Solvatochromic Shift Enables Intracellular Fate Determination of Curcumin Nanocrystals

Drug nanocrystals represent an effective way of delivering poorly water-soluble substances to target tissues and cells. Due to the large specific surface area, nanocrystals promote dissolution; therefore, the drug usually co-exists in both crystalline and dissolved forms. Commonly used analytical methods do not make it possible to easily distinguish between these forms within live cells. The present study reports a novel fluorescence microscopy method that makes it possible to distinguish intracellular forms of curcumin based on differences in fluorescence emission spectra. Due to solvatochromism, crystalline curcumin can be distinguished from curcumin dissolved in the lipidic components of cells. The methodology utilization is demonstrated by investigating the effect of surface stabilization of curcumin nanocrystals on cell uptake by different cell lines: macrophages and epithelial cells. The understanding of factors that control drug nanocrystal phagocytosis makes it possible to better interpret the observed anticancer effects of curcumin nanocrystals and design efficient drug delivery systems.