The direct and indirect effects of attenuated salmonella typhimurium on intestinal tumour epithelium

Mackie, Gillian M ORCID: 0000-0001-7758-6570 (2024). The direct and indirect effects of attenuated salmonella typhimurium on intestinal tumour epithelium. University of Birmingham. Ph.D.

Mackie2024PhD.pdf
Text
Restricted to Repository staff only until 31 July 2025.
Available under License All rights reserved.
Download (8MB) | Request a copy

Abstract

Attenuated Salmonella enterica serovar typhimurium (STm) home to and colonise tumours, where it can induce tumour regression. In this thesis I aimed to identify how STm invade tumour cells and to what extent intracellular invasion is necessary for anti-tumour response. Bulk and single-cell RNA-sequencing were utilised to reveal differences between invasive versus extracellular-restricted Salmonella. ApcMin/+ mice were treated with Salmonella that are invasion-sufficient or extracellular-restricted, then innate immune infiltrate and polyp burden were assessed. I used in vitro models to show that STm preferentially invades proliferating cells in patient and murine tumour organoids. Invasion of tumour cells was dependent on Salmonella binding host cell cholesterol via SipB expression. Previous studies have shown that cell-surface cholesterol is maximal during mitosis, thus I show mechanistic insight into why proliferating cells are preferentially targeted. STmΔaroA induce similar transcriptional changes in both mouse and human tumour organoids in vitro when restricted to the extracellular space or permitted to invade. I generated and validated a strain of STm which cannot invade intracellularly, STmΔaroAΔsipB, but I show with oral gavage of ApcMin/+ mice
that this mutant can colonise the polyp environment in vivo. This extracellular survival resulted in similar innate cell recruitment but led to superior clearance of polyps, which warrants further investigation. In summary, STm specifically infects proliferating tumour cells via binding of cell surface cholesterol, which has implications for utilisation of bacteria as intracellular drug delivery systems. Intracellular invasion appears to be dispensable for the therapeutic effect, as we see reduction of polyps with STmΔaroAΔsipB; this double mutant may then represent a superior and safer bacterial cancer therapy agent.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):