During tumor growth, cancer cells increase their oxygen and nutrients demand necessitating the formation of new blood vessels to supply these fuels. Tumor angiogenesis, the formation of new blood vessels from pre-existing ones, is considered the major mechanism of tumor vascularization. Over more than 40 years, numerous molecules have been studied in preclinical and clinical trials to inhibit tumor angiogenesis such as vascular endothelial growth factor (VEGF) antibodies. These anti-angiogenic strategies have shown numerous limitations in the clinical practice. One of these limitations is that cancer cells can use non-angiogenic mechanisms to obtain oxygen and nutrients. Vessel co-option (VCO) is a mechanism in which cancer cells hijack pre-existing blood vessels instead of developing new blood vessels through the angiogenesis process. Overcoming VCO as a resistance mechanism to anti angiogenic therapies is a new challenge in cancer research.

Considering that pre-existing blood vessels are quiescent, the hypothesis is that the inhibition of vessel quiescence can be a good strategy for inhibiting VCO. The main goal of this project is to test if the inhibition of vessel quiescence induced by bone morphogenetic protein 9 (BMP9) through ALK1 receptor, promotes VCO inhibition and it is a good anti-tumor strategy to use in combination with chemotherapies, immunotherapies or anti angiogenic drugs. Moreover, potential biomarkers of non-angiogenic vs angiogenic growth are aimed to be identified using MALDI-Imaging (MSI).

For this purpose, lung metastastes have been generated by injecting 4T1 cells (breast cancer) intravenously. Once pulmonary metastases are established, animals were treated with either placebo or PF-03446962 (an antibody against ALK1 receptor) three times during two weeks. At the endpoint of the in vivo procedure, lungs were harvested, stained with haematoxylin-eosin and analyzed by MALDI Imaging. Data processing and analysis with SCiLS™ software allowed the isolation of the tumor region of interest as well as the region close to the blood vessels. Preliminary results revealed differences between the spectra of the selected regions of interest (ROI) and allowed the characterization of a specific "biomolecular" signatures of them. Then, general tissue microextractions were done to identify some peptides present in the tissue surface by LCMS and assign these identifications to specific features present in the detected biomolecular signatures. Some of these peptides were found to be related to platelet activation, blood coagulation, the formation of fibrin clots and angiogenesis giving us a new perspective on the associated mechanisms of the VCO used by the tumors.