Fig 2: PARP7 induction using AHR agonists sensitizes prostate cancer cells to growth inhibition by RBN2397. A, Effect of RBN2397 on AR− (PC3, DU145) and AR+ (CWR22Rv1, VCaP) prostate cancer lines treated with AHR agonists BBQ and FICZ to induce PARP7. In A, D–H, each condition reflects eight biological replicates, error bars show the SD, and ****, P < 0.0001; ***, P < 0.001; **, <0.01. B, Dead cell detection by Trypan blue staining after culturing cells in the presence or absence of RBN2397 and BBQ for 6 days (slower growing VCaP and CWR22Rv1) and 3 days (faster growing PC3-AR and PC3). The experiments were performed in triplicate, error bars show the SD, and ***, P < 0.001; **, <0.01, *, <0.05; ns, not significant. C, Phase contrast microscopy showing the morphology of cells treated with AHR agonist and RBN2397. The treatments for CWR22Rv1 were performed as part of the experiments shown in Fig. 2C involving R1881 and RBN2397. A similar image for CWR22Rv1 cells with vehicle alone (−) is used in both Fig. 2C and 4C. D, RBN2397 dose–response curve of PC3-AR cells treated with BBQ. E, RBN2397 dose–response curve of DU145 cells treated with BBQ. F, RBN2397 dose–response curve of VCaP cells treated with BBQ. G, Stable knockdown of PARP7 blunts the growth-inhibitory effects of RBN2397 in CWR22Rv1 cells treated with BBQ. H, Stable knockdown of PARP7 blunts the growth-inhibitory effects of RBN2397 in PC3-AR cells treated with BBQ.

Fig 3: PARP7 expression in prostate cancer. A, Violin plots (boxplot inserted) showing PARP7 expression levels in CPM in normal prostate, primary tumors and metastatic AR− and AR+ tumors. The red line indicates the level of PARP7 in the VCaP cell line required for RBN2397-mediated growth inhibition and the gray line shows the basal level of PARP7 in VCaP cells. P values calculated for pairwise comparisons using the Wilcoxon test are indicated (***, <0.001; **, <0.01; *, < 0.05; ns, not significant). All compared values come from the recount3 project. B, Scatter plots comparing expression of PARP7 with AR and AHR in primary tumors (left), metastatic AR− tumors (middle), and metastatic AR+ tumors (right). Spearman correlation coefficients and P values are shown on the plots. C, Boxplots comparing enrichment scores for HALLMARK_INTERFERON_ALPHA_RESPONSE gene set, calculated using GSVA method between lung (LUAD) and prostate (PRAD) primary tumor samples (left); between high PARP7 expression (top quartile, n = 124) and low PARP7 expression (bottom quartile, n = 124) in prostate primary tumor samples (middle); between high PARP7 expression (top quartile, n = 128) and low PARP7 expression (bottom quartile, n = 128) in lung primary tumor samples (right). The P values from Wilcoxon rank-sum tests are shown on the plots.