Multimodal Positron Emission Tomography Imaging to Quantify Uptake of 89Zr-Labeled Liposomes in the Atherosclerotic Vessel Wall.

Nanotherapy has recently emerged as an experimental treatment option for atherosclerosis. To fulfill its promise, robust noninvasive imaging approaches for subject selection and treatment evaluation are warranted. To that end, we present here a positron emission tomography (PET)-based method for quantification of liposomal nanoparticle uptake in the atherosclerotic vessel wall. We evaluated a modular procedure to label liposomal nanoparticles with the radioisotope zirconium-89 (89Zr). Their biodistribution and vessel wall targeting in a rabbit atherosclerosis model was evaluated up to 15 days after intravenous injection by PET/computed tomography (CT) and PET/magnetic resonance imaging (PET/MRI). Vascular permeability was assessed in vivo using three-dimensional dynamic contrast-enhanced MRI (3D DCE-MRI) and ex vivo using near-infrared fluorescence (NIRF) imaging. The 89Zr-radiolabeled liposomes displayed a biodistribution pattern typical of long-circulating nanoparticles. Importantly, they markedly accumulated in atherosclerotic lesions in the abdominal aorta, as evident on PET/MRI and confirmed by autoradiography, and this uptake moderately correlated with vascular permeability. The method presented herein facilitates the development of nanotherapy for atherosclerotic disease as it provides a tool to screen for nanoparticle targeting in individual subjects' plaques.

Prospective Study of Systemic Yttrium-90 Elution during Radioembolization of Hepatic Metastases.

PURPOSE: To evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (90Y) radioembolization and differences in BR based on delivery method. MATERIALS AND METHODS: Twenty participants with hepatic metastases undergoing first radioembolization were prospectively enrolled from December 2017 to June 2018. Blood samples were drawn at baseline and 0, 10, 20, 60, and 120 minutes after 90Y administration. BR was measured with a γ-counter and scaled by estimated blood volume. Percentage of instilled radioactivity in the bloodstream was calculated as area under the fitted curve, and differences between delivery methods were examined with nonparametric statistical tests. RESULTS: In 10 participants, resin microspheres were instilled with 50% Isovue 300 diluted in saline solution in the D line, and 10 others were treated with dextrose 5% in water (D5W) in the D line. Median administered activities were 944 MBq (range, 746-1,993 MBq) and 1,213 MBq (range, 519-2,066 MBq), respectively. Fraction of 90Y in blood was significantly higher with dilute contrast agent than with D5W (median, 0.5% of injected activity vs 0.2%; P = .001). Among all participants, the maximum activity delivered was 2,066 MBq, and a maximum of 1% of administered radioactivity was measured as free 90Y in blood. Assuming these highest-case values and complete decay of all free 90Y in bone, a dose to red marrow of 132.3 mGy was calculated by Organ Level INternal Dose Assessment/EXponential Modeling. CONCLUSIONS: Blood sampling after radioembolization allowed for estimation of the time-activity curve and BR. Delivery with 50% contrast agent in saline solution resulted in a significant increase in BR vs D5W, even though the total BR for both groups was nominal.

Automation of pattern recognition analysis of dynamic contrast-enhanced MRI data to characterize intratumoral vascular heterogeneity.

PURPOSE: To automate dynamic contrast-enhanced MRI (DCE-MRI) data analysis by unsupervised pattern recognition (PR) to enable spatial mapping of intratumoral vascular heterogeneity. METHODS: Three steps were automated. First, the arrival time of the contrast agent at the tumor was determined, including a calculation of the precontrast signal. Second, four criteria-based algorithms for the slice-specific selection of number of patterns (NP) were validated using 109 tumor slices from subcutaneous flank tumors of five different tumor models. The criteria were: half area under the curve, standard deviation thresholding, percent signal enhancement, and signal-to-noise ratio (SNR). The performance of these criteria was assessed by comparing the calculated NP with the visually determined NP. Third, spatial assignment of single patterns and/or pattern mixtures was obtained by way of constrained nonnegative matrix factorization. RESULTS: The determination of the contrast agent arrival time at the tumor slice was successfully automated. For the determination of NP, the SNR-based approach outperformed other selection criteria by agreeing >97% with visual assessment. The spatial localization of single patterns and pattern mixtures, the latter inferring tumor vascular heterogeneity at subpixel spatial resolution, was established successfully by automated assignment from DCE-MRI signal-versus-time curves. CONCLUSION: The PR-based DCE-MRI analysis was successfully automated to spatially map intratumoral vascular heterogeneity. Magn Reson Med 79:1736-1744, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Monitoring early response to chemoradiotherapy with 18F-FMISO dynamic PET in head and neck cancer.

PURPOSE: There is growing recognition that biologic features of the tumor microenvironment affect the response to cancer therapies and the outcome of cancer patients. In head and neck cancer (HNC) one such feature is hypoxia. We investigated the utility of 18F-fluoromisonidazole (FMISO) dynamic positron emission tomography (dPET) for monitoring the early microenvironmental response to chemoradiotherapy in HNC. EXPERIMENTAL DESIGN: Seventy-two HNC patients underwent FMISO dPET scans in a customized immobilization mask (0-30 min dynamic acquisition, followed by 10 min static acquisitions starting at ∼95 min and ∼160 min post-injection) at baseline and early into treatment where patients have already received one cycle of chemotherapy and anywhere from five to ten fractions of 2 Gy per fraction radiation therapy. Voxelwise pharmacokinetic modeling was conducted using an irreversible one-plasma two-tissue compartment model to calculate surrogate biomarkers of tumor hypoxia (k 3 and Tumor-to-Blood Ratio (TBR)), perfusion (K 1 ) and FMISO distribution volume (DV). Additionally, Tumor-to-Muscle Ratios (TMR) were derived by visual inspection by an experienced nuclear medicine physician, with TMR > 1.2 defining hypoxia. RESULTS: One hundred and thirty-five lesions in total were analyzed. TBR, k 3 and DV decreased on early response scans, while no significant change was observed for K 1 . The k 3 -TBR correlation decreased substantially from baseline scans (Pearson's r = 0.72 and 0.76 for mean intratumor and pooled voxelwise values, respectively) to early response scans (Pearson's r = 0.39 and 0.40, respectively). Both concordant and discordant examples of changes in intratumor k 3 and TBR were identified; the latter partially mediated by the change in DV. In 13 normoxic patients according to visual analysis (all having lesions with TMR = 1.2), subvolumes were identified where k 3 indicated the presence of hypoxia. CONCLUSION: Pharmacokinetic modeling of FMISO dynamic PET reveals a more detailed characterization of the tumor microenvironment and assessment of response to chemoradiotherapy in HNC patients than a single static image does. In a clinical trial where absence of hypoxia in primary tumor and lymph nodes would lead to de-escalation of therapy, the observed disagreement between visual analysis and pharmacokinetic modeling results would have affected patient management in <20% cases. While simple static PET imaging is easily implemented for clinical trials, the clinical applicability of pharmacokinetic modeling remains to be investigated.

Understanding the pharmacological properties of a metabolic PET tracer in prostate cancer.

Generally, solid tumors (>400 mm(3)) are inherently acidic, with more aggressive growth producing greater acidity. If the acidity could be targeted as a biomarker, it would provide a means to gauge the pace of tumor growth and degree of invasiveness, as well as providing a basis for predicting responses to pH-dependent chemotherapies. We have developed a (64)Cu pH (low) insertion peptide (pHLIP) for targeting, imaging, and quantifying acidic tumors by PET, and our findings reveal utility in assessing prostate tumors. The new pHLIP version limits indiscriminate healthy tissue binding, and we demonstrate its targeting of extracellular acidification in three different prostate cancer models, each with different vascularization and acid-extruding protein carbonic anhydrase IX (CAIX) expression. We then describe the tumor distribution of this radiotracer ex vivo, in association with blood perfusion and known biomarkers of acidity, such as hypoxia, lactate dehydrogenase A, and CAIX. We find that the probe reveals metabolic variations between and within tumors, and discriminates between necrotic and living tumor areas.

PET Imaging of Extracellular pH in Tumors with (64)Cu- and (18)F-Labeled pHLIP Peptides: A Structure-Activity Optimization Study.

pH (low) insertion peptides (pHLIP peptides) target acidic extracellular environments in vivo due to pH-dependent cellular membrane insertion. Two variants (Var3 and Var7) and wild-type (WT) pHLIP peptides have shown promise for in vivo imaging of breast cancer. Two positron emitting radionuclides ((64)Cu and (18)F) were used to label the NOTA- and NO2A-derivatized Var3, Var7, and WT peptides for in vivo biodistribution studies in 4T1 orthotopic tumor-bearing BALB/c mice. All of the constructs were radiolabeled with (64)Cu or [(18)F]-AlF in good yield. The in vivo biodistribution of the 12 constructs in 4T1 orthotopic allografted female BALB/c mice indicated that NO2A-cysVar3, radiolabeled with either (18)F (4T1 uptake; 8.9 ± 1.7%ID/g at 4 h p.i.) or (64)Cu (4T1 uptake; 8.2 ± 0.9%ID/g at 4 h p.i. and 19.2 ± 1.8% ID/g at 24 h p.i.), shows the most promise for clinical translation. Additional studies to investigate other tumor models (melanoma, prostate, and brain tumor models) indicated the universality of tumor targeting of these tracers. From this study, future clinical translation will focus on (18)F- or (64)Cu-labeled NO2A-cysVar3.

Chemoenzymatic strategy for the synthesis of site-specifically labeled immunoconjugates for multimodal PET and optical imaging.

The complementary nature of positron emission tomography (PET) and optical imaging (OI) has fueled increasing interest in the development of multimodal PET/OI probes that can be employed during the diagnosis, staging, and surgical treatment of cancer. Due to their high selectivity and affinity, antibodies have emerged as promising platforms for the development of hybrid PET/OI agents. However, the lack of specificity of many bioconjugation reactions can threaten immunoreactivity and lead to poorly defined constructs. To circumvent this issue, we have developed a chemoenzymatic strategy for the construction of multimodal PET/OI immunoconjugates that have been site-specifically labeled on the heavy chain glycans. The methodology consists of four steps: (1) the enzymatic removal of the terminal galactose residues on the heavy chain glycans; (2) the enzymatic incorporation of azide-bearing galactose (GalNAz) residues into the heavy chain glycans; (3) the strain-promoted click conjugation of chelator- and fluorophore-modified dibenzocyclooctynes to the azide-modified sugars; and (4) the radiolabeling of the immunoconjugate. For proof-of-concept, a model system was created using the colorectal cancer-targeting antibody huA33, the chelator desferrioxamine (DFO), the positron-emitting radiometal (89)Zr, and the near-infrared fluorescent dye Alexa Fluor 680. The bioconjugation strategy is robust and reproducible, reliably producing well-defined and immunoreactive conjugates labeled with (89)Zr, Alexa Fluor 680, or an easily and precisely tuned mixture of the two reporters. In in vivo PET and fluorescence imaging experiments, a hybrid (89)Zr- and Alexa Fluor 680-labeled huA33 conjugate displayed high levels of specific uptake (>45% ID/g) in athymic nude mice bearing A33 antigen-expressing SW1222 colorectal cancer xenografts.

Targeting breast tumors with pH (low) insertion peptides.

Extracellular acidity is associated with tumor progression. Elevated glycolysis and acidosis promote the appearance of aggressive malignant cells with enhanced multidrug resistance. Thus, targeting of tumor acidity can open new avenues in diagnosis and treatment of aggressive tumors and targeting metastatic cancers cells within a tumor. pH (low) insertion peptides (pHLIPs) belong to the class of pH-sensitive agents capable of delivering imaging and/or therapeutic agents to cancer cells within tumors. Here, we investigated targeting of highly metastatic 4T1 mammary tumors and spontaneous breast tumors in FVB/N-Tg (MMTV-PyMT)634Mul transgenic mice with three fluorescently labeled pHLIP variants including well-characterized WT-pHLIP and, recently introduced, Var3- and Var7-pHLIPs. The Var3- and Var7-pHLIPs constructs have faster blood clearance than the parent WT-pHLIP. All pHLIPs demonstrated excellent targeting of the above breast tumor models with tumor accumulation increasing over 4 h postinjection. Staining of nonmalignant stromal tissues in transgenic mice was minimal. The pHLIPs distribution in tumors showed colocalization with 2-deoxyglucose and the hypoxia marker, Pimonidazole. The highest degree of colocalization of fluorescent pHLIPs was shown to be with lactate dehydrogenase A, which is related to lactate production and acidification of tumors. In sum, the pHLIP-based targeting of breast cancer presents an opportunity to monitor metabolic changes, and to selectively deliver imaging and therapeutic agents to tumors.

Noninvasive Imaging of PSMA in prostate tumors with (89)Zr-Labeled huJ591 engineered antibody fragments: the faster alternatives.

Engineered antibody fragments offer faster delivery with retained tumor specificity and rapid clearance from nontumor tissues. Here, we demonstrate that positron emission tomography (PET) based detection of prostate specific membrane antigen (PSMA) in prostatic tumor models using engineered bivalent antibodies built on single chain fragments (scFv) derived from the intact antibody, huJ591, offers similar tumor delineating properties but with the advantage of rapid targeting and imaging. (89)Zr-radiolabeled huJ591 scFv (dimeric scFv-CH3; (89)Zr-Mb) and cysteine diabodies (dimeric scFv; (89)Zr-Cys-Db) demonstrated internalization and similar Kds (∼2 nM) compared to (89)Zr-huJ591 in PSMA(+) cells. Tissue distribution assays established the specificities of both (89)Zr-Mb and (89)Zr-Cys-Db for PSMA(+) xenografts (6.2 ± 2.5% ID/g and 10.2 ± 3.4% ID/g at 12 h p.i. respectively), while minimal accumulation in PSMA(-) tumors was observed. From the PET images, (89)Zr-Mb and (89)Zr-Cys-Db exhibited faster blood clearance than the parent huJ591 while tumor-to-muscle ratios for all probes show comparable values across all time points. Ex vivo autoradiography and histology assessed the distribution of the probes within the tumor. Imaging PSMA-expressing prostate tumors with smaller antibody fragments offers rapid tumor accumulation and accelerated clearance; hence, shortened wait periods between tracer administration and high-contrast tumor imaging and lower dose-related toxicity are potentially realized.

(89)Zr-labeled paramagnetic octreotide-liposomes for PET-MR imaging of cancer.

PURPOSE: Dual-modality PET/MR platforms add a new dimension to patient diagnosis with high resolution, functional, and anatomical imaging. The full potential of this emerging hybrid modality could be realized by using a corresponding dual-modality probe. Here, we report pegylated liposome (LP) formulations, housing a MR T(1) contrast agent (Gd) and the positron-emitting (89)Zr (half-life: 3.27 days), for simultaneous PET and MR tumor imaging capabilities. METHODS: (89)Zr oxophilicity was unexpectedly found advantageous for direct radiolabeling of preformed paramagnetic LPs. LPs were conjugated with octreotide to selectively target neuroendocrine tumors via human somatostatin receptor subtype 2 (SSTr2). (89)Zr-Gd-LPs and octreotide-conjugated homolog were physically, chemically and biologically characterized. RESULTS: (89)Zr-LPs showed reasonable stability over serum proteins and chelator challenges for proof-of-concept in vitro and in vivo investigations. Nuclear and paramagnetic tracking quantified superior SSTr2-recognition of octreotide-LP compared to controls. CONCLUSIONS: This study demonstrated SSTr2-targeting specificity along with direct chelator-free (89)Zr-labeling of LPs and dual PET/MR imaging properties.

Efficient (18)F-labeling of large 37-amino-acid pHLIP peptide analogues and their biological evaluation.

Solid tumors often develop an acidic microenvironment, which plays a critical role in tumor progression and is associated with increased level of invasion and metastasis. The 37-residue pH (low) insertion peptide (pHLIP) is under study as an imaging platform because of its unique ability to insert into cell membranes at a low extracellular pH (pH(e) < 7). Labeling of peptides with [(18)F]-fluorine is usually performed via prosthetic groups using chemoselective coupling reactions. One of the most successful procedures involves the alkyne-azide copper(I) catalyzed cycloaddition (CuAAC). However, none of the known "click" methods have been applied to peptides as large as pHLIP. We designed a novel prosthetic group and extended the use of the CuAAC "click chemistry" for the simple and efficient (18)F-labeling of large peptides. For the evaluation of this labeling approach, a D-amino acid analogue of WT-pHLIP and an L-amino acid control peptide K-pHLIP, both functionalized at the N-terminus with 6-azidohexanoic acid, were used. The novel 6-[(18)F]fluoro-2-ethynylpyridine prosthetic group, was obtained via nucleophilic substitution on the corresponding bromo-precursor after 10 min at 130 °C with a radiochemical yield of 27.5 ± 6.6% (decay corrected) with high radiochemical purity ≥98%. The subsequent Cu(I)-catalyzed "click" reaction with the azido functionalized pHLIP peptides was quantitative within 5 min at 70 °C in a mixture of water and ethanol using Cu-acetate and sodium L-ascorbate. [(18)F]-D-WT-pHLIP and [(18)F]-L-K-pHLIP were obtained with total radiochemical yields of 5-20% after HPLC purification. The total reaction time was 85 min including formulation. In vitro stability tests revealed high stability of the [(18)F]-D-WT-pHLIP in human and mouse plasma after 120 min, with the parent tracer remaining intact at 65% and 85%, respectively. PET imaging and biodistribution studies in LNCaP and PC-3 xenografted mice with the [(18)F]-D-WT-pHLIP and the negative control [(18)F]-L-K-pHLIP revealed pH-dependent tumor retention. This reliable and efficient protocol promises to be useful for the (18)F-labeling of large peptides such as pHLIP and will accelerate the evaluation of numerous [(18)F]-pHLIP analogues as potential PET tracers.

Pre-clinical investigation of astatine-211-parthanatine for high-risk neuroblastoma.

Astatine-211-parthanatine ([211At]PTT) is an alpha-emitting radiopharmaceutical therapeutic that targets poly(adenosine-diphosphate-ribose) polymerase 1 (PARP1) in cancer cells. High-risk neuroblastomas exhibit among the highest PARP1 expression across solid tumors. In this study, we evaluated the efficacy of [211At]PTT using 11 patient-derived xenograft (PDX) mouse models of high-risk neuroblastoma, and assessed hematological and marrow toxicity in a CB57/BL6 healthy mouse model. We observed broad efficacy in PDX models treated with [211At]PTT at the maximum tolerated dose (MTD 36 MBq/kg/fraction x4) administered as a fractionated regimen. For the MTD, complete tumor response was observed in 81.8% (18 of 22) of tumors and the median event free survival was 72 days with 30% (6/20) of mice showing no measurable tumor >95 days. Reversible hematological and marrow toxicity was observed 72 hours post-treatment at the MTD, however full recovery was evident by 4 weeks post-therapy. These data support clinical development of [211At]PTT for high-risk neuroblastoma.

In vivo visualization of PARP inhibitor pharmacodynamics.

BACKGROUND[18F]FluorThanatrace ([18F]FTT) is a radiolabeled poly (adenosine diphosphate-ribose) polymerase inhibitor (PARPi) that enables noninvasive quantification of PARP with potential to serve as a biomarker for patient selection for PARPi therapy. Here we report for the first time to our knowledge noninvasive in vivo visualization of drug-target engagement during PARPi treatment.METHODSTwo single-arm, prospective, nonrandomized clinical trials were conducted at the University of Pennsylvania from May 2017 to March 2020. PARP expression in breast cancer was assessed in vivo via [18F]FTT PET before and after initiation of PARPi treatment and in vitro via [125I]KX1 (an analog of [18F]FTT) binding to surgically removed breast cancer.RESULTSThirteen patients had baseline [18F]FTT PET. Nine of these then had resection and in vitro evaluation of [18F]FTT uptake with an analog and uptake was blocked with PARPi. Of the other 4 patients, 3 had [18F]FTT PET uptake, and all had uptake blocked with treatment with a therapeutic PARPi. Initial in vivo [18F]FTT tumor uptake ranged from undetectable to robust. Following initiation of PARPi therapy, [18F]FTT uptake was not detectable above background in all cases. In vitro tumor treatment with a PARPi resulted in 82% reduction in [125I]KX1 binding.CONCLUSION[18F]FTT noninvasively quantifies PARP-1 expression. Early results indicate ability to visualize PARPi drug-target engagement in vivo and suggest the utility of further study to test [18F]FTT PET as a predictive and pharmacodynamic biomarker.TRIAL REGISTRATIONClinicalTrials.gov identifiers NCT03083288 and NCT03846167.FUNDINGMetavivor Translational Research Award, Susan G. Komen for the Cure (CCR 16376362), Department of Defense BC190315, and Abramson Cancer Center Breakthrough Bike Challenge.

Breast Cancer 18F-ISO-1 Uptake as a Marker of Proliferation Status.

The σ2 receptor is a potential in vivo target for measuring proliferative status in cancer. The feasibility of using N-(4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-2-(2-18F-fluoroethoxy)-5-methylbenzamide (18F-ISO-1) to image solid tumors in lymphoma, breast cancer, and head and neck cancer has been previously established. Here, we report the results of the first dedicated clinical trial of 18F-ISO-1 in women with primary breast cancer. Our study objective was to determine whether 18F-ISO-1 PET could provide an in vivo measure of tumor proliferative status, and we hypothesized that uptake would correlate with a tissue-based assay of proliferation, namely Ki-67 expression. Methods: Twenty-eight women with 29 primary invasive breast cancers were prospectively enrolled in a clinical trial (NCT02284919) between March 2015 and January 2017. Each received an injection of 278-527 MBq of 18F-ISO-1 and then underwent PET/CT imaging of the breasts 50-55 min later. In vivo uptake of 18F-ISO-1 was quantitated by SUVmax and distribution volume ratios and was compared with ex vivo immunohistochemistry for Ki-67. Wilcoxon rank-sum tests assessed uptake differences across Ki-67 thresholds, and Spearman correlation tested associations between uptake and Ki-67. Results: Tumor SUVmax (median, 2.0 g/mL; range, 1.3-3.3 g/mL), partial-volume-corrected SUVmax, and SUV ratios were tested against Ki-67. Tumors stratified into the high-Ki-67 (≥20%) group had SUVmax greater than the low-Ki-67 (<20%) group (P = 0.02). SUVmax exhibited a positive correlation with Ki-67 across all breast cancer subtypes (ρ = 0.46, P = 0.01, n = 29). Partial-volume-corrected SUVmax was positively correlated with Ki-67 for invasive ductal carcinoma (ρ = 0.51, P = 0.02, n = 21). Tumor-to-normal-tissue ratios and tumor distribution volume ratio did not correlate with Ki-67 (P > 0.05). Conclusion:18F-ISO-1 uptake in breast cancer modestly correlates with an in vitro assay of proliferation.

Targeting PARP-1 with Alpha-Particles Is Potently Cytotoxic to Human Neuroblastoma in Preclinical Models.

Alpha-emitters can be pharmacologically delivered for irradiation of single cancer cells, but cellular lethality could be further enhanced by targeting alpha-emitters directly to the nucleus. PARP-1 is a druggable protein in the nucleus that is overexpressed in neuroblastoma compared with normal tissues and is associated with decreased survival in high-risk patients. To exploit this, we have functionalized a PARP inhibitor (PARPi) with an alpha-emitter astatine-211. This approach offers enhanced cytotoxicity from conventional PARPis by not requiring enzymatic inhibition of PARP-1 to elicit DNA damage; instead, the alpha-particle directly induces multiple double-strand DNA breaks across the particle track. Here, we explored the efficacy of [211At]MM4 in multiple cancers and found neuroblastoma to be highly sensitive in vitro and in vivo Furthermore, alpha-particles delivered to neuroblastoma show antitumor effects and durable responses in a neuroblastoma xenograft model, especially when administered in a fractionated regimen. This work provides the preclinical proof of concept for an alpha-emitting drug conjugate that directly targets cancer chromatin as a therapeutic approach for neuroblastoma and perhaps other cancers.

Tumor-Specific Zr-89 Immuno-PET Imaging in a Human Bladder Cancer Model.

PURPOSE: Tumor-specific molecular imaging is an important tool for assessing disease burden and treatment response. CA19.9 is an important tumor-specific marker in several malignancies, including urothelial carcinoma. [89Zr]DFO-HuMab-5B1 (MVT-2163) is a CA19.9-specific antibody-based construct that has been validated in preclinical animal models of lung, colorectal, and pancreatic malignancies for positron emission tomography (PET) imaging and is currently in a phase I trial for pancreatic cancer (NCT02687230). Here, we examine whether [89Zr]DFO-HuMab-5B1 may be useful in defining urothelial malignancies. PROCEDURES: Surface expression of CA19.9 was confirmed in the human bladder cancer line HT 1197. The radioimmunoconjugate [89Zr]DFO-HuMab-5B1 was injected into mice bearing HT 1197 xenografts, and followed by PET imaging, ex vivo experiments including biodistribution, histology and autoradiography, and analysis of blood samples for shed antigen levels were performed. RESULTS: [89Zr]DFO-HuMab-5B1 specifically accumulates in HT 1197 engrafted tumors when imaged with PET. Ex vivo biodistribution of organs and autoradiography of engrafted tumors confirm our construct's specific tumor binding. The target antigen CA19.9 was not found to be shed in vitro or in vivo. CONCLUSIONS: [89Zr]DFO-HuMab-5B1 can be used to delineate urothelial carcinomas by PET imaging and may provide tumor-specific information prior to, during, and after systemic therapies.

Imaging EGFR and HER3 through 89Zr-labeled MEHD7945A (Duligotuzumab).

Tumor resistance to treatment paved the way toward the development of single agent drugs that target multiple molecular signatures amplified within the malignancy. The discovered crosstalk between EGFR and HER3 as well as the role of HER3 in mediating EGFR resistance made these two receptor tyrosine kinases attractive targets. MEHD7945A or duligotuzumab is a single immunotherapy agent that dually targets both molecular signatures. In this study, a positron emission tomography (PET) companion diagnostic to MEHD7945A is reported and evaluated in pancreatic cancer. Tumor accretion and whole body pharmacokinetics of 89Zr-MEHD7945A were established. Specificity of the probe for EGFR and/or HER3 was further examined.

18F-Fluoromisonidazole Kinetic Modeling for Characterization of Tumor Perfusion and Hypoxia in Response to Antiangiogenic Therapy.

Multiparametric imaging of tumor perfusion and hypoxia with dynamic 18F-fluoromisonidazole (18F-FMISO) PET may allow for an improved response assessment to antiangiogenic therapies. Cediranib (AZD2171) is a potent inhibitor of tyrosine kinase activity associated with vascular endothelial growth factor receptors 1, 2, and 3, currently in phase II/III clinical trials. Serial dynamic 18F-FMISO PET was performed to investigate changes in tumor biomarkers of perfusion and hypoxia after cediranib treatment. Methods: Twenty-one rats bearing HT29 colorectal xenograft tumors were randomized into a vehicle-treated control group (0.5% methylcellulose daily for 2 d [5 rats] or 7 d [4 rats]) and a cediranib-treated test group (3 mg/kg daily for 2 or 7 d; 6 rats in both groups). All rats were imaged before and after treatment, using a 90-min dynamic PET acquisition after administration of 42.1 ± 3.9 MBq of 18F-FMISO by tail vein injection. Tumor volumes were delineated manually, and the input function was image-derived (abdominal aorta). Kinetic modeling was performed using an irreversible 1-plasma 2-tissue compartmental model to estimate the kinetic rate constants K1, K1/k2, and k3-surrogates for perfusion, 18F-FMISO distribution volume, and hypoxia-mediated entrapment, respectively. Tumor-to-blood ratios (TBRs) were calculated on the last dynamic frame (80-90 min). Tumors were assessed ex vivo by digital autoradiography and immunofluorescence for microscopic visualization of perfusion (pimonidazole) and hypoxia (Hoechst 33342). Results: Cediranib treatment resulted in significant reduction of mean voxelwise 18F-FMISO TBR, K1, and K1/k2 in both the 2-d and the 7-d groups (P < 0.05). The k3 parameter was increased in both groups but reached significance only in the 2-d group. In the vehicle-treated groups, no significant change in TBR, K1, K1/k2, or k3 was observed (P > 0.2). Ex vivo tumor analysis confirmed the presence of hypoxic tumor regions that nevertheless exhibited relatively lower 18F-FMISO uptake. Conclusion:18F-FMISO kinetic modeling reveals a more detailed response to antiangiogenic treatment than a single static image is able to reveal. The reduced mean K1 reflects a reduction in tumor vascular perfusion, whereas the increased k3 reflects a rise in hypoxia-mediated entrapment of the radiotracer. However, if only late static images are analyzed, the observed reduction in 18F-FMISO uptake after treatment with cediranib may be mistakenly interpreted as a global decrease, rather than an increase, in tumor hypoxia. These findings support the use of 18F-FMISO kinetic modeling to more accurately characterize the response to treatments that have a direct effect on tumor vascularization and perfusion.