Nanomotor-Enabled pH-Responsive Intracellular Delivery of Caspase-3: Toward Rapid Cell Apoptosis

Direct and efficient intracellular delivery of enzymes to cytosol holds tremendous therapeutic potential while remaining an unmet technical challenge. Herein, an ultrasound (US)-propelled nanomotor approach and a high-pH-responsive delivery strategy are reported to overcome this challenge using caspase-3 (CASP-3) as a model enzyme. Consisting of a gold nanowire (AuNW) motor with a pH-responsive polymer coating, in which the CASP-3 is loaded, the resulting nanomotor protects the enzyme from release and deactivation prior to reaching an intracellular environment. However, upon entering a cell and exposure to the higher intracellular pH, the polymer coating is dissolved, thereby directly releasing the active CASP-3 enzyme to the cytosol and causing rapid cell apoptosis. <i>In vitro</i> studies using gastric cancer cells as a model cell line demonstrate that such a motion-based active delivery approach leads to remarkably high apoptosis efficiency within a significantly shorter time and with a lower amount of CASP-3 compared to other control groups not involving US-propelled nanomotors. For instance, the reported nanomotor system can achieve 80% apoptosis of human gastric adenocarcinoma cells within only 5 min, which dramatically outperforms other CASP-3 delivery approaches. These results indicate that the US-propelled nanomotors may act as a powerful vehicle for cytosolic delivery of active therapeutic proteins, which would offer an attractive means to enhance the current landscape of intracellular protein delivery and therapy. While CASP-3 is selected as a model protein in this study, the same nanomotor approach can be readily applied to a variety of different therapeutic proteins

Model of therapeutic effect of GM1-NPs.

<p>GM1-coated nanoparticles act as decoys to absorb CT produced by <i>V</i>. <i>cholerae</i> before it can bind to epithelial cells to stimulate cAMP production and epithelial chloride secretion, and inhibit sodium absorption.</p

Nanomotor-Enabled pH-Responsive Intracellular Delivery of Caspase-3: Toward Rapid Cell Apoptosis

Direct and efficient intracellular delivery of enzymes to cytosol holds tremendous therapeutic potential while remaining an unmet technical challenge. Herein, an ultrasound (US)-propelled nanomotor approach and a high-pH-responsive delivery strategy are reported to overcome this challenge using caspase-3 (CASP-3) as a model enzyme. Consisting of a gold nanowire (AuNW) motor with a pH-responsive polymer coating, in which the CASP-3 is loaded, the resulting nanomotor protects the enzyme from release and deactivation prior to reaching an intracellular environment. However, upon entering a cell and exposure to the higher intracellular pH, the polymer coating is dissolved, thereby directly releasing the active CASP-3 enzyme to the cytosol and causing rapid cell apoptosis. <i>In vitro</i> studies using gastric cancer cells as a model cell line demonstrate that such a motion-based active delivery approach leads to remarkably high apoptosis efficiency within a significantly shorter time and with a lower amount of CASP-3 compared to other control groups not involving US-propelled nanomotors. For instance, the reported nanomotor system can achieve 80% apoptosis of human gastric adenocarcinoma cells within only 5 min, which dramatically outperforms other CASP-3 delivery approaches. These results indicate that the US-propelled nanomotors may act as a powerful vehicle for cytosolic delivery of active therapeutic proteins, which would offer an attractive means to enhance the current landscape of intracellular protein delivery and therapy. While CASP-3 is selected as a model protein in this study, the same nanomotor approach can be readily applied to a variety of different therapeutic proteins

Neutralization of CT activity with GM1-NPs.

<p>(A) A fixed concentration (10 ng/mL) of CT was combined with increasing amounts of the indicated nanoparticles, and the mixtures were added to confluent monolayers of human HCA7 intestinal epithelial cells. After 2 h, levels of secreted cAMP were determined in the supernatants by ELISA (n = 3; mean ± SD). (B) A fixed amount (1 μg/mL) of the indicated nanoparticles were combined with increasing concentrations of CT, the mixtures were added to HCA7 monolayers for 2 h, and levels of secreted cAMP levels were measured by ELISA (n = 3; mean ± SD). (C) GM1-NPs or control PEG-NPs were added to HCA7 monolayers, which were then infected for 2 h with live <i>V</i>. <i>cholerae</i> or left uninfected, and secreted cAMP was determined (n = 3; mean ± SD; *p<0.05 vs PEG-NPs).</p

Preparation and physical characterization of GM1-coated nanoparticles.

<p>(A) Schematic of GM1-NP fabrication. Poly(lactic-co-glycolic acid) (PLGA) dissolved in acetonitrile (CH₃CN) is added to an aqueous solution containing GM1. After acetonitrile evaporation, nanoparticles with a polymeric core and a lipid shell are formed. (B) Intensity-weighted size distribution of representative preparations of GM1-NPs and control PEG-NPs, and PLGA-NPs with a PLGA core but without a lipid shell. (C) Zeta potential of the indicated nanoparticle preparations (n = 3; mean ± SD; *p<0.05 vs. PLGA-NPs). (D) Nanoparticle size measurements over two weeks of incubation in distilled water or PBS (n = 3; mean ± SD). (E) Transmission electron micrograph of GM1-NPs.</p

<i>In vivo</i> efficacy of GM1-NPs against CT and live <i>V</i>. <i>cholerae</i>.

<p>(A) Ligated intestinal loops were prepared in the distal small intestine of adult C57BL/6 mice, and injected with PBS as a control, or with 2.5 μg CT, without and with prior addition of GM1-NPs or control PEG-NPs. Fluid accumulation in the loops was determined after 4 h, and related to loop length (each point represents one animal, horizontal lines are geometric means; *p<0.05 vs PEG-NPs). (B) Loops were injected with PBS as a control, or live <i>V</i>. <i>cholerae</i> with GM1-NPs or control PEG-NPs. Fluid accumulation was determined after 16 h (each point represents one animal, horizontal lines are geometric means; *p<0.05 vs PEG-NPs). (C) Images of representative intestinal loops. (D) cAMP was measured in the luminal fluid collected from loops after injection of live <i>V</i>. <i>cholera</i>e with GM1-NPs or control PEG-NPs (n = 3; mean ± SD; *p<0.05 vs PEG-NPs).</p

Functional stability of GM1-NPs in the presence of intestinal luminal factors.

<p>(A) Intensity-weighted size distribution of GM1-NPs incubated 30 min in distilled water or diluted porcine bile solution (1:16 dilution in water). (B) Fluorescence imaging of DiD-labeled GM1-NPs absorbed with FITC-CTB and incubated for 30 min in 1:16 diluted porcine bile solution. (C) GM1-NPs were loaded with FITC-CTB for 30 min, washed, and resuspended in luminal fluid from the small intestine of normal adult mice, or PBS as a control. After incubation for 24 h at 37°C, particle-bound and free FITC-CTB were separated by dialysis, and bound FITC-CTB was measured by fluorescence spectroscopy and related to the initial amount bound (mean ± SD, n = 3). Background readings were obtained with free FITC-CTB without GM1-NPs. (D) Fecal homogenates from mice were mixed 1:1 with GM1-NPs or PEG-NPs in culture media, and incubated for 1 h at 37°C, after which CT (10 ng/mL) was added for an additional 1 h before addition to HCA7 monolayers. After 2 h, cAMP levels in the supernatants were determined by ELISA (mean ± SD, n = 3; *p<0.05 vs PEG-NPs).</p

Modulating Antibacterial Immunity via Bacterial Membrane-Coated Nanoparticles

Synthetic nanoparticles coated with cellular membranes have been increasingly explored to harness natural cell functions toward the development of novel therapeutic strategies. Herein, we report on a unique bacterial membrane-coated nanoparticle system as a new and exciting antibacterial vaccine. Using <i>Escherichia coli</i> as a model pathogen, we collect bacterial outer membrane vesicles (OMVs) and successfully coat them onto small gold nanoparticles (AuNPs) with a diameter of 30 nm. The resulting bacterial membrane-coated AuNPs (BM-AuNPs) show markedly enhanced stability in biological buffer solutions. When injected subcutaneously, the BM-AuNPs induce rapid activation and maturation of dendritic cells in the lymph nodes of the vaccinated mice. In addition, vaccination with BM-AuNPs generates antibody responses that are durable and of higher avidity than those elicited by OMVs only. The BM-AuNPs also induce an elevated production of interferon gamma (INFγ) and interleukin-17 (IL-17), but not interleukin-4 (IL-4), indicating its capability of generating strong Th1 and Th17 biased cell responses against the source bacteria. These observed results demonstrate that using natural bacterial membranes to coat synthetic nanoparticles holds great promise for designing effective antibacterial vaccines

Micromotor Pills as a Dynamic Oral Delivery Platform

Tremendous progress has been made during the past decade toward the design of nano/micromotors with high biocompatibility, multifunctionality, and efficient propulsion in biological fluids, which collectively have led to the initial investigation of <i>in vivo</i> biomedical applications of these synthetic motors. Despite these recent advances in micromotor designs and mechanistic research, significant effort is needed to develop appropriate formulations of micromotors to facilitate their <i>in vivo</i> administration and thus to better test their <i>in vivo</i> applicability. Herein, we present a micromotor pill and demonstrate its attractive use as a platform for <i>in vivo</i> oral delivery of active micromotors. The micromotor pill is comprised of active Mg-based micromotors dispersed uniformly in the pill matrix, containing inactive (lactose/maltose) excipients and other disintegration-aiding (cellulose/starch) additives. Our <i>in vivo</i> studies using a mouse model show that the micromotor pill platform effectively protects and carries the active micromotors to the stomach, enabling their release in a concentrated manner. The micromotor encapsulation and the inactive excipient materials have no effects on the motion of the released micromotors. The released cargo-loaded micromotors propel in gastric fluid, retaining the high-performance characteristics of <i>in vitro</i> micromotors while providing higher cargo retention onto the stomach lining compared to orally administrated free micromotors and passive microparticles. Furthermore, the micromotor pills and the loaded micromotors retain the same characteristics and propulsion behavior after extended storage in harsh conditions. These results illustrate that combining the advantages of traditional pills with the efficient movement of micromotors offer an appealing route for administrating micromotors for potential <i>in vivo</i> biomedical applications

Micromotor Pills as a Dynamic Oral Delivery Platform

Tremendous progress has been made during the past decade toward the design of nano/micromotors with high biocompatibility, multifunctionality, and efficient propulsion in biological fluids, which collectively have led to the initial investigation of <i>in vivo</i> biomedical applications of these synthetic motors. Despite these recent advances in micromotor designs and mechanistic research, significant effort is needed to develop appropriate formulations of micromotors to facilitate their <i>in vivo</i> administration and thus to better test their <i>in vivo</i> applicability. Herein, we present a micromotor pill and demonstrate its attractive use as a platform for <i>in vivo</i> oral delivery of active micromotors. The micromotor pill is comprised of active Mg-based micromotors dispersed uniformly in the pill matrix, containing inactive (lactose/maltose) excipients and other disintegration-aiding (cellulose/starch) additives. Our <i>in vivo</i> studies using a mouse model show that the micromotor pill platform effectively protects and carries the active micromotors to the stomach, enabling their release in a concentrated manner. The micromotor encapsulation and the inactive excipient materials have no effects on the motion of the released micromotors. The released cargo-loaded micromotors propel in gastric fluid, retaining the high-performance characteristics of <i>in vitro</i> micromotors while providing higher cargo retention onto the stomach lining compared to orally administrated free micromotors and passive microparticles. Furthermore, the micromotor pills and the loaded micromotors retain the same characteristics and propulsion behavior after extended storage in harsh conditions. These results illustrate that combining the advantages of traditional pills with the efficient movement of micromotors offer an appealing route for administrating micromotors for potential <i>in vivo</i> biomedical applications