The effect of specimen processing on radiolabeled monoclonal antibody biodistribution

In vivo monitoring of distributional transport kinetics and extravasation of quantum dots in living rat liver

Although the unique optical properties of surface-modified quantum dots (QDs) have attracted wide interest in molecular biology and bioengineering, there are very few reports of their in vivo biodistribution, due to a lack of analytical techniques for characterizing the dynamic variation of QDs in living animals. In this study, we used an in vivo online monitoring system and a batch-wise elemental analytical method to investigate the biodistribution/extravasation of various surface-modified CdTeSe/ZnS (QDs) in rat liver. It is found that the surface modification dictated not only the blood retention profile but also the degree of extravasation and the clearance of extracellular QDs, making it an important variable for regulating the transfer and exchange process of QDs among three physiological compartments-bloodstream, extracellular space and Kupffer cells/hepatocytes.

Imaging of renal cancer using positron emission tomography with 2-deoxy-2-(18F)-fluoro-D-glucose: pilot animal and human studies

The feasibility of imaging renal cancers with 2-deoxy-2-[18F]-fluoro-D-glucose (FDG) and whole-body positron emission tomographic scanning was assessed in nude mice with human renal adenocarcinoma xenografts and then in 5 patients with primary renal cancer (4 adenocarcinomas and 1 transitional cell carcinoma). In nude mouse biodistribution studies tumor FDG uptake was maximal at 0.33 to 2 hours but tumor-to-blood ratios increased continuously to 7.8/l. by 4 hours after intravenous FDG injection. In all 5 patients primary and metastatic tumors were imaged within 1 hour by FDG positron emission tomography following intravenous injection of the FDG. By contrast, an hepatic hemangioma did not accumulate FDG. In summary, FDG metabolic and anatomical imaging of primary and metastatic renal cancer is feasible and in these pilot studies appears to be a promising imaging methodology that may be further enhanced by delayed imaging times. Additional study in a larger number of patients is essential to define better the accuracy and potential clinical use of this method.

Uptake of 2-deoxy, 2-(18F) fluoro-D-glucose in bladder cancer: animal localization and initial patient positron emission tomography

An orthotopically transplanted, locally metastasizing rat bladder tumor model was developed to evaluate the extent of uptake of fluoro-deoxy-glucose (FDG) in bladder cancer. Significant uptake of FDG in localized bladder tumors in rats was shown, with an average tumor-to-blood ratio of 39 at 2 hours after intravenous FDG administration. Metastases (3 nodal and 1 peritoneal) also showed significant uptake of FDG, with an average metastasis-to-blood ratio of 21.7, and tumor involved-to-normal lymph node ratio of 5.3. Because FDG is excreted in the urine, urinary FDG potentially could prevent the use of FDG/positron emission tomography (FDG/PET) scanning for localized bladder cancer. Bladder lavage successfully reduced the retention of FDG in the normal rat bladder, with an estimated uptake ratio of tumor-to-normal bladder of 13.1 after 5 ml. saline irrigation. Based on these data, we performed an FDG/PET scan of a patient with biopsy proved recurrent intravesical bladder cancer after radiation therapy. Computerized tomography (CT) of the pelvis showed abnormalities consistent with radiation scarring and extravesical tumor. Due to the scarring, the extent of tumor growth could not be determined. The patient also had pulmonary opacities seen on chest radiography. The FDG/PET scan of this patient showed significant extravesical uptake in the pelvis, confirming the abnormality noted on CT. Good images of the clinically apparent metastases in the chest also were obtained. These preliminary data indicate that FDG/PET imaging of bladder cancer is feasible and it may provide new information for the diagnosis and staging of patients with bladder cancer.

Improved monoclonal antibody tumor/background ratios with exchange transfusions

Blood exchange transfusions were performed in nude rats with subcutaneous HTB77 human ovarian carcinoma xenografts in an attempt to improve specific monoclonal antibody (MoAb) tumor/non-tumor uptake ratios. Animals were injected intravenously with both 131I-5G6.4 specific and 125I-UPC-10 non-specific MoAb. Twenty-four hours later 65-80% of the original blood was exchanged with normal heparinized rat blood and then these rodents were sacrificed. Exchange transfusion significantly (P less than 0.05) decreased normal tissue activities of 131I (except for muscle) by 63-85%, while tumor activity decreased only 5%. Tumor to background ratios increased from 0.1-0.8 to 2.3-6.3. Exchange transfusions substantially enhance tumor/normal tissue antibody uptake ratios and, along with plasmapheresis, may be useful in enhancing antibody localization in vivo, particularly for therapy.

Systemic perfusion: a method of enhancing relative tumor uptake of radiolabeled monoclonal antibodies

We evaluated the feasibility of systemic vascular perfusion with saline (mimicking plasmapheresis) as a method to enhance tumor-specific monoclonal antibody (MoAb) tumor/background ratios. Initially, groups of rats were injected intravenously (i.v.) with 131I-5G6.4 MoAb (murine IgG2aK reactive with ovarian carcinoma). These animal's radioactivity levels were determined by dose calibrator and they were imaged before and after perfusion which was conducted at 4 or 24 h post-antibody injection. Animals were sacrificed after perfusion, as were controls, and normal organ radioactivity levels determined. In addition, nude mice bearing HTB77 ovarian cancers subcutaneously were injected i.v. with 131I-5G6.4 MoAb and were imaged before and after systemic perfusion with saline 24 h post-5G6.4 injection. Perfusion in rats dropped whole-body 5G6.4 levels significantly at both perfusion times (P less than 0.0005). The drop in whole-body radioactivity with perfusion was significantly greater for the animals perfused at 4 h post i.v. 5G6.4 antibody injection (48.3 +/- 5.1%) than for those perfused at 24 h post i.v. antibody injection (32.9 +/- 2.9%) (P less than 0.025). In the nude mice with ovarian cancer xenografts, gamma camera images of tumors were visually and quantitatively (by computer image analysis) enhanced by perfusion, with a 2.33-fold greater decline in whole body uptake than in the tumor (P less than 0.05). These studies show that (1) much background antibody radioactivity can be removed using whole-body perfusion with saline, (2) that the decline in whole body activity is larger with 4 than 24 h perfusion and (3) tumor imaging can be enhanced by this approach.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiolabeled antibodies, albumin and antimony sulfide colloid: a comparison as lymphoscintigraphic agents

The kinetics of lymph node and systemic uptake of members of three different classes of lymphoscintigraphic agents were studied in normal laboratory rats. 99mTc antimony trisulfide colloid (TcSbC), 99mTc human serum albumin (TcHSA), 125I 5G6.4 (a murine IgG2ak monoclonal antibody), 125I 763.24T (a murine IgG1), and 125I FT166 ( a murine IgM monoclonal) all current or potential lymphoscintigraphic agents, were injected subcutaneously into the hind foot pads of healthy rats. Ipsilateral and contralateral popliteal lymph nodes were sampled up to 4 h post-injection. Subcutaneous injection resulted in far higher nodal uptake for all agents than i.v. delivery with ipsilateral popliteal node/blood ratios 1 h postsubcutaneous injection of: for TcSbC (1900) greater than 125I IgM (497) greater than TcHSA (72) greater than 125I Intact IgG2a or 125I IgG1 at approximately 10. Thus, while all agents achieve popliteal node/blood ratios far greater than unity, TcSbc has the greatest absolute and relative nodal accumulation, greater than the 125I IgM monoclonal antibody and TcHSA. Uptake of the intact 125I IgG antibodies is lowest. These data suggest that TcSbC in particular, as well as TcHSA and IgM may be most useful as non-specific nodel imaging agents, while the lower background activity of the IgGs may make targeting specific antigen in nodes more feasible.

Radioimmunodiagnosis of human-derived squamous cell carcinoma

Squamous cell carcinomas (SCC) of the head and neck are common and aggressive tumors. A murine IgG 2aK monoclonal antibody (A9) reactive with most SCCs was radiolabeled with I-131 and tested for localization and imaging ability in groups of nude mice bearing SCC tumors derived from two patients with head and neck cancer (UM-SCC-2 and UM-SCC-11B). The mice also received I-125 labeled isotype-matched control antibody UPC-10 for double-label counting. Animals were imaged at multiple time points post-injection and sacrificed 7-10 days later for assessment of the tissue distribution of the radiopharmaceuticals. In general, the tumors were visualized satisfactorily on gamma camera images of both the UM-SCC-2 and UM-SCC-11B tumor-bearing animals. While localization of the A9 antibody was mainly due to antibody specificity in the UM-SCC-2 tumor-bearing animals, there was also a large component of non-specific antibody localization in the UM-SCC-11B bearing animals. This may be due to greater central fluid space and or necrosis in the UM-SCC-11B tumors. This study demonstrates the feasibility of imaging human-derived squamous cell carcinomas with radiolabeled monoclonal antibody A9 and holds forth the possibility of therapy of this radiosensitive tumor in a like manner.

Intraperitoneal delivery of monoclonal antibodies: enhanced regional delivery advantage using intravenous unlabeled anti-mouse antibody

Radiolabeled monoclonal antibodies (MAb) delivered intraperitoneally expose cells in contact with peritoneal fluid to considerably higher levels of MAb than if the MAb dose were given intravenously. This regional delivery advantage for intact MAb is present mainly due to the relatively slow exit of MAb from the peritoneal fluid to the blood. Eventually, following i.p. injection, blood levels of MAb rise resulting in exposure of the animal to high systemic MAb levels and potential toxicity. In this series of experiments, systemic exposure was minimized by the administration of unlabeled goat polyclonal anti-mouse antibody intravenously from 1 1/2 to 6 h following i.p. MAb injection. This maneuver results in the formation of immune complexes with their subsequent clearance and dehalogenation by the reticuloendothelial system, thus minimizing systemic MAb exposure. This approach, of increasing systemic clearance of MAb, did not alter intraperitoneal MAb levels and thus significantly increased the regional delivery advantage to the peritoneal cavity by 70-100%. This approach provides an immunologic rationale for the further enhancement of MAb delivery to i.p. foci of malignant disease and may have diagnostic and therapeutic utility.

The influence of monoclonal antibody dose on tumor uptake of radiolabeled antibody

The impact of antibody protein dose on tumor accumulation of radiolabeled monoclonal antibody was studied in nude mice with xenografts of human melanomas. 225.28S, a murine monoclonal antibody reactive with a high-molecular weight antigen of melanoma, was radiolabeled with I-125 and administered intraperitoneally to nude mice with human melanoma xenografts. Three days later, the animals were sacrificed, and tumor and normal tissue uptake of I-125 antibody was determined. At doses of 6.25, 62.5, 625 and 1875 ug of monoclonal antibody, there were no significant differences in percent of injected dose reaching the tumor/g of tumor or in the non-tumor uptakes achieved. These findings indicate that in the melanoma system, antibody dose is not a critical determinant of tumor uptake, and additionally indicate that low doses of antibody protein are appropriate for studies involving radioiodinated antibody localization.