Abstract 26P
Background
10% of colorectal cancers (CRC) will have a BRAF mutation (BM). This represents a poor prognostic group. We have developed a novel, metastatic genetically engineered mouse model (GEMM) of BM CRC and derived a prognostic RNA signature.
Methods
3 genes were targeted with the intestine-specific villinCreER: activating Braf V600E/+ (B), deletion of Trp53 fl/fl (P) and activating NOTCH1 intracellular domain Rosa 26N1icd/+ (N) to generate BP (n=29) and BPN (n=50) mice. Mice were induced and aged until clinical endpoint. Neutrophils were targeted in BPN mice with AZD5069 (CXCR2 inhibitor) +/- anti-PD1 antibody or vehicle control from 85 days post Cre induction (DPI). NOTCH1 Activation RNA-Seq Signature (NAS) was developed from BP and BPN murine tumour derived organoids along with previously published Kras G12D PN RNA-Seq data (Jackstadt Cancer Cell 2019) by differential expression analysis (R 4.0.2, limma 3.46) of N+ and N- organoids.
Results
NOTCH1 activation resulted in a larger tumour burden in BPN mice (BP=16mm2 vs BPN=36mm2 p<0.01) with more invasive tumours (T4 disease rate BP=21% vs BPN=61% p<0.01). Median overall survival (OS) was unaffected (190 DPI BP vs 163 DPI BPN p=0.30). 32/50 (64%) of BPN mice developed metastasis compared with 1/29 (3%) of BP mice. BPN metastasis included peritoneal disease (38%) and liver (12%). Endpoint BPN mice had neutrophilia (median 1.2 K/uL BP vs 4.7 K/uL BPN p<0.01). Therefore neutrophils were targeted with CXCR2i +/- anti PD1. 7/12 (58%) of vehicle control mice had metastasis compared to 4/11 (36%) with CXCR2i and 0/7 with CXCR2i + anti PD1 combination (Chi2 p=0.04). Translating the NAS to confident orthologous genes and applying to human CRC datasets, high NAS resulted in a shorter OS (HR=1.26, log rank p=0.01) and shorter RFS (HR=1.26, log rank p<0.01). There were no significant differences in NAS between KRAS mutational status but NAS was higher in BM tumours (t-test p<0.01).
Conclusions
NOTCH1 activation promotes metastasis in a Braf V600E GEMM of CRC. Metastasis is reduced by neutrophil inhibition which synergises with anti PD1 therapy, supporting an actionable phenotype. The NAS identifies a poor prognostic patient group and future work will see if neutrophil targeted therapy could benefit these patients.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Cancer Research UK.
Disclosure
O.J. Sansom: Financial Interests, Institutional, Funding: Novartis, Cancer Research Technology, Redx. All other authors have declared no conflicts of interest.