Therapeutic Targeting of Chemotherapy-Resistant Colorectal Cancer Stem Cells with P73- and Trail-Based Small Molecule

Colorectal cancer (CRC) tumors contain a rare population of self-renewing stem cell-like cells (CRCSCs) that contribute to tumor maintenance and therapy resistance. Therapeutic targeting of CRCSCs could improve treatment response and prolong patient survival.;The endogenous TNF-related apoptosis-inducing ligand (TRAIL) protein selectively induces cell death in cancer cells while sparing normal cells. Small molecule ONC201/TIC10 induces TRAIL-mediated cell death in cancer cells via transcription factor Foxo3a, which is activated by dual inhibition of Akt and ERK. ONC201/TIC10 is currently being tested in phase I/II clinical trials for patients with advanced cancer. This study investigates whether the potent anti-tumor effect of ONC201/TIC10 in CRC involves targeting CRCSCs. ONC201/TIC10 depletes CRCSC markers and prevents chemotherapy-resistant CRCSC-mediated self-renewal in colonosphere assays and xenograft tumor initiation studies in mice. ONC201/TIC10 significantly induces cell surface TRAIL in CRCSCs. ONC201/TIC10-mediated anti-CRCSC effect is significantly blocked by the TRAIL sequestering antibody RIK-2, overexpression of Akt and Foxo3a knockdown. The identification and demonstration of CRCSCs as a target of ONC201/TIC10 provides an innovative biomarker that could be monitored in the clinic.;Tumor suppressor p53 is frequently mutated or inactivated in CRC. In contrast, p53 family member p73 is rarely mutated in CRC and p73 activation elicits p53-like tumor suppression. p53 restoration is known to target CRCSCs, but p73 activation in CRCSCs has not been examined. This study investigates the effects of small molecule prodigiosin-mediated p73 activation on CRCSCs. Prodigiosin reduces chemotherapy-resistant CRCSC-mediated colonosphere formation and xenograft tumor initiation. Mechanistic studies reveal that prodigiosin increases the levels of p73 and reduces levels of the oncogenic N-terminally truncated isoform DeltaNp73 in CRCSCs. Accordingly, p73 knockdown or DeltaNp73 overexpression suppress prodigiosin-mediated CRCSC inhibition. Moreover, prodigiosin increases levels of the transcription factor c-Jun, a regulator of p73 and DeltaNp73. c-Jun knockdown attenuates prodigiosin-mediated DeltaNp73 downregulation, p73 activation and cell death. These findings have previously unrecognized implications for the use of p73 activating therapeutics and DeltaNp73 inhibition for targeting CRCSCs.;Together, these results demonstrate that potent small molecules targeting CRCSCs via tumor suppressive pathways such as p73 and TRAIL are a viable potential approach for robust and durable cancer therapy.