Subcellular real-time imaging of the efficacy of temozolomide on cancer cells in the brain of live mice.

Novel subcellular imaging technology has been developed in order to visualize drug efficacy on single cancer cells in the brain of mice in real time. The efficacy of temozolomide on cancer cells in the brain was determined by observation of subcellular cancer-cell dynamics over time through a craniotomy open window. Dual-color U87 human glioma and Lewis lung carcinoma (LLC) cells, expressing green fluorescent protein (GFP) in the nucleus and red fluorescent protein (RFP) in the cytoplasm, were imaged through the craniotomy open window 10 days after treatment with temozolomide (100 mg/kg i.p. for five consecutive days). After treatment, dual-color cancer cells with fragmented nuclei were visualized, indicating apoptosis. GFP-expressing apoptotic bodies and the destruction of RFP-expressing cytoplasm were also visualized. In addition, the terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay was used to confirm apoptosis visualized by imaging of the behavior of GFP-labeled cancer-cell nuclei. Tumor volume in the treated group was significantly smaller than in the control group (at day 19, p<0.001). The present study demonstrates technology capable of subcellular real-time imaging in the brain that reports induction of cancer-cell apoptosis by therapeutic treatment. More effective drugs for brain cancer and brain metastasis can be screened and can be identified with this technology.