Abstract 2633: Discovery of novel, highly selective inhibitors of PLK4 that demonstrate in vivo regressions in TRIM37 high xenografts

Abstract

Abstract Amplification and copy number alterations of the 17q23 amplicon are common in breast cancer and neuroblastoma and have been associated with early relapse and poor prognosis. Recent work identified a key vulnerability associated with amplicon-driven overexpression of TRIM37 in these tumor types (Meitinger et al. 2020; Yeow et al. 2020). High levels of TRIM37 prevent acentrosomal spindle assembly and render cells mitotically vulnerable to inhibition of polo-like kinase 4 (PLK4), a serine/threonine protein kinase that controls centrosome duplication. We have discovered potent small molecule inhibitors of PLK4 that are highly selective against the kinome, including against the closely related aurora kinases and PLK1-3. Self-regulation of PLK4 protein levels occurs through proteasomal degradation induced by PLK4 trans-autophosphorylation. ORIC PLK4 inhibitors blocked trans-autophosphorylation leading to stabilization of PLK4, thus directly demonstrating target inhibition in cells. Importantly, PLK4 inhibitor induced PLK4 protein stabilization correlated with cell viability, providing a quantifiable pharmacodynamic (PD) association with antitumor activity. Cell viability assessment across a cancer cell line panel revealed that the highly selective ORIC PLK4 inhibitors showed greater potency in TRIM37 high cancer cell lines as compared to TRIM37 low cell lines. In contrast, less selective compounds, including from the clinical literature, did not display differential potency in TRIM37 high versus low cancer cell lines. Importantly, cell potency in TRIM37 high cancer cells was rescued with knockdown of TRIM37, illustrating that selective PLK4 inhibitors are synthetic lethal with TRIM37 amplification. Oral administration of ORIC PLK4 inhibitors resulted in regressions of TRIM37 high xenograft tumors, with corresponding PD effects and no body weight loss. In summary, we have discovered novel, potent, highly selective small molecule inhibitors of PLK4 that are orally bioavailable and confirmed the potential for this new target in treating tumors with high levels of TRIM37. Citation Format: Kyle A. Edgar, Amy Young, Jared Moore, Xi Chen, Wei Fang, Jae H. Chang, Wayne Kong, Jason E. Long, Aleksandr Pankov, Anneleen Daemen, Daniel G. Shore, Robert Warne, Paul Gibbons, Chudi O. Ndubaku, Melissa R. Junttila, Lori S. Friedman. Discovery of novel, highly selective inhibitors of PLK4 that demonstrate in vivo regressions in TRIM37 high xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2633.