Impact of different radiation qualities on molecular and functional changes in cancer cells: role of Hedgehog signaling

Konings Katrien

Promoter

Haustermans Karin, (KUL), karin.haustermans@med.kuleuven.be

SCK•CEN Mentor

Moreels Marjan
marjan.moreels@sckcen.be
+32 14 33 28 16

Expert group

Radiobiology

PhD started

2014-10-01

Short project description

Radiation therapy is the standard care for many types of cancers. One of the most recent advances in this field is hadron therapy, which uses beams of charged particles such as protons and carbon ions to hit the tumor. Of these, proton therapy is by far the most common. The inverted depth-dose profile and the sharp dose fall-off after the Bragg peak offered by charged particle beams allow for a more precise localization of the radiation dosage to the tumor as compared to the conventional used photons (X-rays). As a consequence, the surrounding healthy tissue receives a much lower dose. Besides this ballistic advantage, the use of high-linear energy transfer (LET) carbon ion beams offers also a biological advantage, i.e. a higher relative biological effectiveness (RBE) as compared to conventional low-LET photon therapy. Carbon ion radiation is thus more effective in inducing DNA damage, cell cycle arrest and cell death, thereby accounting for highly lethal effects, even in tumors that are resistant to X-ray irradiation.

 

The response of an irradiated cell depends on the dose, dose-rate, radiation quality, the lapse between the radiation-induced stress and the analysis, and the cell type. Several studies within SCK•CEN and outside have already compared changes in gene expression induced by different radiation qualities. Overall, the number of differentially expressed genes as well as the magnitude of (dose-dependent) gene expression changes was found to be more pronounced after irradiation with particle beams. In the context of the ongoing PhD project of Annelies Suetens performed at the Radiobiology Unit of SCK•CEN, the effect of different radiation qualities (low-LET photons and high-LET protons and carbon ions) on the gene expression of prostate cancer cells in vitro was deeply investigated. The results of this project clearly demonstrated a dose-dependent downregulation in several genes involved in cell migration and motility after carbon ion irradiation. A higher number of genes as well as more pronounced changes in their expression levels were found after carbon ion irradiation compared to X-rays. Further research is however needed to investigate whether the observed molecular changes also influence the cellular 'behavior' after irradiation in terms of cell migration and motility after irradiation, since these are prominent characteristics of cancer progression and metastasis. Assessing both the risks and advantages of high-LET irradiation can contribute to the study of the biological effect on the tumor and will lead to further acceptance and improvement of the clinical outcome of hadron therapy.

 

One important pathway that has been implicated in metastasis is the Hedgehog (Hh) signaling pathway. Several target genes of the Hh pathway are known to play a role in the process of metastasis, including MMP9 and SNAI1. Recent studies demonstrated that this pathway can become activated after exposure to low-LET photons, thereby contributing to radioresistance. Targeting the Hh signaling pathway may thus be a novel strategy to enhance the radioresponse of human cancer cells. Whether high-LET particle radiation also affects the Hh pathway is currently unknown. Preliminary findings obtained at the Radiobiology Unit of SCK•CEN indicate that carbon ion irradiation induces changes in the gene expression of several components and downstream-targets of the Hh pathway.

Objective

Within this PhD proposal, we will investigate the impact of different radiation qualities on Hedgehog signaling in cancer cells.

More specific, we will:

(1) further investigate the cellular and molecular response to low and high doses of different radiation qualities

(2) study how Hh signaling inhibitors can modulate the sensitivity of cancer cells to low and high doses of ionizing radiation of different qualities.

 

Experimental set-up

All experiments will be performed using in vitro human cancer cell lines, more specific a prostate cancer cell line (PC3) and a medulloblastoma cell line (Daoy- will be used. Not only are both cancer type indications for the use of particle therapy, but the Hh signaling pathway seems to play an important role both in the initiation as well as the progression and metastasis of these cancers.

Low-LET X-ray irradiation will be performed at the irradiation facility of SCK•CEN. For irradiation experiments with high-LET beams, we will continue to apply for beam time to different European accelerator facilities including GSI (Darmstadt, Germany), GANIL (Caen, France), and LNS-INFN (Catania, Italy).

To investigate the cellular and molecular response of these cancer cells to low and high doses of different radiation qualities, several experiments will be done: a) analysis of changes in gene expression involved in the Hh pathway and migration pathways, b) cell migration and motility assays to examine the potential changes in cell behavior, and c) colony formation assays to determine clonogenic cell survival.

In the second part of this PhD project, the cancer cell lines will be treated with different Hh signaling inhibitors and their effect on cell survival and cell behavior after irradiation with different radiation qualities will be investigated by means of clonogenic assays and cell migration/motility assays respectively.