Molecularly imprinted polymers in the drug discovery process

Since molecularly imprinted polymers (MIPs) are designed to have a memory for their molecular templates it is easy to draw parallels with the affinity between biological receptors and their substrates. Could MIPs take the place of natural receptors in the selection of potential drug molecules from synthetic compound libraries? To answer that question this review discusses the results of MIP studies which attempt to emulate natural receptors. In addition the possible use of MIPs to guide a compound library synthesis towards a desired biological activity is highlighted. © 2005 Elsevier B.V. All rights reserved.

Tools for fluorescent molecularly imprinted polymers

A linear co-polymer of hexyl acrylate and quinine acrylate was prepared anchored to cellulose filtration membranes. These were used to probe quenching of the tethered fluorophore by test compounds in solution for the validation of imprinted polymer fluorescence studies. The results are compared with simple solution phase quenching studies and also for two membrane-bound imprinted polymers containing the same fluorophore. © 2004 Elsevier B.V. All rights reserved.

Selective recognition of cyclic GMP using a fluorescence-based molecularly imprinted polymer

Guanosine 3′,5′-cyclic monophosphate (cGMP) plays a role as a second messenger in many different biological systems. Given the ubiquitous nature of cGMP, a simple method of detecting cGMP is of interest. To that end a fluorescent polymer with recognition sites for cGMP has been prepared. Its selectivity and sensitivity were investigated and a dose-dependant decrease in fluorescence of the polymer in the presence of cGMP was observed. In contrast, virtually no effect was detected upon application of the structurally similar molecules, guanosine 5′-monophosphate (GMP) and adenosine 3′,5′-cyclic monophosphate (cAMP), thus demonstrating the high selectivity of this polymer. The association constant for the binding of cGMP to the imprinted polymer was determined in order of 3 × 10 5 M -1. A fluorescent, molecularly imprinted polymer that selectively recognises cGMP may have a useful application as a fluorescent chemosensor for cGMP detection in biological samples.

Novel imprinted polymers as artificial enzymes

Derivatives of L-histidine were investigated as suitable models for the Asp-His couple found in the catalytic triad of serine proteases. A combination of molecular dynamics and IH NMR spectroscopy suggested that the most populous conformations of N-acetyl-L-histidine and the N-acetyl-L-histidine anion were predominated by those in which the carboxylate group was gauche to the imidazole ring overcoming steric and electrostatic repulsion, suggesting there is an interaction between the carboxylate group and the imidazole ring. Kinetic studies, using imidazole, N-acetyl-L-histidine and the N-acetyl-L-histidine anion showed that in a DMSO/H20 9: 1 v/v solution, the N-acetyl-L-histidine anion catalysed the hydrolysis of p-nitrophenyl acetate at a greater rate than using either imidazole or N-acetyl-L-histidine as catalyst. This indicates that the carboxylate group affects the nucleophilicity of the unprotonated imidazole ring. 31P MAS NMR spectroscopy was investigated as a new technique for the study of the template molecule environment within the polymer networks. It was found that it was possible to distinguish between template associated with the polymer and that which was precipitated onto the surface, though it was not possible to distinguish between polymer within imprinted cavities and that which was not. Attempts to study the effect of the carboxylate group/imidazole ring interaction in the imprinted cavity of a molecularly imprinted polymer network were hindered by the method used to follow the reaction. It was found though that in a pH 8.0 buffered solution the presence of imprinted cavities increased the rate of reaction for those polymers derived from L-histidine. Some preliminary investigations into the design and synthesis of an MIP which would catalyse the oxy-Cope rearrangement were carried out but the results were inconclusive.

Synthesis and characterisation of imprinted polymeric receptor mimics

Molecularly imprinted polymers (MIPs) are crosslinked polymers containing bespoke functionalised cavities arising from the inclusion of template molecules in the polymerisation mixture and their later extraction. When the polymers are prepared functional polymerisable monomers are included which become part of the polymer matrix and serve to decorate the cavities with functionality appropriate to the template molecules. Overall, binding sites are created which have a memory for the template both in terms of shape and matching functionality. Fluorescent molecularly imprinted polymers have the benefit of a fluorophore in their cavities that may respond to the presence of bound test compound by a change in their fluorescence output. The work presented falls into three main areas. A series of fluorescent MIPs was prepared with a view to generating material capable of mimicking the binding characteristics of the metabolically important cytochrome isoform CYP2D6. The MIPs re-bound their templates and various cross-reactivities were encountered for test compound/drug recognition. One MIP in particular exhibited a rational discrimination amongst the related synthetic templates and was reasonably successful in recognising CYP2D6 substrates from the drug set tested. In order to give some insights into binding modes in MIPs, attempts were made to produce functional monomers containing two or more fluorophores that could be interrogated independently. A model compound was prepared which fitted the dual-fluorophore criteria and which will be the basis for future incorporation into MIPs. A further strand to this thesis is the deliberate incorporation of hydrophobic moieties into fluorescent functional monomers so that the resulting imprinted cavities might be biomimetic in their impersonation of enzyme active sites. Thus the imprinted cavities had specific hydrophobic regions as well as the usual polar functionality with which to interact with binding test compounds.

Towards a polymeric binding mimic for cytochrome CYP2D6

A series of fluorescent molecularly imprinted polymers has been prepared with a view to generating material capable of mimicking the binding characteristics of the metabolically important cytochrome isoform CYP2D6. Such polymers would have the possibility to form the sensing element in a high-throughput assay for the prediction of CYP2D6 affinity. The imprinted polymers possessed binding-dependent fluorescence. They re-bound their templates and various cross-reactivities were encountered for test compound/drug recognition. One polymer in particular exhibited a rational discrimination amongst the related synthetic templates and was reasonably successful in recognising CYP2D6 substrates from a drug panel. © 2005 Elsevier B.V. All rights reserved.

Design and synthesis of potential antimicrobial agents

Tuberculosis is one of the most devastating diseases in the world primarily due to several decades of neglect and an emergence of multidrug-resitance strains (MDR) of M. tuberculosis together with the increased incidence of disseminated infections produced by other mycobacterium in AIDS patients. This has prompted the search for new antimycobacterial drugs. A series of pyridine-2-, pyridine-3-, pyridine-4-, pyrazine and quinoline-2-carboxamidrazone derivatives and new classes of carboxamidrazone were prepared in an automated fashion and by traditional synthesis. Over nine hundred synthesized compounds were screened for their anti mycobacterial activity against M. fortutium (NGTG 10394) as a surrogate for M. tuberculosis. The new classes of amidrazones were also screened against tuberculosis H37 Rv and antimicrobial activities against various bacteria. Fifteen tested compounds were found to provide 90-100% inhibition of mycobacterium growth of M. tuberculosis H37 Rv in the primary screen at 6.25 μg mL-1. The most active compound in the carboxamidrazone amide series had an MIG value of 0.1-2 μg mL-1 against M. fortutium. The enzyme dihydrofolate reductase (DHFR) has been a drug-design target for decades. Blocking of the enzymatic activity of DHFR is a key element in the treatment of many diseases, including cancer, bacterial and protozoal infection. The x-ray structure of DHFR from M. tuberculosis and human DHFR were found to have differences in substrate binding site. The presence of glycerol molecule in the Xray structure from M. tuberculosis DHFR provided opportunity to design new antifolates. The new antifolates described herein were designed to retain the pharmcophore of pyrimethamine (2,4- diamino-5(4-chlorophenyl)-6-ethylpyrimidine), but encompassing a range of polar groups that might interact with the M. tuberculosis DHFR glycerol binding pockets. Finally, the research described in this thesis contributes to the preparation of molecularly imprinted polymers for the recognition of 2,4-diaminopyrimidine for the binding the target. The formation of hydrogen bonding between the model functional monomer 5-(4-tert-butyl-benzylidene)-pyrimidine-2,4,6-trione and 2,4-diaminopyrimidine in the pre-polymerisation stage was verified by 1H-NMR studies. Having proven that 2,4-diaminopyrimidine interacts strongly with the model 5-(4-tert-butylbenzylidene)- pyrimidine-2,4,6-trione, 2,4-diaminopyrimidine-imprinted polymers were prepared using a novel cyclobarbital derived functional monomer, acrylic acid 4-(2,4,6-trioxo-tetrahydro-pyrimidin-5- ylidenemethyl)phenyl ester, capable of multiple hydrogen bond formation with the 2,4- diaminopyrimidine. The recognition property of the respective polymers toward the template and other test compounds was evaluated by fluorescence. The results demonstrate that the polymers showed dose dependent enhancement of fluorescence emissions. In addition, the results also indicate that synthesized MIPs have higher 2,4-diaminopyrimidine binding ability as compared with corresponding non-imprinting polymers.

Selectivity of response in fluorescent polymers imprinted with N1-benzylidene pyridine-2-carboxamidrazones

Fluorescent polymers imprinted with various N1-benzylidene pyridine-2-carboxamidrazones were evaluated for their recognition of the original template and cross-reactivity to similar molecules. Dramatic quenching of fluorescence approaching background levels was observed for most cases where the "empty" MIP was re-exposed to its template. Molecules too large to enter the imprinted cavities gave no reduction of fluorescence. Other compounds were found to quench the fluorescence and are assumed to have entered the imprinted cavities. There is also evidence for partial responses which may give some measure of partial binding. The fluorescence response profiles of substrates containing polycyclic aromatics were found to be quite different from those containing flexible substituents. In order to make this approach more suitable for high-throughput screening a method has been validated wherein the extent of substrate-induced fluorescence quenching may be obtained without having to know how much polymer is present. © 2001 Elsevier Science B.V. All rights reserved.

Studies of recognition and selectivity by fluorescent polymers imprinted with N1-benzylidene pyridine-2-carboxamidrazones

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Narrow bandwidth Bragg gratings imprinted in polymer optical fibers for different spectral windows

The production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs) is reported. Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 600-nm, 850-nm and 1550-nm in several types of polymer optical fibers were inscribed using a scanning technique with a short optical path. The technique allowed the inscription in relative short periods of time. The obtained 3-dB bandwidth varies from 0.22 down to 0.045 nm considering a Bragg grating length between 10 and 25-mm, respectively.

Imprinted hydrogels for tunable hemispherical microlenses

We report on the development of an ultraviolet curable hydrogel, based on combinations of poly(ethylene glycol) dimethacrylate (PEGMA), acrylic acid (AA) and N-Isopropylacrylamide (NIPPAm) for imprint lithography processes. The hydrogel was successfully imprinted to form dynamic microlens arrays. The response rate of the microlenses by volume change to water absorption was studied optically showing tunable focalisation of the light. Important optical refractive index change was measured between the dry and wet state of the microlenses. Our work suggests the use of this newly developed printable hydrogel for various imprinted components for sensing and imaging systems. © 2013 Elsevier B.V. All rights reserved.

Narrow bandwidth Bragg gratings imprinted in polymer optical fibers for different spectral windows

The production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs) is reported. Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 600-nm, 850-nm and 1550-nm in several types of polymer optical fibers were inscribed using a scanning technique with a short optical path. The technique allowed the inscription in relative short periods of time. The obtained 3-dB bandwidth varies from 0.22 down to 0.045 nm considering a Bragg grating length between 10 and 25-mm, respectively.

Narrow bandwidth Bragg gratings imprinted in polymer optical fibers for different spectral windows

The production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs) is reported. Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 600-nm, 850-nm and 1550-nm in several types of polymer optical fibers were inscribed using a scanning technique with a short optical path. The technique allowed the inscription in relative short periods of time. The obtained 3-dB bandwidth varies from 0.22 down to 0.045 nm considering a Bragg grating length between 10 and 25-mm, respectively. © 2013 Elsevier B.V.

Quantifying hydrogel response using laser light scattering

The pH and counter-ion response of a microphase separated poly(methyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) hydrogel has been investigated using laser light scattering on an imprinted micron scale topography. A quartz diffraction grating was used to create a micron-sized periodic structure on the surface of a thin film of the polymer and the resulting diffraction pattern used to calculate the swelling ratio of the polymer film in situ. A potentiometric titration and a sequence of counter ion species, taken from the Hofmeister series, have been used to compare the results obtained using this novel technique against small angle X-ray scattering (nanoscopic) and gravimetric studies of bulk gel pieces (macroscopic). For the first time, the technique has been proven to be an inexpensive and effective analytical tool for measuring hydrogel response on the microscopic scale.

May the contact lens force be with you

FULL TEXT: Like many people one of my favourite pastimes over the holiday season is to watch the great movies that are offered on the television channels and new releases in the movie theatres or catching up on those DVDs that you have been wanting to watch all year. Recently we had the new ‘Star Wars’ movie, ‘The Force Awakens’, which is reckoned to become the highest grossing movie of all time, and the latest offering from James Bond, ‘Spectre’ (which included, for the car aficionados amongst you, the gorgeous new Aston Martin DB10). It is always amusing to see how vision correction or eye injury is dealt with by movie makers. Spy movies and science fiction movies have a freehand to design aliens with multiples eyes on stalks or retina scanning door locks or goggles that can see through walls. Eye surgery is usually shown in some kind of day case simplified laser treatment that gives instant results, apart from the great scene in the original ‘Terminator’ movie where Arnold Schwarzenegger's android character encounters an injury to one eye and then proceeds to remove the humanoid covering to this mechanical eye over a bathroom sink. I suppose it is much more difficult to try and include contact lenses in such movies. Although you may recall the film ‘Charlie's Angels’, which did have a scene where one of the Angels wore a contact lens that had a retinal image imprinted on it so she could by-pass a retinal scan door lock and an Eddy Murphy spy movie ‘I-Spy’, where he wore contact lenses that had electronic gadgetry that allowed whatever he was looking at to be beamed back to someone else, a kind of remote video camera device. Maybe we aren’t quite there in terms of devices available but these things are probably not the behest of science fiction anymore as the technology does exist to put these things together. The technology to incorporate electronics into contact lenses is being developed and I am sure we will be reporting on it in the near future. In the meantime we can continue to enjoy the unrealistic scenes of eye swapping as in the film ‘Minority Report’ (with Tom Cruise). Much more closely to home, than in a galaxy far far away, in this issue you can find articles on topics much nearer to the closer future. More and more optometrists in the UK are becoming registered for therapeutic work as independent prescribers and the number is likely to rise in the near future. These practitioners will be interested in the review paper by Michael Doughty, who is a member of the CLAE editorial panel (soon to be renamed the Jedi Council!), on prescribing drugs as part of the management of chronic meibomian gland dysfunction. Contact lenses play an active role in myopia control and orthokeratology has been used not only to help provide refractive correction but also in the retardation of myopia. In this issue there are three articles related to this topic. Firstly, an excellent paper looking at the link between higher spherical equivalent refractive errors and the association with slower axial elongation. Secondly, a paper that discusses the effectiveness and safety of overnight orthokeratology with high-permeability lens material. Finally, a paper that looks at the stabilisation of early adult-onset myopia. Whilst we are always eager for new and exciting developments in contact lenses and related instrumentation in this issue of CLAE there is a demonstration of a novel and practical use of a smartphone to assisted anterior segment imaging and suggestions of this may be used in telemedicine. It is not hard to imagine someone taking an image remotely and transmitting that back to a central diagnostic centre with the relevant expertise housed in one place where the information can be interpreted and instruction given back to the remote site. Back to ‘Star Wars’ and you will recall in the film ‘The Phantom Menace’ when Qui-Gon Jinn first meets Anakin Skywalker on Tatooine he takes a sample of his blood and sends a scan of it back to Obi-Wan Kenobi to send for analysis and they find that the boy has the highest midichlorian count ever seen. On behalf of the CLAE Editorial board (or Jedi Council) and the BCLA Council (the Senate of the Republic) we wish for you a great 2016 and ‘may the contact lens force be with you’. Or let me put that another way ‘the CLAE Editorial Board and BCLA Council, on behalf of, a great 2016, we wish for you!’