A Calcineurin-Independent Mechanism of Angiogenesis Inhibition by a Nonimmunosuppressive Cyclosporin A Analog

Abstract

Cyclosporin A (CsA) is a widely used immunosuppressant drug. Its immunosuppressive activity occurs through the inhibition of the protein phosphatase calcineurin via formation of a ternary complex with cyclophilin A (CypA). CsA also inhibits endothelial cell proliferation and angiogenesis. This has been thought to occur through calcineurin inhibition as well. However, CsA is also a potent inhibitor of cyclophilins, a class of prolyl isomerases. Because calcineurin inhibition requires binding, and therefore inhibition of CypA, the relative contributions of calcineurin and cyclophilin inhibition in antiangiogenesis have not been addressed. We have taken a chemical biology approach to explore this question by dissociating the two activities of CsA at the molecular level. We have identified a nonimmunosuppressive analog of CsA that does not inhibit calcineurin but maintains inhibition of endothelial cell proliferation and in vivo angiogenesis. The same analog also maintains inhibition of all cyclophilin isoforms tested. We also show that a second, structurally distinct, cyclophilin inhibitor is sufficient to block endothelial cell proliferation. These results suggest that the inhibition of cyclophilins may play a larger role in the antiangiogenic activity of CsA than previously believed, and that cyclophilins may be potential antiangiogenic drug targets.

Cyclosporin A Disrupts Notch Signaling and Vascular Lumen Maintenance

“…This is contradictory to several reports indicating that CSA is a negative regulator of angiogenesis [8, 10, 12, 16, 25]. However, these results do indicate that CSA has a major effect on subsequent maintenance of the vascular system.…”

“…Independently however, cyclophilin A has also been implicated in angiogenesis [16], regulation of VEGF signaling [29], and the development of smooth muscle cells and heart valves [15]. Since CSA suppresses both the calcineurin/NFAT and cyclophilin A signaling pathways, we attempted to discriminate which of these signaling pathways was linked to CSA induced vascular dysfunction.…”

Molecular characterization of circulating tumor cells in patients with ovarian cancer improves their prognostic significance — A study of the OVCAD consortium

“…Whether combining cyclosporine A with cisplatinum can help to overcome PPIA induced chemoresistance in patients with malignant glioma is currently under investigation [31]. In addition, cyclosporin A plays a further potentially useful role as an inhibitor of angiogenesis [30,31], and non-immunosuppressive analogues of might be safely applied as part of an anti-angiogenetic drug regimen [32]. As in our study, PPIC positive CTCs were more likely in follow-up samples of the platinum resistant than in platinum sensitive patients, we speculate that PPIC positive CTCs represent a subpopulation of circulating tumor cells which "survived" chemotherapy and have a more aggressive potential.…”

Drug Modulators of B Cell Signaling Pathways and Epstein-Barr Virus Lytic Activation

“…Luciferase reporter assay. NFAT luciferase reporter assay was performed as described previously (33). Briefly, Jurkat T cells transfected with NFAT reporter construct were seeded into 96-well plates at a density of 5 ϫ 10 4 cells/180 l/well.…”