Evaluating the Pharmacokinetics and Pharmacodynamics of Chemotherapeutics Within a Spatial SILAC-Labeled Spheroid Model System

Tumorshave considerable cellular heterogeneity that is impossibleto explore with simple cell cultures. Spheroid cultures contain pathophysiologicaland chemical gradients similar to in vivo tumors and show complexresponses to therapeutics, similar to a tumor. Using pulsed isotopiclabels, we demonstrate the pronounced differential response of theproteome to the drug Regorafenib, a multikinase inhibitor, in HCT116 spheroids. Regorafenib treatment of outer spheroids inhibits proteinsinvolved in critical pathways such as mTOR signaling, extracellularsignal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK)signaling, and colorectal cancer metastasis signaling, resulting indecreased proliferation and cellular apoptosis. By contrast, analysisof the treated core cells shows upregulation of MAPK1 and KRAS, possiblyimplicating drug resistance within these late apoptotic cells. Thus,pulsed isotopic labeling enables evaluation of the distinct proteomicresponses for cells residing in the different chemical microenvironmentsof the spheroid. This platform promises great utility in assistingresearchers' predictions of pharmacodynamic therapeutic responseswithin complex tumors.