Abstract 5234: Microenvironmental signals dictate disseminated tumor cells (DTCs) fate through regulation of TGFβII and p38α

Abstract

Abstract Metastases develop from disseminated tumor cells (DTCs) years or even decades after primary tumor treatment. This is thought to be due to the ability of residual DTCs to remain dormant, but the mechanisms controlling this state are poorly understood. We have explored whether the target organ microenvironment where DTCs lodge can control their fate and the timing of DTCs dormancy in a HNSCC model. When injected in nude mice, HEp3-GFP cells form tumors with 100% efficiency and spontaneously disseminate to lungs (72% incidence) and bone marrow (BM) (28% incidence). Tracking of GFP-tagged DTCs showed that after ∼2 weeks the quiescent DTCs in lungs start to grow to form overt metastasis in 72% of mice. In contrast, those in the BM remain at constant numbers suggesting a dormant phenotype. Furthermore, DTCs isolated from lungs and expanded in culture (Lu-HEp3) display a high ERK/p38 signaling ratio and are tumorigenic when inoculated in vivo. Meanwhile in vitro expanded BM-HEp3-derived cell lines remain dormant when inoculated in vivo and are characterized by a low ERK/p38 activity ratio (predictive of quiescence for breast fibrosarcoma, squamous carcinoma and colon carcinoma cells) and by increased expression of the key dormancy transcription factors (TFs) Sharp1 and p53. In addition, treatment of THEp3 cells with BM conditioned media inhibits in vivo proliferation, activates TGFβ2 and p38α, and induces the expression of Sharp1 and p53. Moreover, inhibition of TGFβ signaling using a TGFβRI inhibitor, blocks p38 activation and downregulates Sharp1 and p53 in BM-HEp3 cells, suggesting that BM-HEp3 cells dormancy is functionally linked to TGFβ signaling. Importantly, TGFβ2, p38α or Sharp-1 knock down interrupted BM-HEp3 cell dormancy, while overexpression of p38α inhibits lu-HEp3 cells in vivo growth. In addition to that, systemic inhibition of p38α/β with SB203580 or TGFβRI/II with LY364947, dramatically accelerated lung metastasis as well as DTCs, micro- and macro-metastasis burden in growth restricted sites such as, spleen, liver or BM. We propose that reprogramming of DTCs into dormancy in growth restrictive microenvironments might induce a gene network activated by stress signaling mediated at least by TGFβ2 and p38α/β signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5234. doi:1538-7445.AM2012-5234