6 research outputs found
Preloading with Unlabeled CA19.9 Targeted Human Monoclonal Antibody Leads to Improved PET Imaging with <sup>89</sup>Zr-5B1
CA19.9
is one of the most commonly occurring and highest density
antigens in >90% of pancreatic cancers, making it an excellent
target
for monoclonal antibody (mAb)-based imaging and therapy applications.
Preloading of unlabeled antibodies to enhance targeting of a radiolabeled
mAb has been previously described both for imaging and radioimmunotherapy
studies for other targets. We investigated the effect of preloading
with the unmodified anti-CA19.9 antibody 5B1 on the uptake and contrast
of the PET tracer <sup>89</sup>Zr-5B1 in subcutaneous and orthotopic
murine models of pancreatic cancer utilizing Capan-2 xenografts, known
to both express CA19.9 and shed antigen into circulation. Biodistribution
and PET imaging studies with <sup>89</sup>Zr-5B1 alone showed high
levels in the liver, spleen, and lymph nodes of mice with subcutaneous
Capan-2 tumor xenografts when administered without preinjection of
5B1. When unlabeled 5B1 was administered prior to <sup>89</sup>Zr-5B1,
the tracer significantly enhanced image contrast and tumor to tissue
ratios in the same model, and the improvement was related to the time
interval between the injections. Moreover, tumors were clearly delineated
in an orthotopic pancreatic cancer model using our optimized approach.
Taken together, these data suggest that preloading with 5B1 can improve <sup>89</sup>Zr-5B1 imaging of disease in a Capan-2 mouse model and that
exploration of preloading may have clinical utility for ongoing clinical
investigations
Optimization of a Pretargeted Strategy for the PET Imaging of Colorectal Carcinoma via the Modulation of Radioligand Pharmacokinetics
Pretargeted
PET imaging has emerged as an effective strategy for
merging the exquisite selectivity of antibody-based targeting vectors
with the rapid pharmacokinetics of radiolabeled small molecules. We
previously reported the development of a strategy for the pretargeted
PET imaging of colorectal cancer based on the bioorthogonal inverse
electron demand Diels–Alder reaction between a tetrazine-bearing
radioligand and a transcyclooctene-modified huA33 immunoconjugate.
Although this method effectively delineated tumor tissue, its clinical
potential was limited by the somewhat sluggish clearance of the radioligand
through the gastrointestinal tract. Herein, we report the development
and in vivo validation of a pretargeted strategy for the PET imaging
of colorectal carcinoma with dramatically improved pharmacokinetics.
Two novel tetrazine constructs, Tz-PEG<sub>7</sub>-NOTA and Tz-SarAr,
were synthesized, characterized, and radiolabeled with <sup>64</sup>Cu in high yield (>90%) and radiochemical purity (>99%). PET
imaging
and biodistribution experiments in healthy mice revealed that although <sup>64</sup>Cu-Tz-PEG<sub>7</sub>-NOTA is cleared via both the gastrointestinal
and urinary tracts, <sup>64</sup>Cu-Tz-SarAr is rapidly excreted by
the renal system alone. On this basis, <sup>64</sup>Cu-Tz-SarAr was
selected for further in vivo evaluation. To this end, mice bearing
A33 antigen-expressing SW1222 human colorectal carcinoma xenografts
were administered huA33-TCO, and the immunoconjugate was given 24
h to accumulate at the tumor and clear from the blood, after which <sup>64</sup>Cu-Tz-SarAr was administered via intravenous tail vein injection.
PET imaging and biodistribution experiments revealed specific uptake
of the radiotracer in the tumor at early time points (5.6 ± 0.7 %ID/g at 1 h p.i.), high tumor-to-background activity ratios, and rapid
elimination of unclicked radioligand. Importantly, experiments with
longer antibody accumulation intervals (48 and 120 h) yielded slight
decreases in tumoral uptake but also concomitant increases in tumor-to-blood
activity concentration ratios. This new strategy offers dosimetric
benefits as well, yielding a total effective dose of 0.041 rem/mCi,
far below the doses produced by directly labeled <sup>64</sup>Cu-NOTA-huA33
(0.133 rem/mCi) and <sup>89</sup>Zr-DFO-huA33 (1.54 rem/mCi). Ultimately,
this pretargeted PET imaging strategy boasts a dramatically improved
pharmacokinetic profile compared to our first generation system and
is capable of clearly delineating tumor tissue with high image contrast
at only a fraction of the radiation dose created by directly labeled
radioimmunoconjugates
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 <sup>89</sup>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 <sup>89</sup>Zr, Alexa Fluor 680, or an easily and precisely tuned mixture of
the two reporters. In <i>in vivo</i> PET and fluorescence
imaging experiments, a hybrid <sup>89</sup>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
In Vivo Imaging of GLP-1R with a Targeted Bimodal PET/Fluorescence Imaging Agent
Accurate visualization and quantification
of β-cell mass
is critical for the improved understanding, diagnosis, and treatment
of both type 1 diabetes (T1D) and insulinoma. Here, we describe the
synthesis of a bimodal imaging probe (PET/fluorescence) for imaging
GLP-1R expression in the pancreas and in pancreatic islet cell tumors.
The conjugation of a bimodal imaging tag containing a near-infrared
fluorescent dye, and the copper chelator sarcophagine to the GLP-1R
targeting peptide exendin-4 provided the basis for the bimodal imaging
probe. Conjugation was performed via a novel sequential one-pot synthetic
procedure including <sup>64</sup>Cu radiolabeling and copper-catalyzed
click-conjugation. The bimodal imaging agent <sup>64</sup>Cu-E4-Fl
was synthesized in good radiochemical yield and specific activity
(RCY = 36%, specific activity: 141 ÎĽCi/ÎĽg, >98% radiochemical
purity). The agent showed good performance in vivo and ex vivo, visualizing
small xenografts (<2 mm) with PET and pancreatic β-cell mass
by phosphor autoradiography. Using the fluorescent properties of the
probe, we were able to detect individual pancreatic islets, confirming
specific binding to GLP-1R and surpassing the sensitivity of the radioactive
label. The use of bimodal PET/fluorescent imaging probes is promising
for preoperative imaging and fluorescence-assisted analysis of patient
tissues. We believe that our procedure could become relevant as a
protocol for the development of bimodal imaging agents
<sup>18</sup>F‑Based Pretargeted PET Imaging Based on Bioorthogonal Diels–Alder Click Chemistry
A first-of-its-kind <sup>18</sup>F pretargeted PET imaging approach
based on the bioorthogonal inverse electron demand Diels–Alder
(IEDDA) reaction between tetrazine (Tz) and trans-cyclooctene (TCO)
is presented. As proof-of-principle, a TCO-bearing immunoconjugate
of the anti-CA19.9 antibody 5B1 and an AlÂ[<sup>18</sup>F]ÂNOTA-labeled
tetrazine radioligand were harnessed for the visualization of CA19.9-expressing
BxPC3 pancreatic cancer xenografts. Biodistribution and <sup>18</sup>F-PET imaging data clearly demonstrate that this methodology effectively
delineates tumor mass with activity concentrations up to 6.4 %ID/g
at 4 h after injection of the radioligand
PET Imaging of Extracellular pH in Tumors with <sup>64</sup>Cu- and <sup>18</sup>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 (<sup>64</sup>Cu and <sup>18</sup>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 <sup>64</sup>Cu
or [<sup>18</sup>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 <sup>18</sup>F (4T1 uptake; 8.9 ± 1.7%ID/g at 4 h p.i.) or <sup>64</sup>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 <sup>18</sup>F- or <sup>64</sup>Cu-labeled NO2A-cysVar3