Search

Introduction: Chemokine (C-X3-C Motif) Receptor 1 (CX3CR1) is present on a subset of the immune cells in the tumor microenvironment (TME) and plays an essential and diverse role in cancer progression. However, its potential function in the irradiated TME remains unknown.Materials and Methods: Mouse lung cancer model was performed by subcutaneously inoculating Lewis Lung Carcinoma (LLC) cells expressing luciferase (Luc-2) and mCherry cells in CX3CR1GFP/GFP , CX3CR1DTR/+ , and wild–type (WT) mice. Bioluminescence imaging, clonogenic assay, and flow cytometry were used to assess tumor progression, proliferation, and cell composition after radiation.Results: Radiation provoked a significant influx of CX3CR1-expressing immune cells, notably monocytes, into the TME. Co-culturing irradiated LLC cells with CX3CR1-deficient monocytes and macrophages resulted in reduced clonogenic survival and increased apoptosis of the cancer cells. Interestingly, depletion of CX3CR1 in macrophages led to a redistribution of the irradiated LLC cells in the S-phase, parallel to increased expression of cyclin E1, required for cell cycle G1/S transition. In addition, deletion of CX3CR1 expression in macrophages altered the cytokine secretion with a decrease of interleukin-6, a crucial mediator of cancer cell survival and proliferation. Next, LLC cells were injected subcutaneously into CX3CR1DTR/+ mice, sensitive to diphtheria toxin (DT), and WT mice. After injection, tumors were irradiated with 8Gy, and mice were treated with DT, leading to conditional ablation of CX3CR1-expressing cells. After three weeks, CX3CR1 depleted mice displayed reduced tumor progression. Furthermore, combining the S-phase specific chemotherapy gemcitabine with CX3CR1 cell ablation resulted in additional attenuation of tumor progression.Conclusion: CX3CR1-expressing mononuclear cells invade the TME after radiation therapy in a mouse lung cancer model. CX3CR1 cell depletion attenuates tumor progression following radiation and sensitizes the tumor to S–phase-specific chemotherapy. Thus, we propose a novel strategy to improve radiation sensitivity by targeting the CX3CR1-expressing immune cells.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is remarkably resistant to standard modalities, including radiotherapy (RT). The mechanisms of radiation resistance in general, and pancreatic cancer in particular, are poorly understood. We hypothesized that metabolic reprogramming may underlie this radioresistance, and moreover, that it would be possible to exploit these changes in metabolism for therapeutic intent. Experimental Design: We established multiple isogenic models of radioresistant PDAC cells. Metabolic profile was investigated using Nanostring technology, labeled-glucose tracing by liquid chromatography-mass spectrometry, Seahorse analysis and exposure to metabolic inhibitors. Patient-derived xenografts (PDXs) were established from patients treated with radiation and RNA sequencing performed. The PDXs were grouped according to clinical RECIST response to radiation (responsive/stable disease vs disease progression) and differential gene expression analysis was performed. Results: The radioresistant cells overexpressed pyruvate dehydrogenase kinase (PDK) and were radiosensitized by the PDK inhibitor dichloroacetate. In keeping with PDK overexpression, radioresistant cells displayed increased glycolysis and downregulated both the tricarboxylic acid cycle and oxidative phosphorylation. Metabolic flux through the pentose-phosphate pathway (PPP) was increased, as were levels of reduced glutathione; PPP inhibition dramatically potentiated radiation-induced cell death. Critically, the PPP was upregulated in PDXs derived from patients who demonstrated clinical resistance to radiotherapy. High transcription levels of 6PGD, the rate-limiting enzyme of the PPP, were associated with a poor radiological response to radiation therapy (p=0.0004) and a lower overall survival (p=0.004). Conclusions: We demonstrate that radioresistant PDAC cells divert the glycolytic flux from the tricarboxylic acid cycle and oxidative phosphorylation to the PPP, thereby increasing their antioxidant capacity and promoting nucleotide synthesis for DNA repair. Furthermore, we show that PDAC cells can be radiosensitized via PPP inhibition. Exploitation of metabolic vulnerabilities to radiosensitize tumors constitutes a novel approach to pancreatic cancer with a real potential to improve clinical outcomes. Citation Format: Ariel Shimoni-Sebag, Ifat Abramovich, Bella Agranovich, Yaarit Sirovsky, Chani Stossel, Dikla Atias, Maria Raitses-Gurevich, Yulia Glick-Gorman, Ofer Margalit, David Regev, Rotem Tal, Itay Tirosh, Talia Golan, Keren Yizhak, Eyal Gottlieb, Yaacov R. Lawrence. The pentose-phosphate pathway induces pancreatic cancer radioresistance, a preclinical study with clinical validation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2411.

Animal brain-tumor models have demonstrated a synergistic interaction between radiation therapy and a ketogenic diet (KD). Metformin has in-vitro anti-cancer activity, through AMPK activation and mTOR inhibition. We hypothesized that the metabolic stress induced by a KD combined with metformin would enhance radiation's efficacy. We sought to assess the tolerability and feasibility of this approach.A single-institution phase I clinical trial. Radiotherapy was either 60 or 35 Gy over 6 or 2 weeks, for newly diagnosed and recurrent gliomas, respectively. The dietary intervention consisted of a Modified Atkins Diet (ModAD) supplemented with medium chain triglycerides (MCT). There were three cohorts: Dietary intervention alone, and dietary intervention combined with low-dose or high-dose metformin; all patients received radiotherapy. Factors associated with blood ketone levels were investigated using a mixed-model analysis.A total of 13 patients were accrued, median age 61 years, of whom six had newly diagnosed and seven with recurrent disease. All completed radiation therapy; five patients stopped the metabolic intervention early. Metformin 850 mg three-times daily was poorly tolerated. There were no serious adverse events. Ketone levels were associated with dietary factors (ketogenic ratio, p 0.001), use of metformin (p = 0. 02) and low insulin levels (p = 0.002). Median progression free survival was ten and four months for newly diagnosed and recurrent disease, respectively.The intervention was well tolerated. Higher serum ketone levels were associated with both dietary intake and metformin use. The recommended phase II dose is eight weeks of a ModAD combined with 850 mg metformin twice daily.