Abstract 4526: Inhibition of RNA Pol I transcription and induction of nucleolar stress in cancer cells treated with the experimental alpha-adrenergic receptor antagonist JP-1302
Authors: Saproo Sheetanshu , Papadaki Styliani , Espinoza Jaime A. , Bartek Jiri , Lindström Mikael S. 
Published: March 2024

Abstract
The inhibition of ribosome biogenesis through pharmacological means has drawn attention as a potential strategy in cancer therapy. In our previous study we highlighted a novel property of the FDA-approved antimalarial drug amodiaquine, demonstrating its ability to dose-dependently inhibit ribosomal RNA (rRNA) transcription, a critical step in ribosome biogenesis (Espinoza JA, et al Cell Death Diff, 2020). Amodiaquine was found to induce the degradation of the catalytic subunit of RNA polymerase I, known as POLR1A (RPA194), and resulting in nucleolar stress and the stabilization of p53. Notably, RNA Pol I shutdown occurred independently of DNA damage. Motivated by these findings, we sought to find additional inhibitors of ribosome biogenesis. Acridine derivatives display anti-cancer properties. The activity of acridines is mainly attributed to the planarity of these structures, which can intercalate within the DNA structure, and inhibition of chromatin associated protein targets including topoisomerases. JP-1302 is an experimental drug, on a 9-aminoacridine structural scaffold, acting as a selective alpha-2 adrenergic receptor antagonist. It was recently shown that JP-1302 inhibits transcription, blocking RNA Pol II phosphorylation and inhibiting p21 expression at a concentration of 10 μM (Mitchell DC, et al Nat Biotech, 2023). Given JP-1302's structural similarity to other acridine derivatives such as aminacrine, ethacridine, and the experimental compound BMH-21, all known to inhibit RNA Pol I transcription, we hypothesized that JP-1302 might share similar properties. The purpose of our new study was to evaluate JP-1302´s effect on ribosome biogenesis, p53, and cancer cell growth. We show here that JP-1302 acts as an inhibitor of RNA Pol I transcription. Treatment with JP-1302 induced a rapid decrease in the levels of POLR1A, cessation of rRNA synthesis and nucleolar stress already within six hours and at a concentration of 0.5 μM. JP-1302 treatment stabilized wild type p53 and enhanced p21 expression in the osteosarcoma line U2OS. RNA Pol I shutdown occurred in the absence of DNA damage response, as determined by gH2A.X staining. JP-1302 impaired the growth of both p53 wild type and p53 null HCT116 cells with GI50 values of around 0.6 μM, as well as in U2OS cells at 0.8 μM, as determined after 48 hours. Paradoxically, at very low concentrations JP-1302 appeared to transiently stimulate RNA synthesis, a phenomenon that will require further investigation. In conclusion, we identified JP-1302 as a novel inhibitor of ribosomal RNA synthesis, exerting this effect at concentrations that do not induce DNA damage, and independently of p53. Given that JP-1302 passes the blood-brain barrier in rodents, and accumulating in different brain regions, it is of future interest to evaluate this drug in brain tumor models.
Citation Format: Sheetanshu Saproo, Styliani Papadaki, Jaime A. Espinoza, Jiri Bartek, Mikael S. Lindström. Inhibition of RNA Pol I transcription and induction of nucleolar stress in cancer cells treated with the experimental alpha-adrenergic receptor antagonist JP-1302 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4526.