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Page 10 of 14 Tosato et al. J Cancer Metastasis Treat 2021;7:52 https://dx.doi.org/10.20517/2394-4722.2021.120

by AML cells, whereas its ligands angiopoietin-1 and -2 ligands are expressed at abnormally high levels in
[103]
AML bone marrow . AMG386, a peptibody that blocks TIE2-angiopoietin 1/2 binding, has undergone a
[104]
successful initial trial in AML patients and is currently under investigation in combination with AraC
(NCT01555268).

Pre-clinical/clinical development of drugs and strategies for targeting the bone marrow niche in
hematological malignancies is in its early stages. The potential for success of this approach is supported by
the evidence that the niche is a critical component of pathogenesis in MDS, AML, and other hematological
malignancies and contributes to therapy resistance. The timing of intervention with niche targeted therapies
may be important. Observations from AML transplants into irradiated mice suggest that AML sensitivity to
niche-derived signals decreases as the disease advances. In one such example, AML cells from early-stage
disease homed to the endosteal bone marrow and were responsive to Wnt signaling, whereas cells from
more advanced AML homed more centrally in the bone marrow and were less sensitive to Wnt signals .
[105]

CONCLUSION
Research over the past few years has revealed the importance of complex interactions linking the bone
marrow microenvironment with healthy HSC and their malignant counterparts. Initial insight into the bone
marrow niche has evolved to recognize specific cell partners, avenues of cell communication and
biochemical pathways underlying flexible and specific biological outcomes. Some potentially critical
contributors to malignant hematopoietic cell growth have emerged, others are not fully verified, and new
ones will probably be identified. Nonetheless, current knowledge provides opportunities for therapeutic
exploitation of targets already identified as effective to prevent and mitigate the growth of malignant
hematopoietic clones. Either new drugs or more potent versions of current drugs could be effective against
these targets. Recent discoveries also provide opportunities for the identification of new drug targets to
alleviate pro-oncogenic pathways originating from the malignant niche. Drug discovery targeting the niche
and clinical trials to evaluate their safety and effectiveness hold great promise for developing novel
therapeutics for hematological malignancies.

DECLARATIONS
Acknowledgments
The authors wish to thank the members of the Laboratory of Cellular Oncology for their intellectual
contributions to aspects of this review.

Authors’ contributions
Tosato Conceived and drafted the manuscript: Tosato G
Provided intellectual input and contributed to revisions of the manuscript: Feng JX, Ohnuki H, Sim M
Prepared illustrations: Ohnuki H
Edited the manuscript: Feng JX

Availability of data and materials
Not applicable.

Financial support and sponsorship
This work is supported by the Intramural Program of the Center for Cancer Research, National Cancer
Institute, National Institutes of Health.