Prolonged survival associated with immune response in a patient treated with Lym-1 mouse monoclonal antibody

Current results and future applications of radioimmunotherapy management of non-Hodgkin's lymphoma

Monoclonal antibodies labeled with radionuclides have become an important therapeutic tool in the treatment of patients with non-Hodgkin's lymphomas (NHL). At the present time, their use in the US is approved for patients with rituximab-resistant, low-grade, follicular or transformed NHL. Encouraging responses seen in the relapsed and refractory patients have prompted their evaluation in earlier disease or in other histologic sub-types either alone or in combination with conventional chemotherapy. Additionally, they have been included as preparative regimens for stem cell transplant protocols within the context of clinical trials. This review discusses the latest clinical trials and future directions of radioimmunoconjugates in the treatment of NHL, with emphasis on US Food and Drug Administration (FDA) approved radioimmunoconjugates, namely 131I-tositumomab and 90Y-ibritumomab tiuxetan.

Survival benefit associated with human anti-mouse antibody (HAMA) in patients with B-cell malignancies

BACKGROUND

About one-third of patients with relapsed B-cell malignancies develop human anti-mouse antibody (HAMA) following mouse antibody treatment. The purpose of this study was to assess the relationship between HAMA and survival in patients given a mouse anti-lymphoma monoclonal antibody (mAb), Lym-1, directed against a unique epitope of HLA-DR antigen that is up-regulated on malignant B-cells.

METHODS

ELISA was used to quantify HAMA in 51 patients with B-cell malignancies treated with iodine-131 (131I) labeled Lym-1. Sera were collected prior to and following radioimmunotherapy (RIT) with 131I-Lym-1 until documented to be HAMA negative or throughout lifetime. Univariate, then multivariate analyses including other risk factors, were used to analyze the relationship of HAMA to survival. The relationships of HAMA to prior chemotherapies and to absolute lymphocyte counts prior to RIT were also assessed.

RESULTS

Eighteen of 51 patients (35%) developed HAMA following RIT (range of ultimate maximum titers, 6.6-1,802 microg/ml). Using the time dependent Cox proportional hazards model, maximum HAMA titers were associated with survival (P=0.02). HAMA continued to be significant for survival in multivariate analyses that included known risk factors. In Landmark analysis of 39 patients that survived at least 16 weeks, median survival of patients with HAMA less than 5 microg/ml was 61 versus 103 weeks for patients with HAMA equal or greater than 5 microg/ml at 16 weeks (P=0.02). The median survival of the five patients with highest maximum HAMA titers was 244 weeks. At 16 weeks, there was an inverse correlation between the maximum HAMA titer and the number of previous chemotherapies (P<0.003). Absolute lymphocyte counts prior to 131I-Lym-1 treatment for patients that seroconverted were higher than those for patients that did not seroconvert (P=0.01).

CONCLUSIONS

Patients with B-cell malignancies that developed high HAMA titers had longer survival that was not explained by risk factors or histologic grade, suggesting the importance of the immune system.

Selection of aptamers with high affinity and high specificity against C595, an anti-MUC1 IgG3 monoclonal antibody, for antibody targeting

Targeting of antibodies has found a number of applications in assays, anti-idiotypic therapies and vaccine design with a number of anti-idiotypic Abs generated and used in clinical applications, and some currently in clinical trials. Meanwhile, aptamers are a novel and particularly interesting targeting modality, with a unique ability to bind to a variety of targets. Aptamers offer unique benefits compared to other targeting agents, due to their high affinity and selectivity, relatively small size and in vitro synthesis, making them attractive alternatives to Abs and peptides. Aptamers have already been selected against a number of Abs for various applications. We now present a novel methodology for the selection of aptamers against Abs, which minimises the number of steps used and results in molecules that bind to the target Ab with high affinity and specificity. We have used the well-characterised anti-MUC1 monoclonal Ab C595 as an exemplar for raising aptamers against Abs. The methodology is based on the adsorption of the Ab to the surface of a PCR tube and the performance of SELEX selections in the PCR tube, based on elution steps resulting from the denaturation of the Ab on the first PCR amplification cycle. After 10 rounds of selection and amplification, selected aptamers have been characterised using a number of techniques, including fluorescence quenching, ELISA and competition ELISA procedures and a FRET type assay. Aptamers were found to bind their target Ab with a higher affinity than its natural antigenic peptide, as observed in fluorescent quenching and FRET experiments. Furthermore, they were able to displace the antigens from the antibody binding pocket in competition assays. This methodology offers the possibility of rapidly selecting aptamers for antibody targeting that could be used as diagnostic, imaging or therapeutic agents, or as recognition units in immunoassays, and can be potentially useful in raising aptamers against other protein targets.

Advancing role of radiolabeled antibodies in the therapy of cancer

This review focuses on the use of radiolabeled antibodies in the therapy of cancer, termed radioimmunotherapy (RAIT). Basic problems concerned with the choice of antibody, radionuclide, and physiology of the tumor and host are discussed, followed by a review of the pertinent clinical publications of various radioantibody constructs in the treatment of hematopoietic and solid tumors of diverse histopathology, grade, and stage, and in different clinical settings. Factors such as dose rate delivered, tumor size, and radiosensitivity play a major role in determining therapeutic response, while target-to-nontarget ratios and, particularly, circulating radioactivity to the bone marrow determine the principal dose-limiting toxicities. RAIT appears to be gaining a place in the therapy of hematopoietic neoplasms, such as non-Hodgkin's lymphoma: several agents are advancing in clinical trials toward registration, and one has recently been approved by the FDA. Although RAIT of solid tumors has shown less progress, use of pretargeting strategies, such as an affinity-enhancement system consisting of bispecific antibodies separating targeting from delivery of the radiotherapeutic, appears to enhance tumor-to-nontumor ratios, and may increase radiation doses to tumors more selectively than directly labeled antibodies.

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

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

Milestones in the development of Lym-1 therapy

Lym-1, a monoclonal antibody (MAb) that preferentially targets malignant lymphocytes, has induced therapeutic remissions in patients with advanced non-Hodgkin's lymphoma (NHL) or chronic lymphocytic leukemia (CLL) when labeled with iodine-131 (131I). Based on the strategy of fractionating the total radiation dose, trials were designed to define the safety, toxicity, and efficacy of a series of doses of 131I-Lym-1 given 2-6 weeks apart. All patients had disease resistant to standard therapy. 131I-Lym-1 was given after unconjugated Lym-1 and the 131I dose was escalated in Phase I-II trials. Therapy proved safe. The dose-limiting toxicity was thrombocytopenia. Nonhematological toxicities did not exceed grade 2 except for infrequent instances of grade 3 hypotension. In a low-dose (LD) trial of 131I-Lym-1, tumor regression occurred in 25 (83%) of 30 patients and 17 (57 %) had durable remissions; 3 of the remissions were complete. In a maximum tolerated dose (MTD) trial of 131I-Lym-1, 10 (71%) of 14 entries that received at least two doses of 131I-Lym-1 therapy and 11 (52%) of 21 total entries had remissions; 7 of the remissions were complete. All 3 entries in the MTD cohort of 100 mCi/m2 [3.7 MBq/m2] of body surface area had durable complete remissions. Therapeutic remission and human anti-mouse antibody (HAMA) after Lym-1 therapy were associated with increased survival that was significant in multivariate analyses. Evidence for an Ab3 idiotypic network with an antibody cytotoxic for Raji human lymphoma was found in the only patient examined in detail thus far; this patient was studied because she had a high titer, HAMA and prolonged survival. In conclusion, 131I-Lym-1 induced durable remissions in patients with chemotherapy-resistant NHL or CLL and was associated with acceptable toxicity. In a subset of the patients, survival was quite prolonged perhaps related to development of Ab3.

Low-dose, fractionated radioimmunotherapy for B-cell malignancies using 131I-Lym-1 antibody

PURPOSE

This trial was conducted to assess the toxicity and efficacy of 131I-Lym-1 in patients with either malignant B-cell non-Hodgkin's lymphoma (NHL) or chronic lymphocytic leukemia (CLL) using low-dose, fractionated radioimmunotherapy (RIT).

MATERIALS AND METHODS

Thirty adult patients who had advanced B-cell malignancies (25 NHL and 5 CLL) had progressed despite standard therapy; 12 patients entered the trial with Karnofsky performance status (KPS) of equal to or greater than 60. Patients were treated with a series of intravenous doses of 131I-Lym-1 with a goal of reaching a cumulative dose in each patient of at least 300 mCi. All patients were Lym-1 reactive. Clinical responses and immediate toxicity were evaluable in all 30 patients and delayed toxicity in 26.

RESULTS

Toxicity to Lym-1 antibody occurred with 28% of the 176 doses and was transient. Human antimouse antibodies (HAMA) were generated in 30% after a mean of 4 doses, but interrupted therapy in only 10% of the patients. Thrombocytopenia was dose-limiting; there were no deaths due to toxicity. Tumor regression occurred in 25 (83%) of the patients and was great enough, and durable enough, in 17 (57%) to qualify them as responders; 13 NHL patients and 4 CLL patients. Advanced disease often interrupted therapy prematurely. However, 18 patients received at least 180 mCi of 131I-Lym-1; 17 (94%) of these responded to the therapy.

CONCLUSION

Although advanced disease often interrupted therapy prematurely, the results from 131I-Lym-1 therapy are clearly promising and warrant additional trials.