Dendrimer Conjugation Enhances Tumor Penetration and Efficacy of Doxorubicin in Extracellular Matrix-Expressing 3D Lung Cancer Models.

Doxorubicin (DOX) is a chemotherapeutic agent broadly used in the treatment of a range of solid tumors. In spite of its high potency, as is the case for many other chemotherapeutic drugs, there are many challenges associated with the use of DOX in clinical oncology. This is particularly true for DOX in the treatment of lung cancer, where in vitro potency is shown to be very high, but low lung distribution and off-target toxicity (particularly cardiotoxicity) restrict its use. Nanocarrier-based drug delivery systems (nanoDDS) have been shown to help alter biodistribution and alleviate off-target toxicity associated with DOX. While significant understanding exists regarding the design parameters to achieve those clinical benefits, much less is known regarding the design of nanoDDS capable of enhancing tumor penetration of DOX (and other drugs), which is another major factor leading to DOX's reduced efficacy. The purpose of this study was to design a dendrimer-based nanoDDS capable of enhancing the penetration of DOX as measured in an in vitro 3D lung tumor model and to correlate those results with its efficacy. Spheroids formed with the A549 human lung adenocarcinoma cells/murine fibroblast cell line (NIH/3T3 cell line) are shown to produce the essential components of the extracellular matrix (ECM), which is known as a physical barrier that hinders the transport of DOX. DOX was conjugated to generation 4 succinamic acid-terminated poly(amido-amine) (PAMAM) dendrimers (G4SA) through an enzyme-liable tetrapeptide (G4SA-GFLG-DOX), resulting in a nanoDDS with ∼5.5 DOX, -17 mV surface (ζ) potential, and a 10 nm hydrodynamic diameter (HD). The penetration of DOX to the core of the spheroid in terms of DOX fluorescence was determined to be 3.1-fold greater compared to free DOX, which positively correlated with enhanced efficacy as measured by the Caspase 3/7 assay. This improved penetration happens as the interactions between the G4SA-GFLG-DOX and the highly negatively charged ECM are minimized by shielding the protonatable amine of DOX upon conjugation, and the HD of the conjugate is kept smaller than the estimated mesh size of the ECM. Interestingly, the conjugate provided more specificity for DOX to tumor cells compared to fibroblasts, while free DOX is equally distributed in both tumor and fibroblasts as assessed in the coculture spheroids. Growth inhibition studies show that the released DOX maintains its activity and leads to tumor reduction to the same extent as free DOX. The results obtained here are of relevance for the design of dendrimer-based nanoDDS and for the treatment of solid tumors as they provide critical information regarding desirable surface characteristics and sizes for efficient tumor penetration.

Physicochemical and In Vitro Evaluation of Drug Delivery of an Antibacterial Synthetic Benzophenone in Biodegradable PLGA Nanoparticles.

Due to the increasing incidents of antimicrobial-resistant pathogens, the development of new antibiotics and their efficient formulation for suitable administration is crucial. Currently, one group of promising antimicrobial compounds are the benzophenone tetra-amides which show good activity even against gram-positive, drug-resistant pathogens. These compounds suffer from poor water solubility and bioavailability. It is therefore important to develop dosage forms which can address this disadvantage while also maintaining efficacy and potentially generating long-term exposures to minimize frequent dosing. Biodegradable nanoparticles provide one solution, and we describe here the encapsulation of the experimental benzophenone-based antibiotic, SV7. Poly-lactic-co-glycolic-acid (PLGA) nanoparticles were optimized for their physicochemical properties, their encapsulation efficiency, sustained drug release as well as antimicrobial activity. The optimized formulation contained particles smaller than 200 nm with a slightly negative zeta potential which released 39% of their drug load over 30 days. This formulation maintains the antibacterial activity of SV7 while minimizing the impact on mammalian cells.

Effect of the Route of Administration and PEGylation of Poly(amidoamine) Dendrimers on Their Systemic and Lung Cellular Biodistribution.

There are many opportunities in the development of oral inhalation (oi) formulations for the delivery of small molecule therapeutics and biologics to and through the lungs. Nanocarriers have the potential to play a key role in advancing oi technologies and pushing the boundary of the pulmonary delivery market. In this work we investigate the effect of the route of administration and PEGylation on the systemic and lung cellular biodistribution of generation 3, amino-terminated poly(amidoamine) (PAMAM) dendrimers (G3NH2). Pharmacokinetic profiles show that the dendrimers reach their peak concentration in systemic circulation within a few hours after pulmonary delivery, independent of their chemistry (PEGylated or not), charge (+24 mV for G3NH2 vs -3.7 mV for G3NH2-24PEG1000), or size (5.1 nm for G3NH2 and 9.9 nm for G3NH2-24PEG1000). However, high density of surface modification with PEG enhances pulmonary absorption and the peak plasma concentration upon pulmonary delivery. The route of administration and PEGylation also significantly impact the whole body and local (lung cellular) distribution of the dendrimers. While ca. 83% of G3NH2 is found in the lungs upon pulmonary delivery at 6.5 h post administration, only 2% reached the lungs upon intravenous (iv) delivery. Moreover, no measurable concentration of either G3NH2 or G3NH2-24PEG1000 is found in the lymph nodes upon iv administration, while these are the tissues with the second highest mass distribution of dendrimers post pulmonary delivery. Dendrimer chemistry also significantly impacts the (cellular) distribution of the nanocarriers in the lung tissue. Upon pulmonary delivery, approximately 20% of the lung endothelial cells are seen to internalize G3NH2-24PEG1000, compared to only 6% for G3NH2. Conversely, G3NH2 is more readily taken up by lung epithelial cells (35%) when compared to its PEGylated counterpart (24%). The results shown here suggest that both the pulmonary route of administration and dendrimer chemistry combined can be used to passively target tissues and cell populations of great interest, and can thus be used as guiding principles in the development of dendrimer-based drug delivery strategies in the treatment of medically relevant diseases including lung ailments as well as systemic disorders.

Conjugation to Poly(amidoamine) Dendrimers and Pulmonary Delivery Reduce Cardiac Accumulation and Enhance Antitumor Activity of Doxorubicin in Lung Metastasis.

Lung is one of the most common sites to which almost all other primary tumors metastasize. The major challenges in the chemotherapy of lung metastases include the low drug concentration found in the tumors and high systemic toxicity upon systemic administration. In this study, we combine local lung delivery and the use of nanocarrier-based systems for improving pharmacokinetics and biodistribution of the therapeutics to fight lung metastases. We investigate the impact of the conjugation of doxorubicin (DOX) to carboxyl-terminated poly(amidoamine) dendrimers (PAMAM) through a bond that allows for intracellular-triggered release, and the effect of pulmonary delivery of the dendrimer-DOX conjugate in decreasing tumor burden in a lung metastasis model. The results show a dramatic increase in efficacy of DOX treatment of the melanoma (B16-F10) lung metastasis mouse model upon pulmonary administration of the drug, as indicated by decreased tumor burden (lung weight) and increased survival rates of the animals (male C57BL/6) when compared to iv delivery. Conjugation of DOX further increased the therapeutic efficacy upon lung delivery as indicated by the smaller number of nodules observed in the lungs when compared to free DOX. These results are in agreement with the biodistribution characteristics of the DOX upon pulmonary delivery, which showed a longer lung accumulation/retention compared to iv administration. The distribution of DOX to the heart tissue is also significantly decreased upon pulmonary administration, and further decreased upon conjugation. The results show, therefore, that pulmonary administration of DOX combined to conjugation to PAMAM dendrimer through an intracellular labile bond is a potential strategy to enhance the therapeutic efficacy and decrease systemic toxicity of DOX.

Unique insights into the intestinal absorption, transit, and subsequent biodistribution of polymer-derived microspheres.

Polymeric microspheres (MSs) have received attention for their potential to improve the delivery of drugs with poor oral bioavailability. Although MSs can be absorbed into the absorptive epithelium of the small intestine, little is known about the physiologic mechanisms that are responsible for their cellular trafficking. In these experiments, nonbiodegradable polystyrene MSs (diameter range: 500 nm to 5 µm) were delivered locally to the jejunum or ileum or by oral administration to young male rats. Following administration, MSs were taken up rapidly (≤ 5 min) by the small intestine and were detected by transmission electron microscopy and confocal laser scanning microscopy. Gel permeation chromatography confirmed that polymer was present in all tissue samples, including the brain. These results confirm that MSs (diameter range: 500 nm to 5 µm) were absorbed by the small intestine and distributed throughout the rat. After delivering MSs to the jejunum or ileum, high concentrations of polystyrene were detected in the liver, kidneys, and lungs. The pharmacologic inhibitors chlorpromazine, phorbol 12-myristate 13-acetate, and cytochalasin D caused a reduction in the total number of MSs absorbed in the jejunum and ileum, demonstrating that nonphagocytic processes (including endocytosis) direct the uptake of MSs in the small intestine. These results challenge the convention that phagocytic cells such as the microfold cells solely facilitate MS absorption in the small intestine.

Quantitative detection of PLGA nanoparticle degradation in tissues following intravenous administration.

The biodegradable polymer poly(lactic-co-glycolic) acid (PLGA) has been extensively utilized and investigated as a drug delivery system. Although in vivo biodegradation (at specific administration sites only) of PLGA-based drug delivery constructs, such as foams and microparticles, has been studied, quantitative in vivo biodegradation of distributed polymer nanoparticles has not been accomplished and is quintessential for designing formulations to achieve desired pharmacokinetic properties of a drug in a target tissue. We determined the in vivo degradation kinetics of PLGA nanoparticles, of two sizes, distributed in liver, spleen, and lungs following intravenous administration. In addition, we simultaneously determined the amount of polymer in tissues. Nanoparticle degradation in vitro and in vivo appears to be a first-order process, and useful correlations were obtained between in vitro and in vivo tissue degradation of the nanoparticles. The ability to detect in vivo degradation and biodistribution of polymer nanoparticles is a significant milestone for the rational design of degradable nanoparticle-based drug delivery systems capable of delivering the therapeutic agent in a closely predictable manner to target tissue.

Rapid lymph accumulation of polystyrene nanoparticles following pulmonary administration.

PURPOSE: Pulmonary administration of polymeric nanoparticle drug delivery systems is of great interest for both systemic and local therapies. However, little is understood about the relationship of particle size and pulmonary absorption. We investigated uptake and biodistribution of polystyrene nanoparticles (PN) of 50 nm, 100 nm, 250 nm, and 900 nm diameters in mice following administration to lungs via pharyngeal aspiration. METHODS: The amount of PN in tissues was analyzed by gel permeation chromatography (GPC). RESULTS: At 1 h, larger diameter PN (250 nm and 900 nm) had the highest total uptake at around 15% of administered dose, whereas the smaller diameter PN (50 nm and 100 nm) had uptake of only 5-6%. However, at 3 h, the 50 nm PN had the highest total uptake at 24.4%. For each size tested, the highest nanoparticle deposition was observed in the lymph nodes (LN) as compared to other tissues accounting for a total of about 35-50% of absorbed nanoparticles. CONCLUSION: PN size impacts the rate and extent of uptake from lungs and, further, the extent of LN deposition. The extent of uptake and lymph distribution of the model, non-degradable PN lends potential to pulmonary administered, biodegradable polymeric nanoparticles for delivery of therapeutics to regional lymph nodes.

Synergistic effect of intratumoral IL-12 and TNF-alpha microspheres: systemic anti-tumor immunity is mediated by both CD8+ CTL and NK cells.

Neoadjuvant immunotherapy with the combination of intratumoral IL-12 and TNF-alpha encapsulated in poly-lactic acid microspheres (PLAM) generate a greater systemic immune response than either cytokine alone. We sought to examine the effector cells responsible for this synergy using the poorly immunogenic B16 melanoma and MCA205 sarcoma cell lines. Splenocytes from MCA205 bearing mice treated with IL-12 and TNF-alpha PLAM contained significantly more tumor-specific IFN-gamma secreting cells than IL-12 alone. Adoptive transfer of lymphocytes from mice treated by the combination mediated significant tumor regression in mice bearing established pulmonary metastases. In mice bearing bilateral tumors, treatment of the primary with IL-12 and TNF-alpha PLAM, resulted in suppression of contralateral tumor growth. Both the local and distant effects were absent in mice depleted of CD8+ T-cells. In B16 bearing mice with established pulmonary disease, only the combination of intratumoral IL-12 and TNF-alpha resulted in a significant reduction of lung nodules. Both the local and distant effects were eradicated in mice depleted of either CD8+ T-cells or NK cells. The local and sustained release of IL-12 and TNF-alpha using PLAM synergistically activate both a cytotoxic T-cell and NK cell response, although their impact varies with MHC class I expression.

Generation of a tumor-specific systemic response after intratumoral injection of IL-12 and IL-18-loaded polylactic acid microspheres.

We evaluated the impact and mechanism of interleukin (IL)-18 alone or in combination with IL-12 or tumor necrosis factor-alpha when delivered intratumorally via polylactic acid microspheres (PLAMs). C57BL6 mice with established B16 melanomas underwent a single intratumoral injection of IL-12, tumor necrosis factor-alpha, or IL-18 PLAM, alone or in combination. Tumor draining lymph nodes and splenocytes were assessed for specific antitumor response by FACS analysis and IFN-gamma release assay and enzyme-linked immunosorbent spot. Mice with established pulmonary metastases were killed for enumeration of pulmonary metastatic nodules after treatment of the primary tumor. Intratumoral treatment with IL-12 in combination with IL-18 led to significant tumor suppression compared with either cytokine alone. FACS analysis revealed the combination of IL-12 and IL-18 resulted in an increase in the percentage of CD3+ cells within the tumor draining lymph node, attributable to increases in both CD4+ and CD8+ T cells. Both IFN-gamma release assay and enzyme-linked immunosorbent spot demonstrated a significant and substantial increase in tumor-specific response with the combination. Treatment of the primary tumor with IL-12 and IL-18 PLAM led to a significant decrease in pulmonary metastases and improvement in survival compared with either cytokine alone. The systemic effects were abrogated after depletion of CD8+ or natural killer cells, but not CD4+ cells. IL-12 and IL-18, when released intratumorally in a sustained fashion as can be accomplished through the use of PLAM, demonstrate both local effects on tumor growth and the generation of a tumor-specific response capable of eradicating distant disease.