Evaluation of therapeutics in three-dimensional cell culture systems by MALDI imaging mass spectrometry.

Drug penetration into solid tumors is critical for the effectiveness of clinical chemotherapy. Failing to consider the efficiency of drug penetration can lead to fatal recurrence in many cancers. Three-dimensional (3D) cell cultures have served as an important model system and have contributed to valuable assays in drug discovery studies. However, limited methodologies result in incomplete evaluation of the distribution of many anticancer drugs. As a proof-of-concept study, we have applied matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) in HCT 116 colon carcinoma multicellular spheroids to assess the distribution of the anticancer drug, irinotecan. The time-dependent penetration of irinotecan was visualized and the localization of three metabolites as well as the parent drug in treated spheroids was mapped. To validate the identities of the metabolites, we analyzed extracts from drug-treated spheroids using nanoflow liquid chromatography-tandem mass spectrometry (nLC-MS/MS). Ten metabolites were identified with nLC-MS/MS, including those detected by MALDI IMS. This novel approach allows the measurement of drug penetration and distribution in 3D culture mimics and provides a more cost and time-effective approach for the testing of new pharmaceuticals compared to animal models.