Introduction/Background Cancer stem cells (CSCs) are key contributors of cancer traits such as metastasis, recurrence, heterogeneity and drug resistance, leading to poor prognosis and aggressive disease progression. About 85% of patients with high-grade serous ovarian cancer (HGSOC) achieve a clinical remission with a combination of surgery and platinum-based chemotherapy. Although initial response rates to first-line chemotherapy are good, 15-20% of patients will not respond (so called intrinsic resistance) and 25% develop resistance within 6 months. Ovarian Cancer Stem Cells (OCSCs) that exist within the bulk tumor surviving first-line chemotherapy are suggested to be key contributors to resistance, recurrence, and metastasis.
Some of the features of OCSCs are their abilities of self-renewal, quiescence, re-entering cell cycle, and switching between epithelial and mesenchymal states. Deepening our understanding of regulatory elements within OCSCs can provide insight to how these mechanisms are obtained and executed.
One regulatory element worthy of investigation is micro RNAs (miRNAs), a class of small non-coding RNAs that regulate gene expression in the post-transcriptional stage.
Methodology Spheroids from HGSOC cell line OVCAR-3 were generated using Ultra Low Attachment plates. Conventional OVCAR-3, (Parental Monolayer) and OCSC enriched population (Parental Derived Spheroids) whose CSC traits were validated through, western blotting and flow cytometry was RNA-sequenced. After statistical analyses, some differentially expressed miRNAs underwent RT-qPCR, with miRNA specific forward primers and stem-loop primers. OVCAR-3 Resistant Subtypes (Olaparib Resistant Monolayer and Carboplatin Resistant Monolayer) were included in RT-qPCR panel.
Results OCSC traits of spheroid enriched OVCAR-3 culture were substantially increased. After a broad validation process, downregulated hsa-miR-548ah-3p and hsa-miR-let-7b-5p and upregulated hsa-miR-146a-5p and hsa-miR-146b-5p were shown to correlate with spheroid formation ability and basal OCSC surface marker expressions of resistant OVCAR-3 Subtypes.
Conclusion Selected miRNAs appears to have a role in OCSCs and resistance behavior. Further investigation is prospective to unravel their involvement in intrinsic/acquired resistance mechanisms and CSC relationships.
Disclosures Author(s): Deren Demirel, Elif Merve Aydın, İrem Durmaz Şahin
Authors declare no conflict of interest.
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