Abstract 4241: ONC201/TIC10 targets colorectal cancer stem cells and bulk tumor cells via an Akt-Foxo3a-TRAIL-dependent mechanism
Authors: Varun Vijay Prabhu, Joshua E. Allen, David T. Dicker, Wafik S. El-Deiry
Journal: Cancer Research (2015)

Abstract ONC201/TIC10 is a first-in-class anti-tumor agent that induces cell death selectively in cancer cells in vitro and in vivo. ONC201/TIC10 is entering phase I/II clinical trials for patients with advanced cancer. Colorectal tumors contain a small population of stem cell-like cells (cancer stem cells, CSCs) capable of self-renewal that contributes to tumor maintenance, resistance to therapy and disease relapse. We hypothesized that the potent anti-tumor effect of ONC201/TIC10 in colon cancer involves targeting both CSCs and bulk tumor cells. We show that ONC201/TIC10 depletes CSC markers, prevents CSC-mediated colonosphere formation and induces cell surface TRAIL in CSCs in vitro. We further validated these results in xenograft tumor studies in mice, compared the effects of ONC201/TIC10 in CSCs and non-CSCs and validated the mechanism of TRAIL induction in CSCs. ONC201/TIC10 significantly reduces the growth of tumors initiated with sorted Aldefluor(+) CSCs and prevents the passage of these tumors. ONC201/TIC10 upregulates apoptosis markers cleaved caspase-8 and cleaved PARP and downregulates CSC markers ALDH, CD44 and CD133 in the xenograft tumors. In a limiting dilution xenograft tumor initiation assay ONC201/TIC10-treatment decreased tumor initiation and was superior to 5-Fluorouracil treatment. Thus, ONC201/TIC10 inhibits CSC self-renewal in vivo. We have previously described that ONC201/TIC10 exposure leads to transcriptional induction of the TRAIL gene via the transcription factor Foxo3a, which is activated by dual inactivation of Akt and ERK. ONC201/TIC10 reduces levels of phosho-Akt, phospho-ERK, phospho-S294 Foxo3a, phospho-S253 Foxo3a and induces TRAIL in CSC-initiated xenograft tumors. ONC201/TIC10-mediated effects on Akt, ERK, Foxo3a and TRAIL occur in both bulk tumor cells and CSCs. Next, we performed control experiments to confirm the Akt-Foxo3a-TRAIL-dependent mechanism. ONC201/TIC10-mediated depletion of CD44(+) cells was significantly blocked by the TRAIL-sequestering antibody RIK-2. We have previously reported that ONC201/TIC10 upregulates DR5 in tumor cells and disruption of the DR5 death domain decreases ONC201/TIC10-mediated cell death. ONC201/TIC10 increases cell surface DR5 in CSCs and non-CSCs. DR5 knockdown rescues ONC201/TIC10-mediated colonosphere inhibition and depletion of CD44(+) cells further supporting a DR5-TRAIL-dependent mechanism. Overexpression of myristoylated Akt significantly reduces induction of surface TRAIL and rescues depletion of CSC markers and colonosphere inhibition by ONC201/TIC10. Foxo3a knockdown also significantly rescues ONC201/TIC10-mediated colonosphere inhibition and depletion of CD44(+) cells. The identification and demonstration of CSCs as a target further supports the use of ONC201/TIC10 for colorectal cancer therapy and provides an innovative biomarker that could be monitored in the clinic. Citation Format: Varun Vijay Prabhu, Joshua E. Allen, David T. Dicker, Wafik S. El-Deiry. ONC201/TIC10 targets colorectal cancer stem cells and bulk tumor cells via an Akt-Foxo3a-TRAIL-dependent mechanism. [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 4241. doi:10.1158/1538-7445.AM2015-4241