A nude mice model of human rhabdomyosarcoma lung metastases for evaluating the role of polysialic acids in the metastatic process

PSA is an oncodevelopmental antigen usually expressed in human tumors with high metastatic potential. Here we set up a metastatic model in nude mice by using TE671 cells, which strongly express PSA-NCAM. We observed the formation of lung metastases when TE671 cells were injected intravenously, intramuscularly, and intraperitoneally, but not subcutaneously. Intraperitoneal injections also induced peritoneal carcinosis, ascites, and liver metastases. To evaluate the putative role of PSA in the metastatic process we used a specific cleavage of PSA on NCAM by endoneuraminidase-N on intraperitoneal primary tumors. Mice with primary intramuscular tumors were taken as control. Repeated injections of endoneuraminidase-N led to a decrease in PSA expression in primary intraperitoneal nodules and ascites but not in intramuscular primary tumors. Endoneuraminidase-N also increased the delay in ascitic formation and decreased the number of lung or liver metastases in the case of intraperitoneal tumors but not in the case of intramuscular tumors. When metastases occurred in endoneuraminidase-N injected animals, they strongly expressed PSA-NCAM. Therefore, we established a relationship between PSA expression on the surface of primary tumor cells and the metastatic process.

Two-step targeting of xenografted colon carcinoma using a bispecific antibody and 188Re-labeled bivalent hapten: biodistribution and dosimetry studies

Radioimmunotherapy (RIT) is currently being considered for the treatment of solid tumors. Although results have been encouraging for pretargeted 131I RIT with the affinity enhancement system (AES), the radionuclide used is not optimal because of its long half-life, strong gamma emission, poor specific activity, and low beta particle energy. 188Re, though unsuitable for direct antibody labeling, could be used with the AES two-step targeting technique. The purpose of this study was to compare the distribution and dosimetry of a bivalent hapten labeled with 188Re or 125I. For dosimetry calculations and biodistribution data, 125I was substituted for 131I.

METHODS

After preliminary injection of a bispecific anticarcinoembryonic antigen (CEA) or antihapten antibody (Bs-mAb F6-679), AG 8.1 or AG 8.0 hapten radiolabeled with 188Re or 125I was injected into a nude mouse model grafted subcutaneously with a human colon carcinoma cell line (LS-174-T) expressing CEA. A dosimetry study was performed for each animal from the concentration of radioactivity in tumor and different tissues.

RESULTS

Radiolabeling of AG 8.1 with 125I afforded a 40% yield with a specific activity of 11.1 MBq/nmol after purification. Radiolabeling of AG 8.0 with 188Re afforded a 72% yield with a specific activity of 31.82 MBq/nmol. In all experiments, the percentage of tumor uptake of 125I-AG 8.1 was always significantly greater than that of 188Re-AG 8.0. The corresponding tumor-to-tissue ratios reflected uptake values. The least favorable tumor-to-normal tissue ratios in the dosimetry study were 8.1 and 8.5 for 131I (tumor-to-blood ratio and tumor-to-kidney ratio, respectively) and 2.3 for 188Re (tumor-to-intestine ratio).

CONCLUSION

This study indicates that 188Re can be used for radiolabeling of hapten in two-step radioimmunotherapy protocols with the AES technique. 188Re has a greater range than 131I, which should allow the treatment of solid tumors around 1 cm in diameter. Although the method used for hapten radiolabeling did not provide optimal tumor uptake, the use of a bifunctional chelating agent associated with AG 8.1 should solve this problem.

Rhenium-188-labeled anti-neural cell adhesion molecule antibodies with 2-iminothiolane modification for targeting small-cell lung cancer

We have evaluated the potential of 188Re-labeled monoclonal antibodies (MAbs) modified with 2-iminothiolane (2IT) for targeting small-cell lung cancer (SCLC). Radiolabeled MAbs NK1NBL1 and C218 recognizing neural cell adhesion molecule were injected i.v. into athymic mice inoculated with human SCLC tumors, and the biodistribution was examined. NK1NBL1 localized in the tumors better than C218. 188Re-labeled MAbs cleared from the blood faster than 125I-labeled counterparts, resulting in higher tumor-to-blood ratios. In conclusion, the 188Re-labeled MAbs are attractive candidates for imaging and therapy of SCLC.

Pretargeted radioimmunotherapy of human colorectal xenografts with bispecific antibody and 131I-labeled bivalent hapten

We have developed a pretargeting strategy, called the affinity enhancement system (AES), which uses bispecific antibodies to target radiolabeled bivalent haptens to tumor cells. The aim of this study was to evaluate the potential of the AES for the radioimmunotherapy (RIT) of LS174T colorectal xenografts in comparison with RIT with directly labeled F(ab')2 fragment.

METHODS

A total of 6 groups of tumor-bearing mice were treated using anticarcinoembryonic antigen (CEA) x anti-diethylenetriamine pentaacetic acid (DTPA)-In bispecific antibody (BsF(ab')2) and 131I-labeled di-DTPA-In bivalent hapten. Three groups of mice were injected with various activities of 131I-labeled bivalent hapten (75, 96, and 112 MBq) 20 h after administration of BsF(ab)'2. Three other groups were injected with an almost constant activity of labeled hapten (102 MBq) at 3 time periods (15, 30, and 48 h) after BsF(ab')2 administration. For conventional RIT, mice were treated with 96 MBq 131-labeled anti-CEA F(ab')2. Control groups were left untreated. Toxicity and tumor growth were monitored at weekly intervals.

RESULTS

Doses used for conventional RIT induced severe toxicity and resulted in death of several treated animals. Nevertheless, all surviving animals treated with 131I-labeled anti-CEA F(ab')2 relapsed shortly after treatment (tumor growth delay = 48+/-13 d). For animals treated with the AES reagents, toxicity varied with the pretargeting time interval and the administered activity. For 20-h pretargeting time, the maximum tolerated dose was 96 MBq. For all AES RIT except 1 (with 48-h pretargeting time interval and growth delay of 82+/-26 d), no tumor growth was observed over a period of 8 mo. Furthermore, based on clinical and histologic criteria, 33% of the treated mice were considered cured.

CONCLUSION

High cure rates of LS174T colon carcinoma were achieved with the AES, and the flexibility of the pretargeting approach allowed the control of hematologic toxicity, which is the main limitation to dose escalation with conventional RIT.

Radioimmunotherapy of small cell lung carcinoma with the two-step method using a bispecific anti-carcinoembryonic antigen/anti-diethylenetriaminepentaacetic acid (DTPA) antibody and iodine-131 Di-DTPA hapten: results of a phase I/II trial

As small cell lung carcinoma (SCLC) is frequently a widespread disease at diagnosis, highly radiosensitive and often only partially responsive to chemotherapy, radioimmunotherapy (RIT) would appear to be a promising technique for treatment. We report the preliminary results of a Phase I/II trial of RIT in SCLC using a two-step method and a myeloablative protocol with circulating stem cells transplantation. Fourteen patients with proved SCLC relapse after chemotherapy were treated with RIT. They were first injected i.v. with a bispecific (anti-carcinoembryonic antigen/anti-diethylenetriaminepentaacetic acid) monoclonal antibody (20-80 mg in 100 ml of saline solution) and then 4 days later with di-(In-diethylenetriaminepentaacetic acid)-tyrosyl-lysine hapten labeled with 1.48-6.66 GBq (40-180 mCi) of I-131 and diluted in 100 ml of saline solution. In patients receiving 150 mCi or more, circulating stem cells were harvested before treatment and reinfused 10-15 days later. Treatment response was evaluated by CT and biochemical data during the month before and 1, 3, 6, and 12 months after treatment. All patients received the scheduled dose without immediate adverse reactions to bispecific antibody or 1-131 hapten. Toxicity was mainly hematological, with two cases of grade 2 leukopenia and three cases of grade 3 or 4 thrombopenia. Body scanning 8 days after injection of the radiolabeled hapten generally showed good uptake at the tumor sites. Estimated tumor dose was 2.6-32.2 cGy/mCi. Among the 12 patients evaluated to date, we have observed 9 progressions, 2 partial responses (one almost complete for 3 months), and 1 stabilization of more than 24 months. Efficiency and toxicity were dose-related. The maximal tolerable dose without hematological rescue was 150 mCi. These preliminary results are encouraging, and dose escalation is currently continuing to reach 300 mCi. RIT should prove to be an interesting therapeutic method for SCLC, although repeated injections and hematological rescue will probably be required, as well as combination with other treatment modalities.

Toxicity and efficacy of radioimmunotherapy in carcinoembryonic antigen-producing medullary thyroid cancer xenograft: comparison of iodine 131-labeled F(ab')2 and pretargeted bivalent hapten and evaluation of repeated injections

This study compared the toxicity and efficacy of 131I-labeled bivalent hapten pretargeted by anti-carcinoembryonic antigen (CEA)/anti-N alpha-(diethylenetriamine-N,N,N',N''-tetraacetic acid-indium(F6-734) bispecific antibody [affinity enhancement system (AES) reagents] with 131I-labeled anti-CEA F(ab')2 (131I-F6) in mice grafted with a human medullary thyroid carcinoma. Repeated injections of AES reagents were also evaluated. Mice bearing TT tumor xenografts were treated with 37, 74, or 92.5 MBq of AES reagents, two injections of 74 MBq of AES reagents 45 days apart, or 37 or 92.5 MBq of 131I-F6. Control groups were treated with nonspecific 131I-labeled F(ab')2, nonspecific AES reagents, nonradiolabeled F6, F6-734 bispecific antibody, and nonradiolabeled bivalent hapten or received no injection. For AES treatments, bispecific antibody was injected 48 h before the hapten. Animal weight, hematological toxicity, tumor volume, and serum thyrocalcitonin were monitored during 5 months. At 92.5 MBq, weight loss was significantly lower after AES than F6 treatment (P = 0.004). The percentages of leukocyte count changes were significantly lower after AES than F6 at 37 and 92.5 MBq (P = 0.01 and 0.04, respectively). The percentage of platelet count changes was significantly lower with AES at the 92.5-MBq dose level (P = 0.04). In the group injected twice with AES reagents, toxicity was not significantly increased after the second treatment. Tumor response was observed in all cases but was significantly longer with repeated treatments of 74 MBq AES reagents than with a single treatment (P = 0.004). Two complete responses were observed with repeated treatments. Changes in thyrocacitonin level paralleled those in tumor volume. These results indicate that pretargeted radioimmunotherapy was at least as efficient as one-step radioimmunotherapy and markedly less toxic. Repeated treatments with AES reagents increased efficacy without increasing toxicity.

Immunohistology of carcinoembryonic antigen (CEA)-expressing tumors grafted in nude mice after radioimmunotherapy with 131I-labeled bivalent hapten and anti-CEA x antihapten bispecific antibody

We have developed a pretargeting strategy, called the Affinity Enhancement System (AES), which uses bispecific antibodies (BsF(ab')2) to target radiolabeled bivalent haptens to tumor cells. We performed several radioimmunotherapy (RIT) experiments in nude mice grafted with LS174T colon carcinoma or TT medullary thyroid cancer. Mice were treated with 131I-labeled di-DTPA-indium-tyrosyl-lysine bivalent hapten (75-112 MBq) administered 15-48 h after anti-CEA x anti-DTPA-indium BsF(ab')2. Immunohistological studies were performed on tumors at their minimal relative volume (TT), on stabilized tumor nodules (LS174T), and on regrowing tumors (TT and LS174T). Untreated tumors were used as controls. On microscopic examination, regrowing tumors (2 months posttherapy) were similar to untreated tumors with cells showing their respective typical morphology (large cells with a high nucleocytoplasmic ratio for TT, small and very undifferentiated cells for LS174T). However, regrowing tumors showed larger necrotic areas and a higher mitotic index correlated with Ki-67 antigen staining. Immunostaining for CEA was as strong as for controls. By contrast, the immunohistology of TT tumors at their minimal relative volume (1 month posttherapy) or of LS174T residual nodules (8 months posttherapy) showed decreased mitotic indices correlated with poor Ki-67 antigen staining. Some clusters of LS174T presented with features of glandular lumen, which suggested a more differentiated and less aggressive status. In TT tumors, CEA expression remained unchanged (80-100% membrane and cytoplasmic staining), whereas only 70% of the LS174T tumors were stained, with 58% loss of the membrane expression. Repeated treatment early after the tumor has reached its minimal relative volume should thus be efficient and improve the overall efficacy of AES RIT.

Radioimmunotherapy in medullary thyroid cancer using bispecific antibody and iodine 131-labeled bivalent hapten: preliminary results of a phase I/II clinical trial

The toxicity and therapeutic efficacy of escalating doses of anti-carcinoembryonic antigen x anti-N alpha-(diethylenetriamine-N,N,N',N''-tetraacetic acid)-In bispecific monoclonal antibody (F6-734) and iodine 131-labeled bivalent hapten were determined in a Phase I/II trial. A total of 26 patients with recurrences of medullary thyroid cancer documented by imaging and a rise in serum thyrocalcitonin were enrolled. Twenty to 50 mg of F6-734 and 40-100 mCi of 131I-hapten were injected 4 days apart. Quantitative scintigraphy was performed after the second injection for dosimetry estimations in eight cases. Clinical, biological, and morphological follow-up was carried out for 1 year after treatment. The mean percentage of injected activity per gram of tumor at the time of maximum uptake was 0.08% (range, 0.003-0.26%). The tumor biological half-life ranged from 3 to 95 days, and tumor doses ranged from 2.91 to 184 cGy/mCi. The estimated tumor-to-nontumor dose ratios were 43.8 x 53.4, 29.6 x 35.3, 10.9 x 13.6, and 8.4 x 10.0 for total body, red marrow, liver, and kidney, respectively. Grade III/IV hematological toxicity was observed in seven patients, most of them with bone metastases. Among the 17 evaluable patients, 4 pain reliefs, 5 minor tumor responses, and 4 biological responses with decrease of thyrocalcitonin were observed. Nine patients developed human anti-mouse antibody. Dose-limiting toxicity was hematological, and maximum tolerated activity was 48 mCi/m2 in this group of patients, most of whom had suspected bone marrow involvement. The therapeutic responses observed in patients mainly with a small tumor burden are encouraging for the performance of a Phase II trial with minimal residual disease.

Two-step targeting and dosimetry for small cell lung cancer xenograft with anti-NCAM/antihistamine bispecific antibody and radioiodinated bivalent hapten

The "affinity enhancement system," a two-step targeting technique using bispecific antibody and radiolabeled bivalent hapten, has been reported to be useful for carcinoembryonic antigen-expressing tumors. The purpose of this study was to evaluate the efficacy of this method for targeting human small cell lung cancer using an antineural cell adhesion molecule antibody.

METHODS

Antineural cell adhesion molecule/antihistamine bispecific antibody NK1NBL1-679 was prepared by coupling an equimolecular quantity of a Fab' fragment of NK1NBL1 to a Fab fragment of antihistamine 679. Athymic mice inoculated with NCI-H69 small cell lung cancer cells expressing neural cell adhesion molecule were administered bispecific antibody and then 48 h later 125I-labeled bivalent histamine hapten. 125I-labeled intact NK1NBL1 was injected into other groups of mice. Biodistributions were examined as a function of time.

RESULTS

In mice of the two-step targeting, tumor uptake was 2.5 +/- 0.2, 3.2 +/- 0.4, 6.4 +/- 2.0, 7.2 +/- 2.7, 6.1 +/- 2.1 and 2.2 +/- 0.4 %ID/g at 5, 30 min, 5, 24, 48 and 96 h, and tumor-to-blood, tumor-to-liver and tumor-to-kidney ratios were 1.4 +/- 1.1, 10.8 +/- 13.2 and 4.6 +/- 4.7, respectively, at 5 h, whereas 125I-labeled NK1NBL1 showed a tumor uptake of 5.7 +/- 0.4 %ID/g and tumor-to-blood, tumor-to-liver and tumor-to-kidney ratios of 0.3 +/- 0.1, 1.1 +/- 0.2 and 0.9 +/- 0.1, respectively, at 5 h. These results were confirmed by autoradiographic studies, which demonstrated clear tumor-to-normal tissue contrast. Dosimetry showed that the affinity enhancement system could enhance the therapeutic potential of the antineural cell adhesion molecule antibody NK1NBL1.

CONCLUSION

This two-step targeting method seems promising for the diagnosis and therapy of small cell lung cancer.

Pretargeting with the affinity enhancement system for radioimmunotherapy

The pretargeting technique referred to as the Affinity Enhancement System (AES) uses bispecific antibodies and radiolabeled bivalent haptens that bind cooperatively to target cells in vivo. Experimental and clinical data demonstrate that AES can deliver large radiation doses to tumor cells with high tumor to normal tissue contrast ratios and long activity residence time in tumors. Preliminary clinical results of radioimmunotherapy of medullary thyroid carcinomas and lung cancers look promising.

Bispecific antibody and bivalent hapten radioimmunotherapy in CEA-producing medullary thyroid cancer xenograft

The purpose of this study was to compare the toxicity and efficacy of two-step radioimmunotherapy using a bispecific anticarcinoembryonic antigen (CEA)/anti-diethylenetriamine pentaacetic acid (DTPA) antibody (F6-734 bispecific monoclonal antibodies (BsMAbs) and an 131I-di-DTPA-TL bivalent hapten with F(ab')2 fragments of the same directly labeled anti-CEA 131-F6.

METHODS

Eight groups of nude mice subcutaneously grafted with the human TT medullary thyroid cancer cell line were injected once tumor volume reached about 200 mm3. Two groups received 37 or 92.5 MBq (1 or 2 nmol) 131I-di-DTPA-TL 48 h after injection of 2 or 4 nmol F6-734 BsMAb and two groups received 37 or 92.5 MBq (250 microg) 131I-F6. Four control groups were treated respectively with (a) 92.5 MBq nonspecific 131I-734 fragments, (b) 92.5 MBq 131I-di-DTPA-TL 48 h after injection of a mixture of irrelevant F6-679 (anti-CEA/anti-histamine) and G7A5-734 (anti-melanoma/anti-DTPA) BsMAb, (c) 250 microg nonradiolabeled F6, and 250 microg F6-734 BsMAb and then 48 h later 1.25 nmol of nonradiolabeled hapten. A control group received no injections. Toxicity was evaluated by determining animal weight and the number of leukocytes and platelets, and efficacy by variation in tumor volume and thyrocalcitonin during a 90-d period. Histological analysis of tumors and statistical studies were performed.

RESULTS

The time required for the tumor to double in size was respectively 57 and 86 d with 37 and 92.5 MBq F6-734/131I-di-DTPA-TL and 44 and 65 d with 37 and 92.5 MBq 131I-F6. Changes in thyrocalcitonin levels were parallel to those in tumor volume. Weight loss was 5%, leukocyte nadirs respectively 1640+/-838 and 1560+/-1160/mm3 and platelet nadirs 1.46+/-0.52 10(6)/mm3 and 0.73+/-0.38 10(6)/mm3 after injections of 37 and 92.5 MBq F6-734/1311-di-DTPA-TL. Weight loss was respectively 8% and 16%, leukocyte nadirs 50+/-100/mm3 and 175+/-50/mm3 and platelet nadirs 0.71+/-0.18 10(6)/mm3 and 0.48+/-0.11 10(6)/mm3 after injections of 37 and 92.5 MBq 131I-F6.

CONCLUSION

Two-step radioimmunotherapy was as efficient as the one-step system and markedly less toxic.

Delivery of therapeutic doses of radioiodine using bispecific antibody-targeted bivalent haptens

Two-step pretargeting strategies have been designed to deliver radioisotopes to tumors more selectively than directly labeled antibodies or fragments. In this article, we compare quantitatively the potential of these strategies for the radioimmunotherapy of solid tumors.

METHODS

Direct targeting was performed using iodine-labeled IgG and F(ab')2. As two-step strategies, we used the sequential injection of anti-CEA x anti-DTPA-In bispecific F(ab')2 (BsF(ab')2) and monovalent and bivalent DTPA derivatives labeled with iodine. The biodistribution of iodine in nude mice grafted with the LS174T human colorectal carcinoma was monitored in time and used for calculating radiation doses.

RESULTS

In agreement with earlier studies, the IgG was more effective for delivering a radiation dose to the tumor than the F(ab')2 (7.8 versus 0.76 Gy/MBq, respectively) and both were moderately selective with respect to normal tissues (tumor:blood of 2.9 and 1.7, respectively). At their MTD, they should deliver 86 and 34 Gy, respectively, to the tumor. Using a nM-affinity DTPA-In bivalent hapten, the two-step protocol was optimized by varying the dosage of the BsF(ab')2, the stoichiometry of the reagents and the pretargeting time. The saturation of the tumor was obtained by injecting 5 nmol (500 microg) of BsF(ab')2. The pretargeted BsF(ab')2 was saturated by the injection of 0.5 mol of bivalent hapten per mole of antibody. With a 48-hr pretargeting time, the selectivity of the irradiation of the tumor was optimized (tumor:blood of 7.8) but only at the price of a lower efficiency (0.35 versus 0.86 Gy/MBq, 48-hr and 20-hr pretargeting time, respectively). Attempts to increase selectivity by using a microM-affinity DTPA-Y bivalent hapten or by chasing excess circulating radiolabeled hapten with an excess of unlabeled hapten also reduced tumor exposure. The use of a monovalent hapten resulted in both lower efficiency and selectivity. However, the two-step pretargeting of high-affinity bivalent hapten (Affinity Enhancement System, AES) should deliver 30-60 Gy to the tumor with less than 9 Gy to the blood in tumor-bearing mice.

CONCLUSION

Radioimmunotherapy with AES is predicted to be as efficient and with lower hematological toxicity than direct targeting.

Biodistribution and dosimetric study in medullary thyroid cancer xenograft using bispecific antibody and iodine-125-labeled bivalent hapten

The purpose of this study was to evaluate biodistributions and absorbed doses of anti-carcinoembryonic antigen (CEA)/anti-diethylenetriamine pentaacetic acid (DTPA)-indium (anti-DTPA-In) bispecific monoclonal antibody (BsMAb) F6-734 and 125I-labeled DTPA-indium dimer hapten (125I-di-DTPA-In hapten) in athymic mice xenografted with human medullary thyroid cancer.

METHODS

Bispecific monoclonal antibodies F6-679 (anti-CEA/antihistamine) and G7A5-734 (antimelanoma/anti-di-DTPA-In) were used as irrelevant BsMAbs. Athymic mice inoculated with TT medullary thyroid cancer cells expressing CEA were administered BsMAbs F6-734, F6-679 or G7A5-734 and then, 48 hr later, 125I-di-DTPA-In hapten. Iodine-125-labeled F6 F(ab')2 fragment was injected into other groups of mice. Biodistributions were examined at 30 min and 5, 24, 48 and 96 hr after injection of 125I-di-DTPA-In hapten or 125I-labeled F6 F(ab')2.

RESULTS

In mice injected with BsMAb F6-734 and 125I-di-DTPA-In hapten, tumor uptake was 9.1%+/-2.1%, 8.7%+/-3.5%, 8.0%+/-2.3%, 5.1%+/-0.9% and 3.5%+/-1.5% of the injected dose/g at 30 min and 5, 24, 48 and 96 hr, and tumor-to-blood, tumor-to-liver and tumor-to-kidney ratios were 37.0+/-12.5, 32.3+/-10.9 and 10.4+/-2.7 at 24 hr. Iodine-125-F6 F(ab')2 fragment showed a tumor uptake of 7.39% injected dose/g and tumor-to-blood, tumor-to-liver and tumor-to-kidney ratios of 1.8+/-0.6, 7.3+/-2.9 and 3.6+/-1.6 at 24 hr. In mice injected with F6-679 or G7A5-734, tumor uptake and tumor-to-normal tissue ratios were much lower than in the mice injected with F6-734. These results were confirmed by autoradiographic studies that demonstrated clear tumor-to-normal tissue contrast.

CONCLUSION

This two-step targeting method seems very potent for the diagnosis and therapy of human medullary thyroid cancer and other CEA-producing tumors because it combines high tumor uptake and low normal tissue background.

Therapy for colon carcinoma xenografts with bispecific antibody-targeted, iodine-131-labeled bivalent hapten

BACKGROUND

One of the main limitations of radioimmunotherapy (RIT) is the secondary toxicity related to the poor therapeutic indices achieved with labeled whole immunoglobulin (Ig)G or F(ab')2 fragments. To overcome this problem, we have developed a two-step targeting method, which we refer to as the Affinity Enhancement System (AES), using a radiolabeled bivalent hapten and a bispecific antibody recognizing the hapten and a target cell antigen. This method has been applied successfully to immunoscintigraphy in carcinoembryonic antigen (CEA)-expressing carcinoma patients and increased tumor to normal tissue uptake ratios have been achieved. The aim of the current study was to evaluate the application of AES to RIT of CEA-expressing solid tumors in an animal model.

METHODS

Nude mice grafted with LS174T human colorectal carcinoma were treated either with 111 megabecquerels (MBq) of iodine-131 labeled bivalent diethylenetriamine pentaacetic acid (DTPA) hapten 20 hours after pretargeting by anti-CEA x anti-DTPA-indium bispecific antibody or 12 MBq of iodine-131 labeled anti-CEA IgG.

RESULTS

Treatment with the IgG induced only a growth delay of 53 +/- 5 days but all tumors progressed. Treatment with the AES was highly efficient because tumor growth inhibition was achieved over 150 days. Hematologic and overall toxicity of both treatments were equivalent.

CONCLUSIONS

The long term tumor regression consecutive to AES RIT represents a very significant improvement over the use of directly labeled IgG. Toxicity consecutive to AES or IgG RIT were similar despite an administered activity nearly ten times higher with the AES. However, given the efficacy of the AES treatment, a lower dose may afford lower toxicity and significant antitumor effect.

Bivalent hapten-bearing peptides designed for iodine-131 pretargeted radioimmunotherapy

Pretargeting with bispecific antibodies has been used successfully for tumor detection and is now considered for radioimmunotherapy. The advantages of bivalent haptens have been demonstrated in this context. A series of bivalent molecules allowing efficient labeling with radioactive iodine has been designed for use with this new technology. They were based on the histamine-hemisuccinate hapten and prepared by solid phase peptide synthesis. Simultaneous binding of two antibody molecules to one bivalent hapten was possible with low steric hindrance when the two hapten groups were attached to the lateral chains of lysine residues separated by a single amino acid. Bispecific antibodies to the hapten and to carcinoembryonic antigen were shown to mediate specific binding of the haptens to tumor cells in vitro. These experiments demonstrated that the bivalent hapten AG3.0, with a lysyl-D-tyrosyl-lysine connecting chain, possessed the best binding properties. This peptide was used to target iodine-125 to human colon cancer xenografts in nude mice. High tumor uptake and tumor to normal tissue ratios were observed. This peptide thus appears as a good candidate for further development. Asymmetric bivalent haptens, with one histamine-hemisuccinate and one diethylenetriaminepentaacetic acid group, have also been prepared and shown to be capable of binding simultaneously two specific antibody molecules. These peptides should be useful to target radioiodine to cells characterized by the expression of two different antigenic markers.

Targeting BCL1 lymphoma with anti-idiotype antibodies: biodistribution kinetics of directly labeled antibodies and bispecific antibody-targeted bivalent haptens

The mouse BCL1 lymphoma model has been used for evaluating immunotherapy with anti-idiotype (anti-Id) antibodies, including Id immunisation, IgG therapy and bispecific (Bs) antibody-targeted cytotoxicity. Here, we provide quantitative data on the targeting of small (25 +/- 12 mg) intrasplenic BCL1 tumours, using anti-Id IgG, F(ab')2 and anti-Id x anti-hapten BsF(ab')2 covalently labelled with 125iodine, as well as noncovalent complexes of BsF(ab')2 and 125I-labelled bivalent hapten. The results are the following: 1) up to 115% of the injected dose per gram (% ID/g) of spleen can be localised in the first hour, corresponding to approximately 600% ID/g of tumour; 2) localisation is specific for cell-surface Id; 3) optimal doses can overcome circulating Id; 4) circulating Id markedly increases the catabolism of IgG, thus impairing tumour localisation; 5) bivalent reagents are internalised by the target cells; 6) iodine covalently bound to bivalent antibodies [IgG, F(ab')2] is rapidly (T(1/2): 6-9 hr) released from the tumour; in contrast, the bivalent hapten is retained for a longer time (T(1/2): 25 hr); and 7) in the absence of bivalent hapten, the monovalent BsF(ab')2 is not rapidly internalised and dissociates from tumour cell-surface Id. Our results suggest that monovalent anti-Id, lacking Fc, can efficiently be targeted to the BCL1 tumour surface. For radioimmunotherapy, the intracellular targeting of catabolism-resistant 125I-labelled bivalent hapten provides optimal tissue selectivity.

Targeting medullary thyroid carcinomas with bispecific antibodies and bivalent haptens. Results and clinical perspectives

The present article reviews the clinical trials that have been performed in recurrent medullary thyroid carcinoma patients with the Affinity Enhancement System. This technique uses bispecific antibodies to target radiolabelled bivalent haptens to tumour cells. Its sensitivity in the detection of known tumour sites is high (90%) and this technique also achieves good sensitivity (61%) in the detection of occult disease as revealed by abnormal thyrocalcitonin blood levels. Due to its high targeting capacity, this technique is now considered for use as a therapeutic agent in medullary thyroid carcinoma patients.

Bispecific antibody and iodine-131-labeled bivalent hapten dosimetry in patients with medullary thyroid or small-cell lung cancer

The purpose of this study was to estimate the dose delivered to tumor targets and normal tissues after two-step injection of an anti-CEA/anti-DTPA-In (F6-734) bispecific antibody and a 131I-labeled di-DTPA in-TL bivalent hapten in patients with medullary thyroid carcinoma (MTC) and small-cell lung cancer (SCLC).

METHODS

Five patients with persistent disease or recurrences of MTC and five patients with primary SCLC or relapse were studied. In a first step, 0.1 to 0.3 mg/kg of F6-734 bispecific antibody was injected intravenously. Four days later, 6 nmole (5.8 to 9.8 mCi) of 131I-labeled di-DTPA in-TL bivalent hapten were injected. Quantitative imaging was performed during one week after the second injection.

RESULTS

All 5 patients with MTC showed positive immunoscintigraphy (IS). In the smallest visualized and resected tumor (0.8 g), the fraction of injected activity per gram (% ID/g) was 0.1% at Day 3. IS was positive in 4 of the 5 patients with SCLC. The volume of the smallest visualized SCLC tumor was estimated at 11 +/- 2 ml, and tumor uptake was about 0.009% ID/g. Tumor dose estimates ranged from 4.2 to 174 cGy/mCi in patients with MTC and from 1.7 to 8 cGy/mCi in patients with SCLC.

CONCLUSION

High absorbed dose values were calculated for small MTC recurrences. For SCLC recurrences the values were smaller but in the same range as those obtained by other investigators with the one-step technique in lymphoma.

Comparative targeting of human colon-carcinoma multicell spheroids using one- and two-step (bispecific antibody) techniques

In the perspective of radioimmunotherapy (RIT) of micrometastases, we compared, in multicell spheroids (MS), the uptake and retention kinetics of 125I-F(ab)'2 F6 anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb), and the affinity enhancement system (AES) using an anti-CEA/anti-DTPA-indium bispecific antibody (BsMAb) and a 125I-labeled di-DTPA-In-tyrosine-lysine bivalent hapten. We used MS of colorectal tumor cell lines expressing CEA strongly (LS 174T), weakly (HT-29) or not at all (HRT-18). Uptake and retention kinetics of 125I-F(ab)'2 F6 and 125I-BsMAb used alone gave similar results. The highest uptake values, obtained with LS 174T MS, were slightly lower with AES than with 125I-F(ab)'2 F6. However, effective retention half-lives were longer for AES than for 125I-F(ab)'2 F6 or for 111In-labeled monovalent hapten after pre-incubation of spheroids with BsMAb. Autoradiography showed the same slow and heterogeneous distribution of 125I-F(ab)'2 F6 and 125I-BsMAb. These results indicate that the 2-step technique is more favorable for RIT: uptake values were approximately the same but uptake kinetics were more rapid, and retention half-life was longer than with the one-step technique.

Bifunctional antibodies for radioimmunotherapy

In two-step targeting technique using bifunctional antibodies, a nonradiolabeled immunoconjugate with slow uptake kinetics (several days) is initially injected, followed by a small radiolabeled hapten with fast kinetics (several hours) that binds to the bispecific immunoconjugate already taken up by the tumor target. In patients with colorectal or medullary thyroid cancer, clinical studies performed with an anti-CEA/anti-DTPA-indium bifunctional antibody and an indium-111-labeled di-DTPA-TL bivalent hapten showed that tumor uptake was not modified compared to results for F(ab')2 fragments of the same anti-CEA antibody directly labeled with indium-111, whereas the radioactivity of normal tissues was significantly reduced (3- to 6-fold). The fast tumor uptake kinetics (several hours) and high or very high tumor-to-normal tissue ratios obtained with the bifunctional antibody technique are favorable parameters for efficient radioimmunotherapy.

Pharmacokinetic study of anti-interleukin-6 (IL-6) therapy with monoclonal antibodies: enhancement of IL-6 clearance by cocktails of anti-IL-6 antibodies

The use of inhibiting cytokine-binding-proteins (CBPs) such as soluble cytokine receptors and anticytokine antibodies is considered for the treatment of cytokine-dependent diseases. The pleiotropic cytokine interleukin-6 (IL-6) is a target for immunointervention in numerous pathologic situations, including multiple myeloma, B-cell lymphoma, and rheumatoid arthritis. An antitumor response was obtained in the treatment of a patient with multiple myeloma. A controversial issue is to evaluate whether the carrier effect of the CBPs might limit their efficiency in blocking the target cytokine. We analyzed the pharmacokinetics of radiolabeled IL-6 in mice treated with various combinations of anti-IL-6 antibodies. We show that injection of one or two antibodies led to the stabilization of the cytokine. Conversely, simultaneous treatment with three anti-IL-6 antibodies, binding to three distinct epitopes, induced the rapid uptake of the trimeric immune complexes by the liver and the elimination of IL-6 from the central compartment. The use of cocktails of three antibodies binding simultaneously to a cytokine thus provides a new means of enhancing the clearance of the target molecule and should help in the design of antibody-based clinical trials by overcoming the problem of the accumulation of the cytokine in the form of monomeric immune complexes.

Computer calculation of multiple binding equilibrium isotherms: application to the binding of bivalent ligands to antibodies interacting with cell surface Fc-receptors

A method to calculate multiple binding equilibria by looking for a set of complexes satisfying the conservation principle among sets of concentrations of ligands, receptors satisfying the mass action equations is described. The method replaces complex analytical derivations of equations representing the interactions by the minimization of a single function. The method was implemented for use on microcomputers and applied to the calculation of the binding isotherms of the interactions between a bivalent ligand, a bivalent antibody and the cell surface Fc-receptor. The binding parameters were adjusted to experimental data obtained with P388D1 cells, a monoclonal antibody against DTPA-indium complexes and monovalent and bivalent DTPA-indium haptens. The binding of the antibody and of the haptens to P388D1 cells, as a function of antibody or hapten concentration, was satisfactorily represented using a model in which the antibody molecules bind co-operatively to the Fc-receptor in the presence of cross-linking bivalent hapten. The method can thus be used as a general tool for the numeric calculation of complex equilibrium involving simultaneous interactions of multiple receptors and ligands.

Bispecific monoclonal antibody-mediated targeting of an indium-111-labeled DTPA dimer to primary colorectal tumors: pharmacokinetics, biodistribution, scintigraphy and immune response

Eleven patients with primary colorectal carcinoma tumors (4 +/- 2 cm) were given intravenous injections of 1-10 mg of an anti-CEA, anti-In-DTPA bispecific Fab'-Fab monoclonal antibody, and 2-8 days later, were injected with 1.2-4.2 nmol of an 111In-labeled DTPA dimer (6 mCi). The bispecific antibody exhibited good stability and F(ab)'2-like pharmacokinetics. After injection, the 111In-DTPA dimer distributed in a large volume (88 ml/kg-180 ml/kg) and cleared through the kidneys (mean residence time in the whole body: 9 hr-16 hr). Uptake of 111In by the tumor using this two-step technique (1.8%-17.5% injected dose ID/kg, measured from surgical samples 48 hr after hapten injection) was not found significantly lower than that achieved with our reference 111In-labeled anti-CEA F(ab)'2 1 to 4 days after injection in six patients with similar clinical status (5.5%-30.2% ID/kg). In addition, tumor-to-blood and tumor-to-liver uptake ratios were significantly improved (blood 7.8 versus 4.2, liver 2.8 versus 0.8). As a result, low background images allowed detection of 12 of 13 lesions, 4 hr and 24 hr after hapten injection. However, 7 of 11 patients developed HAMA.

Enhanced in vivo targeting of an asymmetric bivalent hapten to double-antigen-positive mouse B cells with monoclonal antibody conjugate cocktails

In order to target specifically double-Ag-positive cells in vivo, we synthesized chemically two mAb conjugates with specificities for both an allelic murine B cell-surface Ag and for a synthetic hapten. One conjugate was designed for its specificities for I-Ek and for N-epsilon-(2,4-DNP)-amino-caproate, and the other one for its reactivity to Lyb-8.2 and to indium-diethylenetriamine pentaacetate. A radiolabeled tracer, containing both the N-epsilon-(2,4-DNP)-amino-caproate and the indium-diethylenetriamine pentaacetate haptens, was obtained by reacting diethylenetriamine pentaacetic acid dianhydride with mono-[N-epsilon-(2,4-DNP)-amino-caproyl]-tyrosyl-lysine and labeling with indium-111. Mice from various strains (CBA/N: I-Ek+, Lyb-8.2+; AKR/N: I-Ek+, Lyb-8.2-; BALB/c: I-Ek-, Lyb-8.2+; and DBA/2: I-Ek-, Lyb-8.2-) were given simultaneous i.v. injections of microgram amounts of less than anti-[N-epsilon-(2,4-DNP)-amino-caproate], anti-I-Ek greater than and of [anti-(indium-diethylene-triaminepentaacetate), anti-Lyb-8.2] antibody conjugates and picomole amounts of the tracer. As expected, specific uptake of the tracer by the spleen was observed in strains where spleen cells expressed at least one Ag (CBA/N, AKR/N, and BALB/c). Furthermore, spleen cells from the double-Ag-positive mouse strain (CBA/N), when compared with spleen cells from single-positive mouse strains, exhibited a significantly higher uptake of the bivalent hapten. This specificity for double-Ag-positive cells, it is suggested, occurs through the formation of stable complexes between both cell-surface Ag, both conjugates, and the asymmetric bivalent hapten. The use of such asymmetric bivalent haptens, together with matched (anti-hapten, anti-cell) antibody conjugates, is proposed as a general method for increasing the in vivo specificity of immunoimaging and radioimmunotherapy.

Enhanced in vivo targeting of an asymmetric bivalent hapten to double-antigen-positive mouse B cells with monoclonal antibody conjugate cocktails

In order to target specifically double-Ag-positive cells in vivo, we synthesized chemically two mAb conjugates with specificities for both an allelic murine B cell-surface Ag and for a synthetic hapten. One conjugate was designed for its specificities for I-Ek and for N-epsilon-(2,4-DNP)-amino-caproate, and the other one for its reactivity to Lyb-8.2 and to indium-diethylenetriamine pentaacetate. A radiolabeled tracer, containing both the N-epsilon-(2,4-DNP)-amino-caproate and the indium-diethylenetriamine pentaacetate haptens, was obtained by reacting diethylenetriamine pentaacetic acid dianhydride with mono-[N-epsilon-(2,4-DNP)-amino-caproyl]-tyrosyl-lysine and labeling with indium-111. Mice from various strains (CBA/N: I-Ek+, Lyb-8.2+; AKR/N: I-Ek+, Lyb-8.2-; BALB/c: I-Ek-, Lyb-8.2+; and DBA/2: I-Ek-, Lyb-8.2-) were given simultaneous i.v. injections of microgram amounts of less than anti-[N-epsilon-(2,4-DNP)-amino-caproate], anti-I-Ek greater than and of [anti-(indium-diethylene-triaminepentaacetate), anti-Lyb-8.2] antibody conjugates and picomole amounts of the tracer. As expected, specific uptake of the tracer by the spleen was observed in strains where spleen cells expressed at least one Ag (CBA/N, AKR/N, and BALB/c). Furthermore, spleen cells from the double-Ag-positive mouse strain (CBA/N), when compared with spleen cells from single-positive mouse strains, exhibited a significantly higher uptake of the bivalent hapten. This specificity for double-Ag-positive cells, it is suggested, occurs through the formation of stable complexes between both cell-surface Ag, both conjugates, and the asymmetric bivalent hapten. The use of such asymmetric bivalent haptens, together with matched (anti-hapten, anti-cell) antibody conjugates, is proposed as a general method for increasing the in vivo specificity of immunoimaging and radioimmunotherapy.

Targeting of indium 111-labeled bivalent hapten to human melanoma mediated by bispecific monoclonal antibody conjugates: imaging of tumors hosted in nude mice

Antibody conjugates were prepared by coupling F(ab')2 or Fab' fragments of an antibody specific for the human high molecular weight-melanoma associated antigen to Fab' fragments of an antibody specific for indium-diethylenetriaminepentaacetate complexes. Monovalent and bivalent haptens were synthesized by reacting the dipeptide tyrosyl-lysine with diethylenetriaminepentaacetic cyclic anhydride. In vitro, the antibody conjugate mediated binding of the 111In-labeled haptens to melanoma cells. In vivo, it allowed specific localization of the haptens in A375 tumors. The bivalent hapten exhibited much higher efficiency at targeting 111In onto cells, both in vitro and in vivo. Antibody conjugate and hapten doses (2 micrograms and 1 pmol, respectively) and the delay between antibody conjugate and tracer injections (24 h) were adjusted to maximize tumor uptake (4% injected dose/g) and tumor to normal tissue contrast (greater than 3) obtained 3 h after injection of the 111In-labeled bivalent hapten. This two-step technique, when compared to direct targeting of 111In-labeled F(ab')2 fragments, provided lower localization of injected activity into the tumor (x 0.25), but higher tumor/tissue ratios, especially with respect to liver (x 7), spleen (x 8), and kidneys (x 10). In addition, high contrast images were obtained within 3 hours, instead of days. Thus, antibody conjugate-mediated targeting of small bivalent haptens, labeled with short half-life isotopes, is proposed as a general method for improving tumor radioimmunolocalization.

In vitro and in vivo targeting of radiolabeled monovalent and divalent haptens with dual specificity monoclonal antibody conjugates: enhanced divalent hapten affinity for cell-bound antibody conjugate

A method of pretargeted immunolocalization of a mouse cell subset, using dual specificity monoclonal antibody conjugates and labeled divalent haptens, is described. Conjugates were prepared by coupling F(ab')2 fragments of an antibody specific for the allelic mouse B cell antigen Lyb8.2, to Fab' fragments of an anti-2,4-dinitrophenyl antibody. Divalent and monovalent haptens were obtained by coupling dinitrophenyl to peptides or to diethylene-triamine-pentaacetic acid. In vitro, divalent haptens bind with higher affinity to mouse spleen lymphocyte-bound than to excess soluble conjugate (affinity enhancement). In vivo, localization of 125I- or 111In-labeled divalent haptens in mouse spleen is much higher than that of the monovalent analogs. Thus, using divalent haptens, a new kind of specificity to target cells was achieved, suggesting that affinity enhancement may improve target to background ratios in radioimmunoscintigraphy.