Abstract 3344: Two different stem cell populations exist in breast cancer to control tumor initiation

Abstract

Abstract The cancer stem cell theory states that a determinate number of cells within a tumor have unique, stem cell-like features to regenerate the entire tumor mass. However, a cancer stem cell may need the right microenvironment to have its greatest tumor initiation potential. We have documented the presence of two stem cell populations within a tumor to yield consistent and most aggressive recapitulation of tumor initiation in vivo. To isolate cancer stem cells, we used the MMTV-PyMT transgenic model of breast cancer in mice to generate stable cell lines from spontaneous breast tumors. Stable in vitro cultures of FACS analyzed cancer stem cells and tumor-residing mesenchymal stem cells were established and tested for tumor initiating ability using two methods of implantation: subcutaneous (s.c.) injection and cleared mammary fat pad (CMFP) injection. To determine the limit of tumor initiation, a highly malignant cancer stem cell culture (419) was injected s.c. This cell culture produced tumors with 1×104, 1×103, and 1×102 cells with 100%, 93%, and 33% tumorigenicity, respectively. In comparison, 100% tumorigenicity was obtained with 1×102 419 cells implanted in the CMFP, a significant increase compared to s.c. injection (Chi-squared, p<0.001). S.c. injection of a less malignant cancer stem cell culture (145) produced tumors less efficiently, with 100% tumorigenicity with 1×104 cells but 13% tumorigenicity with 1×103 cells. To increase tumorigenicity at low cell numbers, cancer stem cell cultures were combined with tumor-residing mesenchymal stem cells just prior to injection. Cancer stem cell cultures were s.c. injected with 1×105 tumor-residing mesenchymal stem cells (383) at the tumor limiting dose, 1×101 for 419 and 1×103 for 145; tumorigenicity increased 160% in the highly malignant cells (419) and 133% in the less malignant cells (145). The tumor-residing mesenchymal stem cells increased tumorigenicity significantly compared to cancer stem cell injection alone (Chi-squared, p<0.002). Control experiments using non-tumorigenic mesenchymal cells did not produce any increase in tumorigenicity. Genome-wide expression profiling experiments were carried out to demonstrate the clinical relevance of the varying malignancy settings in the cancer stem cell and tumor-residing mesenchymal stem cell cultures. Our results suggest that the cellular composition of the local microenvironment within the breast tumors is the major determinant of efficiency of tumor initiation. The addition of tumor-residing mesenchymal stem cells markedly increases the tumor initiation potential of breast cancer stem cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3344.