Molecular imaging of Bcr-Abl phosphokinase in a xenograft model
Ji Yuan Wu1, David J Yang, Laura S Angelo
1Department of Investigational Cancer Therapeutics (Phase I Program), Division of Cancer Medicine, The University of Texas M. D. Anderson Cancer Center, Unit 455, P.O. Box 301402, Houston, TX 77030, USA.
Abstract:
The purpose of this study was to determine whether the Bcr-Abl tyrosine kinase can be assessed by gamma-imaging using an 111In-labeled anti-phosphotyrosine (APT) antibody, and if the response to treatment with imatinib could be detected using this imaging technique. APT antibody was labeled with 111In using ethylenedicysteine (EC) as a chelator. To determine if 111In-EC-APT could assess a nonreceptor tyrosine kinase, xenografts of the human chronic myelogenous leukemia cell line K562 were used. gamma-Scintigraphy of the tumor-bearing mice, before and after imatinib treatment, was obtained 1, 24, and 48 h after they were given 111In-EC-APT (100 microCi/mouse i.v.). 111In-EC-APT is preferentially taken up by Bcr-Abl-bearing tumor cells when compared with 111In-EC-BSA or 111In-EC-IgG1 controls and comparable with the level of uptake of 111In-EC-Bcr-Abl. Imatinib treatment resulted in decreased expression of phospho-Bcr-Abl by Western blot analysis, which correlated with early (4 days after starting imatinib) kinase down-regulation as assessed by imaging using 111In-EC-APT. The optimal time to imaging was 24 and 48 h after injection of 111In-EC-APT. Although tumor regression was insignificant on day 4 after starting imatinib treatment, it was marked by day 14. 111In-EC-APT can assess intracellular phosphokinase activity, and down-regulation of phosphokinase activity predates tumor regression. This technique may therefore be useful in the clinic to detect the presence of phosphokinase activity and for early prediction of response.
Insights
This study shows that 111In-labeled anti-phosphotyrosine (APT) antibody gamma-imaging can detect Bcr-Abl tyrosine kinase activity. This method accurately predicts patient response to imatinib treatment by assessing kinase down-regulation before tumor regression.
Area of Science:
- Oncology
- Radiochemistry
- Molecular Imaging
Background:
- Bcr-Abl tyrosine kinase is a key driver in chronic myelogenous leukemia (CML).
- Assessing Bcr-Abl activity and treatment response typically involves methods like Western blot, which do not provide real-time imaging data.
- Non-receptor tyrosine kinases play crucial roles in cancer, but their in vivo assessment remains challenging.
Purpose of the Study:
- To evaluate the utility of gamma-imaging with an 111In-labeled anti-phosphotyrosine (APT) antibody for assessing Bcr-Abl tyrosine kinase activity.
- To determine if this imaging technique can detect early responses to imatinib treatment in CML models.
Main Methods:
- 111In-labeled anti-phosphotyrosine (APT) antibody was synthesized using ethylenedicysteine (EC) as a chelator.
- Xenografts of K562 human CML cells were used to model Bcr-Abl-positive tumors in mice.
- Gamma-scintigraphy was performed at 1, 24, and 48 hours post-injection of 111In-EC-APT before and after imatinib treatment.
Main Results:
- 111In-EC-APT demonstrated preferential uptake in Bcr-Abl-bearing tumor cells compared to control antibodies.
- Imatinib treatment led to decreased phospho-Bcr-Abl expression, correlating with reduced kinase activity detected by 111In-EC-APT imaging.
- Early kinase down-regulation was observed by day 4, preceding significant tumor regression (observed by day 14).
Conclusions:
- 111In-EC-APT gamma-imaging can successfully assess intracellular phosphokinase activity, specifically targeting Bcr-Abl.
- This imaging modality provides an early prediction of therapeutic response to imatinib, as kinase down-regulation precedes tumor regression.
- This technique holds potential for clinical application in detecting phosphokinase activity and predicting treatment efficacy in CML and potentially other cancers.
