Current contrast agents generally have one function and can only be imaged in monochrome, therefore, the majority of imaging methods can only impart uniparametric information. A single nano-particle has the potential to be loaded with multiple payloads. Such multi-modality probes have the ability to be imaged by more than one imaging technique, which could compensate for the weakness or even combine the advantages of each individual modality. Furthermore, optical imaging using different optical probes enables us to achieve multi-color in vivo imaging, wherein multiple parameters can be read from a single image. To allow differentiation of multiple optical signals in vivo, each probe should have a close but different near infrared emission. To this end, we synthesized nano-probes with multi-modal and multi-color potential, which employed a polyamidoamine dendrimer platform linked to both radionuclides and optical probes, permitting dual-modality scintigraphic and 5-color near infrared optical lymphatic imaging using a multiple excitation spectrally-resolved fluorescence imaging technique. Keywordsdendrimer; scintigraphy; near infrared; fluorescence imaging; multiple modalities; multiple colors; lymphatic imaging No imaging modality is perfect. Each has its own distinct advantages and limitations. The simultaneous use of two or more modalities can help to overcome the limitation of each individual method and increase or improve the information obtained during an examination session. The combined use of Computed Tomography (CT) and Positron Emission Tomography (PET) is a successful example of multi-modal imaging: CT provides high resolution anatomical detail and PET provides functional information 1 . Currently they are very few examples of multi-modal imaging probes that can be detected by more than one technique: dual agents for recognition by both radionuclide and optical imaging 2,3 , or Magnetic Resonance (MR) and optical imaging 4-8 . Furthermore, the conventional imaging methods are generally monochrome and only able to detect one contrast agent at a time, limiting us to single parametric data. Single photon scintigraphy has been shown to have potential for simultaneously detecting two different imaging agents, i.e. technetium-99m and thallium-201, by energy resolution 9 . However, in this case, both the spatial and the energy resolutions were poor and did not allow for the reconstruction of a precise image from each agent. Multi-color optical imaging is simple to achieve with the technique of spectrally resolved imaging. Herein, two or more optical agents can be differentiated on the basis of their different emission spectra. Multi-color imaging is already commonplace in microscopic imaging and is beginning to be utilized for in vivo imaging 10-12 . However, in vivo imaging is essentially limited to long wavelength dyes that emit in the near-infrared (NIR) range (650-850 nm), in order to maximize depth penetration and limit the autofluorescence, background signal 13 .With this in mind we have synthe...
We evaluated the in vivo biodistribution of indium- and yttrium-labeled second-generation polyamidoamine dendrimer (PAMAM) conjugated with 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid (1B4M), a derivative of DTPA. In addition, we conjugated PAMAM-1B4M to humanized anti-Tac IgG (HuTac) and evaluated its in vitro and in vivo properties. PAMAM-1B4M was labeled with 111In at 37-48 MBq/mg (1.0-1.3 mCi/mg) or with 88Y at 3.7-4.8 MBq/mg (0.1-0. 13 mCi/mg), and an aliquot of radiolabeled conjugate was saturated with the corresponding stable yttrium or indium. Nontumor-bearing nude mice were injected intravenously with 55.5-66.6 kBq (1.5-1.8 microCi) of 88Y-labeled PAMAM-1B4M or with 185 kBq (5 microCi) of 111In-labeled PAMAM-1B4M. The mice were then sacrificed at 15 min, 90 min, 1 day, and 4 days postinjection. Then the PAMAM-1B4M was conjugated with HuTac and labeled with 111In at 111-259 MBq/mg (3-7 mCi/mg). Another preparation of 111In-labeled HuTac-PAMAM-1B4M was saturated with stable indium. Immunoreactivity of both preparations and biodistribution in normal mice 1 h after injection and in ATAC4 and A431 tumor-bearing mice 18 h after injection were evaluated and compared with those of 111In-labeled 1B4M-HuTac. We noted significantly higher accumulations (p< 0.05) of 111In-labeled and 88Y-labeled unsaturated PAMAM-1B4M than saturated preparations in the liver, kidney, spleen, and bone at most time points. The whole-body clearance times of unsaturated preparations were significantly slower than those of saturated preparations at all time points, with the exception of 168 h for 111In-labeled PAMAM-1B4M. The saturated preparation of 111In-labeled HuTac-PAMAM-1B4M showed lower hepatic uptake (27 +/- 2%ID/g) than the unsaturated (32 +/- 2%ID/g), but greater than the HuTac-1B4M control (10 +/- 0%ID/g). The splenic uptake showed 15 +/- 1, 38 +/- 5, and 8 +/- 1%ID/g for the saturated, unsaturated, and control, respectively. The biodistribution of the dendrimer conjugated HuTac in normal organs of tumor-bearing mice was similar to nontumor-bearing mice. Specific tumor (ATAC4) uptake was higher than that in nonspecific tumor (A431). In conclusion, we evaluated the biodistribution of radiolabeled PAMAM-1B4M. We noted high accumulation in the liver, kidney, and spleen, which significantly decreased when the chelates were saturated with the stable element. A similar phenomenon was observed between unsaturated and saturated 111In-labeled HuTac-PAMAM-1B4M, indicating that the PAMAM dendrimer had a detrimental effect on biodistribution.
Photoimmunotherapy (PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. Herein we compare two commonly available anti-EGFR monoclonal antibodies, cetuximab and panitumumab, for their effectiveness as PIT agents in EGFR positive tumor models. A photosensitizer, IR-700, conjugated to either cetuximab (cet-IR700) orpanitumumab (pan-IR700), was evaluated using EGFR-expressing A431 and MDAMB468-luc cells in 2D- and 3D-culture. PIT was conducted with irradiation of NIR light after exposure of the sample or animal to each conjugate. In vivo PIT was performed with fractionated exposure of NIR light after injection of each agent into A431 xenografts or a MDAMB468-luc orthotopic tumor bearing model. Cet-IR700 and pan-IR700 bound with equal affinity to the cells in 2D-culture and penetrated equally into the 3D-spheroid, resulting in identical PIT cytotoxic effects in vitro. In contrast, in vivo anti-tumor effects of PIT with cet-IR700 were inferior to that of pan-IR700. Assessment of the biodistribution showed lower accumulation into the tumors and more rapid hepatic catabolism of cet-IR700 compared to pan-IR700. Although cet-IR700 and pan-IR700 showed identical in vitro characteristics, pan-IR700 showed better therapeutic tumor responses than cet-IR700 in in vivo mice models due to the prolonged retention of the conjugate in the circulation, suggesting that retention in the circulation is advantageous for tumor responses to PIT. These results suggest that the choice of monoclonal antibody in photosensitizer conjugates may influence the effectiveness of PIT.
Monoclonal antibodies penetrate bulky tumors poorly after intravenous administration, in part because of specific binding to the target antigen. Experiments presented here demonstrate an analogous phenomenon in micrometastases; poor antibody penetration, attributable to a "binding-site barrier" phenomenon, can be seen in guinea pig micrometastases as small as 300 ,um in diameter. Increasing the dose of antibody can partially overcome this limitation, but at a cost in specificity. Six and 72 hr after injection, animals were sacrificed by CO2 inhalation. Organs were rapidly removed and weighed, and tissue radioactivity was determined. Lung tissues with metastases were frozen immediately in OCT compound (Tissue-Tek, Miles) and then processed for autoradiography and immunostaining. For high-dose experiments, 1000 ,ug of unlabeled D3 was added to 30 ,ug of labeled D3. Autoradiography and Immunostaining. Serial 20-,um sections were cut from the frozen lung tissues. For autoradiography, sections were placed on SB-5 film (Eastman Kodak) and exposed for 1-4 days. When 125I-labeled BL3 was coinjected with I311-labeled D3, images of the latter were obtained shortly after sacrifice, images of the former after eight 131I half-lives.The avidin-biotin peroxidase complex (ABC) method (29) was used to compare Ab and Ag distribution. Briefly, tissue sections were acetone-fixed for 10 min and incubated with blocking serum for 20 min. To assess Ag expression, sections were incubated with D3 Ab (20 ,ug/ml) for 1 hr at room temperature, biotinylated horse anti-mouse IgG for 45 min, ABC for three 30-min periods, and diaminobenzidine (Vector Laboratories). When injected D3 was assessed, incubation with D3 was omitted. Some sections were also stained for blood vessels by use of polyclonal rabbit anti-factor VIII and an alkaline phosphatase substrate, Vector Red (30). RESULTS AND DISCUSSIONIn this study, we have assessed the distribution of i.v. administered mAbs in experimental guinea pig lung micrometastases. Two weeks after i.v. injection of L10 cells, multiple metastases 100-1000 ,um in diameter could be seen in the lungs of all animals. This model (metastasis of guinea pig cancer in guinea pigs) is in many ways more relevant to the Abbreviations: Ab, antibody; mAb, monoclonal Ab; Ag, antigen.
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