A key role for galectin-1 in sprouting angiogenesis revealed by novel rationally designed antibodies.

Galectins are carbohydrate binding proteins that function in many key cellular processes. We have previously demonstrated that galectins are essential for tumor angiogenesis and their expression is associated with disease progression. Targeting galectins is therefore a potential anti-angiogenic and anti-cancer strategy. Here, we used a rational approach to generate antibodies against a specific member of this conserved protein family, i.e. galectin-1. We characterized two novel mouse monoclonal antibodies that specifically react with galectin-1 in human, mouse and chicken. We demonstrate that these antibodies are excellent tools to study galectin-1 expression and function in a broad array of biological systems. In a potential diagnostic application, radiolabeled antibodies showed specific targeting of galectin-1 positive tumors. In a therapeutic setting, the antibodies inhibited sprouting angiogenesis in vitro and in vivo, underscoring the key function of galectin-1 in this process.

A Digital Preclinical PET/MRI Insert and Initial Results.

Combining Positron Emission Tomography (PET) with Magnetic Resonance Imaging (MRI) results in a promising hybrid molecular imaging modality as it unifies the high sensitivity of PET for molecular and cellular processes with the functional and anatomical information from MRI. Digital Silicon Photomultipliers (dSiPMs) are the digital evolution in scintillation light detector technology and promise high PET SNR. DSiPMs from Philips Digital Photon Counting (PDPC) were used to develop a preclinical PET/RF gantry with 1-mm scintillation crystal pitch as an insert for clinical MRI scanners. With three exchangeable RF coils, the hybrid field of view has a maximum size of 160 mm × 96.6 mm (transaxial × axial). 0.1 ppm volume-root-mean-square B 0-homogeneity is kept within a spherical diameter of 96 mm (automatic volume shimming). Depending on the coil, MRI SNR is decreased by 13% or 5% by the PET system. PET count rates, energy resolution of 12.6% FWHM, and spatial resolution of 0.73 mm (3) (isometric volume resolution at isocenter) are not affected by applied MRI sequences. PET time resolution of 565 ps (FWHM) degraded by 6 ps during an EPI sequence. Timing-optimized settings yielded 260 ps time resolution. PET and MR images of a hot-rod phantom show no visible differences when the other modality was in operation and both resolve 0.8-mm rods. Versatility of the insert is shown by successfully combining multi-nuclei MRI ((1)H/(19)F) with simultaneously measured PET ((18)F-FDG). A longitudinal study of a tumor-bearing mouse verifies the operability, stability, and in vivo capabilities of the system. Cardiac- and respiratory-gated PET/MRI motion-capturing (CINE) images of the mouse heart demonstrate the advantage of simultaneous acquisition for temporal and spatial image registration.

Noninvasive visualization of tumoral fibrin deposition using a peptidic fibrin-binding single photon emission computed tomography tracer.

Fibrin deposition plays an important role in the formation of mature tumor stroma and provides a facilitating scaffold for tumor angiogenesis. This study investigates the potential of the (111)In-labeled fibrin-binding peptide EPep for SPECT imaging of intratumoral fibrin deposition. (111)In-EPep and negative control (111)In-NCEPep were synthesized and characterized in vitro. In vivo SPECT images and ex vivo biodistribution profiles and autoradiographs were obtained in a fibrin-rich BT-20 breast cancer mouse model. Furthermore, biodistribution profiles were obtained in the fibrin-poor MDA-MD-231 model. In vitro, (111)In-EPep displayed significantly more binding than (111)In-NCEPep toward human and mouse derived fibrin. SPECT/CT images displayed a marked SPECT signal in the tumor area for BT-20 tumor bearing mice injected with EPep but not for mice injected with NCEPep. Biodistribution profiles of BT-20 tumor bearing mice 3 h post-tracer injection showed significantly higher tumor uptake for EPep with respect to NCEPep (0.39 ± 0.14 and 0.11 ± 0.03% ID g(-1), respectively), whereas uptake in other organs was similar for EPep and NCEPep. Autoradiography of BT-20 tumor sections displayed a high signal for EPep which colocalized with intratumoral fibrin deposits. Histological evaluation of MDA-MB-231 tumor sections displayed no significant tumor stroma and only minute fibrin deposits. Biodistribution profiles in MDA-MB-231 tumor bearing mice 3 h post-injection showed EPep tumor uptake (0.14 ± 0.04% ID g(-1)) which was significantly lower with respect to EPep BT-20 tumor uptake, indicating fibrin-specificity of EPep tumoral uptake. In conclusion, this work demonstrates the potential of EPep SPECT imaging for visualization of tumoral fibrin deposition.

The promise of immuno-PET in radioimmunotherapy.

Immuno-PET as a quantitative imaging procedure before or concomitant with radioimmunotherapy is an attractive option to improve confirmation of tumor targeting and especially assessment of radiation dose delivery to both tumor and normal tissues. General information about PET, PET systems, and quantification is provided in this review. The requirements for an appropriate positron emitter and characteristics of the most attractive candidate emitters for immuno-PET are discussed. An overview of preclinical and clinical immuno-PET studies reported in the literature is provided.

High-quality 124I-labelled monoclonal antibodies for use as PET scouting agents prior to 131I-radioimmunotherapy.

PURPOSE: Monoclonal antibodies (MAbs) labelled with 124I are an attractive option for quantitative imaging with positron emission tomography (PET) in a scouting procedure prior to 131I-radioimmunotherapy (131I-RIT). In this study, three important items in the labelling of MAbs with 124I were introduced to obtain optimal and reproducible product quality: restoration of radiation-induced inorganic deterioration of the starting 124I solution, radiation protection during and after 124I labelling, and synchronisation of the I/MAb molar ratio. METHODS: A new method was applied, using an NaIO3/NaI carrier mix, realising in one step >90% restoration of deteriorated 124I into the iodide form and chemical control over the I/MAb molar ratio. Chimeric MAb (cMAb) U36 and the murine MAbs 425 and E48 were labelled with 124I using the so-called Iodogen-coated MAb method, as this method provides optimal quality conjugates under challenging radiation conditions. As a standardising condition, NaIO3/NaI carrier mix was added at a stoichiometric I/MAb molar ratio of 0.9. For comparison, MAbs were labelled with 131I and with a mixture of 124I, 123I, 126I and 130I. RESULTS: Labelling with 124I in this setting resulted in overall yields of >70%, a radiochemical purity of >95%, and preservation of MAb integrity and immunoreactivity, including at the patient dose level (85 MBq). No significant quality differences were observed when compared with 131I products, while the iodine isotope mixture gave exactly the same labelling efficiency for each of the isotopes, excluding a different chemical reactivity of 124I-iodide. The scouting performance of 124I-cMAb U36 labelled at the patient dose level was evaluated in biodistribution studies upon co-injection with 131I-labelled cMAb U36, and by PET imaging in nude mice bearing the head and neck cancer xenograft line HNX-OE. 124I-cMAb and 131I-cMAb U36 labelled with a synchronised I/MAb molar ratio gave fully concordant tissue uptake values. Selective tumour uptake was confirmed with immuno-PET, revealing visualisation of 15 out of 15 tumours. CONCLUSION: These results pave the way for renewed evaluation of the potential of 124I-immuno-PET for clinical applications.

PET radioimmunoscintigraphy of renal cell cancer using 89Zr-labeled cG250 monoclonal antibody in nude rats.

INTRODUCTION: With the introduction of positron-emitting radionuclides with half-lifes in days, such as 89Zr and 124I, radioimmunoscintigraphy (RIS) with positron-emitter-labeled monoclonal antibodies (moAbs) becomes feasible. RIS, using positron emission tomography (immuno-PET), combines the specific localization of an antibody with the high resolution of a PET camera. In the present study, scintigraphic tumor imaging using chimeric moAb G250 labeled with 89Zr (immuno-PET) or 111In (RIS), and [18F]FDG-(PET) was explored in rats with s.c. renal cell carcinoma (RCC) tumors. METHODS: Nude rats (6-8 rats per group) with s.c. SK-RC-52 tumors were i.v. injected with 4 MBq 111InDTPA-cG250, 20 MBq 89Zr-Df-cG250 or 4 MBq [18F]FDG. Planar 111In-DTPA-cG250 images were obtained 5 minutes, and 24, 48, and 72 hours postinjection (p.i.). 3D PET imaging was performed 5 minutes, and 24, 48, and 72 hours after a 89Zr-Df-cG250 injection and 1 hour after a [18F]FDG injection using a Siemens ECAT EXACT PET camera. Rats were killed after the last imaging session, and the uptake of the radiolabel in the dissected tissues was determined. RESULTS: Both radiolabeled antibody preparations were stable during 4 days of incubation in serum at 37 degrees C, and the immunoreactivity was preserved. Two (2) days after injection, s.c. tumors (100 mg) were clearly visualized, both with 89Zr-Df-cG250 and 111In-DTPA-cG250. Tumors were not visualized with [18F]FDG (uptake in tumor of 0.5 +/- 0.1 %ID/g, 1 hour p.i.). The biodistribution experiments showed an identical uptake in the tumor for both 89Zr-Df-cG250 and 111In-DTPA-cG250 at 3 days p.i. (5.0 +/- 2.4 and 4.9 +/- 2.9 %ID/g, respectively). Blood levels at 3 days p.i. were also identical (1.4 +/- 0.4 versus 1.7 +/- 0.7 %ID/g), and no significant differences were found in the biodistribution of normal tissues between the two radiolabeled cG250 preparations. CONCLUSION: The cG250 antibody can be stably labeled with the positron-emitter 89Zr, while preserving the immunoreactivity of the moAb. In this rat model, the in vivo biodistribution of 89Zr-Df-cG250 was identical to that of 111In-DTPA-cG250. Immuno-PET of RCC is feasible with 89Zr-cG250, and relatively small tumors could be visualized, even without a dedicated PET camera for small animals.

Quantitative 89Zr immuno-PET for in vivo scouting of 90Y-labeled monoclonal antibodies in xenograft-bearing nude mice.

UNLABELLED: Immuno-PET as a scouting procedure before radioimmunotherapy (RIT) aims at the confirmation of tumor targeting and the accurate estimation of radiation dose delivery to both tumor and normal tissues. Immuno-PET with (89)Zr-labeled monoclonal antibodies (mAbs) and (90)Y-mAb RIT might form such a valuable combination. In this study, the biodistribution of (89)Zr-labeled and (88)Y-labeled mAb ((88)Y as substitute for (90)Y) was compared and the quantitative imaging performance of (89)Zr immuno-PET was evaluated. METHODS: Chimeric mAb (cmAb) U36, directed against an antigen preferentially expressed in head and neck cancer, was labeled with (89)Zr using the bifunctional chelate N-succinyldesferrioxamine B (N-sucDf) and with (88)Y using the bifunctional chelate p-isothiocyanatobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (p-SCN-Bz-DOTA). The radioimmunoconjugates were coinjected in xenograft-bearing nude mice, and biodistribution was determined at 3, 24, 48, 72, and 144 h after injection. (89)Zr was evaluated and compared with (18)F in phantom studies to determine linearity, resolution, and recovery coefficients, using a high-resolution research tomograph PET scanner. The potential of PET to quantify cmAb U36-N-sucDf-(89)Zr was evaluated by relating image-derived tumor uptake data (noninvasive method) to (89)Zr uptake data derived from excised tumors (invasive method). RESULTS: (89)Zr-N-sucDf-labeled and (88)Y-p-SCN-Bz-DOTA-labeled cmAb U36 showed a highly similar biodistribution, except for sternum and thigh bone at later time points (72 and 144 h after injection). Small differences were found in kidney and liver. Imaging performance of (89)Zr approximates that of (18)F, whereas millimeter-sized (19-154 mg) tumors were visualized in xenograft-bearing mice after injection of cmAb U36-N-sucDf-(89)Zr. After correction for partial-volume effects, an excellent correlation was found between image-derived (89)Zr tumor radioactivity and gamma-counter (89)Zr values of excised tumors (R(2) = 0.79). CONCLUSION: The similar biodistribution and the favorable imaging characteristics make (89)Zr a promising candidate for use as a positron-emitting surrogate for (90)Y.

Long-lived positron emitters zirconium-89 and iodine-124 for scouting of therapeutic radioimmunoconjugates with PET.

Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. In the present study we evaluated the potential of the positron emitters zirconium-89 ((89)Zr) and iodine-124 ((124)I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (t(1/2) 3.27 and 4.18 days, respectively). After radiolabeling of the head and neck squamous cell carcinoma (HNSCC)-selective chimeric antibody (cMAb) U36, the biodistribution of two diagnostic (cMAb U36-N-sucDf-(89)Zr and cMAb U36-(124)I) and three therapeutic radioimmunoconjugates (cMAb U36-p-SCN-Bz-DOTA-(88)Y-with (88)Y being substitute for (90)Y, cMAb U36-(131)I, and cMAb U36-MAG3-(186)Re) was assessed in mice with HNSCC-xenografts, at 24, 48, and 72 hours after injection. Two patterns of biodistribution were observed, one pattern matching for (89)Zr- and (88)Y-labeled cMAb U36 and one pattern matching for (124)I-, (131)I-, and (186)Re-cMAb U36. The most remarkable differences between both patterns were observed for uptake in tumor and liver. Tumor uptake levels were 23.2 +/- 0.5 and 24.1 +/- 0.7%ID/g for the (89)Zr- and (88)Y-cMAb U36 and 16.0 +/- 0.8, 15.7 +/- 0.79 and 17.1 +/- 1.6%ID/g for (124)I-, (131)I-, and (186)Re-cMAb U36-conjugates, respectively, at 72 hours after injection. For liver these values were 6.9 +/- 0.8 ((89)Zr), 6.2 +/- 0.8 ((88)Y), 1.7 +/- 0.1 ((124)I), 1.6 +/- 0.1 ((131)I), and 2.3 +/- 0.1 ((186)Re), respectively. These preliminary data justify the further development of antibody-PET with (89)Zr-labeled MAbs for scouting of therapeutic doses of (90)Y-labeled MAbs. In such approach (124)I-labeled MAbs are most suitable for scouting of (131)I- and (186)Re-labeled MAbs.

89Zr immuno-PET: comprehensive procedures for the production of 89Zr-labeled monoclonal antibodies.

UNLABELLED: The use of immuno-PET, the combination of PET with monoclonal antibodies (mAbs), is an attractive option to improve tumor detection and mAb quantification. The long-lived positron emitter (89)Zr has ideal physical characteristics for immuno-PET, such as a half-life of 3.27 d, which is compatible with the time needed for intact mAbs to achieve optimal tumor-to-nontumor ratios. Thus far, a major limitation in the use of (89)Zr has been the lack of suitable methods for its stable coupling to mAbs. In this article, practical protocols for reproducible isolation of highly pure (89)Zr and the production of optimal-quality mAb-(89)Zr conjugates are provided. METHODS: (89)Zr was produced by a (p,n) reaction on natural yttrium ((89)Y), isolated with a hydroxamate column, and used for labeling of premodified mAbs. mAbs were premodified with a novel bifunctional derivative of the chelate desferrioxamine B (Df) via a new linker chemistry. To this end, Df was initially succinylated (N-sucDf), temporarily filled with Fe(III), esterified by use of tetrafluorophenol, and then directly coupled to mAbs. Chimeric mAb (cmAb) U36, directed against head and neck cancer, was used for in vitro and in vivo evaluation. The in vitro stability of cmAb U36-N-sucDf-(89)Zr was assessed in human serum, and its in vivo behavior was evaluated by biodistribution and PET imaging studies in tumor-bearing nude mice. A cmAb U36-Df-(89)Zr conjugate containing a previously described succinimide ring-thioether unit in the linker was used as a reference. RESULTS: (89)Zr was produced in large batches (6.5-13.5 GBq) and isolated with improved radionuclidic purity (>99.99%) and high yield (>94%). The Df-premodified mAbs gave (89)Zr-labeling efficiencies of 80% within 30 min, resulting in conjugates with preserved integrity and immunoreactivity. With respect to stability, the novel cmAb U36-N-sucDf-(89)Zr conjugate appeared to be superior to the reference conjugate. In vivo, the novel conjugate demonstrated selective tumor targeting, and on PET images obtained at 24, 48, and 72 h after injection of this conjugate, small tumors in the range of 19-154 mg were readily visualized. CONCLUSION: Methods were developed for improved purification of the long-lived positron emitter (89)Zr. Moreover, a novel bifunctional Df chelate was synthesized for the reproducible coupling of (89)Zr to mAbs. The suitability of such conjugates to detect millimeter-sized tumors in xenograft-bearing nude mice was demonstrated.

Tumor targeting properties of monoclonal antibodies with different affinity for target antigen CD44V6 in nude mice bearing head-and-neck cancer xenografts.

The CD44 protein family consists of isoforms with tissue-specific expression, which are encoded by standard exons and up to 9 alternatively spliced variant exons (v2-v10) of the same gene. The murine MAbs U36 and BIWA-1, directed against overlapping epitopes within the v6 region of CD44, have previously been shown to efficiently target HNSCC. We herein report on the construction of 1 chimeric (BIWA-2) and 2 humanized (BIWA-4 and BIWA-8) derivatives of BIWA-1. Together with U36 and BIWA-1, these new antibodies were evaluated for affinity to the antigen in vitro as well as for biodistribution and efficacy in RIT using nude mice bearing the HNSCC xenograft line HNX-OE. As determined by surface plasmon resonance, the MAbs bound to CD44v6 with an up to 46-fold difference in affinity (K(d) ranging from 1.1 x 10(-8) to 2.4 x 10(-10) M) with the following ranking: mMAb U36 < hMAb BIWA-4 < hMAb BIWA-8 < mMAb BIWA-1 approximately cMAb BIWA-2. To evaluate their in vivo tumor-targeting properties, 2 MAbs with identical murine or human isotype were labeled with either (131)I or (125)I and administered simultaneously (50 microg/10 microCi each) as pairs showing a stepwise decrease in the difference in affinity: U36 vs. BIWA-1 (35.0-fold difference), BIWA-4 vs. BIWA-2 (14.0-fold) and BIWA-4 vs. BIWA-8 (4.0-fold). Biodistribution was assessed at 1, 2, 3 or 4 and 7 days after injection. Remarkably, for all 3 MAb pairs tested, the lower-affinity MAb showed a higher degree and specificity of tumor localization. The difference in tumor localization was more pronounced when the difference in affinity was larger. For example, 3 days after injection, the lower-affinity mMAb U36 showed a 50% higher tumor uptake than the higher-affinity mMAb BIWA-1, while blood levels and uptake in organs were similar. After labeling with (186)Re (300 or 400 microCi), the same MAb pairs showed RIT efficacy consistent with the biodistribution data: (186)Re-U36 was more effective than (186)Re-BIWA-1, (186)Re-BIWA-4 was slightly more effective than (186)Re-BIWA-2 and (186)Re-BIWA-4 and (186)Re-BIWA-8 demonstrated similar efficacy. Based on these data, we conclude that antibodies with markedly lower affinity to a given target antigen (e.g., U36, BIWA-4) may show superior tumor targeting in comparison with higher-affinity versions of these antibodies.