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Suppression of Peutz-Jeghers Polyposis by Targeting Mammalian Target of Rapamycin Signaling

Authors' Affiliations: Departments of ¹ Epidemiology, ² Cancer Genetics, ³ Pathology, ⁴ Carcinogenesis, and ⁵ Molecular Genetics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas

Requests for reprints: Marsha L. Frazier, Unit 1365, Department of Epidemiology, The University of Texas M. D. Anderson Cancer Center, 1155 Pressler Boulevard, Houston, TX 77030. Phone: 713-792-3393; Fax: 713-563-0999; E-mail: mlfrazier{at}mdanderson.org.

Purpose: Peutz-Jeghers syndrome (PJS) is a unique disorder characterized by the development of hamartomas in the gastrointestinal tract as well as increased risks for variety of malignancies. Germ-line mutations of LKB1 cause PJS. We have generated Lkb1^+/– mice, which model human PJS. Rapamycin and its analogues are promising preventive and therapeutic agents that specifically inhibit signaling from mammalian target of rapamycin (mTOR). Hyperactivation of mTOR signaling has been associated with PJS. The objective of the study is to investigate the efficacy of mTOR inhibition in suppressing Peutz-Jeghers polyposis in Lkb1^+/– mice.

Experimental Design: We initiated a trial of rapamycin in Lkb1^+/– mice at 9 months of age (after the onset of polyposis) at the dose of 2 mg/kg/d for a 2-month period. We assessed the efficacy of rapamycin by measuring polyp sizes and tumor burden. To examine the effect of rapamycin on mTOR signaling, phosphorylation levels of S6 were evaluated by immunostaining.

Results: We observed a significant decrease in mean tumor burden (Student's t test, P = 0.023) as well as total tumor burden in rapamycin-treated group compared with control group. Comparison of the polyp size observed in both rapamycin-treated and control groups showed that rapamycin efficiently decreased the tumor burden of large polyps (>8 mm). This inhibition of rapamycin was associated with a decrease in phosphorylated S6 levels in the polyps.

Conclusions: Rapamycin effectively suppresses Peutz-Jeghers polyposis in a mouse model, suggesting that rapamycin or its analogues may represent a new targeted therapy for the treatment of PJS.