Abstract 2501: Rapamycin inhibits epidermal cell proliferation in a xenograft model of tuberous sclerosis skin tumors

Abstract

Abstract Patients with tuberous sclerosis complex (TSC) develop hamartomatous tumors of the skin that have increased dermal fibroblast-like cells and a thickened epidermis. Our previous studies indicate that dermal cells are neoplastic, showing loss of TSC1/TSC2 function and activation of signaling through the mTORC1 pathway, and that overlying epidermal keratinocytes are reactive. The goals of this study were to determine whether TSC skin tumor cells induce epidermal changes and to assess the potential utility and mechanism of action of rapamycin, an mTORC1 inhibitor. TSC2-null skin tumor cells or fibroblasts from patient normal-appearing skin were incorporated into collagen gels overlaid with normal human neonatal keratinocytes, and these constructs were grafted to the backs of nude mice. Mice grafted with TSC tumor cells (n=27) or TSC normal fibroblasts (n=23) received rapamycin (2 mg/kg) (n=24) or an equal volume of vehicle (n=26) by intraperitoneal injection on alternate days for 12 weeks beginning 5 weeks after grafting. Mice were sacrificed 24 hours after the last injection for analysis of the grafts by immunohistochemistry. Grafts containing TSC tumor cells showed greater activation of the mTORC1 signaling pathway than grafts with normal fibroblasts, as shown by greater numbers of dermal cells staining for phosphorylated ribosomal protein S6 (p-S6). Xenografted epidermis overlying TSC tumor cells also showed stronger p-S6 staining than epidermis overlying TSC fibroblasts, replicating what we had observed in TSC skin tumors. Rapamycin treatment of tumor xenografts dramatically inhibited p-S6 staining in both epidermal and dermal cells. Tumor xenografts showed greater epidermal cell proliferation (as determined by staining with anti-Ki-67 specific antibody) than normal xenografts (p=0.009). Rapamycin treatment decreased the number of Ki-67 positive epidermal cells in grafts containing TSC tumor cells (p=0.046) but not in grafts with TSC normal fibroblasts. These results indicate that TSC tumor cells stimulate mTORC1 signaling and proliferation of overlying epidermal cells, and suggest that one of rapamycin effects on TSC skin tumors is through decreasing epidermal cell proliferation. This work was supported by an Idea Development Award (TS080064) from the Congressionally Directed Medical Research Program to Dr. Darling. Dr. Moss was supported by the Intramural Research Program, NIH, NHLBI. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2501.