CD73 as a therapeutic target for pancreatic neuroendocrine tumor stem cells

Abstract

Identification and purification of cancer stem cells (CSCs) lead to the discovery of novel therapeutic targets; however, there has been no study on isolation of the CSC population among pancreatic neuroendocrine tumors (pNETs). This study aimed to identify pNET CSCs and to characterize a therapeutic candidate for pNET CSCs. We identified CSCs by aldehyde dehydrogenase (ALDH) activity in pNET clinical specimens and cell lines. We verified whether or not these cells have the stemness property in vivo and in vitro. ALDHhigh cells, but not control bulk cells, formed spheres, proliferated under hypoxic condition as well as normoxic condition and promoted cell motility, which are features of CSCs. Injection of as few as 10 ALDHhigh cells led to subcutaneous tumor formation, and 105 ALDHhigh cells, but not control bulk cells, established metastases in mice. Comprehensive gene expression analysis revealed that genes associated with mesenchymal stem cells, including CD73, were overexpressed in ALDHhigh cells. Additionally, the in vitro and in vivo effects of an inhibitor of CD73 were investigated. The CD73 inhibitor APCP significantly attenuated in vitro sphere formation and cell motility, as well as in vivo tumor growth observed for ALDHhigh cells. Finally, its expression was evaluated using clinical pNET tissue samples. Immunohistochemical analysis of clinical tissue samples demonstrated CD73 expression was significantly correlated with the invasion into adjacent organs. Since recent studies revealed CD73 as a potential biomarker of anti-PD-1 immune checkpoint therapy, CD73 might be a promising therapeutic target for pNET CSCs.

Immunohistochemical CD73 expression status in gastrointestinal neuroendocrine neoplasms: A retrospective study of 136�patients

“…Moreover, cases involving tumors <10 mm in size with lymphatic and venous invasions are at high risk of lymph node metastasis with regard to colorectal NENs (39). It has also been reported that the immunohistochemical CD73 expression status was significantly correlated with invasion into adjacent organs in pNENs (14). In the present study, lymphatic and venous invasions were more frequent in the NEC group than in the NET group.…”

“…Recent studies identified CD73 as not only a unique biomarker for pNENs cancer stem cells but also a novel molecular target for pNENs therapy (14). CD73 expression is also associated with poor prognosis in several types of tumors (31), including colorectal cancer (32), gastric cancer (33), gallbladder cancer (34), serous ovarian cancer (35), triple negative breast cancer (36), and malignant melanoma (37).…”

“…In mice with defective A 2A AR and CD73, antitumor immunity is enhanced, which reduces the tumor growth (11)(12)(13). Recent studies have revealed that CD73 is identified as not only a unique biomarker for pancreatic NENs (pNENs) cancer stem cells but also a novel molecular target for pNENs therapy (14). We hypothesized that CD73 is expressed on the cytomembrane of GI-NENs with high malignant potential.…”

CD73's Potential as an Immunotherapy Target in Gastrointestinal Cancers

“…In line with these studies, many human tumors overexpress CD73 and associates with poor prognosis (36,(73)(74)(75)(76)(77)(78). CD73 is also linked to drug resistance, epithelial-to-mesenchymal transition (EMT), and cancer cell proliferation and stemness (76,(79)(80)(81)(82)(83)(84). Tumors also grow slower in A2BR-deficient mice and mice treated with A2BR antagonists (85)(86)(87).…”

“…Studies of CD73 in human PDAC tissue have only recently emerged ( Table 2). CD73 is upregulated in PDAC compared to normal pancreatic tissue and correlates with increased tumor size, advanced stage, lymph node involvement, metastasis, and poor prognosis (77,80,172). While PDAC tumors are 100% positive for CD73 expression (172), interesting staining patterns for CD73 are seen.…”