Background: Malignant rhabdoid tumor (MRT) is a rare, highly aggressive pediatric malignancy, particularly develops during infancy and early childhood. In contrast to significant advances in multimodality therapy for other pediatric malignancies, effective therapies for MRT have not been established. The origin of tumor cells in MRT has remained undetermined: however, MRT arises from various parts of body with some preference, eading to the hypothesis that MRT derives from neural crest or its derivatives. CD146 is a cell surface glycoprotein expressed by various neural crest-derived tissues, which has been expected to be a therapeutic target for immunotherapy against various CD146-expressing malignancies, such as melanoma and osteosarcoma. Objective: In the current study, we investigated (1) the expression of CD146 in MRT, (2) tumorigenic potential of CD146-expressing cells in MRT, (3) in vitro and in vivo effect of anti-CD146 neutralizing antibody against MRT, and (4) underlying molecular mechanisms involved in CD146 expression. Material and Method: The expression levels of CD146 in MRT cell lines and clinical samples were investigated by fluorescence-activated cell sorting (FACS) or immunohistochemical analyses. Tumor cells were then sorted by FACS according to the expression of CD146, and purified CD146+ and CD146- cells were characterized by colony-formation, sphere-formation, and invasion assays. In vivo tumorigenic potential was assessed by subcutaneous transplantation of the purified CD146+ and CD146- cells into NOD/Shi-scid, IL-2Rγnull (NOG) mice. We developed rabbit anti-CD146 neutralizing antibody to investigate the effect of blocking CD146 both in vitro and in vivo. DNA microarray was performed by using purified CD146+ and CD146- cells, and the association of candidate pathways was validated by shRNA silencing or treatment of the neutralizing antibody against CD146. Results: The expression of CD146 was observed in all MRT cell lines and clinical samples. Compared to CD146- cells, CD146+ cells in MRT exhibited significantly higher colony-, and sphere-forming potential, and more invasive capacity. The data of xeno-transplant demonstrated that stable engraftment of the purified tumor cells as well as successful engraftment after serial transplantation was exclusively observed in CD146+ cell-injected mice. Furthermore, our anti-CD146 neutralized antibody effectively inhibited both in vitro proliferation and in vivo tumor formation. Microarray analysis showed that various molecular pathways were engaged in higher tumorigeneity in CD146+ cells. Details of underlying mechanisms are now under investigation. Conclusion: Our data shows that CD146 defines a distinct subpopulation with highly tumorigenic and self-renewal capacity in MRT. Notable anti-tumor effect of anti-CD146 neutralizing antibody will facilitate a novel immunotherapy for MRT.

Citation Format: Seishiro Nodomi, Katsutsugu Umeda, Satoshi Saida, Yasumichi Kuwahara, Takayuki Hamabata, Tomoo Daifu, Itaru Kato, Hidefumi Hiramatsu, Ken-ichiro Watanabe, Souichi Adachi, Eiichi Konishi, Hajime Hosoi, Toshio Heike. CD146 is a novel marker of highly tumorigenic populations and a therapeutic target in malignant rhabdoid tumor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1001. doi:10.1158/1538-7445.AM2014-1001