Role of the hypoxic bone marrow microenvironment in 5T2MM murine myeloma tumor progression.
OBJECTIVE
Unlike most other tumors, multiple myeloma (MM) cells have to survive and to grow in a bone marrow (BM) microenvironment which is already hypoxic by nature. BM hypoxia is crucial for normal hematopoiesis. However, how BM hypoxia and MM affect each other is unknown. We addressed this topic in the 5T2MM mouse model.


METHODS
Levels of hypoxia in the BM of control and tumor-bearing mice were analyzed by flow cytometric analysis of pimonidazole hypoxyprobe binding and hypoxia-inducible factor 1alpha (HIF-1alpha) expression. Micro-vessel density was measured by CD31 staining of BM sections for immunohistochemistry. Apoptosis sensitivity of CD45 5T2MM subsets in hypoxic conditions were analyzed by detection of active caspase-3.


RESULTS
Analysis of control and 5T2MM diseased mice injected with pimonidazole hypoxyprobe indicated that both normal BM and myeloma-infiltrated BM are hypoxic. However, the hypoxia in the myelomatous BM was significantly decreased. Analysis of HIF-1alpha expression, a surrogate marker of hypoxia, also demonstrated significantly lower levels of hypoxia in myeloma-infiltrated BM. HIF-1alpha expression was inversely correlated with the micro-vessel density. In vitro culture of 5T2MM cells under hypoxic conditions indicated induction of apoptosis in the CD45- MM-fraction, but not in the CD45+ 5T2MM-cells.


CONCLUSIONS
These data suggest that native BM hypoxia is advantageous for the tumor-initiating CD45+ 5T2MM-cells. Together with the decreased hypoxia in myeloma-infiltrated BM it also indicates that myeloma-associated angiogenesis is functional and permissive for the expansion of CD45- 5T2MM-cells. All together the data raise the possibility of an important role of BM hypoxia in myeloma tumor progression.
Asosingh
Kewal
K
Department of Pathobiology, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave., NB40, Cleveland, OH 44195, USA. asosink@ccf.org
De Raeve
Hendrik
H
de Ridder
Mark
M
Storme
Guy A
GA
Willems
Angelo
A
Van Riet
Ivan
I
Van Camp
Benjamin
B
Vanderkerken
Karin
K
D000818:Animals; D017209:Apoptosis; D001854:Bone Marrow Cells / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D015687:Cell Hypoxia; D018450:Disease Progression; D005434:Flow Cytometry; D006410:Hematopoiesis; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D017493:Leukocyte Common Antigens / Q000096:biosynthesis; D051379:Mice; D009101:Multiple Myeloma / Q000378:metabolism / Q000473:pathology*; D009389:Neovascularization, Pathologic; D009593:Nitroimidazoles / Q000494:pharmacology
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009593:Nitroimidazoles; C033815:pimonidazole; D017493:Leukocyte Common Antigens; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases