Treating MDS for most patients is “slightly different” from the general principle of cancer treatment which is to get rid of mutated cells by killing them with cytotoxic drugs, says MDS expert, Professor John Pimanda.

“The therapeutic principle in MDS for patients who are not eligible for a potentially curative allogeneic bone marrow transplant is not so much to eradicate the mutated cells but to get them to function better; to improve blood cell production.

“And that goes back to some fundamental principles of biology that underlie the development of MDS,” explains Prof. Pimanda, Director, Adult Cancer Program, Lowy Cancer Research Centre, University of New South Wales (UNSW).

New therapies is the greatest unmet need in MDS, “and to develop new therapies you need to understand the disease”.

What drives Prof. Pimanda’s research

Azacitidine (Vidaza®) is a hypomethylating agent that has been available on Australia’s Pharmaceutical Benefits Scheme (PBS) for the treatment of high-risk MDS since 2011.

Prof. Pimanda, also a consultant haematologist at the Prince of Wales Hospital, Sydney, became interested in why half the patients responded to the drug and half didn’t, and among the responders why there were a few patients with a “very long-term response”, whereas most patients relapsed on treatment.

“You have to give this drug as a lifelong therapy, but there seemed to be lots of unresolved questions about the biology of MDS,” he said.

“The available treatments were inadequate and the mechanism of action of hypomethylating agents in relation to MDS seemed to be assumed knowledge as experimental research had not been done in sufficient depth.

“Also, technologies were evolving very fast. The questions we couldn’t ask 20 or even two years ago can now be asked, to get a more fundamental understanding of what goes on in a blood stem cell in MDS and the bone marrow environment in which they reside.”

About MDS

MDS is a blood stem cell disorder and patients present with reduced blood counts.

“They could be anaemic; their white cell counts could be low, their platelet counts could be low,” said Prof. Pimanda.

“We do a bone marrow biopsy to look at the bone marrow, which is where blood stem cells and other precursors reside and from where blood is produced and matures before going into the bloodstream.

“In MDS, there could be an accumulation of immature blood cells in the bone marrow due to abnormal maturation, which results in the low blood counts.

“MDS is a genetic disorder where there are mutations in blood stem cells and the presentation varies significantly. Some patients have low-risk MDS and others have a very high-risk MDS.

“That risk assessment is based on the number of blood cell types that are altered, how low the blood cell counts are, the proportion of immature cells that accumulate in the bone marrow, and the number and types of chromosomal changes in these cells.

“And whether they’ve got low-risk or high-risk MDS is important as it has an impact on the patient’s prognosis and the treatments that are available and that patients are eligible to receive.”

Prof. Pimanda also explained that when we are young, we have tens of thousands of blood stem cells in the bone marrow that can be recruited at any one time to generate blood cells, and billions and billions of cells are produced each day.

“But as we age, at around 70 years, the number of blood stem cells that are recruited to produce blood dramatically reduces,” he said.

“Stem cells don’t reside in isolation, they live in an environment in the bone marrow where there are lots of support cells that nourish, nurture, and regulate the proliferation [rapid increase] and maturation of these blood stem cells.

“As we get older, the environment in our bone marrow changes, and that may account for why we have fewer blood stem cells that are recruited to produce blood, and some of these blood stem cells may have acquired mutations appropriate to their environment.

“But the important thing to understand is that you can have mutations in your blood stem cells and not have any apparent abnormalities in your blood counts.”

“If you examine blood cells in detail, in people in their 70s, 80s and 90s, 10-20% of them might have evidence of what we call clonal haematopoiesis, where some of their blood is being produced by blood stem cells that have got mutations in them, but their blood counts are not affected,” said Prof. Pimanda.

“The presence of clonal haematopoiesis is linked with increasing the baseline risk of non-haematological conditions amongst which the data is strongest for atherosclerotic cardiovascular disease.

“It seems as though there are these cells that have been produced that look normal, the blood counts are normal, but their behaviour isn’t the same.

“This is a natural consequence of aging. But in some people, this then seems to progress, and the progression may not be linear.

“You can’t predict who’s going to then get MDS and it might go straight on to AML, or nothing might happen, and that is often the case.

“Patients age and pass away for other reasons, completely unrelated to clonal haematopoiesis,” he said.

MDS mutations and the risk of evolving to AML

Prof. Pimanda said the problem in MDS is it’s not one gene that’s mutated but many genes, and there are multiple mutations in the stem cells.

“At the moment, if a patient has got abnormal blood counts and the bone marrow looks abnormal, you can make a diagnosis and you can give a risk categorisation. We still don’t assign risk in MDS based on single or clusters of gene mutations, but this may change as we gather more evidence and the availability of targeted therapies,” he said.

“Increasingly patients with MDS will have a panel of genes assessed for mutations at diagnosis.

“With more data, we’d be able to assign a risk based on their genetic marker; the risk of the patient evolving into high-grade AML.

“In AML there are particular mutations, like FLT3 mutations and IDH mutations, and there are therapies that can be used to target those mutations.

“The time will come when this will be the case for certain types of MDS as well, but we are not at that point yet and we need more available therapies,” said Prof. Pimanda.

“I’d like to see more therapies that are designed to improve the production of blood from mutated cells that can still produce blood but are just not doing it effectively enough.

“Of course, you have cells that acquire other mutations that are more dangerous and that increases your risk of getting AML.

“Once you’ve identified that subpopulation and you have a targeted therapy for that mutation, then you would want to use that drug, because then it’s not curing MDS, it’s just reducing a risk of getting AML.

“In the future we may look at reducing that risk of the MDS evolving to AML by using targeted therapies.”

Treating MDS

If MDS occurs, “you have abnormal blood counts that require treatment”, said Prof. Pimanda.

“If you’re anaemic, you need blood transfusions. If your white cell count is low, you might need some cytokines that boost blood cell production and some prophylactic antibiotics, antifungals, or antivirals because these patients are at risk of getting infections. And if their platelet count is low, you’re at risk of bleeding.

“Transfusions and cytokine support may need to be given to patients with a low-risk MDS,” he said.

“If you have multiple blood counts that are perturbed and the immature cells are accumulating in your bone marrow, that puts you at a higher risk of developing AML or bone marrow failure, and your life expectancy is reduced if you aren’t treated with a disease modifying drug,” said Prof. Pimanda.

Azacitidine is in this group of drugs, and it’s used for high-risk MDS.

“If a patient is diagnosed with high-risk MDS, their haematologist would consider a bone marrow transplant, if they are eligible for one,” Prof. Pimanda said.

“It’s a curative option that should be on the cards for high-risk MDS, if the patient is fit and has a donor.

“And other therapies may be used as a temporising measure until a patient is suitable for transplant, bearing in mind that there are transplant-related mortalities and patients may not want to take that risk, as it is an arduous process.

“For patients of advanced age who may be fragile and not have access to a bone marrow transplant, curative options should be considered but may not be available.

“Azacitidine is really the first-line disease modifying drug that we have,” he said.

This drug is given as an injection under the skin for seven days, followed by three weeks off in each 28-day cycle.

“But four to six cycles of treatment are needed before you can determine if the patient has responded or not,” said Prof. Pimanda.

“That’s a nerve-wracking wait, and patient’s blood counts drop, they get infections… it’s not an easy journey.

“The response could be that their blood counts go up and their immature cell proportions in their bone marrow have dropped. That would be fantastic but in the real world the response rates are about 35-40%.

“Azacitidine is not a curative therapy, so when patients respond they need to stay on treatment.

“The median overall survival is about 15-16 months, which is a considerable extension of life expectancy compared to having supportive treatment, such as blood transfusions and prophylactic antibiotics, which is eight to nine months.”

Prof. Pimanda said azacitidine treatment failed for patients because they either stop responding to the drug or the drug becomes toxic and they can no longer tolerate it, or a patient progresses to acute leukaemia which requires more intensive chemotherapy.

“In AML, you would want to get rid of the malignant cells, measure minimal residual disease, and keep an eye out for relapse by measuring mutations in your blood stem cells.

“That is not how MDS works,” said Prof. Pimanda.

“In MDS, your mutated cells are producing blood. What you want is for the cells, even your mutated cells, to produce more blood. Even though they might look abnormal or not function perfectly, the fact that your blood counts have gone up is related to long-term survival.”

Of the 20 patients Prof. Pimanda recruited to his first azacitidine clinical trial, when azacitidine was not available in Australia, two are still alive, 13 years after they started treatment.

“There are patients I’ve seen on multiple trials who are very long-term responders to treatment,” he said.

“They may hold some of the answers as to how we should go about combining treatments for more patients to get those long-term responses.”

The downside is, they need to come in every day for seven days every month, for an injection.

“You would rather give them a tablet, especially when you want to keep patients out of hospital with the pandemic, the aim being it’s more convenient giving oral therapy instead of by injection.”

Oral azacitidine study

An oral form of azacitidine, Onureg® (previously known as CC-486) has been FDA-approved for AML but hasn’t been registered for use in MDS. It’s given for three weeks of a four-week cycle.

Prof. Pimanda ran a Phase II trial in Australia for CC-486 in MDS which closed last year. It was funded by Celgene/BMS and sponsored by UNSW.

“It was an important study to do. We’re still crunching all the data and hope to publish those results this year,” said Prof. Pimanda

There were 40 patients with high-risk MDS recruited to the trial across 11 centres in NSW. First, they were given Vidaza® (injectable azacitidine) for six cycles (approximately six months), then they swapped over to the tablet form, Onureg® (oral azacitidine) for a further six cycles.

“The purpose of that trial was to understand and measure drug absorption, to make sure similar amounts of drug were being absorbed by the bone marrow and blood cells, whether you get the injection or tablet form.

“A few patients are still on the trial. They are in their second or third year of treatment and they are long-term responders to the tablet form.

“They get ongoing access to oral azacitidine as long as they continue to respond to the drug.”

Improving MDS treatment

“Where we need to look now is how we can improve treatment,” said Prof. Pimanda, “because you start your [azacitidine] treatment with less than a 50% chance of success.

“There is another drug, a related compound called decitabine, but the injectable form has never been available in Australia.

“Inqovi®, also called ASTX727, is an oral form of decitabine combined with another drug, cedazuridine, that slows the breakdown of the drug in the liver so more of the drug is available to act on your body’s tissues.”

ASTX727 has received both U.S. Food & Drug Administration (FDA) and Australian Therapeutic Goods Administration (TGA) approval for high-risk MDS, as part of a Project Orbis application.

Prof. Pimanda said that although a head-to-head study of ASTX727 has never been done with azacitidine, “historical comparisons are that they should be equivalent in their response rates and tolerance”.

“And although the Pharmaceutical Benefits Advisory Committee (PBAC) approved use of this formulation for MDS, patients can’t access the drug just yet.”

However, a Phase I investigator-driven clinical trial, led by Prof. Pimanda is due to open early 2022. This study, funded by the Medical Research Future Fund (MRFF), will give Australian patients with high-risk MDS access to two new drugs not currently available here – ASTX727 combined with another drug, defactinib.

“Our hope is that the response rates with ASTX727 in combination with defactinib are going to be better than with ASTX727 alone, due to increased incorporation of the latter,” said Prof. Pimanda.

“Drugs such as azacitidine and decitabine need to be incorporated into dividing cells. MDS stem cells that are resistant to azacitidine don’t divide as much as stem cells that respond to azacitidine due to high levels of a protein that make them more adherent to non-haematological cells in the bone marrow.

“Defactinib interferes with the function of this protein and promotes cell proliferation and azacitidine/decitabine incorporation.

“We are also hoping that responses will be more sustained because this is not a curative treatment,” he said.

Living with MDS

With MDS, often you are able to live with the disease, said Prof. Pimanda.

“You don’t need to eradicate the mutated cells from your bone marrow, you just need to have adequate amounts of blood produced and that does translate to longer survival.”

The question Prof. Pimanda asks is, how can we improve blood production?

“The insights we’re getting are that the clinical presentation in MDS is not only about your blood stem cells, and their mutations.

“There are all these cells (stromal, vascular, bone, neural) in the bone marrow that support our blood stem cells, and immune cells that interact with maturing blood cells,” he said.

Due to the recent evolution of technologies, “now we can look at all these components at a single cell level”.

“We can look at patients before they receive the drug [azacitidine or decitabine] and after they receive the drug, to see what is happening, not just in their blood stem cells but also in their bone marrow environment – to the cells that support blood stem cells and immune cells that detect and respond to pathology.

“We can look at what happens differently in those patients who respond to azacitidine, especially those who respond for a very long time, as opposed to those who don’t respond.

“There’s much more to MDS than just the mutations in their blood stem cells,” explained Prof. Pimanda, and some answers may reside in the supporting cells.

“So, what’s changing in those supporting cells in response to azacitidine that allows these patients to get those mutated cells to produce more blood?” he asks.

“That’s the area [of research] we are particularly interested in now.

“When you take a drug, all the cells in the body see the drug, not just your blood stem cells, and the drug is changing not just your blood stem cells but the entire bone marrow environment.

“We think it’s a reprogramming process. It’s not just killing cells; it’s reprogramming them to function better,” said Prof. Pimanda.

Low-risk MDS treatment

Most people with MDS have low-risk disease.

“They’re anaemic and some patients come in every month for a blood transfusion, and over the years they get iron overload,” said Prof. Pimanda.

Lowering their transfusion dependence is a big thing because they accumulate iron and the more transfusions they receive, the more iron they accumulate, necessitating iron chelation therapy combined with blood transfusions.

There are therapies such as erythropoietin and luspatercept that are used in other OECD* jurisdictions to reduce transfusion requirements in MDS but are not listed on the PBS.

“Luspatercept is expensive, and I don’t think patients could afford it without it being approved by the PBAC,” said Prof. Pimanda.

It acts on the bone marrow environment, increasing blood production, and thereby reducing transfusion dependence.

“The hope is that if you have an infusion of this drug, rather than a blood transfusion, that it reduces the risk of transfusion-related problems.”

In Europe, a hormone, erythropoietin is approved for patients with chronic anaemia and low levels of circulating erythropoietin, but it hasn’t been registered for use in Australia.

“These decisions are made on a cost/benefit analysis and the company needs to be sufficiently interested in pushing it through [the approval process] because it is quite a laborious process,” said Prof. Pimanda.

“I think patients do get the short end of the stick, and physicians have fewer treatment options as a consequence.”

“Even Vidaza took quite a long time to be approved here in Australia. It was available overseas for a number of years before it was approved here, and it was clearly effective.”

What’s on the MDS horizon – venetoclax and magrolimab

Prof. Pimanda discussed “two things on the horizon” to watch out for.

As background, he explained that venetoclax (Venclexta®), is a BCL-2 inhibitor that has been very successful in treating CLL, and the combination of azacitidine and venetoclax has been used in the treatment of elderly AML patients and was recently registered in Australia for use in low-blast AML.

MDS, a related disorder, chronic myelomonocytic leukaemia (CMML), and low-blast AML are all eligible for treatment with azacitidine on the PBS. Low-blast AML is similar to MDS, but the mature cell number is a bit higher than in high-risk MDS, but not sufficient to classify it as high-risk AML.

There are early-phase trials using the combination of venetoclax and azacitidine in high-risk MDS, but they are not currently available in Australia.

“We need to always be cautious of things that work in Phase I and Phase II trials,” said Prof. Pimanda, “because quite often the results look spectacular in early phase trials”.

“But when you run multi-centre trials with large numbers of patients with a randomised arm, the benefit doesn’t look all that great. So, you need to really wait for the Phase III trial results to come through before these combinations are actually registered for use.

“Also, one of the issues with MDS is that drugs like venetoclax are cytotoxic. The cells die and the intention is to kill these mutated cells. Now with azacitidine, the therapeutic intent is slightly different. You might be killing some of these cells, but the cells are also being reprogrammed into functioning better.”

MDS is slightly different, as mentioned at the beginning of this article.

“We want more blood production from these mutated cells, it’s not just a question of getting rid of them because if you get rid of them, you expect there to be residual healthy blood stem cells in the bone marrow to take over production, and that may not always be the case,” Prof. Pimanda explained.

“Some of the work that we have done demonstrates that there is a paucity of residual blood stem cells that are free of MDS mutations in the bone marrow of some patients.

“The therapeutic principle in MDS is to optimise blood cell production, and that seems to be what azacitidine is doing; rather than getting rid of these mutated cells, it appears to improve their function.

“But when your immature cell number accumulates in your bone marrow, the risk of accumulating multiple mutations and getting AML increases, and cytotoxic treatment like venetoclax and azacitidine tends to then reduce this immature cell burden.

“I think venetoclax and azacitidine is a great combination to get people ready for transplant but as to their long-term responses, I think we need to really wait and see the results.

“We don’t have long-term data, even for early-phase trials.

“So, watch this space. I want to see what the survival rate for the Phase III data looks like for high-risk MDS, which is a few years away,” said Prof. Pimanda, who doesn’t think there is sufficient understanding, even amongst the scientific community, about the blood cells that are being produced and are in circulation in MDS.

“These cells that are being produced carry MDS mutations, and there are very few non-mutated cells in circulation, even after treatment.

“The therapeutic principle in AML is to get rid of your malignant cells and let your healthy cells take over.

“But in MDS, this could be challenging if there are not that many mutation-free stem cells left to take over.”

Prof. Pimanda said the “other interesting combination” is azacitidine and magrolimab, and early-phase trials are being done in Australia.

He describes magrolimab as an antibody that blocks CD47, a ‘don’t eat me’ signal on cells. Expression of these ‘don’t eat me signals’ block immune cells from getting rid of abnormal cells by recognising ‘eat me’ signals. Many variants of these blocking antibodies are under investigation in AML.

“And, as often is the case, the AML studies are then extended to high-risk MDS. I think that one needs to be a bit cautious in doing that because they are not the same disease and their therapeutic endpoints are a bit different,” he reiterated.

MDS research in the Pimanda lab

“A lot of work needs to be done to improve the long-term outcomes of MDS patients,” said Prof. Pimanda whose lab focuses on MDS-based research.

There are post-doctoral researchers, research assistants, PhD students and Honours students in his lab.

“We run clinical trials, we collect patient samples from those clinical trials, and do the laboratory work using these samples, and if we make fundamental discoveries these data inform the type of questions that need to be asked in the next clinical trial,” he said.

“Everything is informed and iterative and it’s a slow process.

“It requires a team of experimental and computational scientists producing and analysing data to make discoveries that have translational potential.

“Engaging pharma to support a trial concept and working with clinical trial experts, clinicians, and patient support groups to open a trial based on a laboratory discovery is difficult but rewarding.

“The ultimate goal of course is to eventually register a new therapy that improves outcomes; a goal that can be very challenging to achieve in practise.”

Prof. Pimanda said others performing laboratory-based MDS research in Australia include, Carl Walkley and Louise Purton in Melbourne, Devendra Hiwase in South Australia, Anoop Enjeti in Newcastle, Dan Thomas (on CMML) also in SA, and Ashwin Unnikrishnan in Sydney, to name a few.

Prof. Pimanda’s first clinical trial goes back to 2009 when patients didn’t have access to azacitidine.

“We got Vidaza from Celgene on a compassionate access program that I ran between 2009-2011 and we asked questions about why patients were and weren’t responding.

“Ashwin Unnikrishnan, who was a post-doctoral researcher in my lab at the time, discovered that in the patients who were not responding to azacitidine, their cells were not cycling.

“Next was a Phase II trial comparing the absorption of Vidaza versus CC-486, that we ran from 2018-2021 with Professor Mark Polizzotto, a haematologist and clinical trials expert. This trial involved dozens of haematologists across NSW and their patients. These patients benefited from access to the oral drug, and we are using samples from this trial for a Leukaemia Foundation-funded research project.

“Lachy Vaughan, a haematologist and PhD student in my laboratory who Ashwin and I jointly supervise, used patient samples from the very first compassionate access program that I ran in 2009-2011 and made the observations that formed the basis for the MRFF-funded trial that will give patients access to a new combination of oral therapies.

“We’re putting the protocol through ethics at the moment to get the Phase I trial up and running.”

“Although it may have taken 10 years to get to this point, along the way patients got access to azacitidine, and access to the CC-486 oral compound on the Phase II trial that has just concluded.

“And if we can demonstrate that drug absorption levels are similar in the two treatment arms of that trial, that would be good,” said Prof. Pimanda.

“This is the sort of data pharma needs to pursue registration of their compound in a particular clinical context; to supplant injectable azacitidine with the oral form, for example.

“Where we are headed, is to use new technologies to gain a better understanding of the bone marrow environment in MDS patients who respond or don’t respond.

“We collected patient samples from the trial that just concluded to address these questions.

“When patients participate in trials, they’re really contributing to the next chapter of research”

“And if one disease needs therapeutic innovations, it’s MDS.”

Leukaemia Foundation-funded MDS research

Prof. Pimanda’s lab is in the second year of a two-year Translational Research Program grant**, co-funded by the Leukaemia Foundation, the Leukemia & Lymphoma Society (LLS), and Snowdome Foundation.

“I will be presenting a progress report to the LLS American counterparts in October,” he said.

“One of the components of the project is doing a pharmacological/genetic screen looking for targets that might sensitise MDS cells to azacitidine.

“We have done that screen and found an interesting target that we are pursuing,” said Prof. Pimanda, who can’t talk in detail about the findings until the work is completed, hopefully, later this year.

“As part of the grant, together with Professor Richard Lock at the Children’s Cancer Institute, we have made MDS xenografts from patients’ materials from the Phase II oral azacitidine trial, using a new mouse model.

“That’s exciting because it gives us a tool to do our own pre-clinical drug testing,” he said.

In the third component of the grant, Prof. Pimanda is looking at bone marrow stomal cells and immune cells.

“The funding from the Leukaemia Foundation has been absolutely essential to fund the salaries of the people who have been doing this work. Without them, the work would not happen,” he said.

“And it has leveraged more funding from the National Health and Medical Research Council to expand the work.

“We need expert scientists to run the clinical trials, process patient samples, put the samples into mice and run those experiments, and to perform the multi-omic single cell experiments.

“It’s a big research ecosystem and one grant isn’t nearly enough. But every grant is absolutely critical, because if you lose expertise, the whole ecosystem is in danger of collapse,” said Prof. Pimanda.

How and why Prof. Pimanda chose to study MDS

An interest in the biological sciences at high school in Sri Lanka led Prof. Pimanda to study medicine at the University of Colombo. He completed two years before the universities were shut due to civil unrest in the country, and he transferred to the University of New South Wales.

“That was a pivotal transition and a very formative experience,” he said, referring to Sydney’s academic environment at the time, that “intricately linked medical practice to active basic research, not just translation”.

Understanding research principles and methodology, then using clinical knowledge to apply it appropriately is important, he said.

John completed his medical studies in Sydney and being more interested in the analytical side of medicine, he chose haematology as his speciality because it combined “both a laboratory and a clinical side”.

“While practising haematology I was more attracted to the cause and the mechanism of the disease and to a desire to explore basic principles in haematology,” he said.

His question – why are treatments often so ineffective? – led him to study science as a discipline and after doing his PhD at UNSW with Phil Hogg, a biochemist and cancer biologist, he went to Cambridge in the UK on an RG Menzies/CJ Martin NHMRC fellowship to study blood stem cell development and gene regulation with Tony Green and Bertie Göttgens.

“I didn’t actually study MDS or AML or any blood disorders in Cambridge, but I did a deep dive into blood development in the embryo and learnt a suite of new cutting-edge techniques in the fast-evolving field of molecular biology and genomics.”

When Dr Pimanda returned to Sydney, he had the opportunity of dual roles, as a clinical academic at UNSW and a consultant haematologist at Prince of Wales Hospital, and his interest in understanding the process of gene regulation in human blood cells saw him pivot from mouse models to studying human blood cell development.

“The fundamental principles that underlie healthy blood stem cell proliferation and differentiation are corrupted in leukaemia. There are similarities and differences, and you can’t treat one without understanding and preserving the other,” he explained.

“In 2008, when thinking of an area of clinical interest where I could apply the basic experimental platforms that I was setting up at UNSW to understand how human healthy blood cells develop and mature, the natural disease to study was MDS.”

*Organisation for Economic Co-operation and Development.

**This Translational Research Program grant for lifesaving Australian blood cancer clinical research is co-funded by the Leukaemia Foundation, Leukemia & Lymphoma Society (U.S.) and Snowdome Foundation. Total funding: USD600,000 over three years.