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Peptide haptens [PubMed]

Clinical trials with bispecific antibodies

Application of multivalent antibodies [PubMed]

Rodents

[PubMed]

The use of [^99mTc]-DSPL was evaluated for the visualization of atherosclerotic lesions caused by proliferating smooth muscle cells in the femoral arteries of ApoE knockout mice and pretargeted with a Z2D3-F(ab')₂-anti-DTPA-F(ab')₂ bsmAb (Z2D3 is a murine chimeric Ab that specifically binds to an as yet uncharacterized complex lipid antigen that is produced only by proliferating smooth muscle cells) (3). For this study, Sprague-Dawley rats (n = 5 animals) were given an intramuscular injection of surrogate Z2D3 antigen-coated polystyrene beads (SAB) in the right hind leg; for use as controls, an equal number of unmodified beads (UMB) were injected into the left hind leg of the animals (3). The following day, all the animals were given an intravenous injection of the bsmAb, and 24 h later each animal was injected with 6.6 MBq (0.18 mCi) [^99mTc]-DSPL. Serial gamma planar whole-body images of the animals were recorded at 2 h and 24 h after the [^99mTc]-DSPL injection. At 2 h p.i., the SAB lesions were visible, but radioactivity was observed in the blood pool as well. At 24 h p.i., the SAB lesions, the liver, kidneys, and the bladder of the animals were clearly visible in the posteroanterior images of the rodents. Following the imaging session, the animals were euthanized, and normal thoracic muscle tissue and muscle areas injected with the SAB and the UMB were excised to determine the amount radioactivity present in the tissues. All results were presented as % of injected dose per gram tissue (% ID/g). Right leg muscle tissue harvested from four of the five rats injected with the bsmAb-coated polymer showed a significantly higher accumulation (P = 0.03) of radioactivity (0.000822 ± 0.00019% ID/g) compared with either the UMB (0.000525 ± 0.00017% ID/g) or the thoracic muscle (0.000467 ± 0.00017% ID/g; P = 0.01) areas. Presence of SAB in the right leg muscle area was confirmed by microscopic examination of the tissue.

In another study with rats (n = 4 animals), it was shown that femoral deendothelialization lesions in the left leg of the animals that were pretargeted with Z2D3-F(ab')₂-anti-DTPA-F(ab')₂ bsmAb could be visualized with [^99mTc]-DSPL (3). The mean ratio of tracer in the left femoral artery segment was 1.8 ± 0.7-fold higher (P = 0.04) than the control femoral artery segment in the right leg of the same animals.

Lung metastatic melanoma lesions pretargeted with the 2C5–6C31H3 bsMAb (prepared by conjugating an antinucleosomal targeting Ab (2C5) that recognizes a nucleosomal pan cancer antigen with an anti-DTPA Ab (6C31H3; the capturing Ab)) could be visualized using [^99mTc]-DSPL with SPECT (4). Mice (n = 5 animals) bearing B16-F10 cell metastatic tumors in the lungs were injected intravenously (i.v.) with 10 μg 2C5–6C31H3 bsmAb to pretarget the lesions 24 h before the imaging session (4). Control animals (n = 4 mice) bearing the tumors did not receive the pretargeting bsmAb. All the animals received an i.v. injection of ~37 MBq (~1.34 mCi) [^99mTc]-DSPL, and gamma planar images of the rodents were acquired at various time points ranging from 1 h p.i. to 24 h p.i. At 1 h p.i., the metastatic lesions were visible in the lungs of the pretargeted animals, but not in the non-pretargeted mice. In all the animals, the label was rapidly cleared through the kidneys, and there was little accumulation of the tracer in the liver. Presence of radioactivity in the lung lesions was confirmed with SPECT/computed tomography imaging.

The biodistribution of [^99mTc]-DSPL was studied in mice bearing lung metastatic melanoma lesions pretargeted with the 2C5–6C31H3 bsmAb (n = 5 animals) (4). For use as controls, non-pretargeted mice bearing lung metastatic melanoma lesions were injected with [^99mTc]-DSPL alone (n = 4 animals). Another group of normal mice (without the metastatic lesions in the lungs) were pretargeted with bsMab or the anti-DTPA Ab and injected with [^99mTc]-DSPL (n = 3 animals/treatment group). To determine the amount of radioactivity accumulated in the various organs of interest, all the animals were euthanized at 24 h p.i. The amount of label accumulated in the whole lungs of the pretargeted group was 3.20 ± 2.06% ID/g, which was significantly higher than the uptake of radioactivity in the lungs of the control group (0.40 ± 0.15% ID/g; P = 0.01). The amount of radioactivity in the lungs of normal animals injected with the bsMab or the anti-DTPA Ab was 0.15 ± 0.01% ID/g (P ≤ 0.001 and P = 0.032 for the bsMab or the anti-DTPA Ab mice, respectively). The lung to liver ratio of the bsMAb-pretreated animals was reported to be 5.25.

[^99mTc/¹¹¹In]-DSPL was shown to be suitable for the visualization of bsmAb-pretargeted human prostate cancer PC-3 cell xenograft tumors in SCID mice (5). For these studies, the intact 6C31H3 anti-DTPA Ab and its Fab' fragment were linked to the bombesin peptide to obtain Bom-bsCx and Bom-bsFx, respectively. Bombesin has a very high affinity for the gastrin-releasing peptide receptors (Bom; also designated as the Bom receptor) that are overexpressed on PC-3 cells. In separate studies, mice bearing the PC-3 cell tumors were pretargeted with Bom-bsCx and Bom-bsFx, respectively, and [^99mTc/¹¹¹In]-DSPL was used to visualize the lesions with scintigraphy (5). At the end of the imaging session, the rodents were euthanized, and all organs of interest were retrieved to determine the amount of radioactivity accumulated in the different tissues.

In the first study, mice bearing the xenograft tumors were pretargeted with an injection of Bom-bsCx (n = 4 animals) (5). Control animals were pretargeted with either 6C31H3 alone (n = 3 animals) or Bom alone (n = 2 animals). Twenty-four hours later, the animals (under anesthesia) were injected with 7.03 ± 1.74 MBq (259 ± 64.38 μCi) or 6.88 ± 1.89 MBq (373 ± 69.93 μCi) [¹¹¹In]-DSPL for gamma planar imaging at time points ranging from 5 min p.i. to 24 h p.i. From the images it was evident that the radioactivity was excreted rapidly through the kidneys, and there was little accumulation of tracer in the liver or heart of the animals. The xenograft tumors were clearly visible within 1–3 h p.i. in animals pretargeted with Bom-bsCx. No lesions were visible in the control animals. The amount of radioactivity accumulated in tumors of animals pretargeted with Bom-bcCx was 1.21 ± 0.35% ID/g, which was ~5.5-fold higher than accumulation in tumors in mice pretreated with either Bom or 6C31H3 alone (0.22 ± 0.08% ID/g; P = 0.001). The amount of radioactivity detected in the liver, spleen, and salivary glands of animals pretargeted with Bom-bcCx were ~0.5% ID/g, ~0.4% ID/g, and ~0.4% ID/g, respectively.

In the second study, the mice bearing PC-3 cell xenograft tumors were pretargeted with Bom-bsFx (n = 4 animals), and the control animals (n = 3 mice) were pretargeted with Bom alone. For scintigraphy the animals were injected with 50.0 ± 5.34 MBq (1.85 ± 0.18 mCi) [^99mTc]-DSPL 24 h later, and whole-body images were acquired from the rodents as described above. No accumulation of radioactivity was observed in the liver of these animals, and the tracer was excreted primarily through the kidneys. With [^99mTc]-DSPL, the lesions were visible in the animals within 1–3 h p.i. At 24 h p.i., the uptake of radioactivity from [^99mTc]-DSPL in the tumors was 15-fold higher than that in the control lesions (6.54 ± 1.58% ID/g versus 0.44 ± 0.17% ID/g; P = 0.002). The amount of tracer in the liver and spleen of animals pretargeted with Bom-bsFx was ~2.0% ID/g and ~1.5% ID/g, respectively. All other organs showed an accumulation of <1.0% ID/g radioactivity.

From these studies, the investigators concluded that [^99mTc/¹¹¹In]-DSPL can be used for the detection of minute tumors that have been pretargeted with an appropriate bsMab (5).

Other Non-Primate Mammals

[PubMed]

No reference is currently available.

Non-Human Primates

[PubMed]

No reference is currently available.