VEGFA isoform expression and its regulation of the Tumour Microenvironment in Soft Tissue Sarcoma

Soft Tissue Sarcomas (STS) are a heterogeneous group of tumours of mesenchymal origin. Their diagnosis is challenging; few new treatments have become available. As a result, novel treatments are needed. Targeting angiogenic pathways and immune regulatory mechanisms within the tumour microenvironment (TME) might provide promising results. Published studies have shown that fibrosarcomas expressing VEGFA120 (fsVEGFA120) isoform in mice led to formation of poorly functioning vasculature and increased metastasis to the lung that was more sensitive to anti-VEGFA therapy in contrast to fsVEGFA18. Unpublished analysis of RNAseq data from these fsVEGFA120 revealed expression enrichment in PD-1 signalling and PD-L1. Further bioinformatics analysis from The Cancer Genome Atlas-SARComa in our laboratory revealed decrease overall survival and increased expression of PD-L1 signalling pathways in myxofibrosarcoma (MFS) patients with increased VEGFA121 mRNA. This PhD thesis aimed to build on these preliminary studies additional evidence of VEGFA isoform measurement as a potential biomarker for the use of anti-VEGFA and immune checkpoint inhibitors in MFS. Previous studies used immunocompromised mice; thus, new models of sarcoma are needed in immunocompetent mice. Firstly, this thesis characterised the TME of tumours grown from the T241 fibrosarcoma cell line in C57Bl6J mice. Then new cell lines were made from T241 cells that expressed increased levels of VEGFA120 or VEGFA188. Both cell lines were characterised in vitro, with only VEGFA188 being characterised in vivo using immunocompetent mice due to time constraints. In vitro characterisations showed differences between cells lines overexpressing the different VEGFA isoforms, including morphology, migration speed, ECM expression, and mesenchymal markers suggesting isoform expression can regulate the TME. In vivo characterisation of VEGFA188 tumours showed a tendency to regression after initial growth, which might suggest increased anti-tumoural immune cells activity. VEGFA188 tumours had a more mature vasculature and similar or lower immune cell infiltrations compared to WT tumours. A new data set was created by combining the VORTEX and TCGA SARC data to increase pleomorphic patient numbers. Analysis of this new dataset showed patients with high VEGFA121 expression had enriched expression of host-immune response genes and PD-1 signalling. Our findings indicate that VEGFA isoform expression is associated with changes that may be advantageous for an improved therapeutic response in MFS patients.