Abstract
In this study we have focused on the response of SKBR-3 cells to both single 17-DMAG treatment as well as its combination with photodynamic therapy with hypericin. Low concentrations of 17-DMAG without any effect on survival of SKBR-3 cells significantly reduced metabolic activity, viability and cell number when combined with photodynamic therapy with hypericin. Moreover, IC10 concentation of 17-DMAG resulted in significant increase of SKBR-3 cells in G1 phase of the cell cycle, followed by an increase of cells in G2 phase when combined with photodynamic therapy. Furthermore, 17-DMAG already decreased HER2, Akt, P-Erk1/2 and survivin protein levels in SKBR-3 cells a short time after its application. In this regard, 17-DMAG protected also SKBR-3 cells against both P-Erk1/2 as well as survivin upregulations induced by photodynamic therapy with hypericin. Interestingly, IC10 concentration of 17-DMAG led to total depletion of Akt, P-Erk1/2 proteins and to decrease of survivin level at 48 h. On the other hand, 17-DMAG did not change HER2 relative expression in SKBR-3 cells, but caused a significant decrease of HER2 mRNA in MCF-7 cells characterized by low HER2 expression. These results show that targeting HSP90 client proteins increases the efficiency of antineoplastic effect of photodynamic therapy in vitro.
Highlights
The HER2 oncoprotein is an important therapeutic target in the treatment of invasive breast cancers associated with poor disease-free survival and resistance to chemotherapy [1]
The cells were incubated with different concentrations (0.84–210 nM) of hypericin (AppliChem, Darmstadt, Germany) and/or 17-DMAG (0.5–500 nM) (Alexis Biochemical, Lausen, Switzerland) in dark conditions for 24 h followed by photosensitization and further 24 or 48 h incubation of cells in a humidified 5% CO2 atmosphere, protected from light
We have studied the effect of single 17-DMAG as well as its combination with hypericin-photodynamic therapy (PDT)
Summary
The HER2 oncoprotein is an important therapeutic target in the treatment of invasive breast cancers associated with poor disease-free survival and resistance to chemotherapy [1]. The application of monoclonal antibody against HER2-trastuzumab has shown beneficial effects when combined with docetaxel and platinum salts [3] or paclitaxel and carboplatin [4,5], its use beyond first-line therapy might develop resistance to this agent In this regard, inhibition of PTEN [6], overexpression of IGF-IR [7] and MUC4 [8] and increased level of VEGF protein [9] could play a significant role. We have demonstrated hypericin-PDT mediated degradation of HER2 receptor in the same cell line via lysosomal activity [23] These results as well as known facts about HSP90-directed agent benzoquinone ansamycin-geldanamycin led us to determine the effect of combination of PDT and HSP90 inhibitor on the response of HER2 overexpressed SKBR-3 cells in vitro. Instead of geldanamycin we used a less toxic and more soluble form of geldanamycin – 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG)
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