Radiotherapy induces an increase in serum antioxidant capacity reflecting tumor response

Background and purpose

Radiotherapy (RT) is a mainstay component of treatment for patients with head and neck squamous cell carcinoma (HNSCC), but responses vary. As RT relies upon oxidative damage, antioxidant expression in response to RT-induced reactive oxygen species (ROS) could compromise treatment response. We aimed to examine local and systemic antioxidant responses to increased RT-induced ROS in relation to treatment success.

Materials and methods

Nuclear factor erythroid 2-related factor 2 (NRF2), the main antioxidant transcription factor, was immunofluorescently stained in FaDu cells and in tumor biopsies of patients with oral cavity/oropharynx HNSCC before and after five fractions of RT. Besides, total antioxidant capacity (TAC) was analyzed in HNSCC tumor cells in vitro and in serum of HNSCC patients before, during, and after RT.

Results

Data revealed an increase in NRF2 expression and TAC in head and neck cancer cells in vitro over the course of 5 daily fractions of 2 Gy. In accordance, also in patients' tumors NRF2 expression increased, which was associated with increased serum TAC during RT. Increasing serum TAC was related to impaired local tumor control.

Conclusion

Radiation induced NRF2 expression and upregulated TAC, which may compromise the effect of RT-induced ROS. Changes in serum TAC during RT could serve as a novel predictor of treatment outcome in HNSCC patients.Medical Ethics Review Committee (CMO) approval - CMO number: 2007/104.

Tamoxifen induces radioresistance through NRF2-mediated metabolic reprogramming in breast cancer

BACKGROUND

Recently, we reported that tamoxifen-resistant (TAM-R) breast cancer cells are cross-resistant to irradiation. Here, we investigated the mechanisms associated with tamoxifen-induced radioresistance, aiming to prevent or reverse resistance and improve breast cancer treatment.

METHODS

Wild-type ERα-positive MCF7 and ERα-negative MDA-MB-231 breast cancer cells and their TAM-R counterparts were analyzed for cellular metabolism using the Seahorse metabolic analyzer. Real-time ROS production, toxicity, and antioxidant capacity in response to H₂O₂, tamoxifen, and irradiation were determined. Tumor material from 28 breast cancer patients before and after short-term presurgical tamoxifen (ClinicalTrials.gov Identifier: NCT00738777, August 19, 2008) and cellular material was analyzed for NRF2 gene expression and immunohistochemistry. Re-sensitization of TAM-R cells to irradiation was established using pharmacological inhibition.

RESULTS

TAM-R cells exhibited decreased oxygen consumption and increased glycolysis, suggesting mitochondrial dysfunction. However, this did not explain radioresistance, as cells without mitochondria (Rho-0) were actually more radiosensitive. Real-time measurement of ROS after tamoxifen and H₂O₂ exposure indicated lower ROS levels and toxicity in TAM-R cells. Consistently, higher antioxidant levels were found in TAM-R cells, providing protection from irradiation-induced ROS. NRF2, a main activator of the antioxidant response, was increased in TAM-R cells and in tumor tissue of patients treated with short-term presurgical tamoxifen. NRF2 inhibition re-sensitized TAM-R cells to irradiation.

CONCLUSION

Mechanisms underlying tamoxifen-induced radioresistance are linked to cellular adaptations to persistently increased ROS levels, leading to cells with chronically upregulated antioxidant capacity and glycolysis. Pharmacological inhibition of antioxidant responses re-sensitizes breast cancer cells to irradiation.

Imageable Biomarkers for Radiotherapy Response

Ideally, each patient with a malignancy who is eligible for radiation therapy should receive the most tumoricidal form of this this treatment with the lowest possible risk of toxicity. To overcome radiotherapy resistance, some patients would benefit from a more aggressive approach. This could be treatment intensification, for example by acceleration of the treatment to prevent the negative effects of accelerated tumor cell proliferation, or by boosting certain areas to specifically address intrinsic radioresistance, or a combination of radiotherapy with, for example, a hypoxic cell sensitizer or chemotherapy to reduce the radiotherapy resistance caused by hypoxia. For some patients, one of these approaches can be beneficial but for others could lead to unacceptable side effects. Therefore, it is highly desirable to make the selection upfront. The use of imageable biomarkers could be the key to a more patient-tailored treatment. Different biomarkers for hypoxia and proliferation that could be valuable for radiotherapy are discussed here, including their mechanism, the imaging procedure, quantification, and the value of the results.

Monitoring hypoxia and vasculature during bevacizumab treatment in a murine colorectal cancer model

The purpose of this study was to assess the effect of bevacizumab on vasculature and hypoxia in a colorectal tumor model. Nude mice with subcutaneous LS174T tumors were treated with bevacizumab or saline. To assess tumor properties, separate groups of mice were imaged using (18) F-Fluoromisonidazole (FMISO) and (18) F-Fluorodeoxyglucose (FDG) positron emission tomography or magnetic resonance imaging before and 2, 6 and 10 days after the start of treatment. Tumors were harvested after imaging to determine hypoxia and vascular density immunohistochemically. The T2 * time increased significantly less in the bevacizumab group. FMISO uptake increased more over time in the control group. Vessel density significantly decreased in the bevacizumab-treated group. The Carbonic anhydrase 9 (CAIX) and glucose uptake transporter 1 (GLUT1) fractions were higher in bevacizumab-treated tumors. However, the hypoxic fraction showed no significant difference. Bevacizumab led to shorter T2 * times and higher GLUT1 and CAIX expression, suggesting an increase in hypoxia and a higher glycolytic rate. This could be a mechanism of resistance to bevacizumab. The increase in hypoxia, however, could not be demonstrated by pimonidazole/FMISO, possibly because distribution of these tracers is hampered by bevacizumab-induced effects on vascular permeability and perfusion.

18F-FLT PET changes during radiotherapy combined with cetuximab in head and neck squamous cell carcinoma patients

AIM

Early treatment response of head and neck cancer to radiotherapy concomitant with cetuximab was monitored by repetitive PET imaging with the proliferation tracer 18F-FLT.

PATIENTS, METHODS

Five head and neck cancer patients, treated with radiotherapy and concomitant cetuximab following cetuximab induction, received four 18F-FLT PET-CT scans before and during treatment. Changes in SUVpeak, SUVmean and CT- and PET-segmented gross tumour volumes were evaluated, as were correlations with immunohistochemical staining for Epidermal Growth Factor Receptor (EGFR) and Ki-67 (proliferation marker) in pre-treatment tumour biopsies.

RESULTS

18F-FLT PET measured tumor responses to the induction dose of cetuximab varied from 43% SUVpeak decrease to 47% increase. After start of radiotherapy 18F-FLT PET parameters decreased significantly in all patients. No associations were found between PET parameters and EGFR or Ki-67 expression levels.

CONCLUSION

Proliferation of head and neck carcinomas shows a varying response to cetuximab induction, but consistently decreases after addition of radiotherapy.

Hypoxia and tumor metabolism in radiation oncology: targets visualized by positron emission tomography

Due to the amazing leap of technology in radiation oncology in the past few years, cancer treatment will become more individualized. Molecular imaging with PET contributed to this with its many tracers available, each of them visualizing a specific feature of a tumor and its microenvironment revealing the biological characteristics of cancer. Hypoxia is of interest as hypoxic tumor cells are associated with lower disease control because of an increased resistance to cytotoxic treatment. This is especially the case for radiotherapy. Treatment adaptations overcoming the negative effect of hypoxia have shown promising results. Several hypoxia tracers are available of which [18F]FMISO is studied most extensively, however other tracers are studied as well and the search for highly specific and reproducible PET tracers is still ongoing. Wide experience has been gained with the use of [18F]FDG PET as it is used on a routine basis for diagnosing and staging of cancer. Although not a specific marker for hypoxia, increased metabolic rate reflects increased proliferation and glycolysis indicating increased treatment resistance. Molecular imaging by means of PET creates an opportunity to provide personalized care, with optimal disease control, minimal toxicity and best cost-effectiveness.

Monitoring the effects of bevacizumab beyond progression in a murine colorectal cancer model: a functional imaging approach

Clinical studies have shown that bevacizumab beyond progression to first line therapy is beneficial for overall survival in advanced stage colorectal cancer. We studied the utility of several functional imaging modalities to assess the efficacy of bevacizumab beyond progression (BBP). All BALB/c mice with s.c. LS174T xenografts were treated with capecitabine, oxaliplatin and bevacizumab combination therapy. Tumor volume was assessed using caliper measurements. Increase of 1.5 times the initial volume on two subsequent measurements, was considered progression. In half of the mice bevacizumab treatment was continued (n = 13) after progressive disease was established, while the others received saline injections (n = 12). Within 3 days after progression, multi-modal imaging was performed using FDG-PET, diffusion weighted imaging, T2* and dynamic contrast enhanced MRI. Measurements were repeated 7 and 10 days after the first measurements. Afterwards, tumors were analyzed for expression of carbonic anhydrase IX, glucose transporter 1, 9 F1 to stain the vasculature and Ki67 to assess proliferation. In the BBP group tumor growth after progression was reduced compared to the control group (p < 0.01). FDG-PET showed a trend towards lower FDG uptake in the BBP group (p = 0.08). DWI, T2* and DCE-MRI parameters were not significantly different between both groups. The immunohistochemical analyses showed higher CAIX-positive fraction (p < 0.01) and lower Ki67 expression (p = 0.06) in the BBP group. The relative vascular area was significantly lower in the BBP group (p = 0.03). GLUT-1 expression and vascular density did not significantly differ between both groups. Bevacizumab after progression resulted in significant changes in the tumor proliferation and microenvironment compared to discontinuation of bevacizumab. FDG-PET may be sensitive to BBP-induced effects.

Reproducibility and biological basis of in vivo T(2)* magnetic resonance imaging of liver metastasis of colorectal cancer

In this study, the reproducibility of T2* MR imaging in colorectal liver metastases was assessed and T2* values were correlated with the expression of the hypoxia-related markers GLUT-1 and CA-IX as well as the relative vascular area, and the vessel density in resected tumors. The reproducibility of T2* was analyzed in 18 patients with in total 22 colorectal liver metastases using the Bland and Altman method for the 16th, 50th, and 84th percentile values. Immunohistochemical staining was performed on 17 resected tumors obtained from 16 patients. The median T2* of all liver metastases was 25.0 ± 5.6 ms vs. 23.0 ± 4.1 ms (median ± st.dev.) in normal liver. The coefficient of repeatability was 11.2 ms and the limits of agreement were -13.2 ms and 9.1 ms for median T2* values. On average, T2* showed fair reproducibility. No correlations between T2* values, hypoxia- and vascularity-related markers were observed.

SU-E-T-06: A Mathematical Explanation to Tumor's Response to Perfusion and Hypoxic Fraction after Radiation

PURPOSE

To develop a dynamic model that explains oxygen dynamics between the microvascular perfusion and the hypoxic cell population inside a tumor.

METHODS

Bussink et al (Radiat Res 153(4), p.398 (2000)) observed fast oxygen dynamics, faster than cell-death. Based on a simplified three-compartment-model: the microvasculature, well-oxygenated, and hypoxic tumor cell populations. We applied a first-order differential model for the tumor's transient response as a function of oxygen content within the blood vessels. The sink terms in our model for each compartment are fast changing parameters because radiation rapidly changes the oxygen consumption of the tumor cell in a time scale which is much faster than the population changes of the tumor. Transportation balance condition is also applied for each compartment.

RESULTS

Our simulation results can explain the experimental data in Bussink et al's (Radiat Res 153(4), p.398 (2000)) paper. We provide an explanation for the relative complex behavior of the microvascular perfusion after radiation that emphasizes the role of dynamic metabolic changes in addition to population changes.

CONCLUSIONS

A newly developed dynamic model leads our understanding to the interrelationship between microvascular oxygen content within the blood vessels and the hypoxia state of the tumor to a deeper level, which has the potential to provide the theoretical foundation for the patient' specific adaptive radiotherapy.