Picoliter-volume inkjet printing into planar microdevice reservoirs for low-waste, high-capacity drug loading

Oral delivery of therapeutics is the preferred route for systemic drug administration due to ease of access and improved patient compliance. However, many therapeutics suffer from low oral bioavailability due to low pH and enzymatic conditions, poor cellular permeability, and low residence time. Microfabrication techniques have been used to create planar, asymmetric microdevices for oral drug delivery to address these limitations. The geometry of these microdevices facilitates prolonged drug exposure with unidirectional release of drug toward gastrointestinal epithelium. While these devices have significantly enhanced drug permeability in vitro and in vivo, loading drug into the micron-scale reservoirs of the devices in a low-waste, high-capacity manner remains challenging. Here, we use picoliter-volume inkjet printing to load topotecan and insulin into planar microdevices efficiently. Following a simple surface functionalization step, drug solution can be spotted into the microdevice reservoir. We show that relatively high capacities of both topotecan and insulin can be loaded into microdevices in a rapid, automated process with little to no drug waste.

Fabrication of Sealed Nanostraw Microdevices for Oral Drug Delivery

The oral route is preferred for systemic drug administration and provides direct access to diseased tissue of the gastrointestinal (GI) tract. However, many drugs have poor absorption upon oral administration due to damaging enzymatic and pH conditions, mucus and cellular permeation barriers, and limited time for drug dissolution. To overcome these limitations and enhance oral drug absorption, micron-scale devices with planar, asymmetric geometries, termed microdevices, have been designed to adhere to the lining of the GI tract and release drug at high concentrations directly toward GI epithelium. Here we seal microdevices with nanostraw membranes-porous nanostructured biomolecule delivery substrates-to enhance the properties of these devices. We demonstrate that the nanostraws facilitate facile drug loading and tunable drug release, limit the influx of external molecules into the sealed drug reservoir, and increase the adhesion of devices to epithelial tissue. These findings highlight the potential of nanostraw microdevices to enhance the oral absorption of a wide range of therapeutics by binding to the lining of the GI tract, providing prolonged and proximal drug release, and reducing the exposure of their payload to drug-degrading biomolecules.

Miniaturized iPS-Cell-Derived Cardiac Muscles for Physiologically Relevant Drug Response Analyses

Tissue engineering approaches have the potential to increase the physiologic relevance of human iPS-derived cells, such as cardiomyocytes (iPS-CM). However, forming Engineered Heart Muscle (EHM) typically requires >1 million cells per tissue. Existing miniaturization strategies involve complex approaches not amenable to mass production, limiting the ability to use EHM for iPS-based disease modeling and drug screening. Micro-scale cardiospheres are easily produced, but do not facilitate assembly of elongated muscle or direct force measurements. Here we describe an approach that combines features of EHM and cardiospheres: Micro-Heart Muscle (μHM) arrays, in which elongated muscle fibers are formed in an easily fabricated template, with as few as 2,000 iPS-CM per individual tissue. Within μHM, iPS-CM exhibit uniaxial contractility and alignment, robust sarcomere assembly, and reduced variability and hypersensitivity in drug responsiveness, compared to monolayers with the same cellular composition. μHM mounted onto standard force measurement apparatus exhibited a robust Frank-Starling response to external stretch, and a dose-dependent inotropic response to the β-adrenergic agonist isoproterenol. Based on the ease of fabrication, the potential for mass production and the small number of cells required to form μHM, this system provides a potentially powerful tool to study cardiomyocyte maturation, disease and cardiotoxicology in vitro.

Micro/nanofabricated platforms for oral drug delivery

The oral route of drug administration is most preferred due to its ease of use, low cost, and high patient compliance. However, the oral uptake of many small molecule drugs and biotherapeutics is limited by various physiological barriers, and, as a result, drugs suffer from issues with low solubility, low permeability, and degradation following oral administration. The flexibility of micro- and nanofabrication techniques has been used to create drug delivery platforms designed to address these barriers to oral drug uptake. Specifically, micro/nanofabricated devices have been designed with planar, asymmetric geometries to promote device adhesion and unidirectional drug release toward epithelial tissue, thereby prolonging drug exposure and increasing drug permeation. Furthermore, surface functionalization, nanotopography, responsive drug release, motion-based responses, and permeation enhancers have been incorporated into such platforms to further enhance drug uptake. This review will outline the application of micro/nanotechnology to specifically address the physiological barriers to oral drug delivery and highlight technologies that may be incorporated into these oral drug delivery systems to further enhance drug uptake.

Planar bioadhesive microdevices: a new technology for oral drug delivery

The oral route is the most convenient and least expensive route of drug administration. Yet, it is accompanied by many physiological barriers to drug uptake including low stomach pH, intestinal enzymes and transporters, mucosal barriers, and high intestinal fluid shear. While many drug delivery systems have been developed for oral drug administration, the physiological components of the gastro intestinal tract remain formidable barriers to drug uptake. Recently, microfabrication techniques have been applied to create micron-scale devices for oral drug delivery with a high degree of control over microdevice size, shape, chemical composition, drug release profile, and targeting ability. With precise control over device properties, microdevices can be fabricated with characteristics that provide increased adhesion for prolonged drug exposure, unidirectional release which serves to avoid luminal drug loss and enhance drug permeation, and protection of a drug payload from the harsh environment of the intestinal tract. Here we review the recent developments in microdevice technology and discuss the potential of these devices to overcome unsolved challenges in oral drug delivery.

Fabrication of micropatterned polymeric nanowire arrays for high-resolution reagent localization and topographical cellular control

Herein, we present a novel approach for the fabrication of micropatterned polymeric nanowire arrays that addresses the current need for scalable and customizable polymer nanofabrication. We describe two variations of this approach for the patterning of nanowire arrays on either flat polymeric films or discrete polymeric microstructures and go on to investigate biological applications for the resulting polymeric features. We demonstrate that the micropatterned arrays of densely packed nanowires facilitate rapid, low-waste drug and reagent localization with micron-scale resolution as a result of their high wettability. We also show that micropatterned nanowire arrays provide hierarchical cellular control by simultaneously directing cell shape on the micron scale and influencing focal adhesion formation on the nanoscale. This nanofabrication approach has potential applications in scaffold-based cellular control, biological assay miniaturization, and biomedical microdevice technology.

Planar microdevices for enhanced in vivo retention and oral bioavailability of poorly permeable drugs

The development of novel oral drug delivery platforms for administering therapeutics in a safe and effective manner through the harsh gastrointestinal environment is of great importance. Here, the use of engineered thin planar poly(methyl methacrylate) (PMMA) microdevices is tested to enhance oral bioavailability of acyclovir, a poorly permeable drug. Acyclovir is loaded into the unidirectional drug releasing microdevice reservoirs using a drug entrapping photocross-linkable hydrogel matrix. An increase in acyclovir permeation across in vitro caco-2 monolayer is seen in the presence of microdevices as compared with acyclovir-entrapped hydrogels or free acyclovir solution. Cell proliferation studies show that microdevices are relatively nontoxic in nature for use in in vivo studies. Enhanced in vivo retention of microdevices is observed as their thin side walls experience minimal peristaltic shear stress as compared with spherical microparticles. Unidirectional acyclovir release and enhanced retention of microdevices achieve a 4.5-fold increase in bioavailability in vivo as compared with an oral gavage of acyclovir solution with the same drug mass. The enhanced oral bioavailability results suggest that thin, planar, bioadhesive, and unidirectional drug releasing microdevices will significantly improve the systemic and localized delivery of a broad range of oral therapeutics in the near future.

Changes in solvent accessibility of wild-type and deamidated βB2-crystallin following complex formation with αA-crystallin

Aberrant protein interactions can lead to aggregation and insolubilization, such as occurs during cataract formation. Deamidation, a prevalent age-related modification in the lens of the eye, decreases stability of the major lens proteins, crystallins. The mechanism of deamidation altering interactions between αA-crystallin and βB2-crystallin was investigated by detecting changes in solvent accessibility upon complex formation during heating. Solvent accessibility was determined by measuring hydrogen/deuterium exchange levels of backbone amides by high-resolution mass spectrometry. Deuterium levels in wild type βB2-crystallin increased 50-60% in both domains following complex formation with αA-crystallin. This increased solvent accessibility indicated a general loosening along the backbone amides. Peptides with the greatest deuterium increases were located at the buried monomer-monomer interface, suggesting that the βB2 dimer was disrupted. The only region where the deuterium levels decreased was in βB2 peptide 123-139, containing an outside loop, and may be a potential site of interaction with αA. Mimicking deamidation at the βB2 dimer interface prevented complex formation with αA. When temperatures were lowered, an αA/βB2 Q70E/Q162E complex formed with similar solvent accessibilities as αA/WT βB2. Deamidation did not disrupt specific αA/βB2 interactions but favored aggregation before complex formation with αA. We conclude that deamidation contributes to cataract formation through destabilization of crystallins before they can be rescued by α-crystallin.

(1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol: a potent new neuroprotectant which blocks N-methyl-D-aspartate responses

(1S,2S)-1-(4-Hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (20, CP-101,606) has been identified as a potent and selective N-methyl-D-aspartate (NMDA) antagonist through a structure activity relation (SAR) program based on ifenprodil, a known antihypertensive agent with NMDA antagonist activity. Sites on the threo-ifenprodil skeleton explored in this report include the pendent methyl group (H, methyl, and ethyl nearly equipotent; propyl much weaker), the spacer group connecting the C-4 phenyl group to the piperidine ring (an alternating potency pattern with 0 and 2 carbon atoms yielding the greatest potency), and simple phenyl substitution (little effect). While potent NMDA antagonists were obtained with a two atom spacer, this arrangement also increased alpha 1 adrenergic affinity. Introduction of a hydroxyl group into the C-4 position on these piperidine ring resulted in substantial reduction in alpha 1 adrenergic affinity. The combination of these observations was instrumental in the discovery of 20. This compound potently protects cultured hippocampal neurons from glutamate toxicity (IC50 = 10 nM) while possessing little of the undesired alpha 1 adrenergic affinity (IC50 approximately 20 microM) of ifenprodil. Furthermore, 20 appears to lack the psychomotor stimulant effects of nonselective competitive and channel-blocking NMDA antagonists. Thus, 20 shows great promise as a neuroprotective agent and may lack the side effects of compounds currently in clinical trials.

1-(2-Aminoethyl)-3-methyl-8,9-dihydropyrano[3,2-e]indole: a rotationally restricted phenolic analog of the neurotransmitter serotonin and agonist selective for serotonin (5-HT2-type) receptors

A series of rotationally restricted phenolic analogs of the neurotransmitter serotonin has been synthesized with the 5-hydroxyindole portion of serotonin replaced by a dihydropyrano[3,2-e]-indole (1, 3, 4, and 5) and a dihydropyrano[2,3-f]indole (2). The receptor binding profile of these compounds has been studied and compared to the natural substrate serotonin. The dihydropyrano[3,2-e]indole derivatives (1, 3, 4, and 5) possess lower affinity for 5-HT1 receptors but equal or greater affinity for 5-HT2 receptors. Like serotonin, these compounds dose-dependently stimulated phosphatidylinositol turnover in rat brain slices. Moreover, the response to 1-(2-aminoethyl)-3-methyl-8,9-dihydropyrano[3,2-]indole (5, CP-132,484) and 1-(2-aminoethyl)-8,9-dihydropyrano[3,2-e]indole (4) is selectively antagonized by 5-HT2 receptor antagonists establishing these tryptamines as selective 5-HT2 receptor agonists. The high affinity and potency of 5 for 5-HT2 receptors suggests that the C5-hydroxy group in serotonin can function as a hydrogen bond acceptor in a 5-HT2 receptor with a directionality of interaction which is down and away from C6 in serotonin (Figure 5). Furthermore, the potent affinity of these compounds for 5-HT2 receptors coupled with their poor affinity for 5-HT1 receptors indicates that the aminoethyl side chain of serotonin adopts significantly different conformations in 5-HT1 versus 5-HT2 receptors.

Characterization of [3H]CP-96,501 as a selective radioligand for the serotonin 5-HT1B receptor: binding studies in rat brain membranes

3-(1,2,5,6-Tetrahydro-4-pyridyl)-5-n-propoxyindole (CP-96,501) was found to be more selective ligand at the serotonin 5-HT1B receptor than the commonly used 5-HT1B agonist, 3-(1,2,5,6-tetrahydro-4-pyridyl)-5-methoxyindole (RU 24969). In rat brain membranes, the tritiated derivative, [3H]CP-96,501, was found to bind with a high affinity (KD, 0.21 nM) to a single binding site (nH, 1.0). The receptor density of this site (Bmax, 72 fmol/mg of protein) matched that of the 5-HT1B receptor determined with [3H]5-HT. Competition curves of 16 serotonergic compounds in [3H]CP-96,501 binding also indicated a single binding site. The rank order of their binding affinities with this new radioligand showed a high degree of correlation with their affinities at the 5-HT1B receptor determined with [3H]5-HT or [125I]iodocyanopindolol. Serotonergic compounds displayed competitive inhibition of [3H]CP-96,501 binding. In the presence of 5'-guanylylimidodiphosphate [Gpp(NH)p], [3H]CP-96,501 to displace [125I]iodocyanopindolol binding was also decreased. These findings are consistent with the agonist nature of CP-96,501. The results of this study suggest that [3H]CP-96,501 is a useful agonist radioligand for the 5-HT1B receptor.

Separation of alpha 1 adrenergic and N-methyl-D-aspartate antagonist activity in a series of ifenprodil compounds

Ifenprodil (1) represents a new class of N-methyl-D-aspartate (NMDA) antagonist. This drug also possesses potent activity at several other brain receptors (most notably alpha 1 adrenergic receptors). We have prepared the enantiomers and diastereomers of ifenprodil along with a series of partial structures in order to explore the basic structure activity relations within this class of compounds. From this study, it is clear that alpha 1 adrenergic and NMDA receptor activities may be separated by selection of the threo relative stereochemistry. Examination of the optical isomers of threo-ifenprodil (2) reveals that no further improvement in receptor selectivity is gained from either antipode. Individual removal of most of the structural fragments from the ifenprodil molecule generally results in less active compounds although fluorinated derivative 9 with threo relative stereochemistry is somewhat more potent and substantially more selective for the NMDA receptor. Finally a minimum structure for activity in this series (14) has been identified. This stripped-down version of ifenprodil possesses nearly equivalent affinity for the NMDA receptor with no selectivity over alpha 1 adrenergic receptors.