Myeloma stem cells

January 12th 2008 post. A January 9 press release from the Johns Hopkins Kimmel Cancer Center (http://tinyurl.com/3avj8s), confirms what we have been suspecting for a while now, that is, until we get rid of the myeloma STEM cells we won’t get rid of myeloma. I have always thought of myeloma as a sort of big bothersome (to say the least!) weed. We can cut off parts of it, but it will always grow back. That is, until we pull it up by its roots, i.e., the cancerous stem cells.

January 16th 2008 post: I have it, I have it! Yes, the FULL recently published Johns Hopkins myeloma stem cell study that I mentioned a couple of days ago. The study, by the way, was conducted by a team led by Dr. William Matsui and published in the January 1 2008 issue of “Cancer Research.” You can view the abstract here: http://tinyurl.com/2yuru9.

Read here: “Scientists at the Johns Hopkins Kimmel Cancer Center say they have evidence that cancer stem cells for multiple myeloma share many properties with normal stem cells and have multiple ways of resisting chemotherapy and other treatments.” I will try to get my hands on the full study in the next couple of days. This should be a fascinating read.

The researchers transplanted stem cells from four myeloma patients into a bunch of mice that, poor dears, developed myeloma. But when they transplanted plasma cells into mice, they were not able to recreate the cancer. So the stem cells are the culprit, it would seem.

Another finding was that myeloma stem cells were not affected in the least by chemotherapy, which did instead inhibit the growth of myeloma plasma cells. The researchers may also have discovered what makes myeloma stem cells resistant to treatment. How about that?

Before I go on, though, I wanted to mention that another blog reader posted an interesting New York Times article on the controversy surrounding the cancer stem cell theory and other interesting info, so if the issue of stem cells is your cup of tea, please go read Carla’s comment on my “Stem cells and myeloma” post, Jan 12th.

Back to us. I have to admit, reading this stem cell study was not exactly as fun and easy as reading one of the Harry Potter books, but I found it almost as engrossing. The study begins by providing a bit of background, including this: “Early studies examining a murine model of multiple myeloma suggested only a minority of cells were capable of clonogenic growth.” Hmmm, so only a tiny percentage of myeloma cells can clone themselves…I didn’t know that. I thought they were all capable of creating clones. Live and learn.

Myeloma stem cells are mentioned in a 1977 study (full text: http://tinyurl.com/2d8z3n), which, by the way, shows black and white photos of myeloma cells for those who might be interested. Anyway, according to the Johns Hopkins investigators, this early study showed that “the cloning efficiency of primary multiple myeloma specimens was 1 in 1,000 to 100,000 cells. To date, it has remained unclear whether these clonogenic cells are distinct from the plasma cells that constitute the majority of tumor cells.”

Then, in 2004, Dr. Matsui et al published a study (full text: http://tinyurl.com/2233wp) in “Blood” on clonogenic myeloma cells. Clonogenic, by the way, has two meanings: 1. “giving rise to a clone of cells” and 2. “arising from or consisting of a clone.” I went through the 2004 study, which reported that “highly clonogenic cells from both human MM cell lines and primary patient samples do not express CD138, but rather markers that are characteristic of B cells.” This rather baffling sentence will, I hope, become clearer after the upcoming section on CD138 (and part II, which I will post tomorrow, should also help in that sense). The 2004 study also suggested that, like chronic myeloid leukaemia or CML, “MM is another example in which cancer stem cells are a rare cell population that is distinct from the differentiated cells that comprise the bulk of the disease.”

CD138. Now I am going to delve into some rather difficult material that has to do with this thing called CD138. Also known as syndecan-1, CD138 “is “a heparan sulfate proteoglycan expressed on the surface of, and actively shed by, myeloma cells.” I know, I know…Let’s see if this will clarify matters: proteoglycans are “glycoproteins but consist of much more carbohydrate than protein; that is, they are huge clusters of carbohydrate chains often attached to a protein backbone,” according to Prof. Kimball’s Biology Pages. (Hmmm, lots of carbs plus some protein…pasta with meat sauce! )

Seriously though, it doesn’t really matter if we don’t completely grasp what CD138 is. What’s important is that we understand the following excerpt from the 2004 Johns Hopkins study. CD138 “is the most specific marker for normal and MM plasma cells. However, normal CD138+ plasma cells appear to be terminally differentiated and unable to proliferate, and there have been few studies using this marker to study the proliferative capacity of MM cells.”

Not the easiest stuff to digest, eh! Well, let’s see if I can explain what CD138 is in a few simple words (if I make any mistakes, please let me know): in sum, CD138 is a thingie (ok, a proteoglycan) sticking to the surface of regular myeloma cells—the ones, that is, that are NOT able to clone themselves. These are the CD138 “plus” myeloma cells. Patients whose myeloma cells release, or “shed,” CD138 (CD138 “negative” cells) into the serum have a worse prognosis than those whose myeloma cells still have it. Hence it is a helpful prognostic marker (for more info, see this 2002 “Blood” study: http://tinyurl.com/2h26uq). CD138 levels can be measured in MGUS patients, too (see this 2006 “Neoplasma” abstract: http://tinyurl.com/yr9vzd).

A September 2007 “Blood” study (see abstract: http://tinyurl.com/2slg3t) confirms that “High levels of shed syndecan-1 in myeloma patient sera correlate with poor prognosis and studies in animal models indicate that shed syndecan-1 is a potent stimulator of myeloma tumor growth and metastasis.” So again we see that if CD138 is shed into the myeloma “microenvironment,” this is bad news for us (poor prognosis etc.). Interesting aside: this is true for CLL patients as well (see this January 2008 abstract: http://tinyurl.com/3ap8ba). Connections, connections.

January 18th post: Day before yesterday, in part one, we saw that the only myeloma cells capable of cloning themselves are the ones that do not express CD138. The following excerpt from the Johns Hopkins study says it well: “multiple myeloma cell lines and primary bone marrow contain small populations of clonotypic B cells that do not express the characteristic plasma cell surface antigen CD138 and are capable of clonogenic growth and differentiation into multiple myeloma plasma cells in vitro and in vivo.”

Myeloma stem cells, therefore, don’t have CD138 sticking to their surfaces. Herein lies a big difference between regular myeloma cells and myeloma STEM cells: the former have CD138, the latter don’t. Enough said on CD138. Let’s look at other findings now.

I mentioned in my January 12th post that the capable-of-cloning-themselves myeloma cells are resistant to chemotherapy AND look like normal memory B cells AND also display “cellular properties characteristic of normal stem cells, suggesting cancer and normal stem cells share multiple mechanisms that promote drug resistance.” In fact, according to the 2008 stem cell study, both myeloma and normal stem cells have “intracellular detoxifying enzymes,” enzymes that, as I understand it, shoo away the chemo toxins, thus protecting the stem cell from apoptosis. This would provide a good explanation for why myeloma eventually becomes resistant to chemotherapy agents.

So, in sum, what does all this mean? In the researchers’ words, “Because cancer stem cells are a relatively low frequency population in most tumor types, the true inhibition of these cells is likely to be difficult to assess early after treatment, and a prolongation of disease remission would be required to establish such activity.” Well, that doesn’t sound very encouraging, does it?

Back in the middle of November, in a private exchange, a blog reader compared myeloma to a tank of water with a tap and a drain, an analogy he took from the film “Lorenzo’s oil,” (those interested can go read a 2007 update on the real ALD story: http://tinyurl.com/2yjyjx). Anyway, the blasted paraprotein shoots out of the “tap,” and the drain hole (our kidneys) gets rid of it. Myeloma cells, he was told by his haematologist, have a half-life of 5-6 weeks (I have been trying to find an online reference to this, but so far, on the UK freelite website, I found only that the “the serum half-life of intact immunoglobulin IgG is 20-25” days, so I will ask my haematologist about this in February). In other words, the cells stay in the body for that time and are then expelled via the kidneys.

Point is, are stem cells our “tap”? If so, how can we turn it off? I sure would like an answer to those questions! I would like to add that during yesterday’s meeting, Dr. Benelli suggested another “tap” theory to me, which I will be looking into in the next few days. Interesting times.

Concluding remarks. In the short term, yes, this stem cell research is exciting news but that’s what it remains: news. It has little relevance to us patients. For now. It holds promise for the future, though, indeed let’s hope the very near future. A finding that may prove to be useful is that “the developmental signaling pathway Hedgehog is up-regulated in multiple myeloma stem cells and regulates cell fate decisions.” So we meet again, Mr. Hedgehog! Back in early August, on August 2 and 3 to be precise, I wrote about cyclopamine, a poison contained in corn lilies that was found to be a Hedgehog pathway inhibitor (see my page on cyclopamine).

A couple of days ago, in a private exchange, an MMA list member asked me if the stem cell study had changed my supplement plans for the future. I answered yes, it has, in the sense that I hadn’t really thought seriously about taking parthenolide until I read about myeloma stem cells and how parthenolide and DMAPT (water-soluble form of PTL) annihilate leukaemic stem cells in vitro. So parthenolide shot right to the top of my supplements-to-try list. I am now planning to test parthenolide in March, after the Biocurcumax experiment has ended.

Summary of the main points made in the stem cell study, from my point of view:

  1. clonogenic myeloma stem cells do not express the characteristic CD138 antigen.
  2. myeloma stem cells constitute less than 2% of the myeloma “population.”
  3. myeloma stem cells look like memory B cells.
  4. myeloma stem cells display normal stem cell characteristics that protect them “from toxic injury.”
  5. like normal stem cells, nearly all myeloma stem cells (>98%) studied were in the quiescent (dormant, inactive) state, which is possibly another “major mechanism of drug resistance.”
  6. conventional chemotherapy doesn’t affect myeloma stem cells.

January 19th post: A myeloma list member (thank you!) posted the link to a January 17 BBC story (see: http://tinyurl.com/2mol2c) about four-year-old identical twin girls were born with leukaemic stem cells (STEM CELLS!) in their bone marrow.These cells contained “a mutated gene, which forms when the DNA is broken and rejoined at another point. The pre-leukaemic cells are transferred from one twin to the other in the womb through their shared blood supply. But it takes another genetic mutation in early childhood for the cells to cause disease. This second mutation, which may be caused by infection, occurred in Olivia but not Isabella.” In fact, only Olivia developed full-blown leukaemia (acute lymphoblastic leukaemia or ALL). UK researchers examined the twins’ blood, and their findings were published in the January 18 issue of “Science.” The abstract can be read here: http://tinyurl.com/285qjn.

“About 1% of the population is thought to be born with pre-leukaemia cells. Of these, 1% receive the second “hit” that leads to cancer.” Even a simple cold, from other articles that I read online, is apparently able to trigger this second mutation.

Well, this is all very interesting. I remember that, when I was eight years old, my family doctor here in Italy was convinced that I had leukaemia. Unfortunately, my blood tests from that period are probably buried in a box in my parents’ garage in the U.S., but if I am able to locate them some day, they might yield some interesting information that could be relevant to my having myeloma (inactive) today. Could I possibly have had a “second hit” (later in life) that led me to develop this cancer? Well, this is just a random thought on a lazy Saturday evening. Nothing more. And indeed, now that I have written it out, it appears to be unlikely.

But the next time I visit my parents, I will comb through their garage, just in case.

January 24 2008 post. I read and reread (and rereread…) this full study (grazie, Sherlock!) that I reported about in my January 19 post. Definitely one of the the most difficult texts I have ever read, and I have read some labyrinthine stuff, believe me!  Anyway, a few things are clear (more or less…?), so I thought I would post about them today, hoping not to make any huge mistakes…

An important finding is that the pre-leukaemic stem cell population derived from the abnormal merging or, to use a more appropriate technical term, the “chromosomal translocation,” of two genes during pregnancy. From their union sprang a fusion gene called “TEL-AML1,” a clone that forms in one twin inside the womb that “may spread to the other twin via their shared placenta.” It’s a genetic “mistake” that can lead to the development of leukaemia. Or not, as in the case of these British twins.

In fact, the study tells us that “Additional mutations are required for progression to leukaemia,” which means that one twin may develop leukaemia while the other remains healthy, in spite of carrying the “ancestral preleukemic clone.” The researchers found that Isabella (the healthy twin)’s peripheral blood contained a “rare population” of these mononuclear cells, which has remained stable. This would prove that one mutation alone does not trigger full-blown leukaemia.

The “cancer-propagating population,” or “rogue stem cell population,” (which I like better) was present in both twins, but there were differences between the two. In the leukaemic twin, there was “a clonal and more differentiated descendant of the CD34+CD38–/lowCD19+ population in the healthy twin. Consistent with this, the majority of CD34+CD38–/lowCD19+  cells in the leukemic twin express common ALL antigen, CD10; those in the healthy twin do not.”

I know, I know…but this long string of letters and numbers, CD34+CD38–/lowCD19+, simply indicates the cancerous stem cell population. So the healthy twin’s cells present less differentiation, in sum. And her blood does not carry the acute lymphoblastic leukaemia (ALL) antigen, called CD10. Am I the only one who finds this fascinating?  If not, and if you are getting a headache, just skip to the bottom of my post, where I wrote a summary of sorts.

The researchers then injected these pre-leukaemic cells into NOD/SCID mice. NOD (I looked it up out of curiosity) are “non-obese diabetic” mice. SCID are “severe combined immunodeficient” mice. SCID mice are frequently used in research dealing with the immune system in part because they lack the capacity to make T or B lymphocytes (so they cannot fight infections). I must say, I have a hard time reading all these details. When I was a kid, I would burst into tears whenever I heard about suffering, hurt or dead animals of any size. In many ways, I am still that kid. I haven’t been able to watch the “March of the Penguins,” for instance. Or that wonderful movie about migrating birds…(when the hunters began shooting at those beautiful birds…well, you can imagine the rest!) Or even…”Bambi.” I may be the only adult in the western world who hasn’t seen Bambi. But that is neither here nor there. It’s just that these feelings of empathy curtail my current plans to become a molecular scientist in my next life. I think I’d gather up all the mice in the lab and take them home…

But let’s get back to the study. What the team of researchers found was this: “Collectively, our data support the notion that TEL-AML1 can, as a single mutation, generate abnormal cells that resemble the TEL-AML1– expressing CD34+CD38–/lowCD19+ cells observed in the healthy twin.” If I understood this correctly, this means that the researchers were able to reproduce the pre-leukaemic population in the NOD/SCID mice. The transplanted cells resembled those found in the healthy twin’s blood and “displayed B cell differentiation and self-renewal potential in vitro.” They also did not contain the CD10 antigen, like the healthy twin’s peripheral blood cells.

The team then transplanted the rogue stem cells from the “primary” (first bunch of) mice into a bunch of “secondary” NOD/SCID mice: “To investigate whether the TEL-AML1–generated CD34+CD38–/lowCD19+ population can initiate and maintain a ‘preleukemic’ state in vivo, we prospectively isolated these cells from engrafted primary mice and injected them into the tibiae of secondary NOD/SCID recipients.”

These cells not only engrafted but, to the team’s surprise, also “gave rise to more mature B cells (CD38+CD19+), as well as reconstituting a CD34+CD38–/lowCD19+ population.” This means that the stem cell population, or “TEL-AML1–generated CD34+CD38–/lowCD19+ population has significant self-renewal potential.” What does all this mean? It indicates that this CD34+CD38–/lowCD19+ cell is able to reproduce itself, and it “may itself function as a preleukemic stem cell. This proposal is supported by our xenograft modeling studies, which further suggest that TEL-AML1 may be sufficient to generate this population of preleukemic stem cells.” Ok, TEM-AML1 is definitely the bad guy in this scenario.

The team also suggests that there is a hierarchical structure not just in full-blown leukaemia but also in pre-leukaemic cells. I am not sure why this finding is important, but apparently it is. If anybody knows the answer (I don’t have time to look into this matter now), please let me know.

Anyway, the study of the stem cell population, the researchers add, is crucial in order to understand “the function of the first-hit mutation and how it predisposes to leukaemic transformation.” Okay.

The study ends as follows: “The observation that children in lengthy remission can relapse late with a novel leukemic clone, but which nonetheless appears to derive from the identical preleukemic clone that initiated the disease at presentation, suggests that the preleukemic stem cell compartment may persist even when the cells propagating the overt leukemia have been effectively eradicated.” So the model created by these researchers may provide an explanation as to why pre-leukaemic stem cells can resist chemotherapy treatments. When that (resistance) happens, sooner or later the cancer will return.

There have been other studies on twins and ALL. I just wanted to highlight this one, published in “Leukemia” in 2003: http://tinyurl.com/ypom65 In this case, both twins (two years old) developed ALL. Here, too, the researchers suggested that these pre-leukaemic cells formed in the womb and spread from one twin to the other. And the researchers state that “It is likely that one or more additional postnatal genetic events was required for overt leukemogenesis.” Aha, the “two mutations needed” theory that we discussed previously. Okay, that’s it for today. I still have my classes to prepare for tomorrow! Agh!

Summary of the 2008 study, as I understand it:

  1. Acute lymphoblastic leukaemia (ALL) is the most common form of childhood leukaemia.
  2. Researchers identified a “rare population” of CD34+CD38(-/low)CD19+ cells isolated from the TEM-AML1-positive twins.
  3. The leukaemia-causing potential of this small population was confirmed when the researchers were able to transplant the cells of the leukaemic twin into a group of NOD/SCID mice. Successfully. And a second transplantation, from the first to a second group of mice, was also successful. The rogue stem cells survived and proliferated in the second group, too.
  4. This indicates that these cells are self-renewing leukaemic stem cells.
  5. The healthy twin only had one genetic defect, whereas the leukaemic twin also carried a second genetic mutation (the loss of the “uninvolved” normal TEL allele or gene, for the science brains among us).
  6. The second mutation may have been triggered by an infection, which may have led to the development of leukaemia in one of the twins. No second mutation = no leukaemia, then, it would seem.

UPDATE. June 24 2008 post. Sherlock (grazie!) came across and sent me a study by Carol Ann Huff and William Matsui recently published in the “Journal of Clinical Oncology” (June 10 2008) and titled “Multiple myeloma cancer stem cells.”. The abstract can be viewed here: http://tinyurl.com/4yx38s

 

The full study tells us that most myeloma cells are mature and quiescent and lack the ability to clone themselves. The fact that the majority of plasma cells are quiescent suggests that tumor growth is restricted to a specialized cell population.

 

A bit of history. In the 1970s Salmon and Hamburger showed that more than 86% of tumor samples from patients with multiple myeloma were capable of colony formation, and clonogenic growth occurred at a frequency of 1 in 100 to 100,000 cells. This could be explained by one of the following hypotheses: 1. only a small, functionally unique, subset of cancer cells was able to clone itself or 2. all myeloma cells can clone themselves, but only a few express this property at any point in time.

 

From what I wrote in my second paragraph, we can figure out that Huff and Matsui believe that hypothesis 1 is correct. Based on scientific data, they suggest that myeloma stem cells are clonotypic B cells: The ability of clonotypic B cells to recapitulate multiple myeloma in immunodeficient mice suggests that these cells represent the cancer stem cell in multiple myeloma. This part wasn’t easy to follow, but basically some features of clonotypic B cells are similar to those of healthy adult stem cells, such as resistance to toxic injury, and the continual risk of relapse among patients treated with standard therapies suggest that myeloma stem cells should also be relatively drug resistant. They can also self-renew and give rise to differentiated effectors (ie, plasma cells).

 

The scientists tested various novel chemotherapy drugs recently approved for the treatment of myeloma. The myeloma cancer stem cells were relatively resistant to both standard cytotoxic compounds and novel agents in vitro compared with the myeloma plasma cells. This suggests that these drugs work against the bigger population of myeloma cells, the ones that don’t have a cloning ability, but have no effect on the smaller population of stem cells. Nothing new here.

 

For the more scientifically-minded, here are a few comparisons between myeloma stem cells and normal ones: it appears that myeloma stem cells display properties common to normal stem cells, such as expression of membrane-bound drug transporters, intracellular detoxification enzymes, and quiescence. Thus, the chemoresistance of cancer stem cells may be mediated by multiple processes similar to those that protect normal stem cells.

 

The paragraphs that follow deal with therapeutic ways to target myeloma stem cells. For instance, as we know, the aberrant functioning of the Notch, Wnt and Hedgehog pathways is fundamental for the well-being of myeloma stem cells. These pathways therefore represent a good target. Let me add that we have non toxic ways to affect these pathways: curcumin, cyclopamine (by the way, I just read that a new water-soluble form has been developed!), zerumbone, DMAPT…

 

Then we are immersed in a discussion concerning telomerase activity…mamma mia, I confess I had to resort to parts of my brain that I never thought I possessed (!) in order to attempt to understand this section…not easy stuff! But, in essence, telomerase activity is an important process in myeloma, and its inhibition means that myeloma stem cells end up not being able to clone themselves. So, telomerase becomes another target.

 

Another promising target seems to be SOX2 (I wrote a post and page about SOX2 a while ago, by the way), an embryonic transcription factor that is normally turned off after embryonic stem cells differentiate; however, in both MGUS and myeloma patients it becomes reactivated (hah! Figures…).

 

Anyway, even if you don’t understand what this all means (as I don’t, to be honest), the point is this: SOX2 antibodies are present in folks with MGUS but not in those with myeloma. If you are lucky enough to possess those antibodies, you are less likely to develop myeloma. So targeting SOX2 could be another way to injure the myeloma stem cells, since, as Huff and Matsui write, SOX2 is a feature of clonogenic myeloma cells, and stimulation of anti-SOX2 immunity could limit clonogenic tumor growth of primary samples in vitro.

 

The development of new evil-stem-cell-focused treatments won’t happen overnight. That much is clear. New trial designs that incorporate novel end points will be needed to study myeloma stem-cell–targeted therapies. One potential strategy is to incorporate these approaches with existing therapies to determine whether they prevent tumor regrowth and prolong the duration of remissions after cytoreduction with chemotherapeutic or novel agents.

 

The researchers admit that the exact phenotype of the clonogenic cell has not been definitively established and controversy remains. Resolution of the controversy will probably depend on how well patients respond to stem-targeted treatments (read: on long-term outcomes…). Time…time…

 

The study ends as follows: growing knowledge regarding the basic biology of multiple myeloma, such as the identification of prognostic categories based on cytogenetic alterations or transcriptional profiling may allow multiple myeloma to serve as a model system to address general questions regarding cancer stem-cell biology.

 

As a myeloma patient, I confess that I (selfishly) don’t care that much about setting up a model system. I care much more about getting the promising, non toxic, stem-cell-targeting treatments into clinical trials as soon as possible. I’m ready and willing to try them!

 

So, where do I sign?!!!

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