Melanocortin-1 Receptor Expression as a Marker of Progression in Melanoma.

PURPOSE: Melanocortin-1 receptor (MC1R) plays a critical role in human pigmentation and DNA repair mechanisms. MC1R-targeting agents are being investigated in clinical trials in patients with melanoma, yet large studies investigating the rate and degree of MC1R expression in primary and metastatic human melanoma tissue are lacking. METHODS: Using tissue microarrays containing three large cohorts of 225 cases of benign nevi, 189 with primary melanoma, and 271 with metastatic melanoma, we applied quantitative immunofluorescence and immunohistochemistry to comprehensively study MC1R protein expression. RESULTS: We show a stepwise elevation of MC1R expression in different stages of melanoma progression (nevi, primary, metastasis). Higher MC1R expression was seen in deeper (>1 mm) primary lesions and ulcerated lesions and was associated with shorter survival in primary and metastatic tumors. On multivariable analysis, Breslow thickness, male sex, and chronic sun exposure were independent predictors of worse overall survival in the primary melanoma cohort. CONCLUSION: Our data suggest that MC1R might be a valuable drug target in aggressive melanoma. Additional studies are warranted to determine its functional significance in melanoma progression and its utility as a predictive biomarker in patients receiving MC1R-directed therapies.

Intrathecal delivery of nanoparticle PARP inhibitor to the cerebrospinal fluid for the treatment of metastatic medulloblastoma.

The morbidity associated with pediatric medulloblastoma, in particular in patients who develop leptomeningeal metastases, remains high in the absence of effective therapies. Administration of substances directly into the cerebrospinal fluid (CSF) is one approach to circumvent the blood-brain barrier and focus delivery of drugs to the site of tumor. However, high rates of CSF turnover prevent adequate drug accumulation and lead to rapid systemic clearance and toxicity. Here, we show that PLA-HPG nanoparticles, made with a single-emulsion, solvent evaporation process, can encapsulate talazoparib, a PARP inhibitor (BMN-673). These degradable polymer nanoparticles improve the therapeutic index when delivered intrathecally and lead to sustained drug retention in the tumor as measured with PET imaging and fluorescence microscopy. We demonstrate that administration of these particles into the CSF, alone or in combination with systemically administered temozolomide, is a highly effective therapy for tumor regression and prevention of leptomeningeal spread in xenograft mouse models of medulloblastoma. These results provide a rationale for harnessing nanoparticles for the delivery of drugs limited by brain penetration and therapeutic index and demonstrate important advantages in tolerability and efficacy for encapsulated drugs delivered locoregionally.

Melanocortin 1 receptor (MC1R) expression as a marker of progression in melanoma.

Melanocortin-1 receptor (MC1R) plays a critical role in human pigmentation and DNA repair mechanisms. MC1R-targeting agents are being investigated in clinical trials in melanoma patients, yet large studies investigating the rate and degree of MC1R expression in primary and metastatic human melanoma tissue are lacking. Using tissue microarrays containing three large cohorts of 225 cases of benign nevi, 189 with primary melanoma, and 271 with metastatic melanoma, we applied quantitative immunofluorescence and immunohistochemistry to comprehensively study MC1R protein expression. We show a stepwise elevation of MC1R expression in different stages of melanoma progression (nevi, primary, metastasis). Higher MC1R expression was seen in deeper (>1 mm) primary lesions, ulcerated lesions, and mucosal melanomas compared to cutaneous melanomas and was associated with shorter survival in primary and metastatic tumors. On multi-variable analysis, Breslow thickness, ulceration, male sex, and chronic sun exposure were independent predictors of worse overall survival in the primary melanoma cohort. In the metastatic melanoma cohort, MC1R expression and mucosal melanomas were independent predictors of inferior overall survival. Our data suggest that MC1R might be a valuable drug target in aggressive melanoma. Additional studies are warranted to determine its functional significance in melanoma progression and its utility as a predictive biomarker in patients receiving MC1R-directed therapies.

Systematic Literature Review of Machine Learning Algorithms Using Pretherapy Radiologic Imaging for Glioma Molecular Subtype Prediction.

BACKGROUND: The molecular profile of gliomas is a prognostic indicator for survival, driving clinical decision-making for treatment. Pathology-based molecular diagnosis is challenging because of the invasiveness of the procedure, exclusion from neoadjuvant therapy options, and the heterogeneous nature of the tumor. PURPOSE: We performed a systematic review of algorithms that predict molecular subtypes of gliomas from MR Imaging. DATA SOURCES: Data sources were Ovid Embase, Ovid MEDLINE, Cochrane Central Register of Controlled Trials, Web of Science. STUDY SELECTION: Per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 12,318 abstracts were screened and 1323 underwent full-text review, with 85 articles meeting the inclusion criteria. DATA ANALYSIS: We compared prediction results from different machine learning approaches for predicting molecular subtypes of gliomas. Bias analysis was conducted for each study, following the Prediction model Risk Of Bias Assessment Tool (PROBAST) guidelines. DATA SYNTHESIS: Isocitrate dehydrogenase mutation status was reported with an area under the curve and accuracy of 0.88 and 85% in internal validation and 0.86 and 87% in limited external validation data sets, respectively. For the prediction of O6-methylguanine-DNA methyltransferase promoter methylation, the area under the curve and accuracy in internal validation data sets were 0.79 and 77%, and in limited external validation, 0.89 and 83%, respectively. PROBAST scoring demonstrated high bias in all articles. LIMITATIONS: The low number of external validation and studies with incomplete data resulted in unequal data analysis. Comparing the best prediction pipelines of each study may introduce bias. CONCLUSIONS: While the high area under the curve and accuracy for the prediction of molecular subtypes of gliomas are reported in internal and external validation data sets, limited use of external validation and the increased risk of bias in all articles may present obstacles for clinical translation of these techniques.

ImmunoPET Imaging Identifies the Optimal Timepoint for Combination Therapy in Xenograft Models of Triple-Negative Breast Cancer.

(1) Purpose: The glycoprotein non-metastatic melanoma B (gpNMB) is a type 1 transmembrane protein that is overexpressed in numerous cancers, including triple-negative breast cancer (TNBC). Its overexpression is associated with lower overall survival of patients with TNBC. Tyrosine kinase inhibitors such as dasatinib can upregulate gpNMB expression, which has the potential to enhance therapeutic targeting with anti-gpNMB antibody drug conjugates such as glembatumumab vedotin (CDX-011). Our primary aim is to quantify the degree and identify the timeframe of gpNMB upregulation in xenograft models of TNBC after treatment with the Src tyrosine kinase inhibitor, dasatinib, by longitudinal positron emission tomography (PET) imaging with the 89Zr-labeled anti-gpNMB antibody ([89Zr]Zr-DFO-CR011). The goal is to identify the timepoint at which to administer CDX-011 after treatment with dasatinib to enhance therapeutic efficacy using noninvasive imaging. (2) Methods: First, TNBC cell lines that either express gpNMB (MDA-MB-468) or do not express gpNMB (MDA-MB-231) were treated with 2 µM of dasatinib in vitro for 48 h, followed by Western blot analysis of cell lysates to determine differences in gpNMB expression. MDA-MB-468 xenografted mice were also treated with 10 mg/kg of dasatinib every other day for 21 days. Subgroups of mice were euthanized at 0-, 7-, 14-, and 21-days post treatment, and tumors were harvested for Western blot analysis of tumor cell lysates for gpNMB expression. In a different cohort of MDA-MB-468 xenograft models, longitudinal PET imaging with [89Zr]Zr-DFO-CR011 was performed before treatment at 0 (baseline) and at 14 and 28 days after treatment with (1) dasatinib alone (2) CDX-011 (10 mg/kg) alone, or (3) sequential treatment of dasatinib for 14 days then CDX-011 to determine changes in gpNMB expression in vivo relative to baseline. As a gpNMB-negative control, MDA-MB-231 xenograft models were imaged 21 days after treatment with dasatinib, combination of CDX-011 and dasatinib, and vehicle control. (3) Results: Western blot analysis of MDA-MB-468 cell and tumor lysates showed that dasatinib increased expression of gpNMB in vitro and in vivo at 14 days post treatment initiation. In PET imaging studies of different cohorts of MDA-MB-468 xenografted mice, [89Zr]Zr-DFO-CR011 uptake in tumors (SUVmean = 3.2 ± 0.3) was greatest at 14 days after treatment initiation with dasatinib (SUVmean = 4.9 ± 0.6) or combination of dasatinib and CDX-011 (SUVmean= 4.6 ± 0.2) compared with that at baseline (SUVmean = 3.2 ± 0.3). The highest tumor regression after treatment was observed in the combination-treated group with a percent change in tumor volume relative to baseline (%CTV) of -54 ± 13 compared with the vehicle control-treated group (%CTV = +102 ± 27), CDX-011 group (%CTV = -25 ± 9.8), and dasatinib group (%CTV = -23 ± 11). In contrast, the PET imaging of MDA-MB-231 xenografted mice indicated no significant difference in the tumor uptake of [89Zr]Zr-DFO-CR011 between treated (dasatinib alone or in combination with CDX-011) and vehicle-control groups. (4) Conclusions: Dasatinib upregulated gpNMB expression in gpNMB-positive MDA-MB-468 xenografted tumors at 14 days post treatment initiation, which can be quantified by PET imaging with [89Zr]Zr-DFO-CR011. Furthermore, combination therapy with dasatinib and CDX-011 appears to be a promising therapeutic strategy for TNBC and warrants further investigation.

Determining Binding Affinity (KD) of Radiolabeled Antibodies to Immobilized Antigens.

Determining binding affinity (KD) is an important aspect of the characterization of radiolabeled antibodies (rAb). Typically, binding affinity is represented by the equilibrium dissociation constant, KD, and can be calculated as the concentration of antibody at which half the antibody binding sites are occupied at equilibrium. This method can be generalized to any radiolabeled antibody or other protein and peptide scaffolds. In contrast to cell-based methods, the choice of immobilized antigens is particularly useful for validating binding affinities after long-term storage of antibodies, distinguishing binding affinities of fragment antigen-binding region (Fab) arms in bispecific antibody constructs, and determining if there is variability in antigen expression between different cell lines. This method involves immobilizing a fixed amount of antigen to specified wells on a breakable 96-well plate. Then, nonspecific binding was blocked in all wells with bovine serum albumin (BSA). Subsequently, the rAb was added in a concentration gradient to all wells. A range of concentrations was chosen to allow the rAb to reach saturation, i.e., a concentration of antibody at which all antigens are continuously bound by the rAb. In designated wells without immobilized antigen, nonspecific binding of the rAb can be determined. By subtracting nonspecific binding from total binding in the wells with immobilized antigen, specific binding of the rAb to the antigen can be determined. The KD of the rAb was calculated from the resulting saturation binding curve. As an example, binding affinity was determined using radiolabeled amivantamab, a bispecific antibody for epidermal growth factor receptor (EGFR) and cytoplasmic mesenchymal-epithelial transition (cMET) proteins.

PET Imaging in Animal Models of Alzheimer's Disease.

The successful development and translation of PET imaging agents targeting ß-amyloid plaques and hyperphosphorylated tau tangles have allowed for in vivo detection of these hallmarks of Alzheimer's disease (AD) antemortem. Amyloid and tau PET have been incorporated into the A/T/N scheme for AD characterization and have become an integral part of ongoing clinical trials to screen patients for enrollment, prove drug action mechanisms, and monitor therapeutic effects. Meanwhile, preclinical PET imaging in animal models of AD can provide supportive information for mechanistic studies. With the recent advancement of gene editing technologies and AD animal model development, preclinical PET imaging in AD models will further facilitate our understanding of AD pathogenesis/progression and the development of novel treatments. In this study, we review the current state-of-the-art in preclinical PET imaging using animal models of AD and suggest future research directions.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer.

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

[89Zr]ZrDFO-CR011 PET Correlates with Response to Glycoprotein Nonmetastatic Melanoma B-targeted Therapy in Triple-negative Breast Cancer.

There is a need for prognostic markers to select patients most likely to benefit from antibody-drug conjugate (ADC) therapy. We quantified the relationship between pretreatment PET imaging of glycoprotein nonmetastatic melanoma B (gpNMB) with 89Zr-labeled anti-gpNMB antibody ([89Zr]ZrDFO-CR011) and response to ADC therapy (CDX-011) in triple-negative breast cancer. First, we compared different PET imaging metrics and found that standardized uptake values (SUV) and tumor-to-heart SUV ratios were sufficient to delineate differences in radiotracer uptake in the tumor of four different cell- and patient-derived tumor models and achieved high standardized effect sizes. These tumor models with varying levels of gpNMB expression were imaged with [89Zr]ZrDFO-CR011 followed by treatment with a single bolus injection of CDX-011. The percent change in tumor volume relative to baseline (% CTV) was then correlated with SUVmean of [89Zr]ZrDFO-CR011 uptake in the tumor. All gpNMB-positive tumor models responded to CDX-011 over 6 weeks of treatment, except one patient-derived tumor regrew after 4 weeks of treatment. As expected, the gpNMB-negative tumor increased in volume by 130 ± 59% at endpoint. The magnitude of pretreatment SUV had the strongest inverse correlation with the % CTV at 2-4 weeks after treatment with CDX-011 (Spearman ρ = -0.8). However, pretreatment PET imaging with [89Zr]ZrDFO-CR011 did not inform on which tumor types will regrow over time. Other methods will be needed to predict resistance to treatment.

Preclinical Advances in Theranostics for the Different Molecular Subtypes of Breast Cancer.

Breast cancer is the most common cancer in women worldwide. The heterogeneity of breast cancer and drug resistance to therapies make the diagnosis and treatment difficult. Molecular imaging methods with positron emission tomography (PET) and single-photon emission tomography (SPECT) provide useful tools to diagnose, predict, and monitor the response of therapy, contributing to precision medicine for breast cancer patients. Recently, many efforts have been made to find new targets for breast cancer therapy to overcome resistance to standard of care treatments, giving rise to new therapeutic agents to offer more options for patients with breast cancer. The combination of diagnostic and therapeutic strategies forms the foundation of theranostics. Some of these theranostic agents exhibit high potential to be translated to clinic. In this review, we highlight the most recent advances in theranostics of the different molecular subtypes of breast cancer in preclinical studies.

Development of [89Zr]ZrDFO-amivantamab bispecific to EGFR and c-MET for PET imaging of triple-negative breast cancer.

BACKGROUND: Amivantamab is a novel bispecific antibody that simultaneously targets the epidermal growth factor receptor (EGFR) and the hepatocyte growth factor receptor (HGFR/c-MET) that are overexpressed in several types of cancer including triple-negative breast cancer (TNBC). Targeting both receptors simultaneously can overcome resistance to mono-targeted therapy. The purpose of this study is to develop 89Zr-labeled amivantamab as a potential companion diagnostic imaging agent to amivantamab therapy using various preclinical models of TNBC for evaluation. METHODS: Amivantamab was conjugated to desferrioxamine (DFO) and radiolabeled with 89Zr to obtain [89Zr]ZrDFO-amivantamab. Binding of the bispecific [89Zr]ZrDFO-amivantamab as well as its mono-specific "single-arm" antibody controls were determined in vitro and in vivo. Biodistribution studies of [89Zr]ZrDFO-amivantamab were performed in MDA-MB-468 xenografts to determine the optimal imaging time point. PET/CT imaging with [89Zr]ZrDFO-amivantamab or its isotype control was performed in a panel of TNBC xenografts with varying levels of EGFR and c-MET expression. RESULTS: [89Zr]ZrDFO-amivantamab was synthesized with a specific activity of 148 MBq/mg and radiochemical yield of ≥ 95%. Radioligand binding studies and western blot confirmed the order of EGFR and c-MET expression levels: HCC827 lung cancer cell (positive control) > MDA-MB-468 > MDA-MB-231 > MDA-MB-453. [89Zr]ZrDFO-amivantamab demonstrated bispecific binding in cell lines co-expressed with EGFR and c-MET. PET/CT imaging with [89Zr]ZrDFO-amivantamab in TNBC xenografted mice showed standard uptake value (SUVmean) of 6.0 ± 1.1 in MDA-MB-468, 4.2 ± 1.4 in MDA-MB-231, and 1.5 ± 1.4 in MDA-MB-453 tumors, which are consistent with their receptors' expression levels on the cell surface. CONCLUSION: We have successfully prepared a radiolabeled bispecific antibody, [89Zr]ZrDFO-amivantamab, and evaluated its pharmacologic and imaging properties in comparison with its single-arm antibodies and non-specific isotype controls. [89Zr]ZrDFO-amivantamab demonstrated the greatest uptake in tumors co-expressing EGFR and c-MET.

Imaging of HER2 with [89Zr]pertuzumab in Response to T-DM1 Therapy.

Background: The success of human epidermal growth factor receptor 2 (HER2)-targeted therapy depends on accurate characterization of HER2 expression, but current methods available have several limitations. This study aims to investigate the feasibility of [89Zr]pertuzumab imaging to monitor early response to Ado-trastuzumab emtansine (T-DM1) therapy in mice bearing xenografts of HER2-positive breast cancer (BCa). Materials and Methods: Pertuzumab was conjugated to DFO-Bz-NCS and labeled with 89Zr. Mice bearing BT-474 tumors were imaged with [89Zr]pertuzumab and [18F]FDG before and after T-DM1 therapy. Results: Pertuzumab was successfully labeled with 89Zr with a specific activity of 0.740 MBq/µg. Overall [18F]FDG images showed poor delineation of tumors. Using [18F]FDG-PET to measure tumor volume, the volume remained unchanged from 107.6 ± 20.7 mm3 before treatment to 89.87 ± 66.55 mm3 after treatment. In contrast, [89Zr]pertuzumab images showed good delineation of HER2-positive tumors, allowing accurate detection of changes in tumor volume (from 243.80 ± 40.91 mm3 before treatment to 78.4 ± 40.43 mm3 after treatment). Conclusion: [89Zr]pertuzumab may be an imaging probe for monitoring the response of HER2-positive BCa patients to T-DM1 therapy.

Evaluation of [89Zr]trastuzumab-PET/CT in differentiating HER2-positive from HER2-negative breast cancer.

PURPOSE: To evaluate whether tumor uptake of [89Zr]trastuzumab can distinguish HER2-positive from HER2-negative breast cancer. METHODS: Women with HER2-positive (n = 34) and HER2-negative (n = 16) breast cancer underwent PET/CT 5 ± 2 days following [89Zr]trastuzumab administration. HER2 status was determined based on immunohistochemistry and/or fluorescence in situ hybridization of primary or metastatic/recurrent tumor. Tumor [89Zr]trastuzumab uptake was assessed qualitatively and semiquantitatively as maximum standardized uptake value (SUVmax), and correlated with HER2 status. Additionally, intrapatient heterogeneity of [89Zr]trastuzumab uptake was evaluated. RESULTS: On a per-patient basis, [89Zr]trastuzumab-PET/CT was positive in 30/34 (88.2%) HER2-positive and negative in 15/16 (93.7%) HER2-negative patients. Considering all lesions, the SUVmax was not significantly different in patients with HER2-positive versus HER2-negative disease (p = 0.06). The same was true of when only hepatic lesions were evaluated (p = 0.42). However, after excluding hepatic lesions, tumor SUVmax was significantly higher in HER2-positive compared to HER2-negative patients (p = 0.003). A cutoff SUVmax of 3.2, determined by ROC analysis, demonstrated positive-predictive value of 83.3% (95% CI 65.3%, 94.4%), sensitivity of 75.8% (57.7%, 88.9%), negative-predictive value of 50% (24.7%, 75.3%), and specificity of 61.5% (95% 31.6%, 86.1%) for differentiating HER2-positive from HER2-negative lesions. There was intrapatient heterogeneity of [89Zr]trastuzumab uptake in 20% of patients with multiple lesions. CONCLUSIONS: [89Zr]trastuzumab has the potential to characterize the HER2 status of the complete tumor burden in patients with breast cancer, thus obviating repeat or multiple tissue sampling to assess intrapatient heterogeneity of HER2 status.

Evaluation of Next-Generation Anti-CD20 Antibodies Labeled with 89Zr in Human Lymphoma Xenografts.

Radioimmunotherapies with monoclonal antibodies to the B-lymphocyte antigen 20 (CD20) are effective treatments for B-cell lymphomas, but U.S. Food and Drug Administration-approved radioimmunotherapies exclusively use radiolabeled murine antibodies, potentially limiting redosing. The Food and Drug Administration recently approved 2 unlabeled anti-CD20 monoclonal antibodies, obinutuzumab and ofatumumab, termed next generation as they are humanized (obinutuzumab) or fully human (ofatumumab), thus potentially allowing a greater potential for redosing than with previous-generation anti-CD20 antibodies, including rituximab (chimeric) and tositumomab (murine), which contain more murine peptide sequences. We prepared 89Zr-ofatumumab and 89Zr-obinituzumab and assessed their tumor targeting by PET/CT imaging and their biodistribution in a preclinical mouse model with CD20 xenografts to determine whether these antibodies have potential as theranostics or for radioimmunotherapy. Methods: Obinutuzumab, ofatumumab, rituximab, tositumomab, and human IgG (as control) were radiolabeled with 89Zr. Raji Burkitt lymphoma xenografts were established in severe combined immunodeficient mice. Mice with palpable tumors (n = 4-9) were injected with 89Zr-obinutuzumab, 89Zr-ofatumumab, 89Zr-rituximab, 89Zr-tositumomab, or 89Zr-IgG, with small-animal PET/CT images acquired at 1, 3, and 7 d after injection, and then sacrificed for biodistribution analyses. Results: At 1, 3, and 7 d after injection, all anti-CD20 antibodies showed clear tumor uptake on PET/CT, with minimal tumor uptake of IgG. Biodistribution data showed significantly (P < 0.005) higher tumor uptake for obinutuzumab (41.4 ± 7.6 percentage injected dose [%ID]/g), ofatumumab (32.6 ± 17.5 %ID/g), rituximab (28.6 ± 7.6 %ID/g), and tositumomab (28.0 ± 6.5 %ID/g) than IgG (7.2 ± 1.2 %ID/g). Tositumomab had much higher splenic uptake (186.4 ± 49.7 %ID/g, P < 0.001) than the other antibodies. Conclusion:89Zr-labeled obinutuzumab and ofatumumab localized to tumor as well as or better than labeled rituximab and tositumomab, 2 monoclonal antibodies that have been used previously in B-cell lymphoma radioimmunotherapy, and both obinutuzumab and ofatumumab have the potential for repeated dosing.

Targeting HER2 in Nuclear Medicine for Imaging and Therapy.

Since its discovery, the human epidermal growth factor 2 (HER2) has been extensively studied. Presently, there are 2 standard diagnostic techniques to assess HER2 status in biopsies: immunohistochemistry and fluorescence in situ hybridization. While these techniques have played an important role in the treatment of patients with HER2-positive cancer, they both require invasive biopsies for analysis. Moreover, the expression of HER2 is heterogeneous in breast cancer and can change over the course of the disease. Thus, the degree of HER2 expression in the small sample size of biopsied tumors at the time of analysis may not represent the overall status of HER2 expression in the whole tumor and in between tumor foci in the metastatic setting as the disease progresses. Unlike biopsy, molecular imaging using probes against HER2 allows for a noninvasive, whole-body assessment of HER2 status in real time. This technique could potentially select patients who may benefit from HER2-directed therapy and offer alternative treatments to those who may not benefit. Several antibodies and small molecules against HER2 have been labeled with different radioisotopes for nuclear imaging and/or therapy. This review presents the most recent advances in HER2 targeting in nuclear medicine focusing on preclinical and clinical studies.

Preclinical PET imaging of glycoprotein non-metastatic melanoma B in triple negative breast cancer: feasibility of an antibody-based companion diagnostic agent.

High levels of expression of glycoprotein non-metastatic B (gpNMB) in triple negative breast cancer (TNBC) and its association with metastasis and recurrence make it an attractive target for therapy with the antibody drug conjugate, glembatumumab vedotin (CDX-011). This report describes the development of a companion PET-based diagnostic imaging agent using 89Zr-labeled glembatumumab ([89Zr]DFO-CR011) to potentially aid in the selection of patients most likely to respond to targeted treatment with CDX-011. [89Zr]DFO-CR011 was characterized for its pharmacologic properties in TNBC cell lines. Preclinical studies determined that [89Zr]DFO-CR011 binds specifically to gpNMB with high affinity (Kd = 25 ± 5 nM), immunoreactivity of 2.2-fold less than the native CR011, and its cellular uptake correlates with gpNMB expression (r = 0.95). In PET studies at the optimal imaging timepoint of 7 days p.i., the [89Zr]DFO-CR011 tumor uptake in gpNMB-expressing MDA-MB-468 xenografts had a mean SUV of 2.9, while significantly lower in gpNMB-negative MDA-MB-231 tumors with a mean SUV of 1.9. [89Zr]DFO-CR011 was also evaluated in patient-derived xenograft models of TNBC, where tumor uptake in vivo had a positive correlation with total gpNMB protein expression via ELISA (r = 0.79), despite the heterogeneity of gpNMB expression within the same group of PDX mice. Lastly, the radiation dosimetry calculated from biodistribution studies in MDA-MB-468 xenografts determined the effective dose for human use would be 0.54 mSv/MBq. Overall, these studies demonstrate that [89Zr]DFO-CR011 is a potential companion diagnostic imaging agent for CDX-011 which targets gpNMB, an emerging biomarker for TNBC.

[89Zr]Trastuzumab: Evaluation of Radiation Dosimetry, Safety, and Optimal Imaging Parameters in Women with HER2-Positive Breast Cancer.

PURPOSE: The purpose of the present study is to evaluate safety, human radiation dosimetry, and optimal imaging time of [89Zr]trastuzumab in patients with HER2-positive breast cancer. PROCEDURES: Twelve women with HER2-positive breast cancer underwent [89Zr]trastuzumab positron emission tomography (PET)/X-ray computed tomography (CT) twice within 7 days post-injection. Biodistribution data from whole-torso PET/CT images and organ time-activity curves were created using data from all patients. Human dosimetry was calculated using OLINDA with the adult female model. RESULTS: High-quality images and the greatest tumor-to-nontumor contrast were achieved with images performed 5 ± 1 day post-injection. Increased [89Zr]trastuzumab uptake was seen in at least one known lesion in ten patients. The liver was the dose-limiting organ (retention of ∼12 % of the injected dose and average dose of 1.54 mSv/MBq). The effective dose was 0.47 mSv/MBq. No adverse effects of [89Zr]trastuzumab were encountered. CONCLUSION: [89Zr]trastuzumab was safe and optimally imaged at least 4 days post-injection. The liver was the dose-limiting organ.