Dr Alethea Tabor
Research in my laboratory covers a broad range of projects in chemical biology. The underlying theme is the use of synthetic organic chemistry to solve biological problems, by developing tools to peturb, modify and probe biological systems. The development of new synthetic methodology to solve the challenges posed by the synthesis of these molecules, and the use of a range of biophysical techniques to analyse their interactions with the target, are both important parts of ours research. Many of our projects are directed towards biological problems of therapeutic relevance, and we have an extensive network of interdisciplinary collaborations, within UCL, at other institutions, and with industry.
Synthesis and biological activity of the lantibiotics
The lantibiotics are antibacterial peptides, characterised by complicated structures featuring multiple thioether bridges and other post-translational modifications. The lantibiotic nisin has a unique and unprecedented mode of action on bacterial membranes, being able to recognise and specifically bind lipid II (a key component of the biosynthesis of bacterial membranes), followed by pore formation by the nisin/lipid II complex. Although these peptides represent a potential new class of antibiotics to which bacteria have not developed resistance, the difficulties inherent in their synthesis have precluded their development.
We were the
first to develop a method for the solid-phase synthesis of
lanthionine-containing peptides, incorporating lanthionine derivatives such as 1, orthogonally protected with
Aloc/allyl and Fmoc groups. Our method is
unique in being completely regio- and stereoselective, and can allow any number
of rings to be made in sequence.
We have applied this to the synthesis of rings C, A and B of nisin. We have just completed the first solid-phase synthesis of the overlapping bridges of nisin, rings D and E, using a unique quadruply-orthogonal protecting group approach. This approach will enable highly complex lantibiotics to be made, enabling the unique structural and antibacterial properties of these peptides to be investigated.
- B. Mothia, A. N. Appleyard, S. Wadman, A. B. Tabor, “Synthesis of Peptides Containing Overlapping Lanthionine Bridges on the Solid Phase: An Analogue of Rings D and E of the Lantibiotic Nisin” Org. Lett., 13, 4216 – 4219 (2011).
- A. B. Tabor, “The challenge of the lantibiotics: synthetic approaches to thioether-bridged peptides” Org. Biomol. Chem., 9, 7606-7628 (2011).
- S. Bregant, A. B. Tabor, “Orthogonally Protected Lanthionines: Synthesis and Use for the Solid-Phase Synthesis of an Analogue of Nisin Ring C” J. Org. Chem. 70, 2430 -2438 (2005).
Non-viral gene therapy using a cell-targeted ternary vector.
currently working on a highly efficient non-viral gene delivery system, comprising
plasmid DNA, bifunctional peptides which include both cationic sequences to
complex and condense DNA and targeting sequences, and a mixture of cationic and
neutral lipids, which self-assemble to form lipopolyplexes of 100 – 150 nm
diameter. In collaboration with Prof Jayne Lawrence (School of Pharmacy, KCL) and Prof
Helen Hailes we are working on understanding the biophysical properties
of these complexes, their mode of action in vivo and in vitro, and on the design
of new, non-viral gene delivery vectors that will have enhanced targeting
capabilities and . Through the
synthesis of labeled peptides and the application of biophysical techniques
such as fluorescence quenching, FCS and confocal microscopy we have established
the stoichiometry, macromolecular organization, as well as elucidating the mode
of cellular uptake, complex disassembly and delivery of DNA to the nucleus.
This is the first time that a nanostructure of this complexity has been
analysed in this detail.
We have recently developed a range of peptides which are selectively cleaved in the endosome after internalization of the nanocomplexes. These peptides, when co-formulated with cleavable cationic lipids bearing short PEG chains of defined length, give nanocomplexes with exceptionally good transfection properties. These are stable within the systemic circulation and can effectively target tumors in vivo, bringing this technology one step nearer to clinical application. We are now developing this technology for the effective delivery of siRNA to specific cells.
- M. F. Mohd Mustapa, P. C. Bell, C. A. Hurley, A. Nicol, E. Guénin, S. Sarkar, M. J. Writer, S. E. Barker, J. B. Wong, M. A. Pilkington-Miksa, B. Papahadjopoulos-Sternberg, P. Ayazi Shamlou, H. C. Hailes, S. L. Hart, D. Zicha, A B. Tabor, “Biophysical characterization of an integrin-targeted lipopolyplex gene delivery vector” Biochemistry, 46, 12930 – 12944 (2007).
- M. F. Mohd Mustapa, S. M. Grosse, L. Kudsiova, M. Elbs, E.-A. Raiber, J. B. Wong, A. P. R. Brain, H. E. J. Armer, A. Warley, M. Keppler, T. Ng, M. J. Lawrence, S. L. Hart, H. C. Hailes, A. B. Tabor, “Stabilized Integrin-Targeting Ternary LPD (Lipopolyplex) Vectors for Gene Delivery Designed To Disassemble Within the Target Cell”, Bioconj. Chem., 20, 518 – 532 (2009).
- K. Welser, F. Campbell, L. Kudsiova, A. Mohammadi, N. Dawson, S. L. Hart, D. J. Barlow, H. C. Hailes, M. J. Lawrence, A. B. Tabor, “Gene Delivery Using Ternary Lipopolyplexes Incorporating Branched Cationic Peptides: The Role of Peptide Sequence and Branching” Mol. Pharmaceutics, 10, 127 − 141 (2013).
Multifunctional, multimodal nanocomplexes for tumor imaging and therapy:
Based on the self-assembling lipopolyplexes that we have developed to deliver pDNA or siRNA, we are now designing and synthesising theragnostic multifunctional nanocomplexes that will simultaneously deliver DNA, siRNA or small molecule therapeutics to cancer cells, and at the same time enable multimodal imaging by one or more of MRI, PET, SPECT, optical or photoacoustic imaging, to determine both the location of the nanocomplexes and their effect on the target cells. These will serve as exceptionally powerful tools for understanding the effects of different cancer therapies at the cellular and molecular level simultaneously. We have recently published work on toolbox components which can be formulated into multifunctional liposomes and imaged by PET, SPECT, MRI and optical techniques. We have compared these liposomes co-formulated with PEG-2000 lipids with similar lipids co-formulated with our short chain PEG lipids and have shown that the biodistribution and half life in vivo are similar, but that the liposomes formulated with short chain PEG lipids have a much higher cellular uptake.
research in this area is part of the KCL and UCL Comprehensive Cancer Imaging
Centre (CCIC). The CCIC was established in 2008 to facilitate the development
of new imaging agents and technologies and their application for the benefit of
cancer patients. It brings together over 50 research groups in the basic
physical and biomedical sciences with preclinical and clinical investigators
across UCL, KCL and the associated NHS Trust hospitals. Funding for the CCIC
has recently been renewed by Cancer Research UK and the EPSRC until 2018, with
the overall aim of understanding tumor heterogeneity by molecular imaging to
facilitate individualized patient therapies and prediction of treatment
response. Alethea is the lead PI on Signature Programme 3 “Multifunctional
nanoparticles for simultaneous imaging and drug delivery”. We will be developing
our targeted, self-assembling multifunctional nanoparticles to simultaneously
deliver small molecule therapeutics to primary tumors and metastases, and also
deliver optical probes to measure the effects of these therapies at the
molecular level. These nanoparticles will also have appropriate labels for
tracking by two or more imaging modalities (PET, SPECT, optical, MR) in vivo.
We are collaborating with a number of research groups at UCL and KCL on this project, in particular Prof Tony Ng (UCL Cancer Institute/KCL Randall Division) and Prof Xavier Golay (UCL Institute of Neurology).
- N. Mitchell, T. L. Kalber, M. S. Cooper, K. Sunassee, S. L. Chalker, K. P. Shaw, K. L. Ordidge, A. Badar, S. M. Janes, P. J. Blower, M. F. Lythgoe, H. C. Hailes, A. B. Tabor, “Incorporation of paramagnetic, fluorescent and PET/SPECT contrast agents into liposomes for multimodal imaging” Biomaterials, 34, 1179 – 1192 (2013).
Small molecule enzyme inhibitors as potential therapeutic agents:
We are collaborating with two members of the Institute of Structural and Molecular Biology (ISMB) at Birkbeck/UCL, Prof Gabriel Waksman and Prof Ivan Gout in projects to design and synthesise small molecule enzyme inhibitors as potential therapeutic agents. With Professor Waksman, we have developed a new series of 8-amino imidazo[1,2-a]pyrazine derivatives as inhibitors of the VirB11 ATPase HP0525. This enzyme is a key component of the bacterial Type IV secretion system, and inhibitors of this enzyme should disable (rather than killing) bacteria, making it more difficult for them to evolve resistance to these classes of compounds.
- J. R. Sayer, K. Walldén, T. Pesnot, F. Campbell, P. J. Gane, M. Simone, H. Koss, F. Buelens, T. P. Boyle, D. L. Selwood, G. Waksman, A. B. Tabor, “2-And 3-substituted imidazo[1,2-a]pyrazines as inhibitors of bacterial type IV secretion” Bioorganic and Medicinal Chemistry, in press (2014).