Abstract 5072: Mesenchymal stem cells promote osteogenesis and the evolution of apoptosis resistant bone metastatic prostate cancer
Authors: McGuire Jeremy J. , Cook Leah , Frieling Jeremy , Lynch Conor 
Published: August 2015

Abstract
Introduction: Bone metastasis is common in men with advanced prostate cancer. The resultant lesions are incurable and hallmarked by extensive osteoblast activity and osteogenesis. To generate efficacious therapies a better understanding of the mechanisms governing prostate cancer-bone interaction are required. Mesenchymal stem cells (MSCs) can give rise to multiple cell types including osteoblasts. Given that bone is a reservoir for MSCs, we reasoned that MSCs may contribute to the prostate cancer induced bone formation.
Rationale/Hypothesis. Our in vitro data demonstrated that MSCs are highly migratory towards prostate cancer cells. Human and rodent specimens of bone metastatic prostate cancer contain α-smooth muscle actin positive MSC infiltrates. Based on these data, we hypothesized that MSCs contribute to prostate cancer induced osteogenesis.
Methodology. Primary murine bone derived MSCs (CD29+, SCA-1+, CD45-) were isolated. In vivo we used an osteogenic bone metastatic prostate cancer rodent model. Mice were intratibially inoculated with PAIIIs, PAIIIs/MSCs (1:1), or MSCs (n = 8/group, 1×104total cells). Tumor growth was measured via luminescence imaging. Subsequently the tibias were collected for x-ray, μCT and, histological analysis. To delineate cellular and molecular mechanisms involved in MSC-prostate cancer interaction we measured PAIII induced MSC differentiation (alizarin red staining) as well as MSC effects on PAIII growth (luminescence) and apoptosis using cleaved caspase 3 (CC3) (immunoblot and immunofluorescence).
Results. Surprisingly, we observed that MSCs significantly suppressed PAIII prostate cancer growth in-vivo at day 11 (p&lt;0.05). However, between days 11 and 15 MSCs contributed to a significantly faster prostate cancer growth rate compared to PAIII alone (p&lt;0.05) suggesting that MSCs could be contributing to the evolution of a resistant or faster growing clone. Ex vivo analyses with μCT and histomorphometry demonstrated that MSCs significantly enhance prostate cancer induced osteogenesis with an 81% increase in bone formation compared to PAIII alone (p&lt;0.05). In vitro, PAIII conditioned media (CM) significantly stimulated osteoblast differentiation of MSCs (p&lt;0.05). 5-hour treatment of PAIIIs with MSC CM promoted a 3-fold increase in PAIII apoptosis (CC3 positive cells) compared to controls (p&lt;0.05). However, successive exposure of PAIIIs to MSC conditioned media yielded apoptotic resistant PAIIIs. Cytokine array analysis of MSC CM revealed the presence of factors such as Fas ligand that potentially can mediate the observed apoptotic effects.
Conclusions. MSCs contribute to metastatic prostate cancer induced osteogenesis but also can promote the evolution of apoptosis resistant cancer cells. Defining the potential mechanisms involved can lead to new therapies to eradicate incurable bone metastatic prostate cancer.
Citation Format: Jeremy J. McGuire, Leah Cook, Jeremy Frieling, Conor Lynch. Mesenchymal stem cells promote osteogenesis and the evolution of apoptosis resistant bone metastatic prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5072. doi:10.1158/1538-7445.AM2015-5072