Acute lymphoblastic leukemia (ALL) is the most commonly diagnosed cancer in pediatric patients. Recent advances have allowed for improved efficacy of treatment allowing 95% of patients to achieve remission following chemotherapy. However, nearly 20% will have a second recurrence that is often more aggressive and difficult to treat. One reason for this high rate of relapse may be due to the role of the bone marrow microenvironment (BM) consisting of osteoblasts, endothelial cells, adipocytes, and stromal cells as well as extracellular matrix proteins. Interaction between leukemic cells and BM elements activates intracellular signaling pathways that protect ALL cells from chemotherapy. Many of these pathways can be aberrantly activated due to changes in methylation patterns during leukemogenesis. Therefore, utilizing epigenetic modifiers offers a unique approach to overcoming the chemoprotective effects of the BM. The aim of our study is to identify if the combination of the epigenetic drugs azacitidine (DNA methyltransferase inhibitor) and panobinostat (histone deacetylase inhibitor) is successful in overcoming these effects.
We demonstrated that azacitidine and panobinostat are more effective in killing ALL cells in coculture with osteoblasts than chemotherapy alone. This required direct interaction between ALL cells and osteoblasts and could not be replicated when ALL cells were suspended in Transwells above the osteoblast monolayer. Additionally, ALL cells pretreated with non-killing concentrations of azacitidine and panobinostat were sensitized to chemotherapy even in the presence of osteoblasts. These effects were replicated ex vivo in primary ALL patient samples with a variety of cytogenetic characteristics. These patient samples have been xenografted in mice to observe the efficacy of this combination with chemotherapy in comparison to chemotherapy alone.
We also observed that treatment with azacitidine and panobinostat decreases the ability of ALL cells to effectively adhere to osteoblasts, suggesting a role that down-regulation of cell adhesion molecules (CAMs) may play in mediating this response. Due to the need for direct contact of ALL cells with osteoblasts for the chemoprotective effects, we investigated how treatment with azacitidine and panobinostat could affect the expression levels of certain CAMs. We found that N-cadherin was induced in ALL cells in coculture with osteoblasts and that increase was partially reversed by azacitidine and panobinostat. β-catenin, which is known to interact with N-cadherin, was also up-regulated in ALL cells cocultured with osteoblasts and was reversed by azacitidine and panobinostat. These data suggests that azacitidine and panobinostat may overcome microenvironment-induced chemoprotection by decreasing the expression of certain CAMs like N-cadherin and interfering with their downstream signaling pathways.
Citation Format: Anthony Quagliano, Sonali Barwe, Anilkumar Gopalakrishnapillai. Epigenetic drug treatment overcomes osteoblast-induced chemoprotection by suppressing cell adhesion and related signaling [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 5870. doi:10.1158/1538-7445.AM2017-5870