How to make hypericin water-soluble

Hypericin, isolated from Hypericum perforatum, is an effective photodynamic substance as demonstrated by various studies. Practical forms of applications of hypericin solutions for systemic use and introduction into body cavities are, however, lacking. We developed an aqueous solution of hypericin non-covalently bound to polyvinylpyrrolidone (PVP). PVP is a poly-N-vinylamide of various degrees of polymerization and forms of intermolecular crosslinks suitable for diagnostic and therapeutic applications. We used PVP (molecular weights of PVP between 10 kD and 40 kD) as a complex forming agent to prepare hypericin for photodynamic therapy and diagnostics. In pure water, hypericin forms aggregates which are non-soluble and non-fluorescent. The hypericin-PVP complex binds more than 1000 mg of hypericin in presence of 100 g PVP or less and is soluble in 1 liter of pure water. Aqueous complex solutions of hypericin-PVP display a characteristic absorption spectrum and fluorescence emission band around 600 nm wavelength. Varying concentrations of hypericin do not cause a blue- or red-shift in the absorption maximum at 595 nm. Excitation at 200 nm to 500 nm leads to emission at 590 nm; a property conducive to diagnostic investigations both in vitro and in vivo. Furthermore, hypericin-PVP exhibits high photostability in the presence of oxygen and broad band light which ensures reproducible photodynamic therapy and diagnosis.

CONCLUSION

Hypericin forms liquid molecular chromophore complexes in water when bound to PVP thus allowing investigations in biological media.

Pegylation of charged polymer-photosensitiser conjugates: effects on photodynamic efficacy

Conjugates between photosensitisers (PS) and charged polymeric carriers are under investigation for photodynamic therapy of cancer and may allow targeting to certain cell types or compartments in tumours. Covalent attachment of polyethylene glycol to macromolecules (pegylation) may alter their pharmacokinetics, cell type targeting, and photophysical properties. Macrophages may take up large amounts of aggregated PS, thus lessening the selectivity for cancer cells in tumours. We investigated the effect of pegylation on the uptake and phototoxicity of poly-L-lysine chlorin(e6) conjugates with either cationic or anionic charges in two cell lines, human ovarian cancer cells and mouse macrophages. The cationic conjugate after pegylation became less aggregated, consumed less oxygen and had reduced cellular uptake. However, the phototoxicity corrected for cellular uptake increased three- to five-fold. In contrast, the anionic succinylated conjugate on pegylation became more aggregated, consumed similar amounts of oxygen, and had higher cellular uptake. The anionic conjugate showed the highest relative phototoxicity towards both the cell lines (compared to the other three conjugates) and it decreased most towards the macrophages after pegylation. Pegylation reduced the amount of oxygen consumed per chlorin(e6) molecule when photosensitised cells were illuminated. These in vitro studies suggest that pegylation alters the phototoxicity of PS conjugates depending on the effect produced on the aggregation state.

Antagonistic effects of combination photosensitization by hypericin, meso-tetrahydroxyphenylchlorin (mTHPC) and photofrin II on Staphylococcus aureus

Photodynamic therapy involves the application of a photosensitizer activated by visible light to generate cytotoxic reactive oxygen. In addition to clinical investigations, in vitro studies concerning photodynamic potency of sensitizers as well as quantification of illumination procedures are necessary. In our investigation, the objective was to evaluate not only the effects of photosensitizer and light on Gram-positive Staphylococcus aureus, but also to investigate possible synergistic or antagonistic effects of these sensitizers. Therefore, we used hypericin, Photofrin II, porfimer sodium and meso-tetrahydroxyphenylchlorin (mTHPC) alone, as well as in combination. Log-phase cells of S. aureus exhibited a marked sensitivity to white thermal light irradiation in the presence of Photofrin II and mTHPC. However, hypericin caused a rather stimulated growth expressed in increased optical density (OD) and increase of total cell count (TCC) of the culture. Combination sensitization of S. aureus by Photofrin II and mTHPC with hypericin likewise caused a stimulation of bacterial growth. No synergistic effects were obtained by combination of Photofrin II and mTHPC; photoresponse of S. aureus was rather decreased by using combined porphyrins. In comparison, TCC and colony-forming units (CFU) were suppressed in the presence of mTHPC after an illumination procedure as well as in dark reactions. These effects were also obtained in the combination photosensitization by mTHPC and Photofrin II. In the presence the of hypericin, photodynamic effects of mTHPC and Photofrin II were inhibited. It was finally concluded that hypericin in our model is not a proper sensitizer for combination photo-sensitization due to antagonistic effects on photodynamic activity of mTHPC and Photofrin II.