CD44 as a molecular marker to screen cancer stem cells in hypopharyngeal cancer

Abstract

Conclusions: The CD44+ cells have a stronger proliferative capacity and higher tumorigenic potential than the CD44– cells, which suggests that the cancer stem cells of hypopharyngeal cancer may exist in the CD44+ tumor cell population. Therefore, we propose that CD44 is an important biological marker to screen cancer stem cells of hypopharyngeal cancer. Objectives: To study the significance of CD44 as a molecular marker for screening cancer stem cells in hypopharyngeal cancer. Methods: The CD44 expression levels in the hypopharyngeal cancer cell line FaDu were analyzed using flow cytometry. To investigate the biological significance of the CD44+ population, we sorted the CD44+ and CD44– cell populations by using magnetic-associated cell sorting (MACS) technology. After the separation, the purity of the CD44+ cells was determined using flow cytometry. The MTT method was used to detect the different proliferation capabilities of the CD44+ and CD44– cells in vitro. The tumorigenicity of the CD44+ and CD44– cells was determined by injecting CD44+ or CD44– cells (1 × 106 and 1 × 105) into the body of NOD/SCID mice. Results: Some (21.1 ± 1.56)% of the hypopharyngeal cancer cell line FaDu cells expressed CD44. The CD44+ population was efficiently sorted by MACS, and after separation, the purity of the CD44+ cells was (99.4 ± 0.29)%. The MTT assay indicated that the sorted CD44+ cells had a stronger proliferative capacity than the CD44– cells. The tumorigenicity study showed that all the mice injected with 1 × 106 CD44+ cells developed tumors (8/8), half the mice injected with 1 × 106 CD44– cells developed tumors (4/8), 1 of the 8 mice injected with 1 × 105 CD44+ cells developed tumors (12.5%), but none of the mice injected with 1 × 105 CD44– cells developed any tumors (0/8). At the same concentration, the difference in tumorigenic rates between the CD44+ and CD44– groups was statistically significant (Fisher's exact test, p < 0.05). Furthermore, the CD44+ group had a shorter incubation period than the CD44– group. In addition, the average tumor volume of the CD44+ group was (2017.81 ± 538.50) mm3; however, the average tumor volume of the CD44– group was (1153.25 ± 503.18) mm3. The difference was statistically significant (t = 2.67, p < 0.05).