Resistance to the mTOR Inhibitor Temsirolimus Alters Adhesion and Migration Behavior of Renal Cell Carcinoma Cells through an Integrin α5– and Integrin β3–Dependent Mechanism

Abstract

Inhibitors of the mammalian target of rapamycin (mTOR) have improved the treatment of renal cell carcinoma (RCC). However, chronic drug exposure may trigger resistance, limiting the utility of these agents. The metastatic behavior of RCC cells, susceptible (RCC(par)) or resistant (RCC(res)) to the mTOR inhibitor temsirolimus, was investigated. Adhesion to vascular endothelium or immobilized collagen and fibronectin was quantified. Chemotactic motility was evaluated with a modified Boyden chamber assay. Integrin α and β subtype receptors were analyzed by flow cytometry and Western blot analysis. The physiological relevance of the integrins was then determined by blocking studies and small interfering RNA knockdown. Adhesion to endothelial cells and to fibronectin (not to collagen) and chemotaxis were enhanced in RCC(res) compared to RCC(par). RCC(res) detached from fibronectin and motile activity further increased under retreatment with low-dosed temsirolimus. α5 integrin was diminished inside the cell and at the cell surface, whereas the β3 subtype was reduced intracellularly but elevated at the plasma membrane. In RCC(par), blocking α5 surface receptors enhanced RCC-collagen but reduced RCC-fibronectin interaction, whereas the opposite was true for RCC(res). Chemotaxis of RCC(par) but not of RCC(res) was strongly diminished by the α5 antibody. Blocking β3 significantly lowered chemotaxis with stronger effects on RCC(res), compared to RCC(par). Importantly, β3 knockdown reduced chemotaxis of RCC(par) but upregulated the motile behavior of RCC(res). Temsirolimus resistance is characterized by quantitative alterations of integrin α5 and β3 expression, coupled to functional changes of the integrin molecules, and forces a switch from RCC adhesion to RCC migration.

HDAC Inhibition Counteracts Metastatic Re-Activation of Prostate Cancer Cells Induced by Chronic mTOR Suppression

“…Chronic treatment of prostate cancer cells with another mTOR inhibitor, everolimus, has also been associated with increased metastatic activity [ 20 ]. The same increase in metastatic activity has been observed in renal cell carcinoma cells with acquired resistance towards TEM [ 21 ]. It is not yet clear whether mTOR represents the pivotal element triggering invasion.…”

“…Integrin α5 was not only down-regulated in PC3 res cells but was also found to be reduced in TEM-resistant renal cell carcinoma cells [ 21 ] or in prostate cancer cells with acquired resistance to everolimus [ 20 ]. This might reflect a generalized response to chronic mTOR-blockade, although the relevance of this behavior is not totally clear.…”

Amygdalin Influences Bladder Cancer Cell Adhesion and Invasion In Vitro

“…Whether due to an acquired or intrinsic resistance or due to the development of undesired feedback loops remains unclear, but this does indicate that not all bladder cancer patients may profit equally well from amygdalin. In line with this speculation, it has recently been shown that resistance development is accompanied by a functional switch of integrin receptors, driving tumor cells to high motility [12] .…”

Sulforaphane inhibits proliferation and invasive activity of everolimus-resistant kidney cancer cells in vitro

“…Earlier investigations have shown that everolimus-resistance drives RCC cells towards high proliferation and motility [11, 12]. SFN not only reduced growth of everolimus-sensitive tumor cells but also counteracted aggressive proliferative and invasive activity of everolimus-resistant RCC cell lines.…”