New insights into leukemic microenvironment in bone marrow Alexey Bersenev’s journal club Jan. 16, 2009
What is the leukemic niche? Why does it matter? Leukemic microenvironment in bone marrow Hypothesis 1: Similar to normal HSCs - LSCs support hierarchy and depend upon interactions within a specific niche, the LSC niche. Hypothesis 2: If any interactions are specific only for LSC and their niches, they could be a target for therapy What do we know about it?
Human AML LSCs (CD34+/CD38-) in NOG model: 1. home to the endosteal niche of the bone marrow ; 2. win “engraftment competition” with normal hematopoietic stem cells ; 3. rest in G0 cell cycle phase ; 4. m ore likely this mechanism explains why LSCs are chemotherapeutically resistant and cause AML relapse
2. H uman mesenchymal stromal progenitor cells, derived from acute myelogenous leukemic bone marrow samples, have clonal genetic abnormalities (Michael Andreeeff, Blood (ASH Annual Meeting Abstracts) 2008 112: Abstract 2428 Right after winning the competition for the niche, cancer cells start to modify it, making it suitable for themselves. 1. Synergistic interactions between leukemic cells and osteoclast progenitors in bone microenvironment (Laura Calvi, Blood (ASH Annual Meeting Abstracts) 2008 112: Abstract 322) Abnormal cells in BM microenvironment and stroma:
Сell surface receptors expressed on HSC/progenitors, including CD44, ckit, CXCR4 and β1 integrins , seem to be vital for the localization and retention in the bone marrow Scheme of putative migration of stem cells between the bloodstream and bone marrow David A. Williams and Jose A. Cancelas (Nature 2006;444:828 )
1. Requirement for CD44 in homing and engraftment of BCR-ABL-expressing leukemic stem cells. (Krause DS, et al, Nat Med. 2006 Oct;12(10):1175-80) 2. Targeting of CD44 eradicates human acute myeloid leukemic stem cells. (Jin L. et al, Nat Med. 2006 Oct;12(10):1167-74) Targeting of CD44
Targeting of CXCR4 1. The CXCR4 inhibitor AMD3100 disrupts the interaction of multiple myeloma cells with the bone marrow microenvironment and enhances their sensitivity to therapy. (Azab AK, et al. Blood online Jan. 12, 2009) 2. Disruption of Leukemia/Stroma Cell Interactions by CXCR4 Antagonist CTCE-9908 Enhances Chemotherapy-Induced Apoptosis in AML (Michael Andreeff group, Blood (ASH Annual Meeting Abstracts) 2008 112: Abstract 2415
Questions: How do leukemic progenitors home and where do they stay in BM? How do normal HSC/progenitors interact with the leukemic microenviroment? How can we manipulate migration, homing and interaction of leukemic cells with their niches?
<ul><li>Models in vivo: </li></ul><ul><li>Leukemia allogeneic: Donor – Nalm-6 pre-B ALL; Recipient: SCID </li></ul><ul><li>Leukemia xenogeneic 1: human CD34+ transplant (before or after) in leukemic Nalm-6-GFP ALL </li></ul><ul><li>Leukemia xenogeneic 2: Donor - human ALL/AML BM; Recipient: NOD/SCID </li></ul>Detection: Cell tracking techniques + real-time in vivo confocal and multiphoton microscopy imaging
Few CD34+ cells co - localize with tumor upon homing to BM (day 0 ), yet CD34+ cells migrate into tumor niches over time
CD34+ cells in leukemic microenvironment do not response to G-CSF mobilization The malignant microenvironment, or niche, attracts CD34+ cells, but does not maintain CD34+ cell pool size or response to cytokine mobilization
CD34+ cell BM homing is inhibited by pertussis toxin (PTX) treatment in normal, but not leukemic mice Same results with AMD3100 CD34+ cells pre-treatment
AMD3100 does not restore CD34+ cell mobilization in leukemic mice.
SDF-1 ( red ) is highly expressed in the parasagittal sinusoidal region (CD34+ cell homing sites) of control mice Nalm-6–GFP cells ( green ) preferentially home to and proliferate in this area marked down-regulation of SDF-1 expression, here shown at 35 days after Nalm-6–GFP engraftment
CD34+ cells (white) home to the SDF-1–positive parasagittal vascular niches in control mice CD34+ cells aberrantly home to SDF-1+–negative, lateral regions in tumor ( green )–engrafted mice
In vivo imaging demonstrates increased SCF ( red ) expression in a tumor ( green ) - engrafted versus naïve mouse
SCF ( red ) expression is markedly up-regulated in ALL-engrafted versus control mice. CD34+ cells (white) localize to regions of high SCF expression
hSCF (brown) expression in tumor-engrafted BM Human BM biopsy Mouse model
Neutralizing treatment with anti-SCF inhibits CD34+ cell migration into tumor 7 days after CD34+ cell transplant into leukemic mice Same results in long-term (4 weeks)
<ul><li>Normal CD34+ cells engaged by the malignant niche exhibit abnormal behavior ( not maintain their cell pool size or response to cytokine mobilization ) </li></ul><ul><li>SCF mediates CD34+ cell migration into the malignant niche, as well as mobilization failure and decrease in CD34+ cell number in leukemic mice. </li></ul><ul><li>Targeting of SCF – cKit signaling could be potential therapeutic target for disruption leukemic niche </li></ul>Conclusions:
<ul><li>T herapeutic targeting of SCF may increase the hematopoietic reserve and improve outcomes in BM transplantation and autologous stem cell harvest in the setting of hematologic malignancy . </li></ul><ul><li>Also it may improve HSC/progenitor mobilization in patients with leukemia (poor responders) </li></ul>Significance:
"This is not a cure for leukemia , but it's one more tool. We like to hit cancer from all sides. This approach could potentially boost the immune system's response to the cancer by protecting the HPCs that are the source of mature immune cells. It could also maintain the patient's ability to tolerate treatment and to remain active." "If human stem cells respond in the same way as mouse cells do, it could buy us time to apply other therapies" D orothy S ipkins (U of Chicago) Citations:
<ul><li>Do leukemic cells create a new leukemic niche or do they modify already existent HSC niches? </li></ul><ul><li>Do leukemic cells reorganize the molecular microenvironment specifically to entrap HPCs, or is the creation of competitive HPC niches a coincidental side effect of leukemic growth ? </li></ul><ul><li>Is this behavior specific for leukemic cells or any cancer cells metastases in BM can create abnormal niches? </li></ul><ul><li>What other possible mechanisms and pathways are involved? How we can manipulate interaction of leukemic cells with BM microenvironment more efficiently? </li></ul>Questions:
<ul><li>Not pure cell populations used in this study (CD34+ total), we don’t know about stem cells) </li></ul><ul><li>Could NOG mice model be better to track of human leukemic cells? </li></ul><ul><li>What happen with normal HSC after anti-SCF treatment? They should be there as well as some SCF backround in steady-state BM </li></ul>Possible disadvantages: