Improved non-invasive positron emission tomographic imaging of chemotherapy-induced tumor cell death using Zirconium-89-labeled APOMAB®

Purpose The chimeric monoclonal antibody (mAb) chDAB4 (APOMAB®) targets the Lupus associated (La)/Sjögren Syndrome-B (SSB) antigen, which is over-expressed in tumors but only becomes available for antibody binding in dead tumor cells. Hence, chDAB4 may be used as a novel theranostic tool to distinguish between responders and nonresponders early after chemotherapy. Here, we aimed to ascertain which positron emitter, Zirconium-89 ([89Zr]ZrIV) or Iodine-124 ([124I]I), was best suited to label chDAB4 for post-chemotherapy PET imaging of tumor-bearing mice and to determine which of two different bifunctional chelators provided optimal tumor imaging by PET using [89Zr]ZrIV-labeled chDAB4. Methods C57BL/6 J mice bearing subcutaneous syngeneic tumors of EL4 lymphoma were either untreated or given chemotherapy, then administered radiolabeled chDAB4 after 24 h with its biodistribution examined using PET and organ assay. We compared chDAB4 radiolabeled with [89Zr] ZrIV or [124I] I, or [89Zr]Zr-chDAB4 using either DFO-NCS or DFOSq as a chelator. Results After chemotherapy, [89Zr]Zr-chDAB4 showed higher and prolonged mean (± SD) tumor uptake of 29.5 ± 5.9 compared to 7.8 ± 1.2 for [124I] I -chDAB4. In contrast, antibody uptake in healthy tissues was not affected. Compared to DFO-NCS, DFOSq did not result in significant differences in tumor uptake of [89Zr]Zr-chDAB4 but did alter the tumor:liver ratio in treated mice 3 days after injection in favour of DFOSq (8.0 ± 1.1) compared to DFO-NCS (4.2 ± 0.7). Conclusion ImmunoPET using chDAB4 radiolabeled with residualizing [89Zr] ZrIV rather than [124I] I optimized post-chemotherapy tumor uptake. Further, PET imaging characteristics were improved by DFOSq rather than DFO-NCS. Therefore, the radionuclide/chelator combination of [89Zr] ZrIV and DFOSq is preferred for the imminent clinical evaluation of chDAB4 as a selective tumor cell death radioligand.

MR-guided focused ultrasound increases antibody delivery to nonenhancing high-grade glioma

Background High-grade glioma (HGG) remains a recalcitrant clinical problem despite many decades of research. A major challenge in improving prognosis is the inability of current therapeutic strategies to address a clinically significant burden of infiltrating tumor cells that extend beyond the margins of the primary tumor mass. Such cells cannot be surgically excised nor efficiently targeted by radiation therapy. Therapeutic targeting of this tumor cell population is significantly hampered by the presence of an intact blood–brain barrier (BBB). In this study, we performed a preclinical investigation of the efficiency of MR-guided Focused Ultrasound (FUS) to temporarily disrupt the BBB to allow selective delivery of a tumor-targeting antibody to infiltrating tumor. Methods Structural MRI, dynamic-contrast enhancement MRI, and histology were used to fully characterize the MR-enhancing properties of a patient-derived xenograft (PDX) orthotopic mouse model of HGG and to develop a reproducible, robust model of nonenhancing HGG. PET–CT imaging techniques were then used to evaluate the efficacy of FUS to increase 89Zr-radiolabeled antibody concentration in nonenhancing HGG regions and adjacent non-targeted tumor tissue. Results The PDX mouse model of HGG has a significant tumor burden lying behind an intact BBB. Increased antibody uptake in nonenhancing tumor regions is directly proportional to the FUS-targeted volume. FUS locally increased antibody uptake in FUS-targeted regions of the tumor with an intact BBB, while leaving untargeted regions unaffected. Conclusions FUS exposure successfully allowed temporary BBB disruption, localized to specifically targeted, nonenhancing, infiltrating tumor regions and delivery of a systemically administered antibody was significantly increased.

Phase I Imaging and Pharmacodynamic Trial of CS-1008 in Patients With Metastatic Colorectal Cancer

Purpose CS-1008 (tigatuzumab) is a humanized, monoclonal immunoglobulin G1 (IgG1) agonistic antibody to human death receptor 5. The purpose of this study was to investigate the impact of CS-1008 dose on the biodistribution, quantitative tumor uptake, and antitumor response in patients with metastatic colorectal cancer (mCRC). Patients and Methods Patients with mCRC who had received at least one course of chemotherapy were assigned to one of five dosage cohorts and infused with a weekly dose of CS-1008. Day 1 and day 36 doses were trace-labeled with indium-111 (111In), followed by whole-body planar and regional single-photon emission computed tomography (SPECT) imaging at several time points over the course of 10 days. Results Nineteen patients were enrolled. 111In-CS-1008 uptake in tumor was observed in only 12 patients (63%). 111In-CS-1008 uptake and pharmacokinetics were not affected by dose or repeated drug administration. 111In-CS-1008 biodistribution showed gradual blood-pool clearance and no abnormal uptake in normal tissue. No anti–CS-1008 antibody development was detected. One patient achieved partial response (3.7 months duration), eight patients had stable disease, and 10 patients had progressive disease. Clinical benefit rate (stable disease + partial response) in patients with 111In-CS-1008 uptake in tumor was 58% versus 28% in patients with no uptake. An analysis of individual lesions showed that lesions with antibody uptake were one third as likely to progress as those without antibody uptake (P = .07). Death-receptor–5 expression in archived tumor samples did not correlate with 111In-CS-1008 uptake (P = .5) or tumor response (P = .6). Conclusion Death-receptor–5 imaging with 111In-CS-1008 reveals interpatient and intrapatient heterogeneity of uptake in tumor, is not dose dependent, and is predictive of clinical benefit in the treatment of patients who have mCRC.