Project 1: FLASH vs. Standard radiotherapy for treatment of PDAC and sparing normal intestine tissues

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SUMMARY (changes from previous submission denoted with shaded text ) Project 1 will test the overall hypothesis that Proton Radiotherapy delivered in ultra-fast dose rates (>60 Gy/sec), termed FLASH-PRT, controls Pancreatic tumor growth equally well as Standard dose rate (<1 Gy/sec) Proton Radiotherapy (S-PRT), while sparing normal intestinal tissue from acute and delayed toxicity. Successful completion of the proposed studies will lead to better mechanistic understanding of the differential effects of F-PRT compared to S-PRT at the molecular, genetic and organismic level and will define the parameters necessary for the initiation of clinical trials. In preliminary published studies, we demonstrated that compared to S-PRT, F-PRT increases overall survival of model mouse models and also ameliorates late stage toxicity, primarily fibrosis. At the same time, F-PRT was shown to be equipotent to S-PRT in controlling the growth of allografted syngeneic tumors. Studies using single-cell RNA- sequencing (scRNAseq), reveal intriguing differences in gene expression profiles in the response of epithelial stem/progenitor cells to F-PRT compared to S-PRT which coincide with a reduction in the inhibitory effect on progenitor cell proliferation. In Aim 1, we will define the dosimetric and biophysical parameters which deliver maximum normal tissue sparing and anti-tumor effect of F-PRT using syngeneic flank and orthotopic models and Genetically Engineered Mouse model (GEMM) of PanCa. We will then link perform a dose-escalation study using these optimized parameters and focal RT to determine in F-PRT improves overall survival compared to S-PRT . In Aim 2, we will delineate the mechanism of differential response of normal intestinal and liver tissues including epithelium, vascular, immune and circulating cells to S-PRT and F-PRT, using scRNAseq to deconvolute the differential patterns of gene expression elicited by the two modalities. In Aim 3, we will use GEMM with tissue-specific deletion of p53 (epithelium vs. endothelium) to investigate the role of epithelial and endothelial cells respectively, in the response to S-PRT and F-PRT on acute and late toxicity coupled with reduced epithelial barrier loss. We will also test the involvement of the Wnt/β-catenin and R-Spondin signaling in mediating F- PRT sparing of normal intestinal epithelium . This project will benefit from, and contribute to, conceptual advances in the other projects. Information garnered from scRNA-seq will inform experiments on skin toxicity and progenitor cell fate in Project 2, including the canine trial on sarcoma. Results from epithelial-specific and endothelial-specific p53 knockout mice in this project will guide experiments in Projects 2 and Project 3 in sarcoma and lung. Project 3 will generate Carbon and Proton-irradiated intestinal and PanCa samples which will be analyzed by Project 1. Finally, Project 4 will develop a pencil-beam scanning approach which we will employ in the dose-escalation experiments under Aim 1.