Remote loading

Remotely load raw materials into mixer (Dumpers place raw materials into feeder hopper). 

Doxil, the first liposomal drug that was approved by the Food and Drug Administration, in 1995, is a good example of the successful application of a transmembrane inner liposome high/outer liposome low ammonium ion gradient for remote loading of an amphipathic weak base, the anticancer... 

Figure 1 Facing page) (A) Mechanism of remote loading of doxorubicin by transmembrane ammonium sulfate gradient. (B) Collapse of transmembrane ammonium ion gradient in SSL by nonactine induces doxorubicin release. (C) Collapse of transmembrane proton gradient in SSL by nigericin induces collapse of transmembrane ammonium ion gradient followed by release of DOX. Abbreviations. DOX, doxorubicin SSL, sterically stabilized liposome.

Table 2 Characterization of 100nm SSL Remote Loaded with DOX via Transmembrane Ammonium Sulfate Gradient ... 

THE DOXIL EXAMPLE FOR REMOTE LOADING OF AMPHIPATHIC WEAK BASE INTO LIPOSOMES... 

Table 3 Comparison Between 100-nm SSL Remote-Loaded with DOX via Higher Inside/Lower Outside Transmembrane Gradients of Either 250 mM Ammonium Sulfate or of Ammonium Glucuronate...

EXPERIMENTAL DEMONSTRATION OF DOX REMOTE LOADING TO FORM DOXIL... 

SUMMARY OF THE CHARACTERIZATION OE 100NM DOX-SSL REMOTE LOADED WITH DOX VIA TRANSMEMBRANE AS GRADIENT... 

Bolotin EM, Cohen R, Bar LK, et al. Ammonium sulfate gradients for efficient and stable remote loading of amphipathic weak bases into liposomes and ligando-liposomes. J Liposome Res 1994 4 455-479. 

Hwang SH, Maitani Y, Qi XR, Takayama K, Nagai T. Remote loading of diclofenac, insulin and fluorescein isothiocyanate labeled insulin into liposomes by pH and acetate gradient methods. Int J Pharm 1999 179 85-95. 

Early studies in our laboratory on membrane potentials and the uptake of weak bases used for the measurement of ApH led to the recognition that a variety of chemotherapeutic drugs could be accumulated within LUVs exhibiting transmembrane pH gradients (59). This remote-loading technique, so named because drug is loaded into preformed vesicles, is based on the membrane permeability of the neutral form of weakly basic drugs such... 

Remote Loading of Doxorubicin into DSPC Cholesterol (55 45) Large Unilamellar Vesicle... 

Remote Loading of Ciprofloxacin into SPM/Cholesterol Large Unilamellar Vesicles... 

The initial mixture and each time point are then assayed for ciprofloxacin and lipid. Lipid can be quantified using the phosphate assay (64,65) or by liquid scintillation counting. Ciprofloxacin is quantified by an absorbance assay following removal of drug from lipid by a Bligh-Dyer extraction procedure (78) (see below). The percent uptake is determined as described in the section Remote Loading of Doxorubicin into DSPC/Cholesterol (55 45) Large Unilamellar Vesicle. ... 

The observation that improved remote loading of ciprofloxacin could be achieved using ammonium sulfate solutions rather than sodium citrate buffers highlighted the need for further investigation and development of drug-loading methodologies. In this section, we examine an approach in... 

Many of the salts employed in the preparation of remote-loading gradients are commercially available and thus involve nothing more than dissolving... 

Figure 7 The stability of liposomal VCR in liposomes prepared using different triethylammonium ion gradients. VCR can be deformylated under acidic conditions, similar to those found in the intraliposomal lumen of remote-loaded liposomes. (A) The deformylated product is inactive compared to the parent drug. (B) HPLC chromatograms show peaks for both VCR (rt = 9.5 minutes) and deformylated VCR (rt= 11.1 minutes) for liposomes prepared with either sulfate or citrate as the intraliposomal trapping agent and stored for three months at 4°C to 6°C. Abbreviation VCR, vincristine.

Drug encapsulation efficiency Active or remote loading [11] Stable liposome encapsulation of drugs at high drug-to-lipid ratios, Many applications in drug delivery... 

Finally, remote loading and active loading [11] are other methods used to achieve high trapping efficiency in liposome formulations, but unfortunately they can only be applied to a small number of drugs with specific physicochemical properties. This technique will be discussed below in Section 5.3.23. 

Active entrapment and loading stability are dependent on liposome lipid composition, lipid quality, medium composition, and temperature as well as on the pK and hydrophobicity of the base. The ammonium sulfate gradient approach differs from most other chemical approaches used for remote loading of liposomes, since it does not require liposomes with acidic pH interior or an alkaline extraliposomal phase. 

The measure of the craze shape ahead of a propagating crack by Brown and Ward [38] appears consistent with the geometry of the plastic zone according to a Dugdale [33] model of a craze. For a precracked specimen under the remote load (Fig. 3), the craze is represented by a plastic zone similar to a strip at the tip of the crack. The profile of the plastic zone varies from zero at the location (a + Ac) to the value Acr at the crack tip. 

The following chapter introduces a remote loading procedure for anthracyclines focussing on the well-established drug doxorubicin. 

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