Professor Chi-Ming Che, University of Hong Kong, P R China
Interactions of intercalating photooxidising dipyridophenazine metal complexes with DNA
Professor John Kelly, Trinity College Dublin, Republic of Ireland
For many years dipyrido[3,2-a:2’,3’-c]phenazine (dppz) complexes have been extensively studied as probes for DNA.
[Ru(phen)2(dppz)]3+ (phen = 1,10-phenanthroline) has attracted particular attention as it acts as a DNA-light switch, being non-luminescent in water but emitting when bound to DNA. By contrast [Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene)  and [Cr(phen)2(dppz)]3+  are luminescent in aqueous solution but not upon binding to DNA. This is due to reduction of the metal complex excited state by guanine as has been demonstrated by picosecond transient spectroscopy (with both visible and IR monitoring) for [Ru(TAP)2(dppz)]2+  and also for [Re(CO)3(dppzF2)]2+ .
Although it is accepted that the dppz ligand intercalates between the DNA base-pair, the precise mode of binding deduced from spectroscopic and biophysical measurements has been a matter of debate. Recent successful crystallisation by the Cardin group of both Ru(TAP)2(dppz)]2+  and [Ru(phen)2(dppz)]2+  with small defined-sequence DNA has for the first time provided a wealth of information on the interaction of these complexes with DNA and allowed a comparison with other DNA- intercalating molecules
 B M Zeglis et al, Chem Comm, 2007, 44, 4565-4579
 B Elias et al, Chemistry – Eur J, 2008, 14, 369-375.
 M Wojdyla et al, Photochem. Photobiol. Sci, 2010, 9, 1196-1202.
 Q Cao et al, Photochem. Photobiol. Sci, 2011, 10, 1355-1364.
 J P Hall et al, Proc Natl Acad Sci, 2011, 108, 17610-17614
 H Niyazi et al, Nature Chemistry, 2012, in press.
Metal photocleavage of DNA
Dr Samantha Higgins, Virginia Tech, USA
Ru(II) and Os(II) polypyridyl chromophores have been readily studied for applications in DNA photomodification due to their enhanced photophysical and interesting photochemical properties. Coupling a Ru(II) or Os(II) chromophore to a remote bioactive site, such as Pt(II) or Rh(III), through a polyazine bridging ligand provides a supramolecular complex characterized by redox, spectroscopic, and photophysical properties. Studies of the mixed-metal complexes in the presence of DNA show enhanced photoinduced activity using low energy visible light within the therapeutic window (600-900 nm). The supramolecular complexes, [(Ph2phen)2MII(dpp)PtIICl2]Cl2 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline and M = Ru(II) or Os(II)) display unique DNA photobinding and photocleavage properties by utilizing their lowest lying 3metal-to-ligand charge transfer (3MLCT) excited state to facilitate ligand loss at the remote Pt(II) center. Modifying the molecular architecture to [(TL)2MII(dpp)RhIIICl2(TL’)](PF6)3 (TL = terminal ligand on the chromophore, M = Ru(II) or Os(II) and TL’ = terminal ligand on the Rh(III) center) provides for distinctive oxygen independent photobinding and photocleavage features, a result attributed to unit population of the 3MLCT excited state, which is coupled to the lower lying 3metal-to-metal charge transfer (3MMCT) excited state. The varied mechanisms of DNA photocleavage in these supramolecular systems provide a fresh look at mixed-metal systems in photodynamic therapy.
Multifunctional in cellulo probes
Dr James Thomas, University of Sheffield, UK
Ruthenium(II) polypyridyl complexes that interact reversibly with DNA can display high binding affinities and selectivities [1,2] as well as interesting photophysical properties . Although such complexes offer potential as in cellulo probes for luminescence microscopy, poor cellular uptake by live cells restricts the use of such molecules.
In recent studies we have shown that complexes such as 1 and 2 are taken up by both live eukaryotic and prokaryotic cells where they bind to nuclear DNA as evident by both luminescence and transmission electron microscopy suggesting they may find use as cellular specific imaging agents and/or therapeutics .
A distinctive property of 2 - revealed by in vitro and in cellulo studies - is that high affinity binding of specific DNA structures leads to distinctive emission signatures [4,6].Herein we present progress in this area, including structural studies aimed at delineating the cause of this complex’s structural binding preferences .
Acknowledgments: We thank EPSRC for its Life science DTC and PoC fund.
 (a) C Metcalfe, J A Thomas, Chem Soc Rev2003, 32, 214. (b) M R Gill, J A Thomas, Chem Soc Rev, in press.
 P Waywell, V Gonzalez, M R Gill, H A Adams, A J H M Meijer, M P Williamson, J A Thomas, Chem Eur J, 2010, 16, 2407.
 (a) S P Foxon, M Towrie, A W Parker, M Webb, J A Thomas, Angew Chem Int Ed,2007, 46, 3686-3689. (b) V G Gonzalez, T Wilson, I Kurihara, A Imai, J A Thomas, J Otsuki, Chem Commun 2008, 168.
 M R Gill, J Garcia-Lara, S J Foster, C G W Smythe, G Battaglia, J A Thomas, Nat Chem, 2009, 1,662-667.
 M R Gill, H Derat, C G W Smythe, G Battaglia, J A Thomas, ChemBioChem, 2011, 12, 877.
 T Wilson, M P Williamson, J A Thomas, Org Biomol Chem, 2010, 8, 2717.
 T Wilson, P J Costa, V Felix, M P Williamson, J A Thomas, in preparation.
Targeted photodynamic therapy
Professor David Phillips CBE, Imperial College London, UK
Photodynamic therapy, PDT, is a minimally invasive procedure used in treating a range of cancerous diseases, infections, and in ophthalmology to treat the wet form of age-related macular degeneration. The photodynamic action relies upon the simultaneous interaction between a sensitiser molecule [non-toxic in the absence of light], visible light, and molecular oxygen. The sensitiser, usually a porphryin –related molecule, excited initially to the singlet state, intersystem crosses to a longer-lived triplet state, which then produces reactive oxygen species , ROS, primarily singlet oxygen resulting from electronic energy transfer.
Current photodynamic therapy (PDT) of cancer is limited by inefficiencies involved in specifically targeting photosensitisers to tumours. Although antibodies are being explored as targeting vehicles, they present significant challenges, particularly in terms of pharmacokinetics and drug-coupling. We describe here a novel and effective system to attach covalently multiple photosensitiser molecules (both pre-clinical, pyropheophorbide-a and clinically approved, verteporfin photosensitisers) to single-chain Fvs. Further, we demonstrate that not only do the resulting photoimmunoconjugates retain photophysical functionality, they are more potent than either free photosensitiser, effectively killing tumour cells in vitro and in vivo. For example, treatment of human breast cancer xenografts with a photo-immunoconjugate comprising an anti Her-2 scFv linked to 8 molecules of pyropheophorbide-a leads to complete tumour regression. These results give an insight into the important features that make scFvs good carriers for PDT drugs, and provide proof of concept of this unique approach to targeted photodynamic therapy (tPDT). This promises to significantly improve upon current photodynamic therapy for the treatment of cancer and paves the way for clinical application.
A second means of introducing selectivity in PDT is through spatial selection , using two-photon excitation of the sensitiser. This has the advantage of using red or near infra-red light, which greatly enhances tissue penetration. We describe the synthesis of porphyrin dimers with very large two-photon cross sections,carried out by Professor Harry Anderson’s group in Oxford, and their effect in vitro on two cell types, and in sealing blood vessels in vivo.