Abstract A46: A bone marrow vascular niche model to study the effects of a DNA Damage Secretory Program in promoting prostate cancer treatment resistance
Authors: Levesque Christine , Zhao Xin , Ghajar Cyrus M. , Nelson Peter S. 
Published: May 2019

Introduction: Prostate cancer (PC) and other solid tumors generally demonstrate initial responses to genotoxic therapeutics, including chemotherapy and radiotherapy. However, for metastatic cancers, resistance to these modalities occurs predictably. Whereas therapeutic strategies for metastatic disease often rely on DNA-damaging agents, our recent work has demonstrated that normal cells comprising the prostate tumor microenvironment are crucial regulators of cancer cell responses to therapy. These studies indicated that the activation of a DNA-Damage Secretory Phenotype (DDSP) within prostate stroma is a critical mediator of acquired tumor resistance to therapy. However, it is not known whether the bone microenvironment also provides a chemoresistant niche to disseminated cells. Here, we aim to test the hypothesis that activation of the DDSP in the bone microenvironment influences tumor cell proliferation and resistance to genotoxic cancer therapeutics.

Methods: To test this hypothesis, we established a cell culture model of the vascular niche, since recent evidence demonstrates that endothelial cells play an important role in the formation of metastatic niches, where they regulate dormancy, proliferation and survival of disseminated cells. We co-cultured endothelial cells with primary human bone marrow derived mesenchymal stem cells (hBM-MSC) to obtain stable 3-dimensional microvascular networks. This organotypic model of bone marrow-like vasculature was then subjected to escalating doses of γ-radiation (Cs-137; 0, 2 and 10Gy), further seeded with PC cell lines (PC3, 22RV1 and LNCaP C4-2B) and we measured proliferation rates of PC cells. Responses to cancer therapeutics (carboplatin at 0, 1, 10 and 100μM or mitoxantrone at 0, 1, 10 and 100nM) were also established using the same model.

Results: We determined that following γ-radiation of the stromal components, tumor cell proliferation rates differed depending on the composition of the constructed niche. Although variation in responses was observed between prostate cancer cell lines, PC3 cells showed an increase in proliferation on irradiated vascular niche (10Gy), with an average of 17±3 Ki-67 positive cells per cluster as compared to 7±3 Ki-67 positive cells per cluster when seeded on irradiated control hBM-MSC for 10 days. To evaluate the contribution of the vascular niche to tumor resistance to therapy, PC cells seeded on vascular networks were subjected to treatments with carboplatin or mitoxantrone. The relative area of tumor cells for each well was calculated from live-cell imaging and apoptosis was assayed by TUNEL reaction. Mitoxantrone-treated 22RV1 cells showed decreased apoptosis when seeded on vascular niches (% Apoptosis: 6±2 at 100nM mitoxantrone) as opposed cells seeded on control hBM-MSC (% Apoptosis: 14±3 at 100nM mitoxantrone).

Conclusions: These studies suggest that effectors derived from the bone marrow vascular niche are differentially regulated following DNA-damage. Subsequently, those factors may influence tumor cell proliferation and/or resistance to therapy, but may do so in a tumor cell-specific manner. Characterization of the DDSP from the vascular niche could potentially unravel mechanisms of treatment resistance and tumor progression.

Citation Format: Christine Levesque, Xin Zhao, Cyrus M. Ghajar, Peter S. Nelson. A bone marrow vascular niche model to study the effects of a DNA Damage Secretory Program in promoting prostate cancer treatment resistance. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A46.