title: Inhibition of Akt (ser473) phosphorylation and rapamycin-resistant cell growth by knockdown of mammalian target of rapamycin with small interfering RNA in vascular endothelial growth factor receptor-1-targeting vector.
abstract: Previously we developed dicetyl phosphate-tetraethylenepentamine-based polycation liposomes (TEPA-PCL) for use in small interfering RNA (siRNA) therapy. In the present study, mammalian target of rapamycin (mTOR) expression in cancer cells was silenced with mTOR-siRNA (simTOR) formulated in TEPA-PCL modified with Ala-Pro-Arg-Pro-Gly (APRPG), a peptide having affinity for vascular endothelial growth factor receptor-1 (VEGFR-1). We investigated the effects of inhibition of mTOR, focusing on the differences between cells treated with simTOR and those with rapamycin in terms of Akt (ser473) phosphorylation and antiproliferative effects. Rapamycin treatment is known to induce Akt (ser473) phosphorylation which attenuates the antiproliferative effects of rapamycin. As a result, knockdown of mTOR did not alter or only slightly reduced Akt (ser473) phosphorylation in phosphatase and tensin homolog deleted from chromosome 10 (PTEN)-null (LNCaP and MDA-MB-468 cells) and PTEN-positive (DU 145 and MDA-MB-231) cells, although rapamycin induced Akt (ser473) phosphorylation of these cells. Rapamycin suppressed the growth of PTEN-null cells, in which the rapamycin-sensitive mTOR complex 1 (mTORC1) is excessively activated. On the other hand, rapamycin did not suppress the growth of PTEN-positive cells possibly through a negative feedback mechanism via the rapamycin-insensitive mTOR complex 2 (mTORC2) signaling pathway. In contrast, simTOR significantly suppressed the growth of cancer cells regardless of the presence of PTEN, possibly through inhibition of both mTORC1 and mTORC2. These results indicate that mTOR knockdown using APRPG-TEPA-PCL/simTOR is likely to be an effective strategy for cancer siRNA therapy.
authors.affiliation: Department of Medical Biochemistry and Global COE Program, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Koide
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Asai
authors.forename: Keiichi
authors.initials: K
authors.lastname: Furuya
authors.forename: Takuma
authors.initials: T
authors.lastname: Tsuzuku
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kato
authors.forename: Takehisa
authors.initials: T
authors.lastname: Dewa
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nango
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Maeda
authors.forename: Naoto
authors.initials: N
authors.lastname: Oku
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D002455:Cell Division; D045744:Cell Line, Tumor; D055785:Gene Knockdown Techniques; D006801:Humans; D051059:PTEN Phosphohydrolase / Q000235:genetics; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*; D012694:Serine / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics*
chemical_list: D034741:RNA, Small Interfering; D012694:Serine; C546842:MTOR protein, human; D040281:Vascular Endothelial Growth Factor Receptor-1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D051059:PTEN Phosphohydrolase