177Lu labeling of Herceptin and preclinical validation as a new radiopharmaceutical for radioimmunotherapy of breast cancer.
BACKGROUND
In the present study, Herceptin was labeled with lutetium-177 via DOTA, and the necessary preclinical quality control tests (in vitro and in vivo) were performed to evaluate its use as a radioimmunotherapy agent.


METHODS
Herceptin was conjugated to DOTA as a chelator in three different conjugation buffers (ammonium acetate, carbonate and HEPES buffer); each of the resulting conjugates was compared with respect to in vitro characteristics such as number of chelates per antibody, incorporated activity, immunoreactivity and in vitro stability in PBS buffer and blood serum. The biodistribution study and gamma camera imaging were performed in mice bearing breast tumors. To assess the therapeutic effects of (177)Lu-Herceptin, cytotoxicity was investigated for 7 days in a SKBr3 breast cancer cell line.


RESULTS
Carbonate buffer was the best conjugation buffer (number of chelates per antibody: 6; incorporated activity: 81%; immunoreactivity: 87%; buffer stability: 86%; serum stability: 81%, after 4 days). The efficient tumor uptake observed in the biodistribution studies was consistent with the gamma camera image results. At a concentration of 4 μg ml(-1), (177)Lu-Herceptin (surviving cells: 5 ± 0.6% of the total cells) of the total cells corresponded to an approximately eightfold increase in cytotoxicity in comparison to unmodified Herceptin (surviving cells: 43 ± 3.9%).


CONCLUSIONS
The new complex described herein could be considered for further evaluation in animals and potentially in humans as a radiopharmaceutical for use in the radioimmunotherapy of breast cancer. These results may be important for patients who cannot tolerate the therapeutic dosage of Herceptin currently used because of heart problems.
Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box 14115-331, Tehran, Iran.
Samira
S
Rasaneh
Hossein
H
Rajabi
Mohammad Hossein
MH
Babaei
Fariba Johari
FJ
Daha
D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D004353:Drug Evaluation, Preclinical; D005260:Female; D008187:Lutetium / Q000627:therapeutic use*; D051379:Mice; D011786:Quality Control; D016499:Radioimmunotherapy / Q000379:methods*; D011868:Radioisotopes / Q000627:therapeutic use*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D015203:Reproducibility of Results; D000068878:Trastuzumab
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D008187:Lutetium; D000068878:Trastuzumab