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Interaction of photosenzitizer hypericin with polyethylen glycol
Diana Búzová1, Peter Kasák2, Daniel Jancura1, Pavol Miškovský1,3
1Dept. of Biophysics, P.J. Safarik University, Kosice, Slovakia, 2Polymer
Institute SAS, Slovakia, 3International Laser Center, Bratislava, Slovakia
This work presents the results of the study of the influence of different
types of polyethylen glycol (PEG) on solubilization of hypericin (Hyp) in
aqueous solutions. By means of UV-VIS absorption and fluorescence
spectroscopy we have studied the effect of length, molecular weight and
concentration of PEG on the transition of aggregate form of Hyp to its
monomeric form. Hyp is a promising agent for photodynamic therapy (PDT)
of cancer. Hyp under light illumination displays antiproliferative and
cytotoxic effects on many tumor cell lines. Hyp is a lipophilic molecule and
in aqueous environment forms insoluble aggregates. This makes
intravenous injection of this drug problematic and restricts its medical
applications. To overcome these problems, Hyp is usually incorporated into
biological organisms by means of drug delivery systems which increase its
solubility and bioavailability. One of the most popular drug carrier is PEG.
PEG is an uncharged hydrophilic polymer soluble in water composed of the
simple repeating unit HO-(CH2-CH2-O)n-H.
An increase of the intensity of Hyp fluorescence in the presence of PEG
was observed. This increase is proportional to the molecular weight of
molecules of PEG. With respect to the fact that the intensity of Hyp
fluorescence corresponds to the amount of monomeric form of Hyp, we can
conclude that PEG solubilize the aggregates of Hyp in aqueous solution.
A similar study was realized for PEG/cholesterol and PEG/phospholipids
conjugates. The intensity of Hyp fluorescence increases with the increase
of conjugates concentration. We have also determined the dependence of
absorption spectra of Hyp on PEG concentration for PEG molecules with
different molecular weights (from 300 to 8000 g.mol-1). For PEG with low
molecular weights (~ 300-600 g.mol-1), the absorption spectra of Hyp are
similar to the absorption spectra of Hyp in aqueous solution and an
increase of PEG concentration does not significantly changes character of
these spectra. It signifies that low molecular PEG is not suitable for the
monomerization of Hyp aggregates. PEG molecules with high molecular
weights (>1000 g.mol-1) are able to solubilize Hyp aggregates which is
demonstrated by the absorption spectrum of Hyp in their presence similar
to that for monomeric Hyp in organic solvents or lipids.
Acknowledgments: This work was supported by the Slovak Research
and Development Agency under contracts APVV-0449-07, LPP-0072-07
and the Scientific Grant Agency of the Ministry of Education of Slovak
Republic (grant VEGA-0164-09).