Fig. 4: Oral CHK1i in combination with a pan-FGFRi demonstrates synergistic antitumour activity and inhibits acquired resistance to targeted therapy manifested by ecDNA.
From: Enhancing transcription–replication conflict targets ecDNA-positive cancers
a, Chemical structure of BBI-2779. b,c, Dose-dependent induction of RS and associated biomarkers measured by phosphorylated RPA32 Ser8 level using IF (b) and immunoblotting (c). For b, significance determined using ordinary two-way ANOVA, n = 3. d, Differential tumour cell antiproliferation activity of BBI-2779 in COLO320DM and HSR cells (n = 3). e, Embedded FISH image of SNU16 cells demonstrating FGFR2+ ecDNA. SNU16 cells were grown as tumour xenografts in mice. After tumour establishment (approximately 285 mm3), mice were treated with vehicle, BBI-2779 (30 mg kg−1), infigratinib (15 mg kg−1) or BBI-2779 (30 mg kg−1) plus infigratinib (15 mg kg−1) for 25 days (vehicle) or 27 days (other arms). Mean tumour volumes ± s.e.m. are shown (n = 8 mice per group). f, FGFR2 copy number was evaluated by quantitative polymerase chain reaction (qPCR) on tumour DNA. Significance was determined by one-way ANOVA with Tukey’s multiple comparisons. g, Immunoblots of tumour lysates measuring elevated RS, DNA damage and abrogation of oncoprotein FGFR2 expression (n = 3/8 mice per group). h, ecDNA-amplified oncogenes are hypertranscribed, resulting in elevated RS and reliance on CHK1 to manage DNA replication to maintain oncoprotein overexpression and proliferation. CHK1i results in uncontrolled origin firing and failed cell cycle checkpoints, exacerbating RS in ecDNA-enabled tumour cells. Synthetic lethality to CHK1i in ecDNA+-oncogene-amplified tumour cells is synergistic with targeted therapy resulting in enhanced cytotoxicity. Scale bar, 10 µm. PO, oral; QD, once-daily; Q2D, every other day.
