Radiosensitization of heat resistant human tumour cells by 1 hour at 41.1°C and its effect on DNA repair

Abstract

The present study was undertaken to determine if short duration (1-2 h), moderate hyperthermia (41.1 degrees C) could radiosensitize human tumour cells. It was found that moderate hyperthermia (41.1 degrees C), for as little as 1 h, can radiosensitize heat resistant human adenocarcinoma cells, NSY42129 (NSY), provided the cells are irradiated 15 min prior to the end of the heat exposure. Analysis of the survival data showed a 2.5-3-fold increase in the alpha parameter with no significant change in the beta parameter of the survival curve, implying that the cells had become more susceptible to killing by single radiation energy deposition events as opposed to lethal events that require an interaction between two separate energy deposition events. 41.1 degrees C hyperthermia did not affect the induction or repair of alkaline labile DNA damage in a way that correlated with radiosensitivity. In contrast, heat-induced changes in the induction of micronuclei by radiation correlated with changes in cell killing. Therefore, the effect of 41.1 degrees C hyperthermia on the intracellular localization of the DNA double strand break repair protein, Mre11, was measured using in situ immunofluorescence and immunoblotting of soluble and insoluble cellular fractions. The results showed that Mre11 delocalizes from the nucleus as a function of time at 41.1 degrees C. It was then determined if 41.1 degrees C hyperthermia altered the association of Mre11 with its functional partner, Rad50. A significant decrease in the amount of Rad50 recovered with Mre11 occurred under the experimental conditions that produced significant radiosensitization. These results are consistent with the possibility that the heat-induced perturbation in Mre11 localization and its radiation-induced association with Rad50 contributes to an increase in radiosensitivity.

Cell survival and radiosensitisation: Modulation of the linear and quadratic parameters of the LQ model

“…Translocation of the Mre11 DSB repair protein from the nucleus to the cytoplasm has also been implicated (106,111). However, disappearance of Mre11 protein foci at the sites of irradiation-induced DNA DSBs was not observed by pre-incubation of cells at 41˚C (24,27).…”

Peritoneal mesothelioma treated by induction chemotherapy, cytoreductive surgery, and intraperitoneal hyperthermic perfusion

“…The employment of heat, as a fundamental component of this new therapeutic methodology, is justified by its own cancericidal property and chemosensitivity-modulating capacity. The biophysical effects of hyperthermia are not completely understood, but probably include membrane protein denaturation, increased vascular permeability [18,19], alterations in multimolecular complexes such as the insulin receptor [20] and in the cytoskeleton [18], and changes in enzyme complexes for DNA synthesis and repair [21]. Moreover, the architecture of the vasculature in solid tumors is chaotic, resulting in regions with low pH, hypoxia, and low glucose level [22].…”

Radiosensitization with Hyperthermia and Chemotherapeutic Agents: Effects on Linear-Quadratic Parameters of Radiation Cell Survival Curves

“…Recently it was demonstrated that the BRCA-2 protein is transiently inhibited by mild hyperthermia (Krawzcyk et al, 2011). Also translocation of the Mre11 DSB repair protein from the nucleus to the cytoplasm has been implicated (Xu et al, 2002(Xu et al, , 2007. However, disappearance of Mre11 protein foci at the sites of irradiation induced DNA double strand breaks by 41ºC pre-incubation of cells was not observed (Krawzcyk et al, 2011;Bergs, 2007a).…”

“…In a study by Xu et al (1999) 41.1C pre-treatment of cells for 1h did not induce radiosensitization whereas treatment for 2h or more resulted in radiosensitization, in the hyperthermia resistant, but not in the hyperthermia sensitive cell line (Xu et al, 1999]. However, simultaneous treatment of the sensitive cell line with 1h 41.1C hyperthermia and radiation did increase cellular radiosensitivity (Xu et al, 2002). An important mechanism of mild hyperthermia induced radiosensitization in vivo is the reoxygenation of tumors by an increase in blood flow (Vujaskovic et al, 2004;Oleson & Robertson, 1995;Song et al, 1995).…”