Angiogenesis, the growth of new blood vessels and capillaries from pre-existing ones¹, is a process that the ancient Egyptians already observed in the 17th century BCE². When diagnosing tumors, they observed something called a “vessel-tumor”, which they treated with what can now be regarded as the first angiogenesis therapy: Surgical removal of the vessels surrounding the tumor with a heated knife to reduce bleeding³. Even though a huge amount of progress has been made since these ancient times, the early interest in angiogenesis is not that surprising given the fundamental role this process plays in health and disease⁴.

Angiogenesis is crucial in the onset and progression of many diseases, including cancer, macular degeneration, Alzheimer’s disease, vascular fibrosis, inflammation, and kidney failure associated with diabetes. This entails that targeting angiogenesis has a vast therapeutic value in a wide range of diseases. For researchers to study this crucially important process and develop or improve therapies targeting angiogenesis, physiologically representative in vitro models are needed.

Angiogenesis models

An overview of how angiogenesis traditionally has been modeled in vitro has extensively been described^5,6 and summarized in a previous blog: Can you really model angiogenesis in vitro?. However, these models are incomplete because they do not include all aspects of angiogenesis, such as pre-existing blood vessels, they lack essential experimental options, such as luminal access, and often consume a lot of time and resources.

Modern in vitro strategies for angiogenesis research have led to the advancement of models that are now more representative of the in vivo situation⁷. One of those strategies is the use of microfluidic systems⁸, which is extensively discussed in our previous blog post: ”Dissatisfied with Your Angiogenesis Model? Read This”. Briefly, microfluidic systems allow spatial control over fluids in micrometer-sized channels, preferably without artificial membranes between the compartments. This allows mimicking of physiologically relevant characteristics such as lumen perfusion, shear stress, and biochemical gradients. Microfluidic devices, such as the OrganoPlate^®, are promising tools expected to play a significant role in drug discovery. Additionally, the OrganoPlate^® further addresses the need for high throughput, scalability, high-quality imaging, and reproducibility of these platforms.

How to choose the angiogenesis assay that fits your needs?

Thanks to the development of these physiologically relevant platforms, researchers can now access various platforms to develop gradient-driven, three-dimensional angiogenesis assays. So, where do you start your search for the best angiogenesis assay?
The truth is, there is no one-size-fits-all solution. As a matter of fact, modeling angiogenesis requires a customized approach, depending mostly on your research question. You might want to look at sprouting initiation or perform a sprouting inhibitor screen. Maybe you have a specific type of extracellular matrix in mind that you want to include in your model? Or maybe there is a specific type of tissue or tumor that you want to vascularize? There really is no such thing as “THE angiogenesis assay”. Depending on which aspect of angiogenesis you specifically want to investigate and which cells you want to include, different models can be designed.

To enable drug screening, physiologically relevant culture conditions are required while ensuring robustness and scalability. To this end, a perfused 3D angiogenesis assay was developed that includes endothelial cells (ECs) from induced pluripotent stem cells (iPSC), which was tested for its suitability in anti-angiogenic drug screening⁹. The angiogenic sprouting behavior that we observed was comparable to that of primary ECs, and well-known angiogenesis inhibitors (sunitinib and 3PO) significantly reduced the sprouting of both iPSC-ECs and primary ECs. The performance of the assay was quantified and shown to meet the criteria necessary for screening assays. An even more recent example is presented in this poster, describing a high-throughput phenotypic screen of 1,546 compounds in duplicate on a 3D angiogenic sprouting assay. To our knowledge, this is the largest Organ-on-a-Chip screening effort ever on such a complex process.

The OrganoPlate, which was used to perform both angiogenesis assay examples mentioned above, is in this regard future-proof, allowing flexibility and personalization, while maintaining reproducibility and scalability. Many factors can be kept constant across different experiments such as:

• flow profiles;
• position of the extracellular matrix;
• shape of the gradient of the angiogenesis triggers.

At the same time, the platform can be expanded to comprise other cell types, creating further opportunities to answer a wide variety of research questions. Lastly, the microtiter plate format makes it fully compatible with automated imaging and robotic handling.

Taking all this into account, now it is time for you to start your own angiogenesis assays. Which aspect of angiogenesis do you want to investigate? What timeframe are you interested in and which cells should you include? MIMETAS offers full flexibility to build your own model using one of the OrganoPlate^® products. This includes an OrganoReady^™ Angiogenesis assay which contains a pre-grown blood vessel and comes with a standard sprouting mix and assay protocols. We also offer OrganoServices™, where our experienced scientists will screen pro- or anti-angiogenic compounds of your choice in our angiogenesis model so you can focus directly on the data. And last but not least, with the OrganoPlate^® Graft you can now also look at vascularization of different types of organoids and tumors. So let your imagination go wild and start experimenting on your own personalized angiogenesis assay today!

Related resources

References:

1. Risau W. Mechanisms of angiogenesis. Nature. 1997;386(6626):671-4.
2. Cimpean AM, Raica M. Historical Overview of In Vivo and In Vitro Angiogenesis Assays. Methods Mol Biol. 2021;2206:1-13.
3. Willerson JT, Teaff R. Egyptian contributions to cardiovascular medicine. Tex Heart Inst J. 1996;23(3):191-200.
4. Wong BW, Marsch E, Treps L, Baes M, Carmeliet P. Endothelial cell metabolism in health and disease: impact of hypoxia. EMBO J. 2017;36(15):2187-203.
5. Eglen RM, Randle DH. Drug Discovery Goes Three-Dimensional: Goodbye to Flat High-Throughput Screening? Assay Drug Dev Technol. 2015;13(5):262-5.
6. Nowak-Sliwinska P, Alitalo K, Allen E, Anisimov A, Aplin AC, Auerbach R, et al. Consensus guidelines for the use and interpretation of angiogenesis assays. Angiogenesis. 2018;21(3):425-532.
7. van Duinen V, Trietsch SJ, Joore J, Vulto P, Hankemeier T. Microfluidic 3D cell culture: from tools to tissue models. Curr Opin Biotechnol. 2015;35:118-26.
8. Convery N, Neil. G. 30 years of microfluidics. Macro and Nano engineering. 2019;2(March):76-91.
9. van Duinen V, Zhu D, Ramakers C, van Zonneveld AJ, Vulto P, Hankemeier T. Perfused 3D angiogenic sprouting in a high-throughput in vitro platform. Angiogenesis. 2019;22(1):157-65.
   
   

Learn More

You might also be interested in:

• [Application note] Perfused 3D angiogenic sprouting in a high-throughput in vitro platform
• [Webinar] High throughput phenotypic screening in Organ-on-a-Chip: future or reality?
• Read more about Angiogenesis research using the OrganoPlate^®
  
  

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