Formation of drug nanocrystals under nanoconfinement afforded by liposomes

Abstract

a Nanocrystals of drug substances have important therapeutic applications, but their preparation is often difficult due to size control in bottom up approaches, or energetic milling and surface activation in top down processing. In this study, confinement within liposome nanocompartments is demonstrated to enable drug crystallization with a high aspect ratio but limited growth resulting in nanocrystals, using a simple freeze-thaw process which is anticipated to be amenable to large scale preparation. After the freeze-thaw, cryo-transmission electron microscopy (cryoTEM) imaging and cryo-electron tomography revealed that the majority of the liposomes contained a single drug nanocrystal, observed to physically stretch but not burst the liposomes, and the composition of the freeze-thaw medium altered the aspect ratio of the drug nanocrystals. Small angle X-ray scattering and dynamic depolarized light scattering were used to confirm the asymmetric nature of particles in suspension to exclude the cryoTEM preparation process as a contributor to the particle morphology. In assessing potential use in controlled release drug delivery, the in vitro release rate of ciprofloxacin from liposomes containing the nanocrystals revealed that the rate of dissolution of the nanocrystals became the rate controlling step, in contrast to the lipid bilayer rate controlling function prior to the formation of the crystals. The ability to modulate the release rate of the active ingredient in a complex formulation using simple physical means (e.g., freeze/thaw) is an attractive possibility, especially in highly regulated industries such as pharmaceuticals where qualitative and quantitative changes of composition would require extensive safety evaluations.

Effective Treatment of Mycobacterium avium subsp. hominissuis and Mycobacterium abscessus Species Infections in Macrophages, Biofilm, and Mice by Using Liposomal Ciprofloxacin

“…All formulations were provided by Aradigm Corp. (Hayward, CA). The CFI formulation contains 50 mg/ml ciprofloxacin hydrochloride (HCl) in 25 mM histidine, 145 mM NaCl, pH 6.0, buffer encapsulated in liposomes composed of hydrogenated soy phosphatidylcholine and cholesterol, which provide the sustained slow release of the drug (16,17,21). The Linhaliq formulation is a 1:1 volume-to-volume mixture of CFI (50 mg/ml) and free ciprofloxacin (20 mg/ml ciprofloxacin HCl) in an acetate-buffered aqueous formulation at pH 3.3, resulting in a final concentration of 35 mg/ml ciprofloxacin HCl (16,17,21).…”

Emerging Opportunities for Inhaled Antibiotic Therapy

“…For a liposomal formulation that is stable to freeze-thaw, there is potential to transform the encapsulated drug into nanocrystalline form after a simple freeze-thaw procedure [40,41]. The presence of drug nanocrystals creates an additional dissolution barrier to transport across the liposome membrane, thus slowing the rate of drug release as shown for a liposomal ciprofloxacin formulation (Figure 2).…”

“…Pulmaquin, which is a mixture of unencapsulated and liposomally encapsulated ciprofloxacin, provides a kinetic profile with a rapid peak of ciprofloxacin followed by the long tail characteristic of release from the liposomally encapsulated component [39]. Moreover, the release profile of a liposomal antibiotic formulation can be modulated by two simple methods to achieve either a slower [40,41] or faster [42] release rate, or combined with a burst effect [40,41].…”

“…For patients with NTM infections within their alveolar macrophages, more of the drug may be retained in the liposomes containing nanocrystalline ciprofloxacin until after being phagocytosed by the macrophages thus increasing the potential for higher drug concentrations in close proximity to the site of infection. Alternatively, a liposome formulation can be diluted with surfactant under hypotonic conditions to yield liposomes with a faster-release profile, or a burst of drug, or a combination of these two elements as shown in Figure 2 [41]. Thus, using the same drug preparation in conjunction with simple physical or chemical modulation, it may one day be possible to 'fine-tune' the relative amounts of the drug in the form of 'bolus' vs. the amount of the sustained release component, as well as its release rate, to achieve optimum outcome based on the knowledge of the individual patient's disease condition.…”

“…As discussed above, formulation of antibiotics into liposomes has the potential to provide once-daily treatment regimens [1,5,[8][9][10]19,[28][29][30][31][32][39][40][41][42]. Pulmaquin, which is a mixture of unencapsulated and liposomally encapsulated ciprofloxacin, provides a kinetic profile with a rapid peak of ciprofloxacin followed by the long tail characteristic of release from the liposomally encapsulated component [39].…”