Abstract
Cancer initiating cells (CICs) represent a unique cell population essential for the maintenance and growth of tumors. Most in vivo studies of CICs utilize human tumor xenografts in immunodeficient mice. These models provide limited information on the interaction of CICs with the host immune system and are of limited value in assessing therapies targeting CICs, especially immune-based therapies. To assess this, a syngeneic cancer model is needed. We examined the sphere-forming capacity of thirteen murine lung cancer cell lines and identified TC-1 and a metastatic subclone of Lewis lung carcinoma (HM-LLC) as cell lines that readily formed and maintained spheres over multiple passages. TC-1 tumorspheres were not enriched for expression of CD133 or CD44, putative CIC markers, nor did they demonstrate Hoechst 33342 side population staining or Aldefluor activity compared to adherent TC-1 cells. However, in tumorsphere culture, these cells exhibited self-renewal and long-term symmetric division capacity and expressed more Oct-4 compared to adherent cells. HM-LLC sphere-derived cells exhibited increased Oct-4, CD133, and CD44 expression, demonstrated a Hoechst 33342 side population and Aldefluor activity compared to adherent cells or a low metastatic subclone of LLC (LM-LLC). In syngeneic mice, HM-LLC sphere-derived cells required fewer cells to initiate tumorigenesis compared to adherent or LM-LLC cells. Similarly TC-1 sphere-derived cells were more tumorigenic than adherent cells in syngeneic mice. In contrast, in immunocompromised mice, less than 500 sphere or adherent TC-1 cells and less than 1,000 sphere or adherent LLC cells were required to initiate a tumor. We suggest that no single phenotypic marker can identify CICs in murine lung cancer cell lines. Tumorsphere culture may provide an alternative approach to identify and enrich for murine lung CICs. Furthermore, we propose that assessing tumorigenicity of murine lung CICs in syngeneic mice better models the interaction of CICs with the host immune system.
Highlights
Lung cancer is the cause of almost 20% of all cancer deaths in the United States [1]
We hypothesized that day 1 (D1) cells were enriched for cancer initiating cells (CICs) compared to day 7 (D7) cells, as the D7 cells were more likely to be composed of some CICs and greater numbers of differentiated tumor cells
While these xenograft studies allow the identification of a sub-population of cells able to recapitulate a tumor in an immunocompromised mouse, they may not present an accurate picture of the characteristics of true CICs
Summary
Lung cancer is the cause of almost 20% of all cancer deaths in the United States [1]. It accounts for more deaths than the four most common cancers combined. Increasing evidence supports the concept of a specialized population of cells within tumors termed cancer initiating cells (CICs), alternatively ‘‘cancer stem cells’’ or tumor-initiating cells. These cells are thought to be responsible for the tumor’s origin, maintenance, progression, and resistance to therapy. Investigating lung CICs may increase understanding of the origin of lung cancer and may lead to novel therapeutic approaches targeting these cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
