Targeted drug delivery for tumor therapy inside the bone marrow

Bone marrow is the primary hematopoietic organ, which is involved in multiple malignant diseases including acute and chronic leukemia, multiple myeloma, myelodysplastic syndromes, and bone metastases from solid tumors. These malignancies affect normal homeostasis and reshape the bone marrow microenvironment. There are limited treatment options for them because of their inevitable aggravation. The current systemic administration of anticancer agents is difficult to achieve ideal therapeutic dose to suppress tumor growth at bone marrow diseased sites, and is always associated with a high incidence of relapse and severe side effects. The limitations of current treatments urge scientists to develop bone marrow targeted drug delivery systems intended for the treatment of diseased bone marrow, which can improve the efficacy of therapeutic agents and reduce their dose-limiting systemic side effects on healthy tissues. In this review we first present the current opinions on bone marrow vasculature, as well as the molecular and structural interactions between tumor cells and the diseased bone marrow. In the second part, we highlight the different design rationales and strategies of bone marrow delivery systems and their therapeutic applications for the treatment of malignancies inside the bone marrow.