A cell-based neuroprotection assay targeting poly (ADP-ribose) polymerase (PARP) reveals oncology-based potency ranking of clinically used PARP inhibitors (PARPi)


S O Benson1; F M Ismail1; A A Fatokun1
1 Centre for Natural Products Discovery (CNPD), School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK


Poly (ADP-ribose) polymerase inhibitors (PARPi) selectively kill cancer cells that harbour mutation in tumour suppressor genes, such as BRCA1 and BRCA2. Four PARPi are currently used in the clinic as monotherapy for BRCA-mutated cancers. PARPi have, however, also been suggested for repurposing for neurological and neurodegenerative indications, wherein excessive PARP activation leads to neuronal death and PARP inhibition is neuroprotective [1]. We thus examined whether our cell-based assay, originally designed for interrogating PARP-mediated neuronal death, is adaptable to other application contexts by revealing the established, oncology-related rank order of potencies for the PARPi. PARP-dependent cell death (as surrogate for PARP activity) was induced in cultured human cervical adenocarcinoma cells (HeLa) by treatment with the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) (50µM, 25 minutes). The ability of the four PARPi to protect against the cell death (PARP inhibition) was then assessed, 24 h post-MNNG treatment, by quantifying cell viability using MTT. EC50 values were determined using GraphPad and statistical analyses were conducted using one-way ANOVA with Tukey’s post-hoc test, with P<0.05 considered statistically significant. The four PARPi each showed a concentration-dependent protection against MNNG-induced reduction in cell viability, with the following rank order of potencies (EC50 in nM): talazoparib (3.6 ± 0.3) > rucaparib (8.4 ± 1.8) > niraparib (17.1 ± 2.0) > olaparib (23.1 ± 8.9). Although the cell-based EC50 values are higher than the literature-reported IC50 values in cell-free assays, the order of potency was the same and the fold differences in potency relative to olaparib were similar [2]. Our cell-based assay is therefore robust for the characterisation of PARPi for oncological and repurposing applications

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