Rapamycin inhibits proliferation of cells from TSC skin tumors.

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Patients with tuberous sclerosis complex (TSC) develop hamartomatous tumors in multiple organs including the brain, kidneys heart, lungs, and skin. TSC tumors exhibit biallelic mutations in either the TSC1 or TSC2 tumor suppressor gene, resulting in hyperactivation of the mTOR signaling pathway. Earlier, we showed that fibroblast-like cells grown from TSC skin tumors (angiofibromas and periungual fibromas) overexpress EGF receptor and one of its ligands, epiregulin. In the current study, we investigated whether these signaling pathways represent potential therapeutic targets by studying the effects of pharmacological inhibitors of EGFR signaling (AG1478 and U0126) and the PI3K/AKT/mTOR pathway (rapamycin, LY294002 and LY303511) on cell proliferation. We compared fibroblasts grown from TSC patient normal-appearing skin with cells grown from the patient’s periungual fibroma, which lacked the TSC gene product tuberin and contained hyperphosphorylated ribosomal protein S6. Cells in DMEM plus 10% serum were incubated with inhibitors for three days and proliferation measured using the MTT assay. All compounds inhibited cell proliferation in a concentration-dependent manner, but only rapamycin (0.8, 4, 20 nM) inhibited proliferation of TSC tumor cells more than TSC fibroblasts (62, 65, 63% versus 42, 44, 40%, respectively). We also examined the response TSC tumor cells to prolonged rapamycin treatment, using a heterogeneous population of cells from a TSC patient angiofibroma containing 20% cells with allelic deletion of TSC2 as determined by fluorescence in situ hybridization. The percent cells with loss of TSC2 decreased from 20% to 14% for cells incubated with 2 nM rapamycin for one month. These results are consistent with the conclusion that rapamycin suppresses the proliferation of tuberin-null neoplastic cells greater than tuberin-containing cells, and that rapamycin may be useful for the treatment of TSC tumors.