Angiogenesis, the sprouting of new capillaries, is essential for cancer growth. Inhibition of integrins av-beta3/av-beta5, cell surface receptors critical in angiogenesis, induces endothelial apoptosis, disrupts angiogenesis and inhibits brain tumor growth in a mouse model. The potential utility of integrin av-beta3/av-beta5 inhibition in cancer therapy is becoming apparent with the encouraging responses to RGDfV, an integrin-function-blocking peptide that completed a phase-I clinical trial in adults with recurrent gliomas. Despite the emerging use of av-beta3/av-beta5 integrin inhibition in cancer therapy, especially against brain tumors, the molecular mechanism of this inhibition is poorly understood, precluding rational design of combination therapies for future trials. We have shown that integrin inhibition increases intracellular ceramide, a pro-apoptotic lipid second messenger. It is not known whether this ceramide increase is required for the anti-angiogenic action of integrin av-beta3/av-beta5 inhibition. Our recent data suggest that acid sphingomyelinase is critical in this mechanism. We hypothesize that the ceramide increase, generated by acid sphingomyelinase and induced by integrin- av-beta3/av-beta5 inhibition is required for endothelial apoptosis and for the effect of RGDfV against brain tumors in vivo.
Our Specific Aims are: 1) To determine molecular interactions between ceramide, integrins av-beta3/av-beta5 and apoptosis, and 2) To compare the inhibitory effect of RGDfV in WT and ASMase deficient mice using an intracranial mouse brain tumor model. In vitro we will use ASMase-deficient or -competent endothelial cells plated on vitronectin and compare their ceramide and apoptotic responses to RGDfV. In-vivo we will implant intracranial brain tumors in ASMase knockout mice and wild type littermates and determine differences in survival, tumor growth and angiogenesis in RGDfV- or control-treated mice between the groups. Demonstration of a requirement for acid sphingomyelinase in av-beta3/av-beta5 integrin-mediated endothelial apoptosis will be the first evidence for a causal role of ceramide in integrin signaling. Requirement for ceramide metabolism in integrin signaling has potentially far-reaching implications by providing a molecular rationale for combining integrin-inhibiting drugs with agents geared to optimize the ceramide response, resulting in improved anti-cancer efficacy.
| Xu, Jingying; Millard, Melissa; Ren, Xiuhai et al. (2010) c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3 and alphavbeta5 and by disruption of actin. Blood 115:2709-18 |
