How has the antibody been used?
The ch14.18 antibody has been used in clinical trials both as a single agent and in combination with augmenting agents (cytokines) GM-CSF and IL-2. The chimeric antibody has also been tested as a single-agent therapy in two separate trials involving patients with stage 4 neuroblastoma. In a Phase I trial in T?bingen, Germany, nine heavily pretreated patients with stage 4 neuroblastoma were treated with 19 courses of chimeric anti-GD2 antibody at dose levels 30, 40 and 50 mg/m2/day for 5 days per course. The MTD (maximum tolerated dose) was 50 mg/m2/day. No HAMA or HACA responses were seen. In these 9 patients there were 2 complete responses, 2 partial responses, 1 minor response, 1 stable disease, and 3 progressive disease. Similar results were seen in ten patients with refractory neuroblastoma and one with osteosarcoma. Patients in this study received 20 courses of chimeric antibody at dose levels of 10, 20, 50, 100 or 200 mg/m2. Dose escalation was permitted for a single patient if tolerated. The MTD was not reached in this study. Ten patients were evaluable for response and included 1 partial response, 4 mixed responses, and 1 stable disease.
Ch14.18 was well tolerated in both studies with few side effects seen at dosages of 10 mg/m2 or less, and encouraging results were seen in bone marrow and microscopic bone disease. Toxicities in each were similar to those seen with the murine antibody, including pain, tachycardia (rapid heartbeat), hypertension (elevated blood pressure), fever, urticaria (rash or hives) and transient neuropathy (nerve pain). Optic nerve atrophy was seen in two patients in the T?bingen study. Both patients had received prior radiotherapy and this was implicated as the cause of this adverse event. The effect was reversible in both patients. Seven out of ten patients in the latter study did develop a HACA (human anti-chimeric antibody) response as measured in post-treatment serum samples.
The important items to consider from these studies were that the pharmacokinetic and immunological studies in association with these trials have shown that the ch14.18 has a longer plasma half-life and is less immunogenic than its murine counterpart, potentially improving its clinical utility.
Due to the immune suppression caused by neuroblastoma and/or the chemotherapy regimens used for treatment the immune system is often compromised in these patients. Over time it has become clear that the addition of cytokines to monoclonal antibody therapy could significantly improve the effectiveness of therapy by augmenting the immune system. GM-CSF (granulocyte-macrophage colony-stimulating factor) has been found to increase granulocyte cell populations and increase adhesion molecules on lymphocytes, which enhances the ability of the immune system to cause neuroblastoma cell death. GM-CSF has been used in clinical trials in combination with the ch14.18, 14.G2a and 3F8. The results of all four trials suggest that GM-CSF in combination with anti-GD2 monoclonal antibodies improves the anti-tumor response, particularly in bone marrow disease.
Interleukin 2 (IL-2) is a strong pro-inflammatory agent with which affects both the innate and adaptive immune system. IL-2 increases both the number and activation state of natural killer (NK) cells. Activated NK cells bind the Fc portion of the antibody through their FcgRIII and begin the process of causing neuroblastoma cell death. IL-2 also stimulates antigen-specific T cells to kill tumor cells, an example of breaking tolerance to tumor antigens. In a Phase I trial through the Children?s Cancer Group (predecessor to the Children?s Oncology Group, which conducts multi-institutional clinical trials in pediatric oncology in the USA) involving 33 patients, IL-2 was administered by three 96 h infusions over successive weeks, on days 1, 8 and 15. 14.G2a was given as a daily 2 hour infusion on days 9 through 13. This was timed to take advantage of the lymphocytosis and maximal NK cell cytotoxic activity seen in several in vitro analyses carried out prior to the study . One patient had a partial response with a 70% decrease in size of an abdominal tumor over 3 months, facilitating complete resection. Three additional patients had a transient reduction in microscopic bone marrow disease but no reduction in tumor burden in other locations. Serum samples were obtained from these patients and were found to contain sufficient levels of 14.G2a to result in ADCC of GD2-positive tumor cell targets in vitro.
There have only been two studies which have addressed long term survival as it relates to the ch14.18 antibody. The first is a German study whcih has had mixed results. This group of German researchers is the same group that first published a review of this same study in the Journal of Clinical Oncology on September 1, 2004. In this original study they came to the conclusion that the use of the ch14.18 antibody for consolidation treatment of stage IV neuroblastoma had no clear impact on the outcome of patients.
It is important to note some very key considerations regarding this study. First, there is speculation that the schedule and dosing may have been suboptimal. It is believed that antibody therapy is dose dependant, meaning that the larger the dose, the better the result. Many felt that the dose used in the German study of 20 mg/m2/d for 5 days (100 mg/m2) every 2 months was suboptimal. The phase III COG study, ANBL0032, utilizing the ch14.18 antibody used a daily dose 25% higher at 25 mg/m2/d over 4 days (100 mg/m2) every 28 days.
Second, the addition of cytokines in conjunction with antibody therapy has shown a synergistic effect. Research has shown that the antibodies must accomplish three separate tasks to kill a tumor cell:
- the antibody must recognize and bind to the tumor cell;
- it must bind long enough to the tumor cell to recruit the immune system;
- the antibody must convince the immune system to kill the cell.
Since antibody therapy relies on antibody dependant cellular cytotoxicity (ADCC) and/or complement-mediated cytotoxicity (CMC) to kill tumor cells, a strong immune response is required. (3) However, owing to immune suppression from metastatic cancer treatment and/or chemotherapy, this response may be compromised in cancer patients (4, 5, 6). The addition of cytokines to antibody therapy can augment immune response and improve the overall effect of immunotherapy. Several studies, both clinical and preclinical, have shown that the addition of cytokines (like GM-CSF and IL-2) have improved the immune response to antibody therapy. The German study did not include the use of cytokines. Many have speculated that this may be the reason for the lack of efficacy seen in this study.
Finally, the German Study was not a randomized trial. In fact, the retrospective design included patients from both NB90 and NB97 protocols which included a considerable imbalance among the three treatment groups. The study compared patients who received antibody therapy with no maintenance therapy (+AB-MT), patients who did not receive antibody therapy but received maintenance therapy (-AB+MT) and those that did not receive antibody therapy or maintenance therapy (-AB-MT). Most of the patients receiving the ch14.18 antibody underwent the induction regimen utilized in the NB97 protocol. There were significant differences in the induction regimens. Many, but not all, antibody patients underwent an autologous transplant yet all on the maintenance therapy arm did not. In the ?AB+MT group, all patients received the NB90 induction treatment without ASCT. The radiation therapy policy also differed greatly between the two protocols. Furthermore the follow-up time for many of the antibody patients was much shorter than the patients in other arms. Interestingly, cis retinoic therapy was not used in any of these patients. These factors make it very difficult to draw many clear conclusions from this trial. Although univariate analysis did show a significant difference in overall survival, multivariate analysis failed to draw the same conclusion. Finally, it did not show any difference in event free survival. Ultimately, with so many variables and so few patients, it became impossible to draw any clear conclusions with any level of confidence.
However, proabably the most compelling piece of evidence pointing to the potential benefit of ch14.18 for a standpoint of survival came from after further retrospective analysis. It became clear that immunotherapy with ch14.18 as consolidation after intensive chemotherapy may actually prevent late relapses. After observing patients for a median of 9.2 years, in contrast to the earlier report, the paired log rank test now clearly demonstrated an advantage of ch14.18 treatment compared to no additional therapy. (2) This clearly is a more promising result for antibody therapy, however, the study still falls victim to the issues of dose, schedule, design, and lack of cytokines.
The second study to look at the efficacy and survival of patients utilizing ch14.18 is the COG study ANBL0032. Currently the study is ongoing.