CXCR4 and CXCR7 transduce through mTOR in human renal cancer cells

Abstract

Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. However, their efficacy is thought to be limited by feedback loops and crosstalk with other pathways leading to the development of drug resistance. As CXCR4–CXCL12–CXCR7 axis has been described to have a crucial role in renal cancer; the crosstalk between the mTOR pathway and the CXCR4–CXCL12–CXCR7 chemokine receptor axis has been investigated in human renal cancer cells. In SN12C and A498, the common CXCR4–CXCR7 ligand, CXCL12, and the exclusive CXCR7 ligand, CXCL11, activated mTOR through P70S6K and 4EBP1 targets. The mTOR activation was specifically inhibited by CXCR4 antagonists (AMD3100, anti-CXCR4-12G5 and Peptide R, a newly developed CXCR4 antagonist) and CXCR7 antagonists (anti-CXCR7-12G8 and CCX771, CXCR7 inhibitor). To investigate the functional role of CXCR4, CXCR7 and mTOR in human renal cancer cells, both migration and wound healing were evaluated. SN12C and A498 cells migrated toward CXCL12 and CXCL11; CXCR4 and CXCR7 inhibitors impaired migration and treatment with mTOR inhibitor, RAD001, further inhibited it. Moreover, CXCL12 and CXCL11 induced wound healing while was impaired by AMD3100, the anti CXCR7 and RAD001. In SN12C and A498 cells, CXCL12 and CXCL11 promoted actin reorganization characterized by thin spikes at the cell periphery, whereas AMD3100 and anti-CXCR7 impaired CXCL12/CXCL11-induced actin polymerization, and RAD001 treatment further reduced it. In addition, when cell growth was evaluated in the presence of CXCL12, CXCL11 and mTOR inhibitors, an additive effect was demonstrated with the CXCR4, CXCR7 antagonists and RAD001. RAD001-resistant SN12C and A498 cells recovered RAD001 sensitivity in the presence of CXCR4 and CXCR7 antagonists. In conclusion, the entire axis CXCR4–CXCL12–CXCR7 regulates mTOR signaling in renal cancer cells offering new therapeutic opportunities and targets to overcome resistance to mTOR inhibitors.

Cellular and molecular effects of the mTOR inhibitor everolimus

“…Tsaur et al [140] observed increased chemotactic activity of prostate cancer cells resistant to everolimus, a process that was characterized by significant alterations of integrin α2, α5 and α1 expression profiles as well as the reactivation of Akt, whereas treatment of sensitive prostate cancer cells with everolimus resulted in decreased tumour cell chemotaxis, migration and invasion. Similarly, Ierano et al [141] demonstrated that the effect of CXCR (CXC chemokine receptor) 4, CXCR7 and mTOR inhibitors was additive in impairing migration and cell growth. Additionally, they observed that everolimus inhibited CXCL12 (CXC chemokine ligand 12)-induced migration, wound healing and cell growth.…”

“…This echoes a previous study by Bresccia et al [179] who reported that dual inhibition with PI3K and MAPK inhibitors was superior in efficacy to inhibition of a single pathway alone. Recently, Ierano et al [141] described a novel method to resensitize RCC to everolimus treatment via inhibition of the CXCR4-CXCL12-CXCR7 axis. The cross-talk between CXCR4-CXCL12 and PI3K/mTOR has been well established in various cancer cells [26,27,29].…”

Current treatment strategies for inhibiting mTOR in cancer

“…mTORC1 comprises regulatory-associated protein of mTOR (RAPTOR), proline-rich Akt substrate 40 kDa (PRAS40), mammalian lethal with Sec13 protein 8 (mLST8), and DEP domaincontaining mTOR-interacting protein (DEPTOR), which has an inhibitory function on mTORC1. The classical mTORC1 positive inputs are growth factors, chemokines [4], nutrients (glucose, amino acids), and cell energy status (i.e., high ATP:AMP ratio) [1]. Growth factors and cytokines stimulate mTORC1 mainly through the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway ( Figure 1).…”

Molecular Pathways: Targeting the CXCR4–CXCL12 Axis—Untapped Potential in the Tumor Microenvironment

“…Recent studies have shown CXCR4 signaling through mTOR in pancreatic cancer, gastric cancer, and T-cell leukemia cells (10)(11)(12)(13). In human renal cancer cells, CXCL12 induces phosphorylation of the specific mTOR targets, P70S6K and 4EBP1 (14), and CXCR4 and mTOR inhibitors have been reported to impair human renal cancer migration ( Fig. 1; ref.…”