WITHDRAWN: Positron Emission Tomographic imaging of tumor cell death using Zirconium-89-labeled APOMAB® following cisplatin chemotherapy in lung and ovarian cancer xenograft models

Abstract

Purpose. There are no currently approved non-invasive methods for detecting tumor treatment responses within the first few days of treatment. The monoclonal antibody, DAB4, or its chimeric derivative, chDAB4 (APOMAB®), targets the Lupus-associated or Sjögren Syndrome-B antigen (La/SSB). La/SSB is over-expressed in malignancy and is selectively targeted by chDAB4 in cancer cells that have died after DNA-damaging treatment. Therefore, chDAB4 could be used to distinguish between chemotherapy responsive and non-responsive patients. In this study, we performed preclinical validation studies using whole-body Positron-Emission Tomography (PET) to examine tumor and normal tissue uptake of 89Zr-labeled chDAB4 in lung or ovarian tumor-bearing mice, which were left untreated or given cisplatin chemotherapy.Methods. The binding of chDAB4 and its conjugates to dead cisplatin-treated human lung and ovarian cancer cells was assessed in vitro as well as its Fc-dependent effector functions. Mice bearing xenografts of H460 lung cancer or A2780 ovarian cancer cells were untreated or given cisplatin chemotherapy followed 24 hours later by 89Zr-labeled chDAB4. Post-cisplatin tumor responses were monitored using bioluminescence imaging and caliper measurements and 89Zr-labeled chDAB4 tumor uptake was measured using an Albira SI PET imager and PMOD analysis software. On completion of experiments, organs were dissected and biodistribution of 89Zr-labeled chDAB4 was measured using a Hidex gamma-counter.Results. The chDAB4 antibody bound only to dead A2780 and H460 cells, and its binding increased with cisplatin treatment in vitro. The chDAB4 antibody did not exhibit Fc-dependent effector functions. Chemotherapy significantly increased uptake of 89Zr-labeled chDAB4 in tumors but not in normal tissues for each tumor model. The greatest differences in average uptake of 89Zr-labeled chDAB4 in subcutaneous tumors were observed 3 days post-cisplatin chemotherapy compared to untreated mice, and before tumor shrinkage was evident.Conclusion. After administration of cisplatin chemotherapy, tumor xenograft uptake of 89Zr-labeled chDAB4 was detected in vivo by PET imaging. Given that the chDAB4 mAb lacked effector activity and that malignant rather than normal tissues were targeted after chemotherapy, these results support clinical development of chDAB4 as both a predictive marker of chemotherapy response and a theranostic imaging agent, which may guide subsequent delivery of chDAB4-directed antibody drug or radio-conjugate anticancer therapies.