DDDR-30. UNRAVELING THE NOVEL ANTI-TUMOR MECHANISM OF ST-401, A BRAIN PENETRANT MICROTUBULE TARGETING AGENT

Abstract

Abstract Microtubule targeting agents (MTAs) are indispensable medicines to treat a wide range of cancers. While evidence suggests that glioblastoma (GBM) is sensitive to disruptions in microtubule (MT) functions; most MTAs do not reach the brain. To address this limitation, we developed a brain-penetrant MTA, ST-401, that kills patient-derived GBM in culture at nanomolar concentrations, binds to colchicine sites through a unique interaction mode, gently and reversibly inhibits MT assembly and kills cancer cells through a novel anti-tumor mechanism as determined by analysis of its activity in the NCI 60 cancer cell panel compared to the Approved Oncology Agents library (Horne et al. (2020) Neuro-Onc Adv. 3(1): vdaa165).We used flow cytometry to confirm that nocodazole (10-100 nM) treatment of HCT116 cells triggered apoptosis, necrosis, and accumulation of autophagosomes, as well as increase in p-P53. By sharp contrast, ST-401 did not trigger these responses. Live cell imaging showed that NOC preferentially kills HCT116 cells in mitosis whereas ST-401 preferentially kills these cells in interphase. ScRNAseq analysis of NOC and ST-401 treatment of HCT-116 cells showed that ST-401 down-regulates MYC mRNA expression, suggesting that ST-401 might affect MYC function. MYC protein levels are regulated by multiple mechanisms, including phosphorylation at residue Thr58 that promotes its ubiquitination and proteasome degradation. We discovered that ST-401 increases MYC phosphorylation on Thr58 and down-regulates MYC protein expression in both HCT116 and the GBM cell line, U251.Our result suggests that the novel anti-tumor mechanism of ST-401 might involve cell death in interphase and reduced MYC expression. Funded by NIH (CA244213 to NS and NS106924 to NS).