The surprisingly large neutron capture cross-section of 88Zr.

The probability that a nucleus will absorb a neutron-the neutron capture cross-section-is important to many areas of nuclear science, including stellar nucleosynthesis, reactor performance, nuclear medicine and defence applications. Although neutron capture cross-sections have been measured for most stable nuclei, fewer results exist for radioactive isotopes, and statistical-model predictions typically have large uncertainties1. There are almost no nuclear data for neutron-induced reactions of the radioactive nucleus 88Zr, despite its importance as a diagnostic for nuclear security. Here, by exposing 88Zr to the intense neutron flux of a nuclear reactor, we determine that 88Zr has a thermal neutron capture cross-section of 861,000 ± 69,000 barns (1σ uncertainty), which is five orders of magnitude larger than the theoretically predicted value of 10 barns2. This is the second-largest thermal neutron capture cross-section ever measured and no other cross-section of comparable size has been discovered in the past 70 years. The only other nuclei known to have values greater than 105 barns3-6 are 135Xe (2.6 × 106 barns), a fission product that was first discovered as a poison in early reactors7,8, and 157Gd (2.5 × 105 barns), which is used as a detector material9,10, a burnable reactor poison11 and a potential medical neutron capture therapy agent12. In the case of 88Zr neutron capture, both the target and the product (89Zr) nuclei are radioactive and emit intense γ-rays upon decay, allowing sensitive detection of miniscule quantities of these radionuclides. This result suggests that as additional measurements with radioactive isotopes become feasible with the operation of new nuclear-science facilities, further surprises may be uncovered, with far-reaching implications for our understanding of neutron capture reactions.

Recent advances and impending challenges for the radiopharmaceutical sciences in oncology.

This paper is the first of a Series on theranostics that summarises the current landscape of the radiopharmaceutical sciences as they pertain to oncology. In this Series paper, we describe exciting developments in radiochemistry and the production of radionuclides, the development and translation of theranostics, and the application of artificial intelligence to our field. These developments are catalysing growth in the use of radiopharmaceuticals to the benefit of patients worldwide. We also highlight some of the key issues to be addressed in the coming years to realise the full potential of radiopharmaceuticals to treat cancer.

Production and regulatory issues for theranostics.

Theranostics has become a major area of innovation and progress in cancer care over the last decade. In view of the introduction of approved therapeutics in neuroendocrine tumours and prostate cancer in the last 10 years, the ability to provide access to these treatments has emerged as a key factor in ensuring global benefits from this cancer therapy approach. In this Series paper we explore the issues that affect access to and availability of theranostic radiopharmaceuticals, including supply and regulatory issues that might affect the availability of theranostic treatments for patients with cancer.

Trends in nuclear medicine and the radiopharmaceutical sciences in oncology: workforce challenges and training in the age of theranostics.

Although the promise of radionuclides for the diagnosis and treatment of disease was recognised soon after the discovery of radioactivity in the late 19th century, the systematic use of radionuclides in medicine only gradually increased over the subsequent hundred years. The past two decades, however, has seen a remarkable surge in the clinical application of diagnostic and therapeutic radiopharmaceuticals, particularly in oncology. This development is an exciting time for the use of theranostics in oncology, but the rapid growth of this area of nuclear medicine has created challenges as well. In particular, the infrastructure for the manufacturing and distribution of radiopharmaceuticals remains in development, and regulatory bodies are still optimising guidelines for this new class of drug. One issue of paramount importance for achieving equitable access to theranostics is building a sufficiently trained workforce in high-income, middle-income, and low-income countries. Here, we discuss the key challenges and opportunities that face the field as it seeks to build its workforce for the 21st century.

Evaluating the immunologically "cold" tumor microenvironment after treatment with immune checkpoint inhibitors utilizing PET imaging of CD4 + and CD8 + T cells in breast cancer mouse models.

BACKGROUND: Immune-positron emission tomography (PET) imaging with tracers that target CD8 and granzyme B has shown promise in predicting the therapeutic response following immune checkpoint blockade (ICB) in immunologically "hot" tumors. However, immune dynamics in the low T-cell infiltrating "cold" tumor immune microenvironment during ICB remain poorly understood. This study uses molecular imaging to evaluate changes in CD4 + T cells and CD8 + T cells during ICB in breast cancer models and examines biomarkers of response. METHODS: [89Zr]Zr-DFO-CD4 and [89Zr]Zr-DFO-CD8 radiotracers were used to quantify changes in intratumoral and splenic CD4 T cells and CD8 T cells in response to ICB treatment in 4T1 and MMTV-HER2 mouse models, which represent immunologically "cold" tumors. A correlation between PET quantification metrics and long-term anti-tumor response was observed. Further biological validation was obtained by autoradiography and immunofluorescence. RESULTS: Following ICB treatment, an increase in the CD8-specific PET signal was observed within 6 days, and an increase in the CD4-specific PET signal was observed within 2 days in tumors that eventually responded to immunotherapy, while no significant differences in CD4 or CD8 were found at the baseline of treatment that differentiated responders from nonresponders. Furthermore, mice whose tumors responded to ICB had a lower CD8 PET signal in the spleen and a higher CD4 PET signal in the spleen compared to non-responders. Intratumoral spatial heterogeneity of the CD8 and CD4-specific PET signals was lower in responders compared to non-responders. Finally, PET imaging, autoradiography, and immunofluorescence signals were correlated when comparing in vivo imaging to ex vivo validations. CONCLUSIONS: CD4- and CD8-specific immuno-PET imaging can be used to characterize the in vivo distribution of CD4 + and CD8 + T cells in response to immune checkpoint blockade. Imaging metrics that describe the overall levels and distribution of CD8 + T cells and CD4 + T cells can provide insight into immunological alterations, predict biomarkers of response to immunotherapy, and guide clinical decision-making in those tumors where the kinetics of the response differ.

Radiochemistry and In Vivo Imaging of [45Ti]Ti-THP-PSMA.

Titanium-45 (45Ti) is a radionuclide with excellent physical characteristics for use in positron emission tomography (PET) imaging, including a moderate half-life (3.08 h), decay by positron emission (85%), and a low mean positron energy of 0.439 MeV. However, challenges associated with titanium chemistry have led to the underdevelopment of this radionuclide for incorporation into radiopharmaceuticals. Expanding on our recent studies, which showed promising results for the complexation of 45Ti with the tris hydroxypyridinone (THPMe) chelator, the current work aimed to optimize the chemistry and imaging attributes of [45Ti]Ti-THP-PSMA as a new PET radiopharmaceutical. Methods. Radiolabeling of THP-PSMA was optimized with [45Ti]Ti-citrate at varying pHs and masses of the precursor. The stability of the radiolabeled complex was assessed in mouse serum for up to 6 h. The affinity of [45Ti]Ti-THP-PSMA for prostate-specific membrane antigen (PSMA) was assessed using LNCaP (PSMA +) and PC3 (PSMA -) cell lines. In vivo imaging and biodistribution analysis were performed in tumor-bearing xenograft mouse models to confirm the specificity of the tumor uptake. Results. > 95% of radiolabeling was achieved with a high specific activity of 5.6 MBq/nmol under mild conditions. In vitro cell binding studies showed significant binding of the radiolabeled complex with the PSMA-expressing LNCaP cell line (11.9 ± 1.5%/mg protein-bound activity) compared to that with the nonexpressing PC3 cells (1.9 ± 0.4%/mg protein-bound activity). In vivo imaging and biodistribution studies confirmed specific uptake in LNCaP tumors (1.6 ± 0.27% ID/g) compared to that in PC3 tumors (0.39 ± 0.2% ID/g). Conclusion. This study showed a simple one-step radiolabeling method for 45Ti with THP-PSMA under mild conditions (pH 8 and 37 °C). In vitro cell studies showed promise, but in vivo tumor xenograft studies indicated low tumor uptake. Overall, this study shows the need for more chelators for 45Ti for the development of a PET radiopharmaceutical for cancer imaging.

Customizable Porphyrin Platform Enables Folate Receptor PET Imaging Using Copper-64.

Folate receptors including folate receptor α (FRα) are overexpressed in up to 90% of ovarian cancers. Ovarian cancers overexpressing FRα often exhibit high degrees of drug resistance and poor outcomes. A porphyrin chassis has been developed that is readily customizable according to the desired targeting properties. Thus, compound O5 includes a free base porphyrin, two water-solubilizing groups that project above and below the macrocycle plane, and a folate targeting moiety. Compound O5 was synthesized (>95% purity) and exhibited aqueous solubility of at least 0.48 mM (1 mg/mL). Radiolabeling of O5 with 64Cu in HEPES buffer at 37 °C gave a molar activity of 1000 µCi/µg (88 MBq/nmol). [64Cu]Cu-O5 was stable in human serum for 24 h. Cell uptake studies showed 535 ± 12% bound/mg [64Cu]Cu-O5 in FRα-positive IGROV1 cells when incubated at 0.04 nM. Subcellular fractionation showed that most radioactivity was associated with the cytoplasmic (39.4 ± 2.7%) and chromatin-bound nuclear (53.0 ± 4.2%) fractions. In mice bearing IGROV1 xenografts, PET imaging studies showed clear tumor uptake of [64Cu]Cu-O5 from 1 to 24 h post injection with a low degree of liver uptake. The tumor standardized uptake value at 24 h post injection was 0.34 ± 0.16 versus 0.06 ± 0.07 in the blocking group. In summary, [64Cu]Cu-O5 was synthesized at high molar activity, was stable in serum, exhibited high binding to FRα-overexpressing cells with high nuclear translocation, and gave uptake that was clearly visible in mouse tumor xenografts.

PET Imaging of Differentiated Thyroid Cancer with TSHR-Targeted [89Zr]Zr-TR1402.

Thyroid cancer is the most common endocrine cancer, with differentiated thyroid cancers (DTCs) accounting for 95% of diagnoses. While most DTC patients are diagnosed and treated with radioiodine (RAI), up to 20% of DTC patients become RAI refractory (RAI-R). RAI-R patients have significantly reduced survival rates compared to patients who remain RAI-avid. This study explores [89Zr]Zr-TR1402 as a thyroid-stimulating hormone receptor (TSHR)-targeted PET radiopharmaceutical for DTC. [89Zr]Zr-TR1402 was synthesized with a molar activity of 25.9 MBq/nmol by conjugating recombinant human TSH (rhTSH) analogue TR1402 to chelator p-SCN-Bn-deferoxamine (DFO) in a molar ratio of 3:1 (DFO/TR1402) and radiolabeling with 89Zr (t1/2 = 78.4 h, ß+ = 22.7%). As TSHR is absent in commonly available DTC-derived cell lines, TSHR was reintroduced via stable transduction by delivering a lentivirus containing the full-length coding region of the human TSHR gene. Receptor-mediated uptake of [89Zr]Zr-TR1402 was evaluated in vitro in stably transduced TSHR+ and wild-type TSHR- DTC cell lines. In vivo PET imaging was performed on Days 1-3 postinjection in male and female athymic nude mice bearing TSHR+ and TSHR- xenografts, along with ex vivo biodistribution on Day 3 postinjection. In vitro uptake of 1 nM [89Zr]Zr-TR1402 was significantly higher in TSHR+ THJ529T (P < 0.0001) and FTC133 (P < 0.01) cells than in TSHR- THJ529T and FTC133 cells. This uptake was shown to be specific in both TSHR+ THJ529T (P < 0.0001) and TSHR+ FTC133 (P < 0.0001) cells by blocking uptake with 250 nm DFO-TR1402. In vivo PET imaging showed accumulation of [89Zr]Zr-TR1402 in TSHR+ tumors, which was the highest on Day 1. In the male FTC133 xenograft model, ex vivo biodistribution confirmed a significant difference (P < 0.001) in uptake between FTC133+ (1.3 ± 0.1%ID/g) and FTC133- (0.8 ± 0.1%ID/g) tumors. A significant difference (P < 0.05) in uptake was also seen in the male THJ529T xenograft model between THJ529T+ (1.8 ± 0.6%ID/g) and THJ529T- (0.8 ± 0.4%ID/g) tumors. The in vitro and in vivo accumulation of [89Zr]Zr-TR1402 in TSHR-expressing DTC cell lines support the continued preclinical optimization of this approach.

Evaluation of [89Zr]Zr-DFO-2Rs15d Nanobody for Imaging of HER2-Positive Breast Cancer.

One of the most aggressive forms of breast cancer involves the overexpression of human epidermal growth factor receptor 2 (HER2). HER2 is overexpressed in ∼25% of all breast cancers and is associated with increased proliferation, increased rates of metastasis, and poor prognosis. Treatment for HER2-positive breast cancer has vastly improved since the development of the monoclonal antibody trastuzumab (Herceptin) as well as other biological constructs. However, patients still commonly develop resistance, illustrating the need for newer therapies. Nanobodies have become an important focus for potential development as HER2-targeting imaging agents and therapeutics. Nanobodies have many favorable characteristics, including high stability in heat and nonphysiological pH, while maintaining their low-nanomolar affinity for their designed targets. Specifically, the 2Rs15d nanobody has been developed for targeting HER2 and has been evaluated as a diagnostic imaging agent for single-photon emission computed tomography (SPECT) and positron emission tomography (PET). While a construct of 2Rs15d with the positron emitter 68Ga is currently in phase I clinical trials, the only PET images acquired in preclinical or clinical research have been within 3 h postinjection. We evaluated our in-house produced 2Rs15d nanobody, conjugated with the chelator deferoxamine (DFO), and radiolabeled with 89Zr for PET imaging up to 72 h postinjection. [89Zr]Zr-DFO-2Rs15d demonstrated high stability in both phosphate-buffered saline (PBS) and human serum. Cell binding studies showed high binding and specificity for HER2, as well as prominent internalization. Our in vivo PET imaging confirmed high-quality visualization of HER2-positive tumors up to 72 h postinjection, whereas HER2-negative tumors were not visualized. Subsequent biodistribution studies quantitatively supported the significant HER2-positive tumor uptake compared to the negative control. Our studies fill an important gap in understanding the imaging and binding properties of the 2Rs15d nanobody at extended time points. As many therapeutic radioisotopes have single or multiday half-lives, this information will directly benefit the potential of the radiotherapy development of 2Rs15d for HER2-positive breast cancer patients.

Evaluation of a CD206-Targeted Peptide for PET Imaging of Macrophages in Syngeneic Mouse Models of Cancer.

Tumor-associated macrophages (TAMs) are large phagocytic cells that play numerous roles in cancer biology and are an important component of the relationship between immune system response and tumor progression. The peptide, RP832c, targets the Mannose Receptor (CD206) expressed on M2-like macrophages and is cross-reactive to both human and murine CD206. Additionally, it exhibits therapeutic properties through its ability to shift the population of TAMs from an M2-like (protumor) toward an M1-like phenotype (antitumor) and has demonstrated promise in inhibiting tumor resistance in PD-L1 unresponsive melanoma murine models. In addition, it has shown inhibition in bleomycin-induced pulmonary fibrosis through interactions with CD206 macrophages.1,2 Our work aims to develop a novel CD206 positron emission tomography (PET) imaging probe based on RP832c (Kd = 5.64 µM) as a direct, noninvasive method for the assessment of TAMs in mouse models of cancer. We adapted RP832c to incorporate the chelator DOTA to allow for radiolabeling with the PET isotope 68Ga (t1/2 = 68 min; ß+ = 89%). In vitro stability studies were conducted in mouse serum up to 3 h. The in vitro binding characteristics of [68Ga]RP832c to CD206 were determined by a protein plate binding assay and Surface Plasmon Resonance (SPR). PET imaging and biodistribution studies were conducted in syngeneic tumor models. Stability studies in mouse serum demonstrated that 68Ga remained complexed up to 3 h (less than 1% free 68Ga). Binding affinity studies demonstrated high binding of [68Ga]RP832c to mouse CD206 protein and that the binding of the tracer was able to be blocked significantly when incubated with a blocking solution of native RP832c. PET imaging and biodistribution studies in syngeneic tumor models demonstrated uptake in tumor and CD206 expressing organs of [68Ga]RP832c. A significant correlation was found between the percentage of CD206 present in each tumor imaged with [68Ga]RP832c and PET imaging mean standardized uptake values in a CT26 mouse model of cancer. The data shows that [68Ga]RP832c represents a promising candidate for macrophage imaging in cancer and other diseases.

Direct Radiolabeling of Trastuzumab-Targeting Triblock Copolymer Vesicles with 89Zr for Positron Emission Tomography Imaging.

Radiolabeled drug nanocarriers that can be easily imaged via positron emission tomography (PET) are highly significant as their in vivo outcome can be quantitatively PET-traced with high sensitivity. However, typical radiolabeling of most PET-guided theranostic vehicles utilizes modification with chelator ligands, which presents various challenges. In addition, unlike passive tumor targeting, specific targeting of drug delivery vehicles via binding affinity to overexpressed cancer cell receptors is crucial to improve the theranostic delivery to tumors. Herein, we developed 89Zr-labeled triblock copolymer polymersomes of 60 nm size through chelator-free radiolabeling. The polymersomes are assembled from poly(N-vinylpyrrolidone)5-b-poly(dimethylsiloxane)30-b-poly(N-vinylpyrrolidone)5 (PVPON5-PDMS30-PVPON5) triblock copolymers followed by adsorption of a degradable tannin, tannic acid (TA), on the polymersome surface through hydrogen bonding. TA serves as an anchoring layer for both 89Zr radionuclide and targeting recombinant humanized monoclonal antibody, trastuzumab (Tmab). Unlike bare PVPON5-PDMS30-PVPON5 polymersomes, TA- and Tmab-modified polymersomes demonstrated a high radiochemical yield of more than 95%. Excellent retention of 89Zr by the vesicle membrane for up to 7 days was confirmed by PET in vivo imaging. Animal biodistribution using healthy BALB/c mice confirmed the clearance of 89Zr-labeled polymersomes through the spleen and liver without their accumulation in bone, unlike the free nonbound 89Zr radiotracer. The 89Zr-radiolabeled polymersomes were found to specifically target BT474 HER2-positive breast cancer cells via the Tmab-TA complex on the vesicle surface. The noncovalent Tmab anchoring to the polymersome membrane can be highly advantageous for nanoparticle modification compared to currently developed covalent methods, as it allows easy and quick integration of a broad range of targeting proteins. Given the ability of these polymersomes to encapsulate and release anticancer therapeutics, they can be further expanded as precision-targeted therapeutic carriers for advancing human health through highly effective drug delivery strategies.

Sc-HOPO: A Potential Construct for Use in Radioscandium-Based Radiopharmaceuticals.

Three isotopes of scandium─43Sc, 44Sc, and 47Sc─have attracted increasing attention as potential candidates for use in imaging and therapy, respectively, as well as for possible theranostic use as an elementally matched pair. Here, we present the octadentate chelator 3,4,3-(LI-1,2-HOPO) (or HOPO), an effective chelator for hard cations, as a potential ligand for use in radioscandium constructs with simple radiolabeling under mild conditions. HOPO forms a 1:1 Sc-HOPO complex that was fully characterized, both experimentally and theoretically. [47Sc]Sc-HOPO exhibited good stability in chemical and biological challenges over 7 days. In healthy mice, [43,47Sc]Sc-HOPO cleared the body rapidly with no signs of demetalation. HOPO is a strong candidate for use in radioscandium-based radiopharmaceuticals.

Construction of the Bioconjugate Py-Macrodipa-PSMA and Its In Vivo Investigations with Large 132/135La3+ and Small 47Sc3+ Radiometal Ions.

To harness radiometals in clinical settings, a chelator forming a stable complex with the metal of interest and targets the desired pathological site is needed. Toward this goal, we previously reported a unique set of chelators that can stably bind to both large and small metal ions, via a conformational switch. Within this chelator class, py-macrodipa is particularly promising based on its ability to stably bind several medicinally valuable radiometals including large 132/135La3+, 213Bi3+, and small 44Sc3+. Here, we report a 10-step organic synthesis of its bifunctional analogue py-macrodipa-NCS, which contains an amine-reactive -NCS group that is amenable for bioconjugation reactions to targeting vectors. The hydrolytic stability of py-macordipa-NCS was assessed, revealing a half-life of 6.0 d in pH 9.0 aqueous buffer. This bifunctional chelator was then conjugated to a prostate-specific membrane antigen (PSMA)-binding moiety, yielding the bioconjugate py-macrodipa-PSMA, which was subsequently radiolabeled with large 132/135La3+ and small 47Sc3+, revealing efficient and quantitative complex formation. The resulting radiocomplexes were injected into mice bearing both PSMA-expressing and PSMA-non-expressing tumor xenografts to determine their biodistribution patterns, revealing delivery of both 132/135La3+ and 47Sc3+ to PSMA+ tumor sites. However, partial radiometal dissociation was observed, suggesting that py-macrodipa-PSMA needs further structural optimization.

A General Design Strategy Enabling the Synthesis of Hydrolysis-Resistant, Water-Stable Titanium(IV) Complexes.

Despite its prevalence in the environment, the chemistry of the Ti4+ ion has long been relegated to organic solutions or hydrolyzed TiO2 polymorphs. A knowledge gap in stabilizing molecular Ti4+ species in aqueous environments has prevented the use of this ion for various applications such as radioimaging, design of water-compatible metal-organic frameworks (MOFs), and aqueous-phase catalysis applications. Herein, we show a thorough thermodynamic screening of bidentate chelators with Ti4+ in aqueous solution, as well as computational and structural analyses of key compounds. In addition, the hexadentate analogues of catechol (benzene-1,2-diol) and deferiprone (3-hydroxy-1,2-dimethyl-4(1H)-pyridone), TREN-CAM and THPMe respectively, were assessed for chelation of the 45 Ti isotope (t1/2 =3.08 h, ß+ =85 %, Eß+ =439 keV) towards positron emission tomography (PET) imaging applications. Both were found to have excellent capacity for kit-formulation, and [45 Ti]Ti-TREN-CAM was found to have remarkable stability in vivo.

Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications.

The radioactive isotopes scandium-44/47 and lutetium-177 are gaining relevance for radioimaging and radiotherapy, resulting in a surge of studies on their coordination chemistry and subsequent applications. Although the trivalent ions of these elements are considered close homologues, dissimilar chemical behavior is observed when they are complexed by large ligand architectures due to discrepancies between Lu(III) and Sc(III) ions with respect to size, chemical hardness, and Lewis acidity. Here, we demonstrate that Lu and Sc complexes of 1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H3mpatcn) and its corresponding bioconjugate picaga-DUPA can be employed to promote analogous structural features and, subsequently, biological properties for coordination complexes of these ions. The close homology was evidenced using potentiometric methods, computational modeling, variable temperature mass spectrometry, and pair distribution function analysis of X-ray scattering data. Radiochemical labeling, in vitro stability, and biodistribution studies with Sc-47 and Lu-177 indicate that the 7-coordinate ligand environment of the bifunctional picaga ligand is compatible with biological applications and the future investigation of ß-emitting, picaga-chelated Sc and Lu isotopes for radiotherapy.

Evaluation of 177Lu and 47Sc Picaga-Linked, Prostate-Specific Membrane Antigen-Targeting Constructs for Their Radiotherapeutic Efficacy and Dosimetry.

Lu-177-based, targeted radiotherapeutics/endoradiotherapies are an emerging clinical tool for the management of various cancers. The chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) remains the workhorse for such applications but can limit apparent molar activity or efficient charge modulation, which can impact target binding and, as a consequence, target efficacy. Previously, our lab had developed the small, rare earth selective bifunctional chelator, picaga, as an efficient bifunctional chelator for scandium and lutetium isotopes. Here, we assess the performance of these constructs for therapy in prostate-specific membrane antigen (PSMA)-expressing tumor xenografts. To assess the viability of picaga conjugates in conjunction with long in vivo circulation, a picaga conjugate functionalized with a serum albumin binding moiety, 177Lu-picaga-Alb53-PSMA, was also synthesized. A directly comparative, low, single 3.7 MBq dose treatment study with Lu-PSMA-617 was conducted. Treatment with 177Lu-picaga-Alb53-PSMA resulted in tumor regression and lengthened median survival (54 days) when compared with the vehicle (16 days), 47Sc-picaga-DUPA-, 177Lu-picaga-DUPA-, and 177Lu-PSMA-617-treated cohorts (21, 23, and 21 days, respectively).

Production of [89 Zr]Oxinate4 and cell radiolabeling for human use.

[89 Zr]Oxinate4 is a Positron Emission Tomography (PET) tracer for cell radiolabeling that can enable imaging techniques to help better understand cell trafficking in various diseases. Although several groups have synthetized this compound for use in preclinical studies, there is no available data regarding the production of [89 Zr]Oxinate4 for human use. In this report, we describe the detailed production of [89 Zr]Oxinate4 under USP <823> and autologous leukocyte radiolabeling under USP <797>. The final product presented high radiochemical purity and stability at 24 h post synthesis (>99%) and passed in all quality control assays required for clinical use. [89 Zr]Oxinate4 did not compromise the white blood cells viability and did not show considerable cellular efflux up to 3 h post labeling. The translation of this technique into human use can provide insight into several disease mechanisms since [89 Zr]Oxinate4 has the potential to label any cell subset of interest.

[89Zr]-Pertuzumab PET Imaging Reveals Paclitaxel Treatment Efficacy Is Positively Correlated with HER2 Expression in Human Breast Cancer Xenograft Mouse Models.

Paclitaxel (PTX) treatment efficacy varies in breast cancer, yet the underlying mechanism for variable response remains unclear. This study evaluates whether human epidermal growth factor receptor 2 (HER2) expression level utilizing advanced molecular positron emission tomography (PET) imaging is correlated with PTX treatment efficacy in preclinical mouse models of HER2+ breast cancer. HER2 positive (BT474, MDA-MB-361), or HER2 negative (MDA-MB-231) breast cancer cells were subcutaneously injected into athymic nude mice and PTX (15 mg/kg) was administrated. In vivo HER2 expression was quantified through [89Zr]-pertuzumab PET/CT imaging. PTX treatment response was quantified by [18F]-fluorodeoxyglucose ([18F]-FDG) PET/CT imaging. Spearman's correlation, Kendall's tau, Kolmogorov-Smirnov test, and ANOVA were used for statistical analysis. [89Zr]-pertuzumab mean standard uptake values (SUVmean) of BT474 tumors were 4.9 ± 1.5, MDA-MB-361 tumors were 1.4 ± 0.2, and MDA-MB-231 (HER2-) tumors were 1.1 ± 0.4. [18F]-FDG SUVmean changes were negatively correlated with [89Zr]-pertuzumab SUVmean (r = -0.5887, p = 0.0030). The baseline [18F]-FDG SUVmean was negatively correlated with initial [89Zr]-pertuzumab SUVmean (r = -0.6852, p = 0.0002). This study shows PTX treatment efficacy is positively correlated with HER2 expression level in human breast cancer mouse models. Molecular imaging provides a non-invasive approach to quantify biological interactions, which will help in identifying chemotherapy responders and potentially enhance clinical decision-making.

Peptide Based Imaging Agents for HER2 Imaging in Oncology.

Breast cancer continues to be the most lethal cancer type in women and one of the most diagnosed. Understanding Breast cancer receptor status is one of the most vital processes for determining treatment options. One type of breast cancer, human epidermal growth factor receptor 2 (HER2) positive, has approved receptor-based therapies including trastuzumab and pertuzumab that can significantly increase the likelihood of survival. Current methods to determine HER2 status include biopsies with immunohistochemical staining and/or fluorescence in situ hybridization. However, positron emission tomography (PET) imaging techniques using 89Zr-trastuzumab or 89Zr-pertuzumab are currently in clinical trials for a non-invasive, full body diagnostic approach. Although the antibodies have strong specificity to the HER2 positive lesions, challenges involving long post-injection time for imaging due to the blood circulation of the antibodies and matching of long-live isotopes leading to increased dose to the patient leave opportunities for alternative PET imaging probes. Peptides have been shown to allow for shorter injection-to-imaging time and can be used with shorter lived isotopes. HER2 specific peptides under development will help improve the diagnosis and potentially therapy options for HER2 positive breast cancer. Peptides showing specificity for HER2 could start widespread development of molecular imaging techniques for HER2 positive cancers.

Panitumumab-IRDye800CW for Fluorescence-Guided Surgical Resection of Colorectal Cancer.

BACKGROUND: Fluorescence-guided surgery (FGS) is a rapidly advancing field that may improve outcomes in several cancer types. Although screening has decreased colorectal cancer (CRC) mortality, it remains a common and often fatal malignancy. In this study, we sought to identify an optical imaging agent for the application of FGS technology to CRC. METHODS: We compared a panitumumab-IRDye800CW conjugate to an IgG-IRDye800CW isotype control. Mice were implanted with one of three CRC cell lines (LS174T, Colo205, and SW948) and imaged with open- and closed-filed fluorescence imaging systems. Fluorescent contrast was quantified by calculating the ratio between tumor and background fluorescence. After 10 d, the mice were sacrificed, and their tumors stained for microscopic imaging. RESULTS: Panitumumab-IRDye800CW produced significantly greater (P < 0.05) fluorescent contrast in all three cell lines. Average tumor to background ratio was 6.00 versus 2.60 for LS174T, 5.78 versus 2.52 for Colo205, and 4.31 versus 1.70 for SW948. A 1-mg tumor fragment produced significantly greater fluorescent contrast in the Colo205 and SW948 cell lines in the panitumumab-IRDye800CW group. Western blotting for epidermal growth factor receptor (EGFR) and a semiquantitative analysis of EGFR expression noted strong expression in all three cell lines; however, EGFR expression did not directly correlate to tumor to background ratio. CONCLUSIONS: Panitumumab-IRDye800CW produces significantly greater fluorescent contrast than IgG-IRDye800CW in a murine model of CRC and is a suitable agent for the application of FGS technology to CRC.