Single nucleotide polymorphisms of DNA repair genes as predictors of radioresponse

Delivering adaptive radiotherapy to the bladder during radical treatment

Radical radiotherapy to the bladder for muscle-invasive bladder cancer is a challenging treatment to plan and deliver because of organ mobility and its varying volume. The dynamic target volume can be tracked with imaging during the treatment course, enabling an adaptive response and adjustment of the patient’s individual treatment plan. This article summarises the difficulties encountered when treating the bladder, different approaches to patient imaging and adaptive radiotherapy techniques. Ultimately these technological advances support the delivery of a personalised treatment plan to ensure optimal dose delivery to the tumour and simultaneous sparing of adjacent normal tissue.

A single nucleotide polymorphism in inflammatory gene RNASEL predicts outcome after radiation therapy for localized prostate cancer

PURPOSE

To study associations between single nucleotide polymorphisms (SNP) in Ribonuclease L (RNASEL), a gene implicated in inflammation and prostate cancer risk, and outcomes after radiation therapy.

EXPERIMENTAL DESIGN

We followed participants in the prospective US Health Professionals Follow-Up Study treated with radiation therapy for early-stage prostate cancer. Three SNPs were genotyped based on previously determined functional and biological significance. We used multivariable Cox proportional hazards models to assess per-allele associations with the primary outcome defined as time to a composite endpoint including development of lethal prostate cancer or biochemical recurrence.

RESULTS

We followed 434 patients treated with radiation therapy for a median of 9 years. On multivariate analysis, the rs12757998 variant allele was associated with significantly decreased risk of the composite endpoint [HR: 0.65; 95% confidence interval (CI), 0.45-0.94%; P = 0.02] driven by decreased biochemical recurrence (HR: 0.60; 95% CI, 0.40-0.89%; P = 0.01) and men treated with external beam (HR: 0.58; 95% CI, 0.36-0.93%; P = 0.02). In contrast, in 516 men from the same cohort treated with radical prostatectomy, we found no significant impact of this variant on outcome. Furthermore, the rs12757998 variant allele significantly modified the association between androgen deprivation therapy and outcomes after radiation therapy (p-interaction = 0.02).

CONCLUSION

We show an association between RNASEL SNP rs12757998 and outcome after radiation therapy for prostate cancer. This SNP is associated with increased circulating C-reactive protein and interleukin-6, suggesting a potential role for inflammation in the response to radiation. If validated, genetic predictors of outcome may help inform prostate cancer management.

XRCC1 codon 399Gln polymorphism is associated with radiotherapy-induced acute dermatitis and mucositis in nasopharyngeal carcinoma patients

BACKGROUND

To evaluate the association between single nucleotide polymorphisms (SNPs) at the 194 and 399 codons of XRCC1, and the risk of severe acute skin and oral mucosa reactions in nasopharyngeal carcinoma patients in China.

METHODS

114 patients with nasopharyngeal carcinoma were sequentially recruited in this study. Heparinized peripheral blood samples were taken for SNPs analysis before the start of radiation treatment. SNPs in XRCC1 (194Arg/Trp and 399Arg/Gln) gene were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Dermatitis at upper neck and oral mucositis were clinically recorded according to the Common Terminology Criteria for Adverse Events v.3.0.

RESULTS

The variant allele frequencies were 0.289 for XRCC1 194Trp and 0.263 for XRCC1 399Gln. Of the 114 patients, 24 experienced grade 3 acute dermatitis and 48 had grade 3 acute mucositis. The XRCC1 399Arg/Gln was significantly associated with the development of grade 3 dermatitis (Odds Ratio, 2.65; 95% CI, 1.04-6.73; p = 0.037, χ2 = 4.357). In addition, it was also associated with higher incidence of grade 3 mucositis with a borderline statistical significance (Odds Ratio, 2.11; 95% CI, 0.951-4.66; p = 0.065, χ2 = 3.411). The relationship between XRCC1 194Arg/Trp and acute dermatitis, and mucositis was not found.

CONCLUSIONS

Our investigation shows, for the first time, that patients with the XRCC1 399Arg/Gln genotype were more likely to experience severe acute dermatitis and oral mucositis. With further validation, the information can be used to determine personalized radiotherapy strategy.

Genomic determinants of normal tissue toxicity after radiotherapy for head and neck malignancy: a systematic review

Interindividual variations in radiotoxicity responses exist despite uniform treatment protocols. It is speculated that normal genetic variants, particularly single nucleotide polymorphisms (SNPs) may influence normal head and neck (HN) tissue radiotoxicity. This first-ever systematic review was undertaken to evaluate the association of SNPs with normal HN tissues radiotoxicity. Multiple databases (1950-February 2012) were reviewed using a combination of related keywords and MeSH terms. All published HN radiotoxicity studies with sufficient relevant data for extraction were included. The outcomes evaluated were acute and late radiotoxicity endpoints. Methodological quality assessment based on the STrengthening the REporting of Genetic Association (STREGA) statement was performed. Seven articles from 692 articles searched fulfilled the eligibility criteria. Recruited sample sizes were small (range, 32-140). There were 5/7 case-control studies. All studies used multimodality treatment with heterogeneous radiation parameters. Candidate gene approach was used in all studies. Fourteen SNPs from 9 genes were evaluated from the following pathways: DNA damage response, radiation fibrogenesis and oxidative/xenobiotic metabolism. Acute radiotoxicity events were associated with SNPs of DNA repair genes (OR, 3.01-4.08). SNPs of TGFβ1 were associated with osteoradionecrosis (OR, 4.2) and subcutaneous fibrosis. Genetic association studies in HN radiotoxicity currently provide hypothesis-generating findings that require validation in larger studies. Future studies must incorporate critical methodological issues and technological improvements, including using a genome-wide approach. Headway is possible through case-pooling of existing clinical trial data which could create a larger sample size of well-characterized treatment and endpoints. Also, on-going HN cancer clinical trials should consider extending their toxicity evaluation to include genetic association studies.

Strategies to optimize radiotherapy based on biological responses of tumor and normal tissue

Rapid developments in radiation oncology are currently taking place. Radiation-induced responses are being increasingly used for radiotherapy modification based on advancements in radiobiology. In the process of radiation treatment, radiobiological responses of tumor and normal tissue in patients are monitored non-invasively by a variety of techniques including imaging, biological methods and biochemical assays. Information collected using these methods and data on responses are further incorporated into radiotherapy optimization approaches, which not only include the optimization of radiation treatment planning, such as dose distributions in targets and treatment delivery, but also include radiation sensitivity modification and gene radiotherapy of the tumor and normal tissue. Hence, the highest tumor control rate is obtained with the utmost protection being afforded to normal tissue under this treatment modality.

Influence of DNA repair gene polymorphisms on prognosis in inoperable non-small cell lung cancer patients treated with radiotherapy and platinum-based chemotherapy

Polymorphisms in DNA repair genes may modulate not only an individual DNA repair capacity, DNA damage levels and cancer risk but also clinical outcome after DNA damage-inducing anticancer therapy. In this study, we analyzed the association between the XPA -4G>A, XPD Asp312Asn, hOGG1 Ser326Cys, XRCC1 Arg399Gln, XRCC2 -4234G>C, XRCC3 -4541A>G and Thr241Met polymorphisms and prognosis in 250 inoperable non-small cell lung cancer (NSCLC) patients treated with radiotherapy and platinum-based chemotherapy. In univariate model, the XPA-4A and XRCC1 399Gln alleles alone and in combination influenced survival only in stage III group. In multivariate analysis, the XPA-4 GA/AA was associated with poor survival (HR 1.55, p = 0.011 overall and HR 1.72, p = 0.008 in stage III). In chemoradiotherapy group, the XPA-4A carriers were at increased risk of death and progression (HR 1.73, p = 0.013 and HR 1.65, p = 0.016, respectively), especially in stage III (p = 0.008). Moreover, individuals with ≥ 2 XPA/XRCC1 adverse alleles showed a higher risk of death (HR 1.46, p = 0.036 overall; HR 1.85, p = 0.004 in stage III and HR 1.71, p = 0.022 in chemoradiotherapy group) and progression (HR 1.75, p = 0.011 overall and HR 1.93, p = 0.005 in stage III). The XPA-4 GA/AA genotype individually and together with the XRCC1 399Gln was an independent unfavorable prognostic factor in our study. Thus, our findings indicate a prognostic potential of the XPA-4G>A in unresected NSCLC treated with radiotherapy and chemoradiotherapy. The results require validation in an independent population.

The role of microRNA-binding site polymorphisms in DNA repair genes as risk factors for bladder cancer and breast cancer and their impact on radiotherapy outcomes

MicroRNAs (miRNAs) are involved in post-transcriptional regulation of gene expression through binding to messenger RNAs (mRNA) thereby promoting mRNA degradation or altered translation. A single-nucleotide polymorphism (SNP) located within a miRNA-binding site could thus alter mRNA translation and influence cancer risk and treatment response. The common SNPs located within the 3'-untranslated regions of 20 DNA repair genes were analysed for putative miRNA-binding sites using bioinformatics algorithms, calculating the difference in Gibbs free binding energy (ΔΔG) for each wild-type versus variant allele. Seven SNPs were selected to be genotyped in germ line DNAs both from a bladder cancer case-control series (752 cases and 704 controls) and 202 muscle-invasive bladder cancer radiotherapy cases. The PARP-1 SNP rs8679 was also genotyped in a breast cancer case-control series (257 cases and 512 controls). Without adjustment for multiple testing, multivariate analysis demonstrated an association with increased bladder cancer risk with PARP1 rs8679 (P(trend) = 0.05) while variant homozygotes of PARP1 rs8679 were also noted to have an increased breast cancer risk (P = 0.03). In the radiotherapy cases, carriers of the RAD51 rs7180135 minor allele had improved cancer-specific survival (hazard ratio 0.52, 95% confidence interval 0.31-0.87, P = 0.01). This is the first report of associations between DNA repair gene miRNA-binding site SNPs with bladder and breast cancer risk and radiotherapy outcomes. If validated, these findings may give further insight into the biology of bladder carcinogenesis, allow testing of the RAD51 SNP as a potential predictive biomarker and also reveal potential targets for new cancer treatments.

Individualization of cancer treatment from radiotherapy perspective

Radiotherapy is today used in about 50% of all cancer patients, often in multidisciplinary approaches. With major advance in radiotherapy techniques, increasing knowledge on tumor genetics and biology and the continuous introduction of specifically targeted drugs into combined radio-oncological treatment schedules, individualization of radiotherapy is of high priority to further improve treatment outcomes, i.e. to increase long-term tumor cure and/or to reduce chronic treatment toxicity. This review gives an overview on the importance of predictive biomarkers for the field of radiation oncology. The current status of knowledge on potential biomarkers of tumor hypoxia, tumor cell metabolism, DNA repair, cancer stem cells and biomarkers for combining radiotherapy with inhibition of the epidermal growth factor receptor using monoclonal antibodies is described.

A novel radioresistant mechanism of galectin-1 mediated by H-Ras-dependent pathways in cervical cancer cells

Galectin-1 is a lectin recognized by galactoside-containing glycoproteins, and is involved in cancer progression and metastasis. The role of galectin-1 in radiosensitivity has not previously been investigated. Therefore, this study tests whether galectin-1 is involved in the radiosensitivity mediated by the H-Ras signaling pathway using cervical carcinoma cell lines. A knockdown of galectin-1 expression in HeLa cells decreased clonogenic survival following irradiation. The clonogenic survival increased in both HeLa and C33A cells with galectin-1 overexpression. The overexpression or knockdown of galectin-1 did not alter radiosensitivity, whereas H-Ras was silenced in both cell lines. Whereas K-Ras was knocked down, galectin-1 restored the radiosensitivity in HeLa cells and C33A cells. The knockdown of galectin-1 increased the high-dose radiation-induced cell death of HeLa cells transfected by constitutively active H-Ras. The knockdown of galectin-1 inhibited the radiation-induced phosphorylation of Raf-1 and ERK in HeLa cells. Overexpression of galectin-1 enhanced the phosphorylation of Raf-1 and ERK in C33A cells following irradiation. Galectin-1 decreased the DNA damage detected using comet assay and γ-H2AX in both cells following irradiation. These findings suggest that galectin-1 mediates radioresistance through the H-Ras-dependent pathway involved in DNA damage repair.

Identification of SNPs associated with susceptibility for development of adverse reactions to radiotherapy

Although cancer treatment with radiation can produce high cure rates, adverse effects often result from radiotherapy. These toxicities are manifested as damage to normal tissues and organs in the radiation field. In recognition of the substantial variation in the intrinsic response of individuals to radiation, an effort began approximately 10 years ago to discover the genetic markers, primarily SNPs, which are associated with susceptibility for the development of these adverse responses to radiation therapy. The goal of this research is to identify the SNPs that could serve as the basis of an assay to predict which cancer patients are most likely to develop complications resulting from radiotherapy. This would permit personalization and optimization of the treatment plan for each cancer patient.