Abstract B170: Non-lethal heat treatment of cells results in reduction in cancer stem cell fraction and metastatic potential.

Metastatic disease and recurrence have been hypothesized to result from residual cancer stem cells (CSCs), also referred to as tumor-initiating cells, which evade initial treatment. CSCs are thought to have the ability to recapitulate the heterogeneity of the parental tumor, to self-renew, and to maintain their self-renewing potential over long periods of time. Therapeutic targeting of the CSC population, in addition to differentiated malignant cells, may be critical for the successful treatment and elimination residual disease in human cancer. Hyperthermia has been used as an adjuvant treatment in which body tissue is exposed to high temperatures (up to 45 °C) in combination with radiation or chemotherapy. In this study, we test the hypothesis that a major effect of hyperthermia is to weaken or reduce the CSC population, resulting in reduced invasive metastatic potential. A pulmonary metastasis model was used, where tumor cells are administered to a mouse by i.v injection. 4 × 105 cells/mouse will yield between 50 and 250 pulmonary nodules visible on the lung surface. The tumor nodules can be easily visualized by bioluminescence imaging (BLI). For effects of hyperthermia on metastatic potential, a mouse melanoma (B16F10-Luc.) model was used. Thermal treatment consisted of immersing the cells in a heated water bath with temperature maintained for 25 min at 37 °C or 43 °C. After thermal treatment, viable control or heat treated (HT) cells were injected into the mice via tail vein and BLI used to determine the metastatic disease in the lungs. MDA-MB 231-Luc. breast cancer cells were administrated after HT. Primary tumor volume and lung metastasis were measured by BLI. For comparison, MM 231 and B16 cells were analyzed via FACS following the same regimen of sham or heat treating using the combination CD44+/CD133+ markers to separate and count the CSC population. In the control, metastatic disease resulted in a faintly observed signal in 3 days, and a clearly observed signal in 6 days from the lungs. In contrast, the HT group had no signal at either time point. HT cells similarly showed an initial loss of BLI signal due to denaturation of luciferase, however, this was completely recovered within 4 days. Overall viability was not significantly altered by HT. FACS analysis of the MM 231 cells showed a 52.2 % reduction in CD44 and 29.6 % reduction in CD133 expression compared to controls, from 55.2 % of the total to 26.4 % in CD44 and from 49.2 % of the total to 34.6 % in CD133. B16 cells showed a 32.1 % reduction in CD44 expression, but they showed similar CD133. Both B16 and MM 231 tumor model showed significant changes in tumor growth with HT. The tumor volume of HT group was smaller than control and metastatic disease was also significantly reduced in the HT. These results suggest that hyperthermia may be capable of selectively injuring CSCs thereby reducing the incidence of metastatic disease formation. However, hyperthermia has only minimal impact on overall cancer cell survival numbers, and, due to its limited application in time and space, has no effect on CSCs already seeded or in circulation unless whole-body treatment is possible. These facts may explain hyperthermia9s limited clinical efficacy, but also point towards a strategy for leveraging CSC thermal sensitivity to improve outcomes as an adjuvant therapy. Further studies are needed to establish appropriate methods and timing of treatment. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B170. Citation Format: Yoo-Shin Kim, Tae Hoon Lee, Brian E. O9Neill. Non-lethal heat treatment of cells results in reduction in cancer stem cell fraction and metastatic potential. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B170.