Abstract 2497: ONC201 targets cancer stem cells in colorectal, prostate and glioblastoma multiforme tumors via modulation of stem cell-related gene expression
Authors: Prabhu Varun Vijay , Allen Joshua E. , Zhao Dan , Lulla Amriti R. , Kline Christina Leah B. , van den Heuvel A. Pieter J. , Lev Avital , Batchelor Tracy T. , Dicker David T. , Chi Andrew S. , El-Deiry Wafik S. 
Published: July 2016

Abstract
ONC201 is a first-in-class anti-tumor agent that selectively targets cancer cells without observed toxicity. ONC201 is being tested in phase I/II clinical trials for patients with advanced solid tumors and hematological malignancies. Several tumors contain a rare population of cancer stem cells (CSCs) capable of self-renewal that contribute to tumor maintenance and resistance to therapy. We have previously demonstrated that ONC201 targets self-renewing, chemotherapy-resistant colorectal CSCs (Prabhu et al, Cancer Res, 2015). We hypothesized that anti-CSC effects of ONC201 involve changes in stem-cell related gene expression. A targeted network analysis of gene expression profiles of HCT116 p53-null and RKO human colon cancer cells treated with ONC201 revealed that several stem cell-related pathways and proteins are affected with potential implications for anti-CSC effects in diverse tumor types. Specifically, mRNA levels of ID1 (colon/glioblastoma CSC-regulation, 2.5 fold), ID2 (glioma stem cell regulation, 3.2 fold), ID3 (colon/glioma CSC-regulation, 2.9 fold), ALDH7A1 (prostate CSC marker, 2 fold) were significantly downregulated and KLF9 (glioblastoma stem cell inhibitor, 1.5 fold) was significantly upregulated in HCT116 p53-null cells upon ONC201 treatment. Also, mRNA levels of Wnt pathway related genes such as ligand WNT16 (haematopoietic stem cell/prostate cancer resistance-related, 13.5 fold), receptors FZD2 (2.98 fold), FZD4 (3.9 fold) and transcription factor TCF7L2 (3.55 fold) were significantly downregulated. Validation with qRT-PCR indicated that ID2, WNT16 mRNA levels were significantly downregulated while KLF9 mRNA was significantly upregulated in response to ONC201 treatment in HCT116 p53-null cells. Interestingly, ONC201 downregulated mRNA levels of ID1 (2.1 fold) and FZD4 (1.6 fold) in RKO cells but not in ONC201-resistant RKO cells, indicating that CSC-inhibition could serve as a biomarker of ONC201 response. To functionally validate anti-CSC effects of ONC201 in glioblastoma multiforme (GBM) and prostate cancer we determined effects on self-renewal using tumorsphere formation. ONC201 eradicated CSC-enriched 3-dimensional neurosphere culture models of primary GBM samples, including newly diagnosed and recurrent samples. ONC201 potently inhibited in vitro cell proliferation of all 5 lines, with IC50 values of 433 nM (MGG18), 1.46 μM (MGG4), 1.09 μM (MGG8), 3.97 μM (MGG67R) and 688 nM (MGG152). ONC201 significantly reduced tumorsphere formation of 22Rv1, DU145 and PC3 human prostate cancer cells. Additionally, western blotting revealed that Wnt16 was downregulated in LNCaP and 22Rv1 while CSC marker CD44 was downregulated in 22Rv1 cells. Ongoing studies are further validating these potential anti-CSC molecular targets of ONC201 and determining their contribution to the overall anti-CSC and anti-tumor effect of ONC201.
Citation Format: Varun Vijay Prabhu, Joshua E. Allen, Dan Zhao, Amriti R. Lulla, Christina Leah B. Kline, A. Pieter J. van den Heuvel, Avital Lev, Tracy T. Batchelor, David T. Dicker, Andrew S. Chi, Wafik S. El-Deiry. ONC201 targets cancer stem cells in colorectal, prostate and glioblastoma multiforme tumors via modulation of stem cell-related gene expression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2497.