Sarah Able

Nanographene oxide-based radioimmunoconstructs for in vivo targeting and SPECT imaging of HER2-positive tumors

Nanographene oxide (NGO) is a novel nano-wall material that tracks to tumors in vivo, and which, as a consequence of its large surface area, has the capacity to carry a large payload. This study explores the use of anti-HER2 antibody (trastuzumab)-conjugated NGO, radiolabeled with (111)In-benzyl-diethylenetriaminepentaacetic acid (BnDTPA) via ππ-stacking, for functional imaging. In two HER2-overexpressing murine models of human breast cancer, high tumor-to-muscle ratio was achieved, resulting in clear visualization of tumor using single-photon emission computed tomography (SPECT). In the BALB/neuT model and in BALB/c nu/nu mice bearing 231/H2N xenografts, tumor accumulation amounted to 12.7 ± 0.67 and 15.0 ± 3.7% of the injected dose/g (%ID/g) of tumor tissue at 72 h, with tumor-to-muscle ratios of 35:1 and 7:1, respectively. Radiolabeled NGO-trastuzumab conjugates demonstrated superior pharmacokinetics compared to radiolabeled trastuzumab without NGO, with more rapid clearance from the circulation. The use of NGO as a scaffold to build radiolabeled nano-immunoconstructs holds promise for molecular imaging of tumors.

Molecular Radiotherapy Using Cleavable Radioimmunoconjugates That Target EGFR and γH2AX

Many anticancer therapies, including ionizing radiation (IR), cause cytotoxicity through generation of DNA double-strand breaks (DSB). Delivery of therapeutic radionuclides to DNA DSB sites can amplify this DNA damage, for additional therapeutic gain. Herein, we report on two radiopharmaceuticals, radiolabeled with the Auger electron emitter 111In, with dual specificity for both the intranuclear, DNA damage repair signaling protein γH2AX and the EGF receptor (EGFR). The EGFR ligand EGF was conjugated to a fluorophore- or 111In-labeled anti-γH2AX antibody, linked via a nuclear localization sequence (NLS) to ensure nuclear translocation. EGF conjugation was achieved either through a noncleavable PEG linker (PEO6) or a cleavable disulfide bond. Both conjugates selectively bound EGFR on fixed cells and γH2AX in cell extracts. Both compounds enter EGFR-expressing cells in an EGF/EGFR-dependent manner. However, only the cleavable compound was seen to associate with γH2AX foci in the nuclei of irradiated cells. Intracellular retention of the cleavable compound was prolonged in γH2AX-expressing cells. Clonogenic survival was significantly reduced when cells were exposed to IR (to induce γH2AX) plus 111In-labeled cleavable compound compared to either alone and compared to nonspecific controls. In vivo, uptake of 111In-labeled cleavable compound in MDA-MB-468 xenografts in athymic mice was 2.57 ± 0.47 percent injected dose/g (%ID/g) but increased significantly to 6.30 ± 1.47%ID/g in xenografts where γH2AX was induced by IR (P < 0.01). This uptake was dependent on EGF/EGFR and anti-γH2AX/γH2AX interactions. We conclude that tumor-specific delivery of radiolabeled antibodies directed against intranuclear epitopes is possible using cleavable antibody–peptide conjugates. Mol Cancer Ther; 12(11); 2472–82. ©2013 AACR.

Imaging DNA Damage Allows Detection of Preneoplasia in the BALB-neuT Model of Breast Cancer

A prominent feature of many human cancers is oncogene-driven activation of the DNA damage response (DDR) during early tumorigenesis. It has been shown previously that noninvasive imaging of the phosphorylated histone H2A variant H2AX, γH2AX, a DNA damage signaling protein, is possible using 111In-labeled anti-γH2AX antibody conjugated to the cell-penetrating peptide transactivator of transcription (TAT). The purpose of this study was to investigate whether 111In-anti-γH2AX-TAT detects the DDR during mammary oncogenesis in BALB-neuT mice. Methods: Mammary fat pads from BALB-neuT and wild-type mice (age, 40–106 d) were immunostained for γH2AX. 111In-anti-γH2AX-TAT or a control probe was administered intravenously to BALB-neuT mice. SPECT was performed weekly and compared with tumor detection using palpation and dynamic contrast-enhanced MR imaging. Results: γH2AX expression was elevated in hyperplastic lesions in the mammary fat pads of BALB-neuT mice aged 76–106 d, compared with normal fat pads from younger mice and carcinomas from older mice (13.5 ± 1.2 γH2AX foci/cell vs. 5.2 ± 1.5 [P < 0.05] and 3.4 ± 1.1 [P < 0.001], respectively). Serial SPECT imaging revealed a 2.5-fold increase in 111In-anti-γH2AX-TAT accumulation in the mammary fat pads of mice aged 76–106 d, compared with control probe (P = 0.01). The median time to detection of neoplastic lesions by 111In-anti-γH2AX-TAT (defined as >5% injected dose per gram of tissue) was 96 d, compared with 120 and 131 d for dynamic contrast-enhanced MR imaging and palpation, respectively (P < 0.001). Conclusion: DDR imaging using 111In-anti-γH2AX-TAT identified mammary tumors significantly earlier than MR imaging. Imaging the DDR holds promise for the detection of preneoplasia and as a technique for screening cancer-prone individuals.

Synthesis and evaluation of an 18F-labeled derivative of F3 for targeting surface-expressed nucleolin in cancer and tumor endothelial cells

The surface overexpression of nucleolin provides an anchor for the specific attachment of biomolecules to cancer and angiogenic endothelial cells. The peptide F3 is a high‐affinity ligand of the nucleolin receptor (NR) that has been investigated as a carrier to deliver biologically active molecules to tumors for both therapeutic and imaging applications. A site‐specific PEGylated F3 derivative was radiolabeled with [18F]Al‐F. The binding affinity and cellular distribution of the compound was assessed in tumor (H2N) and tumor endothelial (2H‐11) cells. Specific uptake via the NR was demonstrated by the siRNA knockdown of nucleolin in both cell lines. The partition and the plasma stability of the compound were assessed at 37°C. The enzyme‐mediated site‐specific modification of F3 to give NODA‐PEG‐F3 (NP‐F3) was achieved. Radiolabeling with [18F]Al‐F gave 18F‐NP‐F3. 18F‐NP‐F3 demonstrated high affinity for cancer and tumor endothelial cells. The siRNA knockdown of nucleolin resulted in a binding affinity reduction of 50% to 60%, confirming cell surface binding via the NR. NP‐F3 was stable in serum for 2 h. 18F‐NP‐F3 is reported as the first 18F‐labeled F3 derivative. It was obtained in a site‐specific, high‐yield, and efficient manner and binds to surface NR in the low nanomolar range, suggesting it has potential as a tumor and angiogenesis tracer.

Accumulation of 111In-Labelled EGF-Au-PEG Nanoparticles in EGFR-Positive Tumours is Enhanced by Coadministration of Targeting Ligand

The successful use of targeted radionuclide therapy in the treatment of solid tumours may be limited by radioresistance, which necessitates delivery of a high dose of radioactivity. Nanoparticle (NP)-based delivery systems possess a large surface area for attachment of radioisotopes and so offer a solution to this challenge. However, tumour uptake may be limited by rapid hepatic clearance of NP via the mononuclear phagocyte system. Liver uptake is further compounded when epidermal growth factor (EGF) is used as a targeting ligand, as EGF-tagged NP bind the EGF receptor (EGFR), which is expressed to a moderate extent by hepatocytes. This report describes an indium-111 (111In)-labelled PEGylated EGF-tagged gold (Au) NP (111In-EGF-Au-PEG) and an effective strategy of coadministration of targeting ligand to address these issues. Direct attachment of EGF to the surface of Au NP did not compromise surface coating with long-chain PEG. In vitro experiments showed that 111In-EGF-Au-PEG targets EGFR-positive cancer cells (MDA-MB-468): >11% of radioactivity was internalised after incubation for 4 h. In in vivo studies accumulation of NP was observed in MDA-MB-468 xenografts and tumour uptake was enhanced by the coadministration of 15 µg of the unlabelled targeting ligand, EGF, to block hepatic EGFR. Uptake was 3.9% versus 2.8% injected dose/g (%ID/g) of tumour tissue with and without unlabelled EGF, respectively. Coadministration of EGF reduced liver uptake by 25.95% to 7.56 %ID/g. This suggests that the coadministration of unlabelled targeting ligand with radiolabelled PEGylated NP offers a promising strategy for targeting EGFR-positive cancer and for minimising liver uptake.

Targeting Micrometastases: The Effect of Heterogeneous Radionuclide Distribution on Tumor Control Probability

The spatial distribution of radiopharmaceuticals that emit short-range high linear-energy-transfer electrons greatly affects absorbed dose and biological effectiveness. The purpose of this study was to investigate the effect of heterogeneous radionuclide distribution on tumor control probability (TCP) in a micrometastasis model. Methods: The cancer cell lines MDA-MB-468, SQ20B, and 231-H2N were grown as spheroids to represent micrometastases. The intracellular distribution of a representative radiopeptide (111In-labeled epidermal growth factor) and radioimmunotherapeutic (111In-labeled trastuzumab) was determined in cell internalization experiments. The intratumoral distribution was evaluated by microautoradiography of spheroids. γH2AX staining was performed on spheroid sections to correlate DNA damage with radionuclide distribution. Experimental surviving fractions were obtained using clonogenic assays. A random close-packed algorithm, which models the random packing behavior of cells and reflects variation in the radii of cells and nuclei, was used to simulate 3-dimensional spheroids. Calculated survival fractions were generated using an iterative modeling method based on Monte Carlo–determined absorbed dose with the PENELOPE code and were compared with experimental surviving fraction. Radiobiologic parameters deduced from experimental results and Monte Carlo simulations were used to predict the TCP for a 3-dimensional spheroid model. Results: Calculated survival fractions agreed well with experimental data, particularly when an increased value for relative biological effectiveness was applied to self-dose deposited by sources located in the nucleus and when radiobiologic parameters were adjusted to account for dose protraction. Only in MDA-MB-468 spheroids treated with 111In-epidermal growth factor was a TCP of more than 0.5 achieved, indicating that for this cell type the radiopeptide would be curative when targeting micrometastases. This ability is attributed to the relative radiosensitivity of MDA-MB-468 cells, high nuclear uptake of the radiopeptide, and uniform distribution of radioactivity throughout the spheroid. Conclusion: It is imperative to include biologic endpoints when evaluating the distribution of radionuclides in models emulating micrometastatic disease. The spatial distribution of radioactivity is a clear determinant of biological effect and TCP as demonstrated in this study.

Improved outcome of 131I-mIBG treatment through combination with external beam radiotherapy in the SK-N-SH mouse model of neuroblastoma

Purpose To assess the efficacy of different schedules for combining external beam radiotherapy (EBRT) with molecular radiotherapy (MRT) using 131I-mIBG in the management of neuroblastoma. Materials and methods BALB/c nu/nu mice bearing SK-N-SH neuroblastoma xenografts were assigned to five treatment groups: 131I-mIBG 24 h after EBRT, EBRT 6 days after 131I-mIBG, EBRT alone, 131I-mIBG alone and control (untreated). A total of 56 mice were assigned to 3 studies. Study 1: Vessel permeability was evaluated using dynamic contrast-enhanced (DCE)-MRI (n = 3). Study 2: Tumour uptake of 131I-mIBG in excised lesions was evaluated by γ-counting and autoradiography (n = 28). Study 3: Tumour volume was assessed by longitudinal MR imaging and survival was analysed (n = 25). Tumour dosimetry was performed using Monte Carlo simulations of absorbed fractions with the radiation transport code PENELOPE. Results Given alone, both 131I-mIBG and EBRT resulted in a seven-day delay in tumour regrowth. Following EBRT, vessel permeability was evaluated by DCE-MRI and showed an increase at 24 h post irradiation that correlated with an increase in 131I-mIBG tumour uptake, absorbed dose and overall survival in the case of combined treatment. Similarly, EBRT administered seven days after MRT to coincide with tumour regrowth, significantly decreased the tumour volume and increased overall survival. Conclusions This study demonstrates that combining EBRT and MRT has an enhanced therapeutic effect and emphasizes the importance of treatment scheduling according to pathophysiological criteria such as tumour vessel permeability and tumour growth kinetics.

Monitoring response to anti-angiogenic mTOR inhibitor therapy in vivo using 111In-bevacizumab

BackgroundThe ability to image vascular endothelial growth factor (VEGF) could enable prospective, non-invasive monitoring of patients receiving anti-angiogenic therapy. This study investigates the specificity and pharmacokinetics of 111In-bevacizumab binding to VEGF and its use for assessing response to anti-angiogenic therapy with rapamycin.Specificity of 111In-bevacizumab binding to VEGF was tested in vitro with unmodified radiolabelled bevacizumab in competitive inhibition assays. Uptake of 111In-bevacizumab in BALB/c nude mice bearing tumours with different amounts of VEGF expression was compared to that of isotype-matched control antibody (111In-IgG1κ) with an excess of unlabelled bevacizumab. Intratumoural VEGF was evaluated using ELISA and Western blot analysis. The effect of anti-angiogenesis therapy was tested by measuring tumour uptake of 111In-bevacizumab in comparison to 111In-IgG1κ following administration of rapamycin to mice bearing FaDu xenografts. Uptake was measured using gamma counting of ex vivo tumours and effect on vasculature by using anti-CD31 microscopy.ResultsSpecific uptake of 111In-bevacizumab in VEGF-expressing tumours was observed. Rapamycin led to tumour growth delay associated with increased relative vessel size (8.5 to 10.3, P = 0.045) and decreased mean relative vessel density (0.27 to 0.22, P = 0.0015). Rapamycin treatment increased tumour uptake of 111In-bevacizumab (68%) but not 111In-IgGκ and corresponded with increased intratumoural VEGF165.Conclusions111In-bevacizumab accumulates specifically in VEGF-expressing tumours, and changes after rapamycin therapy reflect changes in VEGF expression. Antagonism of mTOR may increase VEGF in vivo, and this new finding provides the basis to consider combination studies blocking both pathways and a way to monitor effects.

Abstract 1062: Imaging DNA damage response (DDR) during oncogenesis.

Introduction: DNA damage repair (DDR) signalling is upregulated during tumorigenesis and acts as a p53-mediated block on proliferation. Expression of the DNA double strand break (DSB) repair protein, γH2AX, is induced by the activated kinases pATM or pATR during oncogenesis. Previously, we showed that γH2AX presents an abundant epitope for non-invasive in vivo imaging of DSBs. We used 111In-labelled anti-γH2AX antibodies, conjugated to the cell penetrating peptide, TAT, to non-invasively image DDR during oncogenesis in a genetically engineered mouse model of HER2/neu-overexpression driven breast cancer. Methods: Balb/neuT mice, genetically modified to express mutated rat neuT under MMTV promotor control, form multiple palpable carcinomas in mammary fat pads when animals are 130 days old. SPECT images were acquired weekly from balb/neuT mice (age 40-140 days; n=23) 24 h after i.v. injection of 111In-labelled anti-γH2AX-Tat or the non-selective agent, 111In-rIgG-Tat using a small animal SPECT/CT scanner. 111In uptake in fat pads was determined using volume of interest analysis. 111In uptake of >5%ID/g was deemed positive. Anatomical and histological changes were assessed at different ages using DCE-MRI imaging and immunohistochemistry. Results: Balb/neuT mice that were 80 days old developed multiple hyperplastic and dysplastic lesions in mammary fat pads. γH2AX foci were observed in these regions in balb/neuT mice that were 80-100 days old (10-15 foci/cell), but were less numerous in overt tumor tissue in 130-day-old mice (4-5 foci/cell). γH2AX foci were not observed in normal tissues in older mice (0 foci/cell), in mammary fat pads in younger mice (0 foci/cell), or in wild type mice (0 foci/cell). Serial SPECT imaging revealed a 7-fold increase in 111In-anti-γH2AX-Tat accumulation in mammary fat pads in mice 80-110 days old (up to 8.5 %ID/g), compared to non-specific control (P=0.0007), but not in younger or older mice (P>0.05). Repeated SPECT imaging itself did not influence tumor occurrence (P>0.05). The median time to detection of positive tissue was 96 days, much sooner than detection of lesions >150 μm by DCE-MRI (117 days), or palpation (130 days) (P Conclusion: Using a γH2AX-targeted radiopharmaceutical, we were able to image the DNA damage response during neuT-mediated oncogenesis in balb/neuT mice. DDR imaging identified neoplastic tissue significantly earlier than anatomical imaging. These results suggest that γH2AX imaging has potential as a screening tool for cancer-prone individuals. Citation Format: Bart Cornelissen, Sarah Able, Veerle Kersemans, Katherine A. Vallis. Imaging DNA damage response (DDR) during oncogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1062. doi:10.1158/1538-7445.AM2013-1062

Abstract 365: DNA double-strand break imaging with anti-γH2AX antibodies does not alter DNA repair kinetics

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Introduction: DNA double-strand breaks (dsb) are caused by exposure to radiotherapy and various anticancer drugs and are very deleterious. Upon dsb formation, histone H2AX is phosphorylated to form γH2AX foci at the break site. We have reported the development of a non-invasive in vivo DNA dsb imaging agent, based on anti-γH2AX IgG, modified by addition of the cell penetrating and nuclear localizing peptide, TAT. It was demonstrated that fluorescent and radiolabelled anti-γH2AX-TAT was internalized into cancer cells, and retained specifically in cells expressing γH2AX foci, through binding to γH2AX. Using in vivo fluorescence and SPECT imaging, we showed tumour uptake correlates with the extent of DNA dsb damage after radiation therapy (Cornelissen et al. Cancer Res 2011 71:4539). Ideally, imaging γH2AX in this way should not alter the physiology/ biology of the imaged organism. Therefore, we investigated the influence of anti-γH2AX-Tat on DNA dsb repair kinetics using comet assays and γH2AX and 53BP1 foci kinetics. These data were applied using a published mathematical model of non-homologous end joining (NHEJ) by Cucinotta et al. (Rad Res 2008 169, 214-222). Methods: A panel of four carcinoma cells (MCF7, MDA-MB-231/H2N, MDA-MB-468, MCF7) was exposed to a range of concentrations of anti-γH2AX-Tat (0 - 0.5 μg/mL) and irradiated 1 h later (IR; 137Cs, 0.95 Gy/min, 0-4 Gy). At selected time points, cells were analysed using γH2AX and 53BP1 foci staining and counting and comet assays. Foci counting was performed automatically using an InCell analyser. Comet assay results were analysed using software developed in house and expressed as Olive Tail Moment. γH2AX foci kinetics data were modelled in silico using a concatenary model or an extended version of the NHEJ model, allowing for anti-γH2AX-Tat binding to γH2AX. The kinetics of dsb formation and resolution were calculated from the model (dsbcal), and validated using comet assay data. Results: The number of γH2AX foci/cell was maximal at 0.5-1 h post IR. The affinity (KD) of anti-γH2AX-Tat for γH2AX was 25 nM. There was a trend towards a dose-dependent increase of the maximum number of foci. The concatenary model revealed no significant differences between treated and non-treated cells. However, using the NHEJ model, a dose-dependent decrease in the rate of phosphorylation of γH2AX was demonstrated (in MCF7 cells exposed to 0-0.5 μg/mL anti-γH2AX-Tat, κPγ = 2507-1462 copy−1 h−1; p 0.05). This was confirmed by comet assays. Conclusion: Anti-γH2AX-TAT binding to γH2AX reduces the rate of formation of new γH2AX foci, but has no significant influence on DNA dsb repair. Therefore, the use of γH2AX-Tat for imaging DNA dsbs does not alter DNA dsb status. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 365. doi:1538-7445.AM2012-365