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.

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.

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.

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 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.

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.