In Vivo Imaging of Drug-Induced Mitochondrial Outer Membrane Permeabilization at Single-Cell Resolution

Center for Systems Biology, Massachusetts General Hospital, Boston 02114, USA.
Cancer Research (Impact Factor: 9.33). 04/2012; 72(12):2949-56. DOI: 10.1158/0008-5472.CAN-11-4096
Source: PubMed


Observing drug responses in the tumor microenvironment in vivo can be technically challenging. As a result, cellular responses to molecularly targeted cancer drugs are often studied in cell culture, which does not accurately represent the behavior of cancer cells growing in vivo. Using high-resolution microscopy and fluorescently labeled genetic reporters for apoptosis, we developed an approach to visualize drug-induced cell death at single-cell resolution in vivo. Stable expression of the mitochondrial intermembrane protein IMS-RP was established in human breast and pancreatic cancer cells. Image analysis was then used to quantify release of IMS-RP into the cytoplasm upon apoptosis and irreversible mitochondrial permeabilization. Both breast and pancreatic cancer cells showed higher basal apoptotic rates in vivo than in culture. To study drug-induced apoptosis, we exposed tumor cells to navitoclax (ABT-263), an inhibitor of Bcl-2, Bcl-xL, and Bcl-w, both in vitro and in vivo. Although the tumors responded to Bcl-2 inhibition in vivo, inducing apoptosis in around 20% of cancer cells, the observed response was much higher in cell culture. Together, our findings show an imaging technique that can be used to directly visualize cell death within the tumor microenvironment in response to drug treatment.

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    • "In the context of the tumor microenvironment, the reasons for variable cancer cell response to treatment further include variations in tissue drug concentration, local oxygen concentration, cytokine profile, interaction between cancer cells, and host immune response. Measuring the response at the single-cell level provides further pharmacokinetic and pharmacodynamic information, which aids drug development and regimen design [11,12]. Fluorescence microscopy can be used to detect cell death at the single-cell level after cancer cells have been labeled by genetically engineered reporters or exogenous fluorescent dyes [13–16]. "
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