Leveraging PET to image folate receptor α therapy of an antibody-drug conjugate

Abstract

Background

The folate receptor α (FRα)-targeting antibody-drug conjugate (ADC), IMGN853, shows great antitumor activity against FRα-expressing tumors in vivo, but patient selection and consequently therapy outcome are based on immunohistochemistry. The aim of this study is to develop an antibody-derived immuno-PET imaging agent strategy for targeting FRα in ovarian cancer as a predictor of treatment success.

Methods

We developed [⁸⁹Zr]Zr-DFO-M9346A, a humanized antibody-based radiotracer targeting tumor-associated FRα in the preclinical setting. [⁸⁹Zr]Zr-DFO-M9346A's binding ability was tested in an in vitro uptake assay using cell lines with varying FRα expression levels. The diagnostic potential of [⁸⁹Zr]Zr-M9346A was evaluated in KB and OV90 subcutaneous xenografts. Following intravenous injection of [⁸⁹Zr]Zr-DFO-M9346A (~90 μCi, 50 μg), PET imaging and biodistribution studies were performed. We determined the blood half-life of [⁸⁹Zr]Zr-DFO-M9346A and compared it to the therapeutic, radioiodinated ADC [¹³¹I]-IMGN853. Finally, in vivo studies using IMG853 as a therapeutic, paired with [⁸⁹Zr]Zr-DFO-M9346A as a companion diagnostic were performed using OV90 xenografts.

Results

DFO-M9346A was labeled with Zr-89 at 37 °C within 60 min and isolated in labeling yields of 85.7 ± 5.7%, radiochemical purities of 98.0 ± 0.7%, and specific activities of 3.08 ± 0.43 mCi/mg. We observed high specificity for binding FRα positive cells in vitro. For PET and biodistribution studies, [⁸⁹Zr]Zr-M9346A displayed remarkable in vivo performance in terms of excellent tumor uptake for KB and OV xenografts (45.8 ± 29.0 %IA/g and 26.1 ± 7.2 %IA/g), with low non-target tissue uptake in other organs such as kidneys (4.5 ± 1.2 %IA/g and 4.3 ± 0.7 %IA/g). A direct comparison of the blood half life of [⁸⁹Zr]Zr-M9346A and [¹³¹I]-IMGN853 corroborated the equivalency of the radiopharmaceutical and the ADC, paving the way for a companion PET imaging study.

Conclusions

We developed a new folate receptor-targeted ⁸⁹Zr-labeled PET imaging agent with excellent pharmacokinetics in vivo. Good tumor uptake in subcutaneous KB and OV90 xenografts were obtained, and ADC therapy studies were performed with the precision predictor.

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