PARENT SESSION

Experimental and Clinical Therapeutics

(PP167) Radiosensitization by the combination of 41°C hyperthermia and indomethacin analogs.

Xu, Mai¹, Wu, M², Crooks, Peter³, Freeman, Michael⁴, Roti Roti, Joseph^*,1, ¹ Radiation and Cancer Biology Division, St. Louis, MO, USA² Department of Radiation Oncology, Taipei, Taiwan, China³ College of Pharmacy, Lexington, KY, USA⁴ Department of Radiation Oncology, Nashville, TN

ABSTRACT- INTRODUCTION: The non-steroidal anti-inflammatory drug, Indomethacin, is commonly used for treatment of patients with arthritis. Recently, it has been shown that indomethacin (>500 M) sensitizes tumor cells to radiation and lowers the threshold temperature required for thermal radiosensitization (Bradbury et al., Cancer Res. 2001, 61:7689-96). However, the molecular mechanisms of indomethacin as a radiosensitizer and/or thermal enhancer are poorly understood. In a previous study we observed that moderate hyperthermia (41°C) delocalized the DNA repair protein, MRE11, from the nucleus into the cytoplasm, influencing the DNA repair complex, containing MRE11, NBS1 and Rab50. Further, hyperthermia induces an increase in the binding of MRE11 with HSP70. In this study we determined if indomethacin had similar effects on the DNA repair protein, MRE11, and the expression of HSP70 as hyperthermia and if these effects could be used as a target for thermal radiosensitizer development. METHODS: Clonogenic assays, immunoblotting, immunoprecipitation, kinase assays and flow cytometry were used in this study. RESULTS: Our results show that MRE11 nuclear delocalization from the nuclear into cytoplasm is detectable at an indomethacin concentration of 250 M and reaches a maximum at 500 M. HSP70 expression is increased up to 2-3 fold by 500 M indomethacin. The indomethacin analog, VJ112-OH, is an effective thermal enhancer at 150 M but has little radiosensitizing effect without hyperthermia. While VJ112-OH with heat caused some delocalization of MRE11 from the nucleus, its main effect was to cause aggregates of MRE11 at the nuclear periphery. VJ112-OH did not inhibit COX2 or ERK1/2 activity at radiosensitizing concentrations. CONCLUSION: The indomethacin analog, VJ112-OH, appears to be a potential thermal enhancer of heat-induced radiosensitization targeting MRE11 more specifically than indomethacin. (Support: PO CA-1104457-01).

Key words: Radiosensitization, Indomethacin Analogs