TRAIL-Mediated Apoptosis in Breast Cancer Cells Cultured as 3D Spheroids

Abstract

TNF-alpha-related-apoptosis-inducing-ligand (TRAIL) has been explored as a therapeutic drug to kill cancer cells. Cancer cells in the circulation are subjected to apoptosis-inducing factors. Despite the presence of these factors, cells are able to extravasate and metastasize. The homotypic and heterotypic cell-cell interactions in a tumor are known to play a crucial role in bestowing important characteristics to cancer cells that leave the primary site. Spheroid cell culture has been extensively used to mimic these physiologically relevant interactions. In this work, we show that the breast cancer cell lines BT20 and MCF7, cultured as 3D tumor spheroids, are more resistant to TRAIL-mediated apoptosis by downregulating the expression of death receptors (DR4 and DR5) that initiate TRAIL-mediated apoptosis. For comparison, we also investigated the effect of TRAIL on cells cultured as a 2D monolayer. Our results indicate that tumor spheroids are enriched for CD44hiCD24loALDH1hi cells, a phenotype that is predominantly known to be a marker for breast cancer stem cells. Furthermore, we attribute the TRAIL-resistance and cancer stem cell phenotype observed in tumor spheroids to the upregulation of cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) pathway. We show that inhibition of the COX-2/PGE2 pathway by treating tumor spheroids with NS-398, a selective COX-2 inhibitor, reverses the TRAIL-resistance and decreases the incidence of a CD44hiCD24lo population. Additionally, we show that siRNA mediated knockdown of COX-2 expression in MCF7 cells render them sensitive to TRAIL by increasing the expression of DR4 and DR5. Collectively, our results show the effect of the third-dimension on the response of breast cancer cells to TRAIL and suggest a therapeutic target to overcome TRAIL-resistance.

Preservation of the 3D Phenotype Upon Dispersal of Cultured Cell Spheroids Into Monolayer Cultures

“…The formation of HDECC and AlDH + subpopulations and elevation in the G1 subpopulation appear to be markers of the 3D phenotype in MCF‐7 cells. This 3D phenotype resembles 3D‐associated features observed in some other cell types [Durand, ; Smart et al, ; Chandrasekaran et al, ]. Thus, our findings strengthen previous results and suggest a general character of the observed distinctions between 3D and 2D states.…”

Taraxacum officinale dandelion extracts efficiently inhibited the breast cancer stem cell proliferation

“…We also discovered that the antiproliferation effects of Dandelion extracts relates to expression of TRAIL and increased of ROS in cells. Indeed, the potential of using TRAIL to destroy putative cancer stem cells has been recognized by others (Chandrasekaran et al, 2014;Yang et al, 2015). Increasing TRAIL expression has previously been shown to promote cancer cell death and to decrease tumor and metastasis development in vivo.…”

Three-dimensional culture systems in cancer research: Focus on tumor spheroid model

“…However, compelling evidences from several studies suggest that the signaling pathways are activated differently in cells within MCTS compared to cells in monolayers. Some recent examples include identifying HER2 homodimerization in MCTS as opposed to HER2 and HER3 heterodimerization in 2D-cultured cells (Pickl et al , 2009), higher HER3 and EGFR activation in tumor spheroids compared to 2D-cultured cells (Pickl et al , 2009), and higher rate of acquired resistance to TRAIL-mediated apoptosis due to decreased expression of death receptors (DR4 and DR5) in breast MCTS (Chandrasekaran et al , 2014). One of the reasons for differential pathway activation between 2D- and 3D-cultured cells is difference in extracellular cues arising from the TME.…”