Characterization of Melanoma Cells Capable of Propagating Tumors from a Single Cell

Abstract

Questions persist about the nature and number of cells with tumor-propagating capability in different types of cancer, including melanoma. In part, this is because identification and characterization of purified tumorigenic subsets of cancer cells has not been achieved to date. Here, we report tumor formation after injection of single purified melanoma cells derived from three novel mouse models. Tumor formation occurred after every injection of individual CD34+p75− melanoma cells, with intermediate rates using CD34−p75− cells, and rarely with CD34−p75+ cells. These findings suggest that tumorigenic melanoma cells may be more common than previously thought and establish that multiple distinct populations of melanoma-propagating cells (MPC) can exist within a single tumor. Interestingly, individual CD34−p75− MPCs could regenerate cellular heterogeneity after tumor formation in mice or multiple passages in vitro, whereas CD34+p75− MPCs underwent self-renewal only, showing that reestablishment of tumor heterogeneity is not always a characteristic of individual cells capable of forming tumors. Functionally, single purified MPCs were more resistant to chemotherapy than non-MPCs. We anticipate that purification of these MPCs may allow a more comprehensive evaluation of the molecular features that define tumor-forming capability and chemotherapeutic resistance in melanoma.

Human CD271-Positive Melanoma Stem Cells Associated with Metastasis Establish Tumor Heterogeneity and Long-term Growth

“…Notably, in these conflicting reports and other studies, different enzymatic procedures have been used to prepare cell fractions from solid melanoma samples. Tumors have been mechanically dissociated followed by enzymatic digestion with collagenase (8), a mix of collagenase and dispase (9), or collagenase and trypsin (10,11,21). Therefore, we addressed whether these different tumor digestion protocols might affect detectability of surface markers used to directly isolate putative tumorigenic melanoma cell populations.…”

Differential AKT dependency displayed by mouse models of BRAFV600E-initiated melanoma

“…Previously, we described a GEM model in which expression of oncogenic BRAF V600E cooperates with PTEN silencing to pro-mote metastatic melanoma (9,26,27). Given the low frequency of PIK3CA mutations in human melanoma, we resolved to test the role of PI3K signaling in cooperation with mutationally activated BRAF V600E in melanomagenesis.…”

Melanoma and the Nervous System – Novel Pathways Mediated by Neurotrophins and Their Receptors

“…The use of sensitive mouse models, such as the NOD/SCID IL2R_(null) mice, demonstrated that cell isolation through p75NTR does not enrich melanoma CSC, and melanoma cells are able to metastasize independently from their expression pattern, being able to reverse their phenotype through clonal expansion (Quintana et al, 2010;Civenni et al, 2011). Consistently, in another study CD34-neg/p75NTR-pos cells from mouse melanomas only rarely form tumors, while the p75NTR-negative counterpart frequently forms tumors, depending on CD34 expression (Held et al, 2010). This suggests that although some lines of evidence point at p75NTR as a good marker for the isolation of melanoma CSC, it may not be the right candidate.…”

“…The "Cancer Stem Cell hypothesis" states that within tumor heterogeneity, only few cells are responsible for tumor initiation and maintenance, sharing with normal stem cells the ability to self renew and to persist in the tissue for years. Although in some tumors, such as leukemia, the CSC model is valid, in melanoma, cells able to initiate tumor formation are not a rare population (Quintana et al, 2010;Held et al, 2010;Roesch et al, 2010). Given the role of NTs and their receptors in melanoma biology, this complex network of growth factors is likely to be involved both in melanoma recurrence and metastasis in the patients.…”