August 9 2007 post: Parthenolide (PTL) is a sesquiterpene lactone (in simple terms, that is a chemical that can cause an allergic reaction, see http://tinyurl.com/2p67dh) extracted from a daisy-like plant called feverfew (Tanacetum parthenium), a medicinal herb that belongs to the sunflower family. Feverfew has been used in European traditional medicine to treat headaches, arthritis and digestive ailments, and also to reduce fevers and relieve menstrual pain. But more importantly, its active component, parthenolide, has been found to kill various cancer cells, including pancreatic, breast cancer, acute myelogeneous leukemia cells, and, ah yes, MM cells.

 

A 2006 study published in Apoptosis (http://tinyurl.com/2dv39g) explains that PTL has anti-inflammatory, anti-microbial and anti-cancer properties, and also activates the tumor-suppressor p53 and inhibits NF-kappaB and STAT-3. Excellent! Thanks to a good friend (grazie!), I have the full study in my possession. In addition to all the above, PTL also induces intracellular oxidative stress, which is manifested by elevation of reactive oxygen species (ROS) levels and activation of c-Jun N-terminal kinase (JNK). Because of the induction of oxidative stress, the researchers conclude that PTL works in a similar manner to Bortezomib, which I thought was quite interesting. In the end, they report: We here demonstrate that an active component of medicinal plants, PTL, induces apoptosis in four different MM cell lines, and the concentrations required for its proapoptotic effect are less than those that induce toxic effects in normal lymphocytes and hematopoietic BM cells. Our results encourage the belief that PTL can be applied clinically in the chemotherapeutic strategy for these MM cells. Another 2006 study (in Chinese, but the abstract can be read in English: http://tinyurl.com/26jzbz) also examined the effect of PTL on MM cells. Apoptosis was again the result.

 

Now, there is a reason why I have not written a post about PTL until today, in spite of its anti-MM effects: it is a blood-thinner. Since I already take curcumin, I am wary of adding another blood-thinner to my daily intake. But I do have a listserv friend whose SMM has been stable for years, and PTL is on his A list of supplements. So who knows? Perhaps some day I will have the courage to stop taking curcumin for a couple of months in order to test parthenolide. Not any time soon, though.

 

Update (August 26 2007): Today I read about a $1.7 million grant awarded to a team of scientists at the James P. Wilmot Cancer Center at the University of Rochester Medical Center for the development of new therapies attacking leukemic stem cells. And one of the substances under examination is parthenolide, which seems to be the first single agent that can attack leukemia at its roots. Hurray! A water-soluble form of parthenolide is expected to enter Phase I clinical trials later this year. I don’t have any time to pursue the topic any further today, but I will be watching it closely. And in the meantime I guess I will be ordering some parthenolide! Oh, this is very exciting!

 

Update, October 3 2007 post. This morning I received a Google Alert concerning a parthenolide water-soluble analog called dimethylamino-parthenolide (or DMAPT for short), which swiftly kills leukemic stem cells (LSCs) from both myeloid and lymphoid leukemias, and is also highly cytotoxic to bulk leukemic cell populations. Molecular studies indicate the prevalent activities of DMAPT include induction of oxidative stress responses, inhibition of NF-kB, and activation of p53. The compound has approximately 70% oral bioavailability. I took this from the abstract, which is publicly available at: http://tinyurl.com/2ytvoa

 

Thanks to a close friend (grazie!), I was lucky enough to get my hands on the full study, which was published in “Blood” on September 5, 2007. Here are a few of the more relevant excerpts. LSCs, the study tells us, are dormant and for that reason do not respond to chemotherapy, which targets only active cells. This is probably why relapses occur. Another problem with conventional leukaemia chemotherapy is that it is very toxic to normal stem cells. Not good.

 

Previous studies, the researchers point out, show that NF-kB, a known regulator of growth and survival, is constitutively active in LSCs but not in normal hematopoietic stem cells (HSCs). Notably, many traditional cancer therapies induce activation of NF-kB, a potentially undesirable characteristic likely to facilitate survival of malignant cells. Now, this is fascinating. I didn’t realize that some conventional chemotherapy actually ACTIVATES NF-kB! Gee whiz. That is not good at all.

 

The study also reports that it is not enough to inhibit NF-kB in order to induce apoptosis in acute myelogenous leukaemia. The tumor suppressor gene p53 needs to be activated, and oxidative stress must also be induced by boosting the levels of reactive oxygen species (ROS) to the point where the cell simply cannot survive any longer (as I understand it). The researchers report that their data suggest that the mechanism of LSC death involves combined inhibition of survival pathways and activation of tumor suppressor and/or stress pathways. They also discuss one of their previous findings, i.e., that the robust apoptosis of primary AML cells can be achieved with a single agent, the plant derived compound parthenolide (PTL), which is known to induce oxidative stress and inhibit NF-kB. Importantly, PTL also effectively eradicates AML stem and progenitor cells in vitro while sparing normal hematopoietic cells. So, parthenolide, or PTL for short, kills acute myelogenous leukemia cells (AML), including AML stem cells, but does not affect normal stem cells. I had actually already mentioned that (see my page), but it’s always good to repeat things, sometimes.

 

As we have seen happen with other compounds such as curcumin, though, PTL is poorly absorbable. So the researchers tested several PTL analogs, finally identifying DMAPT, which is over 1000 fold greater solubility in water relative to PTL. Wow! The study continues: DMAPT effectively eliminates human AML stem and progenitor cells without apparent harm to normal hematopoietic stem and progenitor cells. The compound also eradicates phenotypically primitive blast crisis CML and acute lymphoblastic leukemia (ALL) cells. Excellent.

 

The lab tests were performed using primary human AML, CML, ALL cells, and normal bone marrow (BM) cells. For those who are more scientifically-minded, DMAPT was prepared from the reaction of parthenolide with dimethylamine, and the resulting dimethylamino analog was then converted to its water-soluble fumarate salt.

 

DMAPT was found to induce the apoptosis of dormant leukemic stem cells as well as rapidly dividing active leukemic cells. This is important, of course. Researchers tested DMAPT also on three dogs with advanced CD34-positive spontaneous leukaemia. The dosage, 50-100 mg per kilo, was well tolerated, and the results showed obvious in vivo activity of DMAPT on the dogs’ leukaemic stem cells through inhibition of NF-kB and induction of oxidative stress.

 

The study ends by stating that Taken together, the data indicate that DMAPT mediates in vivo biological changes in leukemia cells that will lead to their impairment and/or death. Moreover, given the strong efficacy of the drug for AML stem and progenitor cells in vitro, we propose that a similar effect is possible in vivo, and provide preliminary evidence that LSC-specific targeting can occur in spontaneous canine leukemia. Based on these preclinical findings, its oral bioavailability, and a favorable toxicology profile, DMAPT is proceeding to human phase I clinical trials in the near future.

 

And in fact, according to a recent University of Rochester Medical Center news release (http://tinyurl.com/28l75m), clinical trials are set to begin in England before the end of the year. Oh, and by the way, DMAPT seems to have an effect on multiple myeloma cells, too, according to Monica Guzman, one of the main researchers. YIPPEE, I say!

 

UPDATE: see my page on “Multiple Myeloma and CD40.”

 

June 4 2008 post. A blogging friend (thank you!!!) sent me the full text of an Indiana University School of Medicine study published in “Clinical Cancer Research” on March 15th 2008. In the abstract (http://tinyurl.com/5xxsu5) we can read that PTL has multifaceted antitumor effects toward both MM cells and the bone marrow microenvironment. Excellent starting point, I’d say! Okay, with no further ado, I will plunge right into the study.

 

The beginning of the full study has some interesting wording: Despite intensive chemotherapy, multiple myeloma (MM) remains an incurable, yet chronic, blood cancer with over 14,000 patients diagnosed and 45,000 patients treated yearly in the United States The interaction of MM cells with the bone marrow microenvironment contributes to the heterogeneous treatment response and drug resistance…Incurable, yet chronic, did you notice that? Hmmm, I think this may be the first study I have looked at so far that mentions the adjective “chronic” in the same breath as “myeloma.” Well, well.

 

Reading on, when myeloma cells adhere to the bone marrow stromal cells (BMSC), that is, to the cells and the supporting tissue that surround the myeloma cells in our bone marrow, NF-kappaB activation in the BMSCs up-regulates interleukin-6 (IL-6) and vascular endothelial growth factors, which further enhance MM cell growth both directly and, in the case of vascular endothelial growth factor, also indirectly via promoting angiogenesis. Vascular endothelial growth factor is abbreviated as VEGF and, in a nutshell, is a tumour-feeder.

 

The researchers identify NF-kappaB as the main culprit in the myeloma proliferation process, since it affects both the tumor cells and the supporting microenvironment.

 

And it just so happens that parthenolide inhibits NF-kappaB (as do curcumin and practically every substance that I have researched and posted about here!). Its anti-tumour effects have been observed in various cancers, including breast, lung, prostate, cholangiocarcinoma, and acute myeloid leukemia. It also increases the effectiveness of chemotherapy, which might be of interest to those who are doing chemo right now.

 

Interesting titbit: one of the anti-myeloma strategies criticized by the Indiana researchers is the use of Bortezomib (Velcade), in this sense: the proteosomal inhibition in normal cells can lead to significant side effects due to the accumulation of toxins, which would otherwise be removed by a fully functional proteosome. The Indiana researchers argue that targeting NF-kappaB might instead lower toxicities while maintaining efficacy. Hmmm.

 

At any rate, the researchers tested parthenolide in myeloma cell lines that had become resistant to dexamethasone and doxorubicin. After 72 hours, PTL inhibited the proliferation of these resistant cells.

 

Now, since I know a few myeloma folks who are taking dexamethasone, here is some info on PTL used with dex. The researchers found out that this combination is synergistic.

 

Here is the gist: Parthenolide activates both the extrinsic and intrinsic apoptotic pathways, whereas other anti-MM treatments, including conventional chemotherapy, radiation, and glucocorticoid, primarily activate the intrinsic apoptotic pathway. We hypothesize that simultaneous activation of both apoptotic pathways may enhance cytotoxicity. Our finding of an additive cytotoxicity with the parthenolide and dexamethasone combination supports this concept.

 

Oh, you may ask what “extrinsic” versus “intrinsic” apoptotic pathway means? Good question. Not easy to answer, but basically the death of a cancer cell can be caused by “die, you scoundrel!!!” signals transmitted by so-called “death receptors” located on the cell’s surface, that is, external (to the cell) signals, or by death signals that originate inside the cell such as those deriving from DNA damage or from chemotherapy.

 

The researchers also found that PTL is toxic only to myeloma cells, not to the surrounding healthy ones. Now, haven’t I read that BEFORE?

 

Parthenolide also attenuated the protective effect of the bone marrow microenvironment on myeloma cells. And IL-6 was unable to protect the myeloma cells from the toxic effect of this powerful plant extract. For the scientifically-minded: Parthenolide inhibited the NF-kappaB–DNA binding and further reversed the effect of TNF-alpha–induced NF-nB activation.

 

The study concludes that parthenolide is effective against MM cells in the context of the bone marrow microenvironment and that its mechanisms of action are both caspase-dependent and independent. In combined therapy, parthenolide is additive and synergistic with dexamethasone and TRAIL, respectively. Our findings provide a rationale for the clinical development of parthenolide. (TRAIL, by the way, stands for TNF-related apoptosis-inducing ligand; basically, it helps induce apoptosis in cancer cells.)

 

How about that?

 

December 8 2008 post. Thanks to a Google Alert, yesterday I learned about a new article written by Craig T. Jordan, Ph.D., an Associate Professor at the James P. Wilmot Cancer Center, U of Rochester School of Medicine. Here is the link to the abstract: http://tinyurl.com/695g3g. As usual, I asked Sherlock (grazieee!) to get the full study for me. Well, this was quite an interesting (and easy) read, which also gave me a few possible clues as to why the DMAPT clinical trial hasn’t yet begun in the UK. But let’s proceed by degrees, as usual.

 

Dr. Jordan brings up an issue that is no news to us: can the same results obtained in laboratory tests be obtained in patients as well? Eh.

 

He then mentions a series of small molecules, such as a proteasome inhibitor named MG-132, which target leukemic stem cells. But I would like to focus on what he writes about the substance that interests me perhaps above all others right now: parthenolide (PTL). As you may recall, I am currently testing a feverfew supplement that contains 3% PTL (the highest % I could find). I am taking the dosage recommended on the bottle, which is minimal, I know, especially since PTL is poorly bioavailable. I read that a group of cancer patients took as many as 4 grams of PTL/day in a 2004 Phase I dose escalation trial. I am presently taking less than one-fourth of that. But my motto is primum non nocere, and I am going to stick to it. I can always increase the dose, right?

 

So let’s see what Dr. Jordan has to say about PTL: Parthenolide, a naturally occurring molecule found in the medicinal plant feverfew, induces apoptosis in acute myeloid leukemia (AML) stem cells. Interestingly, he then mentions celastrol (see my Page on celastrol or “thunder of god”), which targets both “bulk” and stem AML cells. But his focus is on PTL. 

 

And here we get to one of the most promising substances I have come across in my research, one that I dearly hope will quickly turn out to be effective and non toxic in Phase I trials: DMAPT, the PTL analogue. The acronym stands for dimethylamino-parthenolide. (I have a Page on PTL and DMAPT, by the way.)

 

Dr. Jordan tells us that, unlike PTL, DMAPT is readily water soluble and is 70% orally bioavailable. Pharmacologic studies in rodents and dogs have shown the drug to be tolerable well beyond the level at which in vitro activity is observed, without any known associated acute toxicity.

 

As we know from previous studies, in addition to inhibiting NF-kappa B, DMAPT targets ONLY cancerous stem cells, leaving healthy cells alone. And, When canines with severe acute leukemia were treated with 50 mg/kg daily DMAPT, the levels of CD34-positive cells were largely reduced.

 

A detailed description of an experiment conducted on animals (mice, mainly) follows. I won’t go into details, but the results were that leukemic stem cells were impaired, at least in the context of a large animal with a spontaneous leukemia.

 

This paragraph ends with words that sound like a Mozart symphony to my ears: Based on the preclinical findings, the drug is proceeding towards clinical trials. As my darling niece would comment, “Sweet!”

 

Dr. Jordan then provides a possible explanation for why it is taking so long to start the DMAPT clinical trials (this is my own interpretation, mind you, since the reason could merely be endless heaps of red tape): It is still unclear how to effectively assess whether leukemic stem cells are actually being targeted. Ah. Big problem, here.

 

He adds that A targeted agent could be used as part of a maintenance regimen to destroy the residual leukemic stem cells in patients in remission. However, he soon adds, there is no evidence that any of the agents currently available can target leukemia stem cells in a remission patient. Oh.

 

And then we get to a fascinating, thought-provoking excerpt: The biology of cells in minimal residual disease conditions appears to be very different from that of cells found in a de novo and heavy tumor-burden context. This difference can impact whether the drugs work or not. As clinical trials progress, the targeted agents may fail because of the physiology of the tumor cells, not because the drug is ineffective with all leukemic stem cells. Well then, I say, why not test DMAPT also on leukemic/myeloma patients who have never had any conventional treatments? (Not that I have anyone specific in mind…)

 

Reading on, we stumble upon what might be another reason for the DMAPT clinical trial delay: Cancers are heterogeneous, and this is exceptionally true of leukemic stem cells. From patient to patient, molecular markers for stem cells differ greatly. […] This heterogeneity makes determining the frequency of the leukemic stem cell in an individual patient extremely difficult.

 

Dr. Jordan defines leukemic stem cells as highly dynamic and highly unstable. So the question arises: how can they possibly be monitored? In comparison, it would seem that keeping individual tabs on millions of agitated grasshoppers in a field would be a much easier task…

 

As I see it, these seem to be the main problems facing clinical trial investigators: 1. how to identify the stem cells in each individual patient in the first place; 2. how to determine if these cells are being targeted by the specific treatment (DMAPT, e.g.).

 

And here follows something that perhaps for the first time I have seen spelled out in a study: During chemotherapeutic challenge, patients can experience a dramatic change in the phenotype of their leukemic stem cell. From my layperson’s point of view, it would appear that this “dramatic change” would also be a problem.

 

Furthermore, just because your total tumour burden decreases doesn’t necessarily mean that your stem cells have been affected. Another problem.

 

But there seems to be a way of getting around all of this. Dr. Jordan writes that Clinical trials must be temporal and patient-specific. Specimens must be gathered before, during, and after treatment. The phenotype of each patient’s leukemic stem cell population must be defined up front and verified by a functional assay to help quantitate it. In the course of treatment, the population must be continuously monitored […]. It sounds extremely painstaking and time-consuming, doesn’t it?

 

Dr. Jordan’s final considerations: Just as cancers are heterogeneous, so too are leukemic stem cells, and the ability to target and quantitate leukemic stem cells is complicated by this heterogeneity. As research expands our understanding of leukemic stem cell biology and physiology, investigators must incorporate that knowledge into their strategies for targeting and analyses for quantifying leukemic stem cells. They must also determine where agents that target leukemic stem cells will be of most use: as maintenance therapy that targets minimal residual disease in remission patients, or as treatment for relapsed or refractory patients.

 

To this, I would add: “…or as treatment for patients who have not yet had any chemotherapy.”

February 6 2009 (see post) UPDATE: I have had a Google Alert for DMAPT, the parthenolide analogue (see my page on this topic), for ages, now. Whenever I receive a Google Alert on DMAPT, I get all excited, only to discover that it frequently is about a meeting of the Detroit Metropolitan Area Physics Teachers. Aaargh! I am also on a Leukemia and Lymphoma Society alert list for the DMAPT clinical trial, which was supposed to begin months ago in the UK. Until this morning, though, I hadn’t even heard a whisper about the clinical trial that was supposed to begin months ago in the UK.