Safety and biodistribution of ^99mtechnetium-labeled anti-CD44v6 monoclonal antibody BIWA 1 in head and neck cancer patients

The CD44 protein family consists of isoforms, encoded by standard exons and up to nine alternatively spliced variant exons (v2-v10), which are expressed in a tissue-specific way. Expression of v6-containing variants (CD44v6) has been related to aggressive behavior of various tumor types and was shown to be particularly high in squamous cell carcinoma (SCC). Therefore, CD44v6 might be a suitable target for radioimmunoscintigraphy (RIS) and therapy. The present study evaluates the novel high-affinity murine anti-CD44v6 monoclonal antibody (MAb) BIWA 1 for its safety and targeting potential in patients with SCC of the head and neck (HNSCC). Twelve HNSCC patients, who had planned to undergo resection of the primary tumor and neck dissection, were included. Preoperatively, 2, 12, or 52 mg of ^99mTc-labeled MAb BIWA 1 was administered. RIS results obtained 21 h after injection were compared with palpation, computed tomography, and magnetic resonance imaging, with histopathology as the gold standard. Moreover, biodistribution of BIWA 1 was evaluated by radioactivity measurement in blood and bone marrow and in biopsies from the surgical specimen obtained 40 h after injection. The distribution of BIWA 1 in tumor biopsies was analyzed by immunohistochemistry. BIWA 1 integrity in the blood was assessed by high-performance liquid chromatography and related to soluble CD44v6 levels in serum samples. No drug-related adverse events were observed. Human antimouse antibody responses were observed in 11 patients. The diagnostic efficacy of RIS appeared to be comparable for the three BIWA 1 dose levels and for the four diagnostic methods. Besides activity uptake in tumor tissue, minimal accumulation of activity was observed in mouth, lungs, spleen, kidney, bone marrow, and scrotal area. Analysis of tissue biopsies revealed high uptake in tumors, with a mean value of 14.2 ± 8.4% of the injected dose/kg tumor tissue and a mean tumor:blood ratio of 2.0 ± 1.4 at 40 h after injection. Differences among the three dose groups were not statistically significant, although a trend toward lower uptake in the highest dose group was noted. Distribution of BIWA 1 throughout the tumor was heterogeneous for all dose groups, which might be related to the high affinity of the MAb. The mean biological half-life in blood (34.5 ± 6.1 h) was not dose dependent. Extensive complex formation of BIWA 1 was observed in the 2-mg group, most probably with soluble CD44v6 present in the blood, and complex formation relatively diminished upon increase of the MAb dose. BIWA 1 is a promising MAb for targeting HNSCC because it can be safely administered to HNSCC patients, while it shows high and selective tumor uptake. However, BIWA 1 is immunogenic, and therefore a chimerized or humanized derivative of BIWA 1 with intermediate affinity will be used in future clinical trials.