Date: August 31, 2006
by Andrew R Pettitt, MA, PhD, MRCPath
Professor & Consultant Haematologist
Royal Liverpool University Hospital
Campath: Jumping the Gun;
Campath Consolidation — A Home Run?
Campath plus GCSF Can be Dangerous;
Campath Therapy — MRD and Survival;
Campath Looking Better and Better
PCR Negative Remission — Is this a Cure?
To treat CLL effectively, the trick is to kill CLL cells without doing too much collateral damage in the process. Chemotherapy is actually quite good at this in most patients, at least to start with. For many years, chlorambucil was the mainstay of first-line treatment but recent clinical trials indicate that fludarabine is better, and that fludarabine plus cyclophosphamide (FC) is better still, albeit more toxic. Based on these trials, FC has now become the first-line treatment of choice for CLL, at least in Europe. Current trials are investigating whether the outcome can be improved by adding other agents to this chemotherapy ‘backbone’ in the form of additional chemotherapy drugs (e.g., mitoxantrone) or monoclonal antibodies (e.g., rituximab). However, there are some patients who are destined never to respond well to chemotherapy and many more who end up this situation at some stage during the course of their disease. There are many different causes of resistance to chemotherapy in CLL but by far the most important is the inactivation of a gene called p53.
p53 is the ultimate ‘good guy’ in cancer. It reduces the risk of cancer developing in the first place and, if cancer does develop, it keeps the malignant cells in check by slowing their growth, helping chemotherapy and radiotherapy to work, and preventing them from turning nastier than they already are. It does all this though its function as a so-called ‘transcription factor’. A transcription factor is a protein molecule that can bind to the cell’s genetic blueprint, or DNA, and tell the cell what genes to express. In the case of p53, it tells the cell to express genes that stop it dividing or make it commit suicide – a process known as apoptosis. For most of the time, p53 keeps quiet and doesn’t do very much. However, whenever the cell’s DNA is damaged, p53 becomes activated and springs into action. This response of p53 to DNA damage is crucial as it allows the damage to be repaired or gets rid of cells that are beyond repair. In this way, p53 stops the DNA sequence from being corrupted or ‘mutated’. This is crucially important as gene mutations are one of the main causes of cancer and are also responsible for the ‘hotting up’ of cancer that has already developed. The p53 ‘suicide response’ also contributes to the action of chemotherapy drugs, many of which work at least in part by damaging the DNA of cancer cells.
As might be expected, cancer cells try to find ways of getting rid of p53. They can do this by rearranging their DNA so that one copy of the p53 gene is lost (cells have two copies of most genes). This is called a ‘deletion’. Because the p53 gene is located on the short arm of chromosome 17, loss of p53 is sometimes called a ‘17p deletion’ or ‘17p-’ for short. In addition to the p53 gene being lost, its DNA sequence can be altered in a way that stops it from working properly. This is called a ‘p53 mutation’. Despite not working properly, mutated p53 protein is usually over-expressed as the molecule has a longer lifespan than normal or ‘wild-type’ p53. p53 deletions or mutations are present in about 5% of newly diagnosed CLL patients, about 10-15% of patients requiring first-line therapy and up to a half of patients who are resistant to fludarabine-based chemotherapy. Usually, one copy of the p53 gene is lost through deletion and the other copy inactivated by mutation. However, in some patients only one of these abnormalities can be detected.
As might be expected, p53 abnormalities in CLL are strongly linked to rapid growth, ‘hotting up’ of the disease, a poor response to chemotherapy and, for all these reasons, a poor prognosis. Finding new and better ways of treating CLL patients with p53 defects is therefore a major priority. However, to properly face up to the problems caused by loss of p53, consideration needs to be given not only what treatment to give but also to two other questions: when to start treatment and how far to go with it. Each of these issues will be addressed in turn.
First, what treatments can work in CLL patients with p53 defects? In theory there are two ways of trying to kill CLL cells with p53 defects: making good the defect or bypassing it. As yet, nobody has worked out how to get mutated p53 to work properly inside cells, so this approach can be disregarded for the time being. As for bypassing p53, there are two ways of doing this. One approach involves causing so much DNA damage in CLL cells that they die even if a p53 suicide response cannot be elicited. New agents are being developed that inhibit DNA repair and it is hoped that, by combining these agents with chemotherapy, this approach will be effective. An alternative way of bypassing p53 is to avoid DNA damage altogether and use agents that kill CLL cells by other mechanisms. Fortunately, there are two agents in widespread use that do just this and which have an established track record in p53-defective CLL: Campath (otherwise known as alemtuzumab) and steroids.
It should be pointed out that the type of steroids we are dealing here are known as glucocorticoids and have nothing to do with anabolic steroids used by body-builders. Steroids have been used for the treatment of CLL for over 50 years but mostly at low doses as palliation. The naturally occurring steroid cortisol is made by the adrenal glands and plays an important role in limiting inflammation – one of the body’s key defences against infection but which can be dangerous if it gets out of control. Steroids affect most types of immune cells in some way or other but one of their most striking effects is that they kill lymphocytes – both normal ones and leukaemic ones including CLL cells. They do this by penetrating inside the cell and binding to a molecule in the cytoplasm called the glucocorticoid receptor (GR). The GR then moves into the nucleus where it binds to DNA and increases the expression of genes that make the cell commit suicide – very much like p53, in fact.
Steroids at normal doses can be useful in the treatment of CLL, for example to improve bone marrow function before starting chemotherapy in patients who present with very low blood counts. However, routinely giving ordinary doses of steroids alongside chemotherapy adds little or nothing, apart from more side effects. High-dose steroids, however, are another matter altogether. A recent study from the Royal Marsden Hospital, UK, showed that methylprednisolone (HDMP) was a useful treatment for patients with chemoresistant CLL, working in about 50% of patients with p53 defects including some with bulky lymph nodes. Responses were mainly partial and lasted about a year on average. Steroids have a number of side effects including fluid retention, stomach irritation, muscle wasting, thinning of the bones (osteoporosis), raised blood sugar (diabetes), mood swings and infection. However, in the Royal Marsden study, HDMP was generally fairly well tolerated, the main problem being infection, which occurred in about one quarter of patients treated with the regimen. Infections are one of the main complications of steroids. They arise because steroids transiently deplete the body of normal lymphocytes and also stop neutrophils from working properly. Patients on high-dose steroid treatment are therefore usually given infection prophylaxis with co-trimoxazole and aciclovir, together with an ‘H2 antagonist’ or ‘proton-pump inhibitor (PPI)’ to reduce the risk of gastric irritation. Any infections should be investigated and treated promptly. On the plus side, steroids are not toxic to the bone marrow and do not, therefore, lower the haemoglobin level, neutrophil count or platelet count.
In addition to steroids, the other agent with an established track record in p53-defective CLL is alemtuzumab, or Campath. Campath is not really a drug in the traditional sense but rather an ‘antibody’. Antibodies are special proteins made by the immune system in response to infection or vaccination. Their purpose is to get rid of infections. They do this by binding in a very specific way to structures called ‘antigens’ on the surface of invading bacteria, viruses or fungi. Once an antibody binds to its target antigen, other parts of the immune system automatically attack and kill whatever the antibody is stuck onto. By using antibodies that bind to antigens on tumour cells, this natural function of the immune system can be successfully harnessed to treat cancer.
Campath is a good example of such an antibody. It binds to a structure called CD52, which is expressed on the surface of CLL cells. Once CLL cells become coated with Campath, the immune system punches holes in them leading to their destruction. At the clinical level, Campath works in up to 50% of CLL patients who fail fludarabine, including those with p53 defects. Remissions are usually partial and last for about a year on average. The main limitation of Campath is that is does not work well in patients with bulky lymph nodes. On the other hand it is good at clearing out the blood and bone marrow. Campath is administered three times a week and can be given into the vein or under the skin as a simple injection. The main side effect when given intravenously is flu-like symptoms. The main side effect when given under the skin is redness, swelling and soreness at the injection site. Side effects tend to become less problematic during the course of the treatment, which normally lasts about 3-4 months.
The main concern about Campath is that it can trigger infection. This is because its target antigen, CD52, is also expressed on T cells, which play an important role in fighting viral infections. Campath treatment therefore temporarily knocks out this part of the immune system. In the absence of T-cells, trivial viral infections that normally cause coughs and colds can become more serious and result in pneumonia. In addition, viruses that normally hide away in the body in a dormant state can become active and cause major problems. The virus most notorious for doing this is cytomegalovirus, or CMV. Patients receiving therapy with Campath should therefore be monitored weekly for CMV reactivation. The point of doing this is that CMV reactivation usually responds very well to treatment if it is caught early but may cause life-threatening complications if treatment is delayed. Patients on Campath therapy should also receive infection prophylaxis with co-trimoxazole and aciclovir. For reasons that are not entirely clear, Campath may cause mild bone marrow suppression, and sometimes this requires growth factor (G-CSF) injections or even a short break from treatment. However, this problem is usually confined to patients who start off with low blood counts due to heavy bone marrow infiltration with CLL.
So, to summarise so far, we have two established treatments that bypass the p53 pathway and which each work to some extent in about 50% of patients with p53 defects. Steroids are good at shrinking down lymph nodes, whereas Campath is good at clearing out blood and bone marrow. The next logical step was to ask whether using the two agents together could produce better disease control than is achievable with either agent on its own. To test this idea, the ‘CAM-PRED’ protocol was developed. The regimen consists of up to four 28-day cycles. Each cycle consists of methylprednisolone 1g/m2 for the first 5 consecutive days together with Campath 30mg three times a week for the entire month. Because p53-defective CLL cells are genetically unstable, they are likely to be very good at finding ways of becoming resistant to all treatments, including those that work independently of p53. It was therefore considered important to avoid exposing CLL cells to low drugs concentrations that they could adapt to, but rather to go in ‘hard and fast’ with the aim of trying to kill as many CLL cells as quickly as possible before they could have a chance to become resistant. For this reason, Campath is therefore given intravenously for the first month as adequate blood levels are achieved more quickly with this route of administration. Thereafter, Campath levels are topped by subcutaneously injections.
In view of the fact that steroids and Campath are both immunosuppressive, infection surveillance and prophylaxis form an essential and integral part of the CAM-PRED protocol. Patients should receive prophylaxis with co-trimoxazole, aciclovir and itraconazole and undergo weekly surveillance for CMV reactivation. If the neutrophil count falls below 1.0 x 109/l, G-CSF injections and ciprofloxacin prophylaxis is started. Furthermore, any infections should be investigated immediately and thoroughly and appropriate treatment should be started promptly. For safety reasons, the regimen should not be used outside major medical centres that are experienced in dealing with highly immunosuppressed patients and the complications they can develop. The importance of this advice cannot be overstated.
During the rather lengthy process of obtaining all the approvals necessary for a formal UK phase II clinical trial, several patients with p53-defective CLL received the CAM-PRED regimen off trial. It should be stressed that offering experimental treatment outside of clinical trials is generally not to be recommended, especially where a more mainstream alternative treatment is available. Accordingly, all decisions to offer patients CAM-PRED off trial were peer-reviewed by CLL experts within the UK CLL Forum. Results from the first 5 patients to be treated with the regimen were sufficiently provocative to warrant publication. All patients responded to treatment. Three achieved a complete response (CR) and 2 of these became so-called ‘MRD negative’, meaning that the bone marrow contained less than 1 in 10,000 CLL cells. Both of the 2 previously untreated patients in the series achieved a CR. One patient remains in an MRD-negative CR nearly 18 months after finishing treatment. On the negative side, all 5 patients developed infections despite stringent precautionary measures. Some infections were serious but all were ultimately successfully treated. A formal phase II clinical trial is now underway in the UK for both untreated and previously treated patients with p53 defects, and a similar trial involving Campath and dexamethasone is under development by the German CLL Study Group. Hopefully it should not be too much longer before more information is available concerning the effectiveness and toxicity of Campath/high-dose steroid regiments in p53-defective CLL, but for now the approach should still be regarded as experimental.
This is an exciting time as there are a number of new agents in the pipeline that have activity in CLL and which, at least in theory, should not work via the p53 pathway. However, with the possible exception of flavopiridol, which is not widely available, there is as yet no proof that any these agents are active in CLL patients with p53 defects. Obtaining such proof is important. For example, one study found that the antibody rituximab, which should work independently of p53, appeared to be less effective in CLL patients with p53 defects than in other cases. Although this finding was based on a small number of patients and requires confirmation, it does illustrate that theory is not always borne out in practice and highlights the danger of making assumptions about drug action without obtaining formal proof. In order to assess how useful new agents are going to be in the treatment of patients with p53 defects, it is therefore of paramount importance that clinical trials investigating these agents in CLL in should relate outcome to p53 defects.
The tendency of p53-defective CLL to turn nastier with time could be used an argument to start treatment immediately, irrespective of symptoms or progression. However, it is important to remember that all treatments have risks and side effects. Furthermore, there are currently no data to support the idea that early treatment benefits any CLL patients who do not require treatment by conventional criteria. Until such data are available, the usual rules should apply, i.e. treatment should be started for CLL-related symptoms or overt disease progression.
This is a more contentious area. The problem, of course, is that CLL always comes back after treatment. The problem is particularly acute in p53-defective CLL owing to its strong tendency to turn nastier with time and consequently become more difficult to treat. Accordingly, a strong argument can be made for ‘consolidation’ strategies in patients with p53-defective CLL who are lucky enough to have achieved a good remission. Consolidation options for such patients are basically three-fold: further Campath ‘maintenance’, further Campath when the disease progresses at the ‘MRD’ level, and allogeneic transplantation.
The idea behind Campath maintenance is to further reduce the already small size of the CLL clone in the hope of delaying relapse. There is some evidence that this approach can be effective, although it can cause severe bone marrow suppression if standard doses are given too soon after induction chemotherapy. The second approach would be to monitor very closely for minimal residual disease (MRD) and give more Campath at the very earliest sign of progression in order to prevent an overt relapse. This strategy would only work if the disease relapsed slowly in a way that the MRD test could detect and if the disease had not become resistant to Campath. There are, as yet, no data as to support this approach. A third option is allogeneic stem-cell transplantation. This appears to be an effective and possibly curative treatment for CLL, but also has substantial risks associated with it. Importantly, the German CLL3X trial has shown that reduced-intensity-conditioning allogeneic transplantation is as effective in patients with high-risk chromosomal abnormalities including 17p (p53) deletion as in other patients with high-risk CLL. There is very little information about high-dose therapy/autologous stem-cell transplantation in p53-defective CLL. This is probably because such patients rarely achieve sufficiently good responses for HDT/ASCT to be feasible. In theory, it is possible that the sort of cellular damage that this sort of treatment inflicts might be enough to kill p53-defective CLL cells. However, it is perhaps more likely that CLL cells with p53 defects will be relatively resistant to such treatment. In any case, there are no data to show that HDT/ASCT does any good in p53-defective CLL.
Effective treatment options for patients with p53 defects are limited. State-of-the art first-line combination chemotherapy with fludarabine and cyclophosphamide (FC), or with fludarabine, cyclophosphamide and mitozantrone (FCM), does not appear to be particularly effective in this patient group, and the same seems to be true of rituximab, although this requires confirmation. (Editor: mitozantrone is also called mitoxantrone in the U. S.)
We await the results of trials investigating rituximab-chemotherapy combinations but it would be surprising if these regimens were any more effective in this setting. On the other hand, high-dose steroids and Campath seem to have some single-agent activity in patients with chemo-resistant CLL and p53 defects. High-dose steroid-Campath combinations have produced provocative results in a handful of patients with p53 defects but this approach is not without toxicity. Trials are ongoing to define the value of steroid-Campath combinations in p53-defective CLL. Outside of clinical trials, such treatment should be regarded as experimental and used with the utmost discretion. It should probably be reserved for fludarabine-refractory patients with a 17p (p53) deletion and lymph nodes >5cm. Steroid-Campath combinations should always be used with extreme caution, as the toxicity of these regimens has yet to be properly defined and they have plenty of scope to do more harm than good.
1) NCT00292760 - Clinicaltrials.gov listing;
The CAM-PRED trial officially opened in April 2006 in the UK.
The clinicaltrials.gov record does not reflect this yet.
A CAM-DEX trial is in the preparatory stages in Germany.
2) Leukemia - June 2006 online article
A R Pettitt, E Matutes and D Oscier
Alemtuzumab in combination with high-dose methylprednisolone
... in patients with p53 defects.
3) The p53 Gene
Article in CLL Topics about the tumor suppressor gene and its associated protein.
4) Cytogenetics of ATM and TP53
Article in CLL Topics about how these genes act as gatekeepers of cellular health.
Topics article on gene expression and epigenetic silencing.
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