Phase I therapy study of 186Re-labeled chimeric monoclonal antibody U36 in patients with squamous cell carcinoma of the head and neck.

UNLABELLED A phase I therapy study was conducted to determine the safety, maximum tolerated dose (MTD), pharmacokinetics, dosimetry, immunogenicity, and therapeutic potential of 186Re-labeled anti-CD44v6 chimeric monoclonal antibody (cMAb) U36 in patients with squamous cell carcinoma of the head and neck (HNSCC). The potential of a diagnostic study with 99mTc-cMAb U36 to predict the biodistribution of 186Re-cMAb U36 was evaluated. METHODS Thirteen patients with recurrent or metastatic HNSCC were given 750 MBq 99mTc-cMAb U36 (2 mg) followed 1 wk later by a single dose of 186Re-cMAb U36 (12 or 52 mg) in radiation dose-escalating steps of 0.4, 1.0, and 1.5 GBq/m2. After each administration, planar and SPECT images were obtained, and the pharmacokinetics and development of human antimurine as well as anti-cMAb responses were determined. Radiation absorbed doses to tumor, red marrow, and organs were calculated. RESULTS Administration was well tolerated, and excellent targeting of tumor lesions was seen in all patients. Dose-limiting myelotoxicity (thrombocytopenia being most prominent) was the only toxicity observed, resulting in grade 4 myelotoxicity in 2 patients treated with 1.5 GBq/m2. The MTD was established at 1.0 GBq/m2, at which a transient grade 3 thrombocytopenia was seen in 1 patient. One patient showed stable disease for 6 mo after treatment at the MTD. The 2 patients with dose-limiting myelotoxicity showed a marked reduction in tumor size. The reduction was of short duration and, therefore, not considered an objective response. Tumor absorbed doses at MTD ranged from 3.0 to 18.1 Gy. Red marrow doses ranged from 20 to 112 cGy (mean, 51 +/- 16 cGy/GBq) and correlated with platelet nadir (r = 0.8; P < 0.01). Pharmacokinetics varied between patients treated at the same dose level and were accurately predicted by the diagnostic procedure. Five patients experienced a human anti-cMAb response, 1 of which was a human antimouse antibody response. CONCLUSION This study shows that 186Re-cMAb U36 can be safely administered, with dose-limiting myelotoxicity at 41 mCi/m2. The use of cMAb U36 instead of its murine counterpart did not decrease the induction of human antibody responses. The availability of a 99mTc-labeled diagnostic study that can predict the pharmacokinetics of 186Re-cMAb U36 offers the possibility of using such a study for selection of a safe radioimmunotherapy dose.