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Antiepidermal growth factor variant III scFv fragment: effect of radioiodination method on tumor targeting and normal
Sriram Shankar1, Ganesan Vaidyanathan, Chien-Tsun Kuan
1Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Introduction:
MR1-1 is a single-chain Fv (scFv) fragment that binds with high affinity to epidermal growth factor receptor variant III, which is overexpressed on gliomas and other tumors but is not present on normal tissues. The objective of this study was to evaluate four different methods for labeling MR1-1 scFv that had been previously investigated for the radioiodinating of an intact anti-epidermal growth factor receptor variant III (anti-EGFRvIII) monoclonal antibody (mAb) L8A4.
Methods:
The MR1-1 scFv was labeled with (125)I/(131)I using the Iodogen method, and was also radiohalogenated with acylation agents bearing substituents that were positively charged--N-succinimidyl-3-[*I]iodo-5-pyridine carboxylate and N-succinimidyl-4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB)--and negatively charged--N-succinimidyl-3-[*I]iodo-4-phosphonomethylbenzoate ([*I]SIPMB). In vitro internalization assays were performed with the U87MGDeltaEGFR cell line, and the tissue distribution of the radioiodinated scFv fragments was evaluated in athymic mice bearing subcutaneous U87MGDeltaEGFR xenografts.
Results And Conclusion:
As seen previously with the anti-EGFRvIII IgG mAb, retention of radioiodine activity in U87MGDeltaEGFR cells in the internalization assay was labeling method dependent, with SGMIB and SIPMB yielding the most prolonged retention. However, unlike the case with the intact mAb, the results of the internalization assays were not predictive of in vivo tumor localization capacity of the labeled scFv. Renal activity was dependent on the nature of the labeling method. With MR1-1 labeled using SIPMB, kidney uptake was highest and most prolonged; catabolism studies indicated that this uptake primarily was in the form of epsilon-N-3-[*I]iodo-4-phosphonomethylbenzoyl lysine.
Insights
Radioiodination of MR1-1 scFv for cancer targeting showed labeling method affects retention. Internalization assays did not predict in vivo tumor localization, with renal uptake varying by method.
Area of Science:
- Oncology
- Radiochemistry
- Molecular Imaging
Background:
- MR1-1 single-chain Fv (scFv) targets epidermal growth factor receptor variant III (EGFRvIII), overexpressed in gliomas and other tumors.
- EGFRvIII is absent in normal tissues, making MR1-1 a promising targeted therapeutic and diagnostic agent.
- Evaluating labeling methods for MR1-1 scFv is crucial for optimizing its use in radioiodination.
Purpose of the Study:
- To assess four distinct radioiodination methods for the MR1-1 scFv fragment.
- To compare the in vitro and in vivo characteristics of MR1-1 scFv labeled via different techniques.
- To determine the impact of labeling methods on radioiodine retention, tumor localization, and biodistribution.
Main Methods:
- MR1-1 scFv was labeled with Iodine-125/131 using the Iodogen method.
- Radiohalogenation was performed using acylation agents with positive ([*I]SGMIB) and negative ([*I]SIPMB) charges.
- In vitro internalization assays and in vivo tissue distribution studies in athymic mice with U87MGDeltaEGFR xenografts were conducted.
Main Results:
- Radioiodine retention in U87MGDeltaEGFR cells was labeling method-dependent, with [*I]SGMIB and [*I]SIPMB showing prolonged retention.
- Internalization assay results did not correlate with in vivo tumor localization for the labeled scFv fragments.
- Renal activity varied significantly with the labeling method; [*I]SIPMB resulted in the highest and most prolonged kidney uptake.
Conclusions:
- The choice of labeling method critically influences radioiodine retention and biodistribution of MR1-1 scFv.
- In vitro internalization assays are not predictive of in vivo tumor targeting efficacy for this scFv.
- Specific labeling methods, like [*I]SIPMB, lead to significant renal accumulation, primarily as a metabolite.
