Polymorphic Transformation of Drugs Induced by Glycopolymeric Vesicles Designed for Anticancer Therapy Probed by...

Understanding the nature of the drug-polymer interactions in micellar drug delivery systems and what happens with the drug and the polymer once the complex has formed is essential for the rational design of the polymeric matrices suitable for a particular drug. In this work, glycopolymeric vesicles-a block copolymer, poly(1-O-methacryloyl-β-d-fructopyranose)-b-poly(methyl methacrylate), (PFru₃₆-PMMA₁₆₀),-designed to target tumor cells loaded with two drugs, ellipticine and curcumin, were characterized. Advanced solid-state NMR spectroscopy and single-crystal/powder X-ray diffraction (XRD) combined with CASTEP calculations shed light on the nature of the drug, the polymer, and their interactions. While the low drug loading (ca. 5%) ensured that the structure, size, and shape of the polymeric vesicles did not change significantly, the solid-state forms of the drugs changed markedly. Upon loading into the vesicles, ellipticine favored a highly ordered form distinctly different from the bulk drug as indicated by ¹³C solid-state NMR spectroscopy. A detailed analysis of the CASTEP-calculated ¹³C spectra derived from crystallographic data based on the lowest mean absolute error showed the best match with form I. Moreover, ellipticine before loading was found as a new polymorph and was described by single-crystal XRD as a new orthorhombic Form III. Likewise, curcumin, originally present in monoclinic Form I was found to recrystallize as metastable orthorhombic Form II inside the vesicles. Intermolecular interactions between the polymeric vesicles and the drugs, ellipticine as well as curcumin, were detected using 2D ¹H magic angle spinning experiments, indicating that the drugs are localized in the hydrophobic layer of the vesicles.