Summary Cancer stem cells (CSCs) are documented to play a key role in tumorigenesis and therapy resistance. Despite significant progress in clinical oncology, CSC reservoirs remain elusive and difficult to eliminate. Reverse-turn peptidomimetics were characterized as disruptors of CBP/beta-Catenin interactions and represent a promising avenue to curb hyperactive canonical Wnt/beta-Catenin signaling in CSCs. Recent studies suggested Sam68 as a critical mediator of reverse-turn peptidomimetics response in CSC populations. Using computational and biochemical approaches we confirmed Sam68 as a primary target of reverse-turn peptidomimetics. Furthermore, we executed an in silico drug discovery pipeline to identify yet uncharacterized reverse-turn peptidomimetic structures displaying superior anti-CSC activity in transformed pluripotent and colorectal cancer cell models. Thus, we identified YB-0158 as a reverse-turn peptidomimetic small molecule with enhanced translational potential, altering key hallmarks of human colorectal CSCs in patient-derived ex vivo organoids and in vivo serial tumor transplantation.

The histone methyltransferase G9a is well-documented for its implication in neoplastic growth. However, recent investigations have demonstrated a key involvement of this chromatin writer in maintaining the self-renewal and tumor-initiating capacities of cancer stem cells (CSCs). Direct inhibition of G9a’s catalytic activity was reported as a promising therapeutic target in multiple preclinical studies. Yet, none of the available pharmacological inhibitors of G9a activity have shown success at the early stages of clinical testing. Here, we discuss central findings of oncogenic expression and activation of G9a in CSCs from different origins, as well as the impact of the suppression of G9a histone methyltransferase activity in such contexts. We will explore the challenges posed by direct and systemic inhibition of G9a activity in the perspective of clinical translation of documented small molecules. Finally, we will discuss recent advances in drug discovery as viable strategies to develop context-specific drugs, selectively targeting G9a in CSC populations.