Abstract 5087: Thromboxane synthase and thromboxane receptor targeting have anti-angiogenic efficacy in-vivo and reduce angiogenic secretions from human colorectal tumor explants ex-vivo.
Authors: Cathcart Mary-Clare , O'Sullivan Jacintha , Kennedy Breandan N. , Reynolds John V. , Pidgeon Graham P. 
Published: August 2014

Introduction: Colorectal cancer (CRC) is the third most common cancer worldwide. The VEGF inhibitor avastin is commonly used to treat metastatic CRC. However, a poor overall response rate of approximately 40% suggests further anti-angiogenic strategies are warranted. While COX-2 inhibitors are promising, chronic use is associated with increased cardiovascular risk. Downstream of COX-2, the thromboxane (TX) signalling pathway promotes tumour development, and is thought to promote cancer growth via increased tumour-associated angiogenesis. This study aimed to examine the TX signalling pathway as a novel anti-angiogenic target for the treatment of CRC.

Methods: We examined the effect of TX-pathway inhibition (using thromboxane synthase (TXS) inhibitors, thromboxane receptor (TP) antagonists and dual inhibitors; n=15) on blood vessel formation in-vivo using a transgenic zebrafish model (TgEGFP fli-1). Zebrafish larvae were treated with increasing concentrations of these inhibitors 4-6 h post-fertilization (hpf). Fish were fixed at 48hpf and vascular formation assessed under the flouresence microscope by counting of intersegmental vessels (ISV). The most promising TX-pathway inhibitors (ozagrel, seratrodast, AH-23848) were brought forward for further analysis using ex-vivo 3D-explant culturing. Angiogenic protein secretions from CRC tumour explants were assessed following 72 h treatment with these inhibitors using Meso-Scale Discovery multi-spot arrays (7-spot immunoassay system against human VEGF, Ang-1, Ang-2, bFGF, PAI-1, VCAM-1, ICAM-1) and compared with the known anti-angiogenic agent, avastin.

Results: In-vivo vascular screening revealed significant effects on ISV formation for a number of TX-pathway inhibitors. The 3 inhibitors with the greatest effect on vessel formation were ozagrel (TXS inhibitor), seratrodast (TP antagonist) and AH-23848 (TXS/EP4 inhibitor). Treatment with 100uM of these inhibitors reduced vessel formation to 70% (p&lt;0.0001), 40% (p&lt;0.0001) and 35% (p&lt;0.0001) of untreated control for ozagrel, seratrodast and AH-23848 respectively. Human explant culturing revealed that the secretion of a number of angiogenic metabolites from CRC tumour explants was significantly reduced following thromboxane pathway targeting, including VEGF, bFGF, Ang-1, PAI-1 and ICAM.

Conclusion: Thromboxane pathway targeting demonstrates anti-angiogenic effects in-vivo. In CRC patients, these effects may be mediated in part through a reduction in angiogenic protein secretions. Targeting this pathway may be a novel anti-angiogenic approach for the treatment of metastatic CRC alone, or in combination with traditional agents.

Citation Format: Mary-Clare Cathcart, Jacintha O’ Sullivan, Breandan N. Kennedy, John V. Reynolds, Graham P. Pidgeon. Thromboxane synthase and thromboxane receptor targeting have anti-angiogenic efficacy in-vivo and reduce angiogenic secretions from human colorectal tumor explants ex-vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5087. doi:10.1158/1538-7445.AM2013-5087