Quantitative PET imaging of Met-expressing human cancer xenografts with 89Zr-labelled monoclonal antibody DN30

Purpose: Targeting the c-Met receptor with monoclonal antibodies (MAbs) is an appealing approach for cancer diagnosis and treatment because this receptor plays a prominent role in tumour invasion and metastasis. Positron emission tomography (PET) might be a powerful tool for guidance of therapy with anti-Met MAbs like the recently described MAb DN30 because it allows accurate quantitative imaging of tumour targeting (immuno-PET). We considered the potential of PET with either ⁸⁹Zr-labelled (residualising radionuclide) or ¹²⁴I-labelled (non-residualising radionuclide) DN30 for imaging of Met-expressing tumours. Materials and methods: The biodistribution of co-injected ⁸⁹Zr-DN30 and iodine-labelled DN30 was compared in nude mice bearing either the human gastric cancer line GLT-16 (high Met expression) or the head-and-neck cancer line FaDu (low Met expression). PET images were acquired in both xenograft models up to 4 days post-injection (p.i.) and used for quantification of tumour uptake. Results: Biodistribution studies in GTL-16-tumour-bearing mice revealed that ⁸⁹Zr-DN30 achieved much higher tumour uptake levels than iodine-labelled DN30 (e.g. 19.6%ID/g vs 5.3%ID/g, 5 days p.i.), while blood levels were similar, indicating internalisation of DN30. Therefore, ⁸⁹Zr-DN30 was selected for PET imaging of GLT-16-bearing mice. Tumours as small as 11 mg were readily visualised with immuno-PET. A distinctive lower ⁸⁹Zr uptake was observed in FaDu compared to GTL-16 xenografts (e.g. 7.8%ID/g vs 18.1%ID/g, 3 days p.i.). Nevertheless, FaDu xenografts were also clearly visualised with ⁸⁹Zr-DN30 immuno-PET. An excellent correlation was found between PET-image-derived ⁸⁹Zr tumour uptake and ex-vivo-assessed ⁸⁹Zr tumour uptake (R²=0.98). Conclusions: The long-lived positron emitter ⁸⁹Zr seems attractive for PET-guided development of therapeutic anti-c-Met MAbs.