Iminium salt benzochlorins: structure-activity relationship studies

Current status of phthalocyanines in the photodynamic therapy of cancer

Photodynamic therapy is a binary treatment now accepted in clinic for various malignancies in several countries around the world. Phthalocyanine molecules are second-generation photosensitizers with enhanced photophysical and photochemical properties over those of porphyrins. They have been shown to be phototoxic against a number of cell types and tumor models. A great deal of research has been devoted to the elucidation of their mechanism of action and mode of cell death. The present paper reviews phthalocyanine pre-clinical anti-cancer research with emphasis on phthalocyanine induced apoptosis using a silicon phthalocyanine, Pc 4. A brief summary of the latest clinical results using phthalocyanines is presented.

Photodynamic therapy and the development of metal-based photosensitisers

Photodynamic therapy (PDT) is a treatment modality that has been used in the successful treatment of a number of diseases and disorders, including age-related macular degeneration (AMD), psoriasis, and certain cancers. PDT uses a combination of a selectively localised light-sensitive drug (known as a photosensitiser) and light of an appropriate wavelength. The light-activated form of the drug reacts with molecular oxygen to produce reactive oxygen species (ROS) and radicals; in a biological environment these toxic species can interact with cellular constituents causing biochemical disruption to the cell. If the homeostasis of the cell is altered significantly then the cell enters the process of cell death. The first photosensitiser to gain regulatory approval for clinical PDT was Photofrin. Unfortunately, Photofrin has a number of associated disadvantages, particularly pro-longed patient photosensitivity. To try and overcome these disadvantages second and third generation photosensitisers have been developed and investigated. This Review highlights the key photosensitisers investigated, with particular attention paid to the metallated and non-metallated cyclic tetrapyrrolic derivatives that have been studied in vitro and in vivo; those which have entered clinical trials; and those that are currently in use in the clinic for PDT.

Photocatalytic generation of oxygen radicals by the water-soluble bacteriochlorophyll derivative WST11, noncovalently bound to serum albumin

Light-induced radical generation is the hallmark of fundamental processes and many applications including photosynthesis and photodynamic therapy (PDT). In this manuscript, we present two novel observations made upon monitoring light-induced generation of reactive oxygen species (ROS) in aqueous solutions by WST11, a water-soluble derivative of the photosynthetic pigment Bacteriochlorophyll a (Bchl). Using a host of complementary experimental techniques including time-resolved spectroscopy at the subpicosecond to the millisecond range, ESR spectroscopy, electrochemistry, spectroelectrochemistry, oximetry, and protein mass spectroscopy, we first show that in aqueous solutions WST11 generates only superoxide (O(2)(-*)) and hydroxyl (OH*) radicals with no detectable traces of singlet oxygen. Second, we show that WST11 makes a noncovalent complex with human serum albumin (HSA) and that this complex functions as a photocatalytic oxidoreductase at biologically relevant concentrations enabling approximately 15 cycles of electron transfer from the associated HSA protein to molecular oxygen in the solution. These findings rule out the paradigm that porphyrin and chlorophyll based PDT is mainly mediated by formation of singlet oxygen, particularly in vascular targeted photodynamic therapy (VTP) with sensitizers that undergo photoactivation during circulation in the plasma, like [Pd]-Bacteriopheophorbide (WST09, Tookad). At the same time, our findings open the way for new design paradigms of novel sensitizers, since O(2)(-*) and OH* radicals are well-recognized precursors of important pathophysiological processes that can be activated for achieving tumor eradication. Moreover, the finding that promiscuous protein scaffolds become sinks for holes and electrons when holding light-activated pigments provides a new insight to the evolution and action mechanism of natural light activated oxidoreductases (such as photosynthetic reaction centers) and new guidelines for the preparation of synthetic-light converting machineries.

3-[(Methyl-carbamo-yl)amino]-1H-isoindolium chloride

The title compound, C(10)H(12)N(3)O(+)·Cl(-), is a derivative of o-phthaldehyde and methyl-thio-urea. The mol-ecules form dimers through intra- and inter-molecular N-H⋯O hydrogen bonds. The dimers are further linked into chains through one C-H⋯Cl and two N-H⋯Cl hydrogen bonds.

Photophysical and photobiological processes in the photodynamic therapy of tumours

Photodynamic therapy (PDT) is an innovative and attractive modality for the treatment of small and superficial tumours. PDT, as a multimodality treatment procedure, requires both a selective photosensitizer and a powerful light source which matches the absorption spectrum of the photosensitizer. Quadra Logic's Photofrin, a purified haematoporphyrin derivative, is so far the only sensitizer approved for phase III and IV clinical trials. The major drawbacks of this product are the lack of chemical homogeneity and stability, skin phototoxicity, unfavourable physicochemical properties and low selectivity with regard to uptake and retention by tumour vs. normal cells. Second-generation photosensitizers, including the phthalocyanines, show an increased photodynamic efficiency in the treatment of animal tumours and reduced phototoxic side effects. At the time of writing of this article, there were more than half a dozen new sensitizers in or about to start clinical trials. Most available data suggest a common mechanism of action. Following excitation of photosensitizers to long-lived excited singlet and/ or triplet states, the tumour is destroyed either by reactive singlet oxygen species (type II mechanism) and/or radical products (type I mechanism) generated in an energy transfer reaction. The major biological targets of the radicals produced and of singlet oxygen are well known today. Nucleic acids, enzymes and cellular membranes are rapidly attacked and cause the release of a wide variety of pathophysiologically highly reactive products, such as prostaglandins, thromboxanes and leukotrienes. Activation of the complement system and infiltration of immunologically active blood cells into the tumorous region enhance the damaging effect of these aggressive intermediates and ultimately initiate tumour necrosis. The purpose of this review article is to summarize the up-to-date knowledge on the mechanisms responsible for the induction of tumour necrotic reactions.

Purpurins and benzochlorins as sensitizers for photodynamic therapy

Purpurins and benzochlorins are hydrophobic second generation photosensitizers, which have sizable absorption in the 650-780 nm range and exhibit photodynamic activity against tumors after visible light treatment. This review summarizes the published data regarding these compounds: from the spectroscopic, photophysical and photochemical characteristics to the in vivo and in vitro photodynamic inactivation of tumors and normal tissue effects. Some mechanistic studies using both the Sn-etiopurpurin and/or the Cu-benzochlorin derivatives are also reviewed.