Anti‐tumoural activity of the G‐quadruplex ligand pyridostatin against BRCA1/2‐deficient tumours

A, B

FVB female mice were injected intramuscularly with (A) BRCA1‐proficient KP3.33 (Brca1⁺/⁺) or (B) BRCA1/53BP1‐deficient KB1PM5 (Brca1^−/−, Tp53bp1 ^−/− ) mouse mammary tumour cells. Pyridostatin (PDS) was administered intravenously (i.v.; 7.5 mg/kg/day) and talazoparib was administered orally (p.o.; 0.33 mg/kg/day), over the indicated periods of time. Vertical dotted line indicates end of treatment. Tumour volume was measured at the timepoints shown on the graph and expressed relative to tumour volume at the beginning of treatment. Each experimental group included n = 5 mice. Error bars represent SEM. P values were calculated between treated and untreated tumours at day 16, using an unpaired two‐tailed t‐test. ****P ≤ 0.0001; NS, P > 0.05.

C, D

BRCA1‐proficient KP3.33 (Brca1 ^+/+), BRCA1‐deficient KB1PM5 (Brca1 ^−/−) and BRCA1/53BP1‐deficient KB1PM5 (Brca1 ^−/−/Tp53bp1 ^−/−) mouse mammary tumour cells were treated with 2 µM of pyridostatin (PDS) for 24 h and released into fresh medium without pyridostatin. Whole‐cell extracts were prepared 0 to 72 h after release and immunoblotted as indicated. SMC1 was used as a loading control. KAP1 phosphorylation site is indicated in red.

E

BRCA1 ^+/+, BRCA1 ^−/− and BRCA1 ^−/−/TP53BP1 ^−/− RPE‐1 cells were treated with 10 μM of pyridostatin (PDS) or 2 μM of olaparib for 2 days. Whole‐cell extracts were immunoblotted as indicated. KAP1, IRF3 and STAT1 phosphorylation sites are shown in red. SMC1 and GAPDH were used as loading controls.

Figure 3. Pyridostatin impairs growth of PARPi‐resistant BRCA1‐deficient tumours and triggers DNA damage and innate immune responses in BRCA1‐deficient PARPi‐resistant cells.