Cleavable linkers to enhance selectivity of antibody-targeted therapy of cancer

Radioimmunotherapy of cancer utilizes anti-tumor antibodies or antibody fragments conjugated to radionuclides to deliver radiation selectively to tumors. However, radiolabeled proteins deposit radioactivity in normal organs that metabolize or conserve proteins and peptides, primarily liver and kidneys. To accelerate the clearance of radioactivity from normal tissues, linkers between the antibody or antibody fragment and the radioactive moiety have been designed for cleavage in the liver and kidneys, to liberate low molecular weight radioactive species for rapid excretion. Modest success in improving the tumor-to-liver and tumor-to-kidney radiation dose ratios have been achieved in preclinical studies. Such changes when taken to clinical studies have suggested useful impact on therapeutic work. Recent advances in the development of cleavable linkers are described.

Metabolite production in patients with lymphoma after radiometal-labeled antibody administration

Radiometal-labeled monoclonal antibodies are retained longer in tumors than iodinated antibodies, leading to their increased use for radioimmunotherapy. Dissociation of radioiodine from the antibody during metabolism has been documented. We now report metabolites in the plasma of lymphoma patients given 111In- and 90Y-2-iminothiolane-2-[p-(bromoacetamido)benzyl]-1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid-Lym-1 (111In/90Y-2IT-BAD-Lym-1).

METHODS

Nineteen patients with non-Hodgkin's lymphoma (NHL) received 111In- and 90Y-2IT-BAD-Lym-1; 111In was used as a surrogate tracer for 90Y, which emits no gamma-photon. Plasma was obtained up to 7 d and analyzed by high-performance liquid chromatography to determine the fraction of radiolabel associated with monomeric antibody, metabolites, and complexed antibody. Planar images of conjugate views were acquired up to 7 d and used to quantitate 111In in organs and tumors.

RESULTS

Metabolites and complexes were observed in the plasma of every patient who received 111In-2IT-BAD-Lym-1. At 3 d, the mean percentages of 111In in the patients' plasma in monomeric, metabolite, and complexed forms were 54%, 36%, and 10%, respectively. Metabolites of 90Y-2IT-BAD-Lym-1 were formed to a similar extent. In comparison, in groups of breast and prostate cancer patients who received the radioimmunoconjugate 111In-2IT-BAD-m170, 91% and 94% of 111In in the patients' plasma were in monomeric form, respectively. Metabolites and complexes of 111In-2IT-BAD-Lym-1 contributed a mean 10% of the total area under the time-activity curve (AUC) for blood. Little formation of metabolites and complexes occurred in vitro in NHL patient or volunteer plasma or in Raji cell culture. The clinical and in vitro data supported the processing of 111In/90Y-2IT-BAD-Lym-1 in the hepatocytes as the dominant mechanism for the production of metabolites.

CONCLUSION

Metabolites of 111In/90Y-2IT-BAD-Lym-1 accounted for 10% of blood AUC in patients. The therapeutic index was adversely affected by metabolism of 111In/90Y-2IT-BAD-Lym-1 to the extent that the tumor specificity of the radioactive metabolites was lost.

Radioimmunotherapy with (111)In/(90)Y-2IT-BAD-m170 for metastatic prostate cancer

PURPOSE

Over 31,000 Americans die of androgen-independent metastatic prostate cancer each year. New strategies that do not involve hormonal manipulation but instead recognize the biochemical and molecular characteristics of prostate cancer are needed. Radioimmunotherapy (RIT) uses a tumor-specific monoclonal antibody to deliver systemic, targeted radiation to cancer. The objectives of this Phase I study of (111)In-2IT-BAD-m170 (for imaging) and (90)Y-2IT-BAD-m170 (for therapy) were to determine the toxicity and maximum tolerated dose (MTD), the specificity for targeting metastatic prostate cancer, and the efficacy for palliation of pain.

EXPERIMENTAL DESIGN

M170 is a mouse monoclonal antibody that targets adenocarcinomas. Patients with adequate renal and liver function, rising prostate-specific antigen, and androgen-independent metastatic prostate cancer were eligible. After estimation of dosimetry and pharmacokinetics with (111)In-2IT-BAD-m170, a single dose of (90)Y-2IT-BAD-m170 (0.185, 0.370, 0.555, or 0.740 GBq/m(2)) was administered to cohorts of three patients. Pain was assessed objectively by questionnaires before and for 8 weeks after RIT; weekly prostate-specific antigen levels were obtained for 2 months after RIT.

RESULTS

The MTD of (90)Y-2IT-BAD-m170 was 0.740 GBq/m(2) for patients that had up to 10% of the axial skeleton involved with prostate cancer. Toxicity was almost exclusively confined to reversible myelosuppression. Metastatic prostate cancer was targeted by (111)In-2IT-BAD-m170 in all 17 patients. The mean radiation dose delivered to 39 bone and 18 nodal metastases by (90)Y-2IT-BAD-m170 was 10.5 Gy/GBq (range 2.8-25.1). Thirteen of 17 patients reported pain before (90)Y-2IT-BAD-m170; 7 of these 13 had a partial or complete resolution of pain that lasted an average of 4.3 weeks.

CONCLUSIONS

This study determined the MTD of (111)In/(90)Y-2IT-BAD-m170 in patients with metastatic prostate cancer. The drugs were well tolerated, targeted metastases, and temporarily palliated pain.

131I-Lym-1 in mice implanted with human Burkitt's lymphoma (Raji) tumors: loss of tumor specificity due to radiolysis

Preliminary evaluations of 125I-labeled Lym-1, an anti-lymphoma mouse IgG2a monoclonal antibody, demonstrated favorable tumor uptake in mice bearing human Burkitt's lymphoma (Raji) tumors. In this study, the pharmacokinetics of 125I- and 131I-Lym-1, and the dosimetry, efficacy, and toxicity of 131I-Lym-1 in Raji-tumored mice were evaluated.

METHODS

Lym-1 was radioiodinated by the chloramine-T method and analyzed for monomeric fraction and immunoreactivity (antigen cell binding, relative to unmodified Lym-1). Nude mice bearing Raji tumors (20-500 mm3) received 1.5 MBq (40 microCi) 125I-Lym-1, or 1.5, 7.4, 14.8, or 18.5 MBq (40, 200, 400, or 500 microCi) 131I-Lym-1. Pharmacokinetic data (total body and blood clearance and biodistribution) were used to estimate radiation dosimetry. Mini-thermoluminescent dosimetry (TLD) was also used to measure radiation dosimetry directly for 7 days after injection of 131I-Lym-1. Tumor size, survival, body weight, and blood counts were monitored for 60 days to evaluate therapeutic efficacy and toxicity of 131I-Lym-1.

RESULTS

At the time of injection, the mean quality assurance (QA) values for 125I-Lym-1 were 100% monomer and 100% relative immunoreactivity; the corresponding values for 131I-Lym-1 were 73% and 66%, indicating that radiolysis had occurred during the interval between radiolabeling and injection. 125I-Lym-1 exhibited high and sustained concentration in tumors relative to normal organs, whereas 131I-Lym-1 did not. Assuming identical pharmacokinetic behavior to 125I-Lym-1, 131I-Lym-1 would deliver radiation doses of 3.45, 0.83, 1.03, 0.34, and 0.56 Gy per MBq injected (12.8, 3.1, 3.8, 1.3, and 2.1 rad/microCi), to tumor, liver, lungs, total body, and marrow, respectively. When the actual pharmacokinetic data for 131I-Lym-1 (1.5 MBq) were used to estimate dosimetry, corresponding values of 0.51, 0.72, 0.49, 0.31, and 0.41 Gy/MBq (1.9, 2.7, 1.8, 1.1, and 1.5 rad/microCi) were obtained. Similar values were obtained for mice receiving 7.4 or 14.8 MBq of 131I-Lym-1. Similarly, TLD data indicated little preferential radiation dosimetry to tumor. Response rates (cure + CR + PR) for mice receiving 0, 7.4, 14.8, and 18.5 MBq of 131I-Lym-1 were 8%, 7%, 21%, and 45%, respectively. The LD50/30 dose of 131I-Lym-1 was 12.7 MBq (343 microCi).

CONCLUSIONS

125I-Lym-1 exhibited high and sustained concentration in Raji tumors in mice, indicating excellent therapeutic potential for 131I-Lym-1. However, in vitro QA results for 131I-Lym-1 indicated that radiolysis had occurred, and 131I-Lym-1 demonstrated little accumulation in tumor, or preferential radiation dosimetry to tumor in the same model.

Are radiometal-labeled antibodies better than iodine-131-labeled antibodies: comparative pharmacokinetics and dosimetry of copper-67-, iodine-131-, and yttrium-90-labeled Lym-1 antibody in patients with non-Hodgkin's lymphoma

Radioimmunotherapy using radiolabeled monoclonal antibodies against tumor-associated antigens has been efficacious, particularly in the treatment of radiosensitive malignancies such as lymphoma. Antilymphoma monoclonal antibody Lym-1, labeled with copper-67 ((67)Cu), iodine-131 ((131)I), or yttrium-90 ((90)Y), has been effective salvage therapy for patients with non-Hodgkin's lymphoma. Although (131)I has had the dominant role in radioimmunotherapy thus far, several properties of radiometals are preferable. A total of 70 patients with B-lymphocytic non-Hodgkin's lymphoma were studied using (67)Cu-2IT-BAT-Lym-1, (131)I-Lym-1, or (111)In-2IT-BAD-Lym-1. Because (90)Y does not have good emissions for imaging, indium-111 ((111)In), its analogue, was used as a surrogate to estimate (90)Y-2IT-BAD-Lym-1 pharmacokinetics and radiation dosimetry. Subsets of four patients in each group received (67)Cu- and (131)I-labeled Lym-1 or (111)In- and (131)I-labeled Lym-1, allowing direct comparisons of the radioimmunoconjugates. Sequential blood samples and planar images were used to quantitate radioimmunoconjugate in tissues in order to determine pharmacokinetics and radiation dosimetry. (67)Cu-2IT-BAT-Lym-1 and (90)Y-2IT-BAD-Lym-1 exhibited higher cumulated activity concentrations and radiation absorbed doses per unit of administered radioactivity for tumors than did (131)I-Lym-1. The mean tumor cumulated activity (area under the time-activity curve) concentrations per unit of administered radioactivity for (67)Cu-2IT-BAT-Lym-1, (131)I-Lym-1, and (90)Y-2IT-BAD-Lym-1 were 96.89, 33.96, and 43.42 GBq-s/GBq/g, respectively. The mean tumor radiation doses from (67)Cu-2IT-BAT-Lym-1, (131)I-Lym-1, and (90)Y-2IT-BAD-Lym-1 were 2.5, 1.0, and 6.6 Gy/GBq, respectively, because (90)Y deposits more radiation per unit of administered radioactivity. Per unit of administered radioactivity, radiation doses from (67)Cu-2IT-BAT-Lym-1 and (131)I-Lym-1 to normal tissues were similar except that the liver received a higher dose from (67)Cu-2IT-BAT-Lym-1 than from (131)I-Lym-1; radiation doses to normal tissues from (90)Y-2IT-BAD-Lym-1 were generally higher. Consequently, the therapeutic indices (ratio of radiation doses to tumor and normal tissues) for (67)Cu-2IT-BAT-Lym-1, and less generally for (90)Y-2IT-BAD-Lym-1, were more favorable when compared to those for (131)I-Lym-1. Data from the matched subsets of patients showed similar therapeutic indices to those for the groups of patients. (67)Cu-2IT-BAT-Lym-1 showed more potential than (131)I-Lym-1 or (90)Y-2IT-BAD-Lym-1 for non-Hodgkin's lymphoma radioimmunotherapy.

A phase I study of 90Y-2IT-BAD-Lym-1 in patients with non-Hodgkin's lymphoma

BACKGROUND

Prior clinical trials proved that all histologic grades of chemotherapy-resistant B-cell non-Hodgkin's lymphoma (NHL) could respond to radio-immunotherapy (RIT) with 131I-Lym-1 and 67Cu-2IT-BAT-Lym-1. This Phase I study was conducted to determine the safety and maximum tolerated dose (MTD) of 90Y-2IT-BAD-Lym-1.

METHODS

Lym-1 is a mouse monoclonal antibody that preferentially targets malignant B-lymphocytes. 90Y has beta emissions suitable for therapy but no gamma emissions, therefore, 111In-2IT-BAD-Lym-1 is used for imaging. The macrocyclic chelator, DOTA, bound 90Y tightly to form a stable drug. Patients with chemotherapy-resistant NHL received 90Y-2IT-BAD-Lym-1 at administered doses of: 0.185, 0.278, or 0.370 GBq/m2.

RESULTS

Myelotoxicity, especially thrombocytopenia, was dose-limiting. No significant non-hematologic toxicity occurred. Human anti-mouse antibody (HAMA) developed in 3/8 patients. The mean radiation dose to the 33 imaged tumors was 7.0 Gy/GBq. Lung, kidney and liver received mean radiation doses of 1.3, 2.4, and 6.4 Gy/GBq, respectively from 90Y-2IT-BAD-Lym-1. The tumor: body and tumor:bone marrow (by imaging) ratios were 16.4:1 and 5.8:1, respectively. In this Phase I study, 5/8 patients that failed prior chemotherapy had a partial response or stabilization of NHL after RIT.

CONCLUSION

The safety and toxicity of 90Y-2IT-BAD-Lym-1 were determined and the MTD was 0.370 GBq/m2, a dose used in 4 patients. 90Y-2IT-BAD-Lym-1 may be useful for future clinical trials because 90Y is readily available and can deliver potent beta emissions to NHL. Bone marrow support however, will be required for further dose escalation.

Efficacy and toxicity of radioimmunotherapy with (90)Y-DOTA-peptide-ChL6 for PC3-tumored mice

BACKGROUND

Radioimmunotherapy (RIT) is a new therapeutic modality capable of systemic delivery of radionuclides specifically to sites of metastatic cancer. The L6 monoclonal antibody has been shown to target prostate cancer in preclinical studies and, along with chimeric L6 (ChL6), has been used for RIT in breast cancer patients.

METHODS

Pharmacokinetics, blood counts, body weight, and antitumor activity of RIT with (90)yttrium-((90)Y)-DOTA-peptide-ChL6 (75-260 microCi) were determined in nude mice bearing human prostate cancer (PC3) xenografts.

RESULTS

RIT produced durable, dose-dependent antitumor effects with a 100% response rate using 112 microCi and 150 microCi (the maximum tolerated dose) of (90)Y-DOTA-peptide-ChL6. Myelotoxicity was reversible, dose-limiting, and dose-related. RIT was associated with improved survival (P = 0.05). All 5 mice in the 150-microCi group survived the 84-day study period vs. 1/8 (13%) for untreated, tumored control mice.

CONCLUSIONS

(90)Y-DOTA-peptide-ChL6 targets PC3 human prostate cancer xenografts in nude mice and has an antitumor effect. These results provide a basis for future RIT trials for patients with metastatic prostate cancer.

Radiation dosimetry for 90Y-2IT-BAD-Lym-1 extrapolated from pharmacokinetics using 111In-2IT-BAD-Lym-1 in patients with non-Hodgkin's lymphoma

Several monoclonal antibodies, including Lym-1, have proven effective for treatment of hematologic malignancies. Lym-1, which preferentially targets malignant lymphocytes, has induced therapeutic responses and prolonged survival in patients with non-Hodgkin's lymphoma (NHL) when labeled with 131. Because radiometal-labeled monoclonal antibodies provide higher tumor radiation doses than corresponding 131I-labeled monoclonal antibodies, the radiation dosimetry of 90Y-2-iminothiolane-2-[p-(bromoacetamido)benzyl]-1,4,7,10-tetraazacyc lododecane-N,N',N",N"'-tetraacetic acid-Lym-1 (90Y-21T-BAD-Lym-1) is of importance because of its potential for radioimmunotherapy. Although 90Y has attractive properties for therapy, its secondary bremsstrahlung is less suitable for imaging and pharmacokinetic studies in patients. Thus, the pharmacokinetic data obtained for 111In-21T-BAD-Lym-1 in patients with NHL were used to calculate dosimetry for 90SY-21T-BAD-Lym-1.

METHODS

Thirteen patients with advanced-stage NHLwere given a preload dose of unmodified Lym-1 followed by an imaging dose of 111In-21T-BAD-Lym-1. Sequential imaging and blood and urine samples obtained for up to 10 d after infusion were used to assess pharmacokinetics. Using 111In pharmacokinetic data and 90Y physical constants, radiation dosimetry for 90Y-21T-BAD-Lym-1 was determined.

RESULTS

The uptake of 111In-21T-BAD-Lym-1 in tumors was greater than uptakes in the lung and kidney but similar to uptakes in the liver and spleen. The biologic half-time in tumors was greater than in lungs. The mean radiation dose to tumors was 6.57 +/- 3.18 Gy/GBq. The mean tumor-to-marrow (from blood) radiation ratio was 66:1, tumor-to-total body was 13:1, and tumor-to-liver was 1:1. Images of 111In were of excellent quality; tumors and normal organs were readily identified. Mild and transient Lym-1 toxicity occurred in 3 patients.

CONCLUSION

Because of the long residence time of 111In-2IT-BAD-Lym-1 in tumors, high 90Y therapeutic ratios (tumor-to-tissue radiation dose) were achieved for some tissues, but the liver also showed high uptake and retention of the radiometal.

A clinical trial of radioimmunotherapy with 67Cu-2IT-BAT-Lym-1 for non-Hodgkin's lymphoma

Encouraged by the results of 131I-Lym-1 therapy trials for patients with B-cell non-Hodgkin's lymphoma (NHL), this phase I/II clinical trial of 67Cu-2IT-BAT-Lym-1 was conducted in an effort to further improve the therapeutic index of Lym-1-based radioimmunotherapy. Lym-1 is a mouse monoclonal antibody that preferentially targets malignant lymphocytes. 67Cu has beta emissions comparable to those of 131I but has gamma emissions more favorable for imaging. The macrocyclic chelating agent 1,4,7,11-tetraazacyclotetradecane-N,N',N",N"'-tetraacetic acid binds 67Cu tightly to form a stable radioimmunoconjugate in vivo.

METHODS

All 12 patients had stage III or IV NHL that had not responded to standard therapy; 11 had intermediate- or high-grade NHL. At 4-wk intervals, patients received up to four doses of 67Cu-2IT-BAT-Lym-1, 0.93 or 1.85-2.22 GBq/m2 (25 or 50-60 mCi/m2), with the lower dose used when NHL was detected in the bone marrow.

RESULTS

67Cu-2IT-BAT-Lym-1 provided good imaging of NHL and favorable radiation dosimetry. The mean radiation ratios of tumor to body and tumor to marrow were 28:1 and 15:1, respectively. Tumor-to-lung, -kidney and -liver radiation dose ratios were 7.4:1, 5.3:1 and 2.6: 1, respectively. This 67Cu-2IT-BAT-Lym-1 trial for patients with chemotherapy-resistant NHL had a response rate of 58% (7/12). No significant nonhematologic toxicity was observed. Hematologic toxicity, especially thrombocytopenia, was dose limiting.

CONCLUSION

67Cu remains an option for future clinical trials. This study established 67Cu-2IT-BAT-Lym-1 as a safe, effective treatment for patients with NHL.

Dosimetry-based therapy in metastatic breast cancer patients using 90Y monoclonal antibody 170H.82 with autologous stem cell support and cyclosporin A

Radioimmunoconjugates of 170H.82 (m170), a panadenocarcinoma monoclonal antibody, are effective for imaging primary and metastatic breast cancer. To evaluate m170 as a targeting agent for therapy, we developed (111)In- and 90Y-2-iminothiolane-2-[p-(bromoacetamido)benzyl]-1,4,7,10 tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-m170 immunoconjugates with 99% purity by molecular sieving and immunoreactivity comparable to unmodified antibody. (111)In-m170 pharmacokinetic studies were performed prior to each therapy to determine the maximum dose of 90Y-m170 that could be administered without exceeding a limit of 800 rad to the liver, lungs, or kidneys or 250 rad to the whole body or bone marrow for each of three cycles of treatment. Peripheral blood stem cells (PBSCs) were harvested and cyclosporin A (5 mg/kg twice daily) was administered as strategies to ameliorate myelosuppression and prevent the development of HAMA, respectively. An (111)In imaging/pharmacokinetic study was performed, and the 90Y dose was calculated and administered. The liver was the 90Y dose-limiting organ. The mean and range of calculated doses (in rad/mCi) for the five patients evaluated were as follows: whole body, 2.3 (2.1-2.4); liver, 17.8 (12.7-22.2); lung, 6.4 (4.8-7.2); kidney, 6.9 (6.3-11.5); marrow, 3.6 (1.9-4.4); and tumors (n = 25), 71.5 (14.1-141.5). Of the three patients treated, with doses of 37, 54, and 57 mCi of 90Y, one had a partial response, one had measurable tumor reduction but less than a partial response, and one had stable disease for more than 1 month. PBSCs prevented prolonged myelosuppression. The therapeutic responses, coupled with an absence, thus far, of significant adverse sequelae, suggest that this dosimetry-based approach combined with PBSCs may lead to effective therapy when higher 90Y doses are reached.

67Copper-2-iminothiolane-6-[p-(bromoacetamido)benzyl-TETA-Lym-1 for radioimmunotherapy of non-Hodgkin's lymphoma

Copper-67 (67Cu) has ideal properties for radioimmunotherapy. The 62-h half-life is similar to the residence time of antibodies in tumor, and the therapeutic beta emission of 67Cu is comparable to that of 131I. 67Cu, however, has gamma emissions similar to 99mtechnetium that are favorable for imaging. The macrocyclic chelating agent 1,4,7,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid (TETA) binds 67Cu tightly and selectively, facilitating linkage to Lym-1, a mouse monoclonal antibody that preferentially targets malignant lymphocytes. The safety, efficacy, and practicality of 67Cu-2-iminothiolane (2IT)-6-[p-(bromoacetamido)benzyl]-TETA (BAT)-Lym-1 was assessed in this Phase I/II clinical trial for patients with non-Hodgkin's lymphoma (NHL) who had failed standard therapy. Up to four doses of 67Cu-2IT-BAT-Lym-1, 25 or 50-60 mCi/m2/dose (0.93 or 1.85-2.22 GBq/m2/dose, respectively) were administered; the lower dosage was used when NHL was detected in the bone marrow. 67Cu-2IT-BAT-Lym-1 provided good imaging of NHL, had favorable radiation dosimetry, and had a response rate of 58% (7 of 12). Hematological toxicity was dose-limiting, but no significant nonhematological toxicity was observed. The ability to image and treat NHL patients with a single radiopharmaceutical with useful physical properties makes 67Cu-labeled monoclonal antibody an option for future clinical trials, as this study showed that 67Cu-2IT-BAT-Lym-1 was safe, effective, and practical.

Stability of monoclonal antibodies, Lym-1 and ChL6, and 2IT-BAD-Lym-1 immunoconjugate with ultra freezer storage

Use of a single lot of monoclonal antibody (MoAb) or immunoconjugate for clinical studies provides efficiency of scale and consistent characteristics for MoAb-based pharmaceuticals. Lym-1, an anti-lymphoma mouse IgG2 alpha chimeric L6 (ChL6), an anti-adenocarcinoma mouse IgG2 alpha-human IgG1 chimera, and the immunoconjugate 2IT-BAD-Lym-1 were examined for stability following storage.

METHODS

Lym-1, ChL6, and 2IT-BAD-Lym-1 were aliquotted with filtration and stored at -70 degrees C for up to 8.5 years. 2IT-BAD-Lym-1 stored for 6.3 years (lot A) was compared to freshly prepared 2IT-BAD-Lym-1 (lot B). MoAbs were thawed and examined yearly by gel filtration high performance liquid chromatography (HPLC), polyacrylamide gel electrophoresis (PAGE), cellulose acetate electrophoresis (CAE), and Scatchard analysis of antigen binding. 2IT-BAD-Lym-1 was evaluated by HPLC, CAE, and radioimmunoassay. To assure the in vivo significance of the in vitro studies, 2IT-BAD-Lym-1 lots A and B were labeled with 111In and their pharmacokinetics in BALB/c mice were compared.

RESULTS

Lym-1 demonstrated stability over 8.5 years, providing the following ranges of data over the interval: 98-100% chemical purity (HPLC), 96-100% monomeric fraction (CAE), 8.18-8.46 antigen binding pKa (Scatchard). Similar results were obtained for ChL6 for 7.4 years. HPLC and PAGE of Lym-1 and ChL6 have not changed from original manufacturer specifications, and both MoAbs remain sterile and apyrogenic. No significant differences between 2IT-BAD-Lym-1 lots A and B were observed by in vitro evaluation or pharmacokinetics in mice.

CONCLUSIONS

Lym-1, ChL6, and 2IT-BAD-Lym-1 as manufactured and stored for 8.5, 7.4, and 6.3 years, respectively, demonstrated retention of structural and functional integrity.

Radioimmunotherapy of acquired immunodeficiency syndrome (AIDS) associated lymphoma

Standard therapy for AIDS associated NHL (AANHL) is toxic and often ineffective. Radioimmunotherapy (RIT) is an appealing alternative to chemotherapy because of the radiosensitivity of NHL and the ability of the Lym-1 monoclonal antibody to target therapeutic irradiation to NHL while relatively sparing normal tissue. A Phase I/II study of 90Y-2IT-BAD-Lym-1 was designed specifically for RIT of AANHL. The first patient has been treated with 15 mCi (7.5 mCi/m2) of 90Y-2IT-BAD-Lym-1, after an imaging dose of 111In-2IT-BAD-Lym-1. Before RIT, AANHL in the maxillary sinus extended into the oral cavity and axillary adenopathy was present. Imaging showed excellent accumulation of 111In-2IT-BAD-Lym-1 in the tumors. Substantial shrinkage of the oral lymphoma was observed 18 hours after the therapy dose of 90Y-2IT-BAD-Lym-1 and axillary adenopathy had disappeared by one week after RIT. Transient Grade IV myelosuppression was the only notable toxicity. Further RIT cycles were precluded by development of an antibody response (HAMA) against Lym-1. This novel preliminary study has shown that Lym-1 can target AANHL and produce significant tumor regression thereby providing encouragement to proceed with additional patients.

67Cu-versus 131I-labeled Lym-1 antibody: comparative pharmacokinetics and dosimetry in patients with non-Hodgkin's lymphoma

Antilymphoma mouse monoclonal antibody (MoAb) Lym-1, labeled with 67Cu or 131I, has demonstrated promising results in radioimmunotherapy (RIT) for lymphoma. Although 131I has played a central role in RIT thus far, some properties of 67Cu are preferable. A subset of our patients received both 67Cu- and 131I-labeled Lym-1, allowing a comparative evaluation of the two radiopharmaceuticals administered to a matched population of patients. Four patients with B-lymphocytic non-Hodgkin's lymphoma that had progressed despite standard therapy entered trials of 67Cu- and 131I-labeled Lym-1, which were injected 3-26 days apart. Lym-1 was conjugated to 6-[p-(bromoacetamido)benzyl]-1,4,7,11-tetraazacyclotetradecane-N,N ',N",N'"-tetraacetic acid (BAT) via 2-iminothiolane (2IT) and radiolabeled with 67Cu to prepare 67Cu-2IT-BAT-Lym-1; 131I-Lym-1 was preparred by the chloramine-T reaction. Planar imaging was used to quantitate 67Cu-2IT-BAT-Lym-1 or 131I-Lym-1 in organs and tumors daily for 3 days or longer. 67Cu-2IT-BAT-Lym-1 exhibited higher peak concentration in 92% (12 of 13) of tumors and a longer biological half-time in every tumor than 131I-Lym-1. The mean tumor concentration (%ID/g) of 67Cu-2IT-BAT-Lym-1 was 1.7, 2.2, and 2.8 times that of 131I-Lym-1 at 0, 24, and 48 h after injection, respectively. The mean biological half-times of 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 in tumor were 8.8 and 2.3 days, respectively. Consequently, the mean tumor radiation dose delivered by 67Cu-2IT-BAT-Lym-1 was twice that of 131I-Lym-1, 2.8 (range 0.8-6.7), and 1.4 (range 0.4-35) Gy/GBq, respectively. 67Cu-2IT-BAT-Lym-1 delivered a lower marrow radiation dose than 131I-Lym-1; hence, the tumor:marrow therapeutic indices were 29 and 9.7, respectively. Radiation doses from 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 to normal tissues were similar except for liver, which received a higher dose from 67Cu-2IT-BAT-Lym-1. Images obtained with 67Cu-2IT-BAT-Lym-1 were superior. Radiation dosimetry data for 67Cu-2IT-BAT-Lym-1 and 131I-Lym-1 agreed with corresponding data from the larger populations of patients from which the matched population for the current study was drawn. In conclusion, 67Cu-2IT-BAT-Lym-1 given to non-Hodgkin's lymphoma patients in close temporal proximity to 131I-Lym-1 exhibited greater uptake and longer retention in tumor, resulting in higher radiation dose and therapeutic index than 131I-Lym-1. These as well as other factors suggest that 67Cu-2IT-BAT-Lym-1 may be superior to 131I-Lym-1 for RIT.

67Cu-2IT-BAT-Lym-1 pharmacokinetics, radiation dosimetry, toxicity and tumor regression in patients with lymphoma

Lym-1, a monoclonal antibody that preferentially targets malignant lymphocytes, has induced therapeutic responses and prolonged survival in patients with non-Hodgkin's lymphoma when labeled with 1311. Radiometal-labeled antibodies provide higher tumor radiation doses than corresponding 1311 antibodies. 67Cu has an exceptional combination of properties desirable for radioimmunotherapy, including gamma and beta emissions for imaging and therapy, respectively, a biocompatible half-time and absence of pathways contributing to myelotoxicity. The radioimmunoconjugate, 67Cu-21T-BAT-Lym-1, has been shown to be efficacious in nude mice bearing human Burkitt's lymphoma (Raji) xenografts. Based on these results, a clinical study of the pharmacokinetics and dosimetry of 67Cu-21T-BAT-Lym-1 in patients with lymphoma was initiated.

METHODS

Eleven patients with advanced stage 3 or 4 lymphoma were given a preload dose of unmodified Lym-1, then an imaging dose of 126-533 MBq (3.4-14.4 mCi) 67Cu-21T-BAT-Lym-1. Total Lym-1 ranged from 25 to 70 mg dependent on the specific activity of the radioimmunoconjugate and was infused at a rate of 0.5-1 mg/min. Imaging, physical examination, including caliper measurement of superficial tumors, and analysis of blood, urine and fecal samples were performed for a period of 6-13 d after infusion to assess pharmacokinetics, radiation dosimetry, toxicity and tumor regression.

RESULTS

In 7 patients, in whom superficial tumors had been accurately measured, tumors regressed from 18% to 75% (mean 48%) within several days of 67Cu-21T-BAT-Lym-1 infusion. The uptake and biological half-time of 67Cu-21T-BAT-Lym-1 in tumors were greater than those of normal tissues, except the mean liver half-time exceeded the mean tumor half-time. The mean tumor-to-marrow radiation ratio was 32:1, tumor-to-total body was 24:1 and tumor-to-liver was 1.5:1. Images were of very good quality; tumors and normal organs were readily identified. Mild and transient Lym-1 toxicity occurred in 6 patients; 1 patient developed a human antimouse antibody. There were no significant changes in blood counts or serum chemistries indicative of radiation toxicity.

CONCLUSION

Because of the long residence time of 67Cu-21T-BAT-Lym-1 in tumors, high therapeutic ratios were achieved and, remarkably, numerous tumor regressions were observed after imaging doses. The results indicate considerable therapeutic potential for 67Cu-21T-BAT-Lym-1.

Optimized conditions for chelation of yttrium-90-DOTA immunoconjugates

Radioimmunotherapy (RIT) with 90Y-labeled immunoconjugates has shown promise in clinical trials. The macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) binds 90Y with extraordinary stability, minimizing the toxicity of 90Y-DOTA immunoconjugates arising from loss of 90Y to bone. However, reported 90Y-DOTA immunoconjugate product yields have been typically only < or =50%. Improved yields are needed for RIT with 90Y-DOTA immunoconjugates to be practical.

METHODS

(S) 2-[p-(bromoacetamido)benzyl]-DOTA (BAD) was conjugated to the monoclonal antibody Lym-1 via 2-iminothiolane (2IT). The immunoconjugate product, 2IT-BAD-Lym-1, was labeled in excess yttrium in various buffers over a range of concentrations and pH. Kinetic studies were performed in selected buffers to estimate radiolabeling reaction times under prospective radiopharmacy labeling conditions. The effect of temperature on reaction kinetics was examined. Optimal radiolabeling conditions were identified and used in eight radiolabeling experiments with 2IT-BAD-Lym-1 and a second immunoconjugate, DOTA-peptide-chimeric L6, with 248-492 MBq (6.7-13.3 mCi) of 90Y.

RESULTS

Ammonium acetate buffer (0.5 M) was associated with the highest uptake of yttrium. On the basis of kinetic data, the time required to chelate 94% of 90Y (four half-times) under prospective radiopharmacy labeling conditions in 0.5 M ammonium acetate was 17-148 min at pH 6.5, but it was only 1-10 min at pH 7.5. Raising the reaction temperature from 25 degrees C to 37 degrees C markedly increased the chelation rate. Optimal radiolabeling conditions were identified as: 30-min reaction time, 0.5 M ammonium acetate buffer, pH 7-7.5 and 37 degrees C. In eight labeling experiments under optimal conditions, a mean product yield (+/- s.d.) of 91%+/-8% was achieved, comparable to iodination yields. The specific activity of final products was 74-130 MBq (2.0-3.5 mCi) of 90Y per mg of monoclonal antibody. The immunoreactivity of 90Y-labeled immunoconjugates was 100%+/-11%.

CONCLUSION

The optimization of 90Y-DOTA chelation conditions represents an important advance in 90Y RIT because it facilitates the dependable and cost-effective preparation of 90Y-DOTA pharmaceuticals.

Synergistic therapy of breast cancer with Y-90-chimeric L6 and paclitaxel in the xenografted mouse model: development of a clinical protocol

BACKGROUND

Paclitaxel (Taxol) has demonstrated synergistic enhancement of radioimmunotherapy (RIT) of breast cancer with Y-90 labeled antibody ChL6, in the xenografted mouse model. To determine the optimal sequence and timing of RIT and Taxol for a prospective clinical trial, efficacy and dosimetry in mice, and dosimetry in patients receiving RIT alone, were examined.

MATERIALS AND METHODS

Mice bearing human breast cancer xenografts (HBT 3477) received i.v. Y-90-DOTA-peptide-ChL6 (260 microCi), and i.p. Taxol (300 or 600 micrograms) 72, 48, or 24 hours prior to RIT, or 6, 24, 48, or 72 hours after RIT.

RESULTS

Taxol after RIT resulted in cure, CR, or PR of all mice (70/70 tumors) and demonstrated greater therapeutic enhancement (p = 0.001) than Taxol before RIT. Mice receiving 600 micrograms Taxol 48 hours after RIT achieved 88% cure (7/8 tumors). In mice, 57% and 42% of the radiation dose to tumor and marrow, respectively, was delivered from 48-336 hours after RIT; in patients receiving 90Y-DOTA-peptide-ChL6, the corresponding values were 56% and 22%.

CONCLUSIONS

Taxol given approximately 48 hours after RIT provides coincident peak deposition of Taxol and Y-90 in tumor, and no Taxol in the marrow during the major radiation dose to marrow, resulting in therapeutic enhancement without observable additive toxicity. A clinical trial of low dose Taxol given after RIT to patients with metastatic breast cancer is planned.

Combined modality radioimmunotherapy with Taxol and 90Y-Lym-1 for Raji lymphoma xenografts

Despite effective therapies for non-Hodgkin's lymphoma (NHL), the majority of patients are not cured. Radioimmunotherapy (RIT) has shown good results in preclinical and clinical trials even in patients that are non-responsive to standard chemotherapy. To make RIT more effective, agents such as paclitaxel (Taxol), that can enhance radiation effects, are being tested. Nude mice bearing human Burkitt's lymphoma (Raji) xenografts were treated with: 1) 150 or 200 microCi (5.5 or 7.3 MBq) of 90Y-2IT-BAD-Lym-1 alone, 2) 600 micrograms of Taxol alone, 3) 150 or 200 microCi of 90Y-2IT-BAD-Lym-1 plus 600 micrograms of Taxol given 24 hours after RIT, or 4) no treatment. Tumor size, survival, mouse weight and blood counts were monitored to assess efficacy and toxicity. Survival for mice treated in this 84 day trial was: 71% for 90Y-2IT-BAD-Lym-1 (200 microCi) plus Taxol, 29% for Taxol alone, 6% for 90Y-2IT-BAD-Lym-1 (200 microCi) alone and 14% in the untreated group. Average tumor volume in the 90Y-2IT-BAD-Lym-1 (200 microCi) plus Taxol group was reduced by 89 and 99% compared to the RIT alone and Taxol alone groups, respectively. Mice treated with 150 microCi had less toxicity than those treated with 200 microCi of 90Y-2IT-BAD-Lym-1, however, the higher radiation dose, and Taxol, were required for improved survival. Mouse weights and myelotoxicity in the combined modality (RIT plus Taxol) groups were similar to those receiving the same dose of RIT alone. In the Raji tumored nude mouse model, addition of Taxol to 90Y-2IT-BAD-Lym-1, in doses clinically achievable in humans, provided therapeutic synergy without increased or excessive toxicity.

Maximum tolerated dose of 67Cu-2IT-BAT-LYM-1 for fractionated radioimmunotherapy of non-Hodgkin's lymphoma: a pilot study

PURPOSE

Lym-1, a monoclonal antibody (MoAb) that preferentially targets malignant lymphocytes, has induced therapeutic responses in patients with non-Hodgkin's lymphoma (NHL) when labeled with iodine-131 (131I). Radiometal labeled antibodies provide a higher tumor radiation dose than the corresponding 131I labeled antibodies. Based on the strategy of fractionating the total radiation dose, this study was designed to define the maximum tolerated dose (MTD) of the first 2, of a maximum of 4, doses of 67Cu-2IT-BAT-Lym-1 given 4 weeks apart. Additionally, toxicity, radiation dosimetry and efficacy were assessed.

MATERIALS AND METHODS

Patients had Ann Arbor stage IVB NHL, resistant to standard therapy, including multiple chemotherapy regimens. Each dose of 67Cu-2IT-BAT-Lym-1 was given after a preload of unmodified Lym-1. A 10 mCi imaging dose of 67Cu-2IT-BAT-Lym-1 was given in order to assess pharmacokinetics and radiation dosimetry prior to therapy. Based on the MTD for 131I-Lym-1 and comparative dosimetry for 131I-Lym-1 and 67Cu-2IT-BAT-Lym-1, the trial was initiated at 60 millicuries per square meter of body surface area (mCi/m2) in cohorts of 3 patients.

RESULTS

A single cohort of patients proved sufficient to define the MTD as 60 mCi/m2 for each of the first 2 doses of 67Cu-2IT-BAT-Lym-1. The dose-limiting toxicities were grade 3-4 thrombocytopenia and neutropenia. Neutropenic sepsis and bleeding did not occur. Mean radiation dose contributed to the bone marrow by 67Cu in the body and blood was 0.2 (range, 0.2 to 0.3) rads/mCi. Copper-67 incorporated into ceruloplasmin contributed 25% of the dose to marrow from blood. Non-hematologic toxicities did not exceed grade 2. The three patients had substantial tumor regression even after imaging doses of 67Cu-2IT-BAT-Lym-1. After therapy, one response was complete with a duration of 12 months. Radiation doses to tumors in this patient varied from 7.0-21.9 rads/mCi or 5420-7000 total rads from the course of therapy.

CONCLUSION

67Cu-2IT-BAT-Lym-1 provided good imaging, favorable radiation dosimetry and a remarkably high therapeutic index (ratio of tumor to marrow radiation doses). The non-myeloablative MTD for each of 2 doses was 60 mCi/m2.

Yttrium-90-DOTA-peptide-chimeric L6 radioimmunoconjugate: efficacy and toxicity in mice bearing p53 mutant human breast cancer xenografts

The novel radioimmunoconjugate, 90Y-DOTA-peptide-chimeric L6 (ChL6), was designed to reduce radiation to critical normal tissues with an exceptionally stable 90Y chelate moiety and a biodegradable linker. Human breast cancer tumors (HBT 3477) in mice were treated with 90Y-DOTA-peptide-ChL6 to examine the effects of increasing dose on the therapeutic efficacy and toxicity of this new agent.

METHODS

Groups of athymic mice bearing HBT 3477 xenografts received 4.1- to 14.1-MBq doses of 90Y-DOTA-peptide-ChL6 intravenously. The lethal dose (LD)(50/30), general well-being (weight loss), hematotoxicity and therapeutic efficacy were studied.

RESULTS

The LD(50/30) was 12.8 MBq, which corresponded to doses of 17.9 and 50.9 Gy to the total body and tumor (200 mm3), respectively. Deaths were associated with hematotoxicity; no deaths occurred at doses of 9.6 MBq or less. At sublethal doses, the rate of tumor response (cures +/- complete responses + partial responses) increased with increasing dose: 4.1 MBq, 27%; 5.9 MBq, 41%; 8.5 MBq, 69%; and 9.6 MBq, 79% (maximum tolerated dose, MTD). In mice receiving doses of 4.1-9.6 MBq, 6 of 74 (8%) of tumors were cured. Increasing the 90Y dose led to smaller tumor size at nadir and longer tumor regrowth delay but no increase in cure. Although the HBT 3477 p53 gene was found to be mutant resulting in p53 protein not binding DNA breaks, tumors at MTD demonstrated evidence of apoptosis.

CONCLUSION

In the human breast cancer athymic mouse model, 90Y-DOTA-peptide-ChL6 had a high therapeutic index and LD(50/30) leading to a 79% response rate at the MTD. The evidence of apoptosis as a mechanism for this tumor response in p53 mutant breast cancer warrants further studies because these observations are relevant to the treatment of lethal breast cancer.

Enhancement of 67Cu-2IT-BAT-LYM-1 therapy in mice with human Burkitt's lymphoma (Raji) using interleukin-2

BACKGROUND

Lymphomas have been shown to be responsive to 131I immunoconjugates in studies conducted in mice and patients. We have observed that copper 67 (67Cu)-labeled Lym-1 remains in lymphomatous tissue longer than 131I-Lym-1 and, consequently, results in higher absorbed radiation doses to tumors. In addition, recombinant interleukin-2 (rIL-2) has been reported to increase tumor uptake of radiolabeled antibody. Therefore, we examined the efficacy of 67Cu-labeled Lym-1 and the ability of rIL-2 to enhance this efficacy in athymic mice implanted with Raji xenografts.

METHODS

6[p-(bromoacetamido) benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N', N'',N'''-tetraacetic acid (BAT) was conjugated to Lym-1 via 2-iminothiolane (2IT) to prepare 2IT-BAT-Lym-1, which was labeled with 67Cu. Mice with Raji xenografts were treated with 335-500 microCi (12.4-18.0 MBq) of 67Cu-2IT-BAT-Lym-1 with or without 48,000-144,000 IU of rIL-2 once or were treated b.i.d. for 5 days beginning simultaneously with 67Cu-2IT-BAT-Lym-1. Mouse weight, blood counts, and mortality were monitored to assess toxicity, and tumor size was measured to assess efficacy. In addition, groups of mice were sacrificed to assess the biodistribution of 67Cu-2IT-BAT-Lym-1 with and without rIL-2.

RESULTS

In mice treated with 335 microCi of 67Cu-2IT-BAT-Lym-1 alone, 28% of tumors were cured. When 48,000 IU of rIL-2 were added, 50% were cured. The overall response-rate was 50% for both regimens. In mice treated with 400 microCi of 67Cu-2IT-BAT-Lym-1 alone, 42% responded, all of which were cured. When 48,000 IU of rIL-2 were added, 77% of tumors responded, and 38% were cured. Larger or multiple doses of rIL-2 did not result in additional therapeutic enhancement. The tumor uptake and radiation dose after 67Cu-2IT-BAT-Lym-1 were about two times greater when a single dose of rIL-2 was added: This may be the basis for enhanced therapeutic efficacy. Mortality was not altered for 335 microCi or 400 microCi doses of 67Cu-2IT-BAT-Lym-1 by rIL-2 nor were other toxicity parameters. Mortality was increased at 500 microCi by the addition of rIL-2.

CONCLUSIONS

67Cu-2IT-BAT-Lym-1 provided a therapeutic and frequently curative dose of radiation to tumored mice at tolerated doses. The therapeutic effectiveness of 67Cu-2IT-BAT-Lym-1 may have been enhanced by rIL-2.

Importance of temporal relationships in combined modality radioimmunotherapy of breast carcinoma

BACKGROUND

The beneficial effects of radioimmunotherapy (RIT) may result from activation of molecular pathways that lead to programmed cell death (apoptosis). The influences of sequence and timing of 90Y-DOTA-peptide-ChL6 antibody (90Y-ChL6) and anti-epidermal growth factor receptor antibody (ch225) or paclitaxel (Taxol; Bristol-Myers Squibb, Princeton, NJ) on efficacy and toxicity were examined.

METHODS

Groups of human breast carcinoma (HBT 3477) tumored mice received paclitaxel (300 or 600 microg) or ch225 (70, 150, or 350 microg) at various intervals before or after 90Y-ChL6. Mortality, hematologic toxicity, weight loss, and therapeutic efficacy were evaluated.

RESULTS

Mice receiving paclitaxel within 24 hours of 90Y-ChL6 had a 100% response rate; 48% were cured when paclitaxel was given 6 or 24 hours after 90Y-ChL6. When 150 microg ch225 was given 24 hours before 90Y-ChL6, the response and cure rates surpassed those of 90Y-ChL6 alone. Timing of administration was critical, with mortality rates as high as 80% in some groups receiving 350 microg ch225 and 90Y-ChL6.

CONCLUSIONS

In this aggressive human breast carcinoma model, combined 90Y-ChL6 and paclitaxel had a high therapeutic index with many cures. Sequence of administration was critical in order for ch225 or paclitaxel, when combined with 90Y-ChL6, to enhance the response rate.

Yttrium-90/indium-111-DOTA-peptide-chimeric L6: pharmacokinetics, dosimetry and initial results in patients with incurable breast cancer

BACKGROUND

Radioimmunotherapy (RIT) using 131I-Chimeric L6 (ChL6) antibody has shown therapeutic promise for patients with breast cancer. To enhance this potential, a novel immunoconjugate was developed that targets adenocarcinomas like breast cancer and tightly binds yttrium-90 (90Y) for therapy and indium-111 (111In) for imaging. The radioimmunoconjugate consists of a macrocyclic chelator (DOTA) linked to ChL6 by a catabolizable peptide. 90Y-DOTA-peptide-ChL6 was designed to minimize the radiation dose to critical normal tissues, thereby improving the therapeutic index.

MATERIALS AND METHODS

Three patients with incurable metastatic breast cancer received 90Y/111In-DOTA-peptide-ChL6 for 5 pharmacokinetics/dosimetry studies and one of these patients also received 2 therapy doses. Quantitative imaging of 111In and in vitro assay of 90Y and 111In in blood urine and bone marrow samples were obtained.

RESULTS

90Y/111In-DOTA-peptide-ChL6 was prepared at high purity and was stable in vivo. Assays of bone marrow revealed no evidence for escape of 90Y or 111In from the chelate. 111In imaging of tumors was excellent, providing a therapeutic index for tumor to marrow radiation as high as 229 to 1. 90Y and 111In provided comparable pharmacokinetics, as did tracer and therapeutic doses of radioimmunoconjugates. One patients that received 2 therapeutic doses of 90Y-DOTA-peptide-ChL6 showed regression of tumors and tumor markers. Toxicities were relatively minor and no anti-globulin response developed despite 5 immunoconjugate infusions.

CONCLUSIONS

This first study in patients of radioimmunoconjugates with a catabolizable linker between the metal chelator and the antibody confirmed that these novel 90Y/111In-DOTA-peptide-ChL6 radioimmunoconjugates have significant potential. Tracer doses of 111In-DOTA-peptide-ChL6 for imaging predicted the behavior of therapeutic doses of 90Y-DOTA-peptide-ChL6. The latter radioimmunoconjugate induced regression of tumors and tumor markers without significant toxicity. When compared to earlier 131I-ChL6 dosimetry, 90Y-DOTA-peptide-ChL6 provided a therapeutic index several times better.

Synergy of Taxol and radioimmunotherapy with yttrium-90-labeled chimeric L6 antibody: efficacy and toxicity in breast cancer xenografts

Synergistic multimodality therapy is needed for breast cancer. Breast cancer frequently has p53 mutations that result in cells less likely to undergo apoptosis when exposed to DNA damaging therapies. Taxol (paclitaxel) is more effective in the presence of mutant p53. (90)Y-labeled DOTA-peptide-ChL6 ((90)Y-ChL6, where ChL6 is chimeric L6 antibody and DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid) is a novel radioimmunoconjugate for targeting radiation to cancer. It has a stable metal chelator and a peptide linker that can be catabolized by hepatic lysozymes. This study was designed to assess potential synergism between Taxol and (90)Y-ChL6 in a highly anaplastic breast cancer model, HBT 3477. There was no tumor response in mice receiving ChL6 or Taxol alone. In mice receiving (90)Y-ChL6 alone, 79% (15 of 19) of tumors responded although none were cured. If Taxol was administered 24-72 hours before (90)Y-ChL6, again, 79% (23 of 29) of tumors responded but 21% were cured. When Taxol was administered 6 or 24 hours after (90)Y-ChL6, 100% (46 of 46) of tumors responded and 48% were cured. Taxol given with (90)Y-ChL6 did not substantially increase toxicity. Enhancement of the therapeutic effect when Taxol was added to (90)Y-ChL6 therapy for HBT 3477 xenografts was striking. The synergistic therapeutic effect of Taxol with (90)Y-ChL6 may relate to the p53 mutant status and BCL2 expression in HBT 3477 cells, observations that increase the likelihood that the results of this study are relevant to therapy for breast cancer in patients. In conclusion, Taxol seemed to be synergistic with (90)Y-ChL6 in this human breast cancer model. Up to 50% of these anaplastic breast cancer xenografts were cured by combined modality therapy.

Efficacy and toxicity of 67Cu-2IT-BAT-Lym-1 radioimmunoconjugate in mice implanted with human Burkitt's lymphoma (Raji)

Radioimmunotherapy has shown promising results for treatment of radiosensitive malignancies such as lymphoma. Positive responses have been reported in patients with non-Hodgkin's lymphoma treated with 131I-radiolabeled Lym-1, a mouse anti-lymphoma monoclonal antibody. In this study, the efficacy of 67Cu-radiolabeled Lym-1 was examined. Nude mice bearing human Burkitt's lymphoma (Raji) tumors (20-524 mm3) were treated with 12.4, 14.8, 18.5, and 23.3 MBq of 67Cu-2IT-BAT-Lym-1. Tumor size was measured to assess efficacy, and mouse weight, blood counts, and mortality were monitored to assess toxicity. In mice treated with 12.4, 14.8, and 18.5 MBq of 67Cu-2IT-BAT-Lym-1, 50% (9 of 18), 42% (5 of 12), and 50% (3 of 6) of tumors achieved remission or cure; 33% of tumors were cured overall; and significant regrowth delay was observed. The 23.3 MBq dose group did not yield meaningful efficacy data because of high mortality. In control groups receiving 14.8 and 18.5 MBq of the isotype-matched nonspecific monoclonal antibody radioimmunoconjugate, 67Cu-2IT-BAT-L6, 0% (0 of 15) and 17% (2 of 12) of tumors achieved a response; hence, targeted delivery of radiation was the dominant antitumor mechanism of 67Cu-2IT-BAT-Lym-1. LD50/30 for mice treated with 67Cu-2IT-BAT-Lym-1 and -L6 were 21.6 and 20.6 MBq, respectively. In conclusion, 67Cu-2IT-BAT-Lym-1 provided a therapeutic and frequently curative dose of radiation to tumored mice with modest toxicity.

Accurate measurement of copper-67 in the presence of copper-64 contaminant using a dose calibrator

The use of 67Cu-labeled antibodies for the treatment of cancer has advanced to the clinical trial phase. Quantitation of 67Cu radiopharmaceuticals is complicated by the presence of the radioimpurity of 64Cu in 67Cu supplies. Here we report a method to assay 67Cu and 64Cu in a mixed sample with a commonly available instrument, the ionization chamber dose calibrator.

METHODS

The activities of 67Cu and 64Cu in a mixed sample can be calculated from a single-dose calibrator measurement. The calculation requires (1) instrument-specific response coefficients D67 and D64, generated by gauging the instrument for the efficiency of measurement of 67Cu and 64Cu, and (2) a value for the ratio of 67Cu to 64Cu in the sample, routinely provided by major suppliers of 67Cu. D67 and D64 were empirically determined by measuring samples containing known amounts of 67Cu and 64Cu. The samples were also assayed by gamma ray spectroscopy to verify the isotope ratios given by the suppliers.

RESULTS

This method generated accurate response coefficients. At the recommended dose calibrator setting for the measurement of 67Cu, at which D67 = 1.0, the measurement for D67 with this method was 1.02 (+/- 0.04). Isotope ratios provided by the radionuclide suppliers were corroborated by gamma ray spectroscopy.

CONCLUSION

A method is presented by which 67Cu and 64Cu in a mixed sample can be assayed using a dose calibrator. Although the derived numeric constants are only correct for a specific dose calibrator and setting, the method can be adapted for use with any dose calibrator.

Prelabeling of chimeric monoclonal antibody L6 with 90yttrium- and 111indium-1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) chelates for radioimmunodiagnosis and therapy

90Y and 111In have been attached to chimeric monoclonal antibody L6 with a bifunctional chelating agent (DOTA-peptide isothiocyanate). The bifunctional chelating agent was prelabeled with either radiometal and then conjugated to the antibody. Studies in human patients showed excellent 111In single-photon emission computed tomography images of breast cancer lesions 24 h after injection.

Effect of the extent of chelate substitution on the immunoreactivity and biodistribution of 2IT-BAT-Lym-1 immunoconjugates

Trial therapy for lymphoma with the radiolabeled chelate-antibody conjugate 67Cu-2IT-BAT-Lym-1 has been promising. It is desirable to deliver therapeutic doses of radiometal using a minimum amount of 2IT-BAT-Lym-1 to minimize the risks of adverse patient reaction and antigenic response to antibody. This is readily accomplished by increasing the number of metal-binding sites (i.e., chelating agents) conjugated per antibody, but the ability of the antibody to bind antigen and target tumor cells in vivo must not be impaired by the conjugation reaction. To determine the maximum chelator:antibody ratio (c/a) of 2IT-BAT-Lym-1 at which functional integrity is preserved, immunoconjugates with a c/a of 1.3-23 were prepared and examined by radioimmunoassay and competitive antigen binding versus lightly iodinated Lym-1. The biodistribution in tumored mice of conjugates with c/a of 2.1, 4.3, 8.4, and 11.4 also was examined. Conjugates with c/a up to 5 exhibited no loss of immunoreactivity, and conjugates with c/a up to 11 retained 75% or greater immunoreactivity relative to unmodified Lym-1. All conjugates examined competed less effectively than did unmodified Lym-1 for antigen binding, but the effect at c/a 5 was slight. Tumor uptake declined with increasing c/a, but the effect was insignificant at c/a 2.1 and 4.3. Conjugates of c/a 4-5 were found to be optimal for the preparation of radioimmunoconjugate of high specific activity with minimal, if any, loss of functional integrity.

Pharmacokinetics of pretargeted monoclonal antibody 2D12.5 and 88Y-Janus-2-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecanetetraacetic acid (DOTA) in BALB/c mice with KHJJ mouse adenocarcinoma: a model for 90Y radioimmunotherapy

Three-step pretargeting for radioimmunotherapy in BALB/c mice with KHJJ tumors was done with monoclonal antibody (mAb) 2D12.5, which is specific for yttrium-1,4,7,10-tetraazacyclododecanetetraacetic acid (DOTA) but nonspecific for the tumor. Tumor uptake was by passive diffusion of mAb through leaky neovasculature in the tumor. The three steps were: (a) anti-hapten mAb 2D12.5 (0 h); (b) polyvalent haptenprotein conjugate chase (20 h); and (c) 88Y-labeled monovalent DOTA or bivalent Janus-DOTA haptens (21 h) and organ and tumor bioassay (24 h). Rapid tumor (T) uptake and high tumor:blood ratio (T:BL) was seen 3 h after injection after step c. For monovalent 88Y-DOTA, T = 1.7%/g* and T:BL = 16:1; for bivalent 88Y-Janus-DOTA, T = 4.41%/g* and T:BL = 21:1 at 3 h (*, P < 0.001). Blood and bone plus marrow were << 1%/g, and liver was < 1%/g. The 24-h whole body retention was approximately 5% of injected dose with 1% in tumor (20% of total), 1.8% in other organs, and 2.2% in carcass; the 24-h whole body retention of covalent nonspecific antibody conjugates was > 80% of injected dose. The biological half-life in the tumor of 0.9 microCi 88Y-Janus-DOTA was approximately 24 h, measured daily for 5 days. Activity in microCi/g of tumor and blood for 90Y equimolar to the amount of 88Y injected (0.9 microCi 88Y = 0.744 pmol = 36.47 microCi 90Y) was used for calculating the area under the curve of tumor and blood in microCi-h/g of 90Y. The 90Y radiation absorbed dose (RAD) from multiplying microCi-h/g x the 90Y absorbed dose constant, 1.99 RAD-g/microCi-h, gave T = 89 RAD and BL = 3.7 RAD. The therapeutic ratio from RAD T:RAD BL = 24:1. These results indicate that pretargeting 90Y hapten-specific mAb for radioimmunotherapy has considerable promise.

Comparative toxicity studies of yttrium-90 MX-DTPA and 2-IT-BAD conjugated monoclonal antibody (BrE-3)

BACKGROUND

BrE-3 is monoclonal antibody that has promise for imaging and therapy of human adenocarcinoma. Because of observations in therapeutic trials of yttrium-90 (90Y) escape from radioimmunoconjugates and uptake by the skeleton with resultant bone marrow toxicity, the authors attempted to evaluate the importance of this factor by a comparison of the LD50 in healthy mice treated with 90Y that had been chelated with either of two high affinity chelators, methylbenzyldiethylene-triaminepentaacetic acid (MX-DTPA) or bromoacetamidobenzyl-1,4,7,10-tetraazocyclododecane- N,N',N'',N'''-tetraacetic acid (BAD).

METHODS AND RESULTS

Bone marrow hematopoietic toxicity was dose-limiting and the source of death for both chelators. The LD50 for 90Y-BrE-3-MX-DTPA was 220.9 microCi, and that for 90Y-BrE-3-2IT-BAD and was 307.8 microCi. Whole-body autoradiography revealed substantially greater uptake of 90Y in the skeleton when MX-DTPA was used as the chelator.

CONCLUSIONS

These observations suggest that 90Y escape to bone is a significant factor in the maximum tolerated dose of radioimmunoconjugate that can be used in therapeutic trials. These results probably underestimate the importance of 90Y escape since 90Y in the skeleton of patients is likely to be more significant than in mice because more of the 90Y energy is absorbed in the marrow of larger species.

A comparative study of copper-67 radiolabeling and kinetic stabilities of antibody-macrocycle chelate conjugates

BACKGROUND

The development of new chelating agents and radiolabeling protocols is essential to progress in radioimmunotherapy with antibody-chelate conjugates.

METHODS

Immunoconjugates of four polyazamacrocycles with N-bonded acetate groups were prepared by conjugation via 2-iminothiolane to Lym-1, a murine antilymphoma immunoglobulin G2a MoAb. To optimize 67Cu radiolabeling, complexation conditions were explored. The kinetic stabilities in vitro in human serum of four 67Cu labeled immunoconjugates were investigated.

RESULTS

Lym-1-2IT-6-BAT-67Cu, the chelate conjugate of 6-[p-(bromoacetamido)benzyl]-1,4,8,11-tetraazacyclotetradecane- N,N',N''N'''-tetraacetic acid, exhibited excellent kinetic stability in human serum, while Lym-1-2IT-2-BAT-67Cu, prepared from the structural isomer 2-[p-(bromoacetamido)benzyl]-1,4,8,11- tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid, exhibited a markedly higher rate of loss of radiometal. It was observed that the radiolabeling ratio of Lym-1-2IT-6-BAT-67Cu, in mCi per mg immunoconjugate, was limited solely by the specific activity of the radiometal, which varied significantly from lot to lot. This ratio for a given lot of 67Cu can be predicted by a preliminary titration.

CONCLUSIONS

The preparation of 67Cu labeled immunoconjugates of therapeutic quality has been improved by the determination of optimum radiolabeling conditions, and by development of a titration protocol which rapidly and accurately predicts the radiolabeling ratio in mCi per mg immunoconjugate. The surprising difference in the properties of 6-BAT and 2-BAT shows the exquisite dependence of kinetic stability on structure.

Influence of a peptide linker on biodistribution and metabolism of antibody-conjugated benzyl-EDTA. Comparison of enzymatic digestion in vitro and in vivo

Insight into the metabolism of radiolabeled antibodies is important for the design of better radioimaging and therapy agents. To test the effect of linkers that can be cleaved in vivo, we introduced Ala-Leu-Ala-Leu between the antibody Lym-1 and an 111In-labeled benzyl-EDTA. For comparison, we studied a conjugate without the linker. Digestion of the two conjugates in vitro showed that the one with Ala-Leu-Ala-Leu was cleaved rapidly by the liver protease cathepsin B1 (T1/2 approximately 6 h). After 100 h of digestion, reversed-phase HPLC product analysis of the Ala-Leu-Ala-Leu conjugate showed that 48% of the total radioactivity had the same retention time as (p-aminobenzyl)-EDTA(In), and 37% of the total radioactivity had the same retention time as [p-(Ala-Leu-amido)benzyl]-EDTA(In). After 97 h of digestion, the conjugate without the linker had 79% of the radioactivity activity still attached to the protein. We also tested the two conjugates in mice. Ala-Leu-Ala-Leu had only a moderate effect on the whole body and liver clearance in vivo. The excretion of the radioactivity was about 6% per day with the linker and about 3% per day without the linker. HPLC analysis of the urine of a single mouse showed products similar to the in vitro study; 54% of the excreted radioactivity had the same retention time as (p-aminobenzyl)-EDTA(In), while 10% had the retention time of [p-(Ala-Leu-amido)benzyl]-EDTA(In).

Yttrium-90-labeled monoclonal antibody for therapy: labeling by a new macrocyclic bifunctional chelating agent

Yttrium-90 (90Y) is a promising radiometal for therapy of cancer due to its high-energy beta emission and a physical half-life of 2.67 days. Bifunctional chelating agents based on DTPA cyclic anhydride or EDTA do not form Y(III) complexes that are stable under physiologic conditions. A new macrocyclic bifunctional chelating agent based on 1,4,7,10-tetraazacylododecane-N,N',N",N"'-tetraacetic acid (DOTA) forms a stable Y(III) complex. It was converted to p-bromoacetamidobenzyl-DOTA (BAD), and conjugated to monoclonal antibody Lym-1 via 2-iminothiolane, either as the free ligand or as the 88Y chelate. Stability studies of Lym-1-2IT-BAD-88Y in human serum in vitro showed no measurable loss of Y(III) from the ligand over a 25-day period. In Raji-tumored mice, tumor uptake was 16.8% of the injected dose per gram of tissue on Day 3. The bone uptake was 2.0, 3.6, and 2.1% injected dose per gram of tissue on Day 1, 3, and 5, respectively. The biodistribution of the control 88Y-citrate demonstrated continuous increase in bone uptake from 13.8% injected dose per gram on Day 1 to 24.9% injected dose per gram on Day 4.