Engineered Bacteria as living detectors of tumor DNA: A new diagnostic frontier

The identification of tumor-generated DNA must be accurate, minimally invasive, and precise, as it forms a fundamental aspect of effective cancer diagnosis, prognosis, and customized treatment plans. Recent advances in synthetic biology have pioneered the creation of genetically engineered bacteria as innovative biosensors capable of detecting tumor-derived DNA directly in situ. This review explores key developments in designing these microbial sentinels to pinpoint oncogenic DNA alterations, particularly emphasizing KRAS mutations that drive many cancers. By leveraging natural competence and horizontal gene transfer, in combination with CRISPR-Cas tools for selective targeting and integration of mutant DNA sequences, engineered bacteria can distinguish between tumor and wild-type DNA and produce observable reporter outputs. We further elaborate on various molecular engineering strategies using unique genetic circuits, homologous recombination, multiplexed CRISPR systems and safety circuits to improve specificity, sensitivity and biosafety. An additional perspective in the discussion incorporates diverse bacterial species and various cancer types, with a specific emphasis on colorectal and gastrointestinal cancers, while also considering possible applications to other solid tumors. Detection modalities encompass in vitro assays, organoid models, in vivo mouse models, and non-invasive stool sampling, offering an impressive range of platforms for validating biosensors. The positive aspects of these approaches, such as real-time detection, affordability, programmability, and reduced invasiveness, need to be balanced with their negative aspects concerning biosafety, colonization efficiency, and detection sensitivity limitations. Looking forward, this review delves into the translational potential of engineered bacterial biosensors for clinical cancer diagnostics, their integration with therapeutic delivery systems, and future directions that involve multiplexed detection and the incorporation of digital health. Indubitably, engineered bacterial tumor DNA biosensors represent a key fusion of microbiology, synthetic biology, and oncology, aimed at revolutionizing the diagnosis and management of cancers.