ABSTRACT
The glycerophospholipid phosphatidylcholine is the most abundant phospholipid species of eukaryotic membranes and essential for structural integrity and signaling function of cell membranes required for cancer cell growth. Inhibition of choline kinase alpha (CHKA), the first committed step to phosphatidylcholine synthesis, by the selective small-molecule ICL-CCIC-0019, potently suppressed growth of a panel of 60 cancer cell lines with median GI50 of 1.12 µM and inhibited tumor xenograft growth in mice. ICL-CCIC-0019 decreased phosphocholine levels and the fraction of labeled choline in lipids, and induced G1 arrest, endoplasmic reticulum stress and apoptosis. Changes in phosphocholine cellular levels following treatment could be detected non-invasively in tumor xenografts by [18F]-fluoromethyl-[1,2-2H4]-choline positron emission tomography. Herein, we reveal a previously unappreciated effect of choline metabolism on mitochondria function. Comparative metabolomics demonstrated that phosphatidylcholine pathway inhibition leads to a metabolically stressed phenotype analogous to mitochondria toxin treatment but without reactive oxygen species activation. Drug treatment decreased mitochondria function with associated reduction of citrate synthase expression and AMPK activation. Glucose and acetate uptake were increased in an attempt to overcome the metabolic stress. This study indicates that choline pathway pharmacological inhibition critically affects the metabolic function of the cell beyond reduced synthesis of phospholipids.
Subject(s)
Aminopyridines/pharmacology , Cell Transformation, Neoplastic/drug effects , Choline Kinase/antagonists & inhibitors , G1 Phase Cell Cycle Checkpoints/drug effects , Mitochondria/drug effects , Phosphatidylcholines/metabolism , Protein Kinase Inhibitors/pharmacology , Pyridinium Compounds/pharmacology , Signal Transduction/drug effects , Animals , Apoptosis/drug effects , Cell Line, Tumor , Cell Membrane/drug effects , Cell Membrane/metabolism , Choline/metabolism , Citrate (si)-Synthase/metabolism , Endoplasmic Reticulum Stress/drug effects , Female , Fluorescent Antibody Technique , Humans , Metabolomics , Mice , Mice, Inbred BALB C , Mice, Nude , Mitochondria/metabolism , Positron-Emission Tomography , Reactive Oxygen Species/metabolism , Xenograft Model Antitumor AssaysABSTRACT
Herein, we describe a fast and robust method for achieving (68)Ga-labelling of the EGFR-selective monoclonal antibody (mAb) Cetuximab using the bioorthogonal Inverse-electron-Demand Diels-Alder (IeDDA) reaction. The in vivo imaging of EGFR is demonstrated, as well as the translation of the method within a two-step pretargeting strategy.
Subject(s)
Antibodies, Monoclonal, Humanized/chemistry , Isotope Labeling/methods , Positron-Emission Tomography , Animals , Antibodies, Monoclonal, Humanized/immunology , Cell Line, Tumor , Cell Transformation, Neoplastic , Cetuximab , ErbB Receptors/immunology , Gallium Radioisotopes , Humans , Mice , Time FactorsABSTRACT
PURPOSE: The purpose of this paper is to study the association between RGD binding kinetics and αvß3 integrin receptor density in the complex tumor milieu. PROCEDURES: We assessed αvß3 in vitro and by (68)Ga-DOTA-[c(RGDfK)]2 positron emission tomography (PET) in tumors with varying αvß3. RESULTS: Intrinsic αvß3 expression decreased in the order of M21 >>> MDA-MB-231 > M21L in cells. Tumor volume of distribution by PET, V T, was significantly higher in M21 compared to isogenic M21L tumors (0.40 ± 0.01 versus 0.25 ± 0.02; p < 0.01) despite similar microvessel density (MVD) likely due to higher αvß3. V T for MDA-MB-231 (0.40 ± 0.04) was comparable to M21 despite lower αvß3 but in keeping with the higher MVD, suggesting superior tracer distribution. CONCLUSIONS: This study demonstrates that radioligand binding kinetics of PET data can be used to discriminate tumors with different αvß3 integrin expression-a key component of the angiogenesis phenotype-in vivo.
Subject(s)
Blood Vessels/metabolism , Blood Vessels/pathology , Integrin alphaVbeta3/metabolism , Organometallic Compounds , Peptides, Cyclic , Animals , Blotting, Western , Cell Line, Tumor , Female , Flow Cytometry , Humans , Immunohistochemistry , Kinetics , Mice, Inbred BALB C , Mice, Nude , Neoplasms/blood supply , Neoplasms/diagnostic imaging , Neoplasms/pathology , Platelet Endothelial Cell Adhesion Molecule-1/metabolism , Positron-Emission Tomography , Radioactive TracersABSTRACT
PURPOSE: (11)C-Choline-positron emission tomography (PET) has been exploited to detect the aberrant choline metabolism in tumors. Radiolabeled choline uptake within the imaging time is primarily a function of transport, phosphorylation, and oxidation. Rapid choline oxidation, however, complicates interpretation of PET data. In this study, we investigated the biologic basis of the oxidation of deuterated choline analogs and assessed their specificity in human tumor xenografts. EXPERIMENTAL DESIGN: (11)C-Choline, (11)C-methyl-[1,2-(2)H(4)]-choline ((11)C-D4-choline), and (18)F-D4-choline were synthesized to permit comparison. Biodistribution, metabolism, small-animal PET studies, and kinetic analysis of tracer uptake were carried out in human colon HCT116 xenograft-bearing mice. RESULTS: Oxidation of choline analogs to betaine was highest with (11)C-choline, with reduced oxidation observed with (11)C-D4-choline and substantially reduced with (18)F-D4-choline, suggesting that both fluorination and deuteration were important for tracer metabolism. Although all tracers were converted intracellularly to labeled phosphocholine (specific signal), the higher rate constants for intracellular retention (K(i) and k(3)) of (11)C-choline and (11)C-D4-choline, compared with (18)F-D4-choline, were explained by the rapid conversion of the nonfluorinated tracers to betaine within HCT116 tumors. Imaging studies showed that the uptake of (18)F-D4-choline in three tumors with similar radiotracer delivery (K(1)) and choline kinase α expression-HCT116, A375, and PC3-M-were the same, suggesting that (18)F-D4-choline has utility for cancer detection irrespective of histologic type. CONCLUSION: We have shown here that both deuteration and fluorination combine to provide protection against choline oxidation in vivo. (18)F-D4-choline showed the highest selectivity for phosphorylation and warrants clinical evaluation.