The use of photosensitizers to improve the efficiency of radiotherapy

Radiotherapy (RT) is currently the leading therapeutic strategy for prostate cancer (PCa) and a major curative treatment for head and neck squamous cell carcinoma (HNSCC) in combination with surgery or concurrent chemotherapy in advanced stages. Despite advances in radiotherapy leading to the precise delivery of high radiation doses, radioresistance and locoregional recurrence are the major cause of treatment failure. Photodynamic therapy (PDT) is safe, low toxic and selective method of cancer treatment. It utilizes non-invasive elements: photosensitizer (PS) and light of a specific wavelength that is able to photoactivate PS to generate cytotoxic reactive oxygen species (ROS). Highly penetrating X-ray during megavoltage clinical beam radiation can generate visible light in UVA spectrum and activate PSs placed in deep-seated tumors. Megavoltage irradiation can generate UVA light in two ways: 1) directly through photon that travels faster than the speed of light through a medium thereby generating Cherenkov light (called “radiotherapy enhanced with Cherenkov photo-activation” - RECA); 2) through nanoparticle scintillators that convert external X-ray photons to UV light (called X-PDT). X-ray induced PDT has become a promising, novel anti-cancer strategy. The aim of the project is to verify whether the use of PSs during clinical X-ray megavoltage beam irradiation increases the effectiveness of radiotherapy. In the project we will use drugs (ketoprofen, lomefloxacin, doxycycline, 8-methoxypsolaren) with proven phototoxic and anti-cancer properties. We will investigate whether they can serve as photosensitizers in RECA or X-PDT therapies. We will evaluate the phototoxic effect of increasing energy of megavoltage beam radiation (6 MV, 15 MV and 20 MV). Additionally, X-ray induced phototoxicity will be assessed following two irradiation regimens: single high dose irradiation (we will start from 10Gy and then the dose will be downsized to maintain the maximum benefit) or a fractionated dose (3x2.5Gy), which corresponds to the clinical hypofractionated radiotherapy regimen. For X-PDT yttrium oxide (Y2O3) loaded polymer nanospheres will be designed and constructed to serve as scintillator. Additionally, after determining the most efficient photosensitizer, we will construct Y2O3 and PSs co-loaded nanospheres. X-ray induced phototoxic potential of the tested drugs will be assessed against radioresistant HNSCC and PCa. Furthermore we will verify if radioresistant cells subjected to therapeutic regimen combining RT and PDT will be more sensitive to chemotherapeutics standardly used in the clinic and if small molecule inhibitors that target the survival or DNA repair pathways will increase the effectiveness of tested therapy. The efficiency of RECA or X-PDT therapies regimens will be assessed, among others by: examining the viability of cancer cells and the type of induced cell death, assessing ROS production and mitochondrial activity, radiosensitivity determination by colony-forming unit assay. The research hypothesis will be verified on mouse models of human HNSCC and PCa. The potential to trigger anti-tumor immune response and the role of immune cells in the investigated therapeutic regimen will be determined in immunocompetent mouse models of HNSCC and PCa. The project is innovative. Its aim is to develop a novel method of sensitizing cancer cells to radiotherapy using drugs with photosensitizing potential available in the clinic, which can significantly increase the effectiveness of radiotherapy in radiotherapy-resistant head and neck and prostate tumors.