Possession Of Single Nucleotide Polymorphisms In A Series Of Candidate Genes Correlates With Low Levels Of Radiation-Induced Apoptosis And The Development Of Severe Late Adverse Effects Following Curative Intent Radiotherapy

Two complementary approaches for the identification of patients at high risk for the development of severe radiation-induced sequelae (RIS) were used. One method was a determination of radiation-induced CD8 lymphocyte apoptosis (LRIA). The other approach involved the comprehensive screening of a series of candidate genes for single nucleotide polymorphisms (SNPs) and was performed as part of the Gene-PARE project. The purpose of this trial was to assess whether the presence of SNPs in candidate genes and the level of apoptosis correlated with the appearance of radiation-induced normal tissue toxicity. DNA was isolated from blood samples obtained from 16 patients (Group A) who experienced grade 3–4 late sequelae in the KFS 00539-9-1997/SKL 00778-2-1999 prospective study where 399 patients were treated with curative intent radiotherapy for miscellaneous cancers (mainly breast and head and neck). All of the patients were evaluated for LRIA, and a control group (Group B) of 18 patients that did not develop late radiation toxicity was selected for DNA analysis. The DNA samples were screened for SNPs in the ATM, SOD2, XRCC1, XRCC3, TGFB1, and RAD21 genes using denaturing high performance liquid chromatography and the Surveyor nuclease assay. Spearman's correlation coefficient, Fisher's exact test and the Wilcoxon tests were used for statistical analyses. Overall, 13 and 21 patients were found to possess a total of <4 and 4 or more SNPs in the candidate genes screened. In group A, 15/16 patients (94%, 95% CI: 70–100) carried 4 or more SNPs compared to 6/18 (33%, 95% CI: 13–59) in group B (p < 0.001). The probability for the development of grade 3 toxicity was significantly higher (OR 9.3, 95% CI: 1.4–62, p = 0.003) for patients with 4 or more SNPs (0.71, 95% CI: 0.48–0.89) compared to those with <4 SNPs (0.08, 95% CI: 0.01–0.32). The median (range) LRIA was 11% (6–42) and 25% (5–43) in patients with 4 or more SNPs and <4 SNPs, respectively (p = 0.004). The number of SNPs and LRIA were inversely related (r = −0.53, p = 0.0011). Taken individually, the total numbers of SNPs detected in ATM, SOD2, TGFB1, XRCC1, XRCC3, and RAD21 were 2–4 fold greater in group A compared with group B. Finally, median (range) LRIA in patients who experienced grade 3 toxicities and patients with 4 or more SNPs were 9% (5–16.5) and 11% (6–42%), respectively. Median (range) LRIA in patients who experienced no toxicities and patients with <4 SNPs were 26% (20–43) and 25% (5–43), respectively. We have already reported that patients who were characterized with a low LRIA were at high risk for RT-induced sequelae. We now report that patients who possess 4 or more SNPs in a series of candidate genes displayed low levels of LRIA, and were more likely to develop RT-induced late effects compared with subjects with <4 SNPs. This research was supported by Department of the Army grant DAMD 17-02–1-0503.