Second harmonic generation (SHG) microscopy was used to rapidly identify regions of interest for localized confocal Raman spectroscopy and synchrotron X-ray diffraction (XRD) measurements in order to quantify crystallinity within lyophilized Abraxane® powder (protein bound paclitaxel for injectable suspension). Water insoluble noncentrosymmetric crystalline particles ranging from ~1 micrometer to 120 micrometer were identified by SHG, with wide variability in crystal size and frequency observed between several batches of Abraxane®. By targeting the Raman and XRD analysis to these localized regions identified by SHG, the corresponding reduction in background lowered the limits of detection for both Raman and XRD by 2-3 orders of magnitude relative to ensemble averaged measurements. Experimental Raman spectra of SHG active domains in Abraxane® were in good agreement with experimental spectra of pure crystalline paclitaxel. Peaks identified by synchrotron experiments exhibited significant preferred orientation effects complicating quantitative comparisons with powder patterns. However, the XRD peak positions were generally consistent with calculated peaks for paclitaxel crystal forms found in the Cambridge Structural Database. These collective results are consistent with up to 30% of the active ingredient present as poorly soluble crystalline particulates in some batches of Abraxane®.

Finding the needle in the haystack: Characterization of trace crystallinity in a commercial formulation of paclitaxel protein-bound particles by Raman spectroscopy and synchrotron X-ray diffraction enabled by second harmonic generation microscopy

249th National Meeting (2015)

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