Carbon-ion radiotherapy for enhancing treatment response to osteosarcoma
Osteosarcoma (OS) is the most common bone sarcoma, and is treated with surgery, chemotherapy, and radiation therapy. 30-40% of patients treated with curative intent relapse. In patients that recur, survival is less than 20%. OS is highly radioresistant, with poor response to immunotherapy. The first US carbon-ion radiotherapy (CIRT) center is under construction at Mayo Clinic. CIRT has unique physical and biological properties compared with X-rays. Once accelerated, carbon-ions travel through the body and stop in the tumor target, delivering high target dose while sparing healthy tissue. CIRT has also demonstrated a higher relative biological effect (RBE) compared with X-ray, generating among other traits a higher ratio of DNA double strand breaks (DSBs) to single strand breaks. Our preliminary data suggests that CIRT drives cells to repair these DSBs using homologous recombination (HR). Defects in HR repair are observed in approximately 50% of all OS. We hypothesize that for HR-proficient OS we can induce a defect in HR repair pharmacologically to enhance the efficacy of CIRT. OS is characterized by high rates of distant metastases. In our preliminary work we have further found that CIRT enhances immune response in mouse OS models. Mice receiving immunotherapy alone show no response, while CIRT alone reduces tumor size; this effect was enhanced with immunotherapy. Further, half the treated mice demonstrate a robust systemic response, showing suppressed metastasis and regression of a secondary, non-irradiated tumor. Thus, CIRT potentiates OS to immunotherapeutic response, with immune-related and DNA damage pathway-related marker elevation seen. Aim 1: Investigate proteo-transcriptomic signatures of CIRT response in OS. We will characterize OS response to CIRT and DNA repair targeting agents compared with standard of care X-ray using multiomic analyses. U2OS osteosarcoma cells have been treated with varying CIRT doses and a variety of key DNA repair inhibitors. These samples will be analyzed using RNA sequencing and phosphoproteomics to evaluate gene and protein expression changes following treatment, with aim to identify ways to better target particularly HR-proficient OS. Aim 2: Investigate the impact of CIRT on anti-tumor immunity. HR-deficiency leads to poor repair within tumors, increasing cellular mutation burden. In our preliminary data we also found enhanced type 1 interferon signaling following particle therapy in HR deficient cells. We hypothesize that HR-deficient osteosarcoma exposed to CIRT and immunotherapy will demonstrate an enhanced local antitumor effect and improved systemic immune response. We will modify LM8 cells to remove RAD51, disabling the HR pathway, before inoculating in mice and treating with CIRT. CIRT will be conducted at the National Institute of Quantum Science and Technology (Japan) with Dr Shimokawa; this grant will specifically fund multiomic analyses of these samples at Mayo Clinic.