Bacterial cancer therapy in autochthonous colorectal cancer affects tumor growth and metabolic landscape

Abstract

Bacterial cancer therapy (BCT) shows great promise for treatment of solid tumors, yet basic mechanisms of bacterial-induced tumor suppression remain undefined. Attenuated strains of Salmonella enterica serovar Typhimurium ( S Tm) have commonly been used in mouse models of BCT in xenograft and orthotopic transplant cancer models. We aimed to better understand the tumor epithelium–targeted mechanisms of BCT by using autochthonous mouse models of intestinal cancer and tumor organoid cultures to assess the effectiveness and consequences of oral treatment with aromatase A–deficient S Tm ( STm Δ aroA ). STm Δ aroA delivered by oral gavage significantly reduced tumor burden and tumor load in both a colitis-associated colorectal cancer (CAC) model and in a spontaneous Apc min/+ intestinal cancer model. STm Δ aroA colonization of tumors caused alterations in transcription of mRNAs associated with tumor stemness, epithelial-mesenchymal transition, and cell cycle. Metabolomic analysis of tumors demonstrated alteration in the metabolic environment of STm Δ aroA -treated tumors, suggesting that STm Δ aroA imposes metabolic competition on the tumor. Use of tumor organoid cultures in vitro recapitulated effects seen on tumor stemness, mesenchymal markers, and altered metabolome. Furthermore, live STm Δ aroA was required, demonstrating active mechanisms including metabolite usage. We have demonstrated that oral BCT is efficacious in autochthonous intestinal cancer models, that BCT imposes metabolic competition, and that BCT has direct effects on the tumor epithelium affecting tumor stem cells.

Salmonellacancer therapy metabolically disrupts tumours at the collateral cost of T cell immunity

“…1A ). Following tumour induction, mice were orally gavaged with two doses (once per week) of an auxotrophic STm mutant (STm Δ aroA ) which we and others have previously reported to reduce tumour burden in cancer models (Fensterle et al, 2008; Johnson et al, 2021; Mackie et al, 2021).…”

“…In cells cultured with TCM from STm-infected tumours, however, there was no detectable glucose utilisation, consistent with the previous observation of impaired glycolytic enzyme expression. STm treatment of organoids itself depletes glucose (Mackie et al, 2021), however the levels remaining (approximately 4mM) should be sufficient for activation, and supplementation of excess glucose could not restore the phenotype ( Sup. Fig.…”

“… (A) Schematic depicting the asparaginase-deficient attenuated STm mutant and the impaired catalytic reaction. (B) Asparagine was detected by GC-MS analysis of metabolites in tumour organoids ( left ) after 24h infection and after oral 6 doses of STm therapy in vivo (right ) (Dataset taken from Mackie et al, 2021). (C) Splenocytes were cultured with TCM from tumours infected with aroA or ansB and activated with a-CD3/α-CD28 for 24h.…”

“…Salmonella as a tumour-homing vector, and one which can specifically invade Lgr5 + cancer stem cells (Mackie et al, 2021), is uniquely placed to exploit this pathway in tumour control.…”

“…As a metabolic ‘generalist’ (Dandekar et al, 2014), the bacterium can rapidly adapt to harsh tumour microenvironments, alongside potent tumour-homing abilities. We recently demonstrated in colorectal cancer (CRC) models that an attenuated STm mutant can reduce colonic tumour burden in vivo by imposing strong metabolic competition on the tumour, with particular reduction in amino acids, sugars and tricarboxylic acid (TCA) cycle intermediates, as well as specific targeting of tumour stem cells resulting in normalisation of tissue ontogeny (Mackie et al, 2021). The immunological consequences of these changes, however, are hitherto unexplored.…”