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...

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.

The aim of this study was to determine if pulsed high-intensity focused ultrasound (HIFU) exposures could enhance tumor uptake of 111 In-MX-B3, a murine IgG1k monoclonal antibody directed against the Le y antigen. Methods: MX-B3 was labeled with 111 In, purified, and confirmed for its binding to the antigenpositive A431 cell line. Groups of nude mice were inoculated subcutaneously with A431 tumor cells on both hind flanks. A tumor on one flank was treated with pulsed-HIFU; the other tumor was used as an untreated control. Within 10 min after the HIFU exposure, the mice received intravenous 111 In-MX-B3 for imaging and biodistribution studies. Mice were euthanized at 1, 24, 48, and 120 h after injection for biodistribution studies. Results: The HIFU exposure shortened the peak tumor uptake time (24 vs. 48 h for the control) and increased the peak tumor uptake value (38 vs. 25 %ID/g [percentage injected dose per gram] for the control). The HIFU effect on enhancing tumor uptake was greater at earlier times up to 24 h, but the effect was gradually diminished thereafter. The HIFU effect on enhancing tumor uptake was substantiated by nuclear imaging studies. HIFU also increased the uptake of the antibody in surrounding tissues, but the net increase was marginal compared with the increase in tumor uptake. Conclusion: This study demonstrates that pulsed-HIFU significantly enhances the delivery of 111 In-MX-B3 in human epidermoid tumors xenografted in nude mice. The results of this pilot study warrant further evaluation of other treatment regimens, such as repeated HIFU exposures for greater delivery enhancement of antibodies labeled with cytotoxic radioisotopes or pulsed-HIFU exposure in addition to a combined therapy of 90 Y-B3 and taxol to enhance the synergistic effect.

Purpose:To investigate the combined antitumor activity in mice of immunotoxin SS1P and Taxol.Methods: Immunodeficient mice were implanted with A431/K5 tumors expressing mesothelin. Established tumors were treated i.v. with immunotoxin SS1P alone, i.p. with Taxol alone, or with the two agents together. SS1P was radiolabeled with 111 In and used to study the effect of Taxol on its uptake by A431/K5 tumors. Results: Using doses at which either agent alone caused stabilization of tumor growth, the combination was synergistic causing long-lasting complete remissions in many animals. In contrast, synergy was not observed when the same cells were treated with these agents in vitro. Tumor uptake of 111In-SS1P was not affected by treatment withTaxol. Conclusion: The combination of Taxol and SS1P exerts a synergistic antitumor effect in animals but not in cell culture. This effect is not secondary to increased tumor uptake of the immunotoxin. Synergy could be due to improved immunotoxin distribution within the tumor or could involve factors released by other cell types in the tumors.