Abstract 2486: Docetaxel resistant cells display cancer stem cell properties and regulate growth via PI3/Akt signaling

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Abstract Both normal organogenesis and tumor development follow a Gompertzian growth curve. An understanding of the mechanisms operating in these apparently discordant situations, in which growth rate slows as mass increases, may be useful for the treatment of cancer. We have previously shown that encapsulating murine renal adenocarcinoma (RENCA) cells in a double layer of agarose to form spherical macrobeads, undergo Gompertzian growth regulation as tumor colonies within the confines of the inner agarose matrix. As the colonies reach maximal size, the RENCA macrobeads (MBs) secrete factors that also inhibit the proliferation of freely growing target cells outside the MB. In the current study, we report the ability of the tumor colonies within the MB to re-form following the debulking of tumor mass with docetaxel (0.5 μg/ml or 5.0 μg/ml). Docetaxel-resistant cells were assessed for the stem cell marker OCT4 using immunohistochemistry (Abcam ab19857), RT-PCR (Qiagen Cancer Stem Cell PCR Array) and cell migration/invasion (Corning Cell Migration Chemotaxis and Invasion Assay). Docetaxel-resistant cells are shown to be a discrete population of cells that exhibit stem cell-like properties, including prolonged quiescence (>16 wk), OCT4 staining, stem cell gene expression, increased migration and invasion, and in vivo tumor induction. These cancer stem-like properties are dose and time post-treatment dependent with the greatest expression observed in the few surviving cells at 6 wk post-treatment with 5 μg/ml. Tumor growth is observed in syngeneic BALB/c mice following transplantation of a single docetaxel-resistant cell at higher frequencies (≥ 6 of 9) as compared to the grafting of single monolayer cells (0 of 8) at 5 wk when using cells recovered at 6 wk from the 5 μg/ml dose treated MBs. To understand the mechanism of colony growth regulation within the MB, we hypothesized that tumor cells external to the MB would use similar growth control signaling when exposed to RENCA MBs or MB conditioned media. We have previously shown an increase in the activity of the transcription factor MEF2 in cells exposed to RENCA MB conditioned media. To investigate PI3/Akt signaling, a known pathway for MEF2 regulation, in human DU145 prostate tumor cells exposed to MB conditioned media, we used In-Cell and Western blotting. Exposure to RENCA MBs resulted in Akt hyperphosphorylation (≥ 48 hours) and de-phosphorylation of MEF2D in DU145 target cells. These findings support the hypothesis that RENCA MBs, as biological cell systems with the in vitro capability of inhibiting cancer cell proliferation, achieve this effect, at least in part, by signaling through Akt to regulate MEF2D. This effect is being investigated in colorectal patients with progressive disease, following informed consent, who underwent laparoscopic intraperitoneal implantations of RENCA MBs as part of ongoing clinical trials. Citation Format: Prithy C. Martis, Melissa A. Laramore, Hunter L. Gazda, Atira Dudley, Pradeep R. Dumpala, Allyson J. Ocean, Nathaniel Berman, Tapan Parikh, Zoe P. Andrada, Angelica Nazarian, Joanne Thomas, Eugene Akahoho, George Stoms, Alex Yaroshinsky, Thomas J. Fahey, David J. Wolf, Lawrence S. Gazda, Barry H. Smith. Docetaxel resistant cells display cancer stem cell properties and regulate growth via PI3/Akt signaling. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2486.