Dissecting the role of the tumour microenvironment in Drosophila cancer models

Abstract

Cancer research has been a primary focus in medical research for more than a century. The complex and ever-changing nature of cancer requires the use of diverse model systems and interdisciplinary approaches to gain a comprehensive understanding of the mechanisms that drive disease initiation and progression, which is necessary for the development of effective therapies. Identifying new mechanisms that do not involve the tumour itself to combat cancer progression is a promising research area. However, the complexity of physiological processes and limited genetic accessibility of mammalian model systems makes it challenging to study non-tumour autonomous processes in vivo using conventional whole animal models. In recent decades, Drosophila melanogaster, with its potent genetic tools, has emerged as an attractive model system for investigating both tumour-intrinsic and non-tumour-derived processes that contribute to tumour development in vivo. This thesis is focused on exploring the relationships between genetically defined tumours and their microenvironment, including macrophage-like and adipocyte-like cells, called haemocytes and fat body cells, respectively. Our objective has been to examine the impact of signalling from these cells on tumour growth and invasion. In this study, we have used two Drosophila genetically-defined cancer models, (RasV12/ S100A4 and RasV12/ dlgKD) to identify ways in which tumour-host interactions are shared or unique in these two genetic cancer models. Specifically, the RasV12/S100A4 model represents metastatic tumours, while the RasV12/dlgKD model represents the characteristics of invasive tumors marked by the loss of cell polarity. This approach has involved RNA-mediated knockdown of molecules participating in key signalling pathways, such as Drosophila-JAK/STAT (d-JAK/STAT), Drosophila-Toll (d-Toll), and Drosophila-TNF (d- TNF), accompanied by multiparameter optical imaging of in vivo tumours to measure the phenotypic effects. Notably, amongst other findings, we showed that targeting the JAK/STAT receptor within the tumour itself (locally) in a RasV12/dlgKD tumour model restored adult survival. Surprisingly, we found that the tumours were in direct contact with the fat body, and this association was enhanced by knockdown of Drosophila-Toll receptor (d-toll ) in fat body or Drosophila-Toll ligand (d-spz) in haemocytes. the fat body could be equivalent to tumourassociated adipocytes, observed in other models that provide nutrients or other factors to promote tumour growth. Further, we found that knock down d-TNF receptor (d-grnd) in haemocytes leads to anti-tumour activity in RasV12/dlgKD. However, in the RasV12/S100A4 tumour model, we found that knocking down of molecules linked to common immune signalling such as d-TNF, d-Toll, and d-JAK/STAT in haemocytes, led to an increase the number of tumour-associated haemocytes. Notably, when the d-TNF ligand (d-egr) was knocked down in haemocytes, it resulted in a significant increase in primary tumour size but a decrease in invasion. Conversely, knocking down the d-grnd had no effect on tumour volume or invasion. Knocking down d-spz or d-toll had no significant impact on tumour size but led to a significant increase in invasion. In terms of d-JAK/STAT signalling, knockdown of the d- JAK/STAT ligand (d-upd1) or the d-JAK/STAT receptor (d-dome) resulted in a significant decrease in tumour size, while knockdown of the d-JAK/STAT ligand (d-upd2) led to a significant increase in tumour size. No change in tumour size was observed following knockdown of the d-JAK/STAT ligand (d-upd3). The results emphasize the importance of considering the genetic context in such studies, as our findings revealed diverse immune reactions between the two tumour models. However, to comprehensively comprehend the underlying mechanisms behind this differential immune response, further investigation is needed. This has the potential to reveal novel insights and therapeutic opportunities in the field of tumour immunology.