Copper 64-labeled daratumumab as a PET/CT imaging tracer for multiple myeloma.

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 (18F-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 (64Cu; 64Cu-DOTA-Dara). Here, we show that 64Cu-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 64Cu-DOTA-Dara displays a higher resolution and specificity to detect MM cell dissemination than does 18F-FDG PET/CT and was even more sensitive than were bioluminescence signals. We therefore have supporting evidence for using 64Cu-DOTA-Dara as a novel imaging agent for MM.

Template-Catalyzed, Disulfide Conjugation of Monoclonal Antibodies Using a Natural Amino Acid Tag.

The high specificity and favorable pharmacological properties of monoclonal antibodies (mAbs) have prompted significant interest in re-engineering this class of molecules to add novel functionalities for enhanced therapeutic and diagnostic potential. Here, we used the high affinity, meditope-Fab interaction to template and drive the rapid, efficient, and stable site-specific formation of a disulfide bond. We demonstrate that this template-catalyzed strategy provides a consistent and reproducible means to conjugate fluorescent dyes, cytotoxins, or "click" chemistry handles to meditope-enabled mAbs (memAbs) and memFabs. More importantly, we demonstrate this covalent functionalization is achievable using natural amino acids only, opening up the opportunity to genetically encode cysteine meditope "tags" to biologics. As proof of principle, genetically encoded, cysteine meditope tags were added to the N- and/or C-termini of fluorescent proteins, nanobodies, and affibodies, each expressed in bacteria, purified to homogeneity, and efficiently conjugated to different memAbs and meFabs. We further show that multiple T-cell and Her2-targeting bispecific molecules using this strategy potently activate T-cell signaling pathways in vitro. Finally, the resulting products are highly stable as evidenced by serum stability assays (>14 d at 37 °C) and in vivo imaging of tumor xenographs. Collectively, the platform offers the opportunity to build and exchange an array of functional moieties, including protein biologics, among any cysteine memAb or Fab to rapidly create, test, and optimize stable, multifunctional biologics.

Yttrium-90 Anti-CD25-BEAM-Conditioning for Autologous Hematopoietic Cell Transplantation in Peripheral T Cell Lymphoma.

Peripheral T cell lymphomas (PTCL) have a poor prognosis with current treatments. High-dose chemotherapy followed by autologous hematopoietic cell transplant (AHCT) is used as a consolidation strategy after achieving clinical remission with first-line therapy, as well as in chemosensitive relapse if allogeneic transplant is not an option. CD25 is a targetable protein often highly expressed in PTCL. In this phase 1 clinical trial, we tested the addition of beta-emitting 90Y-labeled chimeric anti-CD25 basiliximab (aTac) to BEAM (carmustine, etoposide, cytarabine, melphalan) as conditioning for AHCT in patients with PTCL. Twenty-three AHCT-eligible patients were enrolled, and 20 received therapeutic 90Y-aTac-BEAM AHCT. Radiation doses of 0.4, 0.5 and 0.6 mCi/kg were tested. With no observed dose-limiting toxicities, 0.6 mCi/kg was deemed the recommended phase 2 dose. The most prevalent adverse effect, grade 2 mucositis, was experienced by 80% of patients. As of this report, 6 (30%) of the treated patients had died, 5 due to progressive disease and 1 due to multiple organ failure [median time of death 17 mo (range: 9-21 mo)] post-AHCT. Median follow-up was 24 mo (range: 9-26 mo) overall and 24 mo (range: 13-26 mo) for surviving patients. For patients who received therapeutic 90Y-aTac-BEAM AHCT, the 2-year progression-free and overall survival were 59% (95% CI: 34-77%) and 68% (95% CI: 42-84%), respectively. 90Y-aTac-BEAM appears to be safe as an AHCT conditioning regimen for PTCL, with no increased toxicity over the toxicities historically seen with BEAM alone in this patient population. This trial was registered at www.clinicaltrials.gov as # NCT02342782.

Site specific discrete PEGylation of (124)I-labeled mCC49 Fab' fragments improves tumor MicroPET/CT imaging in mice.

The tumor-associated glycoprotein-72 (TAG-72) antigen is highly overexpressed in various human adenocarcinomas and anti-TAG-72 monoclonal antibodies, and fragments are therefore useful as pharmaceutical targeting vectors. In this study, we investigated the effects of site-specific PEGylation with MW 2-4 kDa discrete, branched PEGylation reagents on mCC49 Fab' (MW 50 kDa) via in vitro TAG72 binding, and in vivo blood clearance kinetics, biodistribution, and mouse tumor microPET/CT imaging. mCC49Fab' (Fab'-NEM) was conjugated at a hinge region cysteine with maleimide-dPEG 12-(dPEG24COOH)3 acid (Mal-dPEG-A), maleimide-dPEG12-(dPEG12COOH)3 acid (Mal-dPEG-B), or maleimide-dPEG12-(m-dPEG24)3 (Mal-dPEG-C), and then radiolabeled with iodine-124 ((124)I) in vitro radioligand binding assays and in vivo studies used TAG-72 expressing LS174T human colon carcinoma cells and xenograft mouse tumors. Conjugation of mCC49Fab' with Mal-dPEG-A (Fab'-A) reduced the binding affinity of the non PEGylated Fab' by 30%; however, in vivo, Fab'-A significantly lengthened the blood retention vs Fab'-NEM (47.5 vs 28.1%/ID at 1 h, 25.1 vs 8.4%/ID at 5 h, p < 0.01), showed excellent tumor to background, better microPET/CT images due to higher tumor accumulation, and increased tumor concentration in excised tissues at 72 h by 130% (5.09 ± 0.83 vs 3.83 ± 1.50%ID/g, p < 0.05). Despite the strong similarity of the three PEGylation reagents, PEGylation with Mal-dPEG-B or -C reduced the in vitro binding affinity of Fab'-NEM by 70%, blood retention, microPET/CT imaging tumor signal intensity, and residual 72 h tumor concentration by 49% (3.83 ± 1.50 vs 1.97 ± 0.29%ID/g, p < 0.05) and 63% (3.83 ± 1.50 vs 1.42 ± 0.35%ID/g, p < 0.05), respectively. We conclude that remarkably subtle changes in the structure of the PEGylation reagent can create significantly altered biologic behavior. Further study is warranted of conjugates of the triple branched, negatively charged Mal-dPEG-A.

A transgene-encoded cell surface polypeptide for selection, in vivo tracking, and ablation of engineered cells.

An unmet need in cell engineering is the availability of a single transgene encoded, functionally inert, human polypeptide that can serve multiple purposes, including ex vivo cell selection, in vivo cell tracking, and as a target for in vivo cell ablation. Here we describe a truncated human EGFR polypeptide (huEGFRt) that is devoid of extracellular N-terminal ligand binding domains and intracellular receptor tyrosine kinase activity but retains the native amino acid sequence, type I transmembrane cell surface localization, and a conformationally intact binding epitope for pharmaceutical-grade anti-EGFR monoclonal antibody, cetuximab (Erbitux). After lentiviral transduction of human T cells with vectors that coordinately express tumor-specific chimeric antigen receptors and huEGFRt, we show that huEGFRt serves as a highly efficient selection epitope for chimeric antigen receptor(+) T cells using biotinylated cetuximab in conjunction with current good manufacturing practices (cGMP)-grade anti-biotin immunomagnetic microbeads. Moreover, huEGFRt provides a cell surface marker for in vivo tracking of adoptively transferred T cells using both flow cytometry and immunohistochemistry, and a target for cetuximab-mediated antibody-dependent cellular cytotoxicity and in vivo elimination. The versatility of huEGFRt and the availability of pharmaceutical-grade reagents for its clinical application denote huEGFRt as a significant new tool for cellular engineering.

Pilot study of HER2 targeted 64 Cu-DOTA-tagged PET imaging in gastric cancer patients.

OBJECTIVE: Human epidermal growth factor receptor 2 (HER2) is an important biomarker for targeted gastric cancer (GC) immunotherapy. However, heterogeneous HER2 overexpression in GC, loss of HER2 expression during therapy, and inability to non-invasively identify HER2 overexpressing tumors impede effective targeting therapies. Improved HER2-specific functional imaging can address these challenges. Trastuzumab is a HER2-directed mAb to treat HER2 overexpressing cancers. The 64 Cu-DOTA-trastuzumab radiotracer is used to detect HER2+ metastatic breast cancer. We aimed to develop 64 Cu-DOTA-trastuzumab PET-CT to detect and characterize tumor uptake in HER2+ or - GC patients. METHODS: We conducted a single-arm phase II pilot study exploring the feasibility of 64 Cu-DOTA-trastuzumab for PET imaging of HER2 overexpressing GC compared to HER2 non-expressing tumors. Eight patients with biopsy-confirmed gastric adenocarcinoma were included. Immunohistochemistry was used to evaluate primary tumor biopsies for HER2 overexpression. Patients were injected with 45 mg of cold trastuzumab followed by 5 mg of 64 Cu-DOTA-trastuzumab. PET-CT scans were performed 24-48 h post radiotracer injection and compared to standard staging CT scans. RESULTS: We observed limited toxicity following 64 Cu-DOTA-trastuzumab injections. While there was uptake of the radiotracer in portions of HER2+ lesions, there was no statistically significant distinction between tumor and background by standardized uptake value analysis. CONCLUSION: Despite the potential of 64 Cu-DOTA-trastuzumab PET imaging of HER2+ metastatic breast cancer, a 5 mg dose of this radiotracer injected 24-48 h before imaging was insufficient to identify HER2+ GC. These results inform future GC imaging studies to optimize biomarker-targeted therapies based on dosage and timing for more clinically relevant imaging.

First-In-Human Pilot PET Immunoimaging Study of 64Cu-Anti-Carcinoembryonic Antigen Monoclonal Antibody (hT84.66-M5A) in Patients with Carcinoembryonic Antigen-Producing Cancers.

Background: PET imaging using radiolabeled immunoconstructs shows promise in cancer detection and in assessing tumor response to therapies. The authors report the first-in-human pilot study evaluating M5A, a humanized anti-carcinoembryonic antigen (CEA) monoclonal antibody (mAb), radiolabeled with 64Cu in patients with CEA-expressing malignancies. The purpose of this pilot study was to identify the preferred patient population for further evaluation of this agent in an expanded trial. Methods: Patients with CEA-expressing primary or metastatic cancer received 64Cu-DOTA-hT84.66-M5A with imaging performed at 1 and 2 days postinfusion. 64Cu-DOTA-hT84.66-M5A PET scan findings were correlated with CT, MRI, and/or FDG PET scans and with histopathologic findings from planned surgery or biopsy performed postscan. Results: Twenty patients received 64Cu-DOTA-hT84.66-M5A. Twelve patients demonstrated positive images, which were confirmed in 10 patients as tumor by standard-of-care (SOC) imaging, biopsy, or surgical findings. Four of the 8 patients with negative imaging were confirmed as true negative, with the remaining 4 patients having disease demonstrated by SOC imaging or surgery. All 5 patients with locally advanced rectal cancer underwent planned biopsy or surgery after 64Cu-DOTA-hT84.66-M5A imaging (4 patients imaged 6-8 weeks after completing neoadjuvant chemotherapy and radiation therapy) and demonstrated a high concordance between biopsy findings and 64Cu-DOTA-hT84.66-M5A PET scan results. Three patients demonstrated positive uptake at the primary site later confirmed by biopsy and at surgery as residual disease. Two patients with negative scans each demonstrated complete pathologic response. In 5 patients with medullary thyroid cancer, 64Cu-DOTA-hT84.66-M5A identified disease not seen on initial CT scans in 3 patients, later confirmed to be disease by subsequent surgery or MRI. Conclusions: 64Cu-DOTA-hT84.66-M5A demonstrates promise in tumor detection, particularly in patients with locally advanced rectal cancer and medullary thyroid cancer. A successor trial in locally advanced rectal cancer has been initiated to further evaluate this agent's ability to define tumor extent before and assess disease response after neoadjuvant chemotherapy and radiotherapy. clinical trial.gov (NCT02293954).

Use of 64Cu-DOTA-Trastuzumab PET to Predict Response and Outcome of Patients Receiving Trastuzumab Emtansine for Metastatic Breast Cancer: A Pilot Study.

We hypothesized that functional imaging with 64Cu-DOTA-trastuzumab PET/CT would predict the response to the antibody-drug conjugate trastuzumab-emtansine (T-DM1). Methods: Ten women with metastatic human epidermal growth factor receptor 2-positive breast cancer underwent 18F-FDG PET/CT and 64Cu-DOTA-trastuzumab PET/CT on days 1 and 2 before treatment with T-DM1. Results: T-DM1-responsive patients had higher uptake than nonresponsive patients. Day 1 minimum SUVmax (5.6 vs. 2.8, P < 0.02), day 2 minimum SUVmax (8.1 vs. 3.2, P < 0.01), and day 2 average SUVmax (8.5 vs. 5.4, P < 0.05) for 64Cu-DOTA-trastuzumab all favored responding patients. Tumor-level response suggested threshold dependence on SUVmax Patients with a day 2 minimum SUVmax above versus below the threshold had a median time to treatment failure of 28 mo versus 2 mo (P < 0.02). Conclusion: Measurement of trastuzumab uptake in tumors via PET/CT is promising for identifying patients with metastatic breast cancer who will benefit from T-DM1.

In vivo imaging of transplanted islets with 64Cu-DO3A-VS-Cys40-Exendin-4 by targeting GLP-1 receptor.

Glucagon-like peptide 1 receptor (GLP-1R) is highly expressed in pancreatic islets, especially on ß-cells. Therefore, a properly labeled ligand that binds to GLP-1R could be used for in vivo pancreatic islet imaging. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), a more stable agonist of GLP-1 such as Exendin-4 is a preferred imaging agent. In this study, DO3A-VS-Cys(40)-Exendin-4 was prepared through the conjugation of DO3A-VS with Cys(40)-Exendin-4. The in vitro binding affinity of DO3A-VS-Cys(40)-Exendin-4 was evaluated in INS-1 cells, which overexpress GLP-1R. After (64)Cu labeling, biodistribution studies and microPET imaging of (64)Cu-DO3A-VS-Cys(40)-Exendin-4 were performed on both subcutaneous INS-1 tumors and islet transplantation models. The subcutaneous INS-1 tumor was clearly visualized with microPET imaging after the injection of (64)Cu-DO3A-VS-Cys(40)-Exendin-4. GLP-1R positive organs, such as pancreas and lung, showed high uptake. Tumor uptake was saturable, reduced dramatically by a 20-fold excess of unlabeled Exendin-4. In the intraportal islet transplantation models, (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated almost two times higher uptake compared with normal mice. (64)Cu-DO3A-VS-Cys(40)-Exendin-4 demonstrated persistent and specific uptake in the mouse pancreas, the subcutaneous insulinoma mouse model, and the intraportal human islet transplantation mouse model. This novel PET probe may be suitable for in vivo pancreatic islets imaging in the human.

Site-specific conjugation of monodispersed DOTA-PEGn to a thiolated diabody reveals the effect of increasing peg size on kidney clearance and tumor uptake with improved 64-copper PET imaging.

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 (t(1/2) = 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 (64)Cu (t(1/2) = 12 h). 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 preconjugated to the chelator DOTA, the conjugates were able to bind radiometals such as (111)In and (64)Cu 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 24 h when radiolabeled with (111)In and 37.9% ID/g of tumor uptake (T/B = 8) at 44 h when radiolabeled with (64)Cu in PET imaging in an animal model. Tumor uptake was significantly improved from the 50% ID/g at 24 h 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.

TAG-72-Targeted α-Radionuclide Therapy of Ovarian Cancer Using 225Ac-Labeled DOTAylated-huCC49 Antibody.

Radioimmunotherapy, an approach using radiolabeled antibodies, has had minimal success in the clinic with several ß-emitting radionuclides for the treatment of ovarian cancer. Alternatively, radioimmunotherapy with α-emitters offers the advantage of depositing much higher energy over shorter distances but was thought to be inappropriate for the treatment of solid tumors, for which antibody penetration is limited to a few cell diameters around the vascular system. However, the deposition of high-energy α-emitters to tumor markers adjacent to a typical leaky tumor vascular system may have large antitumor effects at the tumor vascular level, and their reduced penetration in normal tissue would be expected to lower off-target toxicity. Methods: To evaluate this concept, DOTAylated-huCC49 was labeled with the α-emitter 225Ac to target tumor-associated glycoprotein 72-positive xenografts in a murine model of ovarian cancer. Results:225Ac-labeled DOTAylated-huCC49 radioimmunotherapy significantly reduced tumor growth in a dose-dependent manner (1.85, 3.7, and 7.4 kBq), with the 7.4-kBq dose extending survival by more than 3-fold compared with the untreated control. Additionally, a multitreatment regime (1.85 kBq followed by 5 weekly doses of 0.70 kBq for a total of 5.4 kBq) extended survival almost 3-fold compared with the untreated control group, without significant off-target toxicity. Conclusion: These results establish the potential for antibody-targeted α-radionuclide therapy for ovarian cancer, which may be generalized to α-radioimmunotherapy in other solid tumors.

Anti-CD25 radioimmunotherapy with BEAM autologous hematopoietic cell transplantation conditioning in Hodgkin lymphoma.

High-risk relapsed or refractory (R/R) classical Hodgkin lymphoma (HL) is associated with poor outcomes after conventional salvage therapy and autologous hematopoietic cell transplantation (AHCT). Post-AHCT consolidation with brentuximab vedotin (BV) improves progression-free survival (PFS), but with increasing use of BV early in the treatment course, the utility of consolidation is unclear. CD25 is often expressed on Reed-Sternberg cells and in the tumor microenvironment in HL, and we hypothesized that the addition of 90Y-antiCD25 (aTac) to carmustine, etoposide, cytarabine, melphalan (BEAM) AHCT would be safe and result in a transplantation platform that is agnostic to prior HL-directed therapy. Twenty-five patients with high-risk R/R HL were enrolled in this phase 1 dose-escalation trial of aTac-BEAM. Following an imaging dose of 111In-antiCD25, 2 patients had altered biodistribution, and a third developed an unrelated catheter-associated bacteremia; therefore, 22 patients ultimately received therapeutic 90Y-aTac-BEAM AHCT. No dose-limiting toxicities were observed, and 0.6 mCi/kg was deemed the recommended phase 2 dose, the dose at which the heart wall would not receive >2500 cGy. Toxicities and time to engraftment were similar to those observed with standard AHCT, though 95% of patients developed stomatitis (all grade 1-2 per Bearman toxicity scale). Seven relapses (32%) were observed, most commonly in patients with ≥3 risk factors. The estimated 5-year PFS and overall survival probabilities among 22 evaluable patients were 68% and 95%, respectively, and non-relapse mortality was 0%. aTac-BEAM AHCT was tolerable in patients with high-risk R/R HL, and we are further evaluating the efficacy of this approach in a phase 2 trial. This trial was registered at www.clinicaltrials.gov as #NCT01476839.

Improved targeting of an anti-TAG-72 antibody drug conjugate for the treatment of ovarian cancer.

INTRODUCTION: Ovarian cancer has only a 17% 5-year survival rate in patients diagnosed with late stage disease. Tumor-associated glycoprotein-72 (TAG72), expressed in 88% of all stages of ovarian cancer, is an excellent candidate for antibody-targeted therapy, as it is not expressed in normal human adult tissues, except in the secretory endometrium. METHODS: Using the clinically relevant anti-TAG72 murine monoclonal antibody CC49, we evaluated antibody drug conjugates (ADCs) incorporating the highly potent, synthetic antimitotic agent monomethylauristatin E (MMAE). MMAE was conjugated to CC49 via reduced disulfides in the hinge region, using three different types of linker chemistry, vinylsulfone (VS-MMAE), bromoacetamido (Br-MMAE), and maleimido (mal-MMAE). RESULTS: The drug antibody ratios (DARs) of the three ADCs were 2.3 for VS-MMAE, 10 for Br-MMAE, and 9.5 for mal-MMAE. All three ADCs exhibited excellent tumor to blood ratios on PET imaging, but the absolute uptake of CC49-mal-MMAE (3.3%ID/g) was low compared to CC49-Br-MMAE (6.43%ID/g), at 142 hours. Blood clearance at 43 hours was 38% for intact CC49, about 24% for both CC49-VS-MMAE and CC49-Br-MMAE, and 7% for CC49-mal-MMAE. CC49-VS-MMAE was not further studied due to its low DAR, while CC49-mal-MMAE was ineffective in the OVCAR3 xenograft likely due to its rapid blood clearance. In contrast, CC49-Br-MMAE treated mice exhibited an average of a 15.6 day tumor growth delay and a 40% increase in survival vs controls with four doses of 7.5 or 15 mg/kg of CC49-Br-MMAE. CONCLUSION: We conclude that CC49-Br-MMAE with a high DAR and stable linker performs well in a difficult to treat solid tumor model.

Phase I Study of Yttrium-90 Radiolabeled M5A Anti-Carcinoembryonic Antigen Humanized Antibody in Patients with Advanced Carcinoembryonic Antigen Producing Malignancies.

Background: M5A is a humanized monoclonal antibody (mAb) directed against carcinoembryonic antigen (CEA) The purpose of this first in human phase I dose-escalation trial was to characterize the toxicities and determine the maximum tolerated dose (MTD) of yttrium-90 (90Y)-DOTA-M5A as a single agent and in combination with gemcitabine (gem). Methods: Patients with advanced metastatic CEA-producing malignancies who had progressed on standard therapies were first administered indium-111 (111In)-DOTA-M5A. If tumor targeting was observed, the patient then received the therapy dose of 90Y-DOTA-M5A. Serial scans, blood sampling, and 24 h urine collections were then performed to estimate radiation doses to organs and total body. Assays for human antihuman antibody (HAHA) responses were performed out to 6 months. Results: Of the 18 patients who received 111In-DOTA-M5A, 16 received 90Y-DOTA-M5A therapy; 1 patient at 14 mCi/m2 with gem (150 mg/m2 days 1and 3), 3 patients at 12 mCi/m2 with gem, 6 patients at 12 mCi/m2 without gem, and 6 at 10 mCi/m2 without gem. Prolonged cytopenias resulted in discontinuation of dose escalation with gemcitabine. A single agent MTD of 10 mCi/m2 was established based on dose-limiting hematopoietic toxicities. HAHA immune response was identified in 2 of 16 patients (12.5%). Stable disease at 3 months was seen in 10 patients and 2 patients demonstrated an 88% and 64% decrease in CEA back to normal levels. In 2 patients 111In-DOTA-M5A imaging revealed previously unknown brain metastases. Conclusion: This study demonstrates the potential utility of the 90Y-DOTA-M5A anti-CEA mAb as a therapeutic antibody. There is decreased immunogenicity compared with murine and chimeric mAbs, allowing for the potential of multiple administrations. Combined modality therapy approaches incorporating this agent should continue to be evaluated.

Potent immunomodulatory effects of an anti-CEA-IL-2 immunocytokine on tumor therapy and effects of stereotactic radiation.

While anti-CEA antibodies have no direct effect on CEA-positive tumors, they can be used to direct potent anti-tumor effects as an antibody-IL-2 fusion protein (immunocytokine, ICK), and at the same time reduce the toxicity of IL-2 as a single agent. Using a fusion protein of humanized anti-CEA with human IL-2 (M5A-IL-2) in a transgenic murine model expressing human CEA, we show high tumor uptake of the ICK to CEA-positive tumors with additional lymph node targeting. ICK treated CEA-positive tumors exhibit significant tumor eradication. Analysis of tumor-infiltrating lymphocytes shows a high frequency of both CD8+ and CD4+ T cells along with CD11b positive myeloid cells in ICK treated mice. The frequency of tumor-infiltrating FoxP3+ CD4+ T cells (Tregs) is significantly reduced vs anti-CEA antibody-treated controls, indicating that ICK did not preferentially stimulate migration or proliferation of Tregs to the tumor. Combination therapy with anti-PD-1 antibody did not improve tumor reduction over ICK therapy alone. Since stereotactic tumor irradiation (SRT), commonly used in cancer therapy has immunomodulatory effects, we tested combination SRT+ICK therapy in two tumor model systems. Use of fractionated vs single high dose SRT in combination with ICK resulted in greater tumor inhibition and immunity to tumor rechallenge. In particular, tumor microenvironment and myeloid cell composition appear to play a significant role in the response rate to ICK+SRT combination therapy.

Identifying CD38+ cells in patients with multiple myeloma: first-in-human imaging using copper-64-labeled daratumumab.

18F-Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is one of the most widely used imaging techniques to detect multiple myeloma (MM). Intracellular FDG uptake depicts in vivo metabolic activity, which can be seen in both malignant and nonmalignant cells, resulting in limited sensitivity and specificity. Our group showed preclinically that tracing MM dissemination using a CD38-directed human antibody, daratumumab, that is radioconjugated with 64Cu via the chelator DOTA (64Cu-daratumumab), led to improved sensitivity and specificity over that of FDG. Here, we report the results of a phase 1 trial designed to (1) assess the safety and feasibility of 64Cu-daratumumab PET/CT and (2) preliminarily evaluate and characterize the ability of 64Cu-daratumumab to accurately detect or exclude MM lesions. A total of 12 daratumumab-naive patients were imaged. Prior to the injection of 15 mCi/5 mg of 64Cu-daratumumab, patients were treated with 0 (n = 3), 10 (n = 3), 45 (n = 3), or 95 mg (n = 3) of unlabeled daratumumab to assess its effect on image quality. No significant adverse events were observed from either unlabeled daratumumab or 64Cu-daratumumab. Of the dose levels tested, 45 mg unlabeled daratumumab was the most optimal in terms of removing background signal without saturating target sites. 64Cu-daratumumab PET/CT provided safe whole-body imaging of MM. A trial comparing the sensitivity and specificity of 64Cu-daratumumab PET/CT with that of FDG PET/CT is planned. This trial was registered at www.clinicaltrials.gov as #NCT03311828.

Radioiodinated versus radiometal-labeled anti-carcinoembryonic antigen single-chain Fv-Fc antibody fragments: optimal pharmacokinetics for therapy.

Antibody fragments with optimized pharmacokinetic profiles hold potential for detection and therapy of tumor malignancies. We studied the behavior of three anti-carcinoembryonic antigen (CEA) single-chain Fv-Fc (scFv-Fc) variants (I253A, H310A, and H310A/H435Q; Kabat numbering system) that exhibited differential serum persistence. Biodistribution studies done on CEA-positive tumor xenografted mice revealed that the 111In-labeled I253A fragment with the slowest clearance kinetics (T1/2beta, 27.7 h) achieved the highest tumor uptake (44.6% ID/g at 24 h), whereas the radiometal-labeled H310A/H435Q fragment with the most rapid elimination (T1/2beta, 7.05 h) reached a maximum of 28.0% ID/g at 12 h postinjection. The H310A protein was characterized by both intermediate serum half-life and tumor uptake. The 111In-based biodistribution studies showed that all three fragments were eliminated primarily through the liver, and hepatic radiometal activity correlated with the rate of fragment clearance. The 111In-labeled H310A/H435Q protein exhibited the highest liver uptake (23.5% ID/g at 24 h). Metabolism of the 125I-labeled scFv-Fc proteins resulted in low normal organ activity. Finally, the 125I/111In biodistribution data allowed for dose estimations, which suggest the 131I-labeled scFv-Fc H310A/H435Q as a promising candidate for radioimmunotherapy.

Combining adoptive cellular and immunocytokine therapies to improve treatment of B-lineage malignancy.

Currently, the lineage-specific cell-surface molecules CD19 and CD20 present on many B-cell malignancies are targets for both antibody- and cell-based therapies. Coupling these two treatment modalities is predicted to improve the antitumor effect, particularly for tumors resistant to single-agent biotherapies. This can be shown using an immunocytokine, composed of a CD20-specific monoclonal antibody fused to biologically active interleukin 2 (IL-2), combined with ex vivo expanded human umbilical cord blood-derived CD8(+) T cells, that have been genetically modified to be CD19 specific, for adoptive transfer after allogeneic hematopoietic stem-cell transplantation. We show that a benefit of targeted delivery of recombinant IL-2 by the immunocytokine to the CD19(+)CD20(+) tumor microenvironment is improved in vivo persistence of the CD19-specific T cells, and this results in an augmented cell-mediated antitumor effect. Phase I trials are under way using anti-CD20-IL-2 immunocytokine and CD19-specific T cells as monotherapies, and our results warrant clinical trials using combination of these two immunotherapies.

ImmunoPET, [64Cu]Cu-DOTA-Anti-CD33 PET-CT, Imaging of an AML Xenograft Model.

PURPOSE: Acute myeloid leukemia (AML) is a highly aggressive form of leukemia, which results in poor survival outcomes. Currently, diagnosis and prognosis are based on invasive single-point bone marrow biopsies (iliac crest). There is currently no AML-specific noninvasive imaging method to detect disease, including in extramedullary organs, representing an unmet clinical need. About 85% to 90% of human myeloid leukemia cells express CD33 cell surface receptors, highlighting CD33 as an ideal candidate for AML immunoPET. EXPERIMENTAL DESIGN: We evaluated whether [64Cu]Cu-DOTA-anti-CD33 murine mAb can be used for immunoPET imaging of AML in a preclinical model. MicroCT was adjusted to detect spatial/anatomical details of PET activity. For translational purposes, a humanized anti-CD33 antibody was produced; we confirmed its ability to detect disease and its distribution. We reconfirmed/validated CD33 antibody-specific targeting with an antibody-drug conjugate (ADC) and radioimmunotherapy (RIT). RESULTS: [64Cu]Cu-DOTA-anti-CD33-based PET-CT imaging detected CD33+ AML in mice with high sensitivity (95.65%) and specificity (100%). The CD33+ PET activity was significantly higher in specific skeletal niches [femur (P < 0.00001), tibia (P = 0.0001), humerus (P = 0.0014), and lumber spine (P < 0.00001)] in AML-bearing mice (over nonleukemic control mice). Interestingly, the hybrid PET-CT imaging showed high disease activity in the epiphysis/metaphysis of the femur, indicating regional spatial heterogeneity. Anti-CD33 therapy using newly developed humanized anti-CD33 mAb as an ADC (P = 0.02) and [225Ac]Ac-anti-CD33-RIT (P < 0.00001) significantly reduced disease burden over that of respective controls. CONCLUSIONS: We have successfully developed a novel anti-CD33 immunoPET-CT-based noninvasive modality for AML and its spatial distribution, indicating a preferential skeletal niche.

Rapid and efficient production of radiolabeled antibody conjugates using vacuum diafiltration guided by mathematical modeling.

Increasing interest in the use of radiolabeled antibodies for cancer imaging and therapy drives the need for more efficient production of the antibody conjugates. Here, we illustrate a method for rapid and efficient production of radiolabeled antibody conjugates using vacuum diafiltration guided by mathematical modeling. We apply this technique to the production of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated antibodies at the milligram and gram production scale and achieve radiolabeling efficiencies >95% using In-111. Using vacuum diafiltration, antibody-chelate conjugation and purification can be accomplished within the same vessel, and the entire process can be completed in <24 h. Vacuum diafiltration also offers safer and gentler processing conditions by eliminating the need to keep the retentate vessel under positive pressure through applied gas pressure or shear-inducing restriction points in the retentate flow path. Experimental data and mathematical model calculations suggest there exists a weak binding affinity (approximately 10(4)M(-1)) between the charged chelate molecules (e.g., DOTA) and the antibodies that slows the removal of excess chelate during purification. By analyzing the radiolabeling efficiency as a function of the number of diavolumes, we demonstrate the importance of balancing the removal of free chelate with the introduction of metal contaminants from the diafiltration buffer and also illustrate how to optimize radiolabeling of antibody conjugates under a variety of operating conditions. This methodology is applicable to the production of antibody conjugates in general.