PLK4 inhibition-mediated centrosome amplification drives anti-tumor activity across euploid solid tumors

PLK4 is a master regulator of centriole biogenesis. Knockdown or complete inhibition of PLK4 results in centrosome depletion. Recently, it was demonstrated that normal cells can tolerate centriole depletion by utilizing acentriolar condensates of pericentriolar material to function as microtubule organizing centers during mitosis. High levels of the E3-ubiquitin ligase TRIM37 disrupt the formation of acentriolar condensates and therefore sensitize cells to PLK4 inhibition and represent a biomarker for sensitivity to fully inhibited PLK4. Here, we describe the preclinical characterization of two potent, selective, and orally bioavailable small-molecule PLK4 inhibitors, EXEL-0667 and EXEL-1855. In vitro cell viability assays, including high‑throughput PRISM screening, immunofluorescence‑based assessment of centrosome number, analysis of predictive biomarkers in TCGA datasets, along with in vivo mouse pharmacokinetics and cell line-derived xenograft efficacy studies were used to characterize the mechanism of action and in vivo properties of EXEL‑0667 and EXEL‑1855. Here we show that, like other PLK4 inhibitors described, partial PLK4 inhibition results in centrosome amplification, and only at high concentrations of the inhibitors is centrosome depletion achieved. We show that biomarkers associated with normal centrosome homeostasis, TP53 wild type and near euploid genome, enrich for responders to partial PLK4 inhibition. Unexpectedly, EXEL-1855 demonstrates in vivo efficacy at dose levels consistent with centrosome amplification in a variety of near-euploid tumor models with wild-type TP53. These findings support the use of PLK4 inhibitors across a wider range of tumor indications beyond those with TRIM37-amplification and warrant further assessment. These studies examined whether blocking the activity of PLK4, a protein required for building a cellular structure called a centrosome, which is required for proper cell division of one parent cell into two daughter cells, could be an effective cancer treatment. Assessments of how different doses of PLK4 inhibitors affected centrosome number and which tumor features predicted response were performed. The studies revealed that low PLK4 inhibitor levels caused cells to form extra centrosomes, leading cells to try and divide into more than two daughter cells, while high levels reduced centrosome number, impairing cell division. In mouse models, PLK4 inhibition slowed tumor growth at doses that showed centrosome amplification. These results suggest that PLK4 inhibitors may be effective in a broad range of cancers and support further investigation of this therapeutic approach. Muñoz et al. present in vitro and in vivo characterization of PLK4 inhibitors EXEL-0667 and EXEL-1855 to explore dose-dependent effects on the centrosome. They find that TP53-wild-type, near-euploid tumors show the highest sensitivity even at doses causing centrosome amplification, supporting the use of PLK4-targeting agents.