Theragnostics and Personalized Radionuclide Therapy
Priya Bhusari, Jaya Shukla, Rakhee Vatsa, Gurpreet Singh, Bhagwant Rai Mittal
Department of Nuclear Medicine and PET, PGIMER, Chandigarh, India
Introduction: Her2/neu expressing breast cancers are the most aggressive type of breast cancers. It is associated with worst prognosis. The treatment of widespread metastatic disease is still a challenge despite the advancement in technology. From the past few decades radiolabeled antibodies have emerged as promising targets for targeted treatment of widespread metastatic disease. Trastuzumab is a FDA approved monoclonal antibody used routinely in clinic in combination with other chemotherapy drugs for treatment of Her2 breast cancer. This study was aimed at evaluating the targeting ability of radioimmunoconjugate, Lu-177-Trastuzumab in patients with metastatic HER2 breast cancer disease as a palliative treatment option in these patients.
Methodology: Lu-177-Trastuzumab was developed in-house in hospital radiopharmacy lab. Trastuzumab was radiolabeled with Lu-177 by indirect means using DOTA as the bifunctional chelator. The immunoconjugate DOTA-trastuzumab was characterized using electrophoresis (structural integrity assessment) MALDI-TOF (for calculation of number of chelated molecules) and immunohistochemistry (for binding to HER breast tissue). The radioimmunoconjugate Lu-177-DOTA-Trastuzumab underwent various quality control procedures for determining the radiochemical purity, stability, pyrogenecity and binding to HER2 protein in an in-vitro radiimmunoassay. After obtaining clearance from the institute ethics committee, patients with HER metastatic breast cancer (n = 5) and HER2 negative disease (n = 2) were enrolled in the preliminary study. Low dose of Lu-177-trastuzumab (10 mCi) was administered by slow intravenous injection to the patients for imaging purpose to evaluate the specific targeting ability of the developed radioimmunoconjugate. Planar and SPECT/CT imaging was performed at day 5/7 post administration of the radioimmunoconjugate.
Results: Imaging using Lu-177-trastuzumab demonstrated promising results. The radioimmunoconjugate showed localization in primary and metastatic lesions specifically in histopathology proven HER2 positive patients. Due to low resolution of planar imaging and low abundance of 208 keV gamma photons of Lu-177, not all metastatic sites could be observed on planar gamma camera images. However, SPECT/CT imaging showed localization of the radioimmunoconjugate at the metastatic sites. No tracer uptake could be observed on planar as well as SPECT/CT imaging of the HER2 negative patients. Besides localization at the diseased sites, the radioimmunoconjugate got localized in the liver for upto 7 days of observation. High blood pool retention of the radioimmunoconjugate for upto 4 days post administration indicated imaging to be performed at day 5/7 post administration. The results were promising in terms of specific targeting of the radioimmunoconjugate. However, dosimetry studies need attention before therapeutic doses are decided for liver is indicated as the critical organ.
Conclusion: Lu-177-trastuzumab can be developed with good radiolabeling yield in a hospital radiopharmacy. The radioimmunoconjugate may be a potential treatment option for palliative treatment of HER2 positive metastatic breast cancer patients.
Figure 1.

(a) Whole body images of a 62 yr old female patient having histoathology proven HER2 positive metastatic breast disease post day 1 and day 7 of administration of Lu-trastuzumab. (b) SPECT/CT, CT and SPECT alone sections of the same patient showing localization of Lu-177-trastuzumab at the metastatic site [arrow heads]. (c) CT and (d) SPECT/CT sections of a 57 yr old female patient with histopathology proven HER2 negative disease showing no localization of Lu-177-trastuzumab at the tumor site (arrow heads)

