Selective Radionuclide Delivery for Precise Bone Marrow Niche Alterations

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PROJECT SUMMARY / ABSTRACT The bone marrow niche houses hematopoietic stem cells (HSCs), cells that self-renew and differentiate into vital blood components like white blood cells, red blood cells, and platelets. HSCs are supported by other marrow resident cells, like vascular endothelial cells and stromal cells, that nourish the marrow with essential signals. Unfortunately, radiation and/or chemotherapy used to treat cancer patients injure the bone marrow niche. Damaged bone marrow function places patients at potentially fatal risks from low blood counts. Because blood cancers are exquisitely sensitive to radiation, targeted radiation delivery via radioimmunotherapy, or target- specific antibodies stably linked to radioactive isotopes, has been developed to treat hematologic malignancies, though some have with slow bone marrow recovery. Despite increasing clinical trials evaluating radioimmunotherapies, how these delivered radionuclides impact the cellular, molecular, and systemic mechanisms that regulate the bone marrow niche has yet to be identified. The impact of radioimmunotherapy on the bone marrow niche must be addressed if radioimmunotherapies are to gain traction, and specifics on these mechanisms can be leveraged to minimize radiation-induced marrow toxicity. Further complicating the utility of radioimmunotherapy, radionuclides have distinct payload characteristics with unknown consequences on the bone marrow niche. This proposal will uncover the differential effects of an alpha-emitter (astatine-211) and a beta-emitter (yttrium-90) compared to non-targeted X-ray radiation to procure essential knowledge to advance these technologies clinically. We will report how these radiation types differentially regulate the abundance and function of HSCs, endothelial and stromal cells, essential regulators of hematologic function. We will also compare how radiation targeting impacts bone marrow components by comparing how radioimmunotherapy using a broad hematologic marker (CD45) and more restricted surface marker (CD33) impacts bone marrow components. Experimentally, we will use in vivo competitive transplantation assays in mice to assess long-term and short-term HSC potential as a function of radioimmunotherapy. These studies will be coupled with flow cytometry to quantify how radiation type regulates hematopoietic, vascular, and stromal cell frequency, death, and proliferation. We will leverage cutting-edge confocal imaging with thick femur sections to understand how radioimmunotherapy differentially regulates the three-dimensional bone marrow architecture, critical for vascular niche function and hematologic recovery from irradiation. More importantly, differential gene expression in the HSC, endothelial and stromal cell compartments, as a response to differential radionuclide delivery, will also be quantified using RNA sequence analyses. The results from these experiments stand to identify mechanisms responsible for radiation injury in HSCs, and the endothelial and stromal cell response systems that can be manipulated to derive a desired clinical outcome, and give providers the tools to accelerate bone marrow recovery, or inhibit residual hematopoiesis as desired in bone marrow stem cell transplantation.