Mary S. Newman

Doxorubicin Encapsulated in Liposomes Containing Surface‐Bound Polyethylene Glycol: Pharmacokinetics, Tumor Localization, and Safety in Patients with AIDS‐Related Kaposi's Sarcoma

A study of the plasma pharmacokinetics, tumor localization, and safety of a single dose of doxorubicin encapsulated in liposomes containing surface‐bound polyethylene glycol (PEG‐liposomal doxorubicin) was conducted in patients with Kaposis sarcoma (KS) as a manifestation of acquired immune deficiency syndrome (AIDS). Eighteen patients with AIDS‐KS diagnosed by examination of biopsy specimens were randomly assigned to receive either standard doxorubicin or PEG‐liposomal doxorubicin. Consecutive participants were entered at three dose levels (10, 20, and 40 mg/m2) in ascending fashion. Clearance of PEG‐liposomal doxorubicin was 0.034 L/h/m2 to 0.108 L/h/m2, volume of distribution (Vd) was 2.2 L/m2 to 4.4 L/m2, and half‐lives (t1/2) of the initial decline in the plasma concentration—time curve and of the terminal decline were 3.77 hours and 41.3 hours, respectively. Seventy‐two hours after administration, doxorubicin levels observed in lesions of patients receiving PEG‐liposomal doxorubicin were 5.2 to 11.4 times greater than those found in patients given comparable doses of standard doxorubicin. PEG‐liposomal doxorubicin and standard doxorubicin were roughly equipotent in producing toxicity. Encapsulation in liposomes containing surface‐bound PEG significantly limits the distribution and elimination of doxorubicin, results in greater accumulation of the drug in KS lesions 72 hours after dosing than does standard doxorubicin, and may improve drug efficacy and therapeutic index in the treatment of AIDS‐KS.

Insertion of poly(ethylene glycol) derivatized phospholipid into pre‐formed liposomes results in prolonged in vivo circulation time

Transfer of MPEG1900‐DSPE from micellar phase to pre‐formed liposomes imparts long in vivo circulation half‐life to an otherwise rapidly cleared lipid composition. MPEG1900‐DSPE transfers efficiently and quickly in a time and temperature dependent manner. There is negligible content leakage and a strong correlation between assayed mol% MPEG1900‐DSPE, liposome diameter increase, and pharmacokinetic parameters such as distribution phase half‐life. Since a biological attribute (liposome clearance rate) can be modified by the insertion process, it suggests a simple and economical way to impart site‐specific targeting to a variety of liposome delivery systems. This method is also a convenient way to measure the ‘brush’ thickness of such conjugates directly.

Comparative pharmacokinetics, tissue distribution, and therapeutic effectiveness of cisplatin encapsulated in long-circulating, pegylated liposomes (SPI-077) in tumor-bearing mice

Purpose: The pharmacokinetics (PK), biodistribution and therapeutic efficacy of cisplatin encapsulated in long-circulating pegylated (Stealth®) liposomes (SPI-077) were compared with those of nonliposomal cisplatin in two murine (C26 colon carcinoma and Lewis lung) tumor models. Methods: In therapeutic effectiveness studies, mice bearing murine C26 or Lewis lung tumors received multiple intravenous doses of SPI-077 or cisplatin in a variety of treatment schedules and cumulative doses. In the PK and biodistribution study, mice received a single intravenous bolus injection of 3 mg/kg of either SPI-077 or cisplatin 14 days after inoculation with 106 C26 tumor cells. Plasma and tissues were analyzed for total platinum (Pt) content by graphite furnace (flameless) atomic absorption spectrophotometery (GF-AAS). Results: Efficacy studies showed that SPI-077 had superior antitumor activity compared to the same cumulative dose of cisplatin. When lower doses of SPI-077 were compared to cisplatin at its maximally tolerated dose in Lewis lung tumors, equivalent SPI-077 antitumor activity was seen at only half the cisplatin dose. Higher cumulative doses of SPI-077 were well tolerated and had increased antitumor effect. SPI-077 PK were characterized by a one-compartment model with nonlinear (saturable) elimination, whereas cisplatin PK were described by a two-compartment model with linear elimination. SPI-077 had a 55-fold higher volume of distribution, 3-fold higher peak plasma levels, and a 60-fold larger plasma AUC compared with cisplatin. In addition, SPI-077-treated animals displayed a 4-fold reduction in Pt delivered to the kidneys (primary target organ of toxicity) relative to cisplatin, but a 28-fold higher tumor AUC than cisplatin. Conclusions: Based on the results of our studies, encapsulation of cisplatin in long-circulating pegylated liposomes has overcome limitations experienced with other liposomal cisplatin formulations. SPI-077 has a prolonged circulation time and increased tumor Pt disposition, and its antitumor effect is significantly improved compared to cisplatin in murine colon and lung cancer models.

Long circulating, cationic liposomes containing amino‐PEG‐phosphatidylethanolamine

Ligand attachment to polyethylene glycol (PEG) grafted, long circulating liposomes at the polymer terminus is of interest for targeting but the effect of positively charged groups is unknown. Amino‐polyethylene glycol‐phosphatidylethanolamine (AminoPEG‐PE), prepared in four steps from α‐amino‐ω‐hydroxy‐PEG, was tested for influence on liposome interactions in vivo: blood circulation and biodistribution. Despite surface amines on each liposome conferring cationic behavior, in vivo properties are comparable to those obtained with methoxy‐PEG‐PE. The consequences are profound for targeting and possibly systemic delivery of cationic lipidic‐polynucleotide complexes.

Sterically Stabilized Liposomes: Physical and Biological Properties

Advanced liposomal therapeutics has been attained by liposome surface modification, initially with specific glycolipids and subsequently with surface-grafted PEG, reducing in vivo rapid recognition and uptake, giving prolonged blood circulation, and providing selective localization in tumors and other pathological sites, as described in recent reviews. The result is improved efficacy of encapsulated agents. The surface PEG may produce a steric barrier, as described for colloids. Reduced in vivo uptake may result from inhibition of plasma-protein adsorption, or opsonization, by the steric coating. Several physical studies support this mechanism, including electrophoretic mobility (zeta potential). Our previous results for 2000-dalton PEG indicated a coating thickness about 5 nm, in agreement with independent measurements. We report here results for 750 to 5000-dalton PEGs. The calculated coating thickness increases with molecular weight in a nonlinear fashion. The dependence of blood circulation and tissue distribution on PEG molecular weight correlates with zeta-potential estimates of PEG-coating thickness. Effects on tissue distribution are reported for liver and spleen, the major phagocytic organs. The biological properties of these liposomes depend on the surface polymer rather than the lipid bilayer, yielding important advantages for lipid-mediated control of drug interaction and release without affecting the biodistribution.

Relationship of dose intensity to the induction of palmar-plantar erythrodysesthia by pegylated liposomal doxorubicin in dogs:

1 The multiple dose pharmacokinetics of pegylated liposomal doxorubicin (PL-DOX), known as DOXIL® (US) and CAELYX® (EU), was characterized in dogs and a pharmacokinetic/pharmacodynamic model to identify a relationship between drug exposure and the probability of observing treatment-related palmarplantar erythrodysesthesia (PPE) was developed. 2 Twenty dogs were assigned to PL-DOX groups (2/sex/ group) that received intravenous PL-DOX doses of 0.5 mg/kg q1, 2, or 4 weeks; 1.0 mg/kg q2weeks; or 1.5 mg/kg q4weeks for 12 weeks. Blood was collected for HPLC analysis of doxorubicin concentration pre-dose and periodically up to 120 h after dosing three times during treatment. 3 Plasma drug concentration was modeled using iterative 2-stage analysis. Dermal lesions (PPE) were scored twice weekly for six regions of each dog using a 0-6 severity scale; maximum severity was 36. PPE score data were modeled using an approach in which the% probability of PPE was related to a hypothetical effect site by a series of Hill-type functions. 4 Pharmacokinetics were best modeled as a one-compartment open model. Vss (ml/kg), CLt (ml/hr/kg) and half-life (h) were 44.1, 1.39 and 23.1, respectively. Cmax increased linearly with dose. CLt decreased with repeated doses. 5 A two-compartment pharmacodynamic model, which correctly predicted 97% of the observed lesion severity, was developed to establish the relationship of lesion severity to dose intensity (a measure of drug exposure incorporating the effect of both dose level and dosing frequency, which can be expressed in units of mg/kg/week). The model demonstrated that maximal PPE was positively correlated with dose intensity, the major factor that affects the incidence and severity of dermal lesions. 6 The model can be used to predict acceptable dose intensities in humans utilizing body surface area conversion factors and comparative AUCs for dogs and humans. It predicts that a dose intensity of 10-12.5 mg/m2 of PL-DOX will be well tolerated in patients. The results of recent clinical studies are consistent with this prediction.

Pharmacokinetics and Tissue Disposition in Monkeys of an Antisense Oligonucleotide Inhibitor of Ha-Ras Encapsulated in Stealth Liposomes

AbstractPurpose. This study examined the pharmacokinetics and tissue distribution of an antisense oligonucleotide ISIS 2503, formulated in stealth (pegylated) liposomes (encapsulated) or in phosphate-buffered saline (unencapsulated). Methods. Encapsulated or unencapsulated ISIS 2503 was administered to rhesus monkeys by intravenous infusion. The concentrations of ISIS 2503 and metabolites in blood, plasma, and tissue samples were determined by capillary gel electrophoresis. Results. Plasma concentrations of encapsulated ISIS 2503 decreased mono-exponentially after infusion with a mean half-life of 57.8 hours. In contrast, the concentration of unencapsulated ISIS 2503 in plasma decreased rapidly with a mean half-life of 1.07 hours. Both encapsulated and unencapsulated ISIS 2503 distributed widely into tissues. Encapsulated ISIS 2503 distributed primarily to the reticulo-endothelial system and there were few metabolites observed. In contrast, unencapsulated ISIS 2503 distributed rapidly to tissue with highest concentration seen in kidney and liver. Nuclease-mediated metabolism was extensive for unencapsulated oligonucleotide in plasma and tissues. Conclusions. The data suggest that stealth liposomes protect ISIS 2503 from nucleases in blood and tissues, slow tissue uptake, and slow the rate of clearance from the systemic circulation. These attributes may make these formulations attractive for delivering oligonucleotides to sites with increased vasculature permeability such as tumors or sites of inflammation.

The effect of vincristine-polyanion complexes in STEALTH liposomes on pharmacokinetics, toxicity and anti tumor activity

Abstract Poly(ethylene glycol) (PEG)-derivatized liposome vehicles improve antitumor effectiveness of entrapped anthracyclines and vinca alkaloids. However, the plasma clearance of entrapped vincristine is substantially faster than the lipid phase or other entrapped aqueous markers, suggesting leakage out of the liposome during transit in the blood compartment. We tested the effect of altering the drug’s in vivo leakage rate on pharmacokinetics, toxicity, and antitumor activity of entrapped drug in rodent models. Suramin, heparin, and dextran sulfate were tested for their ability to produce a precipitable complex in vitro. PEG-derivatized liposomes were prepared with the complexing agent inside, and vincristine was driven inside using an ammonium gradient. The resulting preparations were found to have plasma distribution half-lives significantly longer than the formulation without a complex-forming agent. There was no increase in acute lethality, and in the case of the suramin-vincristine complex, the acute lethality was significantly reduced at the highest does level. Anti-tumor activity against the mouse mammary carcinoma MC2 was tested in a multiple-dose study. Free vincristine did not affect the tumor growth rate significantly, but at the same dose level all PEG-coated liposome formulations inhibited tumor growth markedly. The suramin containing formulation was as effective as the formulation lacking polyanion, but the heparin and dextran sulfate containing formulations were less effective. Thus, compounds which form insoluble complexes with vincristine alter in vivo plasma distribution phase pharmacokinetics without increasing acute lethality, but without a corresponding increase in anti-tumor activity.

The Population Pharmacokinetics of Amphotericin B Colloidal Dispersion in Patients Receiving Bone Marrow Transplants

The purpose of this study was to identify the pharmacokinetics of Amphotericin B Colloidal Dispersion in patients undergoing bone marrow transplantations with systemic fungal infections and to assess the influence of ABCD on renal function. Seventy-five patients (42 females, 33 males) with a median age of 34.5 years and median weight of 70.0 kg were enrolled in the study. The plasma concentration data was available in 51/75 patients and was best described by a two-compartment model; both plasma clearance and volume of distribution increased with escalating doses; the overall average terminal elimination half-life was 29 h. Serum creatinine values over the duration of therapy were available in 59/75 patients. Overall, there was no net change in renal function over the duration of therapy.