Abstract 3341: TP508 sensitizes cancer stem cells to radiation and delays brain cancer cell relapse in vitro

Abstract

Abstract In 2014, approximately 70,000 adults and 4,500 children are expected to be diagnosed with brain cancer in the U.S alone, making this disease the second leading cause of cancer related deaths in children and young adults. Currently available therapies such as radio/chemotherapy are ineffective in completely eradicating the tumor bulk and cancer stem cells within the tumor, thus allowing recurrence of the disease. Therefore, it is important to develop novel therapeutics that sensitize cancer cells to make them more susceptible to radiation therapy and reduce the number of viable cancer stem cells. Preliminary data showed that injection of TP508, a 23 amino acid thrombin derived peptide drug, increased brain tumor shrinkage post-radiation therapy (RT) in mice. To study this phenomenon, we chose to use an in vitro model of tumor relapse that selects for and allows quantification of tumor stem cells in 3D spheroid cultures. Our goal was to determine whether TP508 could specifically sensitize cancer stem cells to the effects of RT and prevent or delay stem cell mediated in vitro tumor relapse. Medulloblastoma (Daoy) cells were grown as 3D spheroids in vitro to select for the growth of stem cells. Primary spheroids were treated on day 5 with either saline or TP508 (0.5mg/mL), and exposed to radiation (10Gy) on day 7 using a Cs137 source. One day post-RT, cells were dissociated and cultured as secondary spheroids to determine the stemness or relapse potential of the cells following RT. Daily images were taken to quantify neurosphere formation. Spheroids were also analyzed for viability, apoptosis, proliferation (PCNA), and for stem cell markers (CD133/LGR5/CD44/DCLK1/Sox-2), using western blots, flow cytometry, and immuno-fluorescent staining. TP508 treatment of Daoy cell spheroids prior to RT significantly delayed the formation of secondary spheroids, decreased cell viability, number of proliferating cells, and the number of cells expressing cancer stem cell markers. Thus, in this in vitro assay, TP508 sensitized cancer stem cells to the effects of RT and delayed relapse of brain tumor stem cells in vitro. These findings suggest that injection of TP508 prior to RT treatment may sensitize cancer stem cells to radiation and help prevent brain tumor relapse. Studies are underway to determine the mechanism by which TP508 sensitizes cancer stem cells to RT and whether TP508 has similar effects on other types of cancer stem cells. This work was supported by NCI Contract # HHSN261201300076C to DC. Citation Format: Stephanie M. Moya, Carla Kantara, Laurie Sower, Darrell H. Carney. TP508 sensitizes cancer stem cells to radiation and delays brain cancer cell relapse in vitro. [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 3341. doi:10.1158/1538-7445.AM2015-3341