ST-401: A BRAIN-PENETRANT MICROTUBULE-TARGETING AGENT THAT KILLS CANCER CELLS IN INTERPHASE

Abstract Microtubule targeting agents (MTAs) are indispensable medicines to treat a wide range of cancers, and evidence suggests that glioblastoma is sensitive to disruptions in microtubule (MT) functions; but most MTAs do not cross the blood brain barrier. To address this limitation, we developed a brain-penetrant MTA, ST-401, that inhibited the growth of human glioblastoma in culture at nanomolar concentrations (Horne et al. (2020) Neuro-Onc Adv. 3(1): vdaa165). Of note, ST-401 binds to the colchicine site, inhibits tubulin assembly and reversibly reduces MT dynamics in cells with a milder activity compared to the reference MTA, nocodazole. Pharmacokinetic analysis of ST-401 in mice shows brain penetration reaching antitumor concentrations, and in vivo testing of ST-401 demonstrated significant antitumor and radiosensitizing activities. Testing of ST-401 on the NCI 60 cancer cell panel indicated that its anti-tumor activity 1) did not correlate with any of the compounds tested thus far and 2) only weakly correlated with MTAs that act through alternate mechanisms [Taxol and Vinblastine]. Thus, ST-401 may kill cancer cells through a novel mechanism related to disruption of MT function that is different from MTAs tested thus far on the NCI 60 cancer cell panel. As initial step to discover this novel mechanism of action, we studied the anti-tumor activity of ST-401 and nocodazole in HCT116 cells in culture. As expected, low concentrations (30 and 100 nM) of nocodazole killed HCT116 cells in mitosis and increased p-P53; by contrast these low concentrations of ST-401 killed HCT116 cells in interphase and did not increase p-P53. Our study shows that the brain-penetrant MTA, ST-401, kills cancers in interphase, a response that contrasts with the activity of the reference MTA nocodazole. ST-401 represents a promising chemical scaffold to develop brain-penetrant therapeutics for the treatment of patients diagnosed with glioblastoma.