J. Shukla (Chandigarh, India)
PGIMER - Postgraduate Institute of Medical Education and Research, ChandigarhAuthor Of 1 Presentation
80P - Radiolabelled Trastuzumab Fab as a theranostic molecule for HER2 positive breast cancers
Abstract
Background
Inherited genes, hormonal imbalance, environmental factors, and mutation in genes are responsible for the development of breast cancer in females. Nowadays, passive immunotherapy is used to combat cancer. Trastuzumab is a humanized monoclonal antibody (mAb) and has a pronounced effect when used as adjuvant therapy, but high doses (4-8 mg/kg) and greater molecular weight (MW) increases liver retention. To fill this hiatus, antibody fragments (Fab) are generated and showed similar target specificity. The radiolabelling of Fab may provide the theranostic application in breast cancer patients.
Methods
The Fab was generated from mAb trastuzumab and characterized by MALDI-TOF. The purified Fab was standardized for conjugation with bifunctional chelating agent DTPA. The purified conjugated Fab-DTPA product was considered for radiolabelling with Ga-68, Lu-177. The radionuclide and radiochemical purity of the product was determined. HER2 binding efficacy was checked on SKBR3 cells along with the bio-layer interferometry (BLI) technique. After quality control checks: sterility, pyrogenicity, human serum, and PBS stability; radiolabelled Fab-DTPA was subjected to molecular imaging. PET and SPECT imaging were correlated with LABC and histopathologically HER2 proven cases.
Results
The generated Fab (45 kDa) and Fab-DTPA (47 kDa) was confirmed by MALDI-TOF. Radiochemical purity of 68Ga/177Lu-Fab-DTPA was > 99 %. The high specificity of 177Lu-Fab-DTPA towards HER2 receptor was confirmed. The binding kinetic analysis (Kd)was 2 nM for Fab and 20 nM for Fab-DTPA. The products were stable and free from bacterial, fungal contamination up to 21 days, and endotoxin concentration (5-7 EU/mL) was found within the limit (175 EU/injection). The IC50 value calculated from the MTT assay of Lu-177 DTPA Fab was 71.1 nM (IC50 of trastuzumab 121.06 nM). PET/CT imaging of the patient was performed, MIP of 68Ga-Fab DTPA showed SUVmax-6 in the left breast which was concordant to 18F-FDG with SUVmax-11. SPECT/CT imaging with 177Lu- Fab-DTPA showed significant uptake in IHC proven HER2 breast cancer, while 18F-FDG showed SUVmax-17.
Conclusions
Radiolabelled Fab-DTPA can be used as a theranostic molecule for HER2 positive breast cancers.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.