Summary
A bioRxiv preprint reports that engineered Salmonella strain AD51, combined with intratumoral IFNγ, reduced tumour burden in mouse ovarian cancer and melanoma models. The findings are preclinical.
Researchers report that an engineered Salmonella enterica strain, AD51, combined with intratumoral interferon gamma (IFNγ), reduced tumour burden in mouse ovarian cancer and melanoma models. In a bioRxiv preprint, the authors report reductions of 75% and 84%, respectively, compared with untreated controls (p < 0.0001 for both comparisons). The findings are from animal models, not a clinical cancer treatment study.
Engineering bacteria to use a tumour metabolite
Kynurenine is a product of tryptophan metabolism that can contribute to an immune-suppressive tumour environment. The researchers engineered tumour-targeting S. enterica to break down this metabolite inside tumours.
Their initial strain, VNP20009, was equipped with the bacterial enzyme kynureninase (KynU) and a kynurenine transporter. The authors report that this enabled efficient degradation of intratumoral kynurenine. The later strain, AD51, combined KynU production controlled by quorum sensing with growth dependent on kynurenine availability and tumour targeting.
Quorum sensing is a form of bacterial communication that responds to signals associated with cell density. In AD51, it controls KynU expression. The design therefore links bacterial activity to two local conditions: the availability of kynurenine and the bacterial quorum-sensing signal. The intended effect is to make the bacteria both consume a tumour-associated metabolite and couple their growth to its presence.
Results in mouse cancer models
The authors report that AD51 induced immune activation and had better antitumour efficacy. Adding exogenous IFNγ directly into tumours enhanced immune activation and antitumour effects, which the authors describe as synergistic. With this combination, tumour burden was 75% lower in the ovarian cancer model and 84% lower in the melanoma model than in untreated controls.
The approach is notable because it combines a metabolite-targeting bacterium with an immune signal, rather than relying on bacterial delivery alone. The results support further investigation of engineered microbes as a way to alter the metabolic conditions that shape antitumour immunity.
The study is a preprint, and its reported efficacy comes from murine ovarian cancer and melanoma models. It establishes a preclinical direction for research; whether the approach can be made safe and effective in people is a separate question.