5.1 Liposomal formulations for the treatment of cancer and other diseases are the most common form of nanotechnology-enabled drug products submitted for market approval and in clinical application at the present time. The accurate characterization of their physical-chemical properties is critical to support the development and assessment of such products (2). In particular, size, size distribution, shape, and physical stability are key properties (among others) that have been widely identified as critical quality attributes (CQAs) for liposomal drug products.

5.1.1 Asymmetrical-flow field-flow fractionation (AF4) is a chromatographic-like technique that uses hydrodynamic forces to gently separate analytes into their component populations according to size and diffusivity (3 and 4). The fractionated sample then passes through one or more online detectors chosen specifically for the application requirements. The combination of low-shear separation, tolerance for complex matrices, and exceptionally broad size range make AF4 a technique of choice for application to nanotechnology-enabled drug products such as liposomes (13, 5-9).

5.1.2 Multi-detector AF4 is suitable for research and development, manufacturing quality control, product stability/shelf-life testing and regulatory assessments.

5.1.3 There are multiple assumptions inherent in the application of MD-AF4, including the appropriateness of models used to interpret online light scattering data and the compatibility of the analyte and matrix with the membrane that forms the surface of the accumulation wall in the fractionation channel. Other assumptions are detector or analyte specific.

5.2 Chemical components of the mobile phase must not induce agglomeration of liposomes or otherwise significantly alter their physical properties.

5.3 Discretion should be used in the interpretation of size data obtained by different scattering detectors using different scattering models and modes of analysis.

5.4 The Current Good Manufacturing Practice for Finished Pharmaceuticals (see 21 CFR 211.194(a)(2)) and the ICH Harmonized Tripartite Guideline on Validation of Analytical Procedures Q2(R1) (10), state that the suitability of all test methods shall be verified under actual conditions of use.

5.5 MD-AF4 can be compared with batch mode dynamic light scattering (DLS) for the determination of liposome mean size and size distribution, where MD-AF4 provides deconvolution of complex mixtures yielding a more accurate assessment of the populations present. Batch mode DLS (see, for instance, Test Method E3247) provides a rapid, low-cost approach that can be used to screen materials prior to analysis by MD-AF4. The latter requires substantially more analyst time and effort along with appropriate training and expertise. Qualitatively, MD-AF4 offers greater insight into the physical complexity of a sample via the fractionation process in combination with multiple detectors.

1.1 This test method describes a measurement procedure to reproducibly separate component size populations present within liposomal drug formulations and to characterize their associated size and size distribution. The method can also yield information on the shape and physical stability of the liposomes and is applicable to measurements in the presence of serum proteins. Fractions can be collected for off-line analysis using various techniques not specified in this test method.

1.2 This test method applies to uni-lamellar and multi-lamellar liposomes that are designed for drug delivery and which are dispersed in a native solution that is aqueous in nature. The method is generally applicable over a particle size range (radius) of approximately 10 nm to 250 nm, and for injected lipid mass from 20 µg to 200 µg.

1.3 This test method is based on the multi-detector asymmetrical-flow field-flow fractionation (MD-AF4) technique as configured on a typical commercial instrument platform with online detectors such as multi-angle (static) light scattering (MALS), dynamic light scattering (DLS), ultraviolet-visible (UV-Vis) absorbance, and differential refractive index (dRI) (1).2

1.4 This method does not address liposome composition. Refer to Test Methods E3297, E3323, or E3324 for lipid quantification.

1.5 Units—The values stated in SI units are to be regarded as standard. Where appropriate, cgs units are given in addition to SI.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.