A Novel Magnetically Targeted Intramedullary (MagIC-TI) Xenograft Model for Precise Leukemia Modeling and Drug Resistance Evaluation in the Bone Marrow Niche.

Acute myeloid leukemia (AML) remains a therapeutic challenge due to drug resistance and relapse, which are often driven by the protective bone marrow (BM) niche. Conventional xenograft models fail to adequately recapitulate this niche-specific pathophysiology. To overcome this limitation, a novel magnetically targeted intramedullary (MagIC-TI) xenograft model was developed. Magnetically labeled doxorubicin (DOX)-resistant HL60 cells (Mag-Re) were injected into the femurs of NSG (nonobese diabetic [NOD] Cg-PrkdcscidIL2rgtm1Wjl/SzJ) mice using a patented microinjection syringe under localized magnetic guidance. With the MagIC-TI model, rapid (day 1) and specific (100% by day 7) leukemic engraftment was achieved within the femoral BM, whereas intravenous (IV) injection led to delayed (mean 23.67 ± 10.26 days) and disseminated engraftment. Bioluminescence imaging, histopathological analysis, flow cytometry, and molecular assays confirmed that disease was localized in the MagIC-TI model. In contrast, extramedullary infiltration, predominantly in the lungs, spleen, liver, and kidneys, was observed early in progression in the IV model. The MagIC-TI model discriminated drug responses, showing effective tumor burden reduction with homoharringtonine (HHT) and unequivocal DOX resistance, a distinction that was obscured in heterogeneous IV models. Furthermore, employing a semisolid decalcification (SSD) system preserved green fluorescent protein (GFP) fluorescence, enabling high-resolution visualization of engrafted cells within bone tissue. The MagIC-TI model enables BM-targeted, rapid, and efficient leukemic engraftment and allows discrimination of drug sensitivity and resistance. This model provides a robust and reproducible platform for modeling the leukemia BM niche and for preclinical evaluation of niche-directed therapies.