Exploring intracellular fate of drug nanocrystals with crystal-integrated and environment-sensitive fluorophores

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Visualization and correlation of drug release of risperidone/clozapine microspheres in vitro and in vivo based on FRET mechanism

This study addresses the challenging task of quantitatively investigating drug release from PLGA microspheres after in vivo administration. The objective is to employ Förster resonance energy transfer (FRET) to visualize drug-encapsulated microspheres in both in vitro and in vivo settings. The primary goal is to establish a quantitative correlation between FRET fluorescence changes and microsphere drug release. The study selects drugs with diverse structures and lipid solubility to explore release mechanisms, using PLGA as the matrix material. Clozapine and risperidone serve as model drugs. FRET molecules, Cy5 and Cy5.5, along with Cy7 derivatives, create FRET donor-acceptor pairs. In vitro results show that FRET fluorescence changes align closely with microsphere drug release, particularly for the Cy5.5-Cy7 pair. In vivo experiments involve subcutaneous administration of microspheres to rats, tracking FRET fluorescence changes while collecting blood samples. Pharmacokinetic studies on clozapine and risperidone reveal in vivo absorption fractions using the Loo-Riegelman method. Correlating FRET and in vivo absorption data establishes an in vitro-in vivo relationship (IVIVR). The study demonstrates that FRET-based fluorescence changes quantitatively link to microsphere drug release, offering an innovative method for visualizing and monitoring release in both in vitro and in vivo settings, potentially advancing clinical applications of such formulations.

Nanocrystal technologies in biomedical science: From the bench to the clinic

The pharmaceutical industry is grappling with a pressing crisis in drug development characterized by soaring R&D costs, setbacks in blockbuster drug development due to poor aqueous solubility, and patent-related limitations on newly approved molecules. To combat these challenges, diverse strategies have emerged to enhance the solubility and dissolution rates of Biopharmaceutics Classification System (BCS) II and IV drug molecules. Enter drug nanocrystals, a revolutionary nanotechnology-driven, carrier-free colloidal drug delivery system. This review provides a comprehensive insight into nanocrystal strategies, stabilizer selection criteria, preparation methods, advanced characterization techniques, the evolving nanocrystal technological landscape, current market options, and exciting clinical prospects for reshaping the future of pharmaceuticals.

A novel electrospun nanofiber system with PEGylated paclitaxel nanocrystals enhancing the transmucus permeability and in situ retention for an efficient cervicovaginal cancer therapy

Overcoming the vaginal barrier to achieve sufficient drug penetration and retention is a huge obstacle for drug delivery in chemotherapeutics for cervical cancer. In this study, we investigate the feasibility of a novel composite nanocrystal/nanofiber system for improving the transmucus penetration and, thus, enhancing retention and drug delivery to the lesion of a cervicovaginal tumor. Herein, paclitaxel (PTX) was sequentially formulated in the form of nanocrystals, coated with polydopamine (PDA), and modified with PEG. The nanocrystals (NCs@PDA-PEG) were creatively fabricated to create a composite nanofibrous membrane (NCs@PDA-PEG NFs) by using an electrospinning technique. The morphology, size distribution, drug loading, encapsulation efficiency, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectra, in vitro release, in vivo vaginal retention, apoptosis index, anti-tumor efficacy in a murine cervicovaginal tumor model, and local irritation were characterized. The NCs@PDA-PEG were formulated in a cube-like shape with an average size of 385.6 ± 35.47 nm; they were dispersed in electrospun nanofibers, and the drug loading was 7.94 %. The XRD curves indicated that the phase state of PTX changed after the creation of the nanocrystals. The FTIR spectra showed that the drug and the excipients were compatible with each other. In vitro delivery showed that the dissolution of PTX in the electrospun nanofibers was significantly faster than that when using bulk PTX. Compared with the PTX NC NFs, the NC@PDA-PEG NFs exhibited prolonged vaginal residence, superior transmucus penetration, minimal mucosal irritation, and significant tumor inhibition efficacy after the intravaginal administration of the NFs in tumor-bearing mice. In conclusion, by acting as novel pharmaceutical repositories, NCs@PDA-PEG NFs can be promising candidates for non-invasive local treatment, leading to efficient tumor inhibition in cervicovaginal cancer.

Intravenous nanocrystals: fabrication, solidification, in vivo fate, and applications for cancer therapy

INTRODUCTION

Intravenous nanocrystals (INCs) have shown intrinsic advantages in antitumor applications, particularly their properties of high drug loading, low toxicity, and controllable size. Therefore, it has a very bright application prospect as a drug delivery system.

AREAS COVERED

The ideal formulation design principles, fabrication, solidification, in vivo fate of INCs, the applications in drug delivery system (DDS) and the novel applications are covered in this review.

EXPERT OPINION

It is vital to select a suitable formulation and fabrication method to produce a stable and sterile INCs. Besides, the type of stabilizers and physical characteristics can also influence the in vivo fate of INCs, which is worthy of further studying. Based on wide researches about applications of INCs in cancer, biomimetic INCs are concerned increasingly for its favorable compatibility. The output of these studies suggested that INCs-based drug delivery could be a novel strategy for addressing the delivery of the drug that faces solubility, bioavailability, and toxicity problems.

Exploring the translocation behaviours in vivo of herpetrione amorphous nanoparticles via oral delivery

Nanotechnology has been a primary strategy to enhance oral bioavailability of poorly water soluble drugs. However, the limited information in vivo fate of impedes the development of nanoparticles via the oral delivery, especially the amorphous nanoparticles with high energy states are rarely reported. This study is to track the translocation of oral herpetrione amorphous nanoparticles (HPE-ANPs). We prepare amorphous particles (ANPs) of various sizes (200 nm and 450 nm), which are embedded with an aggregation-caused quenching (ACQ) dyes for tracking the intact nanoparticles. Nanoparticles remain in the gastrointestinal tract (GIT) for 8 h following oral administration, suggesting that most ANPs was mainly degraded or absorbed in the small intestine. Ex vivo imaging shows that the fluorescent signals are observed in the GIT and liver but not in other organs, which attributed to low absorption of integral nanoparticles. Besides, HPE-ANPs may be directly interact with GIT epithelia, and ileum provides better absorption than the jejunum. Cellular studies prove that integral HPE-ANPs can be taken up by enterocyte, while it penetrates cell monolayers only small amounts. In conclusion, we speculate that the drug in the form of integral nanoparticles and small molecules may be co-absorbed to improve bioavailability in vivo.

Dual Antimelanogenic Effect of Nicotinamide-Stabilized Phloretin Nanocrystals in Larval Zebrafish

Melanin is a kind of dark insoluble pigment that can cause pigmentation and free-radical clearance, inducing melasma, freckles, and chloasma, affecting the quality of life of patients. Due to poor water solubility and low safety, the absorption of poorly water-soluble drugs is limited by the hinderance of a skin barrier. Therefore, it is necessary to develop new, safe, and highly efficient drugs to improve their transdermal absorption efficiency and thus to inhibit the production of melanin. To address these issues, we developed a new nicotinamide (NIC)-stabilized phloretin nanocrystals (PHL-NCs). First, NC technology significantly increased the solubility of PHL. The in vitro release results indicated that at 6 h, the dissolution of the PHL-NIC-NCs was 101.39% ± 2.40% and of the PHL-NCs was 84.92% ± 4.30%, while that of the physical mixture of the two drugs was only 64.43% ± 0.02%. Second, NIC acted not only as a stabilizer to enlarge the storage time of PHL-NIC-NCs (improved to 10-day in vitro stability) but also as a melanin transfer inhibitor to inhibit melanin production. Finally, we verified the melanin inhibition effect of PHL-NIC-NCs evaluated by the zebrafish model. It showed that 0.38 mM/L PHL-NIC-NCs have a lower tyrosinase activity at 62.97% ± 0.52% and have less melanin at 36.57% ± 0.44%. The inhibition effect of PHL-NCs and PHL-NIC-NCs was stronger compared to the positive control arbutin. In conclusion, the combination of NIC and PHL achieves better inhibition of tyrosinase and inhibition of melanin production through synergism. This will provide a direction to the subsequent development of melanin-inhibiting drugs and the combined use of pharmaceutical agents.

Biological and Intracellular Fates of Drug Nanocrystals through Different Delivery Routes: Recent Development Enabled by Bioimaging and PK Modeling

Nanocrystals have contributed to exciting improvements in the delivery of poorly water-soluble drugs. The biological and intracellular fates of nanocrystals are currently under debate. Due to the remarkable commercial success in enhancing oral bioavailability, nanocrystals have originally been regarded as a simple formulation approach to enhance dissolution. However, the latest findings from novel bioimaging tools lead to an expanded view. Intact nanocrystals may offer long-term durability in the body and offer drug delivery capabilities like those of other nano-carriers. This review renews the understanding of the biological fates of nanocrystals administered via oral, intravenous, and parenteral (e.g., dermal, ocular, and pulmonary) routes. The intracellular pathways and dissolution kinetics of nanocrystals are explored. Additionally, the future trends for in vitro and in vivo quantification of nanocrystals, as well as factors impacting the biological and intracellular fates of nanocrystals are discussed. In conclusion, nanocrystals present a promising and underexplored therapeutic opportunity with immense potential.

Development of Abiraterone Acetate Nanocrystal Tablets to Enhance Oral Bioavailability: Formulation Optimization, Characterization, In Vitro Dissolution and Pharmacokinetic Evaluation

Abiraterone acetate is a prodrug of abiraterone used in combination with prednisone as a standard therapeutic strategy for hormone-resistant prostate cancer (mCRPC). Due to the poor solubility and permeability, the release and absorption of abiraterone acetate are low and reduce its bioavailability. In this project, abiraterone acetate tablets prepared using nanocrystal technology were developed to overcome the drawbacks of normal tablets by enhancing in vitro dissolution rate and oral bioavailability. The abiraterone acetate nanocrystal suspensions were prepared by top-down wet milling method using a planetary ball mill with the mixture of Poloxamer 407 and Poloxamer 188 as the optimized stabilizer at a ratio of 7:1. The optimized nanocrystals were freeze-dried and characterized using DLS, TEM, DSC, and XRD. The abiraterone acetate nanocrystal tablets significantly improve the in vitro dissolution rate of abiraterone acetate compared to raw materials. Although exhibiting a similar dissolution rate compared to the Zytiga^® tablets, the nanocrystal tablets significantly improve the oral bioavailability with C_max and AUC_0–t being 3.51-fold and 2.80-fold higher, respectively, in the pharmacokinetic study. The present data indicate that nanocrystal is a promising strategy for improving the dissolution and bioavailability of abiraterone acetate.

The Study of Cyclosporin A Nanocrystals Uptake and Transport across an Intestinal Epithelial Cell Model

Cyclosporin A nanocrystals (CsA-NCs) interaction with Caco-2 cells were investigated in this study, including cellular uptake and transport across Caco-2 cell monolayers. CsA-NCs of 165 nm, 240 nm and 450 nm were formulated. The dissolution of CsA-NCs was investigated by paddle method. The effect of size, concentration and incubation time on cellular uptake and dissolution kinetics of CsA-NCs in cells were studied. Uptake mechanisms were also evaluated using endocytotic inhibitors and low temperature (4 °C). The cell monolayers were incubated with each diameter CsA-NCs to evaluate the effect of size on the permeation characteristics of CsA across the intestinal mucosa. The results of dissolution study showed that 165 nm CsA-NC had the highest dissolution rate followed by 240 CsA-NC and finally 450 nm CsA-NC. The saturation of cell uptake of CsA-NCs was observed with the increase of incubation concentration and time. 240 nm and 450 nm CsA-NCs had the lowest and highest uptake efficiency at different time and drug concentration, respectively. The uptake of all three-sized CsA-NCs declined significantly in some different degree after the pre-treatment with different endocytosis inhibitors. 165 nm CsA-NC showed a highest transport capacity across monolayers at the same concentration and time. The results suggest that the size of CsA-NCs can not only affect the efficiency of cellular uptake, but also the type of endocytosis. Decreasing particle size of CsA-NCs can improve transport capacity of CsA through cell monolayer.

The long-circulating effect of pegylated nanoparticles revisited via simultaneous monitoring of both the drug payloads and nanocarriers

The long-circulating effect is revisited by simultaneous monitoring of the drug payloads and nanocarriers following intravenous administration of doxorubicin (DOX)-loaded methoxy polyethylene glycol-polycaprolactone (mPEG-PCL) nanoparticles. Comparison of the kinetic profiles of both DOX and nanocarriers verifies the long-circulating effect, though of limited degree, as a result of pegylation. The nanocarrier profiles display fast clearance from the blood despite dense PEG decoration; DOX is cleared faster than the nanocarriers. The nanocarriers circulate longer than DOX in the blood, suggesting possible leakage of DOX from the nanocarriers. Hepatic accumulation is the highest among all organs and tissues investigated, which however is reversely proportionate to blood circulation time. Pegylation and reduction in particle size prove to extend circulation of drug nanocarriers in the blood with simultaneous decrease in uptake by various organs of the mononuclear phagocytic system. It is concluded that the long-circulating effect of mPEG-PCL nanoparticles is reconfirmed by monitoring of either DOX or the nanocarriers, but the faster clearance of DOX suggests possible leakage of a fraction of the payloads. The findings of this study are of potential translational significance in design of nanocarriers towards optimization of both therapeutic and toxic effects.

Surface Decoration via Physical Interaction of Cupric Diethyldithiocarbamate Nanocrystals and Its Impact on Biodistribution and Tumor Targeting

The vascular wall is the first physiologic barrier that circulating nanoparticles (NPs) encounter, which also is a key biological barrier to cancer drug delivery. NPs can continually scavenge the endothelium for biomarkers of cancer, and the chance of NPs' extravasation into the tumors can be enhanced. Here, we envision P-selectin as a target for specific delivery of drug nanocrystals to tumors. The cupric diethyldithiocarbamate nanocrystals (CuET NCs) were first prepared by an antisolvent method, and then nanocrystals were coated with fucoidan via physical interaction. The fucoidan-coated CuET nanocrystals (CuET@Fuc) possess high drug loading and have the ability to interact with human umbilical vein endothelial cells expressing P-selectin, which transiently enhances the endothelial permeability and facilitates CuET@Fuc extravasation from the peritumoral vascular to achieve higher tumor accumulation of drugs than bare CuET NCs. The CuET NC shows poorer anticancer efficacy than CuET@Fuc at the same dose of CuET. Upon repeated dosing of CuET@Fuc for 2 weeks, no mortality was observed in treated melanoma-bearing mice, while the mortality in the control group and excipient-treated groups reached 23%. The growth rate of melanoma in the CuET@Fuc-treated group was significantly lower than those in other groups. Furthermore, an acute toxicity study revealed that CuET@Fuc is a safe formulation for cancer treatment.

Sub-50 nm ultra-small organic drug nanosuspension prepared by cavi-precipitation and its brain targeting potential

The purpose of this study was to show whether it is possible to prepare sub 100 nm or preferably sub-50 nm drug nanosuspension (NS) of suitable quality for intravenous administration. Furthermore, we have studied how the brain targeting potential of such small size organic NS differs from relatively bigger size NS. Two combination technologies (cavi-precipitation, H96) and a standard high-pressure homogenization (HPH) technology were used to prepare drug NS of different sizes. The cavi-precipitation process generated the smallest AmB NS, i.e., 27 nm compared to 79 nm by H96 technology and 252 nm by standard HPH technology. Dialysis of the nanosuspension in the original dispersion media was found to be the most efficient solvent removal method without negatively affecting particle size. The removal of organic solvent was found to drastically improve the stability of the formulations. The protein adsorption pattern shows that the small size NS particles obtained by the cavi-precipitation process have the potential to circulate longer in the bloodstream and have the potential to be taken up by the blood-brain barrier. The cavi-precipitation process generated ultrafine NS particles, which fulfilled the quality requirements for intravenous administration and offer a potential solution for brain targeting.

Nanocrystals for Improving Oral Bioavailability of Drugs: Intestinal Transport Mechanisms and Influencing Factors

With the limitation of solubility and dissolution rate of insoluble drugs, following oral administration, they would rifely prove poor and volatile bioavailability, which may fail to realize its therapeutic value. The drug nanocrystals are perceived as effective tactic for oral administration of insoluble drugs attributes to possess many prominent properties such as elevating dissolution rate and saturation solubility, high drug loading capacity, and improving oral bioavailability. Based on these advantages, the application of nanocrystals in oral drug delivery has acquired significant achievement, and so far more than 20 products of drug nanocrystals have been confirmed in the market. However, the oral absorption of drug nanocrystals is still facing huge challenges due to the limitation of many factors. Intrinsic properties of the drugs and complex physiological environment of the intestinal tract are the two most important factors affecting the oral bioavailability of drugs. In addition, the research on the multi-aspect mechanisms of nanocrystals promoting gastrointestinal absorption and bioavailability has been gradually deepened. In this review, we summarized recent advances of the nanocrystals delivered orally, and provided an overview to the research progress for crossing the intestinal tract transport mechanisms of the nanocrystals by some new research techniques. Meanwhile, the factors relevant to the transport of drug nanocrystals were also elaborated in detail. Graphical Abstract.

Intracellular uptake of nanocrystals: Probing with aggregation-induced emission of fluorescence and kinetic modeling

Nanocrystal formulations have been explored to deliver poorly water-soluble drug molecules. Despite various studies of nanocrystal formulation and delivery, much more understanding needs to be gained into absorption mechanisms and kinetics of drug nanocrystals at various levels, ranging from cells to tissues and to the whole body. In this study, nanocrystals of tetrakis (4-hydroxyphenyl) ethylene (THPE) with an aggregation-induced emission (AIE) property was used as a model to explore intracellular absorption mechanism and dissolution kinetics of nanocrystals. Cellular uptake studies were conducted with KB cells and characterized by confocal microscopy, flow cytometry, and quantitative analyses. The results suggested that THPE nanocrystals could be taken up by KB cells directly, as well as in the form of dissolved molecules. The cellular uptake was found to be concentration- and time-dependent. In addition, the intracellular THPE also could be exocytosed from cells in forms of dissolved molecules and nanocrystals. Kinetic modeling was conducted to further understand the cellular mechanism of THPE nanocrystals based on first-order ordinary differential equations (ODEs). By fitting the kinetic model against experimental measurements, it was found that the initial nanocrystal concentration had a great influence on the dynamic process of dissolution, cellular uptake, and exocytosis of THPE nanocrystals. As the nanocrystal concentration increased in the culture media, dissolution of endocytosed nanocrystals became enhanced, subsequently driving the efflux of THPE molecules from cells.

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Nanocrystals of Tetrakis(4-hydroxyphenyl) ethylene (THPE), an aggregation-induced emission (AIE) probe was used as a model.

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THPE nanocrystals could be taken up in forms of dissolved molecules and nanocrystals.

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The dynamic process of dissolution, cellular uptake, and exocytosis of THPE nanocrystals was concentration-dependent.

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Exocytosis of intracellular THPE-NCs bore different kinetics and/or mechanisms compared with endocytosis.

The contribution of absorption of integral nanocrystals to enhancement of oral bioavailability of quercetin

In this study, self-discriminating hybrid nanocrystals was utilized to explore the biological fate of quercetin hybrid nanocrystals (QT-HNCs) with diameter around 280 nm (QT-HNCs-280) and 550 nm (QT-HNCs-550) following oral and intravenous administration and the contribution of integral nanocrystals to oral bioavailability enhancement of QT was estimated by comparing the absolute exposure of integral QT-HNCs and total QT in the liver. Results showed that QT-HNCs could reside in vivo as intact nanocrystals for as long as 48 h following oral and intravenous administration. A higher accumulation of integral QT-HNCs in liver and lung was observed for both oral and intravenous administration of QT-HNCs. The particle size affects the absorption and biodistribution of integral QT-HNCs and total QT. As compared to QT-HNCs-550, QT-HNCs-280 with smaller particle size is more easily absorbed, but dissolves faster in vivo, leading to higher distribution of QT (146.90 vs. 117.91 h·μg/mL) but lower accumulation of integral nanocrystals (6.8 2e10 vs. 15.27e10 h·[p/s]/[µW/cm²]) in liver following oral administration. Due to its slower dissolution and enhanced recognition by RES, QT-HNCs-550 with larger diameter shows higher liver distribution for both of QT (1015.80 h·μg/mL) and integral nanocrystals (259.63e10 h·[p/s]/[µW/cm²]) than those of QT-HNCs-280 (673.82 & 77.66e10 h·[p/s]/[µW/cm²]) following intravenous administration. The absolute exposure of integral QT-HNCs in liver following oral administration of QT-HNCs are 8.78% for QT-HNCs-280 and 5.88% for QT-HNCs-550, while the absolute exposure of total QT for QT-HNCs-280 and QT-HNCs-550 are 21.80% and 11.61%, respectively. Owing to imprecise quantification method, a surprisingly high contribution of integral QT-HNCs to oral bioavailability enhancement of QT (40.27% for QT-HNCs-280 and 50.65% for QT-HNCs-550) was obtained. These results revealed significant difference in absorption and biodistrbution between integral nanocrystals and overall drugs following oral and intravenous administration of QT-HNCs, and provided a meaningful reference for the contribution of integral nanocrystals to overall bioavailability enhancement.

Temperature and pH Responsive Light-Harvesting System Based on AIE-Active Microgel for Cell Imaging

A highly emissive microgel is synthesized by polymerizing tetraphenylethene (TPE) based comonomers, acrylic acid, NIPAM, and permanent crosslinker ethylenebisacrylamide (BIS) (named as TPE microgel), which exhibited temperature responsive fluorescence emission. Rhodamine B (RhB), a positively charged molecule, is then inserted onto the surface of fabricated microgels through electrostatic interaction. As a result, a novel artificial light harvesting system with high energy transfer efficiency is constructed (named as TPE microgel-RhB light harvesting system), which is the first light harvesting system based on TPE microgels presenting dual response to pH and temperature. MTT assay indicates the fabricated TPE microgel and TPE microgel-RhB light harvesting system has good cytocompatibility. The strong fluorescence and good cytocompatibility make them perfect candidates for cell imaging. The prepared emissive microgel and light-harvesting system with desirable fluorescent property not only provide a new strategy for the fabrication of tunable luminescent nanomaterials, but also expand potential applications in the fields of stomach recognition, temperature sensors, and drug delivery.

Synergistic Antitumor Effects on Drug-Resistant Breast Cancer of Paclitaxel/Lapatinib Composite Nanocrystals

Drug resistance presents serious difficulties for cancer treatment. A combination of paclitaxel (PTX) and lapatinib (LAPA) shows potentials in multiple drug resistant cancers in the clinic, but it is almost impossible to deliver these two drugs to the tumor at the same time with the best proportion by simple co-administration of the respective current formualtions for their different pharmacokinetic profiles. Here composite nanocrystals of PTX and LAPA (cNC) were designed with a ratio of 2:1 (w/w), which was their intracellular ratio at the best synergistic efficacy on a drug-resistant cancer cell line (MCF-7/ADR). Such cNC were prepared using a bottom-up method to achieve a nearly spherical appearance and a narrow size distribution of 95.1 ± 2.1 nm. For nanocrystal stabilization, Polyethylene glycol (PEG) coating was introduced into the cNC via polydopamine (PDA) coating in order to get a PEGylated composite nanocrystal (cNC@PDA-PEG) with nanoscale size (170.5 ± 1.4 nm), considerable drug loading (PTX: 21.33 ± 1.48%, LAPA: 10.95 ± 1.24%) and good stability for at least 4 days in plasma-containing buffers. Differential scanning calorimeter (DSC) and XRD data both indicated the different crystalline states of the cNC as well as the cNC@PDA-PEG in comparison with bulk drugs. In vitro release data showed that PTX and LAPA were gradually and completely released from cNC@PDA-PEG in 3 days, while drug release from bulk drugs or cNC was only 30%. cNC@PDA-PEG also showed negligible hemolysis in vitro. Cellular uptake experiments in the MCF-7/ADR cell line showed that the nanocrystals entered the cells in a complete form through endocytosis and then released the drug in the cell. cNC@PDA-PEG inhibits the growth of this drug-resistant cell more effectively than the unmodified version (cNC). In summary, PEGylated PTX and LAPA composite nanocrystals showed the potential for treament of drug-resistant tumors by simultaneously delivering two drugs to tumor cells with the best proportion.

Rilpivirine-associated aggregation-induced emission enables cell-based nanoparticle tracking

Antiretroviral therapy (ART) has improved the quality and duration of life for people living with human immunodeficiency virus (HIV) infection. However, limitations in drug efficacy, emergence of viral mutations and the paucity of cell-tissue targeting remain. We posit that to maximize ART potency and therapeutic outcomes newer drug formulations that reach HIV cellular reservoirs need be created. In a step towards achieving this goal we harnessed the aggregation-induced emission (AIE) property of the non-nucleoside reverse transcriptase inhibitor rilpivirine (RPV) and used it as a platform for drug cell and subcellular tracking. RPV nanocrystals were created with endogenous AIE properties enabling the visualization of intracellular particles in cell and tissue-based assays. The intact drug crystals were easily detected in CD4⁺ T cells and macrophages, the natural viral target cells, by flow cytometry and ultraperformance liquid chromatography tandem mass spectrometry. We conclude that AIE can be harnessed to monitor cell biodistribution of selective antiretroviral drug nanocrystals.

Synthesis of a long acting nanoformulated emtricitabine ProTide

While antiretroviral therapy (ART) has revolutionized treatment and prevention of human immunodeficiency virus type one (HIV-1) infection, regimen adherence, viral mutations, drug toxicities and access stigma and fatigue are treatment limitations. These have led to new opportunities for the development of long acting (LA) ART including implantable devices and chemical drug modifications. Herein, medicinal and formulation chemistry were used to develop LA prodrug nanoformulations of emtricitabine (FTC). A potent lipophilic FTC phosphoramidate prodrug (M2FTC) was synthesized then encapsulated into a poloxamer surfactant (NM2FTC). These modifications extended the biology, apparent drug half-life and antiretroviral activities of the formulations. NM2FTC demonstrated a >30-fold increase in macrophage and CD4+ T cell drug uptake with efficient conversion to triphosphates (FTC-TP). Intracellular FTC-TP protected macrophages against an HIV-1 challenge for 30 days. A single intramuscular injection of NM2FTC, at 45 mg/kg native drug equivalents, into Sprague Dawley rats resulted in sustained prodrug levels in blood, liver, spleen and lymph nodes and FTC-TP in lymph node and spleen cells at one month. In contrast, native FTC-TPs was present for one day. These results are an advance in the transformation of FTC into a LA agent.

"Locked" cancer cells are more sensitive to chemotherapy

The treatment of metastatic cancer is a great challenging issue throughout the world. Conventional chemotherapy can kill the cancer cells and, whereas, would exacerbate the metastasis and induce drug resistance. Here, a new combinatorial treatment strategy of metastatic cancer was probed via subsequentially dosing dual nanomedicines, marimastat-loaded thermosensitive liposomes (MATT-LTSLs) and paclitaxel nanocrystals (PTX-Ns), via intravenous and intratumoral injection. First, the metastasis was blocked and cancer cells were locked in the tumor microenvironment (TME) by delivering the matrix metalloproteinase (MMP) inhibitor, MATT, to the tumor with LTSLs, downregulating the MMPs by threefold and reducing the degradation of the extracellular matrix. And then, the "locked" cancer cells were efficiently killed via intratumoral injection of the other cytotoxic nanomedicine, PTX-Ns, along with no metastasis and 100% inhibition of tumor growth. This work highlights the importance of the TME's integrity in the chemotherapy duration. We believe this is a generalized strategy for cancer treatment and has potential guidance for the clinical administration.

Towards more accurate bioimaging of drug nanocarriers: turning aggregation-caused quenching into a useful tool

One of the current challenges in the monitoring of drug nanocarriers lies in the difficulties in discriminating the carrier-bound signals from the bulk signals of probes. Environment-responsive probes that enable signal switching are making steps towards a solution to this problem. Aggregation-caused quenching (ACQ), a phenomenon generally regarded as unfavorable in bioimaging, has turned out to be a promising characteristic for achieving environment-responsiveness and eliminating free-probe interference. So-called ACQ probes emit fluorescence when dispersed molecularly within the carrier matrix but quench immediately and absolutely once they are released into the ambient aqueous environment upon the degradation of the nanocarriers. Therefore, the fluorescence observed represents integral nanocarriers. Based on this rationale, the in vivo fates of various nanocarriers have been explored using live imaging equipment, with very interesting findings revealing the role of the particles. The current applications are however restricted to nanocarriers with highly hydrophobic matrices (lipid or polyester nanoparticles) or with a hydrophobic core-hydrophilic shell structure (micelles). The ACQ-based bioimaging strategy is emerging as a promising tool to achieve more accurate bioimaging of drug nanocarriers. This review article provides an overview of the ACQ phenomenon and the rationale for and examples of applications, as well as the limitations of the ACQ-based strategy, with a focus on improving the accuracy of bioimaging of nanoparticles.

Aggregation-induced emission (AIE) fluorophores as imaging tools to trace the biological fate of nano-based drug delivery systems

The vigorous development of nanotechnology has been accompanied by an equally strong interest and research efforts in nano-based drug delivery systems (NDDSs). However, only a few NDDSs have been translated into clinic thus far. One of the important hurdles is the lack of tools to comprehensively and directly trace the biological fate of NDDSs. Recently, aggregation-induced emission (AIE) fluorophores have emerged as attractive bioimaging tools due to flexible controllability, negligible toxicity and superior photostability. Herein, we recapitulate the current advances in the application of AIE fluorophores to monitor NDDSs both in vitro and in vivo. Particularly, we discuss the cellular fates of self-indicating and stimuli-responsive NDDSs with AIE fluorophores. Moreover, we highlight the in vivo application of AIE agents on the long-term tracking of therapeutics and the multi-modal monitoring of diagnostics in NDDSs. Challenges and opportunities in AIE-guided exploration of NDDSs are also discussed in detail.

Hybrid drug nanocrystals

Nanocrystals show promise to deliver poorly water-soluble drugs to yield systemic exposure. However, our knowledge regarding the in vivo fate of nanocrystals is in its infancy, as nanocrystallization is simply viewed as an approach to enhance the dissolution of drug crystals. The dying crystal phenomenon inspired the development of hybrid nanocrystals by physically embedding fluorophores into the crystal lattice. This approach achieved concurrent therapy and bioimaging and is well-established to study pharmacokinetics and nanocrystal dissolution in vivo. Nanocrystals also offer the advantage of long-term durability in the body for interacting with biological tissues and cells. This review introduces the hybrid nanocrystal technique, including the theoretical concepts, preparation, and applications. We also discuss the latest development in self-discriminative hybrid nanocrystals utilizing environment-responsive probes. This review will stimulate further development and application of nanocrystal-based drug delivery systems for theranostic strategies.

Drug nanocrystals: Fabrication methods and promising therapeutic applications

The drug nanocrystals (NCs) with unique physicochemical properties are now considered as a promising drug delivery system for poorly water-soluble drugs. So far >20 formulations of NCs have been approved in the market. In this review, we summarized recent advances of NCs with emphasis on their therapeutic applications based on administration route and disease states. At the end, we present a brief description of the future perspectives of NCs and their potential role as a promising drug delivery system. As a strategy for solubilization and bioavailability enhancement, the NCs have gained significant success. Besides this, the function of NCs is still far from developed. The emerging NC-based drug delivery approach would widen the applications of NCs in drug delivery and bio-medical field. Their in vitro and in vivo fate is extremely unclear; and the development of hybrid NCs with environment-sensitive fluorophores may assist to extend the scope of bio-imaging and provide better insight to their intracellular uptake kinetics, in vitro and in vivo.

Enhanced Delivery of Imatinib into Vaginal Mucosa via a New Positively Charged Nanocrystal-Loaded in Situ Hydrogel Formulation for Treatment of Cervical Cancer

The present study was carried out to investigate the potential of cationic functionalization on imatinib nanocrystals to improve the mucoadhesiveness and, thus, delivery to the lesion of cervicovaginal tumors. Amino-group-functionalized imatinib nanocrystals (NC@PDA-NH₂) were prepared with near-spheroid shape, nanoscale size distribution, positive zeta potential, and relatively high drug content with the aid of the polydopamine-coating technique. Efficient interaction between NC@PDA-NH₂ and mucin was proven by mucin adsorption which was related to the positive zeta-potential value of NC@PDA-NH₂ and the change in the size distribution on mixing of NC@PDA-NH₂ and mucin. Cellular uptake, growth inhibition, and apoptosis induction in cervicovaginal cancer-related cells demonstrated the superiority of NC@PDA-NH₂ over unmodified nanocrystals. For practical intravaginal administration, NC@PDA-NH₂ was dispersed in Pluronic F127-based thermosensitive in situ hydrogel, which showed suitable gelation temperature and sustained-release profiles. In comparison with unmodified nanocrystals, NC@PDA-NH₂ exhibited extended residence on ex vivo murine vaginal mucosa, prolonged in vivo intravaginal residence, and enhanced inhibition on the growth of murine orthotopic cervicovaginal model tumors indicated by smaller tumor size, longer median survival time, and more intratumor apoptosis with negligible mucosal toxicity. In conclusion, cationic functionalization endowed NC@PDA-NH₂ significant mucoadhesiveness and, thus, good potential against cervicovaginal cancer via intravaginal administration.

Amorphous Nanosuspensions Aggregated from Paclitaxel⁻Hemoglobulin Complexes with Enhanced Cytotoxicity

Amorphous nanosuspensions (ANSs) enable rapid release and improved delivery of a poorly water-soluble drug; however, their preparation is challenging. Here, using hemoglobin (Hb) as a carrier, ANSs aggregated from paclitaxel (PTX)⁻Hb complexes were prepared to improve delivery of the hydrophobic anti-cancer agent. An affinity study demonstrated strong interaction between Hb and PTX. Importantly, the complexes could aggregate into <300 nm ANSs with high drug loading, which acidic condition facilitated their formation. Furthermore, the ANSs possessed improved cytotoxicity against cancer cells over the crystalline nanosuspensions. Taken together, ANSs aggregated from PTX⁻Hb complexes were developed, which could kill cancer cells with high efficiency.

Tracking translocation of self-discriminating curcumin hybrid nanocrystals following intravenous delivery

Nanocrystals hold great potential as parenteral delivery carrier systems for poorly water-soluble drugs. Elucidation of the in vivo fate of parenteral nanocrystals is of pharmacological, toxicological and mechanistic significance. However, it is of tremendous difficulty to monitor real-time translocation of nanocrystals in vivo owing to progressive dissolution of nanocrystals and a lack of workable tools to probe nanocrystals. In this study, self-discriminating hybrid nanocrystals (SDHNs) of a model drug curcumin (CUR) were developed by embedding traces of environment-responsive fluorescent dyes into the crystalline lattices of CUR. The SDHNs glow, but the released dyes aggregate and quench spontaneously due to the aggregation-caused quenching (ACQ) effect. Following intravenous administration into rats, a large fraction of CUR nanocrystals are cleared from blood rapidly and accumulate mainly in liver and lung. A small fraction circulate in blood for at least 48 h. Long circulating might be attributable to the surface coating with poloxamer 188, a stabilizer used during preparation; nevertheless, the ultimate fate of nanocrystals ends in reticulo-endothelial organs and tissues. It is implied that parenteral delivery provide sustained release and prolonged pharmacological efficacy, but concomitantly raise concerns of local toxicity in vital organs and tissues, especially when the active ingredients are highly toxic.

Hierarchical theranostic nanomedicine: MRI contrast agents as a physical vehicle anchor for high drug loading and triggered on-demand delivery

A hierarchical hybrid nanocarrier enables an extremely high drug loading by interfacial deposition, pH-dependent drug release and MRI signal amplification.