HOX/PBX Inhibition Attenuates Tsc2-Null Cell Viability and Lung Metastasis in Lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a rare lung disease that exclusively affects premenopausal women. LAM is caused by infiltration of metastasizing atypical smooth muscle-like cells into the lungs leading to progressive respiratory failure. Though the origin of these cells remains elusive, LAM cells carry loss-of-function mutations in the Tuberous Sclerosis Complex (TSC1/TSC2) genes, leading to hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1) and aberrant cell growth. There is no cure for LAM. The greatest barriers to finding a cure for LAM include its undetermined origin and unclear underlying pathogenesis. Our integrative single cell omics analyses of LAM lung identified the activation of uterine-similar HOX/PBX transcriptional network in LAM cells compared to other cells, suggesting that the uterus is the primary origin of LAM. HOX/PBX signaling is critical for female reproductive tract development and maintenance, and their overexpression is implicated in some female reproductive cancers. The objective of this study is to elucidate cellular and molecular mechanisms by which HOX/PBX signaling may regulate LAM pathogenesis, with hopes to uncover novel therapeutic strategies to cure LAM. We hypothesize that blockade of HOX/PBX attenuates LAM patient-derived (TSC2-null) cell viability and lung metastasis in LAM. We first confirmed HOX/PBX dimerization in LAM cells using immunofluorescence and immunoprecipitation assays. Using cell viability assays including crystal violet assay and MTT, we found that treatment with a cell-permeable HOX/PBX antagonist (HXR9) decreased TSC2-null cell growth and viability in vitro (*p<0.05, n=3/treatment group). We also showed that inhibiting HOX/PBX dimerization enhanced apoptosis and necroptosis in TSC2-null cells compared to controls using immunoblotting. Finally, using a xenograft mouse model of LAM, we tracked lung metastasis in vivo (Xenogen IVIS Spectrum System) and quantified total photon flux in the chest region. We found that pharmacologic and molecular suppression of HOX/PBX attenuates lung metastasis of LAM cells (*p<0.05, n=4/group). Our findings suggest that HOX/PBX signaling is critical for LAM progression and should be explored as a potential therapeutic target for LAM. Funding Sources: Public: National Heart Lung and Blood Institute (R01HL153045) and Department of Defense (W81XWH-19-1-0474). Private: LAM Foundation (LAM0141E01-20). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.