Abstract 5803: Role of Neuropilin 2 in osteoclasts promoting prostate cancer bone metastasis

Background: Bone metastasis is one of the major clinical concerns that causes skeletal related malignancies and increased mortality. Bone is one of the preferred sites for metastatic prostate cancer. The tumor cells interact with bone cells (osteoblasts and osteoclasts) resulting in an imbalance in the bone homeostasis causing metastatic bone disease. Unlike other cancers, the bone maturation promoted by metastatic prostate cancer (PCa) leads to increased osteoblastic activity resulting in osteoblastic bone lesions. However, bone resorption promoted by PCa cells precedes bone production leading to release of growth factors that aid PCa cells to develop into an overt metastasis. Our preliminary data indicated a non-tyrosine kinase receptor Neuropilin 2 (NRP2) is expressed in osteoclasts (OC) induced by PCa cells. The objective of our current study is to study the role of NRP2 in PCa-induced OCs. We hypothesize that PCa-induced NRP2 expression in OC is necessary for low osteolytic activity and that it negatively regulates the OCs leading to PCa bone metastasis. Methods: Mouse OC precursors were isolated from bone marrow of C57BL/6 mice and differentiated into OCs under conditions of RANKL and M-CSF and in conditioned medium (CM) collected from PCa cell line LNCaP C4-2B (promotes high osteoblastic and low osteoclastic activity) and PC3 (predominantly osteoclastic activity) to mimic the conditions in normal bone and PCa bone metastasis. NRP2 expression at protein and mRNA was evaluated. TRAP staining and activity were conducted to confirm the differentiation of OCs. Results & Discussion: We observed that NRP2 was expressed in OCs induced under standard conditions and in PC3 and C4-2B CM. TRAP staining and activity confirmed the differentiation of OCs under these conditions. Interestingly, depletion of NRP2 and treatment either in standard conditions or C4-2B CM exhibited a drastic increase in osteoclastogenesis. However, NRP2-depleted OC precursors when treated with PC3 CM showed no change in osteoclastogenesis. These findings advocate a role of NRP2 in inhibiting osteoclastic activity in PCa bone metastasis and osteolytic PCa evades NRP2 inhibition. Protein analysis of the time course of NRP2 in OC in PC3 CM and C4-2B CM showed a differential NRP2 expression. This difference in the NRP2 levels can be impacted at either transcription or post-translational level. No change was observed in the NRP2 expression at transcriptional level in both the conditions suggesting that this difference can be due to either translation or rapid degradation of NRP2. Using in-vitro and transgenic mice, we will examine how PC3 CM-induced OCs escapes the inhibition of NRP2. We will also determine whether NRP2 expression regulates the transcription of genes involved in OC differentiation and activation. Together, this approach will elucidate the role of NRP2 axis on OCs in promoting PCa-induced bone metastasis and will aid in determining whether NRP2 axis can be a therapeutic target. Note: This abstract was not presented at the meeting. Citation Format: Navatha shree Polavaram, Arup Bag, Sohini Roy, Samikshan Dutta, Kaustubh Datta. Role of Neuropilin 2 in osteoclasts promoting prostate cancer bone metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5803. doi:10.1158/1538-7445.AM2017-5803