Bone Abstracts

Rationale and hypothesis: In ~70% of advanced prostate cancer (PCa) patients, incurable bone metastases are a significant cause of morbidity and mortality. It has been shown that in models of PCa, bone metastases are initiated by a minor subset (<1% of total cell population) that are mitotically quiescent and which have undergone epithelial to mesenchymal transition (EMT). Recent studies have shown that various P2 receptors regulate invasiveness/EMT in different types of cancers including PCa. Therefore, we hypothesised that alterations in the expression of P2 receptors are associated with the PCa metastasis-initiating cells.

Objectives: To study the gene expression profile of the fourteen P2 receptors in PCa metastasis-initiating cells.

Methodology: In our previous studies, we have developed methods to track quiescent tumour cells both in vitro and in vivo, based on their fluorescent lipophilic dyes retention when not dividing and shown that these cells have an increased capacity to form metastases. Using these models and quantitative RT-PCR and RNA-Seq techniques, we compared gene expression profile of P2 receptors between FACS sorted quiescent and non-quiescent populations in two human PCa cell lines, covering both osteolytic (PC3 cells) and osteosclerotic (C4 2B4 cells) bone metastases.

Results: Results showed that P2X3, X4, X5, X7, Y₁, Y₄, Y₁₃, and Y₁₄ receptors transcripts were expressed in both cell lines in vitro. The expression of P2RX4 and P2RX7 were significantly increased in quiescent, metastasis initiating populations. Analysis of the expression of these genes also suggested up-regulation of P2RX4 and P2RX7 in PCa cells growing in bone of immunocompromised mouse as xenografts, compared to cultured populations.

Conclusion: These data suggest the involvement of P2 receptors, particularly the receptors of ATP – P2X4 and P2X7 receptor, in the development of PCa bone metastasis and identify these genes and the pathways they regulate as potential novel therapeutic targets for preventing/suppressing metastases.