John F Callan

University of Ulster, Aontroim, Northern Ireland, United Kingdom

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Publications (66)293.78 Total impact

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    ABSTRACT: A new chemosensor L has been synthesized using Schiff base reaction of pyridoxal with hydrazine and characterized by various spectroscopic techniques such as FTIR, H-1 NMR and mass spectrometry. The anion recognition ability of the synthesized sensor has been investigated by UV-vis, fluorescence and H-1 NMR methods. Among the tested anions, the developed sensor shows a naked-eye detectable color change from colorless to red and spectral changes in the presence of fluoride and acetate ions due to the partial deprotonation of the sensor. With a micromolar detection limit, the developed sensor is highly efficient and may be utilised for the colorimetric detection of fluoride/acetate ions. The developed sensor has been successfully fabricated in to the INHIBIT logic gate at molecular level.
    Full-text · Article · Feb 2016 · Indian Journal of Chemistry Section a
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    Full-text · Dataset · Jan 2016
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    ABSTRACT: Nanomedicine has evolved with the use of biological compounds such as proteins, peptides and DNA. These hydrophilic and often highly charged compounds require a delivery system to allow effective transport and release at the site of action. These new biological therapeutics have not replaced the more traditional smaller molecule, but instead are working synergistically to the benefit of the end user. To that end, drug delivery systems are now required to encapsulate both larger hydrophilic compounds as well as the smaller and generally more hydrophobic compound. This review highlights the emerging role in drug delivery of amphiphilic polymers that by their very nature can associate with compounds of differing physicochemical properties, in particular the role of micelles, polymersomes and nanocapsules.
    Full-text · Article · Jan 2016 · Therapeutic delivery
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    Full-text · Dataset · Nov 2015
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    ABSTRACT: The interest in Quantum Dots as a class of nanomaterials has grown considerably since their discovery by Ekimov and Efros in the early 1980s. Although this early work focussed primarily on CdSe-based nanocrystals, the field has now expanded to include various classes of nanoparticles with different types of core, shell or passivation chemistry. Such differences can have a profound effect on the optical properties and potential biocompatibility of the resulting constructs. Although QDs have predominantly been used for imaging and sensing applications, more examples of their use as therapeutics are beginning to emerge. In this chapter we discuss the progress made over the past decade in developing QDs for imaging and therapeutic applications.
    Full-text · Article · Nov 2015 · Topics in current chemistry
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    ABSTRACT: In this manuscript we describe the preparation of an oxygen-loaded microbubble (O2MB) platform for the targeted treatment of pancreatic cancer using both sonodynamic therapy (SDT) and antimetabolite therapy. O2MB were prepared with either the sensitiser Rose Bengal (O2MB-RB) or the antimetabolite 5-fluorouracil (O2MB-5FU) attached to the microbubble (MB) surface. The MB were characterised with respect to size, physical stability and oxygen retention. A statistically significant reduction in cell viability was observed when three different pancreatic cancer cell lines (BxPc-3, MIA PaCa-2 and PANC-1), cultured in an anaerobic cabinet, were treated with both SDT and antimetabolite therapy compared to either therapy alone. In addition, a statistically significant reduction in tumour growth was also observed when ectopic human xenograft BxPC-3 tumours in SCID mice were treated with the combined therapy compared to treatment with either therapy alone. These results illustrate not only the potential of combined SDT/antimetabolite therapy as a stand alone treatment option in pancreatic cancer, but also the capability of O2-loaded MBs to deliver O2 to the tumour microenvironment in order to enhance the efficacy of therapies that depend on O2 to mediate their therapeutic effect. Furthermore, the use of MBs to facilitate delivery of O2 as well as the sensitiser/antimetabolite, combined with the possibility to activate the sensitiser using externally applied ultrasound, provides a more targeted approach with improved efficacy and reduced side effects when compared with conventional systemic administration of antimetabolite drugs alone.
    Full-text · Article · Nov 2015 · Biomaterials
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    ABSTRACT: A new sensitiser (4) for use in photodynamic therapy (PDT) has been developed to enable control ROS production as a function of pH. This pH dependent PDT behaviour was tested in HeLa cells and in SCID mice bearing human xenograft pancreatic cancer (BxPC-3) tumours.
    Full-text · Article · Sep 2015 · Chemical Communications

  • No preview · Article · Sep 2015

  • No preview · Article · Sep 2015
  • Jordan Atchison · James Davis · John F. Callan

    No preview · Article · Sep 2015
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    ABSTRACT: A strategy to probe supramolecular nanocarriers and their cargo in the intracellular space was developed on the basis of fluorescence measurements and energy transfer. It relies on the covalent attachment of an energy donor, or acceptor, to the macromolecular backbone of amphiphilic polymers and the noncovalent encapsulation of a complementary acceptor, or donor, in the resulting micelles. In aqueous environments, these macromolecules self-assemble into nanostructured constructs and bring the complementary chromophores in close proximity to enable efficient energy transfer. These supramolecular assemblies travel from the extracellular to the intracellular space and retain their integrity in the process. Indeed, donors and acceptors remain close to each other after internalization and excitation of the former chromophores translates into significant intracellular emission from the latter. Furthermore, these supramolecular assemblies exchange their components with fast kinetics in aqueous dispersions, because of the reversible character of the noncovalent contacts holding them together. As a result, micelles incorporating exclusively the donors and nanocarriers containing only the acceptors scramble their chromophoric building blocks, upon mixing, to allow the transfer of energy. These dynamic processes can be reproduced in the intracellular environment with the sequential incubation of cells with the two sets of complementary nanostructured assemblies. Thus, these operating principles and choice of supramolecular synthons are particularly valuable to monitor self-assembling nanocarriers and their cargo inside living cells and can facilitate the elucidation of the behavior of these promising delivery vehicles in a diversity of biological specimens.
    Full-text · Article · Aug 2015 · Langmuir
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    ABSTRACT: An amphiphilic polymer with multiple decyl and oligo(ethylene glycol) chains attached to a common poly(methacrylate) backbone assembles into nanoscaled particles in aqueous environments. Hydrophobic anthracene and borondipyrromethene (BODIPY) chromophores can be co-encapsulated within the self-assembling nanoparticles and transported across hydrophilic media. The reversible character of the noncovalent bonds, holding the supramolecular containers together, permits the exchange of their components with fast kinetics in aqueous solution. Incubation of cells with a mixture of two sets of nanoparticles, pre-loaded independently with anthracene or BODIPY chromophores, results in guest scrambling first and then transport of co-entrapped species to the intracellular space. Alternatively, incubation of cells with the two sets of nanocarriers in consecutive steps permits the sequential transport of the anthracene and BODIPY chromophores across the plasma membrane and only then allows their co-encapsulation within the same supramolecular containers. Both mechanisms position the two sets of chromophores with complementary spectral overlap in close proximity to enable the efficient transfer of energy intracellularly from the anthracene donors to the BODIPY acceptors. In the presence of iodine substituents on the BODIPY platform, intersystem crossing follows energy transfer. The resulting triplet state can transfer energy further to molecular oxygen with the concomitant production of singlet oxygen to induce cell mortality. Furthermore, the donor can be excited with two near-infrared photons simultaneously to permit the photoinduced generation of singlet oxygen intracellularly under illumination conditions compatible with applications in vivo. Thus, these supramolecular strategies to control the excitation dynamics of multichromophoric assemblies in the intracellular environment can evolve into valuable protocols for photodynamic therapy.
    Full-text · Article · Jul 2015 · Nanoscale
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    ABSTRACT: A new anion selective chemosensor L was derived through a direct condensation reaction between pyridoxal and thiosemicarbazide. Sensor L showed selective recognition and sensing ability towards F- and AcO- anions through naked-eye detectable color change from colorless to light yellow, appearance of a new charge transfer absorption band at 404 nm and significant “turn-on” fluorescence at 506 nm. The detection limit of L as a fluorescent ‘turn-on’ sensor for the analysis of F- and AcO- was estimated to be 0.10 M. The anion sensing mechanisms of L was supported with 1H NMR and DFT results. Finally, the cytoxicity effect of L and its ability to image intracellular F- ions in the living HeLa cells was investigated.
    No preview · Article · Jun 2015 · RSC Advances
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    ABSTRACT: Luminescent sensors and switches continue to play a key role in shaping our understanding of key biochemical processes, assist in the diagnosis of disease and contribute to the design of new drugs and therapies. Similarly, their contribution to the environment cannot be understated as they offer a portable means to undertake field testing for hazardous chemicals and pollutants such as heavy metals. From a physiological perspective, the Group I and II metal ions are among the most important in the periodic table with blood plasma levels of H(+), Na(+) and Ca(2+) being indicators of several possible disease states. In this review, we examine the progress that has been made in the development of luminescent probes for Group I and Group II ions as well as protons. The potential applications of these probes and the mechanism involved in controlling their luminescent response upon analyte binding will also be discussed.
    Full-text · Article · Mar 2015 · Chemical Society Reviews
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    ABSTRACT: A polymeric hydrogel containing a photoinduced electron transfer (PET) based probe for Zn(II) has been formulated into the wells of a 96-well plate. Upon addition of Zn(II) ions to selected wells, the fluorescence of the gel was observed to increase in a concentration dependent manner in the 0.25 – 1.75 mM range. The millimolar binding constant observed for this probe is higher than that reported for other Zn(II) probes in the literature and offers the possibility to determine the concentration of this ion in environments where the Zn(II) concentration is high. The combination of the multi-well plate set-up with fluorescence detection offers the possibility of high-throughput screening of Zn(II) using low sample volumes in a timely manner. To the best of our knowledge, this is the first reported example of a polymeric hydrogel sensor for zinc with capability for use in fluorescence multi-well plate assay.
    No preview · Article · Feb 2015 · New Journal of Chemistry
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    ABSTRACT: Tumour hypoxia represents a major challenge in the effective treatment of solid cancerous tumours using conventional approaches. As oxygen is a key substrate for Photo-/Sono-dynamic Therapy (PDT/SDT), hypoxia is also problematic for the treatment of solid tumours using these techniques. The ability to deliver oxygen to the vicinity of the tumour increases its local partial pressure improving the possibility of ROS generation in PDT/SDT. In this manuscript, we investigate the use of oxygen-loaded, lipid-stabilised microbubbles (MBs), decorated with a Rose Bengal sensitiser, for SDT-based treatment of a pancreatic cancer model (BxPc-3) in vitro and in vivo. We directly compare the effectiveness of the oxygen-loaded MBs with sulphur hexafluoride (SF6)-loaded MBs and reveal a significant improvement in therapeutic efficacy. The combination of oxygen-carrying, ultrasound-responsive MBs, with an ultrasound-responsive therapeutic sensitiser, offers the possibility of delivering and activating the MB-sensitiser conjugate at the tumour site in a non-invasive manner, providing enhanced sonodynamic activation at that site. Copyright © 2015. Published by Elsevier B.V.
    No preview · Article · Feb 2015 · Journal of Controlled Release
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    ABSTRACT: Sonodynamic therapy (SDT) has emerged as a promising option for the minimally invasive treatment of solid cancerous tumours. SDT requires the combination of three distinct components: a sensitising drug, ultrasound, and molecular oxygen. Individually, these components are non-toxic but when combined together generate cytotoxic reactive oxygen species (ROS). The major advantage of SDT over its close relative photodynamic therapy (PDT), is the increased penetration of ultrasound through mammalian tissue compared to light. As a result, SDT can be used to treat a wider array of deeper and less accessible tumours than PDT. In this article, we critically review the current literature on SDT and discuss strategies that have been developed in combination with SDT to enhance the therapeutic outcome.
    Full-text · Article · Jan 2015 · International Journal of Hyperthermia
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    ABSTRACT: The field of therapeutics is evolving to include a greater proportion of higher molecular weight, hydrophilic biological compounds. To cater for this new era in healthcare the concomitant development of appropriate drug delivery systems is essential to aid cellular permeation. In this manuscript we present the synthesis, characterisation and biological evaluation of a charge neutral polymersome (Ps) based drug delivery system (DDS) using an amphiphilic pegylated random copolymer. A detailed dynamic light scattering study revealed that the hydrodynamic diameter of the Ps can be tailored to a specific size simply by varying the quantities and ratios used during the preparation step. The zeta potential of this new drug delivery system was determined to be -0.095±0.037mV, the encapsulation efficiency of FITC-CM-dextran (4KDa) was 70%, the uptake of Fitc-CM-Dextran by Hela cells was increased 4-fold when encapsulated within the polymersomal system. The facile preparation, high loading capacity and size tuneable nature of this Ps renders it a promising alternative to the ever growing array of currently available Ps. Copyright © 2015 Elsevier B.V. All rights reserved.
    No preview · Article · Jan 2015 · International Journal of Pharmaceutics
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    ABSTRACT: Microbubbles (MBs) have recently emerged as promising delivery vehicles for sensitiser drugs in sonodynamic therapy (SDT). The ability to selectively destroy the MB and activate the sensitizer using an external ultrasound trigger could provide a minimally invasive and highly targeted therapy. While lipid MBs have been approved for use as contrast agents in diagnostic ultrasound, the attachment of sensitiser drugs to their surface results in a significant reduction in particle stability. In this manuscript, we prepare both lipid and polymer (PLGA) MBs with rose bengal attached to their surface and demonstrate that PLGA MB conjugates are significantly more stable than their lipid counterparts. In addition, the improved stability offered by the PLGA shell does not hinder their selective destruction using therapeutically acceptable ultrasound intensities. Furthermore, we demonstrate that treatment of ectopic human tumours (BxPC-3) in mice with the PLGA MB-rose bengal conjugate and ultrasound reduced tumour volume by 34% 4 days after treatment while tumours treated with the conjugate alone increased in volume by 48% over the same time period. Therefore, PLGA MBs may offer a more stable alternative to lipid MBs for the site specific delivery of sensitisers in SDT.
    No preview · Article · Nov 2014 · Langmuir
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    ABSTRACT: Objectives This study aimed to develop and characterise a new three-component dental whitening formulation which is as effective as the currently used carbamide peroxide but at significantly lower hydrogen peroxide concentrations. Materials and methods The new formulation (Carbamide Plus) was prepared containing hydrogen peroxide, urea, and sodium tripolyphosphate and compared directly with carbamide peroxide (containing just hydrogen peroxide and urea). To evaluate the clinical effectiveness of 5 % Carbamide Plus, a randomised double-blind placebo-controlled clinical trial was conducted comparing the tooth colour of 33 patients using L*a*b* scores at baseline and after a 2-week whitening treatment. The behaviour of the three components in solution was determined by 1H and 31P NMR spectroscopy and pH dilution experiments. Results This clinical trial revealed that 5 % whitening gels containing Carbamide Plus were as effective as those containing 10 % carbamide peroxide. 1H and 31P NMR spectroscopy revealed strong intermolecular interactions between hydrogen peroxide and both urea and sodium tripolyphosphate (STPP) with little apparent interaction between urea and STPP. Conclusions In this manuscript, we postulate that this increased whitening efficiency is due to a marked increase in local pH upon dilution which destabilises the hydrogen peroxide and expedites the whitening process. We postulate Carbamide Plus to be a three-component adduct with two molecules of carbamide peroxide binding to a central STPP unit with no direct interaction between STPP and urea. There were no statistically significant differences between Carbamide Plus and 10 % carbamide peroxide in tooth-whitening achieved at 2 weeks. These results were recorded following 2 weeks of 2-h daily wear of at-home trays. Clinical relevance Carbamide Plus offers the potential of using significantly lower levels of hydrogen peroxide concentration to achieve similar dental whitening effects.
    No preview · Article · Nov 2014 · Clinical Oral Investigations

Publication Stats

2k Citations
293.78 Total Impact Points

Institutions

  • 2010-2015
    • University of Ulster
      • • Biomedical Sciences Research Institute
      • • School of Biomedical Sciences
      • • School of Pharmacy and Pharmaceutical Science
      Aontroim, Northern Ireland, United Kingdom
  • 2007-2009
    • The Robert Gordon University
      • School of Pharmacy and Life Sciences
      Aberdeen, Scotland, United Kingdom
  • 2004-2008
    • Queen's University Belfast
      • School of Chemistry and Chemical Engineering
      Béal Feirste, Northern Ireland, United Kingdom