We have recently reported that a radioiodinated, DTPA-appended peptide, designated IMP-R1, is a residualizing iodine label that overcomes many of the limitations that have impeded the development of residualizing iodine for clinical use. In this study the potential of 131I-IMP-R1-RS7, an internalizing anti-EGP-1 monoclonal antibody, was evaluated by performing preclinical therapy studies in nude mice bearing Calu-3 human non-small cell carcinoma of the lung xenografis. Elimination of 6 of 9 established tumors (mean tumor volume=0.3 cm(3)) was observed using a single dose of 350 microCi/mouse of 131I-IMP-R1-RS7, with all animals tolerating the dose. At the same dose and specific activity of 131I-RS7, labeled using the conventional chloramine-T method, there were four deaths, and one complete remission in nine treated mice. At the maximum tolerated dose of conventionally 131I-labeled RS7, 275 microCi, mean stable disease for approximately 5 weeks was observed, with no complete responses. Specificity of the therapeutic effect was shown in an isotype-matched control experiment, where 131I-IMP-R1-RS7 was markedly more effective than the (131)I-IMP-R1-labeled control antibody. These studies demonstrate that (131)I-IMP-R1-RS7 provides a therapeutic advantage in comparison to conventional 131I-labeled RS7, as predicted by the increased tumor accretion observed previously in targeting studies. A direct comparison of the maximum tolerated doses of (131)I-IMP-R1-RS7 (350 microCi) and 90Y-DOTA-RS7 (105 microCi) was performed in this tumor model using large established tumors (mean tumor volume=0.85 cm(3)). Anti-tumor efficacy and toxicity of the two treatments were comparable.

Animals↗

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The role of radiolabeled antibodies in the treatment of non-Hodgkin's lymphoma: the coming of age of radioimmunotherapy.

This review summarizes the current clinical status of radioimmunotherapy (RAIT) in the treatment of patients with non-Hodgkin's lymphoma (NHL), as a prototype of the advances of RAIT in the management of cancer. Four radiolabeled antibody products are progressing towards commercialization for the RAIT of NHL: 131I-tositumomab (Bexxar), 90Y-ibritumomab tiuxetan, 90Y-epratuzumab (hLL2), and 131I-Lym-1. All except epratuzumab are murine monoclonal antibodies (Mabs) labeled with an isotope, except that ibritumomab (Zevalin) adds chimeric rituximab to the product, whereas epratuzumab is solely a humanized Mab. Bexxar and Zevalin target CD20, epratuzumab binds to CD22, and Lym-1 reacts with HLA-DR. Clinical studies have shown that all four antibody products can be safe and efficacious. Bexxar has been shown to induce responses that are relatively better than the prior chemotherapy, and has also been shown to be effective in combination with chemotherapy as a frontline therapy of low-grade and transformed NHL. However, since it is a fully murine Mab, it did show a approximately 60% HAMA rate in untreated patients. Zevalin has been found to be more effective than rituximab, its naked chimeric Mab counterpart, as well as in chemotherapy-relapsed low-grade NHL patients. Both radiolabeled epratuzumab and Lym-1 have shown efficacy in patients who have failed chemotherapy, either with low-grade or aggressive forms of NHL. It appears that Bexxar and Zevalin will be the first two radiolabeled antibodies that may be available for widespread use in the U.S., and will mark the final introduction of RAIT as an approved cancer treatment modality. Future studies will help define the role of these RAIT products in the management of NHL, especially as part of a multimodal therapy of this disease.

Antibodies, Monoclonal↗

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Localization of pancreatic cancer with radiolabeled monoclonal antibody PAM4.

Experimental animal studies were performed with (111)In-labeled PAM4 anti-MUC1 antibody along with (111)In-labeled control antibody. Tumor uptake of radiolabeled PAM4 was significantly higher than for the control antibody at all time points. When normalized to a blood dose of 1500 cGy as an estimate of myelotoxicity, (90)Y-labeled PAM4 would provide 5344 cGy to the tumor, whereas an equitoxic dose of (90)Y-labeled control antibody would provide only 862 cGy to the tumor. In addition to the animal studies, five patients with proven pancreatic cancer were administered either (131)I-PAM4 IgG (n=2) or 99mTc-PAM4 Fab' (n=3). Tumor targeting was observed in four out of five patients. By immunohistochemistry, PAM4 was non-reactive with tumor from the one patient not targeted. Dosimetry from the patients given (131)I-PAM4 predicted that tumors would receive 10-20 cGy/mCi with tumor/red marrow dose ratios ranging from 3 to 10. Based upon these results, we have established a phase-I (111)In-labeled PAM4 imaging and (90)Y-labeled PAM4 therapy trial.

Aged↗

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Specifically targeting the CD22 receptor of human B-cell lymphomas with RNA damaging agents.

Targeting CD22 on human B-cells with a monoclonal antibody conjugated to a cytotoxic RNAse causes potent and specific killing of the lymphoma cells in vitro. This translates to anti-tumor effects in human lymphoma models in SCID mice. RNA damage caused by RNAses could be an important alternative to standard DNA damaging chemotherapeutics. Moreover, targeted RNAses may overcome problems of toxicity and immunogenicity associated with plant or bacterial toxin containing immunotoxins.

Animals↗

PubMedDate not supplied

Experimental pretargeting studies of cancer with a humanized anti-CEA x murine anti-[In-DTPA] bispecific antibody construct and a (99m)Tc-/(188)Re-labeled peptide.

The aim of this study was to localize (99m)Tc and (188)Re radionuclides to tumors, using a bispecific antibody (bsMAb) in a two-step approach where the radionuclides are attached to novel peptides incorporating moieties recognized by one arm of the bsMAb. A chemically cross-linked human/murine bsMAb, hMN-14 x 734 (Fab' x Fab'), anti-carcinoembryonic antigen [CEA] x anti-indium-DTPA was prepared as a prelude to constructing a fully humanized bsMAb for future clinical application. N,N'-o-Phenylenedimaleimide was used to cross-link the Fab' fragments of the two antibodies at their hinge regions. This construct was shown to be >92% pure and fully reactive with CEA and a divalent (indium)DTPA-peptide. For pretargeting purposes, a peptide, IMP-192 [Ac-Lys(In-DTPA)-Tyr-Lys(In-DTPA)-Lys(TscG-Cys-)-NH(2) ¿TscG = 3-thiosemicarbazonylglyoxyl¿], with two indium-DTPAs and a chelate for selectively binding (99m)Tc or (188)Re, was synthesized. IMP-192 was formulated in a "single dose" kit and later radiolabeled with (99m)Tc (94-99%) at up to 1836 Ci/mmol and with (188)Re (97%) at 459-945 Ci/mmol of peptide. [(99m)Tc]IMP-192 was shown to be stable by extensive in vitro and in vivo testing and had no specific uptake in the tumor with minimal renal uptake. The biodistribution of the hMN-14 x murine 734 bsMAb was compared alone and in a pretargeting setting to a fully murine anti-CEA (F6) x 734 bsMAb that was reported previously [Gautherot, E., Bouhou, J., LeDoussal, J.-M., Manetti, C., Martin, M., Rouvier, E., and Barbet, J. (1997) Therapy for colon carcinoma xenografts with bispecific antibody-targeted, iodine-131-labeled bivalent hapten. Cancer 80 (Suppl.), 2618-2623]. Both bsMAbs maintained their integrity and dual binding specificity in vivo, but the hMN-14 x m734 was cleared more rapidly from the blood. This coincided with an increased uptake of the hMN-14 x m734 bsMAb in the liver and spleen, suggesting an active reticuloendothelial cell recognition mechanism of this mixed species construct in naive mice. Animals bearing GW-39 human colonic cancer xenografts were injected with bsMAb (15 microg) and after allowing 24 or 72 h for the bsMAb constructs to clear from the blood (hMN-14 and murine F6 x 734, respectively), [(188)Re]IMP-192 (7 microCi) or [(99m)Tc]IMP-192 (10 microCi) was injected at a bsMAb:peptide ratio of 10:1. Tumor uptake of [(99m)Tc] or [(188)Re]IMP-192 was 12.6 +/- 5.2 and 16.9 +/- 5.5% ID/g at 3 h postinjection, respectively. Tumor/nontumor ratios were between 5.6 and 23 to 1 for every major organ, indicating that early imaging with (99m)Tc will be possible. Radiation absorbed doses showed a 4.8-, 7.2-, and a 12.6 to 1.0 tumor to blood, kidney, and liver ratios when (188)Re was used. Although this new bsMAb pretargeting approach requires further optimization, it already shows very promising targeting results for both radioimmunodetection and radioimmunotherapy of colorectal cancer.

Animals↗

PubMedDate not supplied

Conjugation of phenyl isothiocyanate derivatives of carborane to antitumor antibody and in vivo localization of conjugates in nude mice.

A systematic study of the conjugation of 1-(p-isothiocyanatophenyl)-1,2-dicarba-closo-[2-3H]dodeca borane(12), 3H-1, and 7-(p-isothiocyanatophenyl)dodecahydro-7,8-dicarba-nido -[8-3H] undecaborate(1-)ion, 3H-2, to the murine monoclonal anti-CSAp antibody, Mu-9, was carried out to compare charged and uncharged boron cages in their effect upon antibody loading. Approximately one neutral cage and four of the anionic cages were successfully linked to antibody in two separate conjugates which were subsequently radioiodinated and evaluated in vivo. No significant loss of the antibody or its immunoreactivity was observed in either case. In nude mice bearing GW-39 tumor xenografts the conjugate containing the anionic carborane derivative showed a reduced tumor uptake although the tumor:non-tumor ratio was similar to that of the native antibody. The carborane cage in 2 was radiolabeled with 125I followed by attempts to purify and conjugate product 4 to a model goat IgG protein. This exploratory conjugation study was undertaken as a prelude to linking new conjugation reagents, which contain multiple anionic boron cages, to antitumor antibodies. The latter conjugates are required to maximize boron loading for the purpose of neutron-capture therapy.

Animals↗

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Radiolabeling of monoclonal antibodies and fragments with technetium and rhenium.

Explore the source record for details and available documents.

Animals↗

PubMedDate not supplied

Pretargeting for cancer radioimmunotherapy with bispecific antibodies: role of the bispecific antibody's valency for the tumor target antigen.

The use of a divalent effector molecule improves bispecific antibody (bsMAb) pretargeting by enabling the cross-linking of monovalently bound bsMAb on the cell surface, thereby increasing the functional affinity of a bsMAb. In this work, it was determined if a bsMAb with divalency for the primary target antigen would improve bsMAb pretargeting of a divalent hapten. The pretargeting of a (99m)Tc-labeled divalent DTPA-peptide, IMP-192, using a bsMAb prepared by chemically coupling two Fab' fragments, one with monovalent specificity to the primary target antigen, carcinoembryonic antigen (CEA), and to indium-loaded DTPA [DTPA(In)], was compared to two other bsMAbs, both with divalency to CEA. One conjugate used the whole anti-CEA IgG, while the other used the anti-CEA F(ab')(2) fragment to make bsMAbs that had divalency to CEA, but with different molecular weights to affect their pharmacokinetic behavior. The rate of bsMAb blood clearance was a function of molecular weight (IgG x Fab' < F(ab')(2) x Fab' < Fab' x Fab' conjugate). The IgG x Fab' bsMAb conjugate had the highest uptake and longest retention in the tumor. However, when used for pretargeting, the F(ab')(2) x Fab' conjugate allowed for superior tumor accretion of the (99m)Tc-IMP-192 peptide, because its more rapid clearance from the blood enabled early intervention with the radiolabeled peptide when tumor uptake of the bsMAb was at its peak. Excellent peptide targeting was also seen with the Fab' x Fab' conjugate, albeit tumor uptake was lower than with the F(ab')(2) x Fab' conjugate. Because the IgG x Fab' bsMAb cleared from the blood so slowly, when the peptide was given at the time of its maximum tumor accretion, the peptide was captured predominantly by the bsMAb in the blood. Several strategies were explored to reduce the IgG x Fab' bsMAb remaining in the blood to take advantage of its 3-4-fold higher tumor accretion than the other bsMAb conjugates. A number of agents were tested, including those that could clear the bsMAb from the blood (e.g., galactosylated or nongalactosylated anti-id antibody) and those that could block the anti-DTPA(In) binding arm [e.g., DTPA(In), divalent-DTPA(In) peptide, and DTPA coupled to bovine serum albumin (BSA) or IgG]. When clearing agents were given 65 h after the IgG x Fab' conjugate (time of maximum tumor accretion for this bsMAb), (99m)Tc-IMP-192 levels in the blood were significantly reduced, but a majority of the peptide localized in the liver. Increasing the interval between the clearing agent and the time the peptide was given to allow for further processing of the bsMAb-clearing agent complex did not improve targeting. At the dose and level of substitution tested, galacosylated BSA-DTPA(In) was cleared too quickly to be an effective blocking agent, but BSA- and IgG-DTPA(In) conjugates were able to reduce the uptake of the (99m)Tc-IMP-192 in the blood and liver. Tumor/nontumor ratios compared favorably for the radiolabeled peptide using the IgG x Fab'/blocking agent combination and the F(ab')(2) x Fab' (no clearing/blocking agent), and peptide uptake 3 h after the blocking agent even exceeded that of the F(ab')(2) x Fab'. However, this higher level of peptide in the tumor was not sustained over 24 h, and actually decreased to levels lower than that seen with the F(ab')(2) x Fab' by this time. These results demonstrate that divalency of a bsMAb to its primary target antigen can lead to higher tumor accretion by a pretargeted divalent peptide, but that the pharmacokinetic behavior of the bsMAb also needs to be optimized to allow for its clearance from the blood. Otherwise, blocking agents will need to be developed to reduce unwanted peptide uptake in normal tissues.

Animals↗

PubMedDate not supplied

Thiolations, 99mTc labelings, and animal in vivo biodistributions of divalent monoclonal antibody fragments.

A number of divalent monoclonal antibody fragments have been derivatized with a bifunctional reagent containing a latent thiol group, and the conjugates were thiol-deprotected by exposure to aqueous hydroxylamine. This two-step procedure enabled convenient 99mTc labeling of thiolated MAb divalent fragments, using either performed 99mTc-glucoheptonate or [99mTc] pertechnetate and single-vial lyophilized formulations of the conjugate and tin. Nonspecific incorporation of radiolabel was negligible, if any, when using nonthiolated antibodies. In animal biodistributions, in nude mice bearing LS174T human colon carcinoma xenografts, the 99mTc-labeled MAb divalent fragments studied were found to result in a 3-fold reduction in the kidney uptake of radioactivity at 24 h, compared to a 99mTc-Fab, and also to lead to improvements in other tumor:nontumor ratios.

Animals↗