We demonstrate here the effective delivery of a dye payload into cells using 2-nm core gold nanoparticles, with release occurring via place exchange of glutathione onto the particle surface. In vitro experiments demonstrate effective release of drug analogues upon addition of glutathione. Cell culture experiments show rapid uptake of nanoparticle and effective release of payload. The role of glutathione in the release process was demonstrated through improved payload release upon transient increase in glutathione levels achieved via introduction of glutathione ethyl ester into the cell.

Nanoparticles have great potential as controllable drug delivery vehicles because of their size and modular functionality. Timing and location are important parameters when optimizing nanoparticles for delivery of chemotherapeutics. Here we show that positively- and negatively-charged gold nanoparticles carrying either fluorescein or doxorubicin molecules move and localize differently in an in vitro three dimensional model of tumour tissue. Fluorescence microcopy and mathematical modelling showed that uptake, and not diffusion, is the dominant mechanism in particle delivery. Our results suggest that positive particles may be more effective for drug delivery because they are more significantly taken up by proliferating cells. Negative particles, which diffused faster, may perform better when delivering drugs deep into the tissues. An understanding of how surface charge can control tissue penetration and drug release may overcome some of the current limitations in drug delivery.

Platform chemicals composed of 2–6 carbons derived from fossil resources are used as important precursors for making a variety of chemicals and materials, including solvents, fuels, polymers, pharmaceuticals, perfumes, and foods. Due to concerns regarding our environment and the limited nature of fossil resources, however, increasing interest has focused on the development of sustainable technologies for producing these platform chemicals from renewable resources. The techniques and strategies for developing microbial strains for chemicals production have advanced rapidly, and it is becoming feasible to develop microbes for producing additional types of chemicals, including non‐natural molecules. In this study, we review the current status of the bio‐based production of major C2–C6 platform chemicals, focusing on the microbial production of platform chemicals that have been used for the production of chemical intermediates, building block compounds, and polymers. Biotechnol. Bioeng. 2012; 109: 2437–2459. © 2012 Wiley Periodicals, Inc.

Light and life: A photolabile gold nanoparticle has been constructed to serve as a DNA carrier. UV irradiation causes the reversal of the nanoparticle surface charge, resulting in effective DNA release and reactivation of suppressed DNA transcription in vitro. This effect was also observed in living cells, together with efficient internalization of DNA into the nucleus.

No abstract

Phenol is an industrially versatile commodity chemical and is currently produced from fossil resources. Phenol's biological production from renewable resources has been limited due to its toxicity to microorganisms. Here, we simultaneously engineered 18 Escherichia coli strains for the production of phenol using synthetic regulatory small RNA (sRNA) technology. sRNA-based knock-down of the two regulators and overexpression of the genes involved in the tyrosine biosynthetic pathway together with tyrosine phenol-lyase (TPL) in E. coli strains resulted in the production of phenol from glucose. The 18 engineered E. coli strains showed significant differences in the production of tyrosine (i.e. the immediate precursor for phenol), TPL activity, and tolerance to phenol. Among the engineered E. coli strains, the BL21 strain produced phenol most efficiently: 419 mg/L by flask culture and 1.69 g/L by fed-batch culture. The final titer and productivity were further improved through biphasic fed-batch fermentation using glycerol tributyrate as an extractant of phenol. The concentration of phenol in the glycerol tributyrate phase and fermentation broth reached 9.84 and 0.3 g/L, respectively, in 21 hours, which translates into the final phenol titer and productivity of 3.79 g/L and 0.18 g/L/h, respectively. This is the highest titer achieved by microbial fermentation. Although further engineering is required to be competitive with the current petro-based process, the strategies used for the development of the engineered strain and fermentation process will provide a valuable framework for the microbial production of toxic chemicals.

No abstract

Heterogeneous metabolic microenvironments in tumors affect local cell growth, survival, and overall therapeutic efficacy. Hypoxia-inducible-factor-1alpha (HIF-1alpha) is a transcription factor that responds to low-oxygen environments by upregulating genes for cell survival and metabolism. To date, the metabolic effects of HIF-1alpha in three-dimensional tissue have not been investigated. Preliminary experiments have shown that the effects of HIF-1alpha are dependent on glucose availability. Based on this observation, we hypothesized that HIF-1alpha would not affect cell survival and metabolism in the center of spheroids, where the concentrations of oxygen and glucose are low, similar to hypoxic regions found in tumors. To test this hypothesis we used fluorescence microscopy and the tumor cylindroid model to quantify cellular viability in three-dimensional tissue. Isotope labeling and metabolic flux analysis were also used to quantity the intracellular metabolism of wild-type and HIF-1alpha-null spheroids. As hypothesized, cell survival and intracellular metabolism were not different between wild-type and HIF-1alpha-null tissues. In addition, small spheroids, which contain less quiescent cells and are less nutritionally limited, were found to have increased carbon flux through the biosynthetic pentose phosphate and pyruvate carboxylase pathways. These results show how nutrient gradients affect cell growth and metabolism in spheroids and suggest that metabolic microenvironment should be taken into account when developing HIF-1alpha-based therapies.