Fig. 4: Drug resistance and drug-sensitizing variants in PARP1.

a, Base editing screens of PARP1 and PARP2 in the presence of olaparib or niraparib reveal drug-sensitizing and drug resistance variants. Comparison of gRNA z-scores for the control treated arm, olaparib-treated or niraparib-treated arm versus plasmid library is plotted against the amino acid position. Predicted amino acid editing consequences are labeled for drug resistance variants. The position of the catalytic domain of PARP1 and PARP2 is shown. Screening data are the average of two independent screens performed on separate days. b, Competition assays comparing variants in PARP1 that modulate response to olaparib and niraparib. GFP NT gRNA cells were grown in competition with PARP1-edited cells expressing BFP and quantified with flow cytometry after 72 h in the presence or absence of PARP inhibitors (IC₅₀ concentrations; olaparib 510 nM, niraparib 330 nM). Two independent gRNAs installing the I691T variant were tested. Data represent the mean ± s.d. of two independent experiments, each performed in biological triplicate. Unpaired, two-sided Student’s t-test comparing NT gRNAs with gRNAs targeting PARP1; ***P < 0.0001, **P = 0.0004 (I691T) or 0.0002 (M1V), *P = 0.014 (L390S/S391P) or 0.013 (Y829H/L831P). c, Dose response proliferation assay comparing the growth of MHH-ES-1 ABE cells harboring a NT control gRNA or a gRNA installing the PARP1 Y889C variant. Data are the average of two independent experiments, each performed in triplicate. Two-way ANOVA (analysis of variance); ***P < 0.0001. CTG; CellTiter-Glo. d, Crystal structures of PARP1 bound to olaparib (PDB 7AAD)⁸⁴ or niraparib (PDB 7KK5)⁶⁰ comparing the two binding modes of the inhibitors with respect to the Y889 residue. See also Extended Data Fig. 4. Schematic in b created with BioRender.com.