OR34-5 Infiltrating Neutrophils and Neutrophil Elastase (NE) Promote Tumor Growth in a Mouse Model for Lymphangioleiomyomatosis (LAM)

Lymphangioleiomyomatosis (LAM) is a rare disease occurring almost exclusively in women whereby metastatic smooth-muscle cell-like adenomas grow within the lungs, resulting in loss of pulmonary function. LAM cells contain mutations in tuberous sclerosis 1 or 2 genes (TSC1 or TSC2), which leads to heightened mammalian target of rapamycin complex1 (mTORC1) activity and cell proliferation. The LAM cell origin remains unknown; however, we reported that inactivation of the Tsc2 gene in the mouse uterus resulted in myometrial tumors with nearly all known features of LAM, including over-expression of melanocytic markers that are pathognomonic of LAM tumor cells. Approximately 50% of animals developed metastatic myometrial tumors in the lung, suggesting that LAM cells might originate from the uterine myometrium, possibly explaining its overwhelming female prevalence. Estrogen ablation by oophorectomy or aromatase inhibition resulted in nearly complete regression of Tsc2-null myometrial tumors, indicating that, even without TSC2, estradiol is required to maintain tumors. Through RNAseq analysis of genes that are both estrogen and Tsc2 mediated, we identified the serine protease Neutrophil Elastase (NE) as being highly expressed in Tsc2-null uterine tumors. NE is expressed in and secreted by granulocytic neutrophils and myeloid-derived suppressor cells (MDSCs), both of which are known to be upregulated in the blood and stroma of various cancers such as breast, lung, melanoma, and prostate. NE is thought to promote pro-tumorigenic phenotypes such as proliferation, EMT, migration, invasion, and ultimately metastasis. We hypothesize that NE from infiltrating MDSCs promotes LAM tumor progression. Using flow cytometry as well as immunofluorescence, we show increased numbers of MDSCs in the blood, uterus and lungs of Tsc2-null KO mice. Immunodepleting MDSCs results in reduced tumor growth and myometrial thickness, as does blockade of MDSC recruitment to tumors using a CXCR2 antagonist. Interestingly, treatment with the NE inhibitor sivelestat phenocopies the results from MDSC depletion, leading to reduced MDSC accumulation in the tumor site, reduced tumor growth, and less myometrial thickening. Finally, using TSC2-null cell lines, we find that NE promotes aggressive tumor cell behaviors such as migration and proliferation. Thus, our data highlights the importance of MDSCs and their product NE in LAM progression, and identifies novel molecular mediators of LAM tumor growth and invasion.