Genetic Programming by Nitric Oxide-Sensing Gene Switch System in Tumor-Targeting Bacteria.

Recent progress in synthetic biology has enabled bacteria to respond to specific disease signals to perform diagnostic and/or therapeutic tasks. Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) colonization of tumors results in increases in nitric oxide (NO) levels, suggesting that NO may act as a candidate inducer of tumor-specific gene expression. The present study describes a NO-sensing gene switch system for triggering tumor-specific gene expression in an attenuated strain of S. Typhimurium. The genetic circuit was designed to sense NO via NorR, thus initiating the expression of FimE DNA recombinase. This was found to lead sequentially to the unidirectional inversion of a promoter region (fimS), which induced the expression of target genes. Target gene expression in bacteria transformed with the NO-sensing switch system was triggered in the presence of a chemical source of NO, diethylenetriamine/nitric oxide (DETA/NO) in vitro. In vivo results revealed that the gene expression is tumor-targeted, and specific to NO generated by inducible nitric oxide synthase (iNOS) after S. Typhimurium colonization. These results showed that NO was a promising inducer to finely tune the expression of target genes carried by tumor-targeting bacteria.

Targeting of pancreatic cancer cells and stromal cells using engineered oncolytic Salmonella typhimurium.

Pancreatic cancer is resistant to conventional therapeutic interventions, mainly due to abundant cancer stromal cells and poor immune cell infiltration. Here, we used a targeted cancer therapy approach based on attenuated Salmonella typhimurium engineered to express cytolysin A (ClyA) to target cancer stromal cells and cancer cells and treat pancreatic cancer in mice. Nude mice bearing subcutaneous or orthotopic human pancreatic cancers were treated with engineered S. typhimurium expressing ClyA. The tumor microenvironment was monitored to analyze stromal cell numbers, stromal cell marker expression, and immune cell infiltration. The attenuated bacteria accumulated and proliferated specifically in tumor tissues after intravenous injection. The bacteria secreted ClyA into the tumor microenvironment. A single dose of ClyA-expressing Salmonella markedly inhibited growth of pancreatic cancer both in subcutaneous xenograft- and orthotopic tumor-bearing nude mice. Histological analysis revealed a marked decrease in expression of stromal cell markers and increased immune cell (neutrophils and macrophages) infiltration into tumors after colonization by ClyA-expressing bacteria. ClyA-expressing S. typhimurium destroyed cancer stromal cells and cancer cells in mouse models of human pancreatic cancer. This approach provides a novel strategy for combining anticancer and anti-stromal therapy to treat pancreatic cancer.

Bacteria-cancer interactions: bacteria-based cancer therapy.

Recent advances in cancer therapeutics, such as targeted therapy and immunotherapy, have raised the hope for cures for many cancer types. However, there are still ongoing challenges to the pursuit of novel therapeutic approaches, including high toxicity to normal tissue and cells, difficulties in treating deep tumor tissue, and the possibility of drug resistance in tumor cells. The use of live tumor-targeting bacteria provides a unique therapeutic option that meets these challenges. Compared with most other therapeutics, tumor-targeting bacteria have versatile capabilities for suppressing cancer. Bacteria preferentially accumulate and proliferate within tumors, where they can initiate antitumor immune responses. Bacteria can be further programmed via simple genetic manipulation or sophisticated synthetic bioengineering to produce and deliver anticancer agents based on clinical needs. Therapeutic approaches using live tumor-targeting bacteria can be applied either as a monotherapy or in combination with other anticancer therapies to achieve better clinical outcomes. In this review, we introduce and summarize the potential benefits and challenges of this anticancer approach. We further discuss how live bacteria interact with tumor microenvironments to induce tumor regression. We also provide examples of different methods for engineering bacteria to improve efficacy and safety. Finally, we introduce past and ongoing clinical trials involving tumor-targeting bacteria.

Affibody-functionalized Ag2S quantum dots for photoacoustic imaging of epidermal growth factor receptor overexpressed tumors.

Photoacoustic imaging (PAI) is a new and attractive imaging modality, and it has strong potential for application in the early detection of tumors through the use of optically absorbing targeted contrast agents. Ag2S quantum dots (QD) are a promising bionanomaterial and have attracted significant attention in the field of bioimaging. In this study, water-soluble and carboxylic acid group-coated Ag2S QDs with an ultrasmall size (∼8 nm) were synthesized via a one-step method. Their surface plasmon resonance wavelength was determined to be ∼800 nm, which is ideal for PAI. Ag2S QDs were then modified with the epidermal growth factor receptor 1 (EGFR) targeted small protein affibody ZEGFR:1907. The resulted nanoprobe, ZEGFR:1907-Ag2S QDs, was then used for targeted PAI of EGFR-overexpressed tumors. The biodistribution of the nanoprobe was further measured by ex vivo near infrared fluorescence (NIRF) imaging of the dissected tissues. The PAI results showed that ZEGFR:1907-Ag2S QDs specifically image EGFR positive tumors. The biodistribution study revealed that the nanoprobe mainly accumulated in the liver, spleen and tumors; tissue H&E staining studies indicated that the probe has good biocompatibility. Overall, the affibody-functionalized Ag2S QDs are a novel targeted nanoprobe that can be used for specific PAI of tumors.

Tumor-Targeting Peptides: Ligands for Molecular Imaging and Therapy.

The aberrant proliferation of tumor cells and abundant vasculature in tumor tissues are closely correlated with receptors that are specifically dysregulated in tumor cells. These tumor-associated targets are critical in early diagnosis and therapy selection. Ligands such as antibodies, proteins, polypeptides and polysaccharides that specifically bind to these targets can significantly improve the detection and cure rate when used as tumor imaging probes or anti-tumor agents. Compared to other targeting ligands, peptides have attracted increasingly more attention in tumor diagnostics and therapeutics because of their small sizes, high affinity, stability, ease of modification and low immunogenicity. Several peptide-based imaging probes and therapeutic agents have already been used in clinical trials. This review summarizes some of the tumor-associated targets and their corresponding peptides, as well as the potential of these peptides in cancer treatment.

Multifunctional BSA-Au nanostars for photoacoustic imaging and X-ray computed tomography.

We report the synthesis and characterization of bovine serum albumin-capped Au nanostars (BSA-AuNSs) for dual-modal computed tomography (CT)/photoacoustic (PA) imaging application. The BSA-AuNSs have an average size of 85nm, and a surface plasmon resonance (SPR) peak at approximately 770nm. They have excellent biocompatibility, good X-ray attenuation, and great PA contrast enhancement properties. When injected intravenously, liver signal markedly increases in both CT and PA modalities. The in vivo biodistribution studies and pathology results showed that the BSA-AuNSs were mainly excreted through the liver and intestines with no obvious biotoxicity. These results indicate that BSA-AuNSs have high potential to be used as dual-modal CT/PA imaging contrast agents or further used to develop targeted probes. This preliminary study suggests that PA tomography may be used to non-invasively trace the kinetics and biodistribution of the nanoparticles.