Lymphangioleiomyomatosis (LAM) is a rare, multisystem disease of women, consisting of a diffuse proliferation of smooth muscle actin-positive cells (LAM cells), which harbor inactivating mutations in either the TSC1 or TSC2 tumor suppressor gene. These inactivating mutations result in constitutive activation of mammalian/mechanistic TOR (target of rapamycin) complex 1 (mTORC1), which integrates growth factor and nutrient signaling to stimulate cell growth and metabolism. Pulmonary LAM is characterized by associated progressive cystic destruction of the lung parenchyma, recurrent pneumothorax, and chylous pleural effusions. Extrapulmonary proliferative lesions of LAM include renal angiomyolipomas and lymphangiomyomas. LAM can occur as a sporadic disorder where LAM cells harbor somatic inactivating mutations of the TSC1 or TSC2 gene, or in women with Tuberous Sclerosis Complex (TSC).~Rapamycin is an FKBP12-dependent allosteric inhibitor of mTORC1 approved by the FDA for the treatment of LAM and TSC-associated renal angiomyolipomas. Clinical trials of TSC and LAM have shown that 12 month-treatment with rapamycin induces response of renal angiomyolipomas and stabilization of pulmonary function. However, lung function decline and tumor growth resume when treatment is interrupted.~Sensitive and specific biomarkers of response to therapy and/or disease progression, including biomarkers of tumor metabolic activity, would facilitate clinical trials of novel therapeutic agents for LAM and enable optimization of current rapamycin-based regimens.~Our preclinical studies showed that lipogenic pathways can be detected in preclinical animal models of TSC and LAM using PET-based metabolic imaging.~The proposed study aims to quantitatively and non-invasively assess metabolic activity and response to rapamycin in LAM patients using [11C]acetate positron emission tomography (PET) imaging.
This study aims to assess [11C]acetate positron emission tomography (PET)/computed tomography (CT) as a biomarker for renal angiomyolipomas and pulmonary lymphangioleiomyomatosis (LAM) and an early biomarker of response to rapamycin in LAM patients.~[11C]Acetate is a radioactive form of acetate, a nutrient commonly processed in our body's cells to generate fat and energy. Preclinical studies support the hypothesis that TSC tumors enhance lipid synthesis compared to normal tissues, suggesting that quantification of [11C]acetate in these tumors by PET/CT may provide a metabolic biomarker of disease.~Participants in the study will undergo 1 or 2 PET/CT scans over 3 to 6 months at the Massachusetts General Hospital (Boston, MA). [11C]acetate is administered through an intravenous catheter. This small amount of radioactivity is short-lived and eliminated from the body within a few hours.