Fig. 6: Inhibition of p97 potentiates the effect of PARPi.
From: The ubiquitin-dependent ATPase p97 removes cytotoxic trapped PARP1 from chromatin
a, Inhibition of p97 potentiates the cytotoxicity of PARPi. CAL51 cells were exposed to PARPi (talazoparib (left) or olaparib (right)) in the presence of a p97 inhibitor (CB-5083 or CuET) for a period of 14 d. Images are shown for samples exposed to 100 nM CB-5083 and 8 nM CuET. b,c, Drug-response curves for CB-5083 (b) and CuET (c). See also Extended Data Fig. 9a,b. d,e, DNA alkylating agents that are used to induce PARP1 trapping do not enhance the cell-inhibitory effects of CB-5083. PARP1WT and PARP1–/– CAL51 cells were exposed to the alkylating agents MMS (d) or temozolomide (TMZ; e) in combination with either talazoparib (positive control) or CB-5083 for 7 d, after which the cell viability was measured. f, CB-5083 modulates the synthetic lethal effect of PARPi in BRCA2–/– cells. Survival curves from clonogenic survival assays in BRCA2WT and BRCA2–/– DLD1 cells treated with different doses of CB-5083 and talazoparib. Colony formation images and quantification are shown in Extended Data Fig. 9e. g, Inhibition of p97 sensitizes mouse cancer organoid cells to PARPi. WB1P breast cancer organoids with Brca1 and p53 loss-of-function mutations were cultured in the presence of the indicated drugs for 7 d. Bright-field images of organoids are shown in Extended Data Fig. 9f. h, Inhibition of p97 sensitizes a human BRCA1-mutant patient-derived breast cancer organoid to PARPi. KCL014BCPO organoids were cultured in the indicated drugs for 7 d. Bright-field images of the organoids are shown in Extended Data Fig. 9g. b–h, Data are the mean ± s.d. of three biological replicates. i, Model of the processing of trapped PARP1. PARP1 trapped by the presence of PARPi on DNA is processed in a stepwise manner. It is initially SUMOylated in a PIAS4-dependant manner and subsequently ubiquitylated in an RNF4-dependent manner. p97 is recruited to the ubiquitin chains and binds via UFD1 and the ATPase activity of p97 extracts the modified PARP1 from the chromatin. DMSO, dimethylsulfoxide.
