Tracking Drugs and Lipids: Quantitative Mass Spectrometry Imaging of Liposomal Doxorubicin Delivery and Bilayer Fate in Three-Dimensional Tumor Models.

Targeted therapy to the tumor would greatly advance precision medicine. Many drug delivery vehicles have emerged, but liposomes are cited as the most successful to date. Recent efforts to develop liposomal drug delivery systems focus on drug distribution in tissues and ignore liposomal fate. In this study, we developed a novel method to elucidate both drug and liposomal bilayer distribution in a three-dimensional cell culture model using quantitative matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI qMSI) alongside fluorescence microscopy. Imaging liposomal distribution in a cell culture model is challenging, as lipids forming the bilayer are endogenous to the model system. To resolve this issue, we functionalized the bilayer by chemically cross-linking a fluorescent tag to the alkyne-containing lipid hexynoyl phosphoethanolamine (HPE). We synthesized liposomes incorporating the tagged HPE lipid and encapsulated within them doxorubicin, yielding a theranostic liposome capable of both drug delivery and monitoring liposomal uptake. We employed an "in-tissue" MALDI qMSI approach to generate a calibration curve with