Regulation of Transgene Expression by the Natural Sweetener Xylose

Abstract

Next‐generation gene and engineered‐cell therapies benefit from incorporating synthetic gene networks that can precisely regulate the therapeutic output in response to externally administered signal inputs that are safe, readily bioavailable and pleasant to take. To enable such therapeutic control, a mammalian gene switch is designed to be responsive to the natural sweetener xylose and its functionality is assessed in mouse studies. The gene switch consists of the bacterial transcription regulator XylR fused to a mammalian transactivator, which binds to an optimized promoter in the presence of xylose, thereby allowing dose‐dependent transgene expression. The sensitivity of SWEET (sweetener‐inducible expression of transgene) is improved by coexpressing a xylose transporter. Mice implanted with encapsulated SWEET‐engineered cells show increased blood levels of cargo protein when taking xylose‐sweetened water or coffee, or highly concentrated apple extract, while they do not respond to intake of a usual amount of carrots, which contain xylose. In a proof‐of‐concept therapeutic application study, type‐1 diabetic mice engineered with insulin‐expressing SWEET show lowered glycemia and increased insulin levels when administered this fairly diabetic‐compliant sweetener, compared to untreated mice. A SWEET‐based therapy appears to have the potential to integrate seamlessly into patients’ life‐style and food habits in the move toward personalized medicine.

Synthetic Gene Circuits for Regulation of Next‐Generation Cell‐Based Therapeutics

“…Genetically engineered human cells have also been explored as therapeutic agents for an array of diseases other than cancer, such as diabetes, [6,7,9,14,18,21,36,50,154] gouty arthritis, [155] methicillinresistant Staphylococcus aureus infection, [156] and psoriasis, [157] among others. [2] While these studies have demonstrated promise in preclinical settings, the cells have not yet been developed for clinical use.…”

“…[75] Leveraging these molecular elements, we have recently introduced two new orthogonal gene switches that offer tight control in response to xylose or gluconate. [6,7] The expression of heterologous transporters for each metabolite en-hanced their uptake by mammalian cells, establishing highly sensitive gene switches that respond effectively in the lower micromolar range (Figure 3b). The practical application of these gene switches for regulation of transgene expression was demonstrated in mouse studies.…”

“…In response, signaling cascades are initiated, culminating in tailored therapeutic actions aimed at maintaining the signal within a normal physiological range. [3][4][5] External molecular signals primarily involve small molecules, [6][7][8][9][10] but also extend to oligonucleotides [11] and peptides or proteins, [12,13] while physical signals span light of various wavelengths, [14][15][16] electrical currents, [17,18] temperature variations, [19,20] and mechanical forces. [21,22] Within the realm of molecular signals, small molecules offer several advantages, including oral administration, lower production costs, good cell membrane permeability, and immune system evasion.…”

“…[21,22] Within the realm of molecular signals, small molecules offer several advantages, including oral administration, lower production costs, good cell membrane permeability, and immune system evasion. A wide range of small molecules have been used to control protein or mRNA levels in human cells, including ligands for natural or chimeric receptors, [5] ligands for bacterial transcription factors (TFs), [6,7,9] protein dimerization inducers, [23,24] protein degradation inducers, [25,26] riboswitch modulators, [27][28][29] and viral protease inhibitors. [8,30,31] Conversely, actuation via physical signals can also offer several benefits for in vivo regulation of protein expression/activity.…”

A Gene‐Switch Platform Interfacing with Reactive Oxygen Species Enables Transcription Fine‐Tuning by Soluble and Volatile Pharmacologics and Food Additives

“…Synthetic biology has dramatically advanced the rational design and engineering of trigger‐inducible gene switches that enable programming of novel cellular behaviors. For example, in recent years, numerous synthetic gene circuits have been developed that respond to small‐molecular drugs, [ 1 , 2 , 3 ] compounds naturally present in fruits or vegetables, [ 4 , 5 , 6 ] or supplements added during food processing, [ 7 , 8 , 9 ] as well as physical stimuli [ 10 , 11 , 12 , 13 ] to drive therapeutic protein expression in mammalian cells in a dose‐ and spatiotemporally‐controlled manner. [ 14 ] Small‐molecule‐regulated transgene switches offer many advantages, such as easy administration, good reversibility, and scalability.…”