Women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer are candidates for treatment with the anti-HER2 antibody trastuzumab. Assessment of HER2 status in recurrent disease is usually made by core needle biopsy of a single lesion which may not be representative of the larger tumor mass or other sites of disease. Our long-range goal is to develop positron emission tomography (PET) of radiolabeled trastuzumab for systemically assessing tumor HER2 expression and identifying appropriate use of anti-HER2 therapies. The purpose of this study was to evaluate PET-CT of 64Cu-DOTA-trastuzumab for detecting and measuring tumor uptake of trastuzumab in patients with HER2-positive metastatic breast cancer. Methods Eight women with biopsy-confirmed HER2-positive metastatic breast cancer and no anti-HER2 therapy for ≥ 4 mo underwent complete staging, including 18F-fluorodeoxyglucose (FDG)/PET-CT. For 6 of the 8 patients, 64Cu-DOTA-trastuzumab injection (364-512 MBq, 5 mg trastuzumab) was preceded by trastuzumab infusion (45 mg). PET-CT (PET scan duration 1 h) was performed 21-25 (“Day 1”) and 47-49 (“Day 2”) h after 64Cu-DOTA-trastuzumab injection. Scan fields of view were chosen based on 18F-FDG/PET-CT. Lesions visualized relative to adjacent tissue on PET were considered PET-positive; analysis was limited to lesions identifiable on CT. Radiolabel uptake in prominent lesions was measured as maximum single-voxel standardized uptake value (SUVmax). Results Liver uptake of 64Cu was reduced approximately 75% with the 45 mg trastuzumab pre-dose, without significant effect on tumor uptake. The study included 89 CT-positive lesions; detection sensitivity was 77, 89 and 93% for Day 1, Day 2 and 18F-FDG, respectively. On average, tumor uptake was similar for 64Cu-DOTA-trastuzumab and 18F-FDG [SUVmax (mean, range): Day 1 (8.1, 3.0-22.5, n=48); Day 2 (8.9, 0.9-28.9, n=38); 18F-FDG (9.7, 3.3-25.4, n=56)], but the extent of same-lesion uptake was not correlated between the 2 radiotracers. No toxicities were observed, and estimated radiation dose from 64Cu-DOTA-trastuzumab was similar to 18F-FDG. Conclusion 64Cu-DOTA-trastuzumab visualizes HER2-positive metastatic breast cancer with high sensitivity, and is effective in surveying disseminated disease. A 45 mg trastuzumab pre-dose provides a 64Cu-DOTA-trastuzumab biodistribution favorable for tumor imaging. 64Cu-DOTA-trastuzumab/PET-CT warrants further evaluation for assessing tumor HER2 expression and measuring delivery of trastuzumab-based therapy.

Chimeric antigen receptor (CAR) T cell therapy is a promising clinical approach for reducing tumor progression and prolonging patient survival. However, improvements in both the safety and the potency of CAR T cell therapy demand quantitative imaging techniques to determine the distribution of cells after adoptive transfer. The purpose of this study was to optimize Zr-oxine labeling of CAR T cells and evaluate PET as a platform for imaging adoptively transferred CAR T cells. CAR T cells were labeled with 0-1.4 MBq of Zr-oxine per 10 cells and assessed for radioactivity retention, viability, and functionality. In vivo trafficking of Zr-oxine-labeled CAR T cells was evaluated in 2 murine xenograft tumor models: glioblastoma brain tumors with intracranially delivered IL13Rα2-targeted CAR T cells, and subcutaneous prostate tumors with intravenously delivered prostate stem cell antigen (PSCA)-targeted CAR T cells. CAR T cells were efficiently labeled (75%) and retained more than 60% of the Zr over 6 d. In vitro cytokine production, migration, and tumor cytotoxicity, as well as in vivo antitumor activity, were not significantly reduced when labeled with 70 kBq/10 cells. IL13Rα2-CAR T cells delivered intraventricularly were detectable by PET for at least 6 d throughout the central nervous system and within intracranial tumors. When intravenously administered, PSCA-CAR T cells also showed tumor tropism, with a 9-fold greater tumor-to-muscle ratio than for CAR-negative T cells. Zr-oxine can be used for labeling and imaging CAR T cells while maintaining cell viability and function. On the basis of these studies, we conclude thatZr-oxine is a clinically translatable platform for real-time assessment of cell therapies.

Optimal PET imaging of tumors with radiolabeled engineered antibodies requires, among other parameters, matching blood clearance and tumor uptake with the half-life of the engineered antibody. Although diabodies have favorable molecular sizes (50 kDa) for rapid blood clearance (t1/2= 30-60 min) and are bivalent, thereby increasing tumor uptake, they exhibit substantial kidney uptake as their major route of clearance, which is especially evident when they are labeled with the PET isotope 64Cu (t1/2= 12 hr). To overcome this drawback, diabodies may be conjugated to PEG, a modification that increases the apparent molecular size of the diabody and reduces kidney uptake without adversely affecting tumor uptake or the tumor to blood ratio. We show here that site specific attachment of monodispersed PEGn of increasing molecular size (n= 12, 24, and 48) can uniformly increase the apparent molecular size of the PEG-diabody conjugate, decrease kidney uptake and increase tumor uptake, the latter due to the increased residence time of the conjugate in the blood. Since the monodispersed PEGs were pre-conjugated to the chelator DOTA, the conjugates were able to bind radiometals such as 111In and 64Cu that can be used for SPECT and PET imaging, respectively. To allow conjugation of the DOTA-PEG to the diabody, the DOTA-PEG incorporated a terminal Cysteine conjugated to a vinyl sulfone moiety. In order to control the conjugation chemistry, we have engineered a surface thiolated diabody that incorporates two cysteines per monomer (four per diabody). The thiolated diabody was expressed and purified from bacterial fermentation and only needs to be reduced prior to conjugation to the DOTA-PEGn-Cys-VS. This novel imaging agent (a diabody with DOTA-PEG48-Cys-VS attached to introduced thiols) gave up to 80 %ID/g of tumor uptake with a tumor to blood ratio (T/B) of 8 at 24h when radiolabeled with 111In and 37.9% ID/g of tumor uptake (T/B= 8) at 44h when radiolabeled with 64Cu in PET imaging in an animal model. Tumor uptake was significantly improved from the 50% ID/g at 24 hours observed with diabodies that were pegylated on surface Lysine residues. Importantly, there was no loss of immunoreactivity of the site-specific Cys-conjugated diabody to its antigen (TAG-72) compared to the parent, unconjugated diabody. We propose that thiolated diabodies conjugated to DOTAylated monodisperse PEGs have the potential for superior SPECT and PET imaging in a clinical setting.

The goal of this study was to characterize the relationship between tumor uptake of Cu-DOTA-trastuzumab as measured by PET/CT and standard, immunohistochemistry (IHC)-based, histopathologic classification of human epidermal growth factor receptor 2 (HER2) status in women with metastatic breast cancer (MBC). Women with biopsy-confirmed MBC and not given trastuzumab for 2 mo or more underwent complete staging, includingF-FDG PET/CT. Patients were classified as HER2-positive (HER2+) or -negative (HER2-) based on fluorescence in situ hybridization (FISH)-supplemented immunohistochemistry of biopsied tumor tissue. Eighteen patients underwent Cu-DOTA-trastuzumab injection, preceded in 16 cases by trastuzumab infusion (45 mg). PET/CT was performed 21-25 (day 1) and 47-49 (day 2) h afterCu-DOTA-trastuzumab injection. Radiolabel uptake in prominent lesions was measured as SUV Average intrapatient SUV () was compared between HER2+ and HER2- patients. Eleven women were HER2+ (8 immunohistochemistry 3+; 3 immunohistochemistry 2+/FISH amplified), whereas 7 were HER2- (3 immunohistochemistry 2+/FISH nonamplified; 4 immunohistochemistry 1+). Median for day 1 and day 2 was 6.6 and 6.8 g/mL for HER 2+ and 3.7 and 4.3 g/mL for HER2- patients ( < 0.005 either day). The distributions of overlapped between the 2 groups, and interpatient variability was greater for HER2+ than HER2- disease ( < 0.005 and 0.001, respectively, on days 1 and 2). By 1 d after injection, uptake ofCu-DOTA-trastuzumab in MBC is strongly associated with patient HER2 status and is indicative of binding to HER2. The variability within and among HER2+ patients, as well as the overlap between the HER2+ and HER2- groups, suggests a role for Cu-DOTA-trastuzumab PET/CT in optimizing treatments that include trastuzumab.

As a growing number of patients with multiple myeloma (MM) respond to upfront therapies while eventually relapsing in a time frame that is often unpredictable, attention has increasingly focused on developing novel diagnostic criteria to also account for disease dissemination. Positron emission tomography/computed tomography (PET/CT) is often used as a noninvasive monitoring strategy to assess cancer cell dissemination, but because the uptake of the currently used radiotracer 18fluorodeoxyglucose (F-FDG) is a function of the metabolic activity of both malignant and nonmalignant cells, the results frequently lack sufficient specificity. Radiolabeled antibodies targeting MM tissue may detect disease irrespective of cell metabolism. Hence, we conjugated the clinically significant CD38-directed human antibody daratumumab (Darzalex [Dara]) to the DOTA chelator and labeled it with the positron-emitting radionuclide copper 64 (Cu; Cu-DOTA-Dara). Here, we show thatCu-DOTA-Dara can efficiently bind CD38 on the surface of MM cells and was mainly detected in the bones associated with tumor in a MM murine model. We also show that PET/CT based on Cu-DOTA-Dara displays a higher resolution and specificity to detect MM cell dissemination than doesF-FDG PET/CT and was even more sensitive than were bioluminescence signals. We therefore have supporting evidence for using Cu-DOTA-Dara as a novel imaging agent for MM.

Diabodies are non-covalent dimers of single chain antibody fragments (scFvs) that retain the avidity of intact IgG but have more favorable blood clearance than intact IgGs. Radiometals offer a wide range of half lives and emissions for matching imaging and therapy requirements and provide facile labeling of chelate-antibody conjugates. However, due to their high retention and metabolism in the kidney, use of radiometal labeled diabodies can be problematic for both imaging and therapy. Methods Having previously shown that 111In-DOTA-PEG3400-anti-CEA-diabody has similarly high tumor uptake and retention and less than 50% as much kidney uptake and retention as non-PEGylated diabody, we synthesized a similar derivative for an anti-TAG-72-diabody. We also reduced the molecular size of the polydispersed PEG3400 to monodispersed PEG27 and PEG12 (nominal masses of 1188 and 528, respectively). We performed biodistributions of their DOTA conjugates radiolabeled with 125I, 111In, or 64Cu in tumor bearing athymic mice. Results Addition of PEG3400 to the diabody reduced kidney uptake to a level (≈10 %ID/g) comparable to that obtained with radiometal labeled intact IgG. The PEG27 and PEG12 diabody conjugates also demonstrated low kidney uptake without reduction of tumor uptake or tumor to blood ratios. When radiolabeled with 64Cu, the DOTA-PEG12- and PEG27-diabody conjugates gave high contrast PET images of colon cancer xenografts in athymic mice. Conclusion PEGylated diabodies may be a valuable platform for delivery of radionuclides and other agents to tumors.

Introduction Single chain (scFv) antibodies are ideal targeting ligands due to their modular structure, high antigen specificity and affinity. These monovalent ligands display rapid tumor targeting but have limitations due to their fast urinary clearance. Methods An anti-prostate membrane antigen (PSMA) scFv with a site-specific cysteine was expressed and evaluated in a prostate cancer xenograft model by Cu-64 PET imaging. To enhance tumor accumulation, the scFv-cys was conjugated to the co-polymer DSPE-PEG-maleimide that spontaneously assembled into a homogeneous multivalent lipid nanoparticle (LNP). Results The targeted LNP exhibited a 2-fold increase in tumor uptake compared to the scFv alone using two different thiol ester chemistries. The anti-PSMA scFv-LNP exhibited a 1.6 fold increase in tumor targeting over the untargeted LNP. Conclusions The targeted anti-PSMA scFv-LNP showed enhanced tumor accumulation over the scFv alone or the untargeted DOTA-micelle providing evidence for the development of this system for drug delivery. Advances in Knowledge and implications for patient care Anti-tumor scFv antibody fragments have not achieved their therapeutic potential due to their fast blood clearance. Conjugation to a LNP enables multivalency to the tumor antigen as well as increased molecular size for chemotherapy drug delivery.

A series of anti-tumor/anti-chelate bispecific antibody formats were developed for pre-targeted radioimmunotherapy. Based on the anti-carcinoembryonic antigen humanized hT84.66-M5A monoclonal antibody and the anti-DOTA C8.2.5 scFv antibody fragment, this cognate series of bispecific antibodies were radioiodinated to determine their tumor targeting, biodistribution and pharmacokinetic properties in a mouse xenograft tumor model. The in vivo biodistribution studies showed that all the bispecific antibodies exhibited specific high tumor uptake but the tumor targeting was approximately one-half of the parental anti-CEA mAb due to faster blood clearance. Serum stability and FcRn studies showed no apparent reason for the faster blood clearance. A dual radiolabel biodistribution study revealed that the (111)In-DOTA bispecific antibody had increased liver and spleen uptake, not seen for the (125)I-version due to metabolism and release of the radioiodine from the cells. These data suggest increased clearance of the antibody fusion formats by the mononuclear phagocyte system. Importantly, a pre-targeted study showed specific tumor uptake of (177)Lu-DOTA and a tumor : blood ratio of 199 : 1. This pre-targeted radiotherapeutic and substantial reduction in the radioactive exposure to the bone marrow should enhance the therapeutic potential of RIT.