90Y-daclizumab, an anti-CD25 monoclonal antibody, provided responses in 50% of patients with relapsed Hodgkin's lymphoma.

Despite significant advances in the treatment of Hodgkin's lymphoma (HL), a significant proportion of patients will not respond or will subsequently relapse. We identified CD25, the IL-2 receptor alpha subunit, as a favorable target for systemic radioimmunotherapy of HL. The scientific basis for the clinical trial was that, although most normal cells with exception of Treg cells do not express CD25, it is expressed by a minority of Reed-Sternberg cells and by most polyclonal T cells rosetting around Reed-Sternberg cells. Forty-six patients with refractory and relapsed HL were evaluated with up to seven i.v. infusions of the radiolabeled anti-CD25 antibody (90)Y-daclizumab. (90)Y provides strong ß emissions that kill tumor cells at a distance by a crossfire effect. In 46 evaluable HL patients treated with (90)Y-daclizumab there were 14 complete responses and nine partial responses; 14 patients had stable disease, and nine progressed. Responses were observed both in patients whose Reed-Sternberg cells expressed CD25 and in those whose neoplastic cells were CD25(-) provided that associated rosetting T cells expressed CD25. As assessed using phosphorylated H2AX (γ-H2AX) as a bioindicator of the effects of radiation exposure, predominantly nonmalignant cells in the tumor microenvironment manifested DNA damage, as reflected by increased expression of γ-H2AX. Toxicities were transient bone-marrow suppression and myelodysplastic syndrome in six patients who had not been evaluated with bone-marrow karyotype analyses before therapy. In conclusion, repeated (90)Y-daclizumab infusions directed predominantly toward nonmalignant T cells rosetting around Reed-Sternberg cells provided meaningful therapy for select HL patients.

Unexpected Behavior of the Heaviest Halogen Astatine in the Nucleophilic Substitution of Aryliodonium Salts.

Aryliodonium salts have become precursors of choice for the synthesis of (18) F-labeled tracers for nuclear imaging. However, little is known on the reactivity of these compounds with heavy halides, that is, radioiodide and astatide, at the radiotracer scale. In the first comparative study of radiohalogenation of aryliodonium salts with (125) I(-) and (211) At(-) , initial experiments on a model compound highlight the higher reactivity of astatide compared to iodide, which could not be anticipated from the trends previously observed within the halogen series. Kinetic studies indicate a significant difference in activation energy (Ea =23.5 and 17.1 kcal mol(-1) with (125) I(-) and (211) At(-) , respectively). Quantum chemical calculations suggest that astatination occurs via the monomeric form of an iodonium complex whereas iodination occurs via a heterodimeric iodonium intermediate. The good to excellent regioselectivity of halogenation and high yields achieved with diversely substituted aryliodonium salts indicate that this class of compounds is a promising alternative to the stannane chemistry currently used for heavy radiohalogen labeling of tracers in nuclear medicine.

Mechanisms of Cell Killing Response from Low Linear Energy Transfer (LET) Radiation Originating from (177)Lu Radioimmunotherapy Targeting Disseminated Intraperitoneal Tumor Xenografts.

Radiolabeled antibodies (mAbs) provide efficient tools for cancer therapy. The combination of low energy ß(-)-emissions (500 keVmax; 130 keVave) along with a γ-emission for imaging makes (177)Lu (T1/2 = 6.7 day) a suitable radionuclide for radioimmunotherapy (RIT) of tumor burdens possibly too large to treat with α-particle radiation. RIT with (177)Lu-trastuzumab has proven to be effective for treatment of disseminated HER2 positive peritoneal disease in a pre-clinical model. To elucidate mechanisms originating from this RIT therapy at the molecular level, tumor bearing mice (LS-174T intraperitoneal xenografts) were treated with (177)Lu-trastuzumab comparatively to animals treated with a non-specific control, (177)Lu-HuIgG, and then to prior published results obtained using (212)Pb-trastuzumab, an α-particle RIT agent. (177)Lu-trastuzumab induced cell death via DNA double strand breaks (DSB), caspase-3 apoptosis, and interfered with DNA-PK expression, which is associated with the repair of DNA non-homologous end joining damage. This contrasts to prior results, wherein (212)Pb-trastuzumab was found to down-regulate RAD51, which is involved with homologous recombination DNA damage repair. (177)Lu-trastuzumab therapy was associated with significant chromosomal disruption and up-regulation of genes in the apoptotic process. These results suggest an inhibition of the repair mechanism specific to the type of radiation damage being inflicted by either high or low linear energy transfer radiation. Understanding the mechanisms of action of ß(-)- and α-particle RIT comparatively through an in vivo tumor environment offers real information suitable to enhance combination therapy regimens involving α- and ß(-)-particle RIT for the management of intraperitoneal disease.

Synthesis and characterization of gadolinium-Peptidomimetic complex as an αvß3 integrin targeted MR contrast agent.

There is growing interest in small and rigid peptidomimetic αvß3 integrin antagonists that are readily synthesized and characterized and amenable to physiological conditions. Peptidomimetic 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-ß-alanine (IAC) was successfully conjugated to DOTA, complexed with Gd(III) and radiolabeled with (153)Gd. Radioassay results demonstrated specificity of the labeled conjugate by blocking ∼95% binding with the addition of a 50-fold molar excess of cold IAC to the reaction solution. Relaxometry was used to support the hypothesis that the specificity of the Gd-peptidomimetic targeting αvß3 integrin would increase the contrast and therefore enhance the sensitivity of an MRI scan of αvß3 integrin positive tissues. Magnetic resonance imaging of cell pellets (M21 human melanoma) was also performed, and the images clearly show that cells reacted with Gd(III)-DOTA-IAC display a brighter image than cells without the Gd(III)-DOTA-IAC contrast agent. In addition, Gd(III)-DOTA-IAC and IAC, with IC50 of 300nM and 230nM, respectively, are 2.1 and 2.7 times more potent than c(RGDfK) whose IC50 is 625nM. This promising preliminary data fuels further investigation of DOTA-IAC conjugates for targeting tumor associated angiogenesis and αvß3 integrin positive tumors using magnetic resonance imaging.

In vitro and in vivo analysis of indocyanine green-labeled panitumumab for optical imaging-a cautionary tale.

Indocyanine green (IC-Green), the only FDA approved near-infrared (NIR) fluorophore for clinical use, is attractive to researchers for the development of targeted optical imaging agents by modification of its structure and conjugation to monoclonal antibodies (mAbs) or their fragments. IC-Green derivative, ICG-sulfo-OSu (ICG-sOSu), is frequently used for antibody conjugation. However, ICG-sOSu is amphiphilic and readily facilitates aggregation of mAbs that is not easily separable from the desired immunoconjugates. Complications originating from this behavior are frequently overlooked by researchers. This study examined detailed chemical and biological characteristics of an ICG-sOSu-labeled mAb, panitumumab, and provided a clinically applicable strategy to deliver a pure conjugation product. Size-exclusion high-performance liquid chromatography (SE-HPLC) analysis of conjugation reactions, performed at molar reaction ratios of ICG-sOSu: mAb of 5, 10, or 20, resulted in isolable desired ICG-sOSu-panitumumab conjugation product in 72%, 53%, and 19% yields, respectively, with the remainder consisting of high molecular weight aggregates (>150 kDa) 14%, 30%, and 51%, respectively. The HPLC-purified ICG-sOSu-panitumumab products were analyzed by native and SDS polyacrylamide gel electrophoresis (PAGE) followed by optical imaging. Results indicated that the interaction between ICG-sOSu and panitumumab was due to both covalent and noncovalent binding of the ICG-sOSu to the protein. Noncovalently bound dye in the ICG-sOSu-panitumumab conjugate products was removed by extraction with ethyl acetate to further purify the HPLC-isolated conjugation products. With conserved immunoreactivity, excellent target-specific uptake of the doubly purified bioconjugates was observed with minimal liver retention in athymic nude mice bearing HER1-expressing tumor xenografts. In summary, the preparation of well-defined bioconjugate products labeled with commercial ICG-sOSu dye is not a simple process and control of the conjugation reaction ratio and conditions is crucial. Furthermore, absolute purification and characterization of the products is necessitated prior to in vivo optical imaging. Use of validated and characterized dye conjugate products should facilitate the development of clinically viable and reproducible IC-Green derivative and other NIR dye mAb conjugates for optical imaging applications.

Rational design, synthesis, and evaluation of tetrahydroxamic acid chelators for stable complexation of zirconium(IV).

Metals of interest for biomedical applications often need to be complexed and associated in a stable manner with a targeting agent before use. Whereas the fundamentals of most transition-metal complexation processes have been thoroughly studied, the complexation of Zr(IV) has been somewhat neglected. This metal has received growing attention in recent years, especially in nuclear medicine, with the use of (89) Zr, which a ß(+) -emitter with near ideal characteristics for cancer imaging. However, the best chelating agent known for this radionuclide is the trishydroxamate desferrioxamine B (DFB), the Zr(IV) complex of which exhibits suboptimal stability, resulting in the progressive release of (89) Zr in vivo. Based on a recent report demonstrating the higher thermodynamic stability of the tetrahydroxamate complexes of Zr(IV) compared with the trishydroxamate complexes analogues to DFB, we designed a series of tetrahydroxamic acids of varying geometries for improved complexation of this metal. Three macrocycles differing in their cavity size (28 to 36-membered rings) were synthesized by using a ring-closing metathesis strategy, as well as their acyclic analogues. A solution study with (89) Zr showed the complexation to be more effective with increasing cavity size. Evaluation of the kinetic inertness of these new complexes in ethylenediaminetetraacetic acid (EDTA) solution showed significantly improved stabilities of the larger chelates compared with (89) Zr-DFB, whereas the smaller complexes suffered from insufficient stabilities. These results were rationalized by a quantum chemical study. The lower stability of the smaller chelates was attributed to ring strain, whereas the better stability of the larger cyclic complexes was explained by the macrocyclic effect and by the structural rigidity. Overall, these new chelating agents open new perspectives for the safe and efficient use of (89) Zr in nuclear imaging, with the best chelators providing dramatically improved stabilities compared with the reference DFB.

Silica encapsulation of fluorescent nanodiamonds for colloidal stability and facile surface functionalization.

Fluorescent nanodiamonds (FNDs) emit in the near-IR and do not photobleach or photoblink. These properties make FNDs better suited for numerous imaging applications compared with commonly used fluorescence agents such as organic dyes and quantum dots. However, nanodiamonds do not form stable suspensions in aqueous buffer, are prone to aggregation, and are difficult to functionalize. Here we present a method for encapsulating nanodiamonds with silica using an innovative liposome-based encapsulation process that renders the particle surface biocompatible, stable, and readily functionalized through routine linking chemistries. Furthermore, the method selects for a desired particle size and produces a monodisperse agent. We attached biotin to the silica-coated FNDs and tracked the three-dimensional motion of a biotinylated FND tethered by a single DNA molecule with high spatial and temporal resolution.

Orthotopic pleural mesothelioma in mice: SPECT/CT and MR imaging with HER1- and HER2-targeted radiolabeled antibodies.

PURPOSE: To evaluate the potential of anti-human epidermal growth factor receptor (HER)1- and anti-HER2-targeted radiolabeled antibodies and magnetic resonance (MR) imaging for imaging of orthotopic malignant pleural mesothelioma (MPM) in mouse models. MATERIALS AND METHODS: Animal studies with 165 mice were performed in accordance with National Institutes of Health guidelines for the humane use of animals, and all procedures were approved by the institutional Animal Care and Use Committee. Flow cytometry studies were performed to evaluate HER1 and HER2 expression in NCI-H226 and MSTO-211H mesothelioma cells. Biodistribution and single photon emission computed tomography (SPECT)/computed tomography (CT) imaging studies were performed in mice (four or five per group, depending on tumor growth) bearing subcutaneous and orthotopic MPM tumors by using HER1- and HER2-targeted indium 111 ((111)In)- and iodine 125 ((125)I)-labeled panitumumab and trastuzumab, respectively. Longitudinal MR imaging over 5 weeks was performed in three mice bearing orthotopic tumors to monitor tumor growth and metastases. SPECT/CT/MR imaging studies were performed at the final time point in the orthotopic models (n = 3). The standard unpaired Student t test was used to compare groups. RESULTS: Orthotopic tumors and pleural effusions were clearly visualized at MR imaging 3 weeks after tumor cell inoculation. At 2 days after injection, the mean (111)In-panitumumab uptake of 29.6% injected dose (ID) per gram ± 2.2 (standard error of the mean) was significantly greater than the (111)In-trastuzumab uptake of 13.6% ID/g ± 1.0 and the (125)I-panitumumab uptake of 7.4% ID/g ± 1.2 (P = .0006 and P = .0001, respectively). MR imaging fusion with SPECT/CT provided more accurate information about (111)In-panitumumab localization in the tumor, as the tumor was poorly visualized at CT alone. CONCLUSION: This study demonstrates the utility of radiolabeled anti-HER1 antibodies in the imaging of MPM in preclinical models. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12121021/-/DC1.

An overview of targeted alpha therapy.

The effectiveness of targeted α-therapy (TAT) can be explained by the properties of α-particles. Alpha particles are helium nuclei and are ~8,000 times larger than ß(-)-particles (electrons). When emitted from radionuclides that decay via an α-decay pathway, they release enormous amounts of energy over a very short distance. Typically, the range of α-particles in tissue is 50-100 µm and they have high linear energy transfer (LET) with a mean energy deposition of 100 keV/µm, providing a more specific tumor cell killing ability without damage to the surrounding normal tissues than ß(-)-emitters. Due to these properties, the majority of pre-clinical and clinical trials have demonstrated that α-emitters such as (225)Ac, (211)At, (212)Bi, (213)Bi, (212)Pb, (223)Ra, and (227)Th are ideal for the treatment of smaller tumor burdens, micrometastatic disease, and disseminated disease. Even though these α-emitters have favorable properties, the development of TAT has been limited by high costs, unresolved chemistry, and limited availability of the radionuclides. To overcome these limitations, more potent isotopes, additional sources, and more efficient isotope production methods should be addressed. Furthermore, better chelation and labeling methods with the improvements of isotope delivery, targeting vehicles, molecular targets, and identification of appropriate clinical applications are still required.

Preparation of cystamine core dendrimer and antibody-dendrimer conjugates for MRI angiography.

Herein we report the preparation along with the in vivo and in vitro MRI characterization of two generation four and five cystamine core dendrimers loaded with thirty and fifty-eight derivatized Gd-DOTA (G4SS30, G5SS58) respectively. Likewise the development and characterization of two half-dendrimers conjugated to the F(ab')(2) fragment of the monoclonal antibody (mAb) panitumumab functionalized with a maleimide conjugation functional group site (Ab-(G4S15)(4), Ab-(G5S29)(4)) are also described. The in vitro molar relaxivity of the Ab-(G4S15)(4) conjugate, measured at pH 7.4, 22 °C, and 3T showed a moderate increase in relaxivity as compared to Magnevist (6.7 vs 4.0 mM(-1) s(-1)) while the Ab-(G5S29)(4) conjugate was 2-fold higher (9.1 vs 4.0 mM(-1) s(-1)). The data showed that only a high injection dose (0.050 mmol Gd(3+)/kg) produced a detectable contrast enhanced contrast for the Ab-(G4S15)(4) conjugate while a lower dose (0.035 mmol Gd(3+)/kg) was sufficient for the Ab-(G5S29)(4) conjugate. The antibody-SMCC conjugate was purified by a Sephadex G-100 column, and the antibody-dendrimer-based agents were purified by spin filtration using a Centricon filter (50,000 MCO). The protein assay coupled with cysteine and Ellman's assay indicated an antibody to dendrimer ratio of 1:4. The in vivo blood clearance half-lives of the four agents measured at the jugular vein were ~12-22 min.

Synthesis and characterization of αvß3-targeting peptidomimetic chelate conjugates for PET and SPECT imaging.

There is growing interest in small peptidomimetic α(v)ß(3) integrin antagonists that are readily synthesized and characterized and can be easily handled using physiological conditions. Peptidomimetic 4-[2-(3,4,5,6-tetrahydropyrimidine-2-ylamino)ethyloxy]benzoyl-2-[N-(3-amino-neopenta-1-carbamyl)]-aminoethylsulfonyl-amino-ß-alanine (IAC) was successfully conjugated to 1-(1-carboxy-3-carbo-t-butoxypropyl)-4,7-(carbo-tert-butoxymethyl)-1,4,7-triazacyclononane (NODA-GA(tBu)(3)) and 1-(1-carboxy-3-carbotertbutoxymethyl)-1,4,7,10-tetraazacyclododecane (DOTA-GA(tBu)(4)) and radiolabeled with (111)In, (67)Ga and (203)Pb. Results of a radioimmunoassay demonstrated binding to purified α(v)ß(3) integrin when 1-4equiv of integrin were added to the reaction. Based on this promising result, investigations are moving forward to evaluate the NODA-GA-IAC and DOTA-GA-IAC conjugates for targeting tumor associated angiogenesis and α(v)ß(3) integrin positive tumors to define their PET and SPECT imaging qualities as well as their potential for delivery of therapeutic radionuclides.

(111)In- and (203)Pb-Labeled Cyclic RGD Peptide Conjugate as an α(v)ß(3) Integrin-Binding Radiotracer.

Methodology for site-specific modification and chelate conjugation of a cyclic RGD (cRGD) peptide for the preparation of a radiotracer molecular imaging agent suitable for detecting α(v)ß(3) integrin is described. The method involves functionalizing the peptide with an aldehyde moiety and conjugation to a 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) derivative that possesses an aldehyde reactive aminooxy group. The binding assay of the (111)In-labeled peptide conjugate with α(v)ß(3) integrin showed 60% bound when four equivalents of the integrin was added, a reasonable binding affinity for a mono-valent modified RGD peptide.

PET imaging of tumor angiogenesis in mice with VEGF-A-targeted (86)Y-CHX-A″-DTPA-bevacizumab.

Bevacizumab is a humanized monoclonal antibody that binds to tumor-secreted vascular endothelial growth factor (VEGF)-A and inhibits tumor angiogenesis. In 2004, the antibody was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic colorectal carcinoma in combination with chemotherapy. This report describes the preclinical evaluation of a radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for potential use in Positron Emission Tomography (PET) imaging of VEGF-A tumor angiogenesis and as a surrogate marker for (90)Y-based radioimmunotherapy. Bevacizumab was conjugated to CHX-A″-DTPA and radiolabeled with (86)Y. In vivo biodistribution and PET imaging studies were performed on mice bearing VEGF-A-secreting human colorectal (LS-174T), human ovarian (SKOV-3) and VEGF-A-negative human mesothelioma (MSTO-211H) xenografts. Biodistribution and PET imaging studies demonstrated highly specific tumor uptake of the radioimmunoconjugate. In mice bearing VEGF-A-secreting LS-174T, SKOV-3 and VEGF-A-negative MSTO-211H tumors, the tumor uptake at 3 days postinjection was 13.6 ± 1.5, 17.4 ± 1.7 and 6.8 ± 0.7 % ID/g, respectively. The corresponding tumor uptake in mice coinjected with 0.05 mg cold bevacizumab were 5.8 ± 1.3, 8.9 ± 1.9 and 7.4 ± 1.0 % ID/g, respectively at the same time point, demonstrating specific blockage of the target in VEGF-A-secreting tumors. The LS-174T and SKOV3 tumors were clearly visualized by PET imaging after injecting 1.8-2.0 MBq (86)Y-CHX-A″-DTPA-bevacizumab. Organ uptake quantified by PET closely correlated (r(2) = 0.87, p = 0.64, n = 18) to values determined by biodistribution studies. This preclinical study demonstrates the potential of the radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for noninvasive assessment of the VEGF-A tumor angiogenesis status and as a surrogate marker for (90)Y-CHX-A″-DTPA-bevacizumab radioimmunotherapy.

Synthesis and evaluation of a bifunctional chelate for development of Bi(III)-labeled radioimmunoconjugates.

A new bifunctional ligand C-DEPA was designed and synthesized as a component for antibody-targeted radiation therapy (radioimmunotherapy, RIT) of cancer. C-DEPA was conjugated to a tumor targeting antibody, trastuzumab, and the corresponding C-DEPA-trastuzumab conjugate was evaluated for radiolabeling kinetics with (205/6)Bi. C-DEPA-trastuzumab conjugate rapidly bound (205/6)Bi, and (205/6)Bi-C-DEPA-trastuzumab conjugate was stable in human serum for 72 h. The in vitro radiolabeling kinetics and serum stability data suggest that C-DEPA is a potential chelate for preclinical RIT applications using (212)Bi and (213)Bi.

Poly(amidoamine) dendrimer based MRI contrast agents exhibiting enhanced relaxivities derived via metal preligation techniques.

This report presents the preparation and characterization of three [Gd-C-DOTA](-1)-dendrimer assemblies by way of analysis, NMRD spectroscopy, and photon correlation spectroscopy (PCS). The metal-ligand chelates were preformed in alcohol media prior to conjugation to generation 4, 5, and 6 PAMAM dendrimers. The dendrimer-based agents were purified by Sephadex G-25 column chromatography. The combustion analysis, SE-HPLC, and UV-vis data indicated chelate to dendrimer ratios of 28:1, 61:1 and 115:1, respectively. Molar relaxivity measured at pH 7.4, 22 degrees C, and 3 T (29.6, 49.8, and 89.1 mM(-1) s(-1)) indicated the viability of conjugates as MRI contrast agents. 1/T(1) NMRD profiles were measured at 23 degrees C and indicated that at 22 MHz the 1/T(1) reached a plateau at 60, 85, and 140 mM(-1) s(-1) for the generation 4, 5, and 6 dendrimer conjugates, respectively. The PCS data showed the respective sizes of 5.2, 6.5, and 7.8 nm for G-4, 5, and 6 conjugates.

Improved speciation characteristics of PEGylated indocyanine green-labeled Panitumumab: revisiting the solution and spectroscopic properties of a near-infrared emitting anti-HER1 antibody for optical imaging of cancer.

A water-soluble amine-reactive PEGylated analogue of near-infrared emitting dye indocyanine green (5) was synthesized and used to label the anti-HER1 antibody panitumumab (Vectibix) at various equivalents. These conjugates were compared with non-PEGylated analogue conjugate products and the solution speciation analyzed with UV-vis spectrophotometry, size exclusion HPLC, and SDS-PAGE. PEGylation of the bioconjugates was successful in preventing aggregation in solution, a phenomenon observed with the non-PEGylated bioconjugates presumably due to the hydrophobicity of indocyanine green. Competitive radioimmunoassay demonstrated that the targeting moiety of the PEGylated bioconjugates was conserved. Fluorescence microscopy also demonstrated membrane binding of the bioconjugate to HER1-expressing A431 cells. Hence, these bioconjugates are suitable candidates for the in vivo optical imaging of HER1-expressing tumors.

PET imaging of HER1-expressing xenografts in mice with 86Y-CHX-A''-DTPA-cetuximab.

PURPOSE: Cetuximab is a recombinant, human/mouse chimeric IgG(1) monoclonal antibody that binds to the epidermal growth factor receptor (EGFR/HER1). Cetuximab is approved for the treatment of patients with HER1-expressing metastatic colorectal cancer. Limitations in currently reported radiolabeled cetuximab for PET applications prompted the development of (86)Y-CHX-A''-DTPA-cetuximab as an alternative for imaging HER1-expressing cancer. (86)Y-CHX-A''-DTPA-cetuximab can also serve as a surrogate marker for (90)Y therapy. METHODS: Bifunctional chelate, CHX-A''-DTPA was conjugated to cetuximab and radiolabeled with (86)Y. In vitro immunoreactivity was assessed in HER1-expressing A431 cells. In vivo biodistribution, PET imaging and noncompartmental pharmacokinetics were performed in mice bearing HER1-expressing human colorectal (LS-174T and HT29), prostate (PC-3 and DU145), ovarian (SKOV3) and pancreatic (SHAW) tumor xenografts. Receptor blockage was demonstrated by coinjection of either 0.1 or 0.2 mg cetuximab. RESULTS: (86)Y-CHX-A''-DTPA-cetuximab was routinely prepared with a specific activity of 1.5-2 GBq/mg and in vitro cell-binding in the range 65-75%. Biodistribution and PET imaging studies demonstrated high HER1-specific tumor uptake of the radiotracer and clearance from nonspecific organs. In LS-174T tumor-bearing mice injected with (86)Y-CHX-A''-DTPA-cetuximab alone, (86)Y-CHX-A''-DTPA-cetuximab plus 0.1 mg cetuximab or 0.2 mg cetuximab, the tumor uptake values at 3 days were 29.3 +/- 4.2, 10.4 +/- 0.5 and 6.4 +/- 0.3%ID/g, respectively, demonstrating dose-dependent blockage of the target. Tumors were clearly visualized 1 day after injecting 3.8-4.0 MBq (86)Y-CHX-A''-DTPA-cetuximab. Quantitative PET revealed the highest tumor uptake in LS-174T (29.55 +/- 2.67%ID/cm(3)) and the lowest tumor uptake in PC-3 (15.92 +/- 1.55%ID/cm(3)) xenografts at 3 days after injection. Tumor uptake values quantified by PET were closely correlated (r (2) = 0.9, n = 18) with values determined by biodistribution studies. CONCLUSION: This study demonstrated the feasibility of preparation of high specific activity (86)Y-CHX-A''-DTPA-cetuximab and its application for quantitative noninvasive PET imaging of HER1-expressing tumors. (86)Y-CHX-A''-DTPA-cetuximab offers an attractive alternative to previously labeled cetuximab for PET and further investigation for clinical translation is warranted.

Macromolecular and dendrimer-based magnetic resonance contrast agents.

Magnetic resonance imaging (MRI) is a powerful imaging modality that can provide an assessment of function or molecular expression in tandem with anatomic detail. Over the last 20-25 years, a number of gadolinium-based MR contrast agents have been developed to enhance signal by altering proton relaxation properties. This review explores a range of these agents from small molecule chelates, such as Gd-DTPA and Gd-DOTA, to macromolecular structures composed of albumin, polylysine, polysaccharides (dextran, inulin, starch), poly(ethylene glycol), copolymers of cystamine and cystine with GD-DTPA, and various dendritic structures based on polyamidoamine and polylysine (Gadomers). The synthesis, structure, biodistribution, and targeting of dendrimer-based MR contrast agents are also discussed.

Reply to the 'Comment on "Investigation of Zr(iv) and 89Zr(iv) complexation with hydroxamates: progress towards designing a better chelator than desferrioxamine B for immuno-PET imaging"' by A. Bianchi and M. Savastano, Chem. Commun., 2020, 56, D0CC01189D.

The alternative analysis of A. Bianchi and M. Savastano is a valuable contribution to the understanding of the complex systems at stake in the complexation chemistry of Zr4+ by considering polynuclear species. Placed in the context of nuclear medicine where such aggregates are unlikely and considering recent literature data, this however points out that no clear agreement exists to describe such complex formation.

90Y-Daclizumab (Anti-CD25), High-Dose Carmustine, Etoposide, Cytarabine, and Melphalan Chemotherapy and Autologous Hematopoietic Stem Cell Transplant Yielded Sustained Complete Remissions in 4 Patients with Recurrent Hodgkin's Lymphoma.

Background: Despite advances in therapy of Hodgkin's lymphoma (HL), a proportion of patients will not respond or relapse. The authors had previously identified CD25, IL-2Rα, as a target for systemic radioimmunotherapy of HL since most normal cells do not express CD25, but it is expressed by a minority of Hodgkin/Reed-Sternberg (HRS) cells and most Tregs rosetting around HRS cells. Study Design and Treatment: This was a single institution, nonrandomized, open-label phase I/II trial of radiolabeled 90Y-daclizumab, an anti-CD25 monoclonal antibody, BEAM (carmustine, etoposide, cytarabine, and melphalan) conditioning treatment followed by autologous hematopoietic stem cell transplant (ASCT). Four patients with refractory and relapsed HL were treated in this trial with 3 patients receiving a single dose of 564.6-574.6 MBq 90Y-daclizumab and the fourth patient receiving two doses of 580.9-566.1 MBq 90Y-daclizumab followed by high-dose chemotherapy and ASCT. Results: All 4 evaluable patients treated with 90Y-daclizumab obtained complete responses (CRs) that are ongoing 4.5-7 years following their stem cell transplant. The spectrum and severity of adverse events were mild and more importantly none of the patients, including several with multiple therapies before this treatment, developed the myelodysplastic syndrome. Discussion: Targeting by daclizumab was not directed primarily at tumor cells, but rather the nonmalignant CD25-expressing T cells adjacent to the HRS cells and 90Y-daclizumab provided strong enough ß emissions to kill CD25-negative tumor cells at a distance by a crossfire effect. Furthermore, the strong ß irradiation killed normal cells in the tumor microenvironment. Conclusions: 90Y-daclizumab (anti-CD25), high-dose BEAM chemotherapy and ASCT was well tolerated and yielded sustained complete remissions in all 4 patients with recurrent HL patients who completed their treatment. Significance: Despite advances, a proportion of patients with HL will not have a CR to their initial treatment, and some with CRs will relapse. They demonstrated that the addition of 90Y-daclizumab into the preconditioning regimen for refractory and relapsed HL patients with high-dose BEAM chemotherapy and ASCT provided sustained CRs in the 4 patients studied. Two of these patients were highly refractory to multiple prior treatments with bulky disease at entry into this study, including 1 patient who never entered a remission and had failed 6 different therapeutic regimens. Despite the small number of patients treated in this study, the sustained clinical benefit in these patients indicates a highly effective treatment. The daclizumab was directed primarily not at HRS cells themselves but toward nonmalignant T cells rosetting around malignant cells. 90Y provided strong ß emissions that killed antigen nonexpressing tumor cells at a distance by a crossfire effect. Furthermore, the strong ß radiation killed normal cells in the tumor microenvironment that nurtured the malignant cells in the lymphomatous mass. The present study supports expanded analysis of 90Y-daclizumab as part of the regimen of ASCT in patients with refractory and relapsed HL.