Abstract 3787: Effects of hyperthermia on DNA repair capacity and long term survival in ovarian and colon carcinoma cells
Authors: Schaaf Lea , Kuip Heiko Van Der , Mürdter Thomas E. , Ulmer Christoph , Aulitzky Walter E. 
Published: May 2015

Abstract
Background:
Gynecological and gastrointestinal malignancies have the potential to spread into the peritoneal cavity. Peritoneal carcinomatosis is associated with rapid disease progression and poor prognosis. Aggressive cytoreductive surgery combined with intraperitoneal hyperthermic chemotherapy (HIPEC) is actually considered as promising treatment option. However, it is unknown if all cytotoxic drugs currently used in the clinics can be efficiently potentiated by hyperthermia. Furthermore, the mechanisms of hyperthermia induced sensitization of cancer cells to chemotherapy are poorly understood.
Methods:
Two ovarian (Ovcar 3, Ovcar 8) and 2 colon carcinoma cell lines (HCT116, LOVO3) were pulse treated for one hour with clinically relevant dosages of cisplatin, oxaliplatin, doxorubicin, mytomycin C, paclitaxel, and 5-FU at 37°C or 42°C. Long term survival was assessed using colony forming assay. Single and double strand breaks were quantified using alkaline COMET immediately after treatment and in a time course for up to 8 h. Efficacy of DNA repair was determined by γH2AX, Rad51, and P53BP1 foci formation.
Results:
Hyperthermia significantly potentiated cytotoxicity of cisplatin, oxaliplatin, mitomycin C, and doxorubicin in all cell lines investigated. The most prominent effects were observed with doxorubicin leading to an almost complete loss of viability. Of note, hyperthermia did not affect cytotoxicity of paclitaxel and 5-FU.
The molecular mechanism of hyperthermia induced sensitization to doxorubicin was further investigated. Hyperthermia significantly influenced doxorubicin transport since intracellular concentration was approximately doubled at 42°C compared to 37°C. However, despite adjusting the concentration of doxorubicin at 42°C to that observed with 37°C, hyperthermia still potentiated cytotoxicity indicating that other mechanisms are also involved. We detected no differences in the amount of DNA strand breaks immediately after treatment between 37°C and 42°C. However, time course experiments revealed a significant delay in DNA repair at 42°C. Whereas DNA strand breaks were almost completely repaired after 8 h at 37°C, there was hardly any repair detectable at 42°C. This was also mirrored by an enhanced number of γH2AX foci in nuclei of cells treated with doxorubicin at 42°C 3 h after treatment. Interestingly, we observed no differences in the number of Rad51 but a significantly enhanced number of P53BP1 foci at 42°C indicating a shift towards unfaithful non homologous end joining (NHEJ) at higher temperature.
Conclusion:
Hyperthermia significantly potentiated effects of DNA damaging agents such as doxorubicin via two different mechanisms. (1) Enhanced temperature leads to an enhanced uptake or reduced efflux of doxorubicin. (2) Hyperthermia reduces DNA repair capacity and potentially shifts DNA double strand repair to an error-prone NHEJ.
Citation Format: Lea Schaaf, Heiko Van Der Kuip, Thomas E. Mürdter, Christoph Ulmer, Walter E. Aulitzky. Effects of hyperthermia on DNA repair capacity and long term survival in ovarian and colon carcinoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3787. doi:10.1158/1538-7445.AM2014-3787