Research article

Rapamycin delays growth of Wnt-1 tumors in spite of suppression of host immunity

Elena V Svirshchevskaya^1,2 , Jacopo Mariotti² , Mollie H Wright² , Natalia Y Viskova¹ , William Telford² , Daniel H Fowler² and Lyuba Varticovski²

¹  Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS, Miklukho-Maklaya Street 16/10, Moscow 117997, Moscow, Russia

²  National Cancer Institute, NIH, 37 Convent Drive, Bethesda, MD 20892, USA

author email corresponding author email

BMC Cancer 2008, 8:176doi:10.1186/1471-2407-8-176

Published:	21 June 2008

Abstract

Background

Rapamycin, an inhibitor of mammalian target of Rapamycin (mTOR), is an immunosuppressive agent that has anti-proliferative effects on some tumors. However, the role of Rapamycin-induced immune suppression on tumor progression has not been examined.

Methods

We developed a transplantation model for generation of mammary tumors in syngeneic recipients that can be used to address the role of the immune system on tumor progression. We examined the effect of Rapamycin on the immune system and growth of MMTV-driven Wnt-1 mammary tumors which were transplanted into irradiated and bone marrow-reconstituted, or naïve mice.

Results

Rapamycin induced severe immunosuppression and significantly delayed the growth of Wnt-1 tumors. T cell depletion in spleen and thymus and reduction in T cell cytokine secretion were evident within 7 days of therapy. By day 20, splenic but not thymic T cell counts, and cytokine secretion recovered. We determined whether adoptive T cell therapy enhances the anti-cancer effect using ex vivo generated Rapamycin-resistant T cells. However, T cell transfer during Rapamycin therapy did not improve the outcome relative to drug therapy alone. Thus, we could not confirm that suppression of T cell immunity contributes to tumor growth in this model. Consistent with suppression of the mTOR pathway, decreased 4E-BP1, p70 S6-kinase, and S6 protein phosphorylation correlated with a decrease in Wnt-1 tumor cell proliferation.

Conclusion

Rapamycin has a direct anti-tumor effect on Wnt-1 breast cancer in vivo that involves inhibition of the mTOR pathway at doses that also suppress host immune responses.