Comparative Proton and Photon Irradiation Combined with Pharmacological Inhibitors in 3D Pancreatic Cancer Cultures

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly therapy-resistant tumor entity of unmet needs. Over the last decades, radiotherapy has been considered as an additional treatment modality to surgery and chemotherapy. Owing to radiosensitive abdominal organs, high-precision proton beam radiotherapy has been regarded as superior to photon radiotherapy. To further elucidate the potential of combination therapies, we employed a more physiological 3D, matrix-based cell culture model to assess tumoroid formation capacity after photon and proton irradiation. Additionally, we investigated proton- and photon-irradiation-induced phosphoproteomic changes for identifying clinically exploitable targets. Here, we show that proton irradiation elicits a higher efficacy to reduce 3D PDAC tumoroid formation and a greater extent of phosphoproteome alterations compared with photon irradiation. The targeting of proteins identified in the phosphoproteome that were uniquely altered by protons or photons failed to cause radiation-type-specific radiosensitization. Targeting DNA repair proteins associated with non-homologous endjoining, however, revealed a strong radiosensitizing potential independent of the radiation type. In conclusion, our findings suggest proton irradiation to be potentially more effective in PDAC than photons without additional efficacy when combined with DNA repair inhibitors.

Comparative Therapeutic Exploitability of Acute Adaptation Mechanisms to Photon and Proton Irradiation in 3D Head and Neck Squamous Cell Carcinoma Cell Cultures

“…Firstly, we observed equal efficacy of protons and photons regarding the clonogenic survival and DSB induction and repair, which is in line with the notion of similar radiobiological effectiveness between photons and protons [ 7 , 24 ]. Such similarities of photon and proton irradiation have also been found for pancreatic ductal adenocarcinoma [ 21 ], glioma stem cells [ 25 ] and lung cancer [ 26 ]. As a sufficient repair of DNA damage reflects one major determinant of intrinsic cellular radiosensitivity, the similarity in DSB repair in photon- and proton-irradiated cells further underscores our clonogenic survival data.…”

“…As alternative approach and based on our knowledge of the radiosensitizing potential of DNA repair inhibitors [ 15 , 21 , 22 ], we tested whether such inhibitors result in comparable radiosensitization of 3D HNSCC cell cultures exposed to photon or proton irradiation. Our observations in the ATM-deficient HNSCC cell line SKX, which showed higher radiosensitivity to protons relative to photons, prompted us to evaluate the efficacy of pharmacological inhibitors targeting a number of key enzymes of the two major DSB repair pathways non-homologous end joining (NHEJ) and homologous recombination (HR) [ 23 ].…”

“…Although our limited approach to therapeutically exploit the kinome profiles failed, our results about ERK inhibition warrant further in-depth investigations and emphasize the rationale to include kinome analysis into our treatment decision making process. Considering that kinome profiling has been reported to be substantially valuable for investigating radioresistance in other tumor entities e.g., melanoma, pancreatic ductal adenocarcinoma or breast cancer [ 21 , 30 , 31 ], we were able to shed a light on kinase activity changes in HNSCC after proton therapy.…”

“…Cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM, Sigma-Aldrich, Taufkirchen, Germany) supplied with 10% fetal calf serum (FCS, Sigma-Aldrich, Taufkirchen, Germany) and 1% non-essential amino acids (Sigma-Aldrich, Taufkirchen, Germany) at 37 °C in a humidified atmosphere containing 8.5% CO2 at pH 7.4. For all experiments asynchronously growing cells were used within passages 2–5 [ 21 ].…”

Radiosensitizing Pancreatic Cancer with PARP Inhibitor and Gemcitabine: An In Vivo and a Whole-Transcriptome Analysis after Proton or Photon Irradiation

“…Recently, Görte et al evaluated phosphoproteomics changes after photon and proton irradiation and showed that proton therapy stimulates greater phosphoproteome changes compared to photon. Moreover, targeting classical and alternative NHEJ enhanced therapeutic ratio either with photon or proton [ 24 ].…”