(18)F-FDG PET/CT in detection of sarcomatous degeneration of renal angiomyolipoma in setting of tuberous sclerosis

Tuberous Sclerosis Complex (TSC): Renal and Extrarenal Imaging

Tuberous sclerosis complex is a multiorgan syndrome manifesting with several benign and malignant tumors. Complications arising from renal abnormalities are a leading cause of death in patients with tuberous sclerosis complex. Renal cell carcinoma is relatively uncommon, occurring in 2%-4% of patients with tuberous sclerosis complex syndrome, but nonetheless can significantly contribute to morbidity and mortality. Extrarenal manifestations of tuberous sclerosis complex, including within the chest, abdomen and central nervous system, aid in diagnosis. Pathogenesis and management are also discussed, including the importance of the types of renal masses found in these patients.

[18F]Fluorocholine and [18F]Fluoroacetate PET as Imaging Biomarkers to Assess Phosphatidylcholine and Mitochondrial Metabolism in Preclinical Models of TSC and LAM

PURPOSE

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by inactivating mutations of the TSC1 or TSC2 gene, characterized by neurocognitive impairment and benign tumors of the brain, skin, heart, and kidneys. Lymphangioleiomyomatosis (LAM) is a diffuse proliferation of α-smooth muscle actin-positive cells associated with cystic destruction of the lung. LAM occurs almost exclusively in women, as a TSC manifestation or a sporadic disorder (TSC1/TSC2 somatic mutations). Biomarkers of whole-body tumor burden/activity and response to rapalogs or other therapies remain needed in TSC/LAM.

EXPERIMENTAL DESIGN

These preclinical studies aimed to assess feasibility of [¹⁸F]fluorocholine (FCH) and [¹⁸F]fluoroacetate (FACE) as TSC/LAM metabolic imaging biomarkers.

RESULTS

We previously reported that TSC2-deficient cells enhance phosphatidylcholine synthesis via the Kennedy pathway. Here, we show that TSC2-deficient cells exhibit rapid uptake of [¹⁸F]FCH in vivo and can be visualized by PET imaging in preclinical models of TSC/LAM, including subcutaneous tumors and pulmonary nodules. Treatment with rapamycin (72 hours) suppressed [¹⁸F]FCH standardized uptake value (SUV) by >50% in tumors. Interestingly, [¹⁸F]FCH-PET imaging of TSC2-deficient xenografts in ovariectomized mice also showed a significant decrease in tumor SUV. Finally, we found rapamycin-insensitive uptake of FACE by TSC2-deficient cells in vitro and in vivo, reflecting its mitochondrial accumulation via inhibition of aconitase, a TCA cycle enzyme.

CONCLUSIONS

Preclinical models of TSC2 deficiency represent informative platforms to identify tracers of potential clinical interest. Our findings provide mechanistic evidence for testing the potential of [¹⁸F]FCH and [¹⁸F]FACE as metabolic imaging biomarkers for TSC and LAM proliferative lesions, and novel insights into the metabolic reprogramming of TSC tumors.