Luojuan Hu

Micelle‐Based Brain‐Targeted Drug Delivery Enabled by a Nicotine Acetylcholine Receptor Ligand

The blood–brain barrier (BBB) is the key challenge in the development of drugs for diseases of the central nervous system (CNS). The BBB prevents drugs or drug delivery systems from reaching the site of disease because of tight junctions and lack of fenestration. To circumvent this problem, the receptors that are highly expressed on the capillary endothelium of the brain, such as nicotine acetylcholine receptors (nAChRs), have been exploited to facilitate BBB crossing and intracranial transport of drug delivery systems. nAChRs are ligand-gated ion channels that are expressed mainly at the neuromuscular junction of the CNS, including the brain capillary endothelial cells. The extensive expression of nAChRs in the brain and susceptibility to the inhibition by peptide neurotoxins and neurotropic viral proteins endow them with the ability to mediate peptidebased transvascular delivery of various therapeutic agents to the brain. Herein, we report the design of a 16-residue peptide, derived from the loop II region of the snake neurotoxin candoxin, that binds to nAChRs with high affinity. This peptide, termed CDX, enabled drug delivery to the brain when conjugated to paclitaxel-loaded micelles. As a result, tumor growth in intracranial glioblastoma bearing mice was inhibited and their survival was prolonged. Snake neurotoxins are members of the “three-finger toxin” superfamily characterized by three adjacent loops arranged in a flat, leaflike structure. These toxins are known to bind through the second loop to nAChRs with high affinity and selectivity. Candoxin from the Malayan krait Bungarus candidus consists of a single polypeptide chain of 66 amino acid residues with five disulfide bridges, and antagonizes a7 neuronal nAChRs in nanomolar concentrations with poor reversibility. As was shown previously by western blot analysis, and confirmed by using immunocytochemical staining (Figure S8 in the Supporting Information), the a7 neuronal nAChR is richly expressed in primary brain capillary endothelial cells, and is thus ideally suited for candoxin-mediated, brain-targeted drug delivery. For this study, we designed and evaluated three short peptides derived from the loop II region of candoxin, FKESWREARGTRIERG (CDX), SWREARGTRI (Pocket_CDX), and disulfide bridged CFKESWREARGTRIERGC (Cyclo_CDX). To investigate whether or not the candoxin-derived peptides are capable of interacting with rat neuronal nAChRs, we performed a competitive binding assay where different concentrations of peptide competed for receptor binding with radiolabeled I-a-bungarotoxin, which is a potent antagonist of a7 neuronal nAChRs. All three peptides functioned as competitive antagonists of neuronal nAChRs in a dose-dependent manner (Figure S2). CDX displayed a Ki value of 0.187 mm, which is approximately 20– 40 times lower than those of Pocket_CDX and Cyclo_CDX (Table 1). Not surprisingly, CDX is substantially less potent than candoxin in nAChRs binding. The difference in potency is likely attributable, at least in part, to a loss of entropy for CDX, as it is unstructured in aqueous solution, as indicated by circular dichroism spectroscopic analysis (Figure S3).

Transferrin-conjugated polyphosphoester hybrid micelle loading paclitaxel for brain-targeting delivery: Synthesis, preparation and in vivo evaluation

The successful treatment of central nervous system (CNS) disorders is hampered by inefficient drug delivery across the blood-brain barrier (BBB). Transferrin (Tf) could facilitate the transcytosis of coupled nanocarriers through Tf receptor (TfR) mediated pathway. In this study, Tf-modified paclitaxel-loaded polyphosphoester hybrid micells (TPM) was prepared and evaluated for its in vitro and in vivo brain-targeting efficiency. The polyphosphoester hybrid micelle formed a core-shell structure in aqueous solution, and demonstrated high drug entrapping efficiency (89.9±3.4%). In addition, the micelle showed negligible hemolysis even at 2.0 mg/mL. The TPM was 87.85±2.32 nm with ζ potentials -12.33±1.46 mV, and PTX showed sustained release from TPM. TPM demonstrated enhanced cellular uptake and brain accumulation, which were 2 and 1.8-fold of PM, respectively. TPM exhibited strongest anti-glioma activity, and the mean survival time of mice bearing intracranial U-87 MG glioma treated with TPM (39.5 days) was significantly longer than those treated with Taxol® (33.6 days). These results indicated that Tf conjugated micelle could be a promising carrier for brain-targeting drug delivery.

Transferrin-modified c[RGDfK]-paclitaxel loaded hybrid micelle for sequential blood-brain barrier penetration and glioma targeting therapy.

The effective chemotherapy for glioblastoma multiform (GBM) requires a nanomedicine that can both penetrate the blood-brain barrier (BBB) and target the glioma cells subsequently. In this study, Transferrin (Tf) modified cyclo-[Arg-Gly-Asp-d-Phe-Lys] (c[RGDfK])-paclitaxel conjugate (RP) loaded micelle (TRPM) was prepared and evaluated for its targeting efficiency, antiglioma activity, and toxicity in vitro and in vivo. Tf modification significantly enhanced the cellular uptake of TRPM by primary brain microvascular endothelial cells (BMEC) to 2.4-fold of RP loaded micelle (RPM) through Tf receptor mediated endocytosis, resulting in a high drug accumulation in the brain after intravenous injection.The c[RGDfK] modified paclitaxel (PTX) was released from micelle subsequently and targeted to integrin overexpressed glioma cells in vitro, and showed significantly prolonged retention in glioma tumor and peritumoral tissue. Most importantly, TRPM exhibited the strongest antiglioma activity, as the mean survival time of mice bearing intracranial U-87 MG glioma treated with TRPM (42.8 days) was significantly longer than those treated with Tf modified PTX loaded micelle (TPM) (39.5 days), PTX loaded micelle (PM) (34.8 days), Taxol (33.6 days), and saline (34.5 days). Noteworthy, TRPM did not lead to body weight loss compared with saline and was less toxic than TPM. These results indicated that TRPM could be a promising nanomedicine for glioma chemotherapy.

Targeted delivery of a model immunomodulator to the lymphatic system: comparison of alkyl ester versus triglyceride mimetic lipid prodrug strategies.

A lipophilic prodrug approach has been used to promote the delivery of a model immunomodulator, mycophenolic acid (MPA), to the lymphatic system after oral administration. Lymphatic transport was employed to facilitate enhanced drug uptake into lymphocytes, as recent studies demonstrate that targeted drug delivery to lymph resident lymphocytes may enhance immunomodulatory effects. Two classes of lymph-directing prodrugs were synthesised. Alkyl chain derivatives (octyl mycophenolate, MPA-C8E; octadecyl mycophenolate, MPA-C18E; and octadecyl mycophenolamide, MPA-C18AM), to promote passive partitioning into lipids in lymphatic transport pathways, and a triglyceride mimetic prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) to facilitate metabolic integration into triglyceride deacylation-reacylation pathways. Lymphatic transport, lymphocyte uptake and plasma pharmacokinetics were assessed in mesenteric lymph and carotid artery cannulated rats following intraduodenal infusion of lipid-based formulations containing MPA or MPA prodrugs. Patterns of prodrug hydrolysis in rat digestive fluid, and cellular re-esterification in vivo, were evaluated to examine the mechanisms responsible for lymphatic transport. Poor enzyme stability and low absorption appeared to limit lymphatic transport of the alkyl derivatives, although two of the three alkyl chain prodrugs - MPA-C18AM (6-fold) and MPA-C18E (13-fold) still increased lymphatic drug transport when compared to MPA. In contrast, 2-MPA-TG markedly increased lymphatic drug transport (80-fold) and drug concentrations in lymphocytes (103-fold), and this was achieved via biochemical incorporation into triglyceride deacylation-reacylation pathways. The prodrug was hydrolysed rapidly to 2-mycophenoloyl glycerol (2-MPA-MG) in the presence of rat digestive fluid, and 2-MPA-MG was subsequently re-esterified in the enterocyte with oleic acid (most likely originating from the co-administered formulation) prior to accessing the lymphatics and lymphocytes. Importantly, after administration of 2-MPA-TG, the concentrations of free MPA in the mesenteric lymph nodes were significantly enhanced (up to 28 fold) when compared to animals administered equimolar quantities of MPA, suggesting the efficient conversion of the esterified prodrug back to the pharmacologically active parent drug. The data suggest that triglyceride mimetic prodrugs have potential as a means of enhancing immunotherapy via drug targeting to lymphocytes and lymph nodes.

The impact of lymphatic transport on the systemic disposition of lipophilic drugs.

This work investigates the influence of drug absorption route (intestinal lymphatics vs. blood supply) on drug pharmacokinetics and tissue distribution. To achieve this aim, the pharmacokinetics and tissue distribution of model compounds [1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane, DDT; halofantrine] and lipids were assessed following intravenous delivery in lymph lipoproteins or plasma, and were found to differ significantly. For DDT, the clearance (CL) and volume of distribution (Vd ) were higher, whereas for halofantrine, CL and V(d) were lower, after entry in lymph versus plasma due, in particular, to differences in adipose tissue and liver uptake. In a recent study, halofantrine CL and V(d) were similar following entry in lymph or entry in plasma into the systemic circulation of animals predosed with lymph, whereas in the current study, predosing lymph did not influence DDT CL and V(d). For compounds such as DDT, changes to the route of absorption may thus directly impact on pharmacokinetics and tissue distribution, whereas for halofantrine factors that influence lymphatic transport may, by altering systemic lipoprotein concentrations, indirectly impact pharmacokinetics and tissue distribution. Ultimately, careful control of dosing conditions (formulation, prandial state), and thus the extent of lymphatic transport, may be important in assuring reproducible efficacy and toxicity for lymphatically transported drugs.

Glyceride-Mimetic Prodrugs Incorporating Self-Immolative Spacers Promote Lymphatic Transport, Avoid First-Pass Metabolism, and Enhance Oral Bioavailability.

First-pass hepatic metabolism can significantly limit oral drug bioavailability. Drug transport from the intestine through the lymphatic system, rather than the portal vein, circumvents first-pass metabolism. However, the majority of drugs do not have the requisite physicochemical properties to facilitate lymphatic access. Herein, we describe a prodrug strategy that promotes selective transport through the intestinal lymph vessels and subsequent release of drug in the systemic circulation, thereby enhancing oral bioavailability. Using testosterone (TST) as a model high first-pass drug, glyceride-mimetic prodrugs incorporating self-immolative (SI) spacers, resulted in remarkable increases (up to 90-fold) in TST plasma exposure when compared to the current commercial product testosterone undecanoate (TU). This approach opens new opportunities for the effective development of drugs where oral delivery is limited by first-pass metabolism and provides a new avenue to enhance drug targeting to intestinal lymphoid tissue.

Profiling the Role of Deacylation-Reacylation in the Lymphatic Transport of a Triglyceride-Mimetic Prodrug

ABSTRACTPurposeRecent studies have demonstrated the potential for a triglyceride (TG) mimetic prodrug to promote the delivery of mycophenolic acid (MPA) to the lymphatic system. Here, the metabolic pathways that facilitate the lymphatic transport of the TG prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) were examined to better inform the design of next generation prodrugs.MethodsIn vitro hydrolysis experiments in simulated intestinal conditions and in vivo rat lymphatic transport experiments were conducted in the presence and absence of orlistat and A922500 (inhibitors of lipolysis and TG re-esterification, respectively), to evaluate the importance of 2-MPA-TG digestion and re-esterification of 2-MPA-MG (the 2-monoglyceride derivative) in promoting lymphatic transport.Results2-MPA-TG was rapidly hydrolysed to 2-MPA-MG on incubation with fresh bile and pancreatic fluid (BPF), but not in simulated gastric fluid, heat-inactivated BPF or BPF + orlistat. Orlistat markedly decreased lymphatic transport and systemic exposure of 2-MPA-TG derivatives suggesting that inhibition of pancreatic lipase hindered luminal digestion and absorption of the prodrug. A922500 also significantly decreased lymphatic transport of 2-MPA-TG but redirected MPA to the portal blood, suggesting that hindered re-acylation of 2-MPA-MG resulted in intracellular degradation.ConclusionIncorporation into TG deacylation-reacylation pathways is a critical determinant of the utility of lymph directed TG-mimetic prodrugs.

The mesenteric lymph duct cannulated rat model: application to the assessment of intestinal lymphatic drug transport.

The intestinal lymphatic system plays key roles in fluid transport, lipid absorption and immune function. Lymph flows directly from the small intestine via a series of lymphatic vessels and nodes that converge at the superior mesenteric lymph duct. Cannulation of the mesenteric lymph duct thus enables the collection of mesenteric lymph flowing from the intestine. Mesenteric lymph consists of a cellular fraction of immune cells (99% lymphocytes), aqueous fraction (fluid, peptides and proteins such as cytokines and gut hormones) and lipoprotein fraction (lipids, lipophilic molecules and apo-proteins). The mesenteric lymph duct cannulation model can therefore be used to measure the concentration and rate of transport of a range of factors from the intestine via the lymphatic system. Changes to these factors in response to different challenges (e.g., diets, antigens, drugs) and in disease (e.g., inflammatory bowel disease, HIV, diabetes) can also be determined. An area of expanding interest is the role of lymphatic transport in the absorption of orally administered lipophilic drugs and prodrugs that associate with intestinal lipid absorption pathways. Here we describe, in detail, a mesenteric lymph duct cannulated rat model which enables evaluation of the rate and extent of lipid and drug transport via the lymphatic system for several hours following intestinal delivery. The method is easily adaptable to the measurement of other parameters in lymph. We provide detailed descriptions of the difficulties that may be encountered when establishing this complex surgical method, as well as representative data from failed and successful experiments to provide instruction on how to confirm experimental success and interpret the data obtained.

Constitutive Triglyceride Turnover into the Mesenteric Lymph Is Unable to Support Efficient Lymphatic Transport of a Biomimetic Triglyceride Prodrug

The triglyceride (TG) mimetic prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) biochemically integrates into intestinal lipid transport and lipoprotein assembly pathways and thereby promotes the delivery of mycophenolic acid (MPA) into the lymphatic system. As lipoprotein (LP) formation occurs constitutively, even in the fasted state, the current study aimed to determine whether lymphatic transport of 2-MPA-TG was dependent on coadministered exogenous lipid. In vitro incubation of the prodrug with rat digestive fluid and in situ intestinal perfusion experiments revealed that hydrolysis and absorption of the prodrug were relatively unaffected by the quantity of lipid in formulations. In vivo studies in rats, however, showed that the lymphatic transport of TG and 2-MPA-TG was significantly higher following administration with higher quantities of lipid and that oleic acid (C18:1) was more effective in promoting prodrug transport than lipids with higher degrees of unsaturation. The recovery of 2-MPA-TG and TG in lymph correlated strongly (R(2) = 0.99) and more than 97% of the prodrug was associated with chylomicrons. Inhibition of LP assembly by Pluronic L81 simultaneously inhibited the lymphatic transport of 2-MPA-TG and TG. In conclusion, although the TG mimetic prodrug effectively incorporates into TG resynthetic pathways, lipid coadministration is still required to support efficient lymphatic transport.