Identification of Kinases Activated by Multiple Pro-Angiogenic Growth Factors

Abstract

Antiangiogenic therapy began as an effort to inhibit VEGF signaling, which was thought to be the sole factor driving tumor angiogenesis. It has become clear that there are more pro-angiogenic growth factors that can participate in and can substitute for VEGF during tumor vascularization. This has led to the development of multi-kinase inhibitors that simultaneously target multiple growth factor receptors. These inhibitors perform better than monotherapies yet to date no multi-kinase inhibitor targets all receptors known to be involved in pro-angiogenic signaling and resistance inevitably occurs. Given the large number of pro-angiogenic growth factors identified, it may be impossible to simultaneously target all pro-angiogenic growth factor receptors with a single agent. Here we search downstream of the receptors for kinase targets that would be critical to endothelial cell proliferation, irrespective of the growth factor signal. To do this systematically we develop a quantitative endothelial cell proliferation assay and combine it with “kinome regression” or KIR, a recently developed computational and kinase screening method capable of identifying kinases that influence any measurable and quantitative phenotype, such as proliferation. We report the result of this analysis. The kinases implicated by KIR are both expected and unexpected intracellular kinases. Using RNA interference we provide orthogonal evidence of their importance in endothelial cell proliferation. This approach points to a new strategy that can be employed to develop a more complete anti-angiogenic blockade.