Abstract B082: Osteolytic and osteoblastic prostate cancer cells remotely trigger different responses in the bone marrow niche

Abstract

Abstract Background: Prostate cancer (PC) mainly metastasizes to the bone, which is why the bone marrow is an organ of interest when investigating mechanisms for metastasis. Earlier studies have shown that primary tumors have the capability to affect target organs from a distance, inducing so-called premetastatic niches crucial for metastatic establishment. In the formation of the niche, osteoblasts have been proven to play important roles. The present study investigates if the phenotype of PC cells affects the PC-induced differentiation of bone marrow cells, to assess a possible phenotype-specific nature of the metastatic niche. Method: Bone marrow stromal cells (BMSCs) were harvested from femurs from BALB/c nude mice. Cultures were established and after passaging, the cells were stimulated with conditioned media (CM) from the osteoblastic PC cell line LNCaP-19 and the osteolytic PC cell line PC-3. After 72 hours, the cells were harvested and RNA was isolated from the lysate for gene expression analysis. The PC cell lines were also injected subcutaneously together with BMSCs in BALB/c nude mice. When mice had to be sacrificed due to tumor size, tumors and bone marrow was collected for gene expression analysis. Results: Immature BMSCs were proven to be able to differentiate in an osteoblastic or adipocytic direction in vitro. After stimulation with CM from osteolytic PC cells, expression of several genes associated with an osteoblastic phenotype (e.g., Runx2 and Ocn) were downregulated in BMSCs, indicating inhibited osteoblastic differentiation. In contrast, the osteoblastic PC cells induce an immature osteoblastic phenotype with maintained levels of Runx2 and Osx, together with low levels of Ocn. The chemokine Cxcl12, which is related to formation of, and homing to, the premetastatic niche, was induced by osteoblastic PC cells. In the in vivo experiment, the inhibitory effect of osteolytic PC tumors on osteoblast differentiation (Runx2 and Osx) was confirmed. However, an increased expression of Ocn by existing osteoblasts or osteocytes was detected in mice carrying subcutaneous osteolytic PC tumors. Also, the immature osteoblast phenotype induced by the osteoblastic tumors was confirmed. Regarding homing to the metastatic niche, the increased Cxcl12 expression was confirmed in the bone marrow from mice with osteoblastic PC tumors growing subcutaneously. The osteolytic tumors instead induced increased expression of Lox, a protein that affects the integrity of the extracellular matrix. Conclusion: Osteoblastic and osteolytic cell lines had starkly different effects on the bone marrow cells. The osteoblastic PC tumors induced a response from the bone marrow likely to attract cancer cells, together with an immature population of osteoblasts, previously shown to promote hematopoietic stem cell maintenance. On the other hand, the osteolytic tumors inhibit osteoblast differentiation, and prepare the microenvironment for tumor cell arrival by influencing matrix composition of the bone marrow. Taken together, this study demonstrates that PC cell impact on bone marrow cells is dependent on tumor phenotype and may influence the formation of the premetastatic niche in different ways. Citation Format: Daniel Åhs, Andreas Josefsson, Jan-Erik Damber, Karin Welén. Osteolytic and osteoblastic prostate cancer cells remotely trigger different responses in the bone marrow niche [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B082.