Background: Although over half of all lung cancer patients receive radiation therapy as part of their treatment plan, the therapeutic window of radiation is quite small, and it is difficult to deliver tumoricidal doses of radiation without the development of severe adverse effects in the nearby normal tissues. An agent that could sensitize lung cancer tissue to radiotherapy while sparing damage to normal tissues is still an unmet need. Piperlongumine (PPLGM), a natural product of the plant Piper longum has shown potent anti-carcinogenic properties through an ROS-inducing mechanism. Our hypothesis is that PPLGM will sensitize tumor cells to radiation-induced cell death in an orthotopic murine model of lung cancer. Methods: 7-week old female C57BL/6 mice were injected intravenously with 1×106 Lewis lung carcinoma (LLC) cells. Mouse cohorts (n = 30/group) were administered PPLGM (1 mg/kg of body weight) or vehicle daily by oral gavage initiated 7 days post-LLC injection. At 14 days post-LLC injection, 15 mice per treatment cohort were exposed to 12 Gy thoracic X-ray radiation treatment (XRT). Administration of PPLGM or vehicle continued 7 days post-XRT. Mice were euthanized 14 days post-XRT and evaluated for total lung weight and tumor burden using morphometric analysis. Additionally, we assessed the potential for a dual role of PPLGM (0.1-2.5μM) as a radiosensitizer of cancer cells (LLC) and a radioprotector of normal lung cells (pulmonary microvascular endothelial cells (PMVEC)) via clonogenic survival assays. Results: Using LC/MS/MS we were able to detect significantly elevated levels of PPLGM above baseline in mouse plasma and lung tissue. We observed a significant (p<0.01) increase in lung weight (from 0.14 g to 0.36 g), an indicator of tumor burden, that was significantly (p<0.01) reduced by exposure to a tumoricidal dose of XRT. Importantly, while thoracic XRT-alone reduced tumor burden by 48%, administration of PPLGM+XRT radiosensitized tumor and enhanced tumor killing by XRT, leading to a significant (p<0.05) 56% reduction in lung weight. Morphometric analysis of lung sections confirmed that PPLGM-alone significantly (p<0.01) reduced tumor area relative to vehicle, irrespective of radiation exposure. While exposure to XRT significantly (p<0.01) reduced tumor volume by 65% (from 44.4 ± 7.6% to 15.4 ± 4.5% tumor area), lung sections from mice exposed to PPLGM+XRT significantly (p<0.05) potentiated radiation-induced tumor eradication (reduction in tumor area to 5.6 ± 3.0%) above XRT-only exposure. Furthermore, PPLGM significantly (p<0.05) radiosensitized LLC dose-dependently to gamma-radiation killing, while trending towards radioprotecting normal lung cells. Conclusion: These findings provide evidence that PPLGM is a potent radiosensitizing agent that could aid in the eradication of irradiated tumors in the clinical setting.
Funding: Funded in part by NIH-1R21CA178654-01
Citation Format: Anastasia Velalopoulou, Ralph A. Pietrofesa, Raymond Luke, Katie Reindl, Melpo Christofidou-Solomidou. Piperlongumine (PPLGM) has potent tumor-radiosensitizing properties in a mouse model of lung cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1665.