Differential cytotoxic effects induced after photosensitization by hypericin.

The cytotoxic effects of the natural photosensitizing agent hypericin were evaluated. A dramatic difference in the sensitivity of several different human and mouse cell lines towards photoactivated hypericin (4 J cm-2) was demonstrated using a neutral red assay (e.g.

Antitumour activity of photosensitized hypericin on A431 cell xenografts.

The in vivo antitumour activity of the natural photosensitizer hypericin was evaluated. Athymic nude mice xenografted with A431 cells were intraperitoneally administered with different hypericin doses and the tumours were locally irradiated 2 h later with white light (180 J/cm2) using a cold light source. When treatment was started one day after tumour inoculation, a dose-dependent antitumour effect was observed in light-treated animals.

Analysis of the phosphoamino acid content of phosphoproteins.

A method has been developed for the analysis of phosphoserine, phosphothreonine and phosphotyrosine in 32P-phosphoprotein hydrolysates. The hydrolysates are treated with dabsyl reagent (28.8 mM) for 10 min at 70 degrees C.

A comparative analysis of the photosensitized inhibition of growth-factor regulated protein kinases by hypericin-derivatives.

The photodynamic inhibitory effect of hypericin and a number of hypericin-derivatives were investigated in vitro using numerous growth-factor regulated protein kinases including receptor-bound (Insulin-R, EGF-R) and non-receptor (Lyn, c-Fgr, CSK, Syk) protein tyrosine kinases as well as Ser/Thr (PK-C, protein kinase CK-2, CK-1) protein kinases. Modification of the hypericin structure altered significantly the specificity of the protein kinase inhibition. In particular, methylation or attachment of long lipophilic chains to both methyl groups of the hypericin molecule strongly enhanced the specificity toward PK-C.

Analysis of phosphorylhydroxyamino acids present in hydrolyzed cell extracts using dabsyl derivatization.

We have developed a new method for the quantification of phosphoserine, phosphothreonine, and phosphotyrosine as dabsyl derivatives in acid-hydrolyzed extracts of 32P-labeled A431 cells. In the first step the phosphamino acids are concentrated using a disposable anion-exchange column. Subsequently, the phosphoamino acid fraction is treated with dabsyl reagent (28.