Synthetic biology strategies for engineering microbial therapeutics in metabolic diseases and cancer.

Synthetic biology has redefined the therapeutic role of microbes, transforming them from passive commensals or delivery vehicles into programmable living therapeutics capable of sensing, computing, and actuating within host tissues. This transformation is particularly relevant to metabolic disorders and oncological conditions in which pathophysiology is spatially heterogeneous, dynamically regulated and strongly modulated by host-microbe interactions. Engineered bacterial strains and other microbial platforms can be designed to degrade toxic metabolites, replace deficient enzymes or hormones, alter bile-acid and short-chain-fatty-acid profiles, modulate host immunity, and deliver antitumor payloads with spatial precision. In metabolic disorders, early live biotherapeutic programs have demonstrated that engineered Escherichia coli is capable of metabolically degrading phenylalanine in phenylketonuria, thereby providing a clinical proof of mechanism for gut-restricted metabolic interception. In oncology, tumor colonizing bacteria have been engineered to express cytokines, checkpoint inhibitors, lytic toxins, and diagnostic signals, and their application has been recently demonstrated in colorectal cancer detection and localized immunomodulation. Despite this progress, clinical translation remains limited by variable survival and functional activity in vivo, inconsistent engraftment, metabolic and genetic instability, biocontainment requirements, manufacturing complexity, and uncertain dose control, persist in biogenetic engineering. This review highlights chassis selection, circuit architectures, applications for metabolic diseases and cancer, metabolic bottlenecks, and future directions for precision microbial therapeutics.