The arnphipathic anthracycline base doxorubicin (DXR) was accumulated in the aqueous phase of the liposomes where it reached a level as high as 100-fold its concentration in the remote loading medium. Most of the intraliposomal D X R was present in an aggregated state. Eflicient (>90%) and stable loading into the liposomes' and ligandoliposomes' aqueous phase was obtained by using gradients of ammonium sulfate in which the ammonium sulfate concentration in the liposomes was higher than its concentration in the extraliposomal medium [(NH,),SO,)lip. > > [(NH,),SO,)med.]. The "remote" loading is a result of the D X R exchange with ammonia from (NH,),SO,. Both the ammonium and sulfate contribute to high level and stability of the loading. The ammonium sulfate gradient method differs from most other chemical approaches used for remote loading of liposomes since it neither requircs to prepare the liposomes in ijcidic pH, nor to alkalinize the extraliposomal aqucous phase. Although most of the intraliposomal D X R is present in an aggregated gel-like state, the drug is bioavailable. This approach permits the preparation of DXRloaded liposomes of a broad spectrum of types, sizes, and composition, including sterically-stabilized liposomes, irnmunoliposomes, and sterically-stabilized immunoliposomes. Due to the long shelf stability (>6 mo), no "bedside" remote 455

This novel liposomal formulation had a favorable drug-to-phospholipid ratio and prolonged the duration of bupivacaine analgesia in a dose-dependent manner. If these results in healthy volunteers can be duplicated in the clinical setting, this formulation has the potential to significantly impact the management of pain.

OBJECTIVE— The pathogenesis of type 1 diabetes involves autoimmune lymphocytic destruction of insulin-producing β-cells and metabolic dysregulation. An early biomarker of pancreatic islet damage is islet microvascular dysfunction, and alterations in vascular volume, flow, and permeability have been reported in numerous models of type 1 diabetes. Consequently, the ability to noninvasively monitor the dynamics of the pancreatic microvasculature would aid in early diagnosis and permit the assessment, design, and optimization of individualized therapeutic intervention strategies. RESEARCH DESIGN AND METHODS— Here, we used the long circulating paramagnetic contrast agent, protected graft copolymer (PGC) covalently linked to gadolinium-diethylenetriaminepentaacetic acid residues (GdDTPAs) labeled with fluorescein isothiocyanate (PGC-GdDTPA-F), for the noninvasive semiquantitative evaluation of vascular changes in a streptozotocin (STZ)-induced mouse model of type 1 diabetes. Diabetic animals and nondiabetic controls were monitored by magnetic resonance imaging (MRI) after injection of PGC-GdDTPA-F. RESULTS— Our findings demonstrated a significantly greater accumulation of PGC-GdDTPA-F in the pancreata of diabetic animals compared with controls. MRI permitted the in vivo semiquantitative assessment and direct visualization of the differential distribution of PGC-GdDTPA-F in diabetic and control pancreata. Ex vivo histology revealed extensive distribution of PGC-GdDTPA-F within the vascular compartment of the pancreas, as well as considerable leakage of the probe into the islet interstitium. By contrast, in nondiabetic controls, PGC-GdDTPA-F was largely restricted to the pancreatic vasculature at the islet periphery. CONCLUSIONS— Based on these observations, we conclude that in the STZ model of type 1 diabetes, changes in vascular volume and permeability associated with early stages of the disease can be monitored noninvasively and semiquantitatively by MRI.

Initially developed in 1992 as an MR imaging agent, the family of protected graft copolymers (PGC) is based on a conjugate of polylysine backbone to which methoxypoly(ethylene glycol) (MPEG) chains are covalently linked in a random fasion via N-ε-amino groups. While PGC is relatively simple in terms of its chemcial composition and structure, it has proved to be a versatile platform for in vivo drug delivery. The advantages of poly amino acid backbone grafting include multiple available linking sites for drug and adaptor molecules. The grafting of PEG chains to PGC does not compromise biodegradability and does not result in measurable toxicity or immunogenicity. In fact, the biocompatablility of PGC has resulted in its being one of the few 100% synthetic non-proteinaceous macromolecules that has suceeded in passing the initial safety phase of clinical trials. PGC is capable of long circulation times after injection into the blood stream and as such found use early on as a carrier system for delivery of paramagnetic imaging compounds for angiography. Other PGC types were later developed for use in nuclear medicine and optical imaging applications in vivo. Recent developments in PGC-based drug carrier formulations include the use of zinc as a bridge between the PGC carrier and zinc-binding proteins and re-engineering of the PGC carrier as a covalent amphiphile that is capabe of binding to hydrophobic residues of small proteins and peptides. At present, PGC-based formulations have been developed and tested in various disease models for: 1) MR imaging local blood circulation in stroke, cancer and diabetes; 2) MR and nuclear imaging of blood volume and vascular permeability in inflammation; 3) optical imaging of proteolytic activity in cancer and inflammation; 4) delivery of platinum(II) compounds for treating cancer; 5) delivery of small proteins and peptides for treating diabetes, obesity and myocardial infarction. This review summarizes the experience accumulated by various research groups that chose to use PGC as a drug delivery platform.

Bupivacaine-DRV may have a role in achieving safe, effective, and prolonged analgesia in humans.