# Microbots Gene Delivery System Based on Bifidobacteria in a Tumor Model
###### Abstract  
In cancer, the use of microbots based on anaerobic bacteria as specific transporters targeting tumor tissues has been explored since most solid tumors exhibit hypoxic regions. The aim of this study was to develop and characterize magnetic microbots based on _Bifidobacteria_ and iron oxide fluorescent magnetic nanoparticles complexed with chitosan and a hypoxia inducible plasmid. In addition, the efficiency of the microbots for gene delivery to solid tumors was evaluated in an in vivo model by florescence and luminescence. To elaborate microbots, iron oxide fluorescent magnetic nanoparticles complexed with chitosan and a hypoxia-inducible plasmid called nanocomplex (NCs) with a size of 302 nm and a \(\zeta\) potential of +16 mV were obtained and loaded onto _Bifidobacteria_ membranes. Microbots with a diameter between 1-2 \(\upmu\)m were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Microbots were injected intravenously through the tail vein to tumor-bearing mice, and then a magnet was placed to focus them to the tumor area. Forty-eight hours after injection, the biodistribution was determined by florescence and luminescence. The greatest luminescence and fluorescence emitted were found in tumor tissue compared with the normal organs. We created a vector that can be directed by a magnet and deliver genes whose expression is regulated by hypoxic microenvironment of tumor.  
hypoxic tumor; magnetic microbot; nanocomplex; gene delivery; target tumor cells +
Footnote †: journal: Medical  
selves, which include chemotaxis, magnetotaxis, galvanotaxis, and phototaxis [9]. [PERSON] and [PERSON] demonstrated the therapeutic effect of microbots to target MCF-7 cancer cells. Those Micobots consisted of a combinatorial approach of the probiotic _Lactobacillus_ spp. with fluorescent cadmium sulfide nanoparticles [11]. In 2013, [PERSON] et al. demonstrated in an in vivo study that the bacteriobots had chemotactic motility and tumor-targeting ability [4].  
Microbots are one of the most effective vehicles for drug delivery systems [9] since they possess the invasive property of bacteria and can selectively colonize the hypoxic regions of the tumor [10].  
Tumor hypoxia is one of the most important obstacles to conventional cancer treatments [12; 13; 14] and, although it is an unfavorable scenario, is used by microbots since its low oxygen microenvironment serves as an ideal habitat [1]. In this study, we show the use of microbots based on Bifidobacterium and magnetic nanoparticles for gene delivery to a tumor in an in vivo model. For this study, NCs of iron oxide fluorescent magnetic nanoparticles, and chitosan (as a protective agent), a DNA plasmid whose gene expression is controlled by a hypoxic microenvironment, were elaborated. The NCs were attached to the Bifidobacterium membrane to form the microbots, which were characterized by AFM and SEM. Subsequently, microbots were injected intravenously through the tail vein to tumor-bearing mice; after 48 h, the organ or tissue with the expression of the transgene was determined. The transgene is highly expressed in tumor tissue. These microbots are biocompatible and comparatively safe.