Chemical Analysis of Drug Biocrystals: A Role for Counterion Transport Pathways in Intracellular Drug Disposition

In mammals, highly lipophilic small molecule chemical agents can accumulate as inclusions within resident tissue macrophages. In this context, we characterized the biodistribution, chemical composition, and structure of crystal-like drug inclusions (CLDIs) formed by clofazimine (CFZ), a weakly basic lipophilic drug. With prolonged oral dosing, CFZ exhibited a significant partitioning with respect to serum and fat due to massive bioaccumulation and crystallization in the liver and spleen. The NMR, Raman, and powder X-ray diffraction (p-XRD) spectra of CLDIs isolated from the spleens of CFZ-treated mice matched the spectra of pure, CFZ hydrochloride crystals (CFZ-HCl). Elemental analysis revealed a 237-fold increase in chlorine content in CLDIs compared to untreated tissue samples and a 5-fold increase in chlorine content compared to CFZ-HCl, suggesting that the formation of CLDIs occurs through a chloride mediated crystallization mechanism. Single crystal analysis revealed that CFZ-HCl crystals had a dense...