Reprogramming the host inflammatory response to wound healing and cancer through infection and protocell treatment – a study in zebrafish

Abstract

For over a century, it has been apparent that tumours behave somewhat like wounds that fail to heal. A number of studies have established several cellular and molecular parallels between wound healing and cancer, and a key one of these is inflammation, with both wounds and tumours triggering an inflammatory response that plays an essential role in the outcome of these tissue lesions. As a consequence, any potential therapy with the capacity to alter the wound/tumour inflammatory response is now considered clinically relevant. In this regard, infection is known to modulate the inflammatory response to both cancer and wound healing. Serendipitous findings extending back to those of Coley in the early 1900s, have shown cancer remissions occurring upon treatment with heat-killed bacteria, suggesting that infection can enhance, or prime, the host immune response to better recognise and eradicate cancers. During tissue repair, there is evidence that some aspects of the wound inflammatory response may be activated by microbial antigens, although, of course, if infection becomes overwhelming, this can lead to chronic, non-healing wounds. Whilst the longer term consequences of infection on cancer and wound healing have been partially explored, rather little is known about the precise cellular and molecular mechanisms by which bacteria-induced inflammation can influence these consequences, for example, how infection alters the behaviour of inflammatory cells and their cellular interactions with the tissue insult.

Here I used the translucent larval zebrafish (Danio rerio), which has relatively recently become a powerful model of inflammatory-related human conditions, in combination with high-resolution confocal imaging and a novel bespoke automated cell tracking and cell-cell interaction software, to investigate how inflammatory cells behave and interact with repairing wounds and early cancer cells in sterile versus infection conditions. Using this approach, I showed that infection, delivered either systemically or locally, induced changes in the number and behaviour of inflammatory cells recruited to acute wounds and to pre-neoplastic cells, and these alterations led to a significant delay in wound healing, and to a reduction in the number of pre-neoplastic cells, which correlated with increased numbers of pro-inflammatory (tnfα-positive) macrophages. I expanded these studies into adult zebrafish where I observed that infection-induced inflammation inhibits the growth of established human-like melanomas.

Finally, I tested a more therapeutically viable anti-cancer strategy by using a novel particle-based protocell system to selectively load macrophages and neutrophils, via their natural foreign body phagocytic abilities, with immunostimulatory, tumour-suppressing molecules (anti-miR223 or R848). I showed that anti-miR223-loaded protocells or R848-loaded protocells can effectively “reprogramme” macrophages (and neutrophils) towards a more pro-inflammatory, and thus anti-cancer state, in zebrafish (and cultured human macrophages), which led to a significant reduction in both larval pre-neoplastic burden and in the size and number of adult melanomas also.

Date of Award	27 Sept 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Paul B Martin (Supervisor) & Beck J Richardson (Supervisor)