PO-294 Role of fatty acid amide hydrolase (FAAH) in breast development and cancer

Introduction There are three major stages of breast development – embryonic, pubertal, and reproductive. During this complex developmental cycling, the epithelial compartment undergoes several rounds of proliferation, remodelling and cell death to eventually form an organised and functional mammary tree. The very nature of the pathways controlling these processes makes them susceptible to promote tumorigenic processes and ultimately lead to breast carcinoma. Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme that hydrolyzes the endocannabinoid anandamide and related amidated signalling lipids. Here, we aimed at analysing the expression FAAH in breast physio-pathology. Material and methods The expression of FAAH was analysed by immunohistochemistry in a tissue microarray (TMA) containing ≈600 human breast cancer samples and in public microarrays data bases. Cell lines derived from different breast cancer subtypes have been analysed for FAAH expression and the effect of a Knock-out (CRISPR) and overexpression of FAAH examined. FACS and immunofluorescence were also performed to further assess the identity of cell populations. FAAH effects on breast CSC activity was examinated using mammosphere formation and aldehyde dehydrogenase (ALDH) activity assays. Results and discussions We have found that FAAH shows remarkable variations in expression within the human breast epithelial hierarchy. Particularly, FAAH expression is restricted to a certain subset of mature cells in normal breast tissue (i.e. luminal cells), with negligible levels being detected in the progenitor/stem cell subset, In line with this idea, pharmacological inhibition of FAAH with URB597 in the mammary stem cell line HC11 delayed differentiation to mature epithelial cells. In addition, we observed significant differences in duct formation between FAAH KO and WT mice during pubertal development. Our results also correlate low FAAH expression with more undifferentiated phenotypes, high histologic grade, absence of oestrogen receptor and triple-negative phenotype in breast cancer. Consistent with this, we found low FAAH mRNA levels associated with metastasis and poor prognosis gene signatures. Finally, pharmacoinhibition and knocking-out of FAAH in breast cancer lines, enriched the cultures in cancer stem cells. Conclusion Together, our data suggest that FAAH plays a role in breast cell differentiation, both in normal development and in oncologic contexts.