THU551 Glycoprotein-NMB (GPNMB) Is A Potential Lymphangioleiomyomatosis (LAM) Therapeutic Target And Biomarker

Abstract Disclosure: E. Gibbons: None. S.R. Hammes: None. Lymphangioleiomyomatosis (LAM) is a rare, progressive, destructive cystic lung disease affecting almost exclusively female-sexed individuals. Mutations in the tuberous sclerosis (TSC1 or TSC2) genes constitutively activate the mTORC1 pathway, promoting hyperproliferation of smooth muscle cells, creating small tumors throughout the lungs. These tumors, through largely unknown mechanisms, result in the formation of large cysts that replace normal alveolar space. Inhibition of mTORC1 with Sirolimus slows but does not stop LAM progression; therefore, there is a need for new LAM treatment options and biomarkers. Due to LAM’s estrogen sensitivity, female specificity, and metastatic nature, we previously proposed LAM cells originate from the uterine myometrium. We therefore designed a uterine-specific TSC2-null mouse model where all the mice generate uterine tumors characteristic of LAM and half develop lung metastases, suggesting that indeed LAM tumors may be derived from the uterus. Using bulk RNASeq analysis of uterine tissue from our mouse model, when focusing on genes regulated by estrogen and TSC2, we discovered increased expression of melanocytic markers, including Glycoprotein Non-Metastatic Melanoma Protein B (GPNMB), a known oncogenic protein in other cancers. GPNMB was not only highly expressed in our mouse model; it was also expressed intracellularly and on the cell surface of TSC2-null cell lines and in LAM tumor cells from patient lungs and uteri. Notably, the extracellular domain of GPNMB was released from the surface of TSC2-null cell lines, suggesting that the ectodomain may also be released from TSC2-null cells in LAM patients. Here we show that, GPNMB protein and mRNA expression increased when the cells were serum starved, mimicking conditions of a tumor microenvironment. This increase was dependent on mTORC1 signaling and mRNA transcription. Knocking down GPNMB expression by siRNA had minimal effects on TSC2-null cells pro-tumorigenic functions in vitro aside from decreasing invasion. However, knocking out GPNMB in TSC2-null cells using CRISPR/Cas9 significantly decreased mouse xenograft tumor growth. Additionally, treating mice with a GPNMB antibody drug conjugate abrogated xenograft growth, highlighting GPNMB’s potential as a therapeutic target. Also, GPNMB’s ectodomain was released from the cell surface of TSC2-null cells by the proteases Adam10 and 17. Of note, the ectodomain is implicated in mediating GPNMB’s effects on tumor growth, suggesting that Adam10/17 inhibition may mitigate TSC2-null tumor growth. Importantly, the GPNMB ectodomain is a potential serum biomarker of LAM, as there was a significant increase in GPNMB ectodomain levels in patient serum as compared with healthy controls. Furthermore, serum GPNMB levels decreased in most patients after Sirolimus treatment, implicating GPNMB as a potential marker for responsiveness to treatment. Presentation: Thursday, June 15, 2023