Syntheses and preliminary in vivo photodynamic efficacy of benzoporphyrin derivatives from phylloerythrin and rhodoporphyrin XV methyl esters and aspartyl amides

Facile Synthesis of 131-Oxo-porphyrins Possessing Reactive 3-Vinyl or 3-Formyl Group, Protochlorophyll-a/dDerivatives by 17,18-Dehydrogenation of Chlorins

Methyl protopyropheophorbides-a/d were prepared by modification of readily available chlorophyll-a. The key step was oxidation of 131-oxo-chlorin to the corresponding porphyrin, and 2,3-dichloro-5,6-dicyano-p-benzoquinone was effective for 17,18-dehydrogenation. A reduction in oxidation potential of the chlorin was necessary for the oxidation. Facile oxidation was achieved by insertion of zinc as the central metal, reduction of the 13-carbonyl group and/or aggregation by high concentration. The synthetic 131-oxo-porphyrins had vinyl and formyl groups at the 3-position. These groups were very reactive in the molecule and selectively converted to other functional groups.

Multiepitope HER2 targeting enhances photoimmunotherapy of HER2-overexpressing cancer cells with pyropheophorbide-a immunoconjugates

Multi-targeting strategies improve the efficacy of antibody and immunotoxin therapies but have not yet been thoroughly explored for HER2-based cancer treatments. We investigated multi-epitope HER2 targeting to boost photosensitizer immunoconjugate uptake as a way of enhancing photoimmunotherapy. Photoimmunotherapy may allow targeted photodynamic destruction of malignancies and may also potentiate anticancer antibodies. However, one obstacle preventing its clinical use is the delivery of enough photosensitizer immunoconjugates to target cells. Anti-HER2 photosensitizer immunoconjugates were constructed from two monoclonal antibodies (mAb), HER50 and HER66, using a novel method originally developed to label photosensitizer immunoconjugates with the photosensitizer, benzoporphyrin derivative verteporfin. Photosensitizer immunoconjugates were labeled instead with a promising alternative photosensitizer, pyropheophorbide-a (PPa), which required only minor changes to the conjugation procedure. Uptake and phototoxicity experiments using human cancer cells were conducted with the photosensitizer immunoconjugates and, for comparison, with free PPa. SK-BR-3 and SK-OV-3 cells served as HER2-overexpressing target cells. MDA-MB-468 cells served as HER2-nonexpressing control cells. Photosensitizer immunoconjugates with PPa/mAb molar ratios up to approximately 10 specifically targeted and photodynamically killed HER2-overexpressing cells. On a per mole basis, photosensitizer immunoconjugates were less phototoxic than free PPa, but photosensitizer immunoconjugates were selective for target cells whereas free PPa was not. Multiepitope targeted photoimmunotherapy with a HER50 and HER66 photosensitizer immunoconjugate mixture was significantly more effective than single-epitope targeted photoimmunotherapy with a single anti-HER2 photosensitizer immunoconjugate, provided photosensitizer immunoconjugate binding was saturated. This study shows that multiepitope targeting enhances HER2-targeted photoimmunotherapy and maintains a high degree of specificity. Consequently, it seems that multitargeted photoimmunotherapy should also be useful against cancers that overexpress other receptors.

Research advances in the use of tetrapyrrolic photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising new treatment modality for several diseases, most notably cancer. In PDT, light, O2, and a photosensitizing drug are combined to produce a selective therapeutic effect. Lately, there has been active research on new photosensitizer candidates, because the most commonly used porphyrin photosensitizers are far from ideal with respect to PDT. Finding a suitable photosensitizer is crucial in improving the efficacy of PDT. Recent synthetic activity has created such a great number of potential photosensitizers for PDT that it is difficult to decide which ones are suitable for which pathological conditions, such as various cancer species. To facilitate the choice of photosensitizer, this review presents a thorough survey of the photophysical and chemical properties of the developed tetrapyrrolic photosensitizers. Special attention is paid to the singlet-oxygen yield (PhiDelta) of each photosensitizer, because it is one of the most important photodynamic parameters in PDT. Also, in the survey, emphasis is placed on those photosensitizers that can easily be prepared by partial syntheses starting from the abundant natural precursors, protoheme and the chlorophylls. Such emphasis is justified by economical and environmental reasons. Several of the most promising photosensitizer candidates are chlorins or bacteriochlorins. Consequently, chlorophyll-related chlorins, whose PhiDelta have been determined, are discussed in detail as potential photosensitizers for PDT. Finally, PDT is briefly discussed as a treatment modality, including its clinical aspects, light sources, targeting of the photosensitizer, and opportunities.

Synthesis of 18O-Labelled chlorophyll derivatives at carbonyl oxygen atoms by acidic hydrolysis of the ethylene ketal and acetal

The ethylene ketal of pyropheophorbides, chlorophylls possessing the 13-keto carbonyl group and lacking the 13(2)-methoxycarbonyl group, reacted with H(2)(18)O (ca. 95% 18O atom) by acidic hydrolysis to give efficiently and regioselectively 13(1)-18O-oxo-labelled compounds (ca. 92% 18O). The resulting 18O-labelled chlorin was modified by several chemical reactions to afford some derivatives with little loss of the 18O atom. Following the same procedures, 3(1),13(1)-doubly-18O-labelled pyrochlorophyll derivatives were also prepared. All the synthetic 18O-labelled compounds were identified by FAB-mass and vibrational spectra. Especially, in the vibrational spectroscopic results including IR and resonance Raman spectra, an about 30 cm(-1) wavenumber down-shift of the 3- and/or 13-C[double bond]O stretching vibrational bands was observed by exchanging 3(1)- or 13(1)-oxo-oxygen atom from 16O to 18O.