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In vivo imaging of Bcr-Abl overexpressing tumors with a radiolabeled imatinib analog as an imaging surrogate for imatinib.

ABSTRACT: Imatinib mesylate is a tyrosine kinase inhibitor that was approved by the U.S. Food and Drug Administration in 2001 for treatment of many different stages of chronic myeloid leukemia and in 2002 for treatment of gastrointestinal stromal tumors. Imatinib is known to inhibit the dysregulated proliferation of chronic myeloid leukemia, which is associated with the Bcr-Abl kinase; in gastrointestinal stromal tumors, imatinib is known to act via c-Kit kinase inhibition. The objective of this study was to synthesize an (18)F-labeled analog of imatinib not as a primary imaging agent but rather as a tracer for in vivo drug distribution and tracer concentration that can be used as a PET imaging surrogate for imatinib.Molecular modeling studies based on the crystal structure of imatinib bound to the active site of Abl were performed for designing the fluorinated analog. A 2-fluoroethyl analog of imatinib (SKI696) was synthesized using well-established procedures. The selectivity and binding affinity of SKI696 were compared with those of imatinib in vitro. Mice bearing K562 tumor xenografts, which are known to overexpress Bcr-Abl, were imaged with (18)F-SKI696 PET. A biodistribution study was also performed on K562 tumor-bearing mice to which our radiolabeled tracer was administered.The kinase assay verified that imatinib and SKI696 bind to the same targets with similar affinities. The feasibility of using (18)F-SKI696 as a PET agent was examined in vivo, and (18)F-SKI696 PET was shown to visualize K562 tumor xenografts in nude mice. The tumor was visible on PET 1 h after injection, with uptake of 1% of the injected dose. Biodistribution studies in K562-bearing mice were also performed, and the uptake of (18)F-SKI696 (percentage injected dose per gram) for each organ was calculated.The results of the binding assay showed that SKI696 has selectivity and binding affinity comparable to imatinib. Small-animal PET of K562 tumor-bearing mice using (18)F-SKI696 as a PET agent displayed promising tumor uptake and tumor-to-nontarget contrast. Because (18)F-SKI696 has been taken up in vivo by tumors that overexpress Bcr-Abl, we are exploring a possible role for identifying tumors that will respond to imatinib before therapy.

SUBMITTER: Glekas AP

PROVIDER: S-EPMC4429778 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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In vivo imaging of Bcr-Abl overexpressing tumors with a radiolabeled imatinib analog as an imaging surrogate for imatinib.

Glekas Athanasios P AP Pillarsetty Nagavara Kishore NK Punzalan Blesida B Khan Nahida N Smith-Jones Peter P Larson Steven M SM

Journal of nuclear medicine : official publication, Society of Nuclear Medicine 20110715 8

<h4>Unlabelled</h4>Imatinib mesylate is a tyrosine kinase inhibitor that was approved by the U.S. Food and Drug Administration in 2001 for treatment of many different stages of chronic myeloid leukemia and in 2002 for treatment of gastrointestinal stromal tumors. Imatinib is known to inhibit the dysregulated proliferation of chronic myeloid leukemia, which is associated with the Bcr-Abl kinase; in gastrointestinal stromal tumors, imatinib is known to act via c-Kit kinase inhibition. The objectiv ...[more]

PMID: 21764785

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Project description:BackgroundWith the widespread clinical application of tyrosine kinase inhibitors (TKIs), an increasing number of chronic myeloid leukaemia (CML) patients have developed resistance or intolerance to TKIs. BCR/ABL is the oncoprotein of CML. HSP90 is an essential chaperone of BCR/ABL and plays an important role in protein folding and the function of BCR/ABL. Therefore, inhibiting the chaperone function of HSP90 may be an effective strategy for CML treatment and to overcome TKI resistance.MethodsThe effect of KW-2478 on CML cell viability, apoptosis and cell cycle progression was detected by CCK-8 assay or flow cytometry. The levels of BCR/ABL, HSP90 and other signalling proteins were detected by western blots. The mitochondrial membrane potential was detected by flow cytometry combined with JC-1 staining. The interaction between BCR/ABL and HSP90α was detected by coimmunoprecipitation. The effect of KW-2478 on BCR/ABL carcinogenesis in vivo was investigated in CML-like mouse models.ResultsKW-2478 inhibited growth and induced apoptosis of CML cells. KW-2478 inhibited the chaperone function of HSP90α and then weakened the BCR/ABL and MAPK signalling pathways. This treatment also caused an increase in p27 and p21 expression and a decrease in cyclin B1 expression, which led to G2/M phase arrest. The mitochondrial pathway was primarily responsible for KW-2478-induced apoptosis. KW-2478 had a synergistic effect with imatinib in growth inhibition. Notably, KW-2478 had a stronger effect on growth inhibition, apoptosis induction and cell cycle arrest of K562/G01 cells than K562 cells. KW-2478 could effectively prolong the mouse lifespan and alleviate disease symptoms in CML-like mouse models.ConclusionsThis finding demonstrated that KW-2478 had anticancer properties in imatinib-sensitive and imatinib-resistant CML cells and illustrated the possible mechanisms. This study provides an alternative choice for CML treatment, especially for TKI-resistant patients with BCR/ABL amplification and TKI-intolerant patients.

Dataset Information

In vivo imaging of Bcr-Abl overexpressing tumors with a radiolabeled imatinib analog as an imaging surrogate for imatinib.

Publications

In vivo imaging of Bcr-Abl overexpressing tumors with a radiolabeled imatinib analog as an imaging surrogate for imatinib.

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