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Targeting Leukaemia Better

With new molecules and drugs being introduced, leukaemia treatment is undergoing transition, discovers Nancy Singh.

In the '90s, when a patient was diagnosed with leukaemia, after identifying the kind and subtype the doctor administered either chemotherapy or suggested Bone Marrow Transplant (BMT). Circa 2007, after the exact type and subtype is defined, the doctor asks for genetic profiling and molecular diagnosis, analyses the drug sensitivity and then, decides the exact dose calculated on the basis of drug level achieved in that individual with the help of pharmacokinetics. That's the precision and the detailing that goes today with the help of newer technological advances. Drugs have been introduced that precisely attack the cancer cells.

"We have advanced from blanket therapy to the era of response-adapted, individualised therapy" - Dr Shripad Banavali Department of Medical Oncology Tata Memorial Hospital Mumbai

"We 'risk classify' the patient depending on the genetic markers. Technology has helped in identifying the abnormalities faster and more accurately. For instance, 3,000-5,000 genes can be arrayed at one go, with the help of DNA micro-array. The genetic profile gives a complete and clear picture," explains Dr Shripad Banavali, Department of Medical Oncology, Tata Memorial Hospital, Mumbai.

Diagnosis techniques may not have changed much, but they have become more accurate and now identify more markers with the help of Flow Cytometry, Fluorescent in situ hybridisation (FISH) and Spectral Karyotype (SKY technique). Technology has definitely helped in identifying the subtypes accurately, which helps in prognosis depending on which treatment is chosen. "There are a panel of markers today that can be identified such as CD5, CD23, CD20 for Chronic Myeloid Leukaemia (CML) and scientists are always researching to identify new markers, for example CD5 which are known to be responsible for expression of certain stem cells," informs Dr Niti Rashida Narang, Consultant Oncologist, Healthcare Global Enterprises, Bangalore.

With the market abuzz with the newer drugs, stem cell transplant and chemotherapy are fast becoming archaic.

Target, not Transplant

Every treatment has its pitfalls, but the spotlight has always been on BMT. A few years down the line, BMT as a treatment option for CML will become obsolete, predict experts. Way back in 1985, the BMT Journal's editorial had condemned BMT.

The future of BMT is significant as CML is a common form of blood cancer in India. "Median age of presentation is 40 years and hence it affects you at the prime of your life where both the previous generation and next generation are dependent on you, where you are the breadwinner of the family," says Dr MB Agarwal, Head, Department of Haematology, Bombay Hospital, Mumbai.

The reasons for BMT’s expected death as a treatment modality are multifold. SCT/BMT was the second line of treatment and today when the market is flooded with new drugs which are more effective and powerful than the earlier ones, it is slowly moving down to the third line of treatment. These drugs have a high impressive long-term control rate of around 90-95 per cent. Ten years ago, medical treatment with drugs gave a life of just around three to five years for CML. "Hence, transplant was preferred which could cure 50 per cent of patients, kill 25 per cent of patients and the disease could recur in the remaining 25 per cent," informs Dr Agarwal. Also, SCT was expensive and had morbidity and mortality related to the treatment. In the US, SCT costs more than $1,00,000 and entails long stay in the hospital. In fact, some insurance companies still consider this to be an 'experimental' procedure and refuse to pay for SCT-related expenses. Comparatively, the Indian cost for SCT is much cheaper at Rs 5 lakh, but even that is considered unaffordable for many.

Exciting New Frontiers

Leukemic lymphoblasts grow and accumulate in close association with bone marrow mesenchymal cells

Types of AML cells

Types of ALL cells

The year 1998 was a landmark year as the drug 'Glivec' (Imatinib mesylate), introduced by Novartis, opened a new frontier for treatment of CML. "The survival with Glivec has been an impressive 90 per cent during the last six years. Most of these patients have no detectable disease even with the most sophisticated molecular techniques called Polymerase Chain Reaction (PCR). Although the treatment is lifelong, it has given a vision of prolonged life that probably runs to decades with almost no morbidity or mortality compared to transplants," explains Dr Agarwal.

All this has made the medical community feel that the transplant in CML must never be done upfront. Only those patients (less than 5 per cent) who do not respond to Glivec or cannot tolerate Glivec (which is rare) were subjected to transplant. But that has also changed after the recent introduction of two new drugs, Sprycel (Dasatinib) and Tasigna (Nilotinib) working on the same principle as Glivec in the market. They are given to patients of CML who do not respond or tolerate Glivec.

Thus BMT is now the third line of treatment in management of CML. "Transplant may become obsolete or an extremely rare event in managing CML," opines Dr Agarwal.

Precision Attack

In targeted therapy, the drug simply blocks the growth of only cancer cells. It does this by interfering with or attacking the specific 'target' molecules that are required for carcinogenesis and tumour growth. Targeted cancer therapies are supposedly more effective than other treatments like chemotherapy or transplant. They are also less harmful to normal cells.

The defect in CML is generally known as Philadelphia chromosome which happens due to the gene 'bcr-abl' translocation that leads to enhanced production of the enzyme tyrosine kinase. Imatinib blocks the activity of tyrosine kinase. The way Glivec works at the gene level is called 'targeted therapy'.

Though Glivec has worked 'miraculously', there is still a small relapse rate of about five per cent per year that doctors would like to erase. Researchers have found that patients who fail while on therapy have developed subsequent mutations in the BCR-ABL enzyme that alter Glivec's effectiveness. Scientists at St Jude's have revealed that loss of a gene known as Arf, which is frequently mutated in patients with ALL, but not CML, can cause some leukaemias to resist Glivec treatment. Further clinical trials are now under way with drugs that block these mutated forms of BCR-ABL, building upon the benefit that is offered by Glivec and keeping CML under better control.

Drugs such as Rituximab, Trastuzumab and Ibritumomab Tioxetan, Alemtuzumab, and Gemtuzumab ozogamicin apply a form of targeted therapy using monoclonal antibodies. Monoclonal antibodies are a relatively new type of targeted cancer therapy. Scientists have today analysed specific antigens on the surface of leukaemic cells to determine a protein to match the antigen. The companies use protein from animals and humans to synthesise these antibodies that will attach to the target antigen. The technology allows treatment to target specific cells, causing less toxicity to healthy cells. As of now, scientists are trying to understand new antigens that set them apart from normal cells.

Personal Touch

"St Jude's is the first centre to individualise anticancer therapy based on pharmacokinetics" - Dr Ching-Hon Pui Member, Department of Oncology & Co-Leader St Jude's Children Hospital, US

Now, even your medicine is personal again! "Genetic polymorphisms of drug metabolising enzymes, transporters, receptors and targets can affect how individuals respond to treatment. Different people would respond differently to the same drug given at the same doses because of this reason - called pharmacogenetics," reasons Dr Ching-Hon Pui, Member, St Jude Faculty Chair, Department of Oncology Co-Leader.

The world of pharmacogenetics has put the inner world of genes in the spotlight again. Dr Banavali explains, "Currently all children of the same group are given the same X mg/ml of drug. In personalised medicine we don't give it as a 'group'. For the drug actually does not metabolise at the same rate even in a group with the same age, weight and height. Here the drug dose is calculated as per the pharmacokinetics in the individual patient by calculating in-vivo drug levels." Hence, the kind of drug to be given, the appropriate dose and the treatment are decided after analysing the genetic factors. St Jude's Children Hospital in the US is using personalised medicine. "At St Jude, we are studying pharmacogenetic influence on efficacy and toxicity of treatment. We are the first centre (in the world) to individualise anticancer therapy based on pharmacokinetics (drug levels) and pharmacogenetics, which will eventually spread out to other centres within two to five years," says Dr Pui.

There have been many other advances in this field, including the identification of specific genetic abnormalities that are related to the development of cancer or that lead to treatment resistance, and development of sensitive and specific measures to monitor response to treatment.

The era of individuality in cancer therapy is new for oncologists but not for other specialities. "Cardiologists adjust digoxin dosage, infectious disease doctors adjust doses of antibiotics, and neurologists adjust anticonvulsant dosages," adds Dr Pui.

The latest trend is thus to find out molecular genetic abnormalities of cancer cells and to devise treatments targeted at these genes.

The next big leap in therapy would be immunotherapy for cancer treatment where the focus would be on building up the body's immunity. Though at a research stage, this therapy would be more helpful in kinds of cancer showing tumour growth other than leukaemia. "We have developed cellular immunotherapy with genetically modified natural killers to treat future patients with refractory leukaemia," informs Dr Pui.

Future is Molecular

The future is set to be molecules that could be given as a combination therapy. Scientists are evolving newer target molecules everyday. Recently, researchers at the University of Florida have successfully used molecular probes to detect subtle differences in leukaemia cells from patient samples, an achievement that could lead to more effective ways to diagnose and treat cancer.

The strategy, described in a recent issue of ‘Clinical Chemistry’, involves engineering short, single strands of DNA or RNA called 'aptamers' to seek out and bind with specific proteins in body fluids. The scientists designed the aptamers to bind to cells and molecules associated with leukaemia.

Researchers have also found the first evidence that slight molecular differences can exist even within the same samples from patients with adult T-cell leukaemia. The scientists have built designer probes using cancer cells as a template, capitalising on the ability of aptamers to fold into well-defined, three-dimensional structures that bind to targets.

The process relies on the fact that different types of cells exhibit unique surface features, so aptamers can recognise and bind with only these cells even in the presence of other, closely related cells.

The scientists found that three of six aptamers they selected for study adhered to all types of cancerous cells but ignored normal blood and bone marrow cells. In combination, the six aptamers produced distinct patterns that characterise different cancer cells, suggesting that the technique could be used to detect the molecular fingerprints of cancer in people.

The next step forward for developing a clinical diagnostic tool would involve matching patient data with these molecular profiles. After analysing additional patient samples, a database can be built that may one day help doctors select the best treatment strategies. The research team will achieve this by linking the medical histories of patients to specific aptamer binding patterns with the help of which the doctors in the future, may be able to identify patients who belong to a specific molecular binding pattern which could be matched to the database and then would suggest a 'tailored' treatment as per the signature of that cell. Different molecular patterns of cancer patients will point to different treatments.

Ayurveda in Leukaemia

What the sages and the 'vaidyas' used centuries ago has now gained acceptance among oncologists to the extent that instead of being an alternate therapy it has actually become a part of the mainline therapy. We are talking about arsenic. Christian Medical College (CMC), Vellore uses Arsenic Trioxide (As2O3) for Acute Promyelocytic Leukaemia (APL) that constitutes 10-15 per cent of AML population in India. In the early 1990s, As2O3 was found to be extremely effective in treating APL. The mechanism by which As203 induces remission is still under evaluation at CMC. "While some aspects of its cellular effects are clear, the molecular basis for these effects is yet to be defined. A dual effect of As2O3 was noticed on NB4 cell lines. At low doses (o.1-o.5 umol/lt) there was partial differentiation and at higher doses (0.5- 2 umol/lt) there was preferential apoptosis. From the limited data that is available, it appears that As2O3 and All-Trans Retinoic Acid (ATRA) have a synergistic action on APL cell lines," explains Dr Vikram Matthews, Department of Haemotology, CMC. Earlier, it was never given as a standalone drug, but over the years, after research proved its beneficial effects, it is given intravenously to good-risk APL patients even as standalone drug. Interestingly, even though arsenic has been mentioned in the Ayurvedic texts, it was used by the Chinese first, then travelled to New York and then after two years returned to India. It has been used for the past seven to eight years in India. On the emergence of Ayurveda in the modern era, Dr Banavali comments, "Today, a lot of chemotherapeutic agents have their origin in plants, so in a way it has come a full circle."

Blanket to Target

Today, the tests to diagnose leukaemia use antibodies and proteins that have the ability to identify harmful substances, but do not capture subtle variances in the molecular signature of cancer cells. Once an aptamer probe has proved its utility, it can be inexpensively reproduced in a DNA synthesiser.

We are thus on the lines of engineering DNA/RNA strands that identify and bind, and that are so signature specific that a single normal cell would be left unharmed. This promises a better future and hope that we may finally be able to conquer the enemy within with the help of nature's own genetic soldier.

With the development of the Human Genome Project, we have been able to understand the mechanism of development of cancer and therefore the significance of targeted therapy. "We have also been able to understand how to treat cancer through Evidence Based Medicine (EBM)," says Dr Suresh Advani, Consultant Oncologist, Jaslok Hospital. There is still a need to develop new molecules for targeted therapy. "Another area would be 'Proteomics' where we are trying to study and understand the micro-environment required for tumorogeneses, so that in the future we can gauge that environment and administer certain antibodies that help destroy these micro-environment elements," adds Dr Narang.

In the field of leukaemia therapy, we have graduated from the era of 'blanket-therapy' for all, to the era of 'risk-adapted therapy' and at present have advanced to the era of 'response-adapted, individualised therapy'. Targeted therapy is just emerging. Experts say we would be able to cure more patients with the addition of 'immunotherapy' (like NK cell and dendritic cell based vaccines, etc) to our arsenal. Theoretically, it may sound simple to just 'target' cancer cells leaving the normal cells unharmed, but we are still reading the first page of this encyclopaedia called human body and we haven't still found that 'ultimate-cure'. "If the leukaemic cells are the seed and the soil is our body environment, at present, we are still concentrating on the seed. Manipulating the soil will help us much improve the outcome," concludes Dr Banavali.

nancy.singh@expressindia.com