Phase I and Pharmacokinetic Study of HER2-targeted rhuMAb 2C4 (Pertuzumab, RO4368451) in Japanese Patients with Solid Tumors

rhuMAb 2C4 (pertuzumab, RO4368451), a human epidermal growth factor receptor-2 (HER2) targeted antibody that binds to an epitope distinct from trastuzumab, blocks ligand-associated heterodimerization of HER2 with other HER receptor family members. This study evaluated the toxicity, pharmacokinetics and anti-tumor activities of pertuzumab in Japanese patients with solid tumors. Patients with solid tumors refractory to standard therapy were administered pertuzumab 5, 10, 15, 20 and 25 mg/kg intravenously once every 3 weeks. Grade 3 toxicities were considered as dose limiting. The maximum tolerated dose (MTD) was a dose at which two out of six patients had Grade 3 toxicities. Eighteen patients, aged 38-66 (median 57) years, with solid tumors were enrolled and a total of 32 cycles of pertuzumab were administered. Toxicities were generally acceptable. Grade 3 elevation of gamma-glutamyl transpeptidase was observed in one patient at 25 mg/kg and was considered to be dose limiting. MTD was not reached up to a dose level of 25 mg/kg. The serum concentration of pertuzumab declined slowly (terminal half-life is approximately 3 weeks). The AUC proportionally increased over the dose range tested. There was limited evidence of activity (stable disease 2; progressive disease 13; and not evaluable 3); however, tumor shrinkage and tumor marker decrease were observed in an ovarian cancer and a non-small-cell lung cancer patient, respectively. Pertuzumab is well tolerated up to 25 mg/kg. Although objective tumor response was not observed, it is worth evaluating as a flat dose and in combination with other cytotoxics and molecular-targeted agents.