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An effective strategy for increasing the radiosensitivity of Human lung Cancer cells by blocking Nrf2-dependent
Saelooom Lee1, Min-Jin Lim, Mi-Hyoung Kim
1Department of Radiation Cancer Research, Korea Institute of Radiological & Medical Sciences, Seoul 139-706, Korea.
Abstract:
Radiotherapy and chemotherapeutic agents can effectively induce apoptosis through generation of reactive oxygen species (ROS). Cancer cells frequently express high levels of ROS-scavenging enzymes, which confer resistance to ROS-mediated cell death. Keap1 (Kelch-like ECH-associated protein 1) sequesters and promotes the degradation of the antioxidant response element-binding transcription factor Nrf2 (nuclear factor erythroid-2-related factor 2). In non-small-cell lung cancer (NSCLC) cell lines and NSCLC patients, Keap1 is often present as a biallelic mutant that results in constitutive activation of Nrf2 function, which contributes to cytoprotection against oxidative stress and xenobiotics. To identify small molecules that inhibit antioxidant responses and increase apoptotic death after radiotherapy, we screened a chemical library containing 8000 synthetic compounds using a cell-based luciferase assay system. 4-(2-Cyclohexylethoxy)aniline (IM3829) inhibited the increase in Nrf2-binding activity and expression of the Nrf2 target genes induced by treatment with tertiary butylhydroquinone or radiation. Combined treatment with IM3829 and radiation significantly inhibited clonogenic survival of H1299, A549, and H460 lung cancer cells. IM3829 significantly increased ROS accumulation in irradiated cells compared with cells exposed to radiation alone and led to apoptotic cell death, as confirmed by caspase-3 and PARP cleavage. In mice bearing H1299 or A549 lung cancer xenografts, IM3829 together with radiation inhibited tumor growth more effectively than radiation alone. Our findings suggest that IM3829 could be a promising radiosensitizer in lung cancer patients, particularly those with high expression of Nrf2.
Insights
This study identifies IM3829 as a novel compound that enhances radiotherapy effectiveness by inhibiting antioxidant responses in cancer cells. IM3829 shows promise as a radiosensitizer for lung cancer treatment, especially in patients with high Nrf2 expression.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Radiotherapy and chemotherapy induce apoptosis via reactive oxygen species (ROS), but cancer cells often resist this through ROS-scavenging enzymes.
- The Keap1-Nrf2 pathway regulates antioxidant responses; mutations in Keap1 lead to constitutive Nrf2 activation, promoting cancer cell survival.
- Non-small-cell lung cancer (NSCLC) frequently exhibits Keap1 mutations, contributing to resistance against oxidative stress.
Purpose of the Study:
- To identify small molecules that inhibit antioxidant responses and sensitize cancer cells to radiotherapy.
- To evaluate the efficacy of IM3829 as a potential radiosensitizer in lung cancer models.
Main Methods:
- Screened 8000 synthetic compounds using a cell-based luciferase assay to find inhibitors of antioxidant responses.
- Assessed the effect of IM3829 on Nrf2 activity, Nrf2 target gene expression, reactive oxygen species (ROS) levels, and apoptosis in NSCLC cell lines.
- Evaluated the combined efficacy of IM3829 and radiation on clonogenic survival in vitro and tumor growth in vivo xenograft models.
Main Results:
- IM3829 inhibited radiation-induced Nrf2 activation and target gene expression.
- Combined IM3829 and radiation significantly reduced clonogenic survival of NSCLC cells (H1299, A549, H460).
- IM3829 increased ROS accumulation and induced apoptosis (caspase-3 and PARP cleavage) in irradiated cells.
- In vivo, IM3829 plus radiation demonstrated superior tumor growth inhibition in NSCLC xenografts compared to radiation alone.
Conclusions:
- IM3829 effectively inhibits the Keap1-Nrf2 antioxidant pathway, enhancing ROS-mediated apoptosis in lung cancer cells.
- IM3829 acts as a potent radiosensitizer, improving the efficacy of radiation therapy in preclinical lung cancer models.
- IM3829 represents a promising therapeutic strategy for lung cancer patients, particularly those with elevated Nrf2 activity due to Keap1 mutations.
