BACKGROUND

Cancer stem cells (CSC) are endowed with multipotency, self-renewal and unique tumorigenic potential. They have been identified as cells with high activity of aldehyde dehydrogenase (ALDH) and high expression of CD44 in head and neck squamous cell carcinoma (HNSCC). The objective of this work is to understand whether salivary gland adenoid cystic carcinoma contain CSCs and whether they exhibit a unique tumorigenic activity in this cancer.

METHODS

We used flow cytometry, salisphere and western blot assays with 3 human ACC cell lines (UM-HACC-2A, UM-HACC-14, UM-HACC-6) to characterize the impact of ALDH activity and CD44 expression. results were verified by orthotopic injection of cells retrieved from a patient-derived xenograft (PDX) model of ACC (UM-PDX-HACC-14) in the submandibular gland of SCID mice. Primary tumor and metastatic spread were evaluated by 2 pathologists blinded for experimental conditions.

RESULTS

The fraction of ALDHCD44 cells in UM-HACC-2A, UM-HACC-14 and UM-HACC-6 ranged from 3% to 8%. ALDHCD44 cells formed more salispheres and expressed higher levels of stem cell markers (e.g., Notch2, Bmi-1) compared to control ALDHCD44 cells. ALDHCD44 cells sorted from the ACC PDX tumors were more tumorigenic upon orthotopic transplantation into submandibular salivary glands and generated more lung metastases than control ACC cells. Strong ALDH1A1 staining was observed in the majority of salivary gland tumors and lung metastases generated by transplantation of ALDHCD44 cells.

CONCLUSIONS

We conclude that salivary gland adenoid cystic carcinoma contain a small population of uniquely tumorigenic cells characterized by high ALDH activity and expression.