Colorectal cancer liver metastases (CLM) remain a significant cause of cancer-related morbidity and mortality. Central to their survival and growth is the process of tumour angiogenesis. Current clinical anti-angiogenic therapies target vascular endothelial growth factor signalling, but resistance to therapy is problematic. The aim of this study was to identify proteins critical for CLM endothelial cell (CLMEC) survival that could be targeted for the development of new anti-angiogenic therapies.
CLMECs and endothelial cells of normal adjacent liver (LECs) were isolated from patients undergoing curative resection. The two cell types were superficially similar, exhibiting markers and functional characteristics expected of endothelial cells. However, a number of differences in protein expression were identified, one of which was the previously unrecognised upregulation of the WEE1 checkpoint-kinase, a target of the small molecule WEE1 inhibitor AZD1775, currently in clinical trials. AZD1775 monotherapy was shown to inhibit proliferation and migration of CLMECs. Investigation of the underlying mechanism suggested induction of double-stranded DNA (DS-DNA) breaks due to a critical nucleotide shortage, which then led to caspase-3 dependent apoptosis. The implication for CLMEC tube formation was striking, with AZD1775 inhibiting branching tube formation by 83%. AZD1775 also had direct anti-cancer activity in a p53-mutated colorectal cancer cell line (HT29). In combination with 5-FU it caused increased caspase-3 dependent apoptosis because of DS-DNA breaks, not premature mitosis, which is thought to be the mechanism of AZD1775 toxicity when used in combination with DNA-damaging agents.
Proteomic screening of matched LECs and CLMECs identified a further 157 differentially expressed proteins, including up-regulation of the established endogenous angiogenesis inhibitors thrombospondin-1 and vascular endothelial growth factor receptor-1. The mechanosensitive, Ca2+ permeable ion channel Piezo1 was identified as another potential anti-angiogenic target in CLMECs. Modulation of the Piezo1 channel with the newly discovered Piezo1 activator Yoda1 is demonstrated for the first time in CLMECs and shown to induce phosphorylation of endothelial nitric oxide synthase.
This study has identified a number of proteins that are differentially expressed in CLMECs, which could be targeted for the development of anti-angiogenic therapies in the treatment of CLM. AZD1775 has anti-angiogenic activity in CLMECs and Piezo1 represents another target which can be investigated in future studies.
