Effects of Low Dose Radiation on Biological Processes in Peri-tumoral and Tumoral Areas n Squamous Cell Skin Cancer

Abstract

Very low dose ionizing radiation (LDR) may have paradoxically beneficial effects via an adaptive response. This adaptive response can mitigate against the potential adverse effects of high-dose radiation therapy and chemotherapy. In this study we aimed to:1.identify the specific molecular details behind the adaptive response to LDR and2.integrate the LDR adaptive response into clinical practice. Our aim was to determine how low dose radiation modifies genetic expression in both healthy and tumor tissue. To determine this, a human clinical trial (n=8) was conducted in 2018 to ascertain the biological effects of integrating 0.1Gy of LDR into standard radiotherapy (2Gy fractions) over the first two weeks of radiation treatment for epidermoid skin cancers. RNA was obtained from skin biopsies and processed for genetic expression using Affymetrix Human gene chips Clarion-D (138K genes). 8 patients with squamous skin cancer, were studied according to the experimental design showed in Figure 1. Biopsy samples were collected and total RNA preparation (100 ng), labeled cRNA synthesis, hybridization, scanning, and image analysis were performed. Changes in biological response were measured using Affymetrix microarrays. Experiments 17F1 and 17F2 were performed in duplicate, and experiments 18F3 and 18F4 were performed in triplicate. Pathway analysis was performed using the Affymetrix Transcriptome Analysis Console software and the Wikipaths database. Comparisons were performed as noted in Table 1. The difference in gene expression in healthy tissues due to LDR exposure is quite low (only 325 genes, mostly downregulated) as noted in Figures 2A and 3A and Tables 2 and 3. The 20 most important biological processes enriched are shown in Figure 4 and include Senescence and Autophagy in malignant cells, and the Genotoxicity Pathway (both downregulated). The difference in gene expression in tumor tissue due to LDR exposure is significantly more pronounced (5,651 genes, mostly upregulated) as noted in Figures 2C and 3C. The 20 most important biological processes enriched are shown in Figures 5 and 6 and Tables 4-6, and include the Allograft rejection pathway in skin cancer (upregulated). Our results suggest that very low doses of radiation (0.1Gy) have a narrow effect on gene expression when applied in the healthy peritumoral area. Down regulated genes predominate, and DNA repair mechanisms are stimulated by the first low dose in healthy tissue.