Possibilities of Radiosensitization and Reduced Invasion After Targeting the SCF/c-Kit Pathway in Human Cancer Cells

Abstract

The SCF/c-Kit pathway is often overexpressed in human tumors leading to an enhanced proliferation and invasion. Resulting therapy resistance and metastasis often are limiting factors of a successfull radiotherapy. It was now tested for NSCLC and prostate cancer cells growing in 2D and 3D whether the inhibition of this pathway can be used to achieve a reduced cancer cell invasion and whether a significant increased radiosensitivity could be achieved. Experiments were performed using different NSCLC (H23, H226, H460, H520, H1299, H1975, A549) and prostate cancer cell lines (DU 145, PC3, LnCAP) growing either under 2D or 3D conditions. SCF was knocked down by siRNA, c-Kit was inhibited by ISCK03 inhibitor and cells were irradiated with 2 Gy or 6 Gy Photons. Cell survival was determined by colony formation assay. Invasion was measured using BioCoat™ Matrigel™ invasion chambers. When grown in 3D a 2-3-fold increase in invasion capability was examined in all NSCLC and prostate cancer cell lines except H520. This could be explained by EMT-like changes (enhanced expression of vimentin and N-cadherin and reduction of E-cadherin) when cells were grown in 3D. Just the opposite trends were found for H520 cells. Knock down of SCF was generally found to result in significantly reduced invasion and in only a minor increase of cellular radiosensitivity (2D and 3D). Only in cells characterized by a massive overexpression of SCF (H520) a significant increase of cellular radiosensitivity could be obtained after SCF knock down. The inhibition of c-Kit by a specific inhibitor was also found to result only in minor radiosensitization. Photon irradiation did not modulate cancer cell invasion (2D and 3D). For the regulation of tumor cell motility and invasion the SCF/c-Kit pathway appears to take a key position. Inhibition of this pathway significantly reduces the cell invasion of human NSCLC and prostate cancer cells under 2D and 3D conditions. In addition our data indicate that generally cell survival and radioresponse are not strongly determined by the SCF/c-Kit pathway. As a consequence targeting SCF or c-Kit only results in increased radiosensitivity when SCF is strongly over expressed as found for H520 cells.