Application of zirconium MOFs in drug delivery and biomedicine

Nanoparticulate metal-organic frameworks (MOFs) have the requisite high storage capacities, tailorable structures, ease of functionalisation, and excellent biocompatibilities for application as nanoscale drug delivery devices (DDSs). Zirconium MOFs in particular combine optimal stability towards hydrolysis and postsynthetic modification with low toxicity, and so are particularly suited for biological applications. This review covers the use of Zr MOFs as DDSs with focus on the different physical properties that makes them attractive for use. The various methods for modifying the surfaces of Zr MOFs are described with pertinent examples of the resulting enhancements in aqueous stability, colloidal dispersion, and stimuli-responsive drug release. The in vitro and in vivo application of Zr MOFs for photodynamic therapy and drug delivery are discussed with respect to the structural features of the MOFs and their surface functionality, and perspectives on their future applications and analogous hafnium MOFs are given

Targeted delivery of platinum-based anticancer complexes

The most widely used anticancer drugs are platinum-based. Their efficacy might be improved by carriers which can transport large numbers of Pt centres, shield the drug from premature activation, and/or deliver Pt specifically to cancer cells using vectors which recognise specific targets. We describe recent progress using functionalized carbon nanotubes (CNTs) and nanorods, hollow Prussian blue (HPB), magnetic iron oxide and gold nanoparticles, liposomes, nanogels and polymers, as well as active targeting by conjugation to biodegradable proteins and peptides (e.g. EGF, heparin, herceptin, somatostatin and TAT). Spatially targeted activation of PtIV prodrugs using light is also a promising approach. Interestingly, use of these new delivery and targeting systems for platinum drugs can lead to species with unusual reactivity which can kill cancer cells by new mechanisms

Applications of Functionalized Fullerenes in Tumor Theranostics

Functionalized fullerenes with specific physicochemical properties have been developed for cancer diagnosis and therapy. Notably, metallofullerene is a new class of magnetic resonance imaging (MRI) contrast-enhancing agent, and may have promising applications for clinical diagnosis. Polyhydroxylated and carboxyl fullerenes have been applied to photoacoustic imaging. Moreover, in recent years, functionalized fullerenes have shown potential in tumor therapies, such as photodynamic therapy, photothermal treatment, radiotherapy and chemotherapeutics. Their antitumor effects may be associated with the modulation of oxidative stress, anti-angiogenesis, and immunostimulatory activity. While various types of novel nanoparticle agents have been exploited in tumor theranostics, their distribution, metabolism and toxicity in organisms have also been a source of concern among researchers. The present review summarizes the potential of fullerenes as tumor theranostics agents and their possible underlying mechanisms are discussed

Targeting the folate receptor: Improving efficacy in inorganic medicinal chemistry

The discovery of the high-affinity, high-specificity folate receptor in mamalian kidney cells, coupled with the ability of folate to enter cells by folate receptor-mediated endocytosis and the subsequent elucidation of the folate receptor’s overexpression in specific cancer cell types; heralded the arrival of the area of chemotherapeutic folate targeting. The application of purely organic folate-based small-molecule drug conjugates that selectively target the folate receptor, which is over expressed in several diseases such as cancer, is well established. The application of inorganic folate-targeted drugs offers significant potential to expand and enhance this therapeutic approach. From the data made available to date, it is apparent that this aspect of inorganic medicinal chemistry is in its youth but has the capability to contribute greatly to cancer research, both in therapy and diagnosis. The union of folate-receptor targeting and inorganic medicine may also lead to the development of treatments for disorders such as chronic-inflammation, tuberculosis, neurodegenerative disease and leishmaniasis. In this review, we summarize what is known about the coordination chemistry of folic acid and the therapeutic potential of such complexes. We also describe approaches adopted to conjugate platinum drugs to folate- or folate-carrier- systems and their prospective ability to overcome problems associated with unwanted side-effects and resistance by improving their delivery and/or selectivity. The literature pertaining to non-platinum metal complex conjugates with folic acid is also reviewed revealing that this is an area that offers significant potential to develop targeted therapeutic approaches in areas such as chemotherapy and molecular imaging for diagnostics

Selective Surface PEGylation of UiO-66 Nanoparticles for Enhanced Stability, Cell Uptake, and pH-Responsive Drug Delivery.

The high storage capacities and excellent biocompatibilities of metal-organic frameworks (MOFs) have made them emerging candidates as drug-delivery vectors. Incorporation of surface functionality is a route to enhanced properties, and here we report on a surface-modification procedure-click modulation-that controls their size and surface chemistry. The zirconium terephthalate MOF UiO-66 is (1) synthesized as ∼200 nm nanoparticles coated with functionalized modulators, (2) loaded with cargo, and (3) covalently surface modified with poly(ethylene glycol) (PEG) chains through mild bioconjugate reactions. At pH 7.4, the PEG chains endow the MOF with enhanced stability toward phosphates and overcome the "burst release" phenomenon by blocking interaction with the exterior of the nanoparticles, whereas at pH 5.5, stimuli-responsive drug release is achieved. The mode of cellular internalization is also tuned by nanoparticle surface chemistry, such that PEGylated UiO-66 potentially escapes lysosomal degradation through enhanced caveolae-mediated uptake. This makes it a highly promising vector, as demonstrated for dichloroacetic-acid-loaded materials, which exhibit enhanced cytotoxicity. The versatility of the click modulation protocol will allow a wide range of MOFs to be easily surface functionalized for a number of applications

The Photosensitizer Temoporfin (mTHPC) – Chemical, Pre‐clinical and Clinical Developments in the Last Decade†‡

This review follows the research, development and clinical applications of the photosensitizer 5,10,15,20‐tetra(m‐hydroxyphenyl)chlorin (mTHPC, temoporfin) in photodynamic (cancer) therapy (PDT) and other medical applications. Temoporfin is the active substance in the medicinal product Foscan® authorized in the EU for the palliative treatment of head and neck cancer. Chemistry, biochemistry and pharmacology, as well as clinical and other applications of temoporfin are addressed, including the extensive work that has been done on formulation development including liposomal formulations. The literature has been covered from 2009 to early 2022, thereby connecting it to the previous extensive review on this photosensitizer published in this journal [Senge, M. O. and J. C. Brandt (2011) Photochem. Photobiol. 87, 1240–1296] which followed its way from initial development to approval and clinical application

Hybrid materials for biomedical applications

Ο καρκίνος είναι μια παγκόσμια αιτία θανάτου και ανακαλύπτονται νέοι τρόποι απεικόνισης και θεραπείας. Προτάθηκε ένα νέο υβριδικό υλικό αποτελούμενο από κβαντικές τελείες άνθρακα (CQDs), οξείδιο του ψευδαργύρου (ZnO) και πορφυρίνη, που προοριζόταν να είναι ταυτόχρονα απεικονιστικό και θεραπευτικό υλικό. Η ηλεκτροχημική διαδικασία κβαντικών τελειών άνθρακα είναι μια χαμηλού κόστους ,καινοτόμος μέθοδος. Οι εξαιρετικές ιδιότητες φθορισμού των CQDs τα καθιστούν πολλά υποσχόμενο υλικό για μοριακή απεικόνιση. Τα παράγωγα της πορφυρίνης έχουν τη δυνατότητα να χρησιμοποιηθούν στη φωτοδυναμική θεραπεία. Τα νανοσωματίδια ZnO λόγω της ενισχυμένης διαπερατότητάς τους και του αποτελέσματος κατακράτησης έχουν τη δυνατότητα να γίνουν ένας πολλά υποσχόμενος αντικαρκινικός παράγοντας. Η τοξικότητα των CQDs, της πορφυρίνης και του Zno δοκιμάστηκε με χρωματομετρικό προσδιορισμό ΜΤΤ σε φυσιολογικές κυτταρικές σειρές HEK231 και καρκινικές κυτταρικές σειρές A549, MCF-7 και MDA-MB-231.Cancer is a worldwide cause of death and new ways of imaging and therapy are being discovered. A new hybrid material was proposed consisted of carbon quantum dots, ZnO and porphyrin, intended to be a theranostic material. Carbon quantum dots electrochemical process is a low cost and innovative method. CQDs excellent fluorescence properties make them promising material for molecular imaging. Porphyrin’s derivatives have the potential to be employed in Photodynamic therapy. ZnO nanoparticles due to their enhanced permeability and retention effect have the potential to become a promising anticancer effect. The toxicity of CQDs, porphyrin and Zno was tested by MTT colorimetric assay in normal cell lines HEK231 and cancer cell lines A549, MCF-7 and MDA-MB-231

The Membrane as a barrier or target in cancer chemotherapy

The overall aim of the project was to investigate the role of the cell membrane as a barrier and/or target for drug action and relate this to the development of strategies for overcoming multiple drug resistance (MDR). The effects of doxorubicin on various bacterial strains expressing different levels of anionic phospholipid were compared. Giowth of wild-type Echerichia coli (E. coli) strain MRE600 was severely affected up to 9 hours following doxorubicin treatment (15uM), but resistance occurred after 9 hours. E. coli strain FIDL1 1 was resistant to doxorubicin (1 O0piM) over 9 hours, however, increasing the anionic lipid content showed little difference in sensitivity. The mouse mammary tumour cell line (EMT6-S) and MDR sub-line (EMT6-R) were characterised with regard to growth kinetics, susceptibility to doxorubicin and membrane lipid composition. The log phase doubling times (h) were found to be 21.8 (EMT6-S)and 25.0 (EMT6-R) and the IC 50 values for doxorubicin to be 2.2 x 10-8 M and 1.8 x 10-6 M for EMT6-S and EMT6-R cells, respectively. No difference was observed between the phospholipid profiles of the two cell lines and total fatty acid composition was similar, however, the level of linoleic acid appeared to be higher in the resistant cells. The photocytotoxicity of the cationic dyes methylene blue (MB), toluidine blue (TBO) and Victoria blue BO (VBBO) against the EMT6 cell lines was compared to the cyotoxic effect of doxorubicin and cis-platinurn. The cytotoxic effect of VBBO was enhanced 10-fold by illumination (7.2 J cm2) in both EMT6-S and EMT6-R cells. In order to overcome resistance, however, the EMT6-R cells required a 10-fold greater level of the dye than the parental cells to reach an IC50 value. By contrast, doxorubicin required almost a 100-fold increase in concentration to overcome this resistance. Pre-treatment of EMT6-S and EMT6-R cells with low concentrations of VBBO resulted in a 2-fold increase in doxorubicin toxicity in both cell lines. Pre-treatment with MB and TBO resulted in a 1.4-fold and 2-fold increase in doxorubicin toxicity, respectively, in the sensitive cells, increasing to 2-fold and 3-fold, respectively in the resistant cells. Glutathione (GSH) depletion of EMT6-S and EMT6-R cells did not enhance the photocytotoxicity of VBBO, suggesting that the primary site of action of VBBO is at an intracellular site not protected by GSH or that the mechanism of action is not via the in situ generation of singlet oxygen. Addition of the chemosensitizer, verapamil (7gM), increased the efficacy of doxorubicin by 2-fold in EMT6-S cells and by 18-fold in EMT6-R cells. By contrast, the presence of verapamil did not increase the cytotoxicity of YBBO in either cell line. A series of compounds, PVB, MVB and MOVB, based on the skeleton of VBBO was examined. VBBO was found to be the most effective photosensitizer. The rate of uptake for VBBO, MVB and PVB appeared to be very similar, whereas that of MOVB was slower. The uptake/dose trend was also similar four all four drugs tested and conelated to the levels of lipophilicity of the agents. Confocal microscopy studies showed all the photosensitizers to be distributed widely throughout the cytoplasm, with considerable accumulation of VBBO and PVB in the perinuclear region. Time course studies showed the intracellular distribution of VBBO in both cell lines to be similar, although uptake of the drug appeared slower in the resistant cell line. VBBO was clearly localised throughout the cytoplasm, in a punctate pattern, which may be consistent with the widespread distribution of mitochondria. No interaction with the plasma membrane was evident. By contrast, doxorubicin was found to localise mainly in the nucleus of the sensitive cell line, whereas no nuclear involvement was seen in the resistant cells. The drug was also effluxed more rapidly from EMT6-R cells than EMT6-S cells. Time course studies with EMT6-S cells showed that the drug clearly interacts with both the plasma membrane and the nucleus. These results indicate that the main modes of action for the two drugs differ markedly, suggesting interaction with both the membrane and the nucleus in the case of doxorubicin, but possibly mitochondrial involvement for VBBO

Mechanisms for Tuning Engineered Nanomaterials to Enhance Radiation Therapy of Cancer.

Engineered nanomaterials that produce reactive oxygen species on exposure to X- and gamma-rays used in radiation therapy offer promise of novel cancer treatment strategies. Similar to photodynamic therapy but suitable for large and deep tumors, this new approach where nanomaterials acting as sensitizing agents are combined with clinical radiation can be effective at well-tolerated low radiation doses. Suitably engineered nanomaterials can enhance cancer radiotherapy by increasing the tumor selectivity and decreasing side effects. Additionally, the nanomaterial platform offers therapeutically valuable functionalities, including molecular targeting, drug/gene delivery, and adaptive responses to trigger drug release. The potential of such nanomaterials to be combined with radiotherapy is widely recognized. In order for further breakthroughs to be made, and to facilitate clinical translation, the applicable principles and fundamentals should be articulated. This review focuses on mechanisms underpinning rational nanomaterial design to enhance radiation therapy, the understanding of which will enable novel ways to optimize its therapeutic efficacy. A roadmap for designing nanomaterials with optimized anticancer performance is also shown and the potential clinical significance and future translation are discussed

The effect of surface functionalisation on cancer cells internalisation and selective cytotoxicity of zirconium metal organic frameworks

A considerable amount of effort has been directed to develop porous materials as drug delivery systems (DDSs) – one of the most promising emerging applications in healthcare, as most anticancer therapeutics have toxic dose dependence due to a lack of tumour selectivity – as their hierarchical porosity can be used to store and release challenging drugs. Among them, Metal-Organic Frameworks (MOFs) – emerging hybrid, highly porous crystalline structures – offer several advantages compared to other available DDS, as they combine desirable features from both organic (biocompatibility, e.g. porous polymers) and inorganic (high loadings, e.g. mesoporous silica) porous materials. MOFs are highly amenable to functionalisation, meaning fine control over their physical properties can be achieved, and thus they have experienced tremendous development during the past decade in many applications. Despite surface engineering being advantageous for diverse fields – in biomedicine, it can both improve stability and dispersion, and provide the possibility of targeted carriers, decreasing the immune system recognition – surface functionalization of MOFs is underdeveloped. The multiple synthetic steps – synthesis, drug loading and surface modification – and the lack of orthogonality between them hinder their industrial manufacturing as DDSs. This thesis focuses on the development of surface functionalisation protocols of Zirconium MOFs, particularly UiO-66, a Zr-terephthalate MOF, the study of their cell internalisation fate and routes and the correlation with their therapeutic activity. During Chapter 1, an introduction to the use of DDSs in anticancer therapy, followed by examples of the most relevant MOFs from a coordination chemistry point of view, is given, in which zirconium MOFs and their synthesis are highlighted. Particular focus is given to the coordination modulation process, in which monodentate modulators are introduced to the MOFs synthesis to compete with the multidentate linkers during nucleation, enhancing properties such as porosity through the induction of defects. Then, the most relevant examples of surface functionalization of Zr MOFs for drug delivery are discussed with respect to the effects on properties such as colloidal dispersion in aqueous solvents, physiological stability, and drug release kinetics. In Chapter 2 different functionalised modulators (i.e p-functionalised benzoic acids, folic acid or biotin) are introduced to UiO-66 synthesis to obtain surface-functionalised UiO-66 with the appropriate size for drug delivery by one-pot synthesis. Full characterisation of the materials shows them to be remarkably porous due to the defects formed when modulators attach to available zirconium positions in the pores and on the surfaces of the MOFs. Furthermore, the use of a carboxylate-containing anticancer metabolic target (dichloroacetic acid, DCA) as a modulator of UiO-66 synthesis is explored, and co-modulated samples, in which both DCA and functionalised modulators are introduced to UiO-66 synthesis, are synthesised and fully characterised, resulting in drug-containing (ca. 20% w/w) surface-functionalised MOFs by one pot syntheses. Importantly, DCA modulation induces a high number of defects, and consequently highly charged nanoparticles which are colloidally stable in aqueous solvents. Particle size control in the DCA modulated synthesis of the UiO family of isoreticular MOFs – including UiO-66 and its bromo, amino and nitro derivatives, and extended structures Zr-Naphthalenedicarboxylate (NDC) and Zr-Biphenyldicarboxylate (BPDC) – is achieved, obtaining ca. 100 nm particles of UiO-66 derivatives and microcrystals of Zr-NDC and Zr-BPDC when ZrCl4 is the metal precursor, and mesoporous < 20 nm UiO-66 derivatives and ca. 200 nm Zr-NDC and Zr-BPDC when ZrOCl2 is used as the metal precursor. The high porosity of the DCA modulated samples, due to DCA attachment to the inner and outer surface at defect sites, allows the loading of a second drug, the well-known anticancer drug 5-fluorouracil (5-FU), into the pores of the isoreticular MOFs to create dual DDSs. Different postsynthetic modes of surface coating, based in both coordination and covalent chemistry, are studied during Chapter 3. The functionalities of the p-functionalised benzoic acid modulators, introduced to UiO-66 structure during Chapter 2, are used to covalently attach short-chain alkanes and long-chain polymers to UiO-66 surface through copper-catalysed azide-alkyne cycloaddition. Exhaustive characterisation confirms that the attachment occurs through covalent chemistry and not through surface adhesion or electrostatic forces. Folic acid and biotin, which are introduced to UiO-66 surface as synthetic modulators during Chapter 2, are also introduced to UiO-66 surface postsynthetically. Colloidal dispersion and stability towards phosphates are investigated and compared to bare MOFs, in order to gain insights into the effect of both surface chemistry and mode of attachment on physical properties. A comprehensive overview of in vitro studies of cellular internalisation of zirconium MOFs is given in Chapter 4, focussing on the relevance of the endocytosis internalisation routes, which are strictly correlated with therapeutic efficacy. The postsynthetic surface functionalisation protocols investigated in Chapter 3 are applied to analogous calcein-loaded UiO-66 samples. Calcein is a fluorescent molecule not able to efficiently cross the cell membrane by itself, and hence serves as an in ideal probe of MOFs cellular internalisation. Its release from bare and poly(ethylene glycol) coated UiO-66 into phosphate buffered saline at pH 7.4 and 5.5, in order to simulate extracellular and intracellular conditions, is found to be pH responsive (more pronounced at 5.5) for all MOFs, but an ideal decrease in calcein release at pH 7.4 occurs only for PEGylated MOFs. Internalisation of calcein-loaded MOFs by HeLa cervical cancer cells is studied by fluorescence assisted cell sorting, highlighting the effects of surface chemistry on endocytosis efficiencies and internalisation mechanisms. A discussion of in vitro studies into anticancer drug delivery from Zr MOFs is provided in Chapter 5, alongside a summary of the therapeutic effects of DCA and approaches to enhance its anticancer efficacy. Experimental assessment of the in vitro anticancer performance towards MCF-7 breast cancer cells of the DCA-containing MOFs of the UiO family of different sizes (ca. 100 nm and <20 nm), synthesised by coordination modulation during Chapter 2, is given. The effect of dual-drug containing MOFs (DCA and 5-FU) is also examined, to investigate the possible synergic effect of the drug combination. Then, the cytoxicity of bare and surface functionalised, DCA-loaded and empty UiO-66 MOFs is studied at first upon incubation with HeLa cells, for which the cellular routes of internalisation were elucidated in Chapter 4. The most promising MOFs are then tested for selective anticancer activity against a series of cancerous and healthy cells lines, and their macrophage uptake and ROS production is also analysed, to determine the effect of surface functionalization. The selective anticancer cytotoxicity of folate-coated MOFs is attributed to a combination of cancer cell targeting and optimal cell internalisation routes. To summarise, the one-pot synthesis of drug-loaded, surface functionalised UiO-66 has been successfully performed, resulting in porous, crystalline MOFs with the appropriate size for drug delivery. The use of a carboxylate-containing anticancer metabolic target as a modulator has been explored for the UiO family of isoreticular MOFs, resulting in well-dispersed nanoMOFs with enhanced anticancer activity, into which a second drug can be loaded, enabling the creation of dual DDSs. A series of postsynthetic surface modifications are performed, enabling the study of the MOF’s properties (colloidal dispersion, physiological stability and biocompatibility) with respect to their surface chemistry and coating mode, but more importantly providing valuable insights into correlations between surface chemistry, routes of cellular internalisation and therapeutic effect