Single-marker identification of head and neck squamous cell carcinoma cancer stem cells with aldehyde dehydrogenase

Abstract

Background: In accord with the cancer stem cell (CSC) theory, only a small subset of cancer cells are capable of forming tumors. We previously reported that CD44 isolates tumorigenic cells from head and neck squamous cell cancer (HNSCC). Recent studies indicate that aldehyde dehydrogenase (ALDH) activity may represent a more specific marker of CSCs.

Methods: Six primary HNSCCs were collected. Cells with high and low ALDH activity (ALDH(high)/ALDH(low)) were isolated. ALDH(high) and ALDH(low) populations were implanted into NOD/SCID mice and monitored for tumor development.

Results: ALDH(high) cells represented a small percentage of the tumor cells (1% to 7.8%). ALDH(high) cells formed tumors from as few as 500 cells in 24/45 implantations, whereas only 3/37 implantations of ALDH(low) cells formed tumors.

Conclusions: ALDH(high) cells comprise a subpopulation cells in HNSCCs that are tumorigenic and capable of producing tumors at very low numbers. This finding indicates that ALDH activity on its own is a highly selective marker for CSCs in HNSCC.

Figure 1

HNSCC cells that have high levels of ALDH expression also express CD44 at high levels. A. HN79 sorted for ALDH expression. P6 represents cells with high levels of ALDH expression (ALDH^high). B. Only HN79 cells with elevated ALDH levels (P6) have been sorted for CD44 expression. The cells in P10 represent the population of cells with high ALDH expression that also express CD44. Approximately 70% of the ALDH high cells are also CD44+.

Figure 2

ALDH^high cells reproduce tumors that are histologically similar to the original tumor. A.) HN84 primary tumor (20×). B.) HN84 tumor resultant from ALDH^high injection (20×).

Figure 3

ALDH^high cells recreate the original tumor heterogeneity for ALDH expression and maintain the distribution of ALDH in cancer cells passaged in the animal model. A. Primary HN84 cancer cells inhibited with DEAB. B. Primary HN84 cancer cells sorted for ALDH expression, 11.1% of the cancer cells are ALDH^high. C. Cancer cells derived from tumors grown in the animal model (passage 1) inhibited with DEAB. D. Cancer cells sorted for ALDH expression from tumor grown in the animal model from HN84 ALDH^high exhibit the same heterogeneity for ALDH expression as the original tumor.

Figure 4

Proposed model for the cancer stem cell compartment in HNSCC.