Rapamycin (Sirolimus) is a natural compound belonging to the macrolide family. It is derived from Streptomyces hygroscopicus isolated from a soil sample from Easter Island in 1972 by Mr. Sehgal of Ayerst Research Labs in Montreal, Quebec. It was named Rapamycin after the native name for Easter Island, Rapa Nui. It is active against fungi and yeast but was found to have immunosuppressive and anti-cancer properties. It is marketed under the trade name Rapamune by Pfizer (formerly Wyeth). Rapamycin provided the stimulus for research on the pivotal mTOR pathway that controls a range of biological processes. Deregulation of the mTOR pathway is implicated in diseases like cancer, diabetes and obesity. The poor solubility and pharmacokinetics of Rapamycin triggered the development of several Rapamycin analogs (rapalogs) such as temsirolimus, everolimus, and ridaforoliumus.
Rapamycin is soluble in DMSO and ethanol, but practically insoluble in water.
|Mechanism of Action||Rapamycin complexes with FK-binding protein (FKBP12 or FKBP12) which then binds to and inhibits the molecular target of Rapamycin (mTOR), a member of the phosphoinositide kinase-related kinase (PIKK) family. mTOR is also known as FRAP (FKBP12-rapamycin-associated protein or RAFT (rapamycin and FKBP12 target). The resulting complex can perturb protein function. Analogs of Rapamycin retain the ability to inhibit mTOR with diminished potency.
mTOR is a large complex that is a receptor for Rapamycin. mTOR signaling network contains a number of tumor suppressor genes. The immunosuppressive activity is due to its actions on mTOR.
Rapamycin is able to inhibit p70 S6 kinase (p70s6k), whose major substrate is the 40S rRNA, it reduces the translation of mRNA that encode for ribosomal proteins, thereby decreasing protein synthesis.
|Cancer Applications||Rapamycin is able to inhibit growth of a number of tumor cell lines including mammary, colon 26, B16 3 melanocarcinoma, and EM ependymoblastoma.
Rapamycin suppresses the immune system by preventing T-cell and B-cells from responding to Interleukin 2 (IL-2), a cytokine that would otherwise induce cell proliferation. It does this in a similar mechanism to how it blocks cancer cell proliferation. One might think its action as an immunosuppressive would be detrimental to its use as an anti-cancer agent but it seems to be the contrary. The evidence suggests that in terms of tumor growth, its anti-cancer activities are dominant over its immunosuppressive effects (Law, 2005).
Endothelial cells in growing tumors have chronic Akt activation, resulting in abnormal tumor blood vessels, that are abnormal in structure and function. Rapamycin may affect tumor growth by acting as an Akt inhibitor and could be used as an angiogenesis inhibitor to inhibit tumor growth and tumor vascular permeability. Angiogenic regulators are involved in the development of blood vessels, and disruption is thought to cause pathological blood vessels (Phung et al, 2006).
|Eukaryotic Cell Culture Applications||Rifampicin was used in IL-2 stimulted T-cells, and found it could disrupt cytokine singnaling, impeding progression through G1/S phase resulting in G1 arrest.
Rapamycin was able to impair human omental and subcutaneous adipocyte differentiation in primary culture. Human preadipocytes in primary culture differentiate into adipocytes without any clonal expansion, unlike 3T3-L1 preadipocytes. Preadipocytes were grown with 100nM Rapamycin added to the differentiation medium. Rapamycin can interrupt adipogenesis independently from its antiproliferative effect. It inhibited the accumulation in intracellular lipid and it inhibited the induction of GPDH activity, a marker for adipogenesis. The pathway regulating human adipocyte differentiation has not been defined. Multiple signaling pathways regulated by mTOR may be operating in the preadipocyte (Bell et al, 2000).
Rapamycin can be used to probe functions of proteins in Rapamycin-based ligand-mediated colocalization systems for bioengineering. It is important to make sure the purity of the Rapamycin derivatives you are using are free of contaminating Rapamycin (Edwards and Wandless, 2007).
Chen et al. used Rapamycin (TOKU-E) to study the mammalian target of rapamycin. "AMPA receptor–mTOR activation is required for the antidepressant-like effects of sarcosine during the forced swim test in rats: insertion of AMPA receptor may play a role"
Bell A, Grunder L and Sorisky A (2000) Rapamycin inhibits human adipocte differentiation in primary culture. Obesity 8(3): 249-254
Dumont FJ and Su Q (1996) Mechanism of action of the immunosuppressant Rapamycin. Life Sci. 58.5 (1996): 373-95 PMID 8594303
Edwards SR and Wandless TJ (2007) The Rapamycin-binding domain of the protein kinase mTOR is a destabilizing domain. J. Biol. Chem. 282(18):13395-13401
Law BK (2005) Rapamycin: An anti-cancer immunosuppressant? Crit. Rev. Oncol. Hematol. 56(1):47-60 PMID 16039868
Li J, Kim SG and Blenis J (2014) Rapamycin: One drug, many effects. Cell Metab. 19(3):373-379
Phung TL, Ziv K and Benamin LE (2006) Pathological angiogenesis is induced by sustained AKt signaling and inhibited by Rapamycin. Cancer Cell 10(2):159-170
Sehgal SN, Baker H and Vezina C (1975) Rapamycin (AY-22,989), a new antifungal antibiotic. II. Fermentation, isolation and characterization. J. Antibiot (Tokyo) 28(10):727-732 PMID 1102509
Seto B (2012) Rapamycin and mTOR: A serendipitous discovery and implications for breast cancer. Clin. Transl. Med. 1:29 PMID 23369283