Nobody has yet tested which cells actually contribute to disease in patients.
Therapies must eliminate all cells with the potential to contribute to disease.

Sean Morrison

One of the best lectures that I’ve heard this year so far was Sean Morrison’s talk at University of Pennsylvania. Research in his lab made me think for the first time about complexity of cancer stem cell concept. For me he is an example of how real basic science should be done.

His “cancer stem cells” talk was recently recorded in the Koch Institute Symposium, held on June 19, 2009 at MIT.

He is talking about some very new unpublished data at the end of the lecture. I’d like to bring your attention to one of the last slide, shows that high frequency of tumorigenic cells (serially transplantable) could be observed not only in highly immunocompromised mice (like NOG), but also in fully immunocompetent histocompatible.

link
copyright: MIT Tech TV

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also read:
Cancer stem cells - how mouse model can change the concept
Complexity of cancer stem cells
Validity of the cancer stem cell concept under discussion

also watch:
Robert Weinberg - Cancer stem cells and malignant progression
Catriona Jamieson - The molecular evolution of leukemic stem cells
Irving Weissman - Stem Cells: Units in Regeneration, Cancer, and Natural Selection
Owen Witte - A Delicate Balance: Stem Cells, Cancer and the Immune Response

Cancer stem cell concept implies identification of selective markers, different from normal cells, which potentially could be targeted by newly designed drugs.

Recently, anti-cancer activity of some well known drugs was discovered, which was shown to rely on targeting of cancer stem cells (CSC). Explanations for some very effective anti-leukemic drug combination were recently found in the laboratories. I’ll give you some examples of “from-bed-to-the-bench” translation coming from leukemia clinic.

Arsenic targets quiescent leukemic stem cell

Ido et al showed that arsenic trioxide specifically targets quiescent leukemia-initiating cells (LIC) in chronic myelogenous leukaemia model. Arsenic trioxide selectively and reversibly decreases PML protein expression on hematopoietic stem cells (HSC) and LIC and causes their impaired quiescence and self-renewal.

Arsenic trioxide-induced cycling increased LIC-killing effect of another anti-leukemic drug - Ara-C, which induces apoptosis of dividing cells. The combination of both drugs was able to inhibit leukemogenesis in secondary BMT unlike Ara-C treatment only. Even more, only by combining these two drugs leads to complete cure (ei LIC eradication) of disease in half of recipient mice.

Authors consider that this mechanism could be a possible explanation of dramatic ability of arsenic to cure acute promyelocytic leukemia (APL). I’d remind you that arsenic has been used for treatment of leukemia for centuries.

Yet another study provides the same explanation for therapeutic efficacy of arsenic with retinoic acid in treatment of APL. These drugs, which successfully have been used in leukemia clinic, acts through degradation of fusion PML-RARA in LIC blocking their self-renewal.

Except APL, arsenic trioxide is active against Glivec (Imatinib)- resistant CML cells and potentiates its efficacy through other then PML mechanisms.

Interferon wakes up dormant hematopoietic stem cells

Two recent studies provided evidences for one possible mechanisms for manipulation of quiescent hematopoietic stem cells (HSC). The first study came from Andreas Trumpp lab and describes how interferon-alpha stimulates HSC proliferation through exit from quiescent state. Sato et al, found that mice, deficient for one of the components of the IFN pathway, have abnormal proliferation of HSC leading to their rapid functional exhaustion.

So far, we don’t know if we can apply this results for targeting quiescent LIC, but it was proposed as possible explanation of IFN efficacy in combinational therapy of CML.

Persistent CML-initiating cells, or CML stem cells, which are protected from imatinib killing by their quiescent status, are probably responsible for the regrowth of the disease.

Strikingly, a handful of CML patients that were first treated with IFN-alpha and then switched to imatinib treatment—a molecularly targeted therapy directed against BCR-ABL, the fusion protein characteristic of CML - experienced persistent remission…

The emerging possibility to explain the stable remission in the patients previously treated with IFN-alpha could be that the exposure to IFN-alpha induced the CML stem cells to exit quiescence and proliferate such that, upon imatinib treatment, they became vulnerable to imatinib rather than remaining protected.

Zileuton selectively targets CML stem cells

Recently, well-known 5-Lipoxygenase inhibitor - Zileuton alone or in combination with Gleevec, was found unexpectedly effective in eradication of LIC. Zileuton is widely used for asthma treatment, where it mechanistically inhibits the Alox5 gene.

The researchers found that CML did not develop in mice without Alox5 because of impaired function of leukemia stem cells. Also, Alox5 deficiency did not affect normal stem cell function, providing the first clear differentiation between normal and cancer stem cells.

Zileuton is not in clinical trial for leukemia treatment yet, but it was proposed in Chen’s study.

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This essay is aimed to show how drug-resistance to one agent (Glivec for instance), discovered in leukemia clinic, could lead to investigation in laboratory and possible explanation by cancer stem cell theory. Targeting of leukemia-initiating cells by additional drugs underlies achieving of successful clinical and cytological remission.

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citations:
Emmanuelle Passegué & Patricia Ernst. IFN-alpha wakes up sleeping hematopoietic stem cells. Nat Med 2009; 15: 612 - 613
A lethal cancer knocked down by one-two drug punch. GEN June 7.

also read:
Salomon P. Stemming out of a new PML era? Cell Death Differ. 2009 Jun 12
Jonathan D. Licht. Acute Promyelocytic Leukemia — Weapons of Mass Differentiation. NEJM 2009;360:928-930

read more:
Stem Cells, Quiescence and Cancer
Regulation of leukemic stem cells self-renewal and quiescence - the role of p21
Complexity of cancer stem cells

Catriona Jamieson - Assistant Professor of Medicine, Division of Hematology-Oncology University of San Diego Medical Center, Director for Stem Cell Research, Moores UCSD Cancer Center

Recently some folks and I were fascinated by a concept based on developing cell capturing and cell trafficking control implantable devices. The concept is based on known receptor-ligand interactions between circulating bone marrow cells or seeded cells and defined factors embedded in the device. This approach may provide a new generation of cell therapies in the future.

Lately, some of these devices entered the commercialization phase and were licensed by companies. I’d like to give you a brief overview of some of these kind of devices.

1. “Jianyi Zhang’s patch”
device-patch: PEGylated fibrinogen, bound with recombinant SDF-1
how it works: Patch implanted in myocardium released SDF-1 - homing factor for hematopoietic (Sca1+/cKit+) cells. Recruited bone marrow progenitor/stem cells to mediate heart muscle and regeneration.
IP: US patent application # 20050118144
phase: experimental
potential application: heart muscle regeneration
publications: Zhang G, et al. Controlled release of stromal cell derived. Factor-1α in situ increases stem cell homing to the infarcted heart. Tissue Eng. 2007;13(8):2063-2071

2. “Michael King’s device”
device: P-selectin–coated microtubes implanted as arteriovenous shunt
how it works: P-selectin triggers mobilization of hematopoietic stem/progenitor cells from bone marrow. Enriched stem cell fraction could be collected and eventually expanded and/or transplanted.
separation of cancer cells - TRAIL-coated device:

…device that filters the blood for cancer and stem cells. When he captures cancer cells, he kills them. When he captures stem cells, he harvests them for later use in tissue engineering, bone marrow transplants…

IP: Michael King’s (U of Rochester) US patents: 20060183223, 20070178084;
Jeffery Karp (MIT), technology exclusively licensed by CellTraffix
phase: experimental-preclinical
potential application: hematology, oncology
publications: Wojciechowski JC, et al. Capture and enrichment of CD34-positive haematopoietic stem and progenitor cells from blood circulation using P-selectin in an implantable device. Br J Haematol. 2008 March; 140(6): 673–681 (OA)

Finally, most intelligent device from new generation:
3. “David Mooney’s device”
devices in work: In situ bioreactive devices (iBD). Examples:

• PLG matrix with mobilized GM-CSF and tumor antigen. G-CSF attracts dendritic cells, which start to expand and present tumor antigen. After release, antigen-presenting dendritic cells migrate to lymphoid organs and activate specific anti-tumor clon of cytotoxic T-cells.
• Alginate scaffold with VEGF and endothelial progenitors. VEGF could attract endogenous endothelial cells or support scaffold-embed ones and stimulate local neovascularization.

IP: David Mooney’s lab at Harvard University US patents; technology licensed by InCytu
phase: experimental-preclinical
potential application: immunotherapy in oncology, tissue regeneration and therapuetic angiogenesis
publications: Ali OA,et al. Infection-mimicking materials to program dendritic cells in situ. Nat Mater. 2009 Feb;8(2):151-8
Silva EA, et al. Material-based deployment enhances efficacy of endothelial progenitor cells. PNAS 2008 Sep 23;105(38):14347-52 (OA)

So, ideally device should be composed of biodegradable material with some mobilized factors and dedicated to recruit desired cell population, modify their qualities and controllably release them for in situ therapy. Development of those devices demonstrates a good example of a multidisciplinary approach, coming from tissue engineering principals. Future development of such devices can provide an absolutely new way of cell-based therapies.

This is the first demonstration of anti-cancer activity in a living organism by cells derived from human embryonic stem cells.

Dan Kaufman (University of Minnesota)

A while ago I wrote about the difficulties on the way to generating functional hematopoietic stem cells from human embryonic stem cells (hESC) and I was even trying to challenge the significance of this research for clinical applications. I’d like to notice that generation of mature blood cells from hESC has been much more successful. Thus functional T-cells, NK cells and erythrocytes were efficiently derived from hESC. But only a few of them have been studied for functionality of derived cells in live organism (in vivo) models, which are very important for estimation of therapeutic potential.

Now Dan Kaufman’s lab from University of Minnesota demonstrate for the first time efficient cancer killing activity in vivo, mediated by immune cells derived from hESC. They generated natural killer (NK) cells using previously published protocol and investigated their anti-cancer activity on the range of tumors in vitro and in mouse leukemia model.

In my opinion this study has 2 most important advantages:
1. They used in vivo mouse model of human leukemia to estimate therapeutic potential of hESC-derived NK cells.
2. The authors compared activity and function of NK cells derived from hESC versus cord blood (CB) derived counterparts. I remember only 1 or 2 studies (correct me if I’m wrong) which were done to functionally compare hESC-derived cell types vs adult stem cell derived counterparts. Surprisingly CB-derived NK cells showed less cytolytic activity versus range of cancer lines in vitro and less anti-tumor activity in mouse model compared to hESC-derived NK!

Remarkably, all mice (13 of 13) treated with hESC-NK cells demonstrated rapid and complete clearance of the primary tumor within two weeks after tumor inoculation. In contrast, mice treated with UCB-NK cells had significantly less anti-tumor activity in vivo, with only 5 out of 13 tumor-free animals treated with UCB-NK cells.

This anti-tumor effect of hESC-derived NK cells (sorted and unsorted) was so strong that there was no cancer recurence observed and it was protective against metastasis.

The author’s explanation of enhanced activity of hESC-derived NK cells is that they are more mature and acquired more activation receptors compare to cord blood, which contain more immature and NK progenitors.

Now, I’d like to notice why if hESC-derived cells will ever reach the clinical endpoint, NK cells will be one of the first candidates:

1 NK cells could be used only for anti-cancer therapies, usually in “nothing to lose” cohort of patients. Allogeneic HLA-mismatched NK cells will be safe and not immunogeneic.