Introduction Epithelial ovarian cancer (EOC) has a unique mode of metastasis with seeding of spheroids in the peritoneum. Our research into EOC spheroid cell biology has provided many new insights into signalling plasticity linked to metastasis. We speculate that EOC cells change their biology between tumour and spheroid states to promote cell survival, yet this switching behaviour is unknown. Here, we describe new results obtained by directly comparing cultured EOC spheroids and the new organoid model.

Methods High-grade serous patient ascites-derived iOvCa cell lines were used to generate spheroids in suspension on ULA plates and organoids using modified patient-derived organoid (PDO) conditions. The Incucyte S3 and IHC were used for growth and morphology comparisons. Immunoblotting was performed to evaluate altered signaling processes from our previous work. RNA-sequencing with bioinformatic analyses was completed on iOvCa lines and 3 newly-developed PDOs. Small molecule inhibitors targeting the G2M checkpoint were tested to observe effects on viability.

Results Organoids appeared heterogeneous with dense or mixed phenotypes, whereas spheroids existed as typical compact, grape-like, or sparse clusters. Organoid growth dynamics were similarly variable amongst lines. As expected, spheroids had high AMP-activated protein kinase T172 phosphorylation and low Akt S473 phosphorylation compared to organoids. Transcriptomic analyses yielded elevated G2M checkpoint in organoids compared to spheroids; preliminary results show that spheroids are resistant to Wee1 and CDK1 inhibition, yet organoids have lower viability.

Conclusions The cellular adaptations of EOC throughout disease progression have become very clear, particularly with the molecular disparities between spheroids and organoids. Our findings support targeting both proliferative and dormant cells; thus, parallel assays using these translational models of advanced EOC are crucial to uncover new therapeutic targets.