MicroRNA-21 inhibitor potentiates anti-tumor effect of radiation therapy in vitro and in vivo

Circulating microRNAs as biomarkers of radiation-induced cardiac toxicity in non-small-cell lung cancer

PURPOSE

Radiation-induced cardiac toxicity (RICT) is an increasingly well-appreciated source of morbidity and mortality in patients receiving thoracic radiotherapy (RT). Currently available methods to predict RICT are suboptimal. We investigated circulating microRNAs (c-miRNAs) as potential biomarkers of RICT in patients undergoing definitive RT for non-small-cell lung cancer (NSCLC).

METHODS

Data from 63 patients treated on institutional trials were analyzed. Prognostic models of grade 3 or greater (G3 +) RICT based on pre-treatment c-miRNA levels ('c-miRNA'), mean heart dose (MHD) and pre-existing cardiac disease (PCD) ('clinical'), and a combination of these ('c-miRNA + clinical') were developed. Elastic net Cox regression and full cross validation were used for variable selection, model building, and model evaluation. Concordance statistic (c-index) and integrated Brier score (IBS) were used to evaluate model performance.

RESULTS

MHD, PCD, and serum levels of 14 c-miRNA species were identified as jointly prognostic for G3 + RICT. The 'c-miRNA and 'clinical' models yielded similar cross-validated c-indices (0.70 and 0.72, respectively) and IBSs (0.26 and 0.28, respectively). However, prognostication was not improved by combining c-miRNA and clinical factors (c-index 0.70, IBS 0.28). The 'c-miRNA' and 'clinical' models were able to significantly stratify patients into high- and low-risk groups of developing G3 + RICT. Chi-square testing demonstrated a marginally significantly higher prevalence of PCD in patients with high- compared to low-risk c-miRNA profile (p = 0.09), suggesting an association between some c-miRNAs and PCD.

CONCLUSIONS

We identified a pre-treatment c-miRNA signature prognostic for G3 + RICT. With further development, pre- and mid-treatment c-miRNA profiling could contribute to patient-specific dose selection and treatment adaptation.

Ionizing radiation-induced growth in soft agar is associated with miR-21 upregulation in wild-type and DNA double strand break repair deficient cells

DNA double strand breaks (DSBs) are a severe threat to genome integrity and a potential cause of tumorigenesis, which is a multi-stage process and involves many factors including the mutation of oncogenes and tumor suppressors, some of which are transcribed microRNAs (miRNAs). Among more than 2000 known miRNAs, miR-21 is a unique onco-miRNA that is highly expressed in almost all types of human tumors and is associated with tumorigenesis through its multiple targets. However, it remains unclear whether there is any functional link between DSBs and miR-21 expression and, if so, does the link contribute to DSB-induced genomic instability/tumorigenesis. To address this question, we used DNA-PKcs-/- (deficient in non-homologous end-joining (NHEJ)) and Rad54-/- (deficient in homologous recombination repair (HRR)) mouse embryonic fibroblasts (MEFs) since NHEJ and HRR are the major pathways for DSB repair in mammalian cells. Our results indicate that levels of miR-21 are elevated in these DSB repair (DSBR) deficient cells, and ionizing radiation (IR) further increases these levels in both wild-type (WT) and DSBR-deficient cells. Interestingly, IR stimulated growth in soft agar and this effect was greatly reduced by blocking miR-21 expression in both WT and DSBR-deficient cells. Taken together, our results suggest that either IR or DSBR-deficient can lead to an upregulation of miR-21 levels and that miR-21 is associated with IR-induced cell growth in soft agar. These results may help our understanding of DSB-induced tumorigenesis and provide information that could facilitate the development of new strategies to prevent DSB-induced carcinogenesis.

Radiosensitizing effect of lapatinib in human epidermal growth factor receptor 2-positive breast cancer cells

Trastuzumab has been widely used for the treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer, however, it cannot easily cross the blood-brain barrier (BBB) and is known to increase the incidence of brain metastases. In contrast, lapatinib has a low molecular weight and can cross the BBB and it could be useful to treat brain metastases in patients with HER2-positive breast cancer.

To explore the impact of lapatinib on radiation response, we conducted an in vitro experiment using SKBR3 and BT474 breast carcinoma cells exhibiting HER2/neu amplification. Lapatinib down-regulated phosphorylated (p)-HER2, p-epidermal growth factor receptor, p-AKT, and p-extracellular signal-regulated kinase. Pretreatment of lapatinib increased the radiosensitivity of SKBR3 (sensitizer enhancement ratio [SER]: 1.21 at a surviving fraction of 0.5) and BT474 (SER: 1.26 at a surviving fraction of 0.5) cells and hindered the repair of DNA damage, as suggested by the prolongation of radiation-induced γH2AX foci and the down-regulation of phosphorylated DNA-dependent protein kinase, catalytic subunit (p-DNAPKcs). Increases in radiation-induced apoptosis and senescence were suggested to be the major modes of cell death induced by the combination of lapatinib and radiation. Furthermore, lapatinib did not radiosensitize a HER2- negative breast cancer cell line or normal human astrocytes.

These findings suggest that lapatinib can potentiate radiation-induced cell death in HER2-overexpressing breast cancer cells and may increase the efficacy of radiotherapy. A phase II clinical trial using lapatinib concurrently with whole-brain radiation therapy (WBRT) is currently being conducted.