Introduction: High-grade serous ovarian cancer (HGSOC) can be divided into four subgroups based on molecular characteristics1,2. The proliferative/C5 subgroup is defined by MYCN-pathway activation and may be associated with stem cell-like behavior3. The majority of HGSOC originate from the secretory cells of the fallopian tube (FT), with both tumours and secretory cells characterised by PAX8 expression4. We have developed pre-malignant C5 sub-type Genetically Engineered Mouse Models (GEMM) to characterise key molecular events in the initiation of this sub-type and to provide an immune-competent model for testing therapeutics.
Methods: We have generated independent GEMM with p53 dysfunction (p53lsl-R172H knock-in5) and over-expression of the MYCN-pathway, using either lsl-MYCN or lsl-lin28b transgenes6 directed by the doxycycline-inducible PAX8 promoter. Murine FT were harvested following two-weeks of transgene activation. One FT was harvested en bloc and paraffin embedded for analysis by H&E and immunohistochemistry for the presence of pre-malignant tubal lesions. The contralateral FT was macro-dissected into distal/mid-FT, which were snap frozen for analysis of gene expression by qRT-PCR and RNAseq. As mice with PAX8-directed expression of oncogenes (±MYCN/lin28b overexpression) developed enlarged kidneys due to renal tubular adenomata, for alternate mice, the mid/distal FT tissue was implanted into the bursae of wild-type CBA/nu mice for observation and later analysis.
Results: FT were harvested from twelve p53lsl-R172H/lsl-lin28b mice and from ten p53lsl-R172H/lsl-MYCN mice (including relevant control mice). Dysplastic lesions were observed in a subset of p53lsl-R172H/lsl-MYCN or lsl-lin28b FT and not in controls. MYCN pathway activation was demonstrated by qRT-PCR analysis.
Conclusion: Over-expression of the MYCN-pathway can drive FT epithelial dysplasia in the presence of p53 dysfunction. RNASeq analysis is being performed to elucidate early genetic events in dysplastic FT. Mice are now being harvested following eight-weeks of doxycycline activation to determine whether more advanced pre-malignant change occurs. CRISPR guides deleting relevant genes including p53, PTEN, Nf1 or Rb1 were generated to delete additional genes in MYCN pathway-transgenic FT, followed by implantation for observation of tumourigenesis.