Zirconium-89 labeled panitumumab: a potential immuno-PET probe for HER1-expressing carcinomas

https://doi.org/10.1016/j.nucmedbio.2013.01.007Get rights and content

Abstract

Introduction

Anti-HER1 monoclonal antibody (mAb), panitumumab (Vectibix) is a fully human mAb approved by the FDA for the treatment of epidermal growth factor receptor (EGFR, HER1)-expressing colorectal cancers. By combining the targeted specificity of panitumumab with the quantitative in vivo imaging capabilities of PET, we evaluated the potential of 89Zr-DFO-panitumumab PET/CT imaging and performed non-invasive, in vivo imaging of HER1 expression and estimated human dosimetry.

Methods

Panitumumab was radiolabeled with 89Zr using a derivative of desferrioxamine (DFO-Bz-NCS) and with 111In using CHX-A” DTPA as bifunctional chelators. Comparative biodistribution/dosimetry of both radiotracers was performed in non-tumor bearing athymic nude mice (n=2 females and n=2 males) over 1-week following i.v. injection of either using 89Zr-DFO-panitumumab or 111In-CHX-A”-DTPA-panitumumab. Micro-PET/CT imaging of female athymic nude mice bearing human breast cancer tumors (n=5 per tumor group) with variable HER1-expression very low (BT-474), moderate (MDA-MB-231), and very high (MDA-MB-468) was performed at over 1 week following i.v. injection of 89Zr-DFO-panitumumab.

Results

Radiochemical yield and purity of 89Zr-Panitumumab was > 70% and > 98% respectively with specific activity 150 ± 10 MBq/mg of panitumumab in a ~ 4 hr synthesis time. Biodistribution of 111In-CHX-A” DTPA -panitumumab and 89Zr-DFO-panitumumab in athymic non-tumor bearing nude mice displayed similar percent injected dose per gram of tissue with prominent accumulation of both tracers in the lymph nodes, a known clearance mechanism of panitumumab. Also exhibited was prolonged blood pool with no evidence of targeted accumulation in any organ. Human radiation dose estimates showed similar biodistributions with estimated human effective doses of 0.578 and 0.183 mSv/MBq for 89Zr-DFO-panitumumab and 111In-CHX-A”-DTPA–panitumumab, respectively. Given the potential quantitative and image quality advantages of PET, imaging of tumor bearing mice was only performed using 89Zr-DFO-panitumumab. Immuno-PET imaging of 89Zr-DFO-panitumumab in mice bearing breast cancer xenograft tumors with variable HER1 expression showed high tumor uptake (SUV > 7) in the MDA-MB-468 high HER1-expressing mice and a strong correlation between HER1-expression level and tumor uptake (R2= 0.857, P < .001).

Conclusions

89Zr-DFO-panitumumab can prepared with high radiochemical purity and specific activity. 89Zr-DFO-panitumumab microPET/CT showed uptake corresponding to HER-1 expression. Due to poor clearance, initial dosimetry estimates suggest that only a low dose 89Zr-DFO-panitumumab shows favorable human dosimetry; however due to high tumor uptake, the use of 89Zr-DFO-panitumumab is expected to be clinically feasible.

Introduction

Positron emission tomography (PET) is a well-established clinical imaging modality used to non-invasively identify disease presence and extent, and to monitor the effect of treatment effects [1], [2], [3], [4]. PET imaging using a radio-labeled monoclonal antibody (immuno-PET) is a very powerful technique to improve tumor detection because it combines the high sensitivity, image spatial resolution and quantitative potential of PET with the specificity of a monoclonal antibody (mAb) [4], [5], [6], [7]. For immuno-PET, the physical half-life of a positron emitter has to be compatible with the biological half-life of a mAb to achieve optimal tumor imaging. Developing a target specific PET imaging probe is one of the challenging areas of current biomedical research.

The epidermal growth factor receptor (EGFR, erb1, HER1) is a glycoprotein belonging to subclass I of the tyrosine kinase receptor super family [8]. This receptor is dysregulated in a variety of cancers, including lung, colorectal, head and neck, prostate, breast, glioma, pancreatic and ovarian cancers [9]. Overexpression of this receptor is associated with disease progression and treatment resistance. The anti-HER1 mAb, panitumumab (Vectibix) is a fully human mAb approved by the FDA for the treatment of HER1-expressing colorectal cancers [10], [11]. Currently, it is being evaluated in patients with other types of HER1-expressing cancers, such as breast, lung, head and neck, renal, and ovarian tumors [12]. Panitumumab binds to domain III of HER1 and is rapidly internalized, leading to downregulation of cell surface HER1. It also arrests the cell cycle and inhibits tumor growth by suppressing the production of proangiogenic factors (VEGF, IL-8) by tumor cells [13]. Moreover, because it is a fully human antibody, panitumumab has minimal immunogenicity when administered intravenously.

In recent years, 89Zr has emerged as a promising positron-emitting radionuclide [14], [15], [16], [17], [18], [19] for diagnostic immuno-PET imaging because of its longer half-life (78.4 h), which provides a close match to the biological half-life of an intact mAb. While its positron yield (22.7%) is less than 18F, the mostly widely used PET radiotracer, it is comparable to other longer lived radiometal based tracers used in human PET imaging (i.e. 64Cu and 86Y) and is inert in the biological system [4]. Moreover, based on recent clinical trials in Europe, 89Zr-labeled mAbs appear to be safe for human injection [4], [18]. 89Zr-immuno-PET with panitumumab as a targeting ligand may be useful as a non-invasive, in vivo, quantitative biomarker of HER1-expression that may be useful in patient selection and monitoring of HER1-targeted therapies.

Herein, we report the production of 89Zr-labeled panitumumab, compare its biodistribution and human dosimetry estimates with that of 111In-CHX-A”-DTPA-panitumumab, and evaluate tumor uptake in three human breast cancer xenografts expressing different levels of HER1.

Section snippets

General

Isothiocyanatobenzyl derivative of desferrioxamine (DFO-Bz-NCS) was obtained from Macrocyclics, Inc. Clinical grade panitumumab was obtained from Amgen, Inc. Water (> 18.2 MΩ.cm at 25°C, Milli Q, Millipore, MA) was purified by passing it through a 10-cm-long column of chelex resin (Bio-Rad Laboratories). All other chemicals, unless otherwise stated, were purchased from Sigma Aldrich (St. Louis, MO). Zirconium-89 was produced at the National Institute of Health (Bethesda, MD) cyclotron facility

Results and discussions

During the course of our investigations, Nayak et al. reported initial studies on 89Zr-labeled panitumumab as an immunoPET probe for colorectal cancer [19]. In our current studies, we validate the use of 89Zr-DFO-panitumumab as a immuno-PET probe in human breast cancer xenografts with variations in HER1 expression: BT-474 (negative control); MDA-MB-231 (moderate expression); and MDA-MB-468 (very high expression). We have additionally compared the biodistribution of 89Zr-DFO-panitumumab with

Conclusions

89Zr-DFO-panitumumab has been prepared with high radiochemical purity and specific activity. The immunoconjugate was found to be stable with respect to loss of the radioisotope in human serum. While the biodistribution showed slow clearance and physiologic uptake in the lymph nodes, when administered to humans at tracer levels, this is not expected to be a problem. Despite these limitations, immuno-PET studies revealed that 89Zr-DFO-panitumumab uptake correlated strongly with HER1 expression.

Acknowledgments

This project has been funded in whole or in part with federal funds from the National Cancer Institute, National Institutes of Health, under Contract No. HHSN261200800001E. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U. S. Government. Authors are grateful to Dr. Lawrence Szajek of cyclotron facility at NIH Bethesda

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