The presence of GM1 in liposomes with entrapped doxorubicin does not prevent RES blockade

Influence of cationic lipid composition on gene silencing properties of lipid nanoparticle formulations of siRNA in antigen-presenting cells

Lipid nanoparticles (LNPs) are currently the most effective in vivo delivery systems for silencing target genes in hepatocytes employing small interfering RNA. Antigen-presenting cells (APCs) are also potential targets for LNP siRNA. We examined the uptake, intracellular trafficking, and gene silencing potency in primary bone marrow macrophages (bmMΦ) and dendritic cells of siRNA formulated in LNPs containing four different ionizable cationic lipids namely DLinDAP, DLinDMA, DLinK-DMA, and DLinKC2-DMA. LNPs containing DLinKC2-DMA were the most potent formulations as determined by their ability to inhibit the production of GAPDH target protein. Also, LNPs containing DLinKC2-DMA were the most potent intracellular delivery agents as indicated by confocal studies of endosomal versus cytoplamic siRNA location using fluorescently labeled siRNA. DLinK-DMA and DLinKC2-DMA formulations exhibited improved gene silencing potencies relative to DLinDMA but were less toxic. In vivo results showed that LNP siRNA systems containing DLinKC2-DMA are effective agents for silencing GAPDH in APCs in the spleen and peritoneal cavity following systemic administration. Gene silencing in APCs was RNAi mediated and the use of larger LNPs resulted in substantially reduced hepatocyte silencing, while similar efficacy was maintained in APCs. These results are discussed with regard to the potential of LNP siRNA formulations to treat immunologically mediated diseases.

Accelerated blood clearance of PEGylated liposomes upon repeated injections: Effect of doxorubicin-encapsulation and high-dose first injection

The "accelerated blood clearance (ABC) phenomenon", causing PEGylated liposomes to be cleared very rapidly from the circulation upon repeated injection, has been reported to occur in rodents and rhesus monkeys. This rapid clearance was reported to be caused by the binding of PEG-specific IgM, which was generated by the first dose of injected liposomes, to the second dose of liposomes and the subsequent activation of complement, serving in turn as an opsonin. Although there are several PEGylated liposomal formulations, such as Doxil/Caelyx loaded with doxorubicin (DXR), in clinical use, the rapid clearance phenomenon has never been reported for such formulations. In the present article, we report that a first injection of PEGylated liposomes containing encapsulated DXR failed to induce the ABC phenomenon. Likewise, no rapid clearance of the test dose was observed when the first dose of "empty" PEGylated liposomes (without DXR) exceeded 5 micromol phospholipids/kg. By contrast, "empty" PEGylated liposomes at a low dose (1 micromol phospholipids/kg) induced the phenomenon as before. Western blot analysis revealed abundant binding of IgM to PEGylated liposomes when these were incubated in serum from rats that had received "empty" PEGylated liposomes. Substantially less binding of IgM was found when the liposomes were incubated in serum from rats treated with DXR-loaded PEGylated liposomes. For both the empty and the DXR-containing liposomes the amounts of IgM binding to the liposomes decreased with an increasing dose of injected liposomes. Serum obtained from rats following injection of empty PEGylated liposomes caused complement activation by addition of PEGylated liposomes in an inversely dose-dependent manner: the lower the dose, the higher the complement activation. By contrast, no complement activation was detected with serum from rats that had been treated with DXR-loaded PEGylated liposomes. These findings suggest that encapsulation of DXR as well as a relatively high lipid dose abrogate the immune response against PEGylated liposomes which is observed with the same liposomes but without DXR and at low doses. Our observations may thus have important implications for the development, evaluation and therapeutic use of liposomal cytotoxic drug formulations requiring multiple injection schemes.

Effect of repetitive administration of Doxorubicin-containing liposomes on plasma pharmacokinetics and drug biodistribution in a rat brain tumor model

PURPOSE

The incorporation of doxorubicin in long-circulating sterically stabilized liposomes (SSL-DXR) alters the pharmacokinetics and biodistribution of doxorubicin and therefore has the potential to alter the pharmacologic properties of doxorubicin. Previously, we showed that repetitive administration of SSL-DXR alters tumor vascular permeability.

EXPERIMENTAL DESIGN

Here, we investigated the effect of weekly i.v. injections of SSL-DXR on plasma pharmacokinetics and drug biodistribution in the orthotopic 9L rat brain tumor model.

RESULTS AND CONCLUSIONS

The pharmacokinetics of free doxorubicin (5.67 mg/kg) did not change with repeat dosing. In contrast, drug concentrations in plasma and brain tumor increased and deposition in liver and spleen decreased after administration of the second of two weekly doses of SSL-DXR. Noncompartmental analysis and descriptive pharmacokinetic models were created to test hypotheses relating to the mechanisms responsible for alterations in SSL-DXR deposition. The analysis suggested that weekly administration of SSL-DXR significantly (P < 0.05) decreased the plasma elimination rate of SSL-DXR (34%) and decreased drug deposition in liver (2-fold) and spleen (3.5-fold). The pharmacokinetic model that best captured the observed 2.5-fold increase in tumor uptake of SSL-DXR mediated by repeat dosing was one that hypothesized that the rates of drug influx/efflux into tumor were increased by the first dose of SSL-DXR. Models that accounted only for residual drug deposited in the tissue or blood by the first weekly injection provided inferior fits to the data. Thus, the effects of repetitive dosing on SSL-DXR deposition in tumor are consistent with a treatment-mediated alteration of tumor vascular permeability.

Trastuzumab and liposomal Doxorubicin in the treatment of mcf-7 xenograft tumor-bearing mice: combination does not affect drug serum levels

PURPOSE

We assessed the combination of doxorubicin or liposomal doxorubicin with trastuzumab for alterations in peak serum drug levels, as these agents are increasingly being paired in the treatment of aggressive breast cancer. We hypothesized that trastuzumab would exhibit a slower rate of elimination from the serum when in combination with liposomal doxorubicin based on the known effects of liposomal doxorubicin on phagocytic cells of the mononuclear phagocyte system (MPS), which are responsible in part for the uptake and degradation of antibodies.

METHODS

Doxorubicin and trastuzumab serum levels were assessed following injection of free doxorubicin, liposomal doxorubicin, or trastuzumab into female RAG2-M mice bearing subcutaneous MCF-7(HER-2) tumors. The effects of combination drug treatment on tumor growth were compared to single-agent treatment.

RESULTS

Peak serum trastuzumab levels were not altered as a result of addition of doxorubicin therapy, nor were doxorubicin levels altered over 24 h as a result of coadministration of trastuzumab. Liposomal doxorubicin administration did result in serum doxorubicin levels 200- to 1000-fold higher than with injection of free doxorubicin.

CONCLUSIONS

For the specific combination of trastuzumab with doxorubicin, either in free or liposomal form, coadministered in mice, there was no impact of one drug on the other in terms of peak serum drug levels or efficacy.

The Liposomal Formulation of Doxorubicin

Doxorubicin is the best known and most widely used member of the anthracycline antibiotic group of anticancer agents. It was first introduced in the 1970s, and since that time has become one of the most commonly used drugs for the treatment of both hematological and solid tumors. The therapy-limiting toxicity for this drug is cardiomyopathy, which may lead to congestive heart failure and death. Approximately 2% of patients who have received a cumulative (lifetime) doxorubicin dose of 450-500 mg?m(2) will experience this condition. An approach to ameliorating doxorubicin-related toxicity is to use drug carriers, which engender a change in the pharmacological distribution of the drug, resulting in reduced drug levels in the heart. Examples of these carrier systems include lipid-based (liposome) formulations that effect a beneficial change in doxorubicin biodistribution, with two formulations approved for clinical use. Drug approval was based, in part, on data suggesting that beneficial changes in doxorubicin occurred in the absence of decreased therapeutic activity. Preclinical (animal) and clinical (human) studies showing that liposomes can preferentially accumulate in tumors have provided a rationale for improved activity. Liposomes represent ideal drug delivery systems, as the microvasculature in tumors is typically discontinuous, having pore sizes (100-780 nm) large enough for liposomes to move from the blood compartment into the extravascular space surrounding the tumor cells. Liposomes, in the size range of 100-200 nm readily extravasate within the site of tumor growth to provide locally concentrated drug delivery, a primary role of liposomal formulation. Although other liposomal drugs have been prepared and characterized due to the potential for liposomes to improve antitumor potency of the encapsulated drug, the studies on liposomal doxorubicin have been developed primarily to address issues of acute and chronic toxicity that occur as a consequence of using this drug. It is important to recognize that research programs directed toward the development of liposomal doxorubicin occurred concurrently with synthetic chemistry programs attempting to introduce safer and more effective anthracycline analogues. Although many of these drugs are approved for use, and preliminary liposomal formulations of these analogues have been prepared, doxorubicin continues to be a mainstay of drug cocktails used in the management of most solid tumors. It will be of great interest to observe how the approved formulations of liposomal doxorubicin are integrated into combination regimes for treatment of cancer. In the meantime, we have learned a great deal about liposomes as drug carriers from over 20 years of research on different liposomal doxorubicin formulations, the very first of which were identified in the late 1970s. This chapter will discuss the various methods for encapsulation of doxorubicin into liposomes, as well as some of the important interactions between the formulation components of the drug and how this may impact the biological activity of the associated drug. This review of methodology, in turn, will highlight research activities that are being pursued to achieve better performance parameters for liposomal formulations of doxorubicin, as well as other anticancer agents being considered for use with lipid-based carriers.

Surface-associated serum proteins inhibit the uptake of phosphatidylserine and poly(ethylene glycol) liposomes by mouse macrophages

Serum proteins, acting as opsonins, are believed to contribute significantly to liposome-macrophage cell association and thus regulate liposome uptake by cells of the mononuclear phagocytic system (MPS). We studied the effect of serum protein on binding and uptake of phosphatidylglycerol-, phosphatidylserine-, cardiolipin-, and N,N-dioleyl-N,N-dimethylammonium chloride- (DODAC) containing as well as poly(ethylene glycol)- (PEG) containing liposomes by mouse bone marrow macrophages in vitro. Consistent with the postulated surface-shielding properties of PEG, protein-free uptake of liposomes containing 5 mol% PEG and either 20 mol% anionic phosphatidylserine or 20 mol% cationic DODAC was equivalent to uptake of neutral liposomes. In contrast to previous reports indicating that protein adsorption to liposomes increases uptake by macrophages, the presence of bound serum protein did not increase the uptake of these liposomes by cultured macrophages. Rather, we found that pre-incubating liposomes with serum reduced the uptake of liposomes containing phosphatidylserine. Surprisingly, serum treatment of PEG-containing liposomes also significantly reduced liposome uptake by macrophages. It is postulated that, in the case of phosphatidylserine liposomes, the bound serum protein can provide a non-specific surface-shielding property that reduces the charge-mediated interactions between liposomes and bone marrow macrophage cells. In addition, incubation of PEG-bearing liposomes with serum can result in a change in the properties of the PEG, resulting in a surface that is better protected against interactions with cells.

Sequestration of adenoviral vector by Kupffer cells leads to a nonlinear dose response of transduction in liver

Systemic administration of a recombinant adenovirus encoding the human interferon-beta gene (H5.110CMVhIFN-beta) results in transduction of hepatocytes and detectable circulating levels of IFN-beta protein. In preclinical studies in mice, we noticed a distinctly nonlinear dose response, with low levels of virus (1-3 x 10(10) viral particles) yielding barely detectable levels of IFN-beta but with a higher viral dose (1 x 10(11) particles) resulting in disproportionately high IFN-beta levels. Further studies showed that transgene expression levels from low viral doses could be dramatically enhanced by coadministering an unrelated recombinant adenovirus (H5.110CMVlacZ), suggesting that there was a viral dose threshold effect for efficient viral transduction and/or IFN-beta expression. This enhancement of reporter expression by a nonreporter adenovirus, effective upon coadministration, was further enhanced by preadministration of H5.110CMVlacZ (up to 8 h), but was ineffective if the helper virus was administered as little as 5 min after the H5.110CMVhIFN-beta reporter virus. Our data suggest that the reticuloendothelial system plays a role in this threshold effect, such that low doses of virus are efficiently taken up by the RES/Kupffer cells without leading to appreciable transgene expression, whereas high doses saturate these cells and are able to productively transduce hepatocytes. A better understanding of this phenomenon could have an impact on gene therapy clinical trial safety and efficacy.

Structural and metabolic consequences of liposome-lipoprotein interactions

The two major proposed uses for liposomes, i.e., drug delivery and mobilization of peripheral deposits of cholesterol, each impose requirements and restrictions on liposomal structure, particularly as it affects interactions with lipoproteins. This chapter focuses on the role of lipoproteins and apolipoproteins in (1) disrupting membrane structure and causing the leakage of liposomal contents by inducing disc formation and (2) marking liposomes for whole-particle uptake by receptors involved in lipoprotein metabolism. Control of membrane stability and whole-particle half-life can be achieved by several strategies, such as membrane stiffening, shielding the membrane surface, and increasing the dose or predosing with "empty" liposomes. The rationales and applicabilities of these strategies are discussed in the contexts of liposomes as drug delivery vehicles and as antiatherogenic particles. Directions for further basic and applied research are also presented.

Clearance properties of liposomes involving conjugated proteins for targeting

This review examines methods of protein conjugation onto liposomes and the effects of surface bound protein on the liposomes' biological behavior. It is evident that the presence of a conjugated protein significantly alters the attributes of targeted liposomes. Specifically, protein conjugation can result in dramatic increases in liposome size, enhanced immunogenicity, and increased plasma elimination. Techniques are discussed for preventing some of the physical (size) and biological (immunogenic) alterations involving the use of PEG-lipids and drug loaded liposomes. In addition, the advantages of conjugating antibodies via carbohydrate moieties, to minimize changes in antibody binding and tertiary structure as well as effectively decreasing plasma elimination, are also discussed. It is, however, apparent that the accessibility of targeted liposomes to extravascular sites is a key step that will require further study and it is, therefore, anticipated that with the development of novel ligands and novel ligand-liposome interactions, the therapeutic utility of targeting strategies will likely be realized.

An immune response to ovalbumin covalently coupled to liposomes is prevented when the liposomes used contain doxorubicin

It is now well established that liposomes with surface associated proteins are immunogenic. Repeated administration of protein coated liposomes elicits the generation of antibodies and the elimination of proteoliposome increases markedly in animals 'immunized' with such liposomes. This immune response compromises the therapeutic potential of liposomal formulations that rely on the use of protein- or peptide-based targeting ligands to enhance cell specificity. Strategies to suppress or inhibit such immune responses must be developed if this technology is going to prove therapeutically viable. This study evaluates whether an immune response to a protein, covalently attached to liposomes by a thioether bond between N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP)-modified-protein and N-(4-(P-maleimidophenyl)butyryl) (MPB)-activated lipids, can be suppressed when the liposomes used contain the anti-cancer drug doxorubicin. To assess this, the highly immunogenic protein ovalbumin was conjugated onto liposomes composed of distearoylphosphatidylcholine/cholesterol (DSPC/Chol) with sufficient poly(ethylene glycol)-modified distearoyl phosphatidylethanolamine (PEG-DSPE) (2 mol%) to prevent liposome aggregation during protein coupling and to engender increased circulation lifetimes. The immune response to these liposomes with and without encapsulated doxorubicin was measured by: (1) monitoring liposome elimination after 3 weekly i.v. injections in C3H/HeJ mice and (2) measuring the anti-ovalbumin antibody levels by an ELISA assay. One week after a single dose of ovalbumin-coated PEG liposomes (50 microg protein/mouse) the immune response resulted in rapid elimination of a second dose of ovalbumin-coated PEG liposomes. Rapid liposome elimination was correlated to generation of high levels (> 9 microg/ml plasma) of circulating anti-ovalbumin IgG. In contrast, anti-ovalbumin antibodies were not detected when the liposomes used contained doxorubicin. Plasma elimination of these drug loaded protein coated liposomes decreased following repeated weekly i.v. doses, an effect that is consistent with liposomal doxorubicin mediated suppression of phagocytic cells in the liver.

Sphingomyelin-cholesterol liposomes significantly enhance the pharmacokinetic and therapeutic properties of vincristine in murine and human tumour models

This study reports on the development of a liposomal formulation of vincristine with significantly enhanced stability and biological properties. The in vitro and in vivo pharmacokinetic, tumour delivery and efficacy properties of liposomal vincristine formulations based on sphingomyelin (SM) and cholesterol were compared with liposomes composed of distearoylphosphatidylcholine (DSPC) and cholesterol. SM/cholesterol liposomes had significantly greater in vitro stability than did similar DSPC/cholesterol liposomes. SM/cholesterol liposomes also had significantly improved biological properties compared with DSPC/cholesterol. Specifically, SM/cholesterol liposomes administered intravenously retained 25% of the entrapped vincristine after 72 h in the circulation, compared with 5% retention in DSPC/cholesterol liposomes. The improved retention properties of SM/cholesterol liposomes resulted in plasma vincristine levels 7-fold higher than in DSPC/cholesterol liposomes. The improved circulation lifetime of vincristine in SM/cholesterol liposomes correlated with increased vincristine accumulation in peritoneal ascitic murine P388 tumours and in subcutaneous solid A431 human xenograft tumours. Increased vincristine delivery to tumours was also accompanied by increased anti-tumour efficacy. Treatment with SM/cholesterol liposomal formulations of vincristine resulted in greater than 50% cures in mice bearing ascitic P388 tumours, an activity that could not be achieved with the DSPC/cholesterol formulation. Similarly, treatment of mice with severe combined immunodeficiency (SCID) bearing solid human A431 xenograft tumours with SM/cholesterol vincristine formulations delayed the time required for 100% increase in tumour mass to > 40 days, compared with 5 days, 7 days and 14 days for mice receiving no treatment or treatment with free vincristine or DSPC/cholesterol formulations of vincristine respectively.

Liposomal doxorubicin-induced toxicity: depletion and impairment of phagocytic activity of liver macrophages

Doxorubicin entrapped within conventional liposomes (200 nm in diameter; lip-Dox) has major toxic effects on liver macrophages of the rat for a considerable period of time following i.v. administration, with respect to both specific phagocytic capacity and cell numbers. At different time-points after injection of lip-Dox or free doxorubicin, radiolabeled, negatively charged, "empty" test liposomes were injected. Phagocytic capacity was determined by isolating the liver macrophages and measuring the amount of macrophage-associated radioactivity. Four subfractions of liver macrophages of different cell-size and with intrinsically different phagocytic capacity were isolated. Twenty-four hours after injection of lip-Dox, the phagocytic capacity of the larger-sized liver macrophages was strongly decreased. The relatively low intrinsic phagocytic capacity of the smaller-sized macrophages was only slightly impaired. Phagocytic capacity after injection of lip-Dox was nearly restored to control values after 14 days. Blood clearance of Klebsiella pneumoniae bacteria after pre-treatment with lip-Dox was strongly decreased. Pre-treatment with the free drug and/or placebo liposomes had no effect on phagocytic and bacterial blood-clearance capacity. A major depletion of the liver macrophage population was observed, as revealed by both macrophage isolation and histology. Only 2 weeks after injection of lip-Dox, the number of cells had returned to that seen in control animals. In view of the important host-defense functions of the liver macrophages, especially in the control of tumor growth and infection, the findings reported here should be taken into consideration when lip-Dox is to be administered in anti-tumor therapy.

Drug distribution and a pulmonary adverse effect of intraperitoneally administered doxorubicin niosomes in the mouse

Niosomes (non-ionic surfactant vesicles) prepared from C16G2 (a hexadecyl-diglycerol ether), and loaded with doxorubicin, were administered intraperitoneally to male AKR mice at dose levels of 0, 2.5, 5.0, and 10.0 mg kg-1. Free drug was given at 10.0 mg kg-1 by the intraperitoneal route. At a dose level of 10.0 mg kg-1, peak doxorubicin levels in the central compartment were attained faster with the free drug than with the niosome formulation. However, the peak plasma levels were similar for the free drug and the niosome preparation at the 10 mg kg-1 dose level. With doxorubicin administered as the niosome preparation by the intraperitoneal route at 2.5, 5.0, and 10.0 mg kg-1, mean peak plasma concentrations of the drug showed a tendency to be dose-related although the differences were not significant. Over the 24 h period of the experiment, with doxorubicin at 10 mg kg-1, the niosome formulation delivered significantly more drug to the plasma compartment than the free drug (p < 0.05). When doxorubicin was given in niosomes at 2.5, 5.0 and 10.0 mg kg-1 by the intraperitoneal route, the resulting levels of doxorubicin in cardiac tissue were not dose related and the differences not significant and, although the mean peak cardiac-tissue concentration was higher in animals receiving the free drug at 10.0 mg kg-1 intraperitoneally than in mice given intraperitoneal doxorubicin niosomes at this dose level, the differences were again not significant. There were clinical signs of toxicity in mice given doxorubicin-containing niosomes intraperitoneally at 5.0 and 10.0 mg kg-1, and at post-mortem an accumulation of fluid in the pleural cavity was evident. These changes were not seen in mice dosed intraperitoneally with free drug at 10 mg kg-1, or in animals given doxorubicin niosomes intraperitoneally at 2.5 mg kg-1. In mice dosed intraperitoneally with doxorubicin niosomes at 12.0 mg kg-1 and at a dose volume of 0.2-0.4 mL, histological examination of the lungs demonstrated a congestion of the alveolar capillaries, and an increased number of acute inflammatory cells in the alveolar walls. There was no histological evidence of lung toxicity in mice dosed with doxorubicin niosomes at 12.0 mg kg-1 when the formulation was administered with the higher dose volume of 1.8-2.0 mL. Importantly there was no histological evidence of lung toxicity in mice dosed with empty niosomes intraperitoneally or with doxorubicin niosomes given intravenously at 12.0 mg kg-1.

Inclusion of ganglioside GM1 into liposome encapsulated hemoglobin does not extend circulation persistence at clinically relevant doses

This investigation has evaluated the substitution of ganglioside GM1 for dimyristoyl phosphatidylglycerol (DMPG) in the preparation of liposome encapsulated hemoglobin (LEH), with the intention of increasing the circulation persistence of this potential oxygen carrier. Although equivalent yields of each formulation were produced by microfluidization, the hemoglobin encapsulation efficiency was greater for GM1-LEH than DMPG-LEH. Similar particle sizes, phospholipid content, methemoglobin levels, and oxygen-carrying capacity were observed for both formulations. Zeta potential measurements to monitor liposomal surface charge showed GM1-LEH to be more electropositive than DMPG-LEH. Using differential scanning calorimetry, similar enthalpy values and hemoglobin structural transition temperatures were determined for both LEH formulations. Circulation persistence of each LEH formulation was determined following a 0.25 ml (1 g phospholipid/Kg body weight) or 0.5 ml (2 g phospholipid/Kg body weight) injection in mice. During the first 18 hours, GM1-LEH was cleared at a faster rate than DMPG-LEH at both dosages studied. Then the remaining liposomes of each formulation were removed with identical circulation profiles until no liposomes were remaining in circulation at either 50 hours (0.25 ml) or 72 hours (0.5 ml) post-injection. These data reveal that the use of ganglioside GM1 to solely increase the circulation persistence of LEH was of little benefit.