Mammalian Target of Rapamycin (mTOR) Regulates Cellular Proliferation and Tumor Growth in Urothelial Carcinoma

Abstract

Mammalian target of rapamycin (mTOR) signaling has been associated with aggressive tumor growth in many cancer models, although its role in urothelial carcinoma (UCC) has not been extensively explored. Expression of phosphorylated mTOR (P-mTOR) and a downstream target, ribosomal S6 protein (P-S6), was identified in 74% (90/121) and 55% (66/121) of muscle-invasive UCCs, respectively. P-mTOR intensity and %positive cells were associated with reduced diseasespecific survival (P ‫؍‬ 0.04, P ‫؍‬ 0.08, respectively). Moreover, P-mTOR intensity corresponded to increased pathological stage (P < 0.01), and mTOR activity was associated with cell migration in vitro. In addition, mTOR inhibition via rapamycin administration reduced cell proliferation in UCC cell lines RT4, T24, J82, and UMUC3 in a dose-dependent manner to 6% of control levels and was significant at 1 nmol/L in J82, T24, and RT4 cells (P < 0.01, P < 0.01, P ‫؍‬ 0.03, respectively) and at 10 nmol/L in UMUC3 cells (P ‫؍‬ 0.03). Reduced proliferation corresponded with reduced P-S6 levels by Western blot, and effects were ablated by pretreatment of cells with mTOR-specific siRNA. No effects of rapamycin on apoptosis were identified by TUNEL labeling or PARP cleavage. Administration of rapamycin to T24-xenografted mice resulted in a 55% reduction in tumor volume (P ‫؍‬ 0.03) and a 40% reduction in proliferation (P < 0.01) compared with vehicle-injected mice. These findings indicate that mTOR pathway activation frequently occurs in UCC and that mTOR inhibition may be a potential means to reduce UCC growth. (Am J Pathol

Expanding therapeutic targets in bladder cancer: the PI3K/Akt/mTOR pathway

“…Inhibition of mTOR signaling with rapamycin reduced cell proliferation and migration in vitro and reduced tumor volume in a T24-xenograft model by 55%. 71 These results were supported by a second study that showed mTOR activation in muscle-invasive UCC, 1,72 with mTOR inhibition preventing the progression of CIS to invasive bladder cancer. 72 Another important role of mTOR in tumor biology is the induction of angiogenesis.…”

“…71 One recent study has identified phospho-S6-a marker of mTOR activity-expression in 55% of muscle-invasive UCCs, with increased expression evident in paired lymph node metastases. The mTOR pathway activity was associated with reduced patient survival and increased pathological stage.…”

Transforming Growth Factor-β Is an Upstream Regulator of Mammalian Target of Rapamycin Complex 2–Dependent Bladder Cancer Cell Migration and Invasion

“…It is likely that other canonical and noncanonical signaling effects of TGF-b can occur in bladder cancer cells, especially given that SMAD2 can influence baseline mTORC2 activity and may affect the activity of mTORC1. Prior studies by our laboratory have shown a critical role for mTORC1 activity in bladder cancer cell proliferation and survival, rather than invasion, 36 although the role of TGF-b in this context is not known.…”

“…We have previously demonstrated that mTOR can influence bladder cancer cell migration and invasion, 7,36 primarily through effects on mTOR complex 2 (mTORC2) induction of RhoA activity. 7 Given the frequent alterations of TGF-b components in advanced bladder cancer and the ability of TGF-b to promote invasion in some cancer cell lines, we tested the ability of TGF-b to mediate motility effects in bladder cancer.…”

Angiogenesis, Lymphangiogenesis and Lymphovascular Invasion: Prognostic Impact for Bladder Cancer Patients

“…Urothelial bladder carcinoma expresses mTOR signaling molecules, providing a rationale for clinical trials evaluating agents targeting this pathway (Tickoo et al, 2011). In fact, some studies using bladder cancer cell lines have demonstrated that sirolimus and related drugs inhibit the growth of cancer cells and decrease their viability (Fechner et al, 2009;Hansel et al, 2010;Pinto-Leite et al, 2009;Schedel et al, 2011). Similar results were obtained when treating bladder cancer animal models with sirolimus or everolimus (Chiong et al, 2011;Oliveira et al, 2011;Parada et al, 2011;Seager et al, 2009;Vasconcelos-Nóbrega et al, 2011).…”