The therapeutic properties of light have been known for thousands of years, but it was only in the last century that photodynamic therapy (PDT) was developed. At present, PDT is being tested in the clinic for use in oncology--to treat cancers of the head and neck, brain, lung, pancreas, intraperitoneal cavity, breast, prostate and skin. How does PDT work, and how can it be used to treat cancer and other diseases?

Photodynamic therapy for cancer

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

An overview of semiconductor photocatalysis

http://nathan.instras.com/MyDocsDB/doc-557.pdf

Photosensitized singlet oxygen and its applications

Heme-Containing Oxygenases

The use of lasers, over the past few decades, has emerged to be highly promising for cancer therapy modalities, most commonly the photothermal therapy method, which employs light absorbing dyes for achieving the photothermal damage of tumors, and the photodynamic therapy, which employs chemical photosensitizers that generate singlet oxygen that is capable of tumor destruction. However, recent advances in the field of nanoscience have seen the emergence of noble metal nanostructures with unique photophysical properties, well suited for applications in cancer phototherapy. Noble metal nanoparticles, on account of the phenomenon of surface plasmon resonance, possess strongly enhanced visible and near-infrared light absorption, several orders of magnitude more intense compared to conventional laser phototherapy agents. The use of plasmonic nanoparticles as highly enhanced photoabsorbing agents has thus introduced a much more selective and efficient cancer therapy strategy, viz. plasmonic photothermal therapy (PPTT). The synthetic tunability of the optothermal properties and the bio-targeting abilities of the plasmonic gold nanostructures make the PPTT method furthermore promising. In this review, we discuss the development of the PPTT method with special emphasis on the recent in vitro and in vivo success using gold nanospheres coupled with visible lasers and gold nanorods and silica-gold nanoshells coupled with near-infrared lasers.

http://wiki.phy.queensu.ca/shughes/images/0/0f/Cancer_3.pdf

Plasmonic photothermal therapy (PPTT) using gold nanoparticles

Acidified nitrite mixtures react with octaethylporphyrin, mesoporphyrin dimethyl ester, and (less effectively) octaethylhaemin to give meso-nitro-derivatives. Such products are also furnished by the reaction of sodium nitrite or nitric oxide with a preparation of the radical cation of zinc(II) octaethylporphyrin. The radical cation also gives meso-substituted derivatives with chloride, thiocyanate, and benzoate ions.Nitrosylhaems are characterised from the reactions of nitric oxide with octaethylhaemin and protohaemin dimethyl ester. The pigment of cured meat, nitrosylprotohaem, has been fully characterised (as its dimethyl ester) for the first time. The reaction of excess of acidified nitrite with octaethylhaemin for a short period gives a product regarded as a mixture of mono- and di-nitrosyl derivatives, but in the presence of ascorbic acid nitrosylocataethylhaem is formed cleanly. Under suitable conditions nitrosylhaems react with secondary amines to generate nitrosamines. The results are discussed in the context of the chemistry of meat curing processes.

Nitrosation and nitrosylation of haemoproteins and related compounds. Part 1. Porphyrins and metalloporphyrins

Coupled oxidation of haemin gives four isomeric biliverdins, which have been isolated and characterised as their dimethyl esters.

Oxidative cleavage of the haem system: the four isomeric biliverdins of the IX series

Various reactions of 1,3,4,7-tetramethylisoindole are described. The tautomerism with the corresponding 1H-iso-indole in various solvents is examined. Autoxidation leads to two compounds which are formulated as 1-hydroxy-and 1-hydroperoxy-1H-isoindole derivatives. The addition of dienophiles is complex : maleic anhydride gives the Diels–Alder adduct (IX) which subsequently isomerises (on melting, or in solution) to give (X). Dimethyl acetylenedicarboxylate gives both 1 : 1 and 1 : 2 adducts : structures are proposed for these compounds. When heated with a metal powder or a metal salt 1,3,4,7-tetramethylisoindole gives the metallo-octamethyltetrabenzporphyrins.

The chemistry of 1,3,4,7-tetramethylisoindole and a route to the tetrabenzporphyrin system

This invention provides novel compounds for therapy of tumors susceptible to necrosis when an appropriate compound is administered followed by illumination with light of a wavelength absorbed by the compound, the compounds being dihydro porphyrins of the formula, or the corresponding tetra-hydro prophyrins: ##STR1## where n=1 to 3 and each substitutent R, the same or different and at the same or different position in its respective substituent phenyl ring, is an hydroxy group.

Raymond Bonnett

Papers

Nitrosation and nitrosylation of haemoproteins and related compounds. Part 1. Porphyrins and metalloporphyrins

Oxidative cleavage of the haem system: the four isomeric biliverdins of the IX series

The chemistry of 1,3,4,7-tetramethylisoindole and a route to the tetrabenzporphyrin system

Dihydroporphyrins and method of treating tumors

Porphyrins in coal