PET Imaging of VLA-4 in a New BRAFV600E Mouse Model of Melanoma.

PURPOSE: Despite unprecedented responses to immune checkpoint inhibitors and targeted therapy in melanoma, a major subset of patients progresses and have few effective salvage options. We have previously demonstrated robust, selective uptake of the peptidomimetic LLP2A labeled with Cu-64 ([64Cu]-LLP2A) for positron emission tomography (PET) imaging in subcutaneous and metastatic models of B16F10 murine melanoma. LLP2A binds with high affinity to very late antigen-4 (VLA-4, integrin α4ß1), a transmembrane protein overexpressed in melanoma and other cancers that facilitates tumor growth and metastasis. Yet B16F10 fails to faithfully reflect human melanoma biology, as it lacks certain oncogenic driver mutations, including BRAF mutations found in ≥ 50 % of clinical specimens. Here, we evaluated the PET tracer [64Cu]-CB-TE1A1P-PEG4-LLP2A ([64Cu]-LLP2A) in novel, translational BRAFV600E mutant melanoma models differing in VLA-4 expression-BPR (VLA-4-) and BPRα (VLA-4+). PROCEDURES: BPR cells were transduced with α4 (CD49d) to overexpress intact cell surface VLA-4 (BPRα). The binding affinity of [64Cu]-LLP2A to BPR and BPRα cells was determined by saturation binding assays. [64Cu]-LLP2A internalization into B16F10, BPR, and BPRα cells was quantified via a plate-based assay. Tracer biodistribution and PET/CT imaging were evaluated in mice bearing subcutaneous BPR and BPRα tumors. RESULTS: [64Cu]-LLP2A demonstrated high binding affinity to BPRα (Kd = 1.4 nM) but indeterminate binding to BPR cells. VLA-4+ BPRα and B16F10 displayed comparable time-dependent [64Cu]-LLP2A internalization, whereas BPR internalization was undetectable. PET/CT showed increased tracer uptake in BPRα tumors vs. BPR tumors in vivo, which was validated by significantly greater (p < 0.0001) BPRα tumor uptake in biodistribution analyses. CONCLUSIONS: [64Cu]-LLP2A discriminates BPRα (VLA-4+) vs. BPR (VLA-4-) melanomas in vivo, supporting translation of these BRAF-mutated melanoma models via prospective imaging and theranostic studies. These results extend the utility of LLP2A to selectively target clinically relevant and therapy-resistant tumor variants toward its use for therapeutic patient care.

Common variants of FTO and the risk of obesity and type 2 diabetes in Indians.

Common variants of fat mass and obesity-associated gene (FTO, fat mass- and obesity-associated gene) have been shown to be associated with obesity and type 2 diabetes in population of European and non-European ethnicity. However, studies in Indian population have provided inconsistent results. Here, we examined association of eight FTO variants (rs1421085, rs8050136, rs9939609, rs9930506, rs1861867, rs9926180, rs2540769 and rs708277) with obesity and type 2 diabetes in 5364 North Indians (2474 type 2 diabetes patients and 2890 non-diabetic controls) in two stages. None of the variants including previously reported intron 1 variants (rs1421085, rs8050136, rs9939609 and rs9930506) showed body mass index (BMI)-dependent/independent association with type 2 diabetes. However, rs1421085, rs8050136 and rs9939609 were associated with obesity status and measures of obesity (BMI, waist circumference and waist-to-hip ratio) in stage 2 and combined study population. Meta-analysis of the two study population results also revealed that rs1421085, rs8050136 and rs9939609 were significantly associated with BMI both under the random- and fixed-effect models (P (random/fixed)=0.02/0.0001, 0.004/0.0006 and 0.01/0.01, respectively). In conclusion, common variants of FTO were associated with obesity, but not with type 2 diabetes in North Indian population.

Multivalency in CXCR4 chemokine receptor targeted iron oxide nanoparticles.

The CXCR4 chemokine receptor is an important biomolecular target in cancer diagnostics and therapeutics. In a new multivalent approach, iron oxide nanoparticles were conjugated with multiple binding units of a low affinity azamacrocylic CXCR4 antagonist. The silica coated nanostructure has good suspension stability, a mode size of 72 nm and high affinity for CXCR4, showing >98% inhibition of anti-CXCR4 mAb binding in a receptor binding competition assay on Jurkat cells.

Molecular Imaging of Very Late Antigen-4 in Acute Lung Injury.

Inflammation plays a central role in the pathogenesis of acute lung injury (ALI) during both the acute pneumonitis stage and progression into the chronic fibroproliferative phase, leading to pulmonary fibrosis. Currently, there is an unmet clinical and research need for noninvasive ways to monitor lung inflammation through targeting of immunoregulatory pathways contributing to ALI pathogenesis. In this study, we evaluated the role of targeted imaging of very late antigen-4 (VLA-4), as a key integrin mediating the adhesion and recruitment of immune cells to inflamed tissues, in quantifying lung inflammation in a mouse model of lipopolysaccharide-induced ALI. Methods: ALI was induced by a single intratracheal administration of lipopolysaccharide (10, 20, or 40 µg per mouse) in C57BL/6J mice. Control mice were intratracheally instilled with sterile phosphate-buffered saline. VLA-4-targeted PET/CT was performed 24 h after intravenous injection of a 64Cu-labeled high-affinity peptidomimetic ligand referred to as 64Cu-LLP2A, which is conjugated with the chelator (1,4,8,11-tetraazacyclotetradecane-1-(methane phosphonic acid)-8-(methane carboxylic acid) and a polyethylene glycol 4 linker, at day 2 after the induction of ALI. Ex vivo biodistribution of 64Cu-LLP2A was determined by γ-counting of harvested organs. The severity of lung inflammation was assessed histologically and by measuring the expression of inflammatory markers in the lung tissue lysates using reverse transcription quantitative polymerase chain reaction. Results: Intratracheal lipopolysaccharide instillation led to an acute inflammatory response in the lungs, characterized by increased expression of multiple inflammatory markers and infiltration of myeloid cells, along with a significant and specific increase in 64Cu-LLP2A uptake, predominantly in a peribronchial distribution. There was a strong correlation between the lipopolysaccharide dose and 64Cu-LLP2A uptake, as quantified by in vivo PET (R = 0.69, P < 0.01). Expression levels of both subunits of VLA-4, that is, integrins α4 and ß1, significantly correlated with the expression of multiple inflammatory markers, including tumor necrosis factor-α, interleukin-1ß, and nitric oxide synthase-2, highlighting the potential of VLA-4 as a surrogate marker of acute lung inflammation. Notably, in vivo 64Cu-LLP2A uptake significantly correlated with the expression of multiple inflammatory markers and VLA-4. Conclusion: Our study demonstrates the feasibility of molecular imaging of VLA-4, as a mechanistically relevant target in ALI, and the accuracy of VLA-4-targeted PET in quantification of ongoing lung inflammation in a murine model.

Novel theranostic agent for PET imaging and targeted radiopharmaceutical therapy of tumour-infiltrating immune cells in glioma.

BACKGROUND: Malignant gliomas are deadly tumours with few therapeutic options. Although immunotherapy may be a promising therapeutic strategy for treating gliomas, a significant barrier is the CD11b+ tumour-associated myeloid cells (TAMCs), a heterogeneous glioma infiltrate comprising up to 40% of a glioma's cellular mass that inhibits anti-tumour T-cell function and promotes tumour progression. A theranostic approach uses a single molecule for targeted radiopharmaceutical therapy (TRT) and diagnostic imaging; however, there are few reports of theranostics targeting the tumour microenvironment. METHODS: Utilizing a newly developed bifunctional chelator, Lumi804, an anti-CD11b antibody (αCD11b) was readily labelled with either Zr-89 or Lu-177, yielding functional radiolabelled conjugates for PET, SPECT, and TRT. FINDINGS: 89Zr/177Lu-labeled Lumi804-αCD11b enabled non-invasive imaging of TAMCs in murine gliomas. Additionally, 177Lu-Lumi804-αCD11b treatment reduced TAMC populations in the spleen and tumour and improved the efficacy of checkpoint immunotherapy. INTERPRETATION: 89Zr- and 177Lu-labeled Lumi804-αCD11b may be a promising theranostic pair for monitoring and reducing TAMCs in gliomas to improve immunotherapy responses. FUNDING: A full list of funding bodies that contributed to this study can be found in the Acknowledgements section.

Preclinical ImmunoPET Imaging of Glioblastoma-Infiltrating Myeloid Cells Using Zirconium-89 Labeled Anti-CD11b Antibody.

PURPOSE: Glioblastoma is a lethal brain tumor, heavily infiltrated by tumor-associated myeloid cells (TAMCs). TAMCs are emerging as a promising therapeutic target as they suppress anti-tumor immune responses and promote tumor cell growth. Quantifying TAMCs using non-invasive immunoPET could facilitate patient stratification for TAMC-targeted treatments and monitoring of treatment efficacy. As TAMCs uniformly express the cell surface marker, integrin CD11b, we evaluated a Zr-89 labeled anti-CD11b antibody for non-invasive imaging of TAMCs in a syngeneic orthotopic mouse glioma model. PROCEDURES: A human/mouse cross-reactive anti-CD11b antibody (clone M1/70) was conjugated to a DFO chelator and radiolabeled with Zr-89. PET/CT and biodistribution with or without a blocking dose of anti-CD11b Ab were performed 72 h post-injection (p.i.) of [89Zr]anti-CD11b Ab in mice bearing established orthotopic syngeneic GL261 gliomas and in non tumor-bearing mice. Flow cytometry and immunohistochemistry of dissected GL261 tumors were conducted to confirm the presence of CD11b+ TAMCs. RESULTS: Significant uptake of [89Zr]anti-CD11b Ab was detected at the tumor site (SUVmean = 2.60 ± 0.24) compared with the contralateral hemisphere (SUVmean = 0.6 ± 0.11). Blocking with a 10-fold lower specific activity of [89Zr]anti-CD11b Ab markedly reduced the SUV in the right brain (SUVmean = 0.11 ± 0.06), demonstrating specificity. Spleen and lymph nodes (myeloid cell rich organs) also showed high uptake of the tracer, and biodistribution analysis correlated with the imaging results. CD11b expression within the tumor was validated using flow cytometry and immunohistochemistry, which showed high CD11b expression primarily in the tumoral hemisphere compared with the contralateral hemisphere with very minimal accumulation in non tumor-bearing brain. CONCLUSION: These data establish that [89Zr]anti-CD11b Ab immunoPET targets CD11b+ cells (TAMCs) with high specificity in a mouse model of GBM, demonstrating the potential for non-invasive quantification of tumor-infiltrating CD11b+ immune cells during disease progression and immunotherapy in patients with GBM.

Towards dual SPECT/optical bioimaging with a mitochondrial targeting, 99mTc(i) radiolabelled 1,8-naphthalimide conjugate.

A series of six different 1,8-naphthalimide conjugated dipicolylamine ligands (L1-6) have been synthesised and characterised. The ligands possess a range of different linker units between the napthalimide fluorophore and dipcolylamine chelator which allow the overall lipophilicity to be tuned. A corresponding series of Re(i) complexes have been synthesised of the form fac-[Re(CO)3(L1-6)]BF4. The absorption and luminescence properties of the ligands and Re(i) complexes were dominated by the intramolecular charge transfer character of the substituted fluorophore (typically absorption ca. 425 nm and emission ca. 520 nm). Photophysical assessments show that some of the variants are moderately bright. Radiolabelling experiments using a water soluble ligand variant (L5) were successfully undertaken and optimised with fac-[99mTc(CO)3(H2O)3]+. Confocal fluorescence microscopy showed that fac-[Re(CO)3(L5)]+ localises in the mitochondria of MCF-7 cells. SPECT/CT imaging experiments on naïve mice showed that fac-[99mTc(CO)3(L5)]+ has a relatively high stability in vivo but did not show any cardiac uptake, demonstrating rapid clearance, predominantly via the biliary system along with a moderate amount cleared renally.

64Cu PET Imaging of the CXCR4 Chemokine Receptor Using a Cross-Bridged Cyclam Bis-Tetraazamacrocyclic Antagonist.

Expression of the chemokine receptor chemokine C-X-C motif receptor 4 (CXCR4) plays an important role in cancer metastasis, in autoimmune diseases, and during stem cell-based repair processes after stroke and myocardial infarction. Previously reported PET imaging agents targeting CXCR4 suffer from either high nonspecific uptake or bind only to the human form of the receptor. The objective of this study was to develop a high-stability 64Cu-labeled small-molecule PET agent for imaging both human and murine CXCR4 chemokine receptors. Methods: Synthesis, radiochemistry, stability and radioligand binding assays were performed for the novel tracer 64Cu-CuCB-bicyclam. In vivo dynamic PET studies were performed on mice bearing U87 (CXCR4 low-expressing) and U87.CXCR4 (human-CXCR4 high-expressing) tumors. Biodistribution and receptor blocking studies were performed on CD1-IGS immunocompetent mice. CXCR4 expression on tumor and liver disaggregates was confirmed using a combination of immunohistochemistry, quantitative polymerase chain reaction, and Western blot. Results:64Cu-CuCB-bicyclam has a high affinity for both the human and the murine variants of the CXCR4 receptor (half-maximal inhibitory concentration, 8 nM [human]/2 nM [murine]) and can be obtained from the parent chelator that has low affinity. In vitro and in vivo studies demonstrate specific uptake in CXCR4-expressing cells that can be blocked by more than 90% using a higher-affinity antagonist, with limited uptake in non-CXCR4-expressing organs and high in vivo stability. The tracer was also able to selectively displace the CXCR4 antagonists AMD3100 and AMD3465 from the liver. Conclusion: The tetraazamacrocyclic small molecule 64Cu-CuCB-bicyclam has been shown to be an imaging agent for the CXCR4 receptor that is likely to be applicable across a range of species. It has high affinity and stability and is suitable for preclinical research in immunocompetent murine models.

Synthesis, crystal structure, and cytotoxicity studies of titanacalix[4 and 8]arene complexes.

Reaction of 5,11,17,23-tetra-tert-butyl-dihydroxy-26,28-bis(2-pentoxy)calix[4]arene (L(OH)2(Opentyl)2) with [TiCl4] afforded the dichlorotitanoacalix[4]arene complex [TiCl2L(O)2(Opentyl)2] (1) in good yield. Hydrolysis of 1 led to the isolation of the complex {[TiL(O)3(Opentyl)]2(µ-OH)(µ-Cl)} (2). Reaction of 5,11,17,23,29,35,41,47-p-tert-butyl-49,50,51,52,53,54,55,56-octapropoxycalix[8]arene (L'(Opropyl)8) with [TiCl4] in refluxing toluene afforded, following work-up, a 35 : 65 mixture (3) of the complex [Ti(NCMe)Cl]2[TiCl(µ-O)]2L' and the silicone grease derived complex [Ti(NCMe)Cl]2[Ti(µ-O)]2[OSi(CH3)2OSi(CH3)2O]L' in which the grease replaces two chloride ligands. The molecular structures of 1·2MeCN, 2·7»MeCN, and 3·10MeCN have been determined. The complexes were studied using in vitro cell assays and were found to have CC50 values in the range 111-186 µM, i.e. they have low toxicity.

Structurally optimised BODIPY derivatives for imaging of mitochondrial dysfunction in cancer and heart cells.

The structural features required for mitochondrial uptake of BODIPY-based optical imaging agents have been explored. The first derivatives of this class of dyes shown to have mitochondrial membrane potential-dependent uptake in both cancer and heart cells have been developed.

Chelator free gallium-68 radiolabelling of silica coated iron oxide nanorods via surface interactions.

The commercial availability of combined magnetic resonance imaging (MRI)/positron emission tomography (PET) scanners for clinical use has increased demand for easily prepared agents which offer signal or contrast in both modalities. Herein we describe a new class of silica coated iron-oxide nanorods (NRs) coated with polyethylene glycol (PEG) and/or a tetraazamacrocyclic chelator (DO3A). Studies of the coated NRs validate their composition and confirm their properties as in vivo T2 MRI contrast agents. Radiolabelling studies with the positron emitting radioisotope gallium-68 (t1/2 = 68 min) demonstrate that, in the presence of the silica coating, the macrocyclic chelator was not required for preparation of highly stable radiometal-NR constructs. In vivo PET-CT and MR imaging studies show the expected high liver uptake of gallium-68 radiolabelled nanorods with no significant release of gallium-68 metal ions, validating our innovation to provide a novel simple method for labelling of iron oxide NRs with a radiometal in the absence of a chelating unit that can be used for high sensitivity liver imaging.