Abstract 4239: Epithelial-like breast cancer stem cells are preferentially sensitive to nanoparticle-mediated hyperthermia
Authors: Paholak Hayley J. , Stevers Nicholas O. , Burnett Joseph P. , Chen Hongwei , McDermott Sean P. , He Miao , Luther Tahra , Clouthier Shawn G. , Wicha Max S. , Sun Duxin 
Published: August 2015

Abstract
Recent studies suggest that breast cancer stem cells (CSCs) exist in distinct mesenchymal-like and epithelial-like states, characterized by the CSC markers CD44+/CD24- and aldehyde dehydrogenase (ALDH) respectfully, and maintain the plasticity to transition between these states in a process regulated by the tumor microenvironment. While initial research investigating the effect of nanoparticle-mediated hyperthermia on CSCs was prompted as the treatment advanced to clinical trials, it is unclear how the two breast CSC populations will respond to such treatment. We examine the efficacy of photothermal therapy (PTT) mediated by degradable iron oxide nanoparticles (IONPs) against the epithelial-like (mesenchymal-epithelial transition [MET]) ALDH+ and mesenchymal-like (epithelial-mesenchymal transition [EMT]) CD44+/CD24-/EpCAM+ breast CSC populations.
Highly crystallized IONPs were synthesized by thermal decomposition and heated with 885 nm near infrared (NIR) laser light. The in vitro effects of PTT using IONPs and NIR laser were first tested in triple negative SUM159 cells using the alamarBlue cell viability assay. With 10 minute PTT at 42 °C as a baseline, increases in either PTT time or temperature decreased the number of viable cells compared to non-treated controls (p &lt; 0.01). Control treatments (IONP-only, laser-only) showed no change.
We examined the efficacy of increasing PTT temperatures on MET and EMT CSCs with flow cytometry. Strikingly, the MET ALDH+ CSCs were more sensitive to PTT (10 min) than bulk SUM159 cells, with the CSC percentage decreasing 3.5-fold with 48 °C PTT. In contrast, the proportion of EMT CD44+/CD24-/EpCAM+ CSCs remained unchanged. Inhibition of CSC self-renewal was demonstrated by mammosphere formation using MCF7 cells. PTT temperatures above 42 °C (10 min) significantly reduced both primary and secondary sphere formation (p &lt; 0.01).
NOD/SCID mice bearing SUM159 xenografts were subjected to 10 minute PTT. Tumor surface temperatures reached 60.1 ± 5.1 °C and 41.8 ± 1.6 °C for 1.0 and 0.5 Watt laser powers, respectively. PTT efficacy on CSCs was analyzed by tumor formation in NOD/SCID mice after secondary implantation. At 72 hours after PTT in primary mice, tumors were harvested, digested, isolated by fluorescence activated cell sorting (FACS), and implanted into secondary mice at limiting dilutions. While both PTT treatments slightly reduced the fraction of tumors formed compared to control secondary mice after 50 days, they delayed tumor formation and drastically reduced tumor volumes. These results suggest that ALDH+ CSCs that drive tumor cell proliferation are highly sensitive to PTT. Together our in vitro and in vivo breast cancer models reveal that MET ALDH+ CSCs are preferentially susceptible to IONP-mediated PTT at 42 °C or higher versus EMT CD44+/CD24-/EpCAM+ CSCs or bulk cancer cells.
Citation Format: Hayley J. Paholak, Nicholas O. Stevers, Joseph P. Burnett, Hongwei Chen, Sean P. McDermott, Miao He, Tahra Luther, Shawn G. Clouthier, Max S. Wicha, Duxin Sun. Epithelial-like breast cancer stem cells are preferentially sensitive to nanoparticle-mediated hyperthermia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4239. doi:10.1158/1538-7445.AM2015-4239