Laser-induced microjet injection into preablated skin for more effective transdermal drug delivery.

A breakthrough in the efficient transdermal delivery of drug via the laser-driven microjet is reported. A single source of laser beam is split into two: one beam ablates a targeted spot on a skin and another beam drives the injector for fast microjet ejection into a preablated spot. This combined ablation and microjet injection scheme using a beam splitter utilizes laser energy sharing between generation of the microhole via ablation and the microjet which is generated using the Er:YAG laser beam at a 2940-nm wavelength and pulse duration. A careful analysis of the injection mechanism is carried out by studying the response of the elastic membrane that separates a driving water unit for bubble expansion from a drug unit for a microjet ejection. The efficiency of the present delivery scheme is evaluated by the abdominal porcine skin test using the fluorescein isothiocyanate staining and the confocal microscopy for quantitative delivery confirmation. The depth of penetration and the injected volume of the drug are also confirmed by polyacrylamide gel tests.

Towards clinical use of a laser-induced microjet system aimed at reliable and safe drug delivery.

An Er:YAG laser with 2940-nm wavelength and 250-µs pulse duration is used to generate a microjet that is ejected at ∼50 m/s in air. The strength of the microjet depends on the bubble dynamics from the beam-water interaction within the driving chamber as well as the discharging of the drug solution underneath the elastic membrane that separates the drug from the driving liquid. The jet characteristics, such as velocity, volume, and level of atomization, are obtained by high-speed camera images taken at 42,000 fps. The enhancements in jet volume (dosage) and repeated jet generation, which are aimed at making the injector suitable for general clinical applications, are achieved. The generation of repeated microjets is achieved with the help of a stepping motor that provides a uniform pressure within the drug reservoir before an ejection occurs through a micro nozzle. Also, two types of human growth hormones are used for monitoring any potential thermal damage to the drug solution due to a repeated laser ablation when driving the microjet. We provide strong evidence to support that the drugs, as they are injected to porcine skins, are free of the damage associated with the present delivery method.

Involvement of the Nrf2-proteasome pathway in the endoplasmic reticulum stress response in pancreatic ß-cells.

The ubiquitin-proteasome system plays a central role in protein quality control through endoplasmic reticulum (ER)-associated degradation (ERAD) of unfolded and misfolded proteins. NF-E2-related factor 2 (Nrf2) is a transcription factor that controls the expression of an array of phase II detoxification and antioxidant genes. Nrf2 signaling has additionally been shown to upregulate the expression of the proteasome catalytic subunits in several cell types. Here, we investigated the role of Nrf2 in tunicamycin-induced ER stress using a murine insulinoma ß-cell line, ßTC-6. shRNA-mediated silencing of Nrf2 expression in ßTC-6 cells significantly increased tunicamycin-induced cytotoxicity, elevated the expression of the pro-apoptotic ER stress marker Chop10, and inhibited tunicamycin-inducible expression of the proteasomal catalytic subunits Psmb5 and Psmb6. The effects of 3H-1,2-dithiole-3-thione (D3T), a small molecule Nrf2 activator, on ER stress were also examined in ßTC-6 cells. D3T pretreatment reduced tunicamycin cytotoxicity and attenuated the tunicamycin-inducible Chop10 and protein kinase RNA-activated-like ER kinase (Perk). The protective effect of D3T was shown to be associated with increased ERAD. D3T increased the expression of Psmb5 and Psmb6 and elevated chymotrypsin-like peptidase activity; proteasome inhibitor treatment blocked D3T effects on tunicamycin cytotoxicity and ER stress marker changes. Similarly, silencing of Nrf2 abolished the protective effect of D3T against ER stress. These results indicate that the Nrf2 pathway contributes to the ER stress response in pancreatic ß-cells by enhancing proteasome-mediated ERAD.

NRF2 blockade suppresses colon tumor angiogenesis by inhibiting hypoxia-induced activation of HIF-1α.

Transcription factor NRF2 is an important modifier of cellular responses to oxidative stress. Although its cytoprotective effects are firmly established, recent evidence suggesting important roles in cancer pathobiology has yet to be mechanistically developed. In the current study, we investigated the role of NRF2 in colon tumor angiogenesis. Stable RNAi-mediated knockdown of NRF2 in human colon cancer cells suppressed tumor growth in mouse xenograft settings with a concomitant reduction in blood vessel formation and VEGF expression. Similar antiangiogenic effects of NRF2 knockdown were documented in chick chorioallantoic membrane assays and endothelial tube formation assays. Notably, NRF2-inhibited cancer cells failed to accumulate HIF-1α protein under hypoxic conditions, limiting expression of VEGF and other HIF-1α target genes. In these cells, HIF-1α was hydroxylated but pharmacological inhibition of PHD domain-containing prolyl hydroxylases was sufficient to restore hypoxia-induced accumulation of HIF-1α. Mechanistic investigations demonstrated that reduced mitochondrial O(2) consumption in NRF2-inhibited cells was probably responsible for HIF-1α degradation during hypoxia; cellular O(2) consumption and ATP production were lower in NRF2 knockdown cells than in control cells. Our findings offer novel insights into how cellular responses to O(2) and oxidative stress are integrated in cancer cells, and they highlight NRF2 as a candidate molecular target to control tumor angiogenesis by imposing a blockade to HIF-1α signaling.

Recognition and accommodation at the androgen receptor coactivator binding interface.

Prostate cancer is a leading killer of men in the industrialized world. Underlying this disease is the aberrant action of the androgen receptor (AR). AR is distinguished from other nuclear receptors in that after hormone binding, it preferentially responds to a specialized set of coactivators bearing aromatic-rich motifs, while responding poorly to coactivators bearing the leucine-rich "NR box" motifs favored by other nuclear receptors. Under normal conditions, interactions with these AR-specific coactivators through aromatic-rich motifs underlie targeted gene transcription. However, during prostate cancer, abnormal association with such coactivators, as well as with coactivators containing canonical leucine-rich motifs, promotes disease progression. To understand the paradox of this unusual selectivity, we have derived a complete set of peptide motifs that interact with AR using phage display. Binding affinities were measured for a selected set of these peptides and their interactions with AR determined by X-ray crystallography. Structures of AR in complex with FxxLF, LxxLL, FxxLW, WxxLF, WxxVW, FxxFF, and FxxYF motifs reveal a changing surface of the AR coactivator binding interface that permits accommodation of both AR-specific aromatic-rich motifs and canonical leucine-rich motifs. Induced fit provides perfect mating of the motifs representing the known family of AR coactivators and suggests a framework for the design of AR coactivator antagonists.

The extended interactions and Gla domain of blood coagulation factor Xa.

The serine protease factor Xa (FXa) is inhibited by ecotin with picomolar affinity. The structure of the tetrameric complex of ecotin variant M84R (M84R) with FXa has been determined to 2.8 A. Substrate directed induced fit of the binding interactions at the S2 and S4 pockets modulates the discrimination of the protease. Specifically, the Tyr at position 99 of FXa changes its conformation with respect to incoming ligand, changing the size of the S2 and S4 pockets. The role of residue 192 in substrate and inhibitor recognition is also examined. Gln 192 from FXa forms a hydrogen bond with the P2 carbonyl group of ecotin. This confirms previous biochemical and structural analyses on thrombin and activated protein C, which suggested that residue 192 may play a more general role in mediating the interactions between coagulation proteases and their inhibitors. The structure of ecotin M84R-FXa (M84R-FXa) also reveals the structure of the Gla domain in the presence of Mg(2+). The first 11 residues of the domain assume a novel conformation and likely represent an intermediate folding state of the domain.