Session Three: Novel approaches to the treatment of WM
- Monoclonal antibody therapy for the treatment of Waldenstrom's Macroglobulinemia, Steven P. Treon, MD
- Radioimmunotherapy for the treatment of Waldenstrom's Macroglobulinemia, Christos Emmanouilides, MD
- Antisense therapy for the treatment of Waldenstrom's Macroglobulinemia, Stanley Frankel, MD
- High dose chemotherapy with stem cell transplantation for the treatment of Waldenstrom's Macroglobulinemia, Nikhil Munshi, MD

Monoclonal antibody therapy for the treatment of Waldenstrom's Macroglobulinemia
Steven P. Treon, MD, Dana-Farber Cancer Institute, Boston, MA

Monoclonal antibodies are constructed of what we call light and heavy protein chains, in a shape that looks very much like the letter "Y," and have proven effective in combating several cancers. An arm of the Y connects with a chemical on the surface of the cancer cell. The tail of the Y connects with one of the immune system's killer cells and allows it to destroy the cancer. But there is a price to pay. Since the antibody was initially produced in mice, it usually provoked an immune reaction in humans, whose system recognized the mouse protein as a foreign substance to be attacked. As the compounds have become more humanized, these reactions have become less of a problem.

Cells have a plethora of distinctive proteins on their surfaces, many of which have been studied. One in particular, which is present on the vast majority of Waldenstrom's cells, is called CD20. One of the monoclonal antibodies we have created, rituximab, binds to this CD20 marker. It then attracts either killer cells or complement proteins, which in turn destroy the cancer cell.

In addition, rituximab treatment has the added advantage that, whereas normal chemotherapy agents adversely affect blood counts, reducing production of red cells, white cells and platelets, therapy with this monoclonal antibody, which attacks only cells bearing the CD20 marker, shows improvement in those counts.

Rituximab is also effective in a high percentage of cases. About sixty percent (60%) of patients receiving rituximab show reduced levels of IgM, and another thirty percent (30%) stabilize; while their IgM levels do not actually go down, they no longer increase. Examination of marrow samples and other tests show that this antibody does a remarkable job of cleaning tumor cells out of the bone marrow.

Experiments are currently being conducted to see whether we can improve the response to treatment with rituximab. The first and most obvious approach is to extend the length of treatment, to increase the duration of exposure of tumor cells to this monoclonal antibody.

So we have been increasing the number of infusions from four (4) to eight (8), usually with an interval between the groups of four.

Another direction of experiment has been to combine rituximab with various existing chemotherapeutic agents we know to be effective against WM. One of the most important of these directions is the combination of rituximab with fludarabine. In what we have seen to date, fludarabine seems to sensitize the cells to the effects of rituximab, and vice versa. So, in one regimen, we give four (4) courses of rituximab, then two (2) each of fludarabine, rituximab again, fludarabine once more, and finally rituximab.

Campath is another monoclonal antibody with which we are experimenting. Campath targets the CD52 antigen on the cancer cell in much the same way rituximab goes after CD20. Normally we begin with infusions three (3) times per week for a period of four (4) weeks. If there is no sign of improvement, we may stop there. Otherwise, we proceed for eight (8) more weeks.

If we can attack either CD20 or CD52 singly, maybe we should combine elements in a two-pronged antibody attack if the patient shows both markers. In other words, we might be able to individualize therapy. Because in addition to CD20 and CD52, there are other possible targets: CD22, CD40, and MUC1 to name but a few.

MUC1 is a long protein extending out from the cell wall, which acts very much like barbed wire. It physically keeps attacking killer cells too far away to do their intended job of killing the cancer cell. Meanwhile, CD59 acts to protect the cancer against complement protein attack, and appears to be a factor when rituximab is ineffective. One of the approaches we might try with Thalidomide or the IMiD's might be to see whether they could neutralize these protective shields so that the antibodies etc. can do their work. We are experimenting with other compounds as well.

Yet one more approach is to create, as we have done, antibodies containing atoms of radioactive elements. These can kill in two ways. They can perform like other monoclonal antibodies in one direction. At the same time, the radiation can kill neighboring cells. The latter kill might not be cancer-specific, but since these cells tend to clump up in the marrow, chances are pretty good what you hit will be what you want to.

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Radioimmunotherapy for the treatment of Waldenstrom's Macroglobulinemia

Christos Emmanouilides, MD, UCLA Medical Center, Los Angeles, CA

There are many molecules that appear on the surface of cancer cells which do not appear on the membranes of normal cells. Monoclonal antibodies are used to attack the cells showing these antigens without attacking healthy cells.

Radioactivity is a known cell killer. But it kills normal cells as well as cancers. What we have tried to do is to use monoclonal antibody techniques to attach radiation sources directly to the cancer cells. By using this kind of targeted radioimmunotherapy, we use radiation against tumor cells while avoiding giving excessive radiation to healthy body parts.

The best isotopes for this purpose appear to be yttrium-90 and iodine-131. The former emits beta particles (electrons); the latter gives off beta particles too, but also emits gamma rays. These rays can propagate through some distance, and therefore not only can they damage healthy tissue far from the tumor, they are also a danger to the administering technicians. Among the products developed for this kind of therapy is Zevalin, a monoclonal antibody containing yttrium-90, which attaches to the CD20 antigen on Waldenstrom's and certain other lymphoma cells

Randomized studies in various low-grade lymphomas have been conducted to compare the efficacy of Zevalin with that of rituximab. Rituxan was studied in and of itself. Compared with it was a combination. Rituxan was administered first to cover the CD20 positive cells in the bloodstream, then Zevalin was given to deal with the cells in the marrow.

The results were clear. Eighty percent (80%) responded to Zevalin as opposed to fifty-six percent (56%) to rituximab alone. Of these, thirty percent (30%) of those receiving Zevalin were deemed to have had a complete response (no disease evident). Rituxan's complete response rate was sixteen percent (16%). The period of remission (time until re-treatment became necessary) was also longer with Zevalin, up to two years as opposed to 8-10 months. There was, however, a price to be paid: greater marrow suppression. Patients receiving Zevalin had lowered white and platelet cell counts.

So what can we say about possible uses for Zevalin? Given its effect on blood counts, it might well be reserved for use after rituximab ceases to be effective. It might also be particularly useful for older patients, say over seventy-five (75). In WM, we should probably be careful about using it in patients with heavy bone marrow involvement; in the heavy concentration that might bring about, the level of radiation in the marrow might become excessive, leading to destruction of too many normal cells along with the cancer.

New experiments are planned with low doses of Zevalin, trying to keep radiation below the .08 millicurie level. If the patient's condition allows, these low-dosage treatments can be repeated. We know from other sources that receiving radiation in multiple small doses seems to be more effective than the same amount of radiation received in a single dose. It might well work that way with Waldenstrom's patients receiving beta radiation from Zevalin.

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Antisense therapy for the treatment of Waldenstrom's Macroglobulinemia
Stanley Frankel, MD, University of Maryland, Baltimore, MD

The treatment of Waldenstrom's macroglobulinemia has taken many forms:

There are therapies that do not treat the underlying disease but relieve some of the symptoms, among them plasmapheresis, which physically rids the blood of the heavy IgM concentration from which many symptoms derive.

There is biologic therapy, used to aid the immune process. Among these is the use of the interferons or Procrit to stimulate, or antibodies like Campath and Rituxan to interact between the immune system and the cancer cell.

Chemotherapy, the use of specific poisons, takes many forms. First there are the alkylating agents, chlorambucil and the like. Slightly different are the nucleoside analogues, fludarabine or Cladribine (2CdA). Thalidomide may produce responses, either alone or with steroids.

And there is radiotherapy, using targeted radiation to kill cancerous cells.
But none of these is curative, either alone or in combination. A few cells always escape destruction.

Antisense therapy takes a different direction. It does not directly go after the bad proteins that cause cells to run amok, but the bad RNA in the cell. The master pattern in the cell is the DNA in its nucleus. From this pattern are created patterns called RNA. This "messenger RNA" then provides the pattern from which individual proteins in the cell are made. What we do is to "cover" the RNA so that it cannot produce proteins. By adding a sulfur group to this "cover," we can destroy the messenger RNA and cause apoptosis (cell death).

One of the basic characteristics of cancer is that its cells do not follow the normal pattern and die when either damaged or no longer needed. A protein strongly present in many cancers, including WM, is called BCL-2. It is a key regulator of apoptosis, and prevents normal cell death. What antisense does is to neutralize BCL-2 activity, so that the cell can die as it should. BCL-2 is more strongly expressed than normal in most lymphomas. What we need to do is to neutralize its effects. This is what Genasense does.

We now have new tools that will tell us what genes in a given cell are turned on and which are turned off. That lets us classify patients according to their gene expression patterns. Hopefully that will allow us to individualize treatments more successfully. We are using this method to determine the workings of BCL-2. We have already discovered, for example, that chemotherapy is less effective if BCL-2 expression is high. We also know that destroying BCL-2 activity should not overly harm the patient, though BCL-2 level is related to creation of albinos and affects lymphocyte levels.

Will antisense therapy work in Waldenstrom's? We don't yet know. But Genasense in addition to chemotherapy kills breast cancers in mice (by downgrading BCL-2). The same combination kills mouse lymphomas and mouse lung cancers. Specifically, we know that untreated lymphoma will kill a mouse in a month. If we administer chemotherapy alone, we double that life span. When Genasense is added, the mice with lymphomas lived the normal life span of a healthy mouse.

Genasense has been tried in combination with rituximab against cultures of human NHL cells. It dramatically increases the kill rate. The same results have been obtained against CLL and multiple myeloma cells. It would appear likely that pre-treatment with Genasense should very effectively sensitize other BCL-2 producing cells, including those of WM, to other agents.

Human Phase I-II trials, testing the safety and preliminary effectiveness of Genasense, have been going on since 1995. It appears fairly safe; few side effects have been seen. It is now in Phase III trials against CLL and MM. If those trials turn out as well as expected, we can expect similarly dramatic effects in the treatment of Waldenstrom's macroglobulinemia.

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High dose chemotherapy with stem cell transplantation for the treatment of Waldenstrom's Macroglobulinemia
Nikhil Munshi, MD, Dana Farber Cancer Institute, Boston, MA

First let us define what is meant by "stem cell transplantation." No attempt is made physically to replace all of a person's marrow. Rather, what we do is to kill, by high doses of chemotherapeutic agents, all of the patient's existing stem cells (the cells from which cells of the blood and lymphatic systems derive) as well as the other cells, some of them cancerous, in the patient's marrow, and then provide a relatively small number of "seed" cells to grow into replacements for those killed. Hopefully by so doing we can start with a clean slate, and what re-grows will be free of malignancy.

In myeloma, normal therapies produce complete response in five percent (5%) of patients studied. The combination of high dose chemotherapy and transplant produces a twenty-two percent (22%) complete response rate. Mean time until relapse is sixty (60) months in the latter case, thirty-seven (37) in the former.

In the case of Waldenstrom's macroglobulinemia, we have little evidence to go on. The studies deal with very small numbers of patients. The problem is further complicated by the fact that most subjects have had previous chemotherapy, which makes the collection of viable stem cells quite difficult. Considering the small available sample of patients, the similarity between Waldenstrom's and MM becomes an important aid in drawing what conclusions we can. The trials so far show a one hundred percent (100%) response rate, with a high reduction in tumor load. Twenty-five percent (25%) of patients studied achieved complete response.

As in other diseases, autologous transplant (using one's own collected stem cells) is safer than allogeneic, in which cells are donated by another individual, matched as closely as possible to the patient. But we have come to realize that with allogeneic transplants it is not necessary to use a heavy enough chemotherapy regimen to kill off all the patient's immune system; the foreign cells attack cancer cells native to the patient, because those cells are foreign to the implanted ones. This needs to be examined more closely.

We can also use a related process. Instead of a transplant, we can create vaccines which sensitize the patient's system, inducing it to treat as foreign the proteins peculiar to the cancer cells. Thus we are using the patient's own immune system, awakened as it were, to fight against the cells of the cancer, which it now regards as invaders.

All of this is a work in progress. We need larger numbers of WM patients to take part in transplant trials, both autologous and allogeneic. And the same can be said for experiments with vaccines.

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