehog pathway inhibitor GANT61-D gave [NiII(GANT61-D)(OH2)3(µ2-SO4)(µ3-SO4)] (1), [PdII(Cl)(GANT61-D)]Cl (2), [PtII(Cl)(GANT61-D)]Cl, and [PtII(CBDCA-2H)(GANT61-D)]. X-ray crystal structure analysis revealed that GANT61-D is a versatile N-donor ligand that can act as a bidentate ligand via the diaminopropane (DAP) N atoms or a tridentate ligand via the DAP N atoms and one dimethylaniline N atom. Protonation constants of the GANT61-D ligand in water and in a 60:40 (w/w) dimethyl sulfoxide-water solvent mixture were determined. Potentiometric and spectroscopic data on the NiII(GANT61-D) system indicate the formation of octahedral 1:1 species with medium stability in solution. 1 and 2 exhibited noteworthy in vitro cytotoxicity against medulloblastoma cancer cells.

Au(III) and Pt(II) Complexes of a Novel and Versatile 1,4-Disubstituted 1,2,3-Triazole-Based Ligand Possessing Diverse Secondary and Tertiary Coordinating Groups.

A novel 1,4-disubstituted 1,2,3-triazole-based ligand, 2-(4-(pyridin-2-yl)-1 H-1,2,3-triazol-1-yl)propane-1,3-diamine (ptpd), which possesses pyridyl and diamino secondary and tertiary coordinating groups was synthesized in excellent yield. The reactivity of 2-(1-phenyl-1 H-1,2,3-triazol-4-yl)pyridine (ptp), di- tert-butyl (2-azidopropane-1,3-diyl)dicarbamate (Boc2-ptpd), and ptpd·3HCl was investigated with Au(III) and Pt(II) precursors. Analysis including X-ray crystal structures of [Au(III)Cl3(ptp)] (1), [Au(III)Cl2(ptpd)][Au(I)Cl2][OH]{[NaAuCl4·2H2O]} n (3), and [Pt(II)Cl2(ptpdH2)][PtCl4] (4) revealed that ptpd (i) serves as a monodentate ligand for Au(III) coordinating to the metal center via the pyridine nitrogen only, (ii) preferentially coordinates Au(III) via the bidentate diamino group over the monodentate pyridine group, (iii) can coordinate Pt(II) in a bidentate fashion via the pyridyl nitrogen and the triazole N-3, and (iv) can bridge two Pt(II) centers through bidentate chelation at the diamino group and bidentate chelation via the pyridyl nitrogen and the triazole N-3. ptpd represents a versatile ligand template for the development of mixed metal complexes.

Development of a novel carboplatin like cytoplasmic trackable near infrared fluorophore conjugate via strain-promoted azide alkyne cycloaddition.

The successful design and pre-clicked synthesis of a non-toxic and cytosol trackable carboplatin-like near infrared fluorophore conjugate via strain-promoted azide alkyne cycloaddition (SPAAC) is reported. Reaction of cis-[Pt(2-azidopropane-1,3-diamine)(cbdca)] (cbdca = cyclobutane-1,1-dicarboxylato) and a bicyclo[6.1.0]non-4-yne near-infrared (NIR) azadipyrromethene fluorophore gave the corresponding clicked Pt-Fluorophore conjugate. The X-ray crystal structure of cis-[Pt(2-azidopropane-1,3-diamine)(cbdca)] was determined featuring the azide on the bidentate 1,3-diaminopropane ligand. The Pt-fluorophore conjugate is the first example of a Pt conjugate clicked via strain-promoted azide alkyne cycloaddition (SPAAC) where the reactive azide handle is on the amine carrier ligand. The in vitro cytotoxicity and widefield fluorescence imaging of the Pt-Fluorophore conjugate in A2780P and A2780cisR cells are described.

Correction: Griffith, D.M., et al. Novel Improved Synthesis of HSP70 Inhibitor, Pifithrin-µ. In Vitro Synergy Quantification of Pifithrin-µ Combined with Pt Drugs in Prostate and Colorectal Cancer Cells. Molecules 2016, 21, 949.

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Novel Improved Synthesis of HSP70 Inhibitor, Pifithrin-µ. In Vitro Synergy Quantification of Pifithrin-µ Combined with Pt Drugs in Prostate and Colorectal Cancer Cells.

We describe a novel improved approach to the synthesis of the important and well-known heat shock protein 70 inhibitor (HSP70), pifithrin-µ, with corresponding and previously unreported characterisation. The first example of a combination study comprising HSP70 inhibitor pifithrin-µ and cisplatin or oxaliplatin is reported. We have determined, using the Chou-Talalay method, (i) moderate synergistic and synergistic effects in co-treating PC-3 prostate cancer cells with pifithrin-µ and cisplatin and (ii) significant synergistic effects including strong synergism in cotreating HT29 colorectal cancer cells with oxaliplatin and pifithrin-µ.

Current and potential applications of bismuth-based drugs.

: Bismuth compounds have been used extensively as medicines and in particular for the treatment of gastrointestinal ailments. In addition to bismuth's well known gastroprotective effects and efficacy in treating H. pylori infection it also has broad anti-microbial, anti-leishmanial and anti-cancer properties. Aspects of the biological chemistry of bismuth are discussed and biomolecular targets associated with bismuth treatment are highlighted. This review strives to provide the reader with an up to date account of bismuth-based drugs currently used to treat patients and discuss potential medicinal applications of bismuth drugs with reference to recent developments in the literature. Ultimately this review aims to encourage original contributions to this exciting and important field.