Endometrial epithelial cell organoids as tools for studying the CD39 family of enzymes and for validating enzyme inhibitors.

Extracellular adenosine triphosphate (ATP) conducts a complex dynamic system of broadly represented cell signaling. Ectonucleotidases are the enzymes with nucleotide hydrolytic ability that regulate ATP levels in physiological and pathological conditions, thus playing a key role in the so-called purinergic signaling. Altered ectonucleotidase expression has been reported in cancer, and the ectonucleoside triphosphate diphosphohydrolase (NTPDase) family of enzymes, with its best-known form NTPDase1 (CD39), is targeted in cancer immunotherapy. The tandem of enzymes CD39-CD73 is responsible for the generation of immunosuppressive adenosine in the tumor microenvironment, and inhibition strategies are of great interest. Organoids have emerged as very convenient models for the study of tumors since they are three-dimensional cultures that retain many of the features of tissue. The present study aims to contribute to improving the methodology and the molecular tools needed for the study of ectonucleotidases in healthy and disease conditions. The study, performed in an endometrial cancer cell model, could be extended to other types of tumors and pathologies in which the purinergic system is involved. We generated organoids from endometrial cancer cells overexpressing NTPDase2 (CD39L1) and NTPDase3 (CD39L3) as fusion proteins with EGFP, and we performed functional assays by adapting <i>in situ</i> cytochemistry protocols. This allowed us to simultaneously detect enzyme activity and protein expression and to demonstrate that organoids can be used to test ectonucleotidase inhibitors-a result that can be used to develop new cancer treatment options.