Subcutaneous delivery of a dendrimer-BH3 mimetic improves lymphatic uptake and survival in lymphoma.

As a malignant tumour of lymphatic origin, B-cell lymphoma represents a significant challenge for drug delivery, where effective therapies must access malignant cells in the blood, organs and lymphatics while avoiding off-target toxicity. Subcutaneous (SC) administration of nanomedicines allows preferential access to both the lymphatic and blood systems and may therefore provide a route to enhanced drug exposure to lymphomas. Here we examine the impact of SC dosing on lymphatic exposure, pharmacokinetics (PK), and efficacy of AZD0466, a small molecule dual Bcl-2/Bcl-xL inhibitor conjugated to a 'DEP®' G5 poly-l-lysine dendrimer. PK studies reveal that the plasma half-life of the dendrimer-drug conjugate is 8-times longer than that of drug alone, providing evidence of slow release from the circulating dendrimer nanocarrier. The SC dosed construct also shows preferential lymphatic transport, with over 50% of the bioavailable dose recovered in thoracic lymph. Increases in dose (up to 400 mg/kg) are well tolerated after SC administration and studies in a model of disseminated lymphoma in mice show that high dose SC treatment outperforms IV administration using doses that lead to similar total plasma exposure (lower peak concentrations but extended exposure after SC). These data show that the DEP® dendrimer can act as a circulating drug depot accessing both the lymphatic and blood circulatory systems. SC administration improves lymphatic exposure and facilitates higher dose administration due to improved tolerability. Higher dose SC administration also results in improved efficacy, suggesting that drug delivery systems that access both plasma and lymph hold significant potential for the treatment of haematological cancers where lymphatic and extranodal dissemination are poor prognostic factors.

Depolymerization of hyaluronan using PEGylated human recombinant hyaluronidase promotes nanoparticle tumor penetration.

Aim: Delivery of nanoparticles (NPs) to tumors can be impeded by high levels of hyaluronan (HA) in the stroma. Enzymatic depolymerization of HA with PEGylated hyaluronidase (PEGPH20) improves the delivery of antibodies to tumors. However, it is unknown whether NP delivery is enhanced by this strategy. Methods: The impact of PEGPH20 pretreatment on the uptake and tumor penetration of model PEGylated polystyrene NPs was studied in mice with orthotopic breast cancers. Results: Tumor oxygenation and NP penetration, but not overall tumor uptake, of 50 nm NPs, was significantly enhanced by PEGPH20 pre-administration. Conclusion: PEGPH20 has the potential to improve intratumoral penetration of NP-based drug delivery systems and enhance access to cancer cells in poorly vascularized regions of the tumor.

Lymph-directed immunotherapy - Harnessing endogenous lymphatic distribution pathways for enhanced therapeutic outcomes in cancer.

The advent of immunotherapy has revolutionised the treatment of some cancers. Harnessing the immune system to improve tumour cell killing is now standard clinical practice and immunotherapy is the first line of defence for many cancers that historically, were difficult to treat. A unifying concept in cancer immunotherapy is the activation of the immune system to mount an attack on malignant cells, allowing the body to recognise, and in some cases, eliminate cancer. However, in spite of a significant proportion of patients that respond well to treatment, there remains a subset who are non-responders and a number of cancers that cannot be treated with these therapies. These limitations highlight the need for targeted delivery of immunomodulators to both tumours and the effector cells of the immune system, the latter being highly concentrated in the lymphatic system. In this context, macromolecular therapies may provide a significant advantage. Macromolecules are too large to easily access blood capillaries and instead typically exhibit preferential uptake via the lymphatic system. In contexts where immune cells are the therapeutic target, particularly in cancer therapy, this may be advantageous. In this review, we examine in brief the current immunotherapy approaches in cancer and how macromolecular and nanomedicine strategies may improve the therapeutic profiles of these drugs. We subsequently discuss how therapeutics directed either by parenteral or mucosal administration, can be taken up by the lymphatics thereby accessing a larger proportion of the body's immune cells. Finally, we detail drug delivery strategies that have been successfully employed to target the lymphatics.

Removal of interstitial hyaluronan with recombinant human hyaluronidase improves the systemic and lymphatic uptake of cetuximab in rats.

Interstitial, e.g. subcutaneous (SC) or intradermal (ID), administration of monoclonal antibodies (mAb) is less invasive than intravenous administration and leads to mAb uptake into both lymphatic and blood capillaries draining the injection site. Interstitial administration, however, is hindered by the presence of hyaluronan (HA), a glycosaminoglycan that is a major fluid barrier in the interstitial space. The transient removal of HA with recombinant human hyaluronidase (rHuPH20) helps facilitate the interstitial administration of often high therapeutic doses of mAb in the clinic. rHuPH20's impact on the systemic pharmacokinetics of several mAbs has been previously described, however effects on route of absorption (lymph vs blood) are unknown. The current study has therefore explored the lymphatic transport and bioavailability of cetuximab and trastuzumab after SC and ID coadministration in the presence and absence of rHuPH20 in rats. After SC administration cetuximab absolute bioavailability increased from 67 % to 80 % in the presence of rHuPH20. Cetuximab recovery in the lymphatics also increased after SC (35.8 % to 49.4 %) and ID (26.7 % to 58.8 %) administration in the presence of rHuPH20. When the injection volume (and therefore dose) was increased 10-fold in the presence of rHuPH20 cetuximab plasma exposure increased approximately linearly (12- and 8.9-fold respectively after SC and ID administration), although the proportional contribution of cetuximab lymphatic transport reduced slightly (6.2-fold increase for both administration routes). In contrast, co-administration with rHuPH20 did not lead to increases in plasma exposure for trastuzumab after SC or ID administration, most likely reflecting the fact that the reported absolute bioavailability of trastuzumab (in the absence of rHuPH20) is high (∼77-99 %). However, lymphatic transport of trastuzumab did increase when coadministered ID with rHuPH20 in spite of the lack of change to overall bioavailability. The data suggest that co-administration with rHuPH20 is able to increase the volume of mAb that can be administered interstitially, and in some instances can increase the amount absorbed into both the blood and the lymph. In the current studies the ability of rHuPH20 to enhance interstitial bioavailability was higher for cetuximab where intrinsic interstitial bioavailability was low, when compared to trastuzumab where interstitial bioavailability was high.

A 30 kDa polyethylene glycol-enfuvirtide complex enhances the exposure of enfuvirtide in lymphatic viral reservoirs in rats.

HIV therapy with anti-retroviral drugs is limited by the poor exposure of viral reservoirs, such as lymphoid tissue, to these small molecule drugs. We therefore investigated the effect of PEGylation on the anti-retroviral activity and subcutaneous lymphatic pharmacokinetics of the peptide-based fusion inhibitor enfuvirtide in thoracic lymph duct cannulated rats. Both the peptide and the PEG were quantified in plasma and lymph via ELISA. Conjugation to a single 5 kDa linear PEG decreased anti-HIV activity three-fold compared to enfuvirtide. Whilst plasma and lymphatic exposure to peptide mass was moderately increased, the loss of anti-viral activity led to an overall decrease in exposure to enfuvirtide activity. A 20 kDa 4-arm branched PEG conjugated with an average of two enfuvirtide peptides decreased peptide activity by six-fold. Plasma and lymph exposure to enfuvirtide, however, increased significantly such that anti-viral activity was increased two- and six-fold respectively. The results suggest that a multi-enfuvirtide-PEG complex may optimally enhance the anti-retroviral activity of the peptide in plasma and lymph.

Gel-Mediated Electrospray Assembly of Silica Supraparticles for Sustained Drug Delivery.

Supraparticles (SPs) composed of smaller colloidal particles provide a platform for the long-term, controlled release of therapeutics in biomedical applications. However, current synthesis methods used to achieve high drug loading and those involving biocompatible materials are often tedious and low throughput, thereby limiting the translation of SPs to diverse applications. Herein, we present a simple, effective, and automatable alginate-mediated electrospray technique for the assembly of robust spherical silica SPs (Si-SPs) for long-term (>4 months) drug delivery. The Si-SPs are composed of either porous or nonporous primary Si particles within a decomposable alginate matrix. The size and shape of the Si-SPs can be tailored by controlling the concentrations of alginate and silica primary particles used and key electrospraying parameters, such as flow rate, voltage, and collector distance. Furthermore, the performance (including drug loading kinetics, loading capacity, loading efficiency, and drug release) of the Si-SPs can be tuned by changing the porosity of the primary particles and through the retention or removal (via calcination) of the alginate matrix. The structure and morphology of the Si-SPs were characterized by electron microscopy, dynamic light scattering, N2 adsorption-desorption analysis, and X-ray photoelectron spectroscopy. The cytotoxicity and degradability of the Si-SPs were also examined. Drug loading kinetics and loading capacity for six different types of Si-SPs, using a model protein drug (fluorescently labeled lysozyme), demonstrate that Si-SPs prepared from primary silica particles with large pores can load significant amounts of lysozyme (∼10 µg per SP) and exhibit sustained, long-term release of more than 150 days. Our experiments show that Si-SPs can be produced through a gel-mediated electrospray technique that is robust and automatable (important for clinical translation and commercialization) and that they present a promising platform for long-term drug delivery.

An Evaluation of Optimal PEGylation Strategies for Maximizing the Lymphatic Exposure and Antiviral Activity of Interferon after Subcutaneous Administration.

Interferon α2 is an antiviral/antiproliferative protein that is currently used to treat hepatitis C infections and several forms of cancer. Two PEGylated variants of interferon α2 (containing 12 and 40 kDa PEGs) are currently marketed and display longer plasma circulation times than that of unmodified interferon. With increasing realization that the lymphatic system plays an important role in the extrahepatic replication of the hepatitis C virus and in the metastatic dissemination of cancers, this study sought to evaluate PEGylation strategies to optimally enhance the antiviral activity and plasma and lymphatic exposure of interferon after subcutaneous administration in rats. The results showed that conjugation with a linear 20 kDa PEG provided the most ideal balance between activity and plasma and lymph exposure. A linear 5 kDa PEG variant also exhibited excellent plasma and lymph exposure to interferon activity when compared to those of unmodified interferon and the clinically available linear 12 kDa PEGylated construct.

'Stealth' lipid-based formulations: poly(ethylene glycol)-mediated digestion inhibition improves oral bioavailability of a model poorly water soluble drug.

For over 20years, stealth drug delivery has been synonymous with nanoparticulate formulations and intravenous dosing. The putative determinants of stealth in these applications are the molecular weight and packing density of a hydrophilic polymer (commonly poly(ethylene glycol) (PEG)) that forms a steric barrier at the surface of the nanoparticle. The current study examined the potential translation of the concepts learned from stealth technology after intravenous administration to oral drug delivery and specifically, to enhance drug exposure after administration of oral lipid-based formulations (LBFs) containing medium-chain triglycerides (MCT). MCT LBFs are rapidly digested in the gastrointestinal tract, typically resulting in losses in solubilisation capacity, supersaturation and drug precipitation. Here, non-ionic surfactants containing stealth PEG headgroups were incorporated into MCT LBFs in an attempt to attenuate digestion, reduce precipitation risk and enhance drug exposure. Stealth capabilities were assessed by measuring the degree of digestion inhibition that resulted from steric hindrance of enzyme access to the oil-water interface. Drug-loaded LBFs were assessed for maintenance of solubilising capacity during in vitro digestion and evaluated in vivo in rats. The data suggest that the structural determinants of stealth LBFs mirror those of parenteral formulations, i.e., the key factors are the molecular weight of the PEG in the surfactant headgroup and the packing density of the PEG chains at the interface. Interestingly, the data also show that the presence of labile ester bonds within a PEGylated surfactant also impact on the stealth properties of LBFs, with digestible surfactants requiring a PEG Mw of ~1800g/mol and non-digestible ether-based surfactants ~800g/mol to shield the lipidic cargo. In vitro evaluation of drug solubilisation during digestion showed stealth LBFs maintained drug solubilisation at or above 80% of drug load and reduced supersaturation in comparison to digestible counterparts. This trend was also reflected in vivo, where the relative bioavailability of drug after administration in two stealth LBFs increased to 120% and 182% in comparison to analogous digestible (non-stealth) formulations. The results of the current study indicate that self-assembled "stealth" LBFs have potential as a novel means of improving LBF performance.