A Polymorphism Within the Promoter of the TGFβ1 Gene Is Associated With Radiation Sensitivity Using an Objective Radiologic Endpoint

doi:10.1016/j.ijrobp.2011.02.064

International Journal of Radiation OncologyBiologyPhysics

Volume 82, Issue 2, 1 February 2012, Pages e247-e255

Presented in part at the American Radium Society Annual Meeting, Cancun, Mexico, May 2–5, 2010.

https://doi.org/10.1016/j.ijrobp.2011.02.064 Get rights and content

Purpose

To evaluate whether single nucleotide polymorphisms (SNPs) in the transforming growth factor-β1 (TGFβ1) gene are associated with radiation sensitivity using an objective radiologic endpoint.

Methods and Materials

Preradiation therapy and serial postradiation therapy single photon emission computed tomography (SPECT) lung perfusion scans were obtained in patients undergoing treatment for lung cancer. Serial blood samples were obtained to measure circulating levels of TGFβ1. Changes in regional perfusion were related to regional radiation dose yielding a patient-specific dose–response curve, reflecting the patient’s inherent sensitivity to radiation therapy. Six TGFβ1 SNPs (-988, -800, -509, 869, 941, and 1655) were assessed using high-resolution melting assays and DNA sequencing. The association between genotype and slope of the dose–response curve, and genotype and TGFβ1 ratio (4-week/preradiation therapy), was analyzed using the Kruskal-Wallis test.

Results

39 white patients with preradiation therapy and ≥6-month postradiation therapy SPECT scans and blood samples were identified. Increasing slope of the dose–response curve was associated with the C(-509)T SNP (p = 0.035), but not the other analyzed SNPs. This SNP was also associated with higher TGFβ1 ratios.

Conclusions

This study suggests that a polymorphism within the promoter of the TGFβ1 gene is associated with increased radiation sensitivity (defined objectively by dose-dependent changes in SPECT lung perfusion).

Introduction

Radiation therapy is an important treatment modality for patients with lung cancer and other thoracic malignancies. Radiation-induced lung injury, including acute pneumonitis and chronic fibrosis, is common and can potentially result in significant morbidity. Currently, the primary means whereby the risk of radiation-induced lung injury is assessed is the radiation dose distribution, including such parameters as mean lung dose and V20 (volume of lung receiving ≥20 Gy).

Several studies have evaluated the association between radiation-induced lung toxicity and levels of circulating cytokines (e.g., preradiation therapy values and/or changes during/after radiation therapy). Multiple cytokines have been implicated, most notably transforming growth factor-β1 (TGFβ1). This is a multifunctional regulator of cell growth and differentiation that stimulates connective tissue formation and decreases collagen degradation, which can result in fibrosis (1). Several studies 2, 3, but not all 4, 5, have shown that increasing serum levels of TGFβ1 after the initiation of radiation therapy is associated with radiation-induced lung injury.

A primary challenge in developing accurate models of radiation-induced lung toxicity is interpatient differences in inherent radiation sensitivity. Rare disorders (e.g., ataxia-telangiectasia) suggest that genetic differences may mediate radiation sensitivity. Indeed, single nucleotide polymorphisms (SNPs) within the TGFβ1 gene have been correlated with several adverse events after radiation therapy, including radiation pneumonitis (6), erectile dysfunction (7), rectal bleeding (7), altered breast appearance (8), breast fibrosis 9, 10, and miscellaneous late adverse reactions (11). However, each of these endpoints is subjective and is potentially liable to observational bias.

As part of Institutional Review Board—approved prospective studies at Duke University, we have performed serial perfusion single photon emission computed tomography (SPECT) scans before, and serially after, thoracic radiation therapy. Radiation therapy leads to dose-dependent changes in regional perfusion, likely from injury to the pulmonary microvasculature, which can be quantified using SPECT imaging. Computer-assisted comparisons of the preradiation and postradiation images provide a quantifiable metric of radiation-induced lung injury and an objective measure of inherent sensitivity to radiation-induced lung damage. Many of these same patients had blood samples collected and stored for correlative studies. We herein assess whether SNPs within the TGFβ1 gene (determined from the stored blood) are associated with radiation sensitivity (assessed objectively from the SPECT lung perfusion scans).

Section snippets

Patient population

As part of Institutional Review Board—approved prospective clinical studies at Duke University, patients undergoing definitive thoracic radiation therapy for lung cancer had preradiation and serial postradiation perfusion SPECT scans. Blood was also drawn at baseline and at multiple time points after the initiation of radiation therapy to measure circulating levels of TGFβ1. Patients were included in the following analysis if they underwent a preradiation SPECT, ≥6-month postradiation SPECT

Patient characteristics

In all, 45 unrelated patients with preradiation and ≥6-month postradiation SPECT scans, and at least one blood sample, were identified. Nonwhite patients were excluded (n = 6), leaving 39 for the present analysis.

The median total radiation dose was 66 Gy (range, 40–86.4). Patients received either conventionally fractionated radiation therapy (n = 29) or accelerated hyperfractionated radiation therapy (n = 10). Chemotherapy was administered to 32 of 39 patients. Patient and treatment

Discussion

An individual’s predisposition for developing pronounced side effects after radiation therapy is almost certainly influenced by underling genetic makeup. Several rare inherited disorders, each associated with defects in DNA repair mechanisms, have been associated with severe reactions to radiation therapy (26). These disorders include ataxia-telangiectasia, Nijmegen breakage syndrome, Fanconi anemia, and DNA ligase IV deficiency, among others. It is probable that patients with more subtle

Conclusion

This small study suggests that a polymorphism within the promoter of the TGFβ1 gene might be associated with radiation sensitivity. Significantly, we used an objective measure of radiation sensitivity, which is independent of the dose and volume of normal tissue irradiated. Additional studies with larger numbers of patients are certainly needed.