SUMMARY PARAGRAPH Synthetic biology is driving a new era of medicine through the genetic programming of living cells 1 , 2 . This transformative approach allows for the creation of engineered systems that intelligently sense and respond to diverse environments, ultimately adding specificity and efficacy that extends beyond the capabilities of molecular-based therapeutics 3 – 6 . One particular focus area has been the engineering of bacteria as therapeutic delivery systems to selectively release therapeutic payloads in vivo 7 – 11 . Here, we engineered a non-pathogenic E. coli to specifically lyse within the tumor microenvironment and release an encoded nanobody antagonist of CD47 (CD47nb) 12 , an anti-phagocytic receptor commonly overexpressed in several human cancers 13 , 14 . We show that delivery of CD47nb by tumor-colonizing bacteria increases activation of tumor-infiltrating T cells, stimulates rapid tumor regression, prevents metastasis, and leads to long-term survival in a syngeneic tumor model. Moreover, we report that local injection of CD47nb bacteria stimulates systemic tumor antigen–specific immune responses that reduce the growth of untreated tumors – providing, to the best of our knowledge, the first demonstration of an abscopal effect induced by an engineered bacterial immunotherapy. Thus, engineered bacteria may be used for safe and local delivery of immunotherapeutic payloads leading to systemic antitumor immunity.

Checkpoint inhibitors have revolutionized cancer therapy but only work in a subset of patients and can lead to a multitude of toxicities, suggesting the need for more targeted delivery systems. Because of their preferential colonization of tumors, microbes are a natural platform for the local delivery of cancer therapeutics. Here, we engineer a probiotic bacteria system for the controlled production and intratumoral release of nanobodies targeting programmed cell death–ligand 1 (PD-L1) and cytotoxic T lymphocyte–associated protein-4 (CTLA-4) using a stabilized lysing release mechanism. We used computational modeling coupled with experimental validation of lysis circuit dynamics to determine the optimal genetic circuit parameters for maximal therapeutic efficacy. A single injection of this engineered system demonstrated an enhanced therapeutic response compared to analogous clinically relevant antibodies, resulting in tumor regression in syngeneic mouse models. Supporting the potentiation of a systemic immune response, we observed a relative increase in activated T cells, an abscopal effect, and corresponding increases in systemic T cell memory populations in mice treated with probiotically delivered checkpoint inhibitors. Last, we leveraged the modularity of our platform to achieve enhanced therapeutic efficacy in a poorly immunogenic syngeneic mouse model through effective combinations with a probiotically produced cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF). Together, these results demonstrate that our engineered probiotic system bridges synthetic biology and immunology to improve upon checkpoint blockade delivery.

Summary Multiple mechanisms have been proposed to explain how Rb and p53 tumor suppressor loss lead to chromosome instability (CIN). It was recently shown that Rb pathway inhibition causes overexpression of the mitotic checkpoint gene Mad2 but whether Mad2 overexpression is required to generate CIN in this context is unknown. Here we show that CIN in cultured cells lacking Rb family proteins requires Mad2 upregulation and that this upregulation is also necessary for CIN and tumor progression in vivo. Mad2 is also repressed by p53 and its upregulation is required for CIN in a p53 mutant tumor model. These results demonstrate that Mad2 overexpression is a critical mediator of the CIN observed upon inactivation of two major tumor suppressor pathways. Significance Chromosome instability (CIN) is thought to be the major evolutionary driving force for tumor progression. Here we show that overexpression of the mitotic checkpoint gene Mad2 is required for the CIN observed upon inhibition of the Rb and p53 pathways, two pathways frequently inactivated in human cancer. Our results demonstrate that acquisition of CIN is hard-wired into loss of the major tumor suppressor pathways via hyperactivation of the mitotic checkpoint pathway. The inhibition of these tumor suppressor pathways in the early stages of cancer progression may account for the widespread presence of CIN in tumors in the absence of other genetic events and underscores the therapeutic value of targeting aneuploid cells.

Metastatic cancer patients experience a severe loss of skeletal muscle mass and function known as cachexia. Cachexia is associated with poor prognosis and accelerated death in cancer patients, yet its underlying mechanisms remain poorly understood. Here, we identify the metal transporter ZIP14 as a critical mediator of cancer-induced cachexia. ZIP14 is upregulated in cachectic muscles from mice and patients with metastatic cancer and can be induced by TNF-α and TGF-β cytokines.Strikingly, in vivo manipulation of Zip14 expression has profound impact on muscle atrophy in experimental models of metastasis.We find that ZIP14-mediated zinc uptake in muscle progenitor cells represses the expression of the key myogenic factors MyoD and Mef2c, and blocks muscle-cell differentiation. Importantly, ZIP14-mediated zinc accumulation in differentiated muscle cells induces myosin heavy chain loss. These results highlight a previously unrecognized role for altered zinc homeostasis in muscle during metastatic-cancer-induced cachexia, and implicate ZIP14 as a therapeutic target for its treatment.